Mitsubishi Ecodans ASHP issues...

[back2space]

Evening all, would appreciate your input and advice on the following issue from another forum: As usual I know your the best to ask and I have asked the op to sign up on here so any questions can be asked, I have quoted a few posts and replies etc.

There are also pictures of the unit included:


Hi guys, new to the forum, and please bear with me if I ask something here that's already been asked, I read everything up to post 830 and thought I'd skip ahead for some advice http://images2.moneysavingexpert.com/images/forum_smilies/smile.gif

Ok, quick run down of my install:
2 x 14kw EcoDans heating a 170m/2 house with 31 radiators, mostly doubles (!, yes I know), if you count a hall or a landing as a room then 17 rooms, no buffer tank fitted (as Mitsubishi say no need),
2 x 210 litre DHW tanks,
28mm, 22mm and some 15mm pipe, 4 x 15/60 Grundfos Alpha pumps (2 pull, 2 push).
No seperate zones, most rads have TRV, but all turned to "max on",
400mm loft insulation, 600mm solid stone walls uninsulated due to listing. Full double glazing.
SAP report said 15kw required, and walls have a U value of 1.9.
House is undergoing refurb and not lived in. Heating was set to 10'c, water from Ecodans 22'c @ 17'c ambient ramping to 38'c @ -10'c ambient. No DHW generating set at the moment.
House is an old croft in northern Scotland (KW11 6UA, near Altnaharra, you may have heard of it recently) Recent temps dropped to -16'c and hovered around -10'c for several days.

Last winter the units iced up and failed due to inadequate water flow. Replumbed and sorted that. Both Mitsubishi and the install company are now happy with the water flow. Last winter it got down to -22'c, but the heating was off due to the failures.

This year they have again iced up to the point that the air flow is completely blocked. They try to defrost but fail, go back to heating and build up more ice, try to defrost etc....
Honestly, the ice was a solid sheet 10mm thick covering the back and sides of both units, last year it did this so thickly the fan blades sheared off due to the build up. Caught it this year before that happened.

When we're there and the room stat is set at 18'c the Ecodans easily manage to hit target temp within an hour of a cold start (31 out, 31 return) and the house is up to temp in about 3 hours, so I don't think it's a problem of sizing. They get the DHW tanks up to 58'c in 30 mins when we need it.

When they do a defrost it can be as frequent as 10 mins apart, or as long as 45, I'm sure they've never run for 2 hours without one. It lasts about 2 mins, though I haven't timed it. Interestingly Mitsubishi website says 30 to 120 mins apart, definitely more frequent than that.

When it fails it's different: it says "defrost" on the indoor unit, the outdoor shuts down, then you can hear the compressor start, then it makes a huffing sound and stops. The indoor still says "defrost" but the outdoor is doing nothing. After a couple of mins they then go back to heating mode and the cycle starts again.....it doesn't throw any codes or warnings on the indoor units, and I don't want to take the covers off outside to check as I don't want them to say I've voided my warranty by doing so. Sometimes after several failed defrosts it does a good one and then dumps loads of water out. It seems to fail more over night than during the day for some reason.

While the failures are bad enough it's the electric consumption we're more concerned about. To keep the house at 18'c (overnight 14'c) when outdoors it's ~8'c took roughly 100 kwh / 24hrs. At our rate that's about £11. When people nearby in similar houses with similar insulation are spending about £6 / 24hr heating to 22'c and DHW we're more than a bit concerned! In the temps we've just been having I imagine it would have been substantially higher. At that sort of rate we'd be better off burning £5 notes to keep warm http://images2.moneysavingexpert.com/images/forum_smilies/wink.gif

The only thing I can think of is high humidity causing very frequent defrosts using more electric and dragging the COP right down as a result. We share the valley with a river and according to my weather station thingy humidity is always around the 90% area outdoors (30% indoors). Other than that I can't see any reason why our system doesn't work as promised, and neither can the engineers who have been.

The install company has passed all the info I give them to Mitsubishi, data from my weather station showing indoor & outdoor temps, humidity and wind speed, loads of photo's, and all my observations, and all they said was basically "they're working within parameters, stop bothering us, not our problem".
Real helpful.

The install company is baffled and we're getting a bit worried about our £14k system. I think the next thing they're going to try is to put a buffer tank in but I don't see how that's going to help.

The main problem as far as I can see is the failure to defrost. It's not the fact that the units defrost but fail to melt all the "frost" on them, when they do a succesful defrost they clear completely down to the fins.
It's just that sometimes they try to defrost but fail to complete the cycle, actually, they fail to start the cycle. The indoor unit says "defrosting" but the outdoor unit is completly shut down, doing absolutely nothing. It tries to start the defrost, makes a huffing noise and then totally shuts down. The indoor unit says defrosting for another two mins or so, then kicks back into heating mode. This then sucks more moisture onto the exchanger and it builds up a sheet of ice.
When the exchanger is completly covered, it keeps the ice well below freezing by trying to extract heat from it and any moisture that touches it then adds to the thickness.
Even if a succesfull defrost occurs it leaves a sheet of ice clinging to the frame over the exchanger but not actually touching it so it cannot be defrosted by the unit. This in turn leades to no airflow and extreme electric consumption. Add in ambient sub zero temps and the ice simply stays put. Mitsubishi initially said it's wind chill, there was no wind this time, and the ice was only on the heat exchanger end of the case, so I don't think that's the cause.

Thank you for reading this much, sorry, it did get a bit rambling in places, I tried to keep it short while putting all the info down http://images2.moneysavingexpert.com/images/forum_smilies/smile.gif

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After seeing the pictures I can see that the ice build up on the coils is due to the snow as you also have ice on the surface on the centre of the fan inside which will be from snow blowing into the front and freezing on contact with sub zero temps.

The ice on the coils though I have witnessed on my own units, snow is sucked onto the unit and freezes on contact it then turns to ice when sun shines on it the next day etc. The water has also not drained from inside the unit probably because it has frozen underneath where it would exit from the holes. You need to perhaps put some salt or grit under neath the unit to try to stop this water freezing. My unit looked similar not as bad and only at the bottom inch of the coil due to snow fall behind the unit. The rest of the coil was clear though but you have had much worse temps up there. The blocked coil with ice has then caused air flow loss so the unit has had to work harder and draw more power. However ice should not form as thick as this and the defrost cycles dont look to be lasting long enough but it looks like the unit has been exposed face on into the snow as there is quite a lot on top of the unit as well. This depth of snow will have been sucked into the back of the unit at the same time and stuck straight away.

To me though as evidenced in the side view picture of the units you can clearly see that this is snow that has turned into ice. Snow fall and extremes of temps have been your issue here. The fact then that this hasnt been able to drain away out the bottom has caused these issues.

I was having to go outside and clear the build up of snow from the front and rear of the unit as mine isnt mounted off the ground like yours but my unit is sheltered at the front of the house so wasnt in the wind whereas at the rear we had big drifts of snow and at the front it wasnt too full on. If you was living at the property you perhaps could have been able to go out and assisted in removing some of the ice by pouring on warm water or something. I reckon the same will happen again if it snows bad again but I bet if it was -20C outside and dry you wouldnt have these issues.

I think snow is the culprit here. I dont think the defrost strategy can cope with such extreme conditions and full on snow.

[back2space]

There is suggestion that the defrost strategy is not working properly but mitsi say the unit is working ok and blaming wind chill which again is a possibility when the snow makes contact with the freezing cold casing and coils it quickly builds up then takes time to defrost.

As the op isnt living there at the moment he isnt able to go outside to ensure the drainage holes under neath the unit are clear of ice so that it can drain away any build up of ice etc.




Just to clarify a couple of things http://images2.moneysavingexpert.com/images/forum_smilies/smile.gif
We have two 14kw units so 28kw available to us, 15kw for the house according to SAP report so 28kw should be enough even in the very cold when the units drop off, say they drop 5kw each due to the cold and we should still be in the clear.

18'c is the temp of choice for us, it's nice and warm in the house at that so we're happy. The water outputs from the Ecodans are usually around 31'c and this works with our radiators fine. We have turned the stat up some times to 20'c when we're sitting watching telly (40'c output from them), by using the boost feature, this makes the rads hotter but uses more electricity, so we're happy with 18'c in general http://images2.moneysavingexpert.com/images/forum_smilies/smile.gif

- So it heats the house upto 18C & maintains it at this in a short space of time you say... This confirms that the system has enough capacity... this rules out it being undersized. Your flow temps are fine if they are achieving the indoor temps you are comfortable with.

Snow is not building up behind the units to any extent, we have them off the floor by 9 inches or so, the snow was only about 6 inches deep this year when they failed. Neither had snow fallen from the roof behind them to block up the breathing. There will obviously be some snow gets behind them and sitting on the outdoor pipe work, and snow will be sucked into them, but from what I have seen it's not snow that's causing this it's condensation on the heat exchanger that builds up.

Correct... snow being sucked onto the back of the exhanger can freeze it over in a short space of time - I have seen this with my own unit. It freezes on contact and in a short space of time it would just be recognisable as white ice like in your freezer.

grahamc2003,
nope, not foggy where we are, it was my thought initially as well. It's generally too windy for fog or mist to form, there is pretty much a constant steady breeze down the valley, though the humidity the weather station records is always very high. We have a large loch within the valley and the river draining it runs past my house to the sea 5 miles further up. We don't have salty air to contend with but this is northern Scotland, it only stops raining so it can snow!


The main problem as far as I can see is the failure to defrost. It's not the fact that the units defrost but fail to melt all the "frost" on them, when they do a succesful defrost they clear completely down to the fins. - When is this most noticeable? WHen its snowing, when the weather is cold but dry?

It's just that sometimes they try to defrost but fail to complete the cycle, actually, they fail to start the cycle. The indoor unit says "defrosting" but the outdoor unit is completly shut down, doing absolutely nothing. It tries to start the defrost, makes a huffing noise and then totally shuts down. The indoor unit says defrosting for another two mins or so, then kicks back into heating mode. This then sucks more moisture onto the exchanger and it builds up a sheet of ice. - This indicates a fault with the unit... it should complete its defrost cycle and shouldnt start another defrost for at least half an hour if it did it properly the first time. This is something that needs raising with Mitsi. The sensors on the coil and pipework inside the outdoor unit will detect certain conditions which will cause it to go into defrost... it will then stay in defrost until certain conditions (temps etc) are met and then switch back into heating. If it is below 0C the outdoor fan should not be running & only the compressor will be whirring away when it is defrosting to enable the heat to build up in the coil. If it is running during initial stages of defrost this suggests a fault with the outdoor air temp sensor.

When the exchanger is completly covered, it keeps the ice well below freezing by trying to extract heat from it and any moisture that touches it then adds to the thickness. - Spot on

Even if a succesfull defrost occurs it leaves a sheet of ice clinging to the frame over the exchanger but not actually touching it so it cannot be defrosted by the unit. - Ice should never build upto this level anyway... if defrost cycle worked properly it would never be an issue.

This in turn leades to no airflow and extreme electric consumption. Add in ambient sub zero temps and the ice simply stays put. Mitsubishi initially said it's wind chill, there was no wind this time, and the ice was only on the heat exchanger end of the case, so I don't think that's the cause.

[back2space]

Another quote and reply from the op:


Another thing, these units a brand new. Mitsi did a recall this year due to some faulty compressors or somesuch that could cause the units to literally blow up!
Both my EcoDans were commisioned in early November, they ran for two weeks unattended keeping the house at 10'c with ambients above freezing, all ok. Then we had that cold snap, they were left for 12 days before our next visit.

When we got there we found them partly covered in ice, but reading the electric meter we found that they had eaten 978 kwh (21/11/10 - 4/12/10) or £9 / 24hr average. To keep the house at 10'c!

So I checked the data from my weather station, cheap thing from Maplins but still accurate enough for this. It shows that for a while everything was fine, the system was keeping the house at a steady 8'c. But then the house temps start to drop off, eventually hitting -5'c indoors.

I assume that this is the time that they iced over outside and then just started chewing electric to try to heat the place. I reckon that that £9 a day isn't right, I think it was actually low until they iced up and then it soared as the COP hit 1:1 or worse.

My weather station then records a couple of days above freezing outdoors and some strong sun on the units. I think this has partly thawed them and allowed them to start working again.

Mitsubishi have essentially told my install company it's not their problem, I've seen the emails, and the installers are scratching their heads.
Looks like it may be GSHP for me in the future.. http://images2.moneysavingexpert.com/images/forum_smilies/wink.gif

[Bigfreeze]

First of all you should never have been sold a HP system on a house with rads with the insulation levels you stated. Your bills were always going to be astronomical. 28kw for 170sqm even at your levels of insulation is crazy tho.

Secondly, regardless of what Mitsubishi say, a buffer tank must be used in any system where you have no heat retention capacity such as a UFH screed. The units will cycle too frequently and your compressors will be shot in 5/6 years.

Thirdly, and i'm already on the record for stating this in other threads, the japanese "air to water" units are junk. Incapable of handling extemely low temps and defrosting far too often. Making ridiculous claims about their capabilities.

Your defrosting problem may be a sensor issue but apart from that your best bet is to retain one of the units to cover you're heating until the temp drops below 5C then have a oil or gas boiler back it up. Also, you must fit a buffer tank to the system.

[Bigfreeze]

Just read you're last line. If its at all possible to get these units taken back jump at it. Get a GSHP, but you should really look at your insulation levels because 1.9 is very high.

[desA]

Can the OP please measure the evaporator fin spacing? In my view, this will be a very important factor. For these extreme temperatures, defrost capability will be determined by fin spacing, as the cores already look to be fairly thin (~ 1-2 rows).

The location directly in the snow ingestion zone is absurd. Why not set up a simple canopy, or shelter above the units? Alternatively site them in a slightly more sheltered position.

[back2space]

I have asked the op to register and post on here.

[desA]

What kind of defrost mechanism do these heat-pumps use?

[mad fridgie]

I have seen this happen many times, and tends to happen when you have light floating snow, which is drawn into the coil. You end up with an ice bridge between the coil and the casing. In the early stages the coil after defrost is actually clear of ice, apart from the bridge. The bridge gets bigger, reducing the airflow, increasing ice build up, to the point where the defrost is unable to clear the coil. A cowl to reduce the snow entering is a start. I do not mitsi, so I do not know if you can adjust your termination temp or duration of time

[TiredGeek]

Hi guys, my units :)

As some have said, it could well be snow this year, the units were left running unattended for 12 days during one of the coldest spells for years.
There wasn't a great deal of snow for the area, only about 6 inches, but the temps dropped a lot lower than is normal at this time of year, we normally don't get down to the -20's 'till January / Feb. There was virtually no wind though which is unusual as it usually howls down the valley....

When we had a site survey carried out we discussed positioning of the units and it was decided this was the best place for them as they wouldn't sit in stagnant cold air as there is always a breeze around them here. We were also assured they wouldn't need covering or sheltering in any way, except maybe to stop the snow from the roof above falling behind them.

I'm now of the opinion that no matter what is done to them now, fundamentaly they are not suited to a life that far north in Scotland in the conditions in the valley where my house is.
I think I'll be contacting trading standards for advice to find out my next course of action so that I go about it the right way to ensure a good outcome for me ;)

[TiredGeek]

Just read you're last line. If its at all possible to get these units taken back jump at it. Get a GSHP, but you should really look at your insulation levels because 1.9 is very high.

Yeh, I'm thinking now I'm gonna reject the units as unfit for purpose and push for the company to fit a GSHP at their expense if it costs more than I've already paid.

I'm afraid there's less than no chance to insulate the walls, it's a listed building and they have been sticklers on maintaining all of the "historic" features, even down to what paint we can use. Add that to the fact that they are solid stone about 600mm thick and using lime mortar and plaster and we're extremely limited in what we can do. They did let us replace all the doors and windows with double glazed affairs which has helped reduce drafts greatly. They actually asked us to do this as the ones that were in were very poor copies of the old ones and "the historic timeline couldn't be read clearly". New windows and doors look new and so cannot be confused with the originals, they say. It made sense at the time, honest.

We initially wanted to go for GSHP but a combination of remote location (making it hard to get the trenches dug and sand in them etc) and dry sandy soil put us off and made us look into alternatives. We were promised a system that would work just as well but very slightly more costly to run. Looks like it's failed on both fronts so far.

Can anyone advise me if dry sandy / stony / peaty soil would be any good for a GSHP as I keep getting told different things depending on who I ask....

[back2space]

I personally think you need to get back on at these builders, these units do not appear to be defrosting properly and shouldnt have so much build up of ice on them.

[Bigfreeze]

Yeh, I'm thinking now I'm gonna reject the units as unfit for purpose and push for the company to fit a GSHP at their expense if it costs more than I've already paid.

I'm afraid there's less than no chance to insulate the walls, it's a listed building and they have been sticklers on maintaining all of the "historic" features, even down to what paint we can use. Add that to the fact that they are solid stone about 600mm thick and using lime mortar and plaster and we're extremely limited in what we can do. They did let us replace all the doors and windows with double glazed affairs which has helped reduce drafts greatly. They actually asked us to do this as the ones that were in were very poor copies of the old ones and "the historic timeline couldn't be read clearly". New windows and doors look new and so cannot be confused with the originals, they say. It made sense at the time, honest.

We initially wanted to go for GSHP but a combination of remote location (making it hard to get the trenches dug and sand in them etc) and dry sandy soil put us off and made us look into alternatives. We were promised a system that would work just as well but very slightly more costly to run. Looks like it's failed on both fronts so far.

Can anyone advise me if dry sandy / stony / peaty soil would be any good for a GSHP as I keep getting told different things depending on who I ask....

How dry is the soil? Moist is good, bone dry isn't but neither is sopping wet. You're looking for a good draining soil that maintains some water but not saturated, thats the ideal.

Get rid of these things, just go through this forum alone to see the amount of problems with them. We have air to water units working at temps of -17 this year without any problems but the evaporator on the units we use is about twice the size of the whole outdoor unit in a Mits and the fin spacing about 3 times as wide. You will continually get this problem year in, year out unless you either back one of these units up with a oil boiler when the temps drop, as i suggested earlier. Or preferably get a GSHP installed, with a buffer tank.

I would imagine somewhere about 14kw will cover your heatlosses, so your electricity bill will more than half

[freedom HP]

i note with interest some of the comments above. Freezing like this is usually an issue of lack of capacity. This can be caused by applying the wrong unit or refrigerant shortage or even lack of flow rate through the water circuit. Ive seen hundreds of heat pumps by many different manufacturers that have plodded happily on through the last period of bad weather. Measuring fin spacing and questioning the defrost is a load of bull, Mitsi sell hundreds of these units and there is no inherent design problem with them, they are good units if applied well. Some freeze like this its always the same problem. The units are not big enough.

to test this theory is really easy, next time its cold switch off a 25% of the radiators connected to the system, does the unit maintain the radiator temperature at the set point in the areas where the rads are running? if so it can cope and there are no issues with refrigerant charge etc.

im not a mitsi man but check the data tables for the kit, what capacity should they give in low ambient, check this with the duty being given out, this is only possible with a flow meter and two thermometers and a calculator. As a rough guide most so called 16kW units only give 10kW at -2 ambient if you allow for defrost.

good luck and if you need more help let me know.

[Bigfreeze]

i note with interest some of the comments above. Freezing like this is usually an issue of lack of capacity. This can be caused by applying the wrong unit or refrigerant shortage or even lack of flow rate through the water circuit. Ive seen hundreds of heat pumps by many different manufacturers that have plodded happily on through the last period of bad weather. Measuring fin spacing and questioning the defrost is a load of bull, Mitsi sell hundreds of these units and there is no inherent design problem with them, they are good units if applied well. Some freeze like this its always the same problem. The units are not big enough.

to test this theory is really easy, next time its cold switch off a 25% of the radiators connected to the system, does the unit maintain the radiator temperature at the set point in the areas where the rads are running? if so it can cope and there are no issues with refrigerant charge etc.

im not a mitsi man but check the data tables for the kit, what capacity should they give in low ambient, check this with the duty being given out, this is only possible with a flow meter and two thermometers and a calculator. As a rough guide most so called 16kW units only give 10kW at -2 ambient if you allow for defrost.

good luck and if you need more help let me know.

They are inherently flawed, in that, they were never designed primarily as a Air to water HP, they were designed as AC units. Besides a few electrical changes the outdoor units are exactly the same as the AC. The fin spacing and defrosting requirements are hugely influential in the efficiency of a ASHP. If design does not matter, then we may as well bang a screw compressor and heat exchanger inside and a Searle Evap outside and Voila a perfect ASHP.

28kw on 170sqm, not covering the heatload and you think its under-speced??? Thats 165W per sqm. Even given the weather conditions, unless the guy is living in a wendy house, the units are still overspeced.
The only wrong specification, was that of coupling a HP to a radiator system in a house of that type.

[Gary]

The bottom line is: The defrost is not working properly. Why?

[desA]

Incredibly tight fin spacing on the evaporator, as seems to be the case, is hugely influential on the rate of ice build-up, & the ability for the defrost system to clear it.

I differ with the views in post #15, in this regard. Perhaps this poster could provide more detail on his theories.

I also believe that the situation can be remedied with a few minor modifications. Pulling them out & replacing with GSHP seems to be an incredibly drastic step, in my view. Give the units a decent chance.

[desA]

We have air to water units working at temps of -17 this year without any problems but the evaporator on the units we use is about twice the size of the whole outdoor unit in a Mits and the fin spacing about 3 times as wide.

Yes, indeed.

[ashp 4 life]

This model of unit are installed throughout europe. Including Sweden where my mate installs them. I think blaming the kit is the easy way out, common mistake made by a lot of people.

I'd suggest looking at the bigger picture. Not just the design, but the how the system is being used. If you set the space temp at 10 when it's been designed at 20 then the load is going to be less than half what the SAP calc suggests.

SAP calc is for 15kw and you have 28kw installed. Oversized???

[Oakgreen16v]

The 4th picture shows one unit is clearly defrosting better than the other. Blaming the design of the evaporator and fin spacing is not a valid arguement for this issue. As other posters have identified there are thousands of this model of heat pump in the UK and when the system is applied and installed correctly there is no problem with defrost and the frequency is should certainly not occur as often as has been suggested. The fact that there are percieved to be a greater volume of problems reported on this forum with Jap heat pumps (mainly Mitsi and Daikin) is explained simply by the shear number of their units in the market. (Mitsi account for 34%, Dakin account for 19% of all ASHP sold to the UK market). Inverter driven units do not require a buffer vessel as the load can be changed by altering fan and compressor frequency direct from the unit, however it is not to say a buffer would not have helped in this case but then again the Ecodan is not intended to be joined together, although it is possible.
The problem here is very likely down to lack of flow rate combined with a lack of understanding with regards to the design and application for this system.

[Gary]

Again... it is not defrosting properly. The defrost cycle terminates before the coil is fully defrosted. What terminates the defrost cycle?

[r.bartlett]

This model of unit are installed throughout europe. Including Sweden where my mate installs them. I think blaming the kit is the easy way out, common mistake made by a lot of people.

I'd suggest looking at the bigger picture. Not just the design, but the how the system is being used. If you set the space temp at 10 when it's been designed at 20 then the load is going to be less than half what the SAP calc suggests.

SAP calc is for 15kw and you have 28kw installed. Oversized???

28kw at what outdoor temp?

Oh and it's nice to see a couple of Mitsi UK guy's on here!

[desA]

Again... it is not defrosting properly. The defrost cycle terminates before the coil is fully defrosted. What terminates the defrost cycle?

Makes me wonder what the defrost temp sensor is sensing. Things like on/off settings for the defrost cycle itself, would also be of interest.

Are these hot-gas with 4-way valve defrost systems?

[monkey spanners]

If the problem was down to the fin spacing, and it seems to be accepted that these units are heavily based on their standard split units then surely we should be having the same problems with split systems when heating in the same weather conditions?

[back2space]

If the problem was down to the fin spacing, and it seems to be accepted that these units are heavily based on their standard split units then surely we should be having the same problems with split systems when heating in the same weather conditions?

I agree and my system has been running fine!

[mad fridgie]

A couple of points

The heating units will never be the right size, due the fact the heating load is always varying, it would seem to me that this house requires 500w per degree C of temperature difference (inside/outside)
The heat pump rating is just that a rating at one condition, the client may have 28kw but only at the rated condition, as the ambient changes so does the heating output, basically for every degree C you drop in ambient you loose 2.5% duty and i would also suggest you loose 20% due to defrost (to high i hear you say, the 20% is split, time not heating and heat removed from the heating circuit) This is based upon taking Kw averaged over an hour (further explanation if required)
Re fin spacing, different agruments are available, yes closer fin spacing better heat transfer, but is more suseptable to reduced airflow in frost conditions.
It is a balance (diversity) of the ambient conditions,cost and size. Even in the UK the average ambient is not that low, so on average small fin spacing is acceptable, at times performance will be poor.
Defrost, yes modern designs should cover automated defrost (not relating to performance) and I agree high flows of water should flow the heat pump at all times when the system is running. However in this case ice bridgeing is occuring, which is caused by external factors "snow", how is the software to know if extra defrost time is required to cover this eventuality. I know on older systems, you could extend the defrsot time and increase the termination temperature, which did cure the problem, but was highly in efficient at other times.
We all know when an evap is frozen solid, a standard defrost is never going to clear it! (the fridge guys will understand this more)

[r.bartlett]

If the problem was down to the fin spacing, and it seems to be accepted that these units are heavily based on their standard split units then surely we should be having the same problems with split systems when heating in the same weather conditions?


Crumbs we've had loads of callouts on frozen condensing units....

[Bigfreeze]

If the problem was down to the fin spacing, and it seems to be accepted that these units are heavily based on their standard split units then surely we should be having the same problems with split systems when heating in the same weather conditions?

Splits don't put in the running hours that heat pumps do. They are completely different applications. Making that argument is akin to saying I should use an AC to chill a cold room.

[Bigfreeze]

A couple of points

The heating units will never be the right size, due the fact the heating load is always varying, it would seem to me that this house requires 500w per degree C of temperature difference (inside/outside)
The heat pump rating is just that a rating at one condition, the client may have 28kw but only at the rated condition, as the ambient changes so does the heating output, basically for every degree C you drop in ambient you loose 2.5% duty and i would also suggest you loose 20% due to defrost (to high i hear you say, the 20% is split, time not heating and heat removed from the heating circuit) This is based upon taking Kw averaged over an hour (further explanation if required)
Re fin spacing, different agruments are available, yes closer fin spacing better heat transfer, but is more suseptable to reduced airflow in frost conditions.
It is a balance (diversity) of the ambient conditions,cost and size. Even in the UK the average ambient is not that low, so on average small fin spacing is acceptable, at times performance will be poor.
Defrost, yes modern designs should cover automated defrost (not relating to performance) and I agree high flows of water should flow the heat pump at all times when the system is running. However in this case ice bridgeing is occuring, which is caused by external factors "snow", how is the software to know if extra defrost time is required to cover this eventuality. I know on older systems, you could extend the defrsot time and increase the termination temperature, which did cure the problem, but was highly in efficient at other times.
We all know when an evap is frozen solid, a standard defrost is never going to clear it! (the fridge guys will understand this more)

A decent control system reading air off temps offset against your weather compensation will tell you HP when it needs to defrost.
These units don't work to that logic. The fact that flow is restricted alot of the time when they do defrost (or they have poor flow temps to start off with) means the unit is usually running the compressor at a lower speed, which means less defrosting power, which means less actual defrosting in the time alotted.

[wozza]

I would suggest a snow canopy, and take the guard off the back of the unit so the droplets of water dont turn to ice after defrost and bridge between the coil and guard.
I would definatley look at the defrost strategy and see why it is terminating defrost early, could be lack of water flow as the indoor heat exchanger is getting to cold and terminating the defrost.

[monkey spanners]

Crumbs we've had loads of callouts on frozen condensing units....

See thats where using logic get me....

I guess none of us can say whats wrong with the system without a site visit and a good understanding of these units and their proper aplication, which i have'nt done and don't have....

Jon :)

[monkey spanners]

Splits don't put in the running hours that heat pumps do. They are completely different applications. Making that argument is akin to saying I should use an AC to chill a cold room.


Would a split systems run time not be a function of its duty, the heating load and the thermostat setting?
Are short run times an inherent quality of spit systems?

Jon :)

[back2space]

Would a split systems run time not be a function of its duty, the heating load and the thermostat setting?
Are short run times an inherent quality of spit systems?

Jon :)

My multi split system during the cold weather was running pretty much 12 hours a day none stop then on and off through the night as the set points were lower.

It certainly was not cycling off during the day, ramping down yes but not cycling off.

Now we have milder temps it is cycling off.

[desA]

Reminds me of why the US closes airports during the just-below-to-just-above freezing weather conditions. Excessive ice formation on wings & run-ways - pretty uncontrollable.

In Sweden, for instance, the first snows are wet, slushy & miserable. Once the temps drop well below freezing, the stuff turns to ice & things are great. It's that intermediate time that is utterly miserable.

Perhaps system designers need to think a little more about this cold-not-cold condition & prevent ice formation in the first place?

A few reasonably simple solutions present themselves here.

[back2space]

Anyone seen the Daikin Altherma picture in one of the other posts... worse than the pics above...

http://www.refrigeration-engineer.com/forums/showthread.php?t=29513

http://www.refrigeration-engineer.com/forums/attachment.php?attachmentid=3964&d=1294445399

[wozza]

At first glance it looks installed incorrectly.

Daikin specify the outdoor unit should be mounted 300mm off the floor, so the ice does build up into the unit.
It would also be advisable to fit a base plate heater

[charlie patt]

do you mind me asking what is a base plate heater a form of heater mat? does it only work at low ambient

[wozza]

Charlie,
Your right, it is a heater mat that switches on via the outdoor air sensor when it gets below three degrees.
There is also a heater tape in the kit that does the same, this is installed between the bottom of the coil and the base plate.

[charlie patt]

available via mitsi or a wholesaler?

[wozza]

Charlie,
I,m not sure what is available via Mitsi, the base plate heater that i am talking about is from Daikin.
I know it was amitsi thread but he picture posted by back to space was a Daikin unit.

[charlie patt]

ta for that your never to old to learn

[fixmyheatpump]

Dear Tired Geek,

This is my first post on here mainly fueled by frustration and annoyance after reading about the problem you are experiencing along with some of the advice being provided to you in this thread.

It's obvious you have spent a lot of time writing about your problem on here because you need help and advice having spent a lot of money on a heating system which is not doing what it is meant to do. I know some of the people here are genuinly trying to assist but disappointingly some of the posts are obviously written by non-technical sales people hell-bent on rubbishing either air source heat pumps as a technology or Mitsubishi's Ecodan as a product.

We install, service and maintain a few types of air to water heat pumps and I can assure you Mitsubishi are one, if not the best on the market. I can also say if this 14KW model didn't work down to -25C then they wouldn't put it in their literature. My reasoning behind this is the fact they have just recalled ALL of their 6,000(ish) units because of an isolated issue with ONE system, also if they were being deviant why would they quote -25C when we hardly see this temperature in the UK?

If you would be willing to message me your phone number I'm sure we can assist you with the problem you are experiencing. It would be good to get more information about the whole system and exactly how it's been designed and hydraulically configured over the phone. If it can't be fixed from our conversation we would be willing to give you a fixed (cost only) quotation on a no fix no fee basis to come up and put the system right for you, i'd expect it to be a days work + travelling.

[TiredGeek]

Well the installers have been intouch. They're going to have a good poke about the system with a Mitsubishi tech and see if they can find the problem.

I think it's bridging like other people have said. Nothing can be done about it, they're simply no good for my particular case, probably a very good system for somewhere that isn't as extreme.
Just no good for somewhere that drops below -15'c and then stays around -5'c for weeks at a time.

I honestly don't think they'll ever get it to work reliably, time to push for a GSHP system I think, at least that won't be affected by snow and ice ;)

[Gary]

I think it's bridging like other people have said. Nothing can be done about it, they're simply no good for my particular case, probably a very good system for somewhere that isn't as extreme.
Just no good for somewhere that drops below -15'c and then stays around -5'c for weeks at a time.


But... but... but... The defrost cycle terminates before the coil is fully defrosted.

[desA]

Again, what is the defrost temp sensor sensing?

Gary, perhaps you could walk us through the exact mechanics of how such a defrost system would initiate, run, then terminate? There will also be settings/parameters in the OP's specific system that can be checked.

Tired Greek could then ensure that his system people answer these questions when they review his system.

[Gary]

I have never worked on an Ecodan, nor seen a wiring diagram or a manual. I could only guess at the control strategy, sensor placement. control settings, etc.

What I do know is that if the coil is not fully defrosted, then its heat output will be severely limited.

[yinmorrison]

For what it's worth , my experience with all Manufacturers of A/C Heat Pumps is that during really cold spells ( about -8C and lower ), no matter what the defrost sensor termination temperature is moisture is retained between the fins on completion of defrost cycles and as soon as the unit cuts back on to normal operation the water freezes up almost immediately. The sensor itself may on a section of the coil that is clear of water and by the time it detects a further defrost is necessary ,areas of the coil are pretty solid and never actually clear at all , thus the problem becomes worse. I have actually seen where it has been so bad the coil tubes are crushed and damaged beyond repair as the pipe is so thin. Why else on a Cold Room evaporator would the fins be 5 or 6 per inch.

[Gary]

The sensor itself may on a section of the coil that is clear of water and by the time it detects a further defrost is necessary ,areas of the coil are pretty solid and never actually clear at all , thus the problem becomes worse.

The sensor then should be relocated to the section that clears last. However, I'm betting the manufacturer has the sensor located in the optimum position. Possibly it has come loose or the termination temp is incorrectly adjusted.

[desA]

Some defrost temp sensors are placed on the evap elbows. When the evap temp drops below a certain value, they begin the defrost cycle.

If the ice builds up & begins blocking the evap fins, it would be expected that the evap tube temp would drop - allowing defrost cycle to begin again. There would be no direct way of 'knowing' that ice had formed in the fin section.

Perhaps some manufacturers use more sophisticated methods?

This is a very interesting technical area to explore.

[Gary]

Rise in dT would be the more direct method, but I'm not aware of anyone doing it that way.

[desA]

Rise in dT would be the more direct method, but I'm not aware of anyone doing it that way.

Based on a reduction in evap performance due to ice blockage?

[Gary]

Rise in dT = reduction in airflow

[Gary]

The only other way to substantially raise the dT is to speed up the compressor.

[desA]

For AWHP's, as Tw,out rises, Q'evap reduces, hence dT,evap will reduce automatically. This may present a challenge.

[Gary]

I'm not certain that the difference would be substantial, but in any case we would want the dT defrost initiation point to exceed any dT which could be caused by water temp.

More problematic would be defrost cycles initiated by a dirty coil or fan problems.

[MikeHolm]

Guys, in what way would the seemingly unlimited quantity of heat available at the condenser help in regaining the balance? Assuming that there was a proper sensing function at the evap of course. Boy do i risk sounding dumb.

[MikeHolm]

The question is more about the quantity of heat (or work, not the same thing I know) provided by the comp vs the coming from the condenser.

[desA]

Guys, in what way would the seemingly unlimited quantity of heat available at the condenser help in regaining the balance? Assuming that there was a proper sensing function at the evap of course. Boy do i risk sounding dumb.

Sounds just right for reverse-cycle (4-way valve) defrost. :)

[fixmyheatpump]

Well the installers have been intouch. They're going to have a good poke about the system with a Mitsubishi tech and see if they can find the problem.

I think it's bridging like other people have said. Nothing can be done about it, they're simply no good for my particular case, probably a very good system for somewhere that isn't as extreme.
Just no good for somewhere that drops below -15'c and then stays around -5'c for weeks at a time.

I honestly don't think they'll ever get it to work reliably, time to push for a GSHP system I think, at least that won't be affected by snow and ice ;)

It won't be bridging I've never heard so much bull, and they work at -25C as stated in the manual. We have numerous systems installed and working fine at -15C and some of these are the W85 models which do not have the same low ambient technology as the W14. We've had constant -5C and drops to -15C all over the UK this and last winter so it's not just Scotland that gets these temperatures.

Everything points to the hydrolic water side of the system. This is obvious because you mention you have 4 x 16/60 Alpha pumps in series (2 x push - 2 x pull), this is flawed. By installing pumps in series you only increase the pressure they can overcome not the flow rate, this is done by installing them in parallel. The maximum flow you could possibly be getting out of these with a very low resistance is around 40 l/m, with the plates in the heat pumps and a radiator circuit you have a high resistance so must have low flow rate.

These units need between 20 & 40 l/m each constantly, but Mitsubishi recommend you are as near to the top end as possible, in your case it is between 40 & 80 l/m (nearer to 80 if poss) total balanced equaly between the two units, 15/60's in series are not capable of this no matter how many you have installed. If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it, this would be the only reason they would partially defrost and stop which can be seen in one of your pictures where the top of the coil is defrosted but the bottom is not. Once you get a ON/Off demand from the stat or clock this cycle will start again. At the end of a defrost the fan spins at full speed which blows the moisture away to prevent "bridging" I've witnessed this hundreds of times and it works, so much steam comes out of the front of the units some customers have called thinking they're on fire.

A few questions - Have you got a low loss header installed? If not you need one to get the required flow rates when running two heat pumps on the same hydrolic circuit.

Have you got two flows and two returns coming from the header to outside, one for each heat pump with their own circulator i.e pumps in parallel? If not you need them.

Have you got a flow setter valve installed on either the flow or return to each unit, so two in total? If not you require them to prove and balance the flow rates.

As the whole system is massively oversized for the load you should have some control to switch off one units above a certain ambient to stop the units from cycling, this is simple and cheap with an external thermostat, have you got this installed?

If no to any of these then it is an application & installation error, fact. :)

This is an age old case of proven equipment getting the blame for poor application and installation, can't see the wood for the trees and blaming something we don't understand springs to mind. :(

If you want to waste your own money by ripping them out and installing a ground source system that's your prerogative but don't be upset when you hear of a neighbour with an air source systems that is working fine after being applied and installed correctly.

[Gary]

If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it...

Now, that makes sense. :)

[Bigfreeze]

The question is more about the quantity of heat (or work, not the same thing I know) provided by the comp vs the coming from the condenser.

The heat output from the compressor is only the equiqvalent (or close to) of the electrical input. All other heat output must be collected at the evap. Thats why you're inabilty to collect energy, due to cold weather or poor defrost, has the overriding effect it does on the COP.

[fixmyheatpump]

But... but... but... The defrost cycle terminates before the coil is fully defrosted.


Exactly Gary, as the system works with multiple sensors and very complicated software algorisms it is extremely intelegant and wouldn't stop defrosting until the required parameters were achieved, unless it was protecting itself for some reason.

There are sensors on the water flow pipe and in the plate heat exchanger which it would never let these drop below freezing as it would freeze the water and crack the heat exchanger. If the flow rates are too low then there is no energy in the circuit hence the loop drops to near zero and it stops to protect itself.

They also need to run for 7 minutes before they defrost, the reason is to put enough energy into the loop before it tries to take it out again for defrost. If the system's cycling because they are oversized there is a potential this 7 minutes is not elapsing but again this is an application issue and can be overcome with some simple controls.

I've asked Mitsubishi for their recommendations on combining multiple Ecodans onto the same hydrolic loop just before we took on our first project of this type on. They told me they don't recommend or support it, the reason they gave is not the fact that it can't be done it's because it is more complicated to get right and they don't want people messing it up and giving their equipment a bad name.

In this application the installer has designed it themselves and made a pigs ear of it, this whole thread and equipment bashing is the reason Mitsubishi do not recommend or support this type of set-up. Very frustrating!

[Bigfreeze]

It won't be bridging I've never heard so much bull, and they work at -25C as stated in the manual. We have numerous systems installed and working fine at -15C and some of these are the W85 models which do not have the same low ambient technology as the W14. We've had constant -5C and drops to -15C all over the UK this and last winter so it's not just Scotland that gets these temperatures.

Everything points to the hydrolic water side of the system. This is obvious because you mention you have 4 x 16/60 Alpha pumps in series (2 x push - 2 x pull), this is flawed. By installing pumps in series you only increase the pressure they can overcome not the flow rate, this is done by installing them in parallel. The maximum flow you could possibly be getting out of these with a very low resistance is around 40 l/m, with the plates in the heat pumps and a radiator circuit you have a high resistance so must have low flow rate.

These units need between 20 & 40 l/m each constantly, but Mitsubishi recommend you are as near to the top end as possible, in your case it is between 40 & 80 l/m (nearer to 80 if poss) total balanced equaly between the two units, 15/60's in series are not capable of this no matter how many you have installed. If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it, this would be the only reason they would partially defrost and stop which can be seen in one of your pictures where the top of the coil is defrosted but the bottom is not. Once you get a ON/Off demand from the stat or clock this cycle will start again. At the end of a defrost the fan spins at full speed which blows the moisture away to prevent "bridging" I've witnessed this hundreds of times and it works, so much steam comes out of the front of the units some customers have called thinking they're on fire.

A few questions - Have you got a low loss header installed? If not you need one to get the required flow rates when running two heat pumps on the same hydrolic circuit.

Have you got two flows and two returns coming from the header to outside, one for each heat pump with their own circulator i.e pumps in parallel? If not you need them.

Have you got a flow setter valve installed on either the flow or return to each unit, so two in total? If not you require them to prove and balance the flow rates.

As the whole system is massively oversized for the load you should have some control to switch off one units above a certain ambient to stop the units from cycling, this is simple and cheap with an external thermostat, have you got this installed?

If no to any of these then it is an application & installation error, fact. :)

This is an age old case of proven equipment getting the blame for poor application and installation, can't see the wood for the trees and blaming something we don't understand springs to mind. :(

If you want to waste your own money by ripping them out and installing a ground source system that's your prerogativebut don't be upset when you hear of a neighbour with an air source systems that is working fine after being applied and installed correctly.

The issue with these units is not their inability to do the job in hand. It is their ability to do it efficiently. Sure the system above may well be designed poorly on the hyraulic side and the defrost may not be fully completing because of water flow (which I alluded to in an earlier post). The plain fact of the matter is that the evaporator on these units is poorly designed for the job that is required of it.

You can argue all you want, but anyone who has an ounce of refrigeration knowledge will tell you that the closer your fin spacing the faster you will get ice formation on the coil. In a system that is designed to run for up to 24hrs a day in moist conditions, this is a fatal flaw. Defrost removes vital energy from a house and costs money for no net gain. The more you must defrost and the longer the defrost period, the more it costs.

Anyone with any knowledge of heat pump design knows that, when dealing with a GSHP you can only collect a certain amount of energy from a certain amount of area before you begin to freeze up the ground due to its inabilty to replenish at the rate you extract. That very same principal stands true with ASHP and evaporators. You undersize and you freeze. Freezing means a lower COP, more defrosts and high energy bills. Now you can poo poo other peoples observations on here all you want. The fact remains that they are valid points and just because you install them and have seen them work, doesn't make a case for their efficiency. And at the end of the day, heatpumps are about efficiency.

[fixmyheatpump]

The issue with these units is not their inability to do the job in hand. It is their ability to do it efficiently. Sure the system above may well be designed poorly on the hyraulic side and the defrost may not be fully completing because of water flow (which I alluded to in an earlier post). The plain fact of the matter is that the evaporator on these units is poorly designed for the job that is required of it.

You can argue all you want, but anyone who has an ounce of refrigeration knowledge will tell you that the closer your fin spacing the faster you will get ice formation on the coil. In a system that is designed to run for up to 24hrs a day in moist conditions, this is a fatal flaw. Defrost removes vital energy from a house and costs money for no net gain. The more you must defrost and the longer the defrost period, the more it costs.

Anyone with any knowledge of heat pump design knows that, when dealing with a GSHP you can only collect a certain amount of energy from a certain amount of area before you begin to freeze up the ground due to its inabilty to replenish at the rate you extract. That very same principal stands true with ASHP and evaporators. You undersize and you freeze. Freezing means a lower COP, more defrosts and high energy bills. Now you can poo poo other peoples observations on here all you want. The fact remains that they are valid points and just because you install them and have seen them work, doesn't make a case for their efficiency. And at the end of the day, heatpumps are about efficiency.

I think you're missing the point, the reason Tired Geek originally posted on here was because he wanted advice on why the units are not completing a defrost cycle and freezing up, not because he wanted to hear opinions on ground source being better than air source by ground source salespeople.

So, the reason for his problem is because the units do not have the correct flow rates and possibly because they are cycling, they have not been applied correctly and that is nothing to do with the equipment. Once this is corrected they will not freeze up, the system will not cost as much to run and the fin spacing will stay the same, so that is why those observations can be poo pooed. What you are suggesting is the same as saying "I have an unleaded car I've put diesil in the tank and the reason it doesn't work is because the wheels are too small".

I'm a fridge engineer by trade but that's irrelevant, what you are actually saying in the second paragraph is that Mitsubishi's doctorate design engineers in Japan who designed and patented the Zubadan flash injection circuit/compressor to guarentee operation down to -25C don't have an ounce of refrigeration knowledge. Anybody who has an ounce of common sense would probably disagree with this. I think you need to have a read up on the technology, try here .... h ttp://w w w.mitsubishi-electric-aircon.de/eng/zubadan.php ..... if you want a further explanation let me know and i'll run through it with you.

At the end of the day heat pumps are not just about efficiency they are about cost as well, the amount it costs to install them and the amount at which you will save money over an alternative heating system. If a system costs £20,000 to install have a season COP of 5 but only saves you £300 a year you would be daft to install it as a money saving decision.

The fact that we've installed this system for numerous people who have all seen a drops in their fuel bills and have worked fine through this winter and last does infact make a case for their efficiencies. The fact that I've been to many systems that were performing poorly and found installation issues (including in Scotland) also makes a massive case for what needed to be said here.

[desA]

If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it, this would be the only reason they would partially defrost and stop which can be seen in one of your pictures where the top of the coil is defrosted but the bottom is not.

Would there be an advantage to have a hot-water storage/buffer tank in the circuit, which can allow the heat-pumps to continue full defrost, without robbing the house of too much heat?

[fixmyheatpump]

Would there be an advantage to have a hot-water storage/buffer tank in the circuit, which can allow the heat-pumps to continue full defrost, without robbing the house of too much heat?

Yes a low loss header is just a small buffer vessel so it's the same principle, if you draw off to both units individually with 2 x 15/60's on each circuit you should get the correct flow rates and around 5 degree delta T per unit. You can then draw off to the radiators at a lower flow rate and larger delta T if required and the energy required to defrost will be in the circuit. When the flow rates are low the flow temperature increase quickly and the unit achieves its target so thinks job done i've put the required energy in, however it hasn't so the unit is basically tricked.

As both units are running together and massively oversized a buffer would reduce cycling so this might be the best way to go here but I personally think it would be better from a running cost point of view to stop one of them and it's circulators when the ambient increases and the property load drops.

[mad fridgie]

It won't be bridging I've never heard so much bull, and they work at -25C as stated in the manual. We have numerous systems installed and working fine at -15C and some of these are the W85 models which do not have the same low ambient technology as the W14. We've had constant -5C and drops to -15C all over the UK this and last winter so it's not just Scotland that gets these temperatures.

Everything points to the hydrolic water side of the system. This is obvious because you mention you have 4 x 16/60 Alpha pumps in series (2 x push - 2 x pull), this is flawed. By installing pumps in series you only increase the pressure they can overcome not the flow rate, this is done by installing them in parallel. The maximum flow you could possibly be getting out of these with a very low resistance is around 40 l/m, with the plates in the heat pumps and a radiator circuit you have a high resistance so must have low flow rate.

These units need between 20 & 40 l/m each constantly, but Mitsubishi recommend you are as near to the top end as possible, in your case it is between 40 & 80 l/m (nearer to 80 if poss) total balanced equaly between the two units, 15/60's in series are not capable of this no matter how many you have installed. If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it, this would be the only reason they would partially defrost and stop which can be seen in one of your pictures where the top of the coil is defrosted but the bottom is not. Once you get a ON/Off demand from the stat or clock this cycle will start again. At the end of a defrost the fan spins at full speed which blows the moisture away to prevent "bridging" I've witnessed this hundreds of times and it works, so much steam comes out of the front of the units some customers have called thinking they're on fire.

A few questions - Have you got a low loss header installed? If not you need one to get the required flow rates when running two heat pumps on the same hydrolic circuit.

Have you got two flows and two returns coming from the header to outside, one for each heat pump with their own circulator i.e pumps in parallel? If not you need them.

Have you got a flow setter valve installed on either the flow or return to each unit, so two in total? If not you require them to prove and balance the flow rates.

As the whole system is massively oversized for the load you should have some control to switch off one units above a certain ambient to stop the units from cycling, this is simple and cheap with an external thermostat, have you got this installed?

If no to any of these then it is an application & installation error, fact. :)

This is an age old case of proven equipment getting the blame for poor application and installation, can't see the wood for the trees and blaming something we don't understand springs to mind. :(

If you want to waste your own money by ripping them out and installing a ground source system that's your prerogativebut don't be upset when you hear of a neighbour with an air source systems that is working fine after being applied and installed correctly.
Firstly I think you mis understand bridging, we are not talking about between the fins, but between the fins and the casing, and this is caused by external factors 'snow'. The coil could be completely clear but ice/snow is still on the case. You do have to be a bit unlucky for this to occur, low density snow, prolong periods of temps below 2C
Re water pumps. water pumps are pressure/flow related, increase the pressure drop reduce the flow,
So unless there is no pressure drop in your system, your statement that series pumps will not increase flow is incorrect. The pump selection is very likely to be incorrect, but without having detailed info its a blunt statement.
I am a believer of dedicated water pumps for the heat pumps and deadicted water pumps for the application (low loss header, or balancing pipe), except if there is no control on the heating circuits (underfloor system, constant flow)
Lets look at how much energy is required for defrost.
Face area of the coil looks to about 1M2, lets say ice is 5mm thick (enough to stop air flow), that will give 5litres of ice or just under 5kg of ice (we will call it 5Kg) 5*334= 1670Kj, lets round up to 2000Kj to allow for the coil.
Lets look at your water flow 30l/min (0.5kg/s)
.5*4.2*5 (10.5kj/s) defrost is 7 minutes (420second)
10.5 *420= 4410Kj
thats more than twice whats required.
how much water is required in the system to ensure defrost. Water temp start 35C (for rads i would say quite a bit higher), min water temp 10C to ensure freezing does not occur. 25C TD
4410 / 25 /4.2= 42 LITRES is required in the system to ensure correct defrost. Of course we still have the energy from the compressor to be added to the 4410.

[Bigfreeze]

I think you're missing the point, the reason Tired Geek originally posted on here was because he wanted advice on why the units are not completing a defrost cycle and freezing up, not because he wanted to hear opinions on ground source being better than air source by ground source salespeople.

So, the reason for his problem is because the units do not have the correct flow rates and possibly because they are cycling, they have not been applied correctly and that is nothing to do with the equipment. Once this is corrected they will not freeze up, the system will not cost as much to run and the fin spacing will stay the same, so that is why those observations can be poo pooed. What you are suggesting is the same as saying "I have an unleaded car I've put diesil in the tank and the reason it doesn't work is because the wheels are too small".

I'm a fridge engineer by trade but that's irrelevant, what you are actually saying in the second paragraph is that Mitsubishi's doctorate design engineers in Japan who designed and patented the Zubadan flash injection circuit/compressor to guarentee operation down to -25C don't have an ounce of refrigeration knowledge. Anybody who has an ounce of common sense would probably disagree with this. I think you need to have a read up on the technology, try here .... h ttp://w w w.mitsubishi-electric-aircon.de/eng/zubadan.php ..... if you want a further explanation let me know and i'll run through it with you.

At the end of the day heat pumps are not just about efficiency they are about cost as well, the amount it costs to install them and the amount at which you will save money over an alternative heating system. If a system costs £20,000 to install have a season COP of 5 but only saves you £300 a year you would be daft to install it as a money saving decision.

The fact that we've installed this system for numerous people who have all seen a drops in their fuel bills and have worked fine through this winter and last does infact make a case for their efficiencies. The fact that I've been to many systems that were performing poorly and found installation issues (including in Scotland) also makes a massive case for what needed to be said here.

I've already addressed the issues that tiredgeek had with flow etc on this and other threads and have moved on from that. Solving the defrost issue will not resolve the fact that whether they are derfosted or not these units do not suit the mans application. I've already given him my suggestion regarding dropping one of the units and backing up with oil when the temp drops. You don't even see an issue with rads heating a listed building connected to a heat pump and therefore I question your judgement and also your impartiality, as you, as a vendor, are the only one with vested interests regarding these units.

I am well aware of how these units work and I do not need to be schooled in heat pumps. You car analogy makes no sense at all.

But here is a car analogy for you in return regarding costs and return. If I was driving across the states I sure as hell wouldn't use a Kia, and when I buy a heatpump I want the bloody thing to last more than 8/9 years before I have to invest in a new one. So saving money up front is not what its all about. Do you realise how much money a COP of 5 verus a COP of 3 will save you over 20 years? Check it out and see if your figures stack up then.

Btw the introduction of these units was a reaction to a dropping AC market, an oversupply of manufactured units and taking advantages of economies of scale. They were not designed from the ground up, they were designed as AC units.

[TiredGeek]

Everything points to the hydrolic water side of the system. This is obvious because you mention you have 4 x 16/60 Alpha pumps in series (2 x push - 2 x pull), this is flawed.
These units need between 20 & 40 l/m each constantly, but Mitsubishi recommend you are as near to the top end as possible, in your case it is between 40 & 80 l/m (nearer to 80 if poss) total balanced equaly between the two units,

Each unit has it's own flow and return pumps. 1 x push, 1 x pull per ASHP.

A few questions - Have you got a low loss header installed? If not you need one to get the required flow rates when running two heat pumps on the same hydrolic circuit.

No. They flow and returns are both split off to each ASHP directly from the system. No buffer tank of any type in there.

Have you got two flows and two returns coming from the header to outside, one for each heat pump with their own circulator i.e pumps in parallel? If not you need them.

No header tank, but that's how the pumps are.

Have you got a flow setter valve installed on either the flow or return to each unit, so two in total? If not you require them to prove and balance the flow rates.

Yes. Flow setter on return, 25L flow indicated on each ASHP.

As the whole system is massively oversized for the load you should have some control to switch off one units above a certain ambient to stop the units from cycling, this is simple and cheap with an external thermostat, have you got this installed?

No, but we have tried isolating one unit by tripping the CB and the "plug in electric usage thingy" from the electric company didn't show any significant change in usage. One or two running, it's about £12 / day.
They don't cycle very much, just ramp up and down...

These are good points and it's a shame that when the Mitsubishi technician came out last year he failed to notice any of them.
He did say the flow rate at 18L was too low and he wanted to see at least 20L, which we did by modding the plumbing a bit with more 28mm pipe.
He never mentioned a buffer tank, turning one off etc.

Another issue that hasn't really been touched on yet: the water from a defrost, this just drains through the bottom of the case. When it's really cold it just freezes in there and is building up to threaten the fans. I know a heater would cure it but that's more electric used and I don't want to have to afford it. Any other ideas?

They want to have another look, Mitsubishi and the installers, I'd love them to get it working properly as it fits our needs so much better than GSHP (low starting current, no digging up the garden etc).
Maybe a buffer tank is the answer. With regards to that, isn't bigger better? I have room for at least 300L tank, would that be better than a 100L?

[fixmyheatpump]

These are good points and it's a shame that when the Mitsubishi technician came out last year he failed to notice any of them.
He did say the flow rate at 18L was too low and he wanted to see at least 20L, which we did by modding the plumbing a bit with more 28mm pipe.
He never mentioned a buffer tank, turning one off etc.

Another issue that hasn't really been touched on yet: the water from a defrost, this just drains through the bottom of the case. When it's really cold it just freezes in there and is building up to threaten the fans. I know a heater would cure it but that's more electric used and I don't want to have to afford it. Any other ideas?

They want to have another look, Mitsubishi and the installers, I'd love them to get it working properly as it fits our needs so much better than GSHP (low starting current, no digging up the garden etc).
Maybe a buffer tank is the answer. With regards to that, isn't bigger better? I have room for at least 300L tank, would that be better than a 100L?

It will work once it's right, regardless of it being a listed building or radiators, if the heat losses are less than the output of the units and the radiators are sized correctly there is no reason why it will not.

If you have two pumps per unit but no header or buffer how are they pumping around the heating system, I don't understand exactly how they are installed? Do you have another pump drawing to the heating system?

[desA]

Maybe a buffer tank is the answer. With regards to that, isn't bigger better? I have room for at least 300L tank, would that be better than a 100L?

Have your installers estimate the probable draw off the system to perform defrost under cold conditions ie. not depleting piping energy. This 'spare' energy should be held in the buffer tank. If you have the space, then larger is better - in my view.

I'd be interested in seeing other opinions on this.

[fixmyheatpump]

There should be no need for a buffer cylinder just a header as the units are inverter controlled. If you did want to install one as a header it needs to be small otherwise you will get poor control of the flow temperature, I would say max. 50L.

A rule of thumb for fixed speed systems is 9L per KW but this would be too big for this system as they are inverter driven and increase/reduce their output dependant on flow temperature and ambient temperature.

[TiredGeek]

I must admit I thought of a buffer tank long ago, but for a different reason:
Some of the radiators are a bit noisy due to the high flow rate around the system needed to keep water going thru the Mitsis at an acceptable rate. I was thinking that using two 210L tank (one per ASHP) with the Mitsis only heating them, and running the central heating through the tank coils (so isolating the circuits from each other) would allow high flow to the Mitsis but low to the rads.
The Mitsis keep the tanks hot, the central heating water picks up the heat as it goes through the tank coil and warms the rads.
I thought about just using one water pump per ASHP into the "buffer" on high setting and then the other two pushing / pulling the water to the rads on a lower setting. (maybe use a "solar" tank and utilise both coils for the C heating water?)

It would also allow me to reduce the amount of anti-freeze in the central heating side as this makes the water harder to pump around to some of the more distant rads. At the moment the water is a bit thick (compared to pure water) as the anti-freeze is needed to protect down to -25'c for the ASHP.

I can aslo leave the ASHP keeping the tanks warm 24/7 and just run the heating water pumps morning and night for the heating, or when I want, would this maximise efficiency?

Does any of this make sense? :confused:

If it does work in principal, does anyone know of a cylinder that has 28mm inlet and outlets?

[fixmyheatpump]

I must admit I thought of a buffer tank long ago, but for a different reason:
Some of the radiators are a bit noisy due to the high flow rate around the system needed to keep water going thru the Mitsis at an acceptable rate. I was thinking that using two 210L tank (one per ASHP) with the Mitsis only heating them, and running the central heating through the tank coils (so isolating the circuits from each other) would allow high flow to the Mitsis but low to the rads.
The Mitsis keep the tanks hot, the central heating water picks up the heat as it goes through the tank coil and warms the rads.
I thought about just using one water pump per ASHP into the "buffer" on high setting and then the other two pushing / pulling the water to the rads on a lower setting. (maybe use a "solar" tank and utilise both coils for the C heating water?)

It would also allow me to reduce the amount of anti-freeze in the central heating side as this makes the water harder to pump around to some of the more distant rads. At the moment the water is a bit thick (compared to pure water) as the anti-freeze is needed to protect down to -25'c for the ASHP.

I can aslo leave the ASHP keeping the tanks warm 24/7 and just run the heating water pumps morning and night for the heating, or when I want, would this maximise efficiency?

Does any of this make sense? :confused:

If it does work in principal, does anyone know of a cylinder that has 28mm inlet and outlets?


How is it piped? You can't have 2 pumps per unit and send it around a radiator circuit without a header to seperate the flow, that is your issue.

[fixmyheatpump]

I have a pipe schematic I sent to a customer in Kilmarnock with a similar issue which is now working perfectly.

If you want me to send it over let me know.

[TiredGeek]

If you have two pumps per unit but no header or buffer how are they pumping around the heating system, I don't understand exactly how they are installed? Do you have another pump drawing to the heating system?

I'll try to explain how it's plumbed, it's actually very easy to understand if you could see it.....

The system is as follows: All 31 rads are plumbed onto a 22mm pipe-run thoughout the house, as upstairs and downstairs circuits. These are linked together in two places so there is no actual "upstairs / downstairs" seperate circuits. The early stages of both these runs are in 28mm pipe.
The water pumps are 28mm, the central heating valves are 28mm (the DHW valves and pipes are 22mm 'cos thats the size of the coil through the tank).

So, each ASHP has a push and a pull pump.
One ASHP feeds (and returns) upstairs with 28mm pipe, the other downstairs with 28mm pipe, the flows and returns are linked near the water pumps and further on in the circuit.
Where the 28mm pipes end, they are linked together with 22mm running from upstairs to downstairs, and also branch off to different areas of radiators in 22mm pipe (so in effect, either ASHP can supply water to any rad).

The system seems to work well as each ASHP is getting 25L flow rate, and all the rads get warm equally. The only downside is some rads at the beginning of the downstairs circuit (in the kitchen) are fed directly from the 28mm pipe and are a bit noisy due to the high flow rate.
Even when the upstairs rads are turned off manually the flow rate remains unchanged through the ASHPs.

For DHW it's like this: flow from the ASHP goes through the water pumps (both water pumps are linked here on the output side), they then hit a "T" which diverts the water to the central heating valve or the DHW valve.
If it's doing room heating it goes off to the rads via a 28mm valve.
If it's doing DHW it goes through the 22mm DHW valve, thru the cylinder coil and then hits a "T" with the heating return connected to the other side. Each cylinder return and the heating return goes to the return pump and then the ASHP (In effect each ASHP has it's own cylinder but both are linked at the pumps outputs so either ASHP can heat both cylinders).

Wish I could draw it, much easier to explain :)

[TiredGeek]

I know I'm going to regret this due to spam, but as I can't do PM I'll post an email addy in a modified form ;)

my-forum-name-exactly-as-it-is-at-hotmail-dot-com

Hope that defeats the spam bots......

Just put your e-mail details in your personal profile and the members can pick it up from there.... Frank

[sinewave]

Very intresting this thread! :)

It does sound like your pipework setup is causing control problems possibly?

My own setup albeit using an Altherma uses a low loss header.

I have 28mm flow & return from the indoor unit going to a Vaillant low loss header.

The 2 outputs in 28mm drop down 600mm or so and then T off to 3 22mm heating loops round the house (3 storey house)

Each loop has it's own Grundfoss Alpha2 15-60 pump serving each floor via a programmable room stat and 2 port valves.

The pump from the Altherma does nothing more than pump from the indoor unit to the header and back.

Below pix may explain better!

[desA]

There should be no need for a buffer cylinder just a header as the units are inverter controlled. If you did want to install one as a header it needs to be small otherwise you will get poor control of the flow temperature, I would say max. 50L.

A rule of thumb for fixed speed systems is 9L per KW but this would be too big for this system as they are inverter driven and increase/reduce their output dependant on flow temperature and ambient temperature.

Your system response will depend on the thermal inertia (lag) of the flooring. Practically, the buffer tank volume may not be a huge issue in terms of thermal lag. You'll need to check your loads, I'd imagine.

For radiators, I'd expect that the buffer tank would have some influence on room thermal lags. Would be useful to estimate this.

[TiredGeek]

Neatly done :)

It's making sense to me that a lack of header(s) is causing problems.

The Mitsi doesn't have an inbuilt water pump, so If this is what is needed then I need to re-plumb to a degree.
I'm going to need to really think this through to get it right as the Mitsi also does the DHW, so then where does the header tank go in the circuit, where do the pumps go etc.....

[fixmyheatpump]

Very intresting this thread! :)

It does sound like your pipework setup is causing control problems possibly?

My own setup albeit using an Altherma uses a low loss header.

I have 28mm flow & return from the indoor unit going to a Vaillant low loss header.

The 2 outputs in 28mm drop down 600mm or so and then T off to 3 22mm heating loops round the house (3 storey house)

Each loop has it's own Grundfoss Alpha2 15-60 pump serving each floor via a programmable room stat and 2 port valves.

The pump from the Altherma does nothing more than pump from the indoor unit to the header and back.

Below pix may explain better!

Spot on! This is how it needs to be configured :)

[fixmyheatpump]

Neatly done :)

It's making sense to me that a lack of header(s) is causing problems.

The Mitsi doesn't have an inbuilt water pump, so If this is what is needed then I need to re-plumb to a degree.
I'm going to need to really think this through to get it right as the Mitsi also does the DHW, so then where does the header tank go in the circuit, where do the pumps go etc.....


Will send you the schematic shortly

[TiredGeek]

http://www.arca53.dsl.pipex.com/
(damn, can't post a link..... if you put the usual in front of it, it should work....)

So I need to configure my system to use a low loss header as per the drawing there?

FixMyHeatPump, can you try that email please so we can discuss....... :)

[TiredGeek]

LOL, crossed postings ;)

[back2space]

Some excellent responses guys.

Tiredgeek when they attend show them "fixmyheatpumps" detailed post above.

I feel you will resolve this. Regarding the water draining away you could ensure there is something under the units to stop the water freezing on contact with the ground eg salt under the drain hole.

When u get the defrost working properly I think it will drain out of the unit ok anyway as it will be warm water draining away so majority should drain. Presently your defrosts are not long enough so it doesn't drain away properly.

[frank]

Another issue that hasn't really been touched on yet: the water from a defrost, this just drains through the bottom of the case. When it's really cold it just freezes in there and is building up to threaten the fans. I know a heater would cure it but that's more electric used and I don't want to have to afford it. Any other ideas?
Of all the units I've seen with a similar problem, where the defrost water hits the base plate and then freezes, I've thought that a small 1/4" hot gas pipe spead across the base pan fitted with a small sol valve would do the trick.

Following defrost, the small sol valve would activate, allowing a small proportion of the hot gas discharge to be sent around the base plate, possibly for 10 minutes, but open to suggestions or trials on this.

This would ensure that the base plate remains hot so ice build up is prevented, but.... more importantly, the indoor heating is not inhibited, just runs at a slightly lower capacity during this time.

Another option with this would be to start the hot gas base plate heater 5 minutes before any defrost cycle, therefore making the base plate hot before defrost.

Obviously, this option would need nicorporating into the control logic and not just be an 'add on' fix

I know that the electric base plate heater is available, but from an energy point of view, this remains in circuit based on ambient temps, therefore running for all the time the unit is not in defrost cycle

[TiredGeek]

If there is not enough flow there is not enough energy in the water circuit and the heat pumps will stop defrosting to prevent the water in the plate heat exchanger from freezing and cracking it, this would be the only reason they would partially defrost and stop which can be seen in one of your pictures where the top of the coil is defrosted but the bottom is not. Once you get a ON/Off demand from the stat or clock this cycle will start again. At the end of a defrost the fan spins at full speed which blows the moisture away to prevent "bridging" I've witnessed this hundreds of times and it works, so much steam comes out of the front of the units some customers have called thinking they're on fire.

This makes so much sense I really can't understand why the install company (who are not a small unknown firm) and Mitsubishi's own technicians haven't figured it out ! I have witnessed the first bit where it tries to defrost and gives up, I have passed all the codes the units flashed up when this happened on to both Mitsi tech and the installers, they didn't figure it out.
I agree with the amount of water vapour that blows out, it's like fog when both of them do it. I must say I have worries about this building up on the vent covers in below freezing ambients, but until it's working properly we won't know ;)

I'm now tending to believe that if you say these things will work at the house, if we get them plumbed in correctly, then they will :)
I sure hope it's just a simple replumb job and we're good

[TiredGeek]

OK, more questions :)

1/
I've been looking at low loss headers, and they're pretty simple looking affairs, with a simple purpose.
Is it possible, on a temporary basis just to prove the theory (or if it works, permanently), to knock one up out of pipe fittings?

I'm thinking of a section of 28mm copper, an elbow at the top as the hot feed in from the ASHP, below that a 28mm T for the water out to the radiators, bit more pipe, another 28mm T for the cold return from the rads, and finally another 28mm elbow to return to the ASHP. Basically a low volume 28mm diameter header.

Obviously I'd have to reconfigure some pumps, but do you think this would work? I see no point in spending lots of money to prove a point when I have plenty of fittings lying about.....

2/
For two ASHP, would it be the best to fit a header to each, and then tap off both of these and mix the water further in the system, or use one header with two inputs and two returns for both ASHP to share, and take the water into the system directly from this?

Thanks for all the help guys, we feel much more positive about the prospects of this sytem actually working in the long term now :D

[sinewave]

TG, my low loss header is manufactured by Vaillant and only cost £150+ VAT.

For two units you really need one header with two inputs & returns to the ASHP's though I'm asuming it would work with only one input/return but T'd on the connections.

Vaillant do 3 sizes I believe so you'd probably need the biggest one but at the end of the day it needs specing by a proper comercial heating designer to be sure.

[MikeHolm]

I make all my own low loss headers and the thing to remember is that the ends should be caps, not elbows and that, for the flow rates you are using I would use 50mm pipe with 28mm branches (assuming you can get this type of tee, we are still using imperial measure here). You could also take the opportunity to put a sediment faucet at the bottom which will help with keeping any small bits from the pumps.

[Bigfreeze]

I don't agree that a low loss header is suited to this application, you will be short cycling some warmer water back on top of the return water, which will drag down your efficiency. A buffer is a far better solution. Both heatpumps could feed into the tank and the second machine could be set to only kick in once below a certain temp and if the tank hasn't reached temp in an hour. Low loss headers are suited to oil/gas boilers as the return temp is not as influential as in a heatpump installation

[mad fridgie]

I don't agree that a low loss header is suited to this application, you will be short cycling some warmer water back on top of the return water, which will drag down your efficiency. A buffer is a far better solution. Both heatpumps could feed into the tank and the second machine could be set to only kick in once below a certain temp and if the tank hasn't reached temp in an hour. Low loss headers are suited to oil/gas boilers as the return temp is not as influential as in a heatpump installation
I have to agree and disagree on this one, I do not like the pre manufactured units as it looks as if the water streams will mix, but, I also use a similar system to Mike, I use a vertical pipe in excess of a meter long (50-100mm diameter). Hot flows at the top, cold flows at the bottom.
With a buffer tank, unless you have quite high extremes in temperatures stratification is vey limited especially with the number of flows being injected into the tank. I do like tanks with phase change materials but that another thread.

[MikeHolm]

Speaking of phase change materials, time for a new thread. Stay tuned or beat me to the punch.:)

[Bigfreeze]

I have to agree and disagree on this one, I do not like the pre manufactured units as it looks as if the water streams will mix, but, I also use a similar system to Mike, I use a vertical pipe in excess of a meter long (50-100mm diameter). Hot flows at the top, cold flows at the bottom.
With a buffer tank, unless you have quite high extremes in temperatures stratification is vey limited especially with the number of flows being injected into the tank. I do like tanks with phase change materials but that another thread.

We use buffer vessels (either 300L or 500L most commonly but depending on heatpump size) they are 1.8m tall, our flow from the HP would enter at about 1.4m and return leave at .2m. We find there is usually a 5k difference between the top and bottom of the tank. That is your circuit for the HP and all the heatpump cares about satisfying. It has constant flow rates and allows the lowest return temp possible.

After that you can take the water to the system anyway you wish i.e take an 1 1/4" pipe off the tank at high level and header it off to 2/3/4 pumps on 1" or 3/4" and do similar on the return where you connect back into the tank at a similar height to the HP return

[MikeHolm]

These tanks and the BFs method are standard fare in the solar world. I have seen solar tanks 10m tall and 2m in diameter to create as much stratification as possible and I have made SS tanks 600mm by 3000mm because, as with HPs we want the coldest and un-mixed temps going back to the collector as possible and in the winter, it is sometimes difficult to get 50C needed at the top to prevent triggering of the back up heating system. I will dig through my archives, find a photo and post it.

But, I see Mads point on the design of the header. I would think that the flows will blend quite well before become laminar in the central part with hopefully minimal temp change at the bottom. True, this has been in boiler/solar applications and not HPs but especially with the tighter dT, I don't see the issue.

[TiredGeek]

I have had an idea floating around my head for a while that was aimed at trying to reduce noise in some radiators, but now I'm wondering if it would work and solve both issues.

I'm thinking a 200L DHW tank per ASHP, the flow and return from the HP go into the cylinder via the cold water feed and hot water outlet, not the coil as would be usual. This would give a large amount of water with minimal flow restriction for the HP to draw on for defrost, and the HP is only trying to keep the cylinder at temp. Essentially it's a 200L low loss header, with a coil running through it.

Now, my central heating circuit is run through the coil, picking up the heat from the cylinder and circulating it around the rads.

As the two circuits are now not sharing the same water I can reduce the amount of anti-freeze in the radiators, allowing me to reduce the flow rate through them while still getting heat to all the rads. Slowing the flow will stop the noise I have in some of my radiators.

To me this makes sense, the principal seems sound, but you guys have more knowledge so please correct me if I'm wrong, again :eek:

[Bigfreeze]

I have had an idea floating around my head for a while that was aimed at trying to reduce noise in some radiators, but now I'm wondering if it would work and solve both issues.

I'm thinking a 200L DHW tank per ASHP, the flow and return from the HP go into the cylinder via the cold water feed and hot water outlet, not the coil as would be usual. This would give a large amount of water with minimal flow restriction for the HP to draw on for defrost, and the HP is only trying to keep the cylinder at temp. Essentially it's a 200L low loss header, with a coil running through it.

Now, my central heating circuit is run through the coil, picking up the heat from the cylinder and circulating it around the rads.

As the two circuits are now not sharing the same water I can reduce the amount of anti-freeze in the radiators, allowing me to reduce the flow rate through them while still getting heat to all the rads. Slowing the flow will stop the noise I have in some of my radiators.

To me this makes sense, the principal seems sound, but you guys have more knowledge so please correct me if I'm wrong, again :eek:

Have a look at the buffer set up I proposed above. The tank should be direct feed, no coils and you do not need any antifreeze in the system. You also can control the pump speeds to what ever speed suits as you do not have to worry about flow speeds through the heatpump. Each heatpump would have its only dedicated pump feeding into this tank, guaranteeing you sufficient and constant flow at any particular time

[Bigfreeze]

Have a look at the buffer set up I proposed above. The tank should be direct feed, no coils and you do not need any antifreeze in the system. You also can control the pump speeds to what ever speed suits as you do not have to worry about flow speeds through the heatpump. Each heatpump would have its only dedicated pump feeding into this tank, guaranteeing you sufficient and constant flow at any particular time

You can see the set up on the attached word document

[sinewave]

This is all well & good in theory, but what about in practice?


How many domestic homes will have space for all this paraphanalia?

This is where the low loss header will rule as it needs zero space in comparisson to buffer tanks etc.

You don't get many homes with room for a dedicated ASHP Plant room do you?

:eek:

[Bigfreeze]

This is all well & good in theory, but what about in practice?


How many domestic homes will have space for all this paraphanalia?

This is where the low loss header will rule as it needs zero space in comparisson to buffer tanks etc.

You don't get many homes with room for a dedicated ASHP Plant room do you?

:eek:

Its only the width of a tank, 600 -700mm, and its the diference between a properly designed hydraulic circuit or a half way house designed for an oil boiler. Your choice

[mad fridgie]

This is all well & good in theory, but what about in practice?


How many domestic homes will have space for all this paraphanalia?

This is where the low loss header will rule as it needs zero space in comparisson to buffer tanks etc.

You don't get many homes with room for a dedicated ASHP Plant room do you?

:eek:
In 2 storey houses we normally install the manifolds and a tall skinny low loss header under the stairs.
The object of the buffer and the tall vertical low loss header is to keep maximum seperation between the hot supply and cold return, whilst still having the ability to ensure correct flows.
In the horizontal one in the pic, It would seem that mixing of the hot and cold streams would occur, derating both the heat pump (higher entering water temp) and the heating appliance (lower entering water temp)

[brunstar]

The main problem with heat pumps is the installation, as you can see in the mitsi pictures that the units should be protected from the snow and a snow cover should be installed over the units to stop the snow from accumulating on the unit.

It is evident not just in heat pumps but also in general day to day life that people in the UK are not ready for the snow.

Snow should be cleared from areas.
The other thing is that is if you look behind the unit there is a lot of snow also.

Looking at the Daikin picture, wozza is right the unit is not off the ground, if it is sub zero then how can any condensate get away from the unit.

In relation to the running costs of the Ecodan units i do not think that your running costs are high at all for a 24 hour period.
I am sure that you oil bill or gas bill for a system that has 31 radiators would not be cheap either.

I do feel that a shelter from the snow will solve the majority of your problems.
If you want to reduce the running costs over a 24 hour period, if you are turning them off then try to turn one of them off and reduce the flow temperature so they are ticking ove which will reduce the running costs.
If you do not run out of hot water then try dropping this temperature by a few degrees also this will make a big difference.

[Gary]

I'm betting solving the defrost problem will do wonders for the running costs.

[brunstar]

One thing that we need to check is that are you taking the KW hours of the heat pump only or is this all of the power consumption for the property.
A lot of people have increase power bills with heat pumps but they do forget about the oil or gas bill that they no longer need to pay.
Is this the heat pump KW hours only or the total as lights, power and cookers also add to running costs which we forget about.

[nevgee]

I'm in agreement with Gary here. It's so obvious there is a problem with the defrost cycle. You can postulate all day long about fin spacing etc but this is no different to a cold room or any other application. frost build up over all, is down to the fact that there is insufficient time or heat distribution to the whole coil area to remove the frost. These units are outdoors so subject to every variation of ambient change, unlike a cold store.

The next question is why does the frost build up to such a level? Insufficient time, insufficient defrost heat, insufficient defrost periods?

[mad fridgie]

If you look on picture 1 and 5 you can clearly see thermal bridging between the coil and the case. The coil could and it look likes that is does clear during a defrost, but does not clear the ice build up on the casing. What causes the bridging, incorrect defost, or snow. If snow how do over come the problem, with in the present control scenerio.
Either ensure snow does not enter, or ?????? with the electronics.

[TiredGeek]

What causes the bridging, incorrect defrost, or snow. If snow how do over come the problem, with in the present control scenario.
Either ensure snow does not enter, or ?????? with the electronics.

I can clear this up right away :)
Pictures 4 & 6 show the failure from last year in early November when ambient was only -3'c and there had been no snow at all.
If you look at 4 you can see one unit is fully covered with ice, the other has none.
That is because one had burnt out a fan and blown an internal fuse, shut down, and defrosted in +'c ambients. The other had continued running with damaged fan blades and maintained it's ice by continually trying to heat the house from it. Maybe this year snow blew onto the forming ice sheet and stuck.

This IS a defrost issue. I have witnessed it do it. The indoor control says "defrost", the outdoor starts the cycle, makes a "humph" noise and then shuts down and does nothing (throws code D6 for those in the know).
After a few mins the indoor says "heating eco" and the outdoor starts up and tries to produce heat. This obviously drops the temp of the fins and causes the frost to thicken.
It is now in a cycle from which it cannot escape - no heat output from the unit so nothing for it to draw on to do a defrost = failed defrost, then it tries heating again, no output from unit etc etc.....

I am in touch with someone I will call an EcoDan GOD as he seems to know the specific unit better than Mitsubishi's own tech. A low loss header is going to be tried asap, but unfortunately I won't be able to get it fitted before spring so the system will not be "proven" until they've gone through next winter....
He thinks it's a combination of low water flow and low temp returning water having insufficient energy for the EcoDan to draw on for a defrost (I think I have that right ;)) A low loss header may sort it, it certainly won't hurt.

[brunstar]

Very intresting this thread! :)

It does sound like your pipework setup is causing control problems possibly?

My own setup albeit using an Altherma uses a low loss header.

I have 28mm flow & return from the indoor unit going to a Vaillant low loss header.

The 2 outputs in 28mm drop down 600mm or so and then T off to 3 22mm heating loops round the house (3 storey house)

Each loop has it's own Grundfoss Alpha2 15-60 pump serving each floor via a programmable room stat and 2 port valves.

The pump from the Altherma does nothing more than pump from the indoor unit to the header and back.

Below pix may explain better!

Sinewave, nice install, the only thing that i can see is that your flexies are twisted which will put undue stress on the crimped sections of the pipe.. The red line should run straight along the pipe.

Nice install.

[sinewave]

Funny you should notice that Brun!
That Flexi has leaked from Day 1 and initialy I thought it was the washer which has been replaced twice, but it turns out it's the crimp leaking.
It's twisted due to too much tightening before the faulty crimp was finaly deduced!

The Red line was straight initialy! :D

[brunstar]

some methods use both time initiated before the last defrost, outdoor ambient temperature and outdoor coil temperature aswell as head pressure termination.
Another important point is units as per the air to water can also terminate if the plate heat exchanger temperature goes below zero to protect the plate heat exchanger in the event of low flow through the plate heat exchanger, in my experience they are usually down on water flow rates through the plate heat exchanger as the pipework installed on the water side usually offers too much static pressure if not designed correctly IE: everything in 22mm and 15mm copper.

By increasing the fin spacings this would make the situation worse on an air source heat pump as it would reduce the coil surface area so during a defrost the heat would not be distributed as well and same goes for absorbing heat to evaporate the liquid out of the coil in normal heating operation.
Freezer rooms are ok with wider fin spaces as those rooms usually have a lower humidity and a much more controlled environment.

[TiredGeek]

Well, I've had a header design priced up and it turns out it's about a third of the price of making it myself with 42mm pipe and T pieces :) (£135+ versus nearly £400 in parts)
So that's going to be ordered.
http://www.vaheating.co.uk/headers.html

The only problem I have now is that it's not going to be fitted until this winter is over so there is no way of knowing if it helps with the problem until next year.....

I have found something else that may be of interest to others though.
Amazon do a reptile tank thermometer for £5 that has a long lead with a probe on the end, reads every couple of seconds, is accurate to 1'c and does -10'c to +110'c.
I'm attaching one to every damn pipe I have and at least then I know what all my water temps are :D
http://www.amazon.co.uk/LCD-Digital-Thermometer-remote-probe/dp/B001U49TUM

[MikeHolm]

Well, I've had a header design priced up and it turns out it's about a third of the price of making it myself with 42mm pipe and T pieces :) (£135+ versus nearly £400 in parts)

Google "Flowdrill". I have one of these and with a powerful enough drill you can extrude a tee socket into a pipe. I make my LL headers with it.:)

[TiredGeek]

The header and some swept bends I had them do me arrived today.

They've done a lovely job :)
The header is perfect, brazed joints and it's been polished up to look really nice, the bends are also very nicely done and just what I needed to keep the water flow speedy. Bargain prices (to my mind) and the box they came in could withstand even ParcelFarce as the thing is a custom built wooden affair, weighs a bloody ton!

I'm in no way affiliated with the company, but I believe that if someone does a good job then it should be noted, I'd be the first to complain if it was done badly ;)

[fixmyheatpump]

some methods use both time initiated before the last defrost, outdoor ambient temperature and outdoor coil temperature aswell as head pressure termination.
Another important point is units as per the air to water can also terminate if the plate heat exchanger temperature goes below zero to protect the plate heat exchanger in the event of low flow through the plate heat exchanger, in my experience they are usually down on water flow rates through the plate heat exchanger as the pipework installed on the water side usually offers too much static pressure if not designed correctly IE: everything in 22mm and 15mm copper.

By increasing the fin spacings this would make the situation worse on an air source heat pump as it would reduce the coil surface area so during a defrost the heat would not be distributed as well and same goes for absorbing heat to evaporate the liquid out of the coil in normal heating operation.
Freezer rooms are ok with wider fin spaces as those rooms usually have a lower humidity and a much more controlled environment.

If this was facebook I would "like" this!

[TiredGeek]

Ok, another question. This time about weather compensation.
From what I understand the EcoDan works this fairly crudely, the controler has a "ramp" of temperatures to output the water at relative to the outdoor temp.
So if it's set to do 25'c @ 17'c ambient to 40'c @ -5'c ambient, it measure the temp of the air passing through it, say 5'c, and compares that to it's internal "temperature ramp" and sets the output accordingly, say 30'c.

Am I correct in this thinking or is it a more clever system that compares return temperature of the water and other factors as well?

One other interesting thing I found yesterday.
The company I used supplied me with an instalation manual which we worked from. I happened upon an updated version of this manual, from the same company, whilst poking around on Google. Since they sent me mine which was 25 pages long, it has been somewhat revised and now runs to 68 pages!
I wonder if there's something in there they've learnt since my install, I'll have to read through it and find out.......

[Jon Glanfield]

Hi tired Geek, I just wondered whether you had kept pace with another thread on here, reference flow temperatures on an Altherma.

It might be worth a look. We used a header also constructed by VA Heating on that job, but it is exhibiting the symptoms described by Big Freeze earlier in your thread, namely mixing and artificially affecting the return temp.

There are other issues on that particular job, but it might be an idea to give the buffer idea some research. We have asked Mitsubishi for their views on using a buffer with the Ecodan and will let you know their response if you like.

Cheers

Jon

[MikeHolm]

About outdoor reset controllers: most units base the reset on a value of .5 to 2.5C increase in temp per deg drop outdoor (depending on heating type ie: UFH, rads, scorched air etc) as well a parallel curve to allow the whole thing to shift up or down the scale. Is this the case with the HP programmers?

[Bigfreeze]

Not sure what you mean by outdoor reset controllers Mike. Are you referring to weather compensation?

[MikeHolm]

Yes, a lot of the manufacturers call it outdoor reset as it resets the operating conditions but there are a number of others including weather compensation.

[mad fridgie]

I have a question, temp compensation, i understand the principle and makes great sense, match you heat output with your heat requirement, I also understand that you can adjust your angle of deviation to suit the particular property, but what i do not understand is why on such a system would still have flow issues. Simply energy can be experessed flow * temp difference, so if you are slowing your flow you must have to raise the temp for a give amount of energy, which is counter productive for the efficiency of the heat pump.
Do you guys use air thermostats ( I do not)
Maybe i am not expalining my self well?
Your house losses energy on a second by second basis, in an ideal world we should be able to match the losses second by second. An inverter would seem the way to go (totally variable output within its limits) a fixed speed machine will stop and start, so when running has to produce more energy to compensate for when it was producing none. But what actually heats your home, it is the floor, so are you better to keep the whole floor at a lower temperature with high flow rates or just a small proportion of the floor at a warmer tempertaure at lower flow rates. In my opinion high flow rates and low temps, best for system efficiency, so why do you reduce flow, if you reduce the flow temperature? and then up with an poorly balanced hydronic system, hence the buffer tank masks, poor design. (understand the need for thermal buffer for defrost, different issue)

[MikeHolm]

OK, the first issue is time lag... especially in a floor. There is no need to set and reset every second, every minute will do. Estimating the needs of the house is relatively easy with a well defined program including hysteresis. The problem used to be with single speed pumps (solved) and single stage boilers (solved...to a degree with condensing and modulation, negative pressure gas valves and all that) and with inverter heat pumps (solved to a lesser degree due to the tighter operating tolerances of HPs in general over boilers).

What happens when a really cold wind comes up sucks the heat out of a house within 10 min? No floor heat will compensate easily for that but it certainly does help. I did a loading dock and warehouse for a national supplier and as soon as the door opened, it froze in the building but as soon as the door closed 30 sec and it was warm, but they had 30cm of concrete to hold the heat. That is the same idea as the buffer tank in a way.

As much as I would like to reduce flow rates in the floor to save on pumping power (and tubing degradation over time) I see your point about higher flow rates. Buffer for defrost, low floor temps to keep COP high and a high enough flow rate to ensure that we don't get a 12C delta T over the floor. The slower you go the more liquid temp is lost over the circuit length.

That said, it is difficult for any system to accurately predict the weather future. This is great fun, far more interesting than boiler work.

[Bigfreeze]

It depends on the company. Some you can vary the curve yourself, others are preset at you pick the curve that suits your need best. In the ones you can vary you'll probably have a set up something like this
Outdoor temp Return temp
18 22
0 28
-15 33

which you would adjust depending on insulation levels

[Bigfreeze]

They only have flow issues where stats are involved and when you run stats you're not running true weather compensation so if you have flow issues its down to poor design

[Bigfreeze]

OK, the first issue is time lag... especially in a floor. There is no need to set and reset every second, every minute will do. Estimating the needs of the house is relatively easy with a well defined program including hysteresis. The problem used to be with single speed pumps (solved) and single stage boilers (solved...to a degree with condensing and modulation, negative pressure gas valves and all that) and with inverter heat pumps (solved to a lesser degree due to the tighter operating tolerances of HPs in general over boilers).

What happens when a really cold wind comes up sucks the heat out of a house within 10 min? No floor heat will compensate easily for that but it certainly does help. I did a loading dock and warehouse for a national supplier and as soon as the door opened, it froze in the building but as soon as the door closed 30 sec and it was warm, but they had 30cm of concrete to hold the heat. That is the same idea as the buffer tank in a way.

As much as I would like to reduce flow rates in the floor to save on pumping power (and tubing degradation over time) I see your point about higher flow rates. Buffer for defrost, low floor temps to keep COP high and a high enough flow rate to ensure that we don't get a 12C delta T over the floor. The slower you go the more liquid temp is lost over the circuit length.

That said, it is difficult for any system to accurately predict the weather future. This is great fun, far more interesting than boiler work.

Weather comp will usually take an average temp over the course of an hour and adapt the required return temp to that level. Even if the weather changed dramaticly its highly unlikely that the house temp would change much in that time so the HP usually has plenty of time to keep pace.

Ideally you'd try to have a DT of 5C across your floor which would give you 5C across your condenser, which would be optimum for HP performance

[mad fridgie]

Have you guys ever used a black thermostat?

[mad fridgie]

Temp compensation is not used a lot in NZ, many would like to say it is because of our unique conditions, but it comes down to how the houses are built and finished/furnished. Temp lag is normally the biggest issue.
I have seen many a good system fail, because the interior designer decides as an after thought that a 2 inch **** pile carpet through out the house would make the house look good.

[Bigfreeze]

Black thermostat?

[Bigfreeze]

We have plenty of those here too. More concerned about the final finish than the actual structure of the house and the insulation, but things are getting better. Carpets are a killer for ufh systems as the underlay used is rarely correct

[MikeHolm]

Sorry Mad, what is a black thermostat?

Not just carpets but really thick hardwood floors cause trouble.
We've been having some 15-18C temp swings lately so the same issues can exist here as in NZ. It, unfortunately, makes the case for fast acting systems like scorched air. I will never give up on the floor heating...the dogs love it too much.

[mad fridgie]

Black thermostat!
Story line first. In NZ the buzz word at the moment is "Passive", which most just equate to heaps of windows (but that is another issue) north facing (we are in southern hemisphere), but many simply do not understand about thermal mass. The sun is very strong in NZ even in winter, so even when cold outside dry bulb temp in the sun you do feel warm and houses do warm up through lots of windows (they cool down just as quick because of the poor quality of the windows installed) How do they make the most of the energy, a simple black strip in frount of the windows (absorbs heat) but nothing like the total that could be absorbed. What i have done in the past is have a manual over ride on the water pump (on) while the heat pump is off. The water pipes pass through the dark strip picking up energy and transfers the energy evenly through the house's concrete floor. How would you control this automatically. "A black thermostat" which I believe measures infra-red radiation, basically measuring the strength of the sun, not the temperature. Could this be incorparated into your temp compensation systems

[sumsor]

Hi Mad,
I'm working on two houses in QT at the moment.
We have a proper BMS setup to control UFH, Gas Boilers, HWHP, Radiators and a VRV system.
The system alows for weather compensation depending on o/s temperature and infrared radiation. The system controls the water temperature for UFH and Radiators and is also linked to the VRV system to offset the room sensor readings on days with lots of sunshine and low o/s temperature.
Haven't seen this in a domestic install yet though.

[mad fridgie]

Hi Sumsor,
A couple of houses in QT, nice, at least you should a reasonable budget to complete a decent job. Not like in ChCh, always on the cheap.
I never got to use the infrared control (pet client passed on), so never took it any futher. But in my opinion must be a benefit in a total control system
Do you have any info on the radiation sensor/ black stat you could post on RE, I am sure many would be interested

[sumsor]

Hi Mad,

all the controls gear is Siemens.
I'll try and get some more information, it would be intersting how the control is integrated into the system(values, setpoints, etc.) as well. I'll talk to the programmer when I get a chance.
In this special case it should be a great benefit as the whole housefront is glass.
http://www.sharearchitecture.co.nz/jagged-edge-queenstown-p-191.html

[MikeHolm]

OK, if by black stat we could use a radiation sensor or a pyranometer, we have been using them for years for testing light levels in the solar world. Gives you a w/m2 reading. What you do with that info is up to you. The ones we use look like a glass ball mounted on the roof. Your situation is different as ours has to have super high accuracy and also measures the suns angles etc.

I work on a lot of passive solar houses, comes with the territory, and i design the floor heating to take the heat to the colder areas of the house and I set the pump to circulate but so far only on a timer in parallel with the boiler or whatever.

I think we could devise a low cost sensor to do as you suggest, I'll send it to the design department for consideration (that would be the other side of the brain, the unused part)

[hjcmb]

Hi everybody, am new to the site, but wanted to join to tell you of an ASHP that i saw today that, i believe, is a game changer. Why? - because:

at A-19 it has a COP of 3.27 on a flow temp of 62c
at A0 it has a COP of 4.7 on a flow temp of 80c
at A+15 it has a COP of 6.83 on a flow temp of 81c

All models, there is a cmprehensive range from 4.5kw all the way up to 30kw off shelf, but will make bigger to order, have a db reading of 40 or below

All above figures confirmed as authentic by BSRIA

It uses a Sanyo compressor, Danfoss parts, but is not complex. I saw, and felt the 10kw and the 15kw in action, and they are phenomenal.

Now the real USP. They are totally retro fit friendly onto an existing radiator system, do not require or use an accumulator, just an exiting hot water tank, do not require back up, and get this, the 4.5kw is GBP3,007 installed, the 10kw is GBP3,815 installed, and the 30kw is GBP12,908 installed.

On those COP figures the ammortization is sub 3 years, even without the RHI.

To me a complete no-brainer.

[mad fridgie]

Hi everybody, am new to the site, but wanted to join to tell you of an ASHP that i saw today that, i believe, is a game changer. Why? - because:

at A-19 it has a COP of 3.27 on a flow temp of 62c
at A0 it has a COP of 4.7 on a flow temp of 80c
at A+15 it has a COP of 6.83 on a flow temp of 81c

All models, there is a cmprehensive range from 4.5kw all the way up to 30kw off shelf, but will make bigger to order, have a db reading of 40 or below

All above figures confirmed as authentic by BSRIA

It uses a Sanyo compressor, Danfoss parts, but is not complex. I saw, and felt the 10kw and the 15kw in action, and they are phenomenal.

Now the real USP. They are totally retro fit friendly onto an existing radiator system, do not require or use an accumulator, just an exiting hot water tank, do not require back up, and get this, the 4.5kw is GBP3,007 installed, the 10kw is GBP3,815 installed, and the 30kw is GBP12,908 installed.

On those COP figures the ammortization is sub 3 years, even without the RHI.

To me a complete no-brainer.
Nice set of numbers, what brand is it, and do you have a website. Must be a new technology

[hjcmb]

Hi Mad Fridgie - web site is http://ethp-ltd.com/aboutecotec.html but that only shows previous generation, (the one i saw today). The new generation is on its way to UK as we speak. They are updating the website also, as all the tech notes apply only to the previous generation. The owners have only just taken over the company from previous management - but definately know their stuff.

[Bigfreeze]

:

at A-19 it has a COP of 3.27 on a flow temp of 62c
at A0 it has a COP of 4.7 on a flow temp of 80c
at A+15 it has a COP of 6.83 on a flow temp of 81c
.

Can you explain how this is possible seen as it improves on anything currently on the market by about 50%. And thats over the top machines out there which would be 3 times the price. Seems a little too good to be true, if you don't mind me saying. Any affiliation to the company btw?

[Bigfreeze]

just fit dimplex

problem solved!:D


Or problem created, depending on how you look at it :) :)

[hjcmb]

I agree - I can't explain, but I've seen it in operation. All I can say is that they have gone back to drawing board and started from the beginning again - nothing was taken for granted. I was about to sign to install the Sanyo CO2 ECO, which had the best performance on the market, until I saw this in operation. On the 15kw machine, the flow pipe was too hot to touch in less than a minute. The other incredible thing - they were rigged up in a wharehouse, and running they were barely louder than a deep freeze. No I am not connected to the company at all - but I can tell you I wish I was. I shall be installing these - they sell themslves.

[mad fridgie]

at A-19 it has a COP of 3.27 on a flow temp of 62c

Done some calcs on this.
Ambient -19C, with a massive evap giving all benefit of doubt suction SST -21C
2 stage compression and 99% isentropic efficiency (for each stage)
Using every last ounce of discharge super heat and no heat losses from the system and excellent liquid sub cooling SCT 52C.
heat out put 9.8Kw input 2.7Kw cop 3.63, but then we need to include the fans, pump and defrost.
I do not think so, using the best of off the shelf components. Maybe they have invented some new, that being the case then is a world beater no just in heat pumps but all refrigeration.
Looked at the site, equipment looks good, COPs of 3.6 at ambinet of 0C and 45C water more realistic, can not wait to see the innovation

[Bigfreeze]

What the hell does the flow pipe being hot in less than a minute prove. I can get a flow pipe up to 80C in less than 30 secs if I starve it of water. Won't be efficient but it will be hot. Best of luck with the sales, I'll wait for some deeper info before I follow suit

[Bigfreeze]

at A-19 it has a COP of 3.27 on a flow temp of 62c

Done some calcs on this.
Ambient -19C, with a massive evap giving all benefit of doubt suction SST -21C
2 stage compression and 99% isentropic efficiency (for each stage)
Using every last ounce of discharge super heat and no heat losses from the system and excellent liquid sub cooling SCT 52C.
heat out put 9.8Kw input 2.7Kw cop 3.63, but then we need to include the fans, pump and defrost.
I do not think so, using the best of off the shelf components. Maybe they have invented some new, that being the case then is a world beater no just in heat pumps but all refrigeration.
Looked at the site, equipment looks good, COPs of 3.6 at ambinet of 0C and 45C water more realistic, can not wait to see the innovation

Theres two monkeys on a bike inside the casing driving the compressor and keeping the electrical consumption down. Only time the power kicks in is when they go on tea break

[mad fridgie]

Theres two monkeys on a bike inside the casing driving the compressor and keeping the electrical consumption down. Only time the power kicks in is when they go on tea break

Shush, keep your secrets to your self, or do you have a world wide patent on this already (or only in Ireland)
How many Kws do you get from a banana or do find peanuts are better value for money

[Bigfreeze]

One step ahead MF, patented, with first shipment of monkeys in transit. Our tests have shown that bananas and mild electrical shock gets the best bang for your buck, especially on the defrost cycle :) :)

[MikeHolm]

Bananas are on their way out, too squishy. You need a high energy compact source.....ummmmm...I've got it Uranium.....or darn, killed the monkey.

[Bigfreeze]

They're a bugger for clogging up the condenser alright :D

[MikeHolm]

As Gary would say "airflow, airflow, airflow". How does a banana change the PH, you will have to use titanium stainless condenser?

[Bigfreeze]

Mike, you're just ruining this for me now. I thought I was on a winner with this one. One of them tore a hamstring this morning and I didn't have enough hot water for my shower

[Jon Glanfield]

I rang Ecotec about these units, the guy I spoke to didn't know anything about them and said he would ask someone more senior to ring me, he hasn't to date.....................

[Bigfreeze]

Jon, don't you know the technology behind these things is so top secret that they can't even tell their customers!!

[MikeHolm]

shhhh, he is not supposed to know about the monkeys

[TiredGeek]

Guys, could this be my problem? The monkey has frozen to death?????

[MikeHolm]

You were probably feeding him too many bananas and the condenser got clogged.

[Bigfreeze]

I think t'was the monkeys that installed yours tiredgeek :)

[MikeHolm]

It is all a question of energy in/energy out...the monkeys cannot eat frozen bananas so they throw them at the condenser causing massive damage and since there is no input of energy to the monkeys they freeze to death. BF cannot take his shower and Tiredgeek gets to do a service call but it is a big problem because the monkeys were supposed to be shipped from Ireland and somehow 2 and 2 were not put together as it was a bank holiday so Tiredgeek (TG for short) could not do his service call as the supplier did not have a set of replacement monkeys and BF had cold showers for....ohh maybe 3 or more days as the courier somehow decided it was better to go watch the Isle of Mann TT (he got side tracked). No idea where the monkeys are now.

[MikeHolm]

Comments on the technical aspects of this system are appreciated

[brunstar]

Most units in the industry which are market leaders use algorithms which are calculated, this works on compressor frequency, time, outdoor ambient, condensing temperature and more than one sensor on the outdoor coil.
The termination is a combination of head pressure control, coil temperatures and on a wet system peak freeze can also terminate the defrost, peak freeze is a protection which terminates a defrost in teh event the system does not have enough water flow through the plate heat exchanger to stop it freezing.