ASHP heating flow temperature

[rob75]

Hi all!

I've only had my Ecodan ASHP running for just over a month, and it is only now that we are experienicng very cold weather in the UK that it is being given a thorough test.

When the unit was comissioned the flow temoerature for the heating was set at 50 degrees. I'd noticed that the house was cold, and even with the room thermostat set to 25 degrees the room temperature would not get much over 16! So I have adjusted the flow temperature to 55 degrees and very quickly the house feels signficantly warmer and the rads are uncomfortable to touch for more than a couple of seconds.

Is 55 a reasonable temperature to set for the heating flow temperature? Does anyone know what a traditional gas boiler operates as. I know ASHP run at a lower temperature so I want to ensure I've not set it too high and therefore dropping the efficiency of my system.

Any feedback or suggestions would be appreciated.

Thanks,

Rob.

[back2space]

Hi all!

I've only had my Ecodan ASHP running for just over a month, and it is only now that we are experienicng very cold weather in the UK that it is being given a thorough test.

When the unit was comissioned the flow temoerature for the heating was set at 50 degrees. I'd noticed that the house was cold, and even with the room thermostat set to 25 degrees the room temperature would not get much over 16! So I have adjusted the flow temperature to 55 degrees and very quickly the house feels signficantly warmer and the rads are uncomfortable to touch for more than a couple of seconds.

Is 55 a reasonable temperature to set for the heating flow temperature? Does anyone know what a traditional gas boiler operates as. I know ASHP run at a lower temperature so I want to ensure I've not set it too high and therefore dropping the efficiency of my system.

Any feedback or suggestions would be appreciated.

Thanks,

Rob.

Hi Rob

Have you tried running it at 50 but leaving it on all day in this weather so as the temps of the house do not drop as low?

If you are running it at 55 then its going to be working harder and becoming less efficient but if running at 55C is the only way to get your house to reasonable temps then so be it.

At these low outdoor temps efficiency always takes a fall.

Radiator systems will run at between 55-80C. If you havent had your radiators oversized to allow for the cooler flow temps of the heat pump then you will have to run it hotter. For example our gas boiler at home is set at 75C in the winter, in spring/summer its running at perhaps 55/65C as we dont need as much heat,.

Underfloor heating runs at lower temps between 40-50C.

Just make sure that there are no backup heaters coming on to boost the flow temp... there shouldnt be but it has been known that they come on.

[rob75]

Hi back2space - yes I had tried leaving the system on 24/7 but it did not help. Since upping the temp. to 55 though the house is a lot warmer. I think I just have to take a hit with less efficiency during the colder months. I do not have over-sized rads nor underfloor heating so I may look into these options too!

I have noticed though that although I have set the flow to 55 the target temperature on the Mitsubishi programmer only displays 53 at present - with actual also 52-53. I don't understand this but this is a question for Mitsubishi users I guess!

Regards,

Rob.

[back2space]

Hi back2space - yes I had tried leaving the system on 24/7 but it did not help. Since upping the temp. to 55 though the house is a lot warmer. I think I just have to take a hit with less efficiency during the colder months. I do not have over-sized rads nor underfloor heating so I may look into these options too!

I have noticed though that although I have set the flow to 55 the target temperature on the Mitsubishi programmer only displays 53 at present - with actual also 52-53. I don't understand this but this is a question for Mitsubishi users I guess!

Regards,

Rob.

If your target temp is 55C and the small temperature that shows 52/53C that is the actual flow temperature it has achieved so far... it will be trying to achieve 55C but hasnt got there yet. If that makes sense.

[rob75]

That makes sense but the large temperature text displayed should be the target temperature - this I guess should be what I have set the flow to be (55). But this also shows 52-53.

Rob.

[back2space]

That makes sense but the large temperature text displayed should be the target temperature - this I guess should be what I have set the flow to be (55). But this also shows 52-53.

Rob.

When does it show 55 then? When you adjust it?

[rob75]

Yes in the setup - says 55.

Rob.

[back2space]

Yes in the setup - says 55.

Rob.

So when you change the flow temp it momentarily shows 55? THen changes?

[RSTC]

Agree with Back2Space. The problem may not be the heatpump but rads not sized correctly for use with low temperature hot water systems. Is this a 'retro-fit'?

[back2space]

Agree with Back2Space. The problem may not be the heatpump but rads not sized correctly for use with low temperature hot water systems. Is this a 'retro-fit'?


If the radiators were oversized you could run the heat pump at a lower temperature and get the same heat output from them.

IF they are not then they are sized for a high flow temp from a gas boiler so you will have to run them at a higher temp.

[Bigfreeze]

A couple of points.

50C is too high a temp for a heat pump to be working to consistently. 55 is even worse. At an air temp of 2C and a water temp of 50C your heat pump would have a COP of about 2.5. At the outside temps we're experiencing at the moment the COP could be as low as 1.5, making it no more than a glorified immersion.

You need to look at the rads. They need to be able to provide the room temp you need at no more than 40C. Jaga do very good rads in this area. As a strict rule you should stick to ufh with temps below 35c to see a return from the HP.

Also, if you are planning on progressing in the HP business and getting recommendations I suggest you stay away from the "modified air_conditioners" available from the big AC companies and go find a proper Heat pump manufacturer who design their units from the ground up and don't have to defrost every 20 mins.

[aa44]

50C is too high a temp for a heat pump to be working to consistently. 55 is even worse. At an air temp of 2C and a water temp of 50C your heat pump would have a COP of about 2.5. At the outside temps we're experiencing at the moment the COP could be as low as 1.5, making it no more than a glorified immersion.


Are you saying that it is too high a temperature for the ASHP because of economics (i.e. low COP) or for some technical reason?



I suggest you stay away from the "modified air_conditioners" available from the big AC companies and go find a proper Heat pump manufacturer who design their units from the ground up and don't have to defrost every 20 mins.

Do you have some recommendations? I am not a heating engineer. I am just starting to build a house in an area that has no mains gas so an air source heat pump seems attractive. As a buyer, the Ecodan looks cheaper and quieter than most of the competition. I would be grateful if you expand a bit further on why you think that it is a bad choice.

Thanks.
Andrew

[back2space]

As a buyer, the Ecodan looks cheaper and quieter than most of the competition. I would be grateful if you expand a bit further on why you think that it is a bad choice.

Thanks.
Andrew

Nothing wrong with the Ecodan Andrew, its a very good system. LIke anything its only as good as the install so if its been installed and you have a big enough system to cope with your demand then you will do great from it.

If not then like anything you wont be satisified with it.

Many many people using the Ecodan and very happy with it.

[Bigfreeze]

Are you saying that it is too high a temperature for the ASHP because of economics (i.e. low COP) or for some technical reason?




Do you have some recommendations? I am not a heating engineer. I am just starting to build a house in an area that has no mains gas so an air source heat pump seems attractive. As a buyer, the Ecodan looks cheaper and quieter than most of the competition. I would be grateful if you expand a bit further on why you think that it is a bad choice.

Thanks.
Andrew

Air heat pumps have a euopean standard at which their COP is rated. The standard is an air temp of 2C and a water outlet of 35C.

For every 1C you increase your water temp you drop your COP by 2%. That means at 50C you have dropped your COP by 30%.
On the air side, a 1C drop in evaporating temp will see a 3% drop in COP.

The reason Mits and Daikin are poor HP's imo is they have a very small evaporater outside with a very dense fin spacing. They're designed for use as Air conditioning units intially which means short periods of running as air can be heated to temp very quickly. This means they defrost naturally more regularly.
When converted to use as heatpumps they have to run for 4 or 5hrs at a time, even up to 16hrs a day in cold weather. They frost over very easily causing the COP to drop and when they switch to reverse cycle defrost they have to cool inside and heat outside. Doing this 2 the 3 times an hour will incur even more heatlosses.

You should look at one of the Austrian Manufacturers who specialise in heatpumps only. Have a look at IDM, Neura, Heliotherm and Ochsner. If set up properly they will all be far superior to the japanese units.

[back2space]

My heat pump has been defrosting every 4 hours or so, the air is very dry outside at the moment.

Even when it has been freezing up on the back it has only been defrosting every couple of hours and no loss of output inside.

[Bigfreeze]

My heat pump has been defrosting every 4 hours or so, the air is very dry outside at the moment.

Even when it has been freezing up on the back it has only been defrosting every couple of hours and no loss of output inside.

Over the space of a year a Mits/Daikin etc will be in the region of 50%-100% more expensive to run than a ASHP designed from the ground up with an evap about double the size of a Japanese unit and a fin spacing 2-3 times wider, if installed in like for like conditions.

I have seen this myself. And I know of many installers who have begun to back away from them despite their low capital costs as the running costs were far higher than specificly designed units

[back2space]

Over the space of a year a Mits/Daikin etc will be in the region of 50%-100% more expensive to run than a ASHP designed from the ground up with an evap about double the size of a Japanese unit and a fin spacing 2-3 times wider, if installed in like for like conditions.

I have seen this myself. And I know of many installers who have begun to back away from them despite their low capital costs as the running costs were far higher than specificly designed units


I see what your saying but running costs are still lower than electric element heating gas boilers in many cases when set at the right flow temps and for UFH.

Defrost cycles may be more regular but they are still very good at what they do. I do see your point though in a unit specifically built as a heat pump system, however these dont cool in the summer I assume?

Calorex specifically design their units as heat pumps only but on another forum a post I am reading at the moment someones unit is not working at below 5C very well at all, and now were below 0C nationwide their house is at about 15c. I feel sorry for them.

[Bigfreeze]

I see what your saying but running costs are still lower than electric element heating gas boilers in many cases when set at the right flow temps and for UFH.

Defrost cycles may be more regular but they are still very good at what they do. I do see your point though in a unit specifically built as a heat pump system, however these dont cool in the summer I assume?

Calorex specifically design their units as heat pumps only but on another forum a post I am reading at the moment someones unit is not working at below 5C very well at all, and now were below 0C nationwide their house is at about 15c. I feel sorry for them.

You can get them to do both. The ones we install do but its never required here in Ireland. I never like cooling through ufh too much as it has to be controlled very tightly, otherwise you end up with condensation problems on the floor.

Calorex, again for me, wouldn't even figure in the top 20 HP's out there at the moment. It is a sickening to see customers who get stuck with units who do not fulfil the promise that the saleperson made to them.

As you said before, poor installs are a huge problem

[r.bartlett]

Over on another forum a guy was raving about ASHP's and Sanyo CO2 in particular being the best of the best

I posted this page which has one running in real world conditions and it isn't really that impressive.. He said he'd get back to Sanyo to comment on the findings but as yet no sight or sound of either!

http://www.elisanet.fi/sanyoco2log/

LAST YEAR:

Average COP: 1.54
Total free energy: 5810.9 kWh
Average free power: 663 W

[Roundflow]

The Sanyo co2 system does work alot better than the traditional refrigerant ASHP's. Alot of the problems I have experienced have been down to application and sizing of the equipment.

[zygote nyc]

Hello guys,

I'm in the US and live in NY and was wandering is you can recommend a system for heating and cooling. I was the list you posted ealier but I don't think they are being sole in the US. Are you familiar with the Fujitsu 9RLS. Is this a good unit for heating compare to the one you been worked with.

fujitsugeneral.com/wallmounted9-12RLS_specs.htm#specs


thanks.

[Bigfreeze]

I recommended your rads on here a few weeks back but the fact that you're on here hawking your products on every thread is putting me right off. I'm sure alot of other guys would feel the same way, so do yourself a favour and lay off