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.
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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.
ta for that your never to old to learn
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.
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 ;)
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.
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.
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.
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.
Rise in dT would be the more direct method, but I'm not aware of anyone doing it that way.
Rise in dT = reduction in airflow
The only other way to substantially raise the dT is to speed up the compressor.
For AWHP's, as Tw,out rises, Q'evap reduces, hence dT,evap will reduce automatically. This may present a challenge.
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.
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.
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.
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 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.
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!
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.
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.
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.
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.
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?
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.
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.
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?
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.
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 :)
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
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!
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.