Air source heat pumps

[The Mud Mouse]

Hi, has anyone out there had any experience of the performance of air source heat pumps.

I am looking to fit one at my place. We are not on mains gas so am looking to find a way to economically heat the house - we currently have LPG.

The manufacturers make all kinds of claims for COP but I was wondering if anyone has any real measured performance. We have a relatively new house with underfloor heating so it will operate at a reasonably low temperature.

Cheers

 

[Darkwood]

There is a thread from last year regarding the legitimacy of the claims of these systems which are often sold in warmer climates have a search around for it, i also watched a tv documentary regarding air source heat pumps in our climate and the programme didn't do the product any favours leaving may customers with massive bills as the imm' heater was the back-up if temp' weren't met by the heat pumps.
It brought up many other concerns too but il leave it to you to look into it deeper.

 

[Rockingit]

I've got six of them going into a new build cul-de-sac that I'm doing at the moment - have to say that I've calculated for 'flat out' loads as I too have some very big doubts, and it gets mighty cold down here on the Levels!

 

[Darkwood]

The Energy Saving Trust started a field trial in 2008 the results of which are due ... i would contact them or seek their input on the systems and until i hear about the conclusion ill remain sceptical due to what ive heard in the past.... i belive poor design or lack of user knowhow can play a big part as to their efficiency.

 

[Earthstore]

I have sold one, working well, also my neighbor has one that has been installed for over a year now, he did have teething troubles but that was install issues, but still cost a lot less that their oil system to run, both of these are Mitsubishi which if memory serves me correct have no back up heat source unlike most other systems.
If circumstances would allow it is what I would choose, and PV of course.

I hope this helps.

 

[CES Heating]

Specified and correctly sized ASHPs do perform as well as any conventional heating system. Unfortunately the bad press seems to surround them owing to both lack of understanding on how to operate the controls by the householder and more often than not a heating installer who does not understand the principles of their operation and has just slung them in.
COPs on data badges need to be scrutinised, look out for COPs being quoted at 7 deg c, put into a heat calculation using a regional average of say -3 and you will get the likely COP.
These units are not plug and play, you have to make sure the house is insulated adequately, the flow and return pipework have to be big enough to get the heat around and the emitters have to be correctly sized for circuit temps of around 40 - 45 deg c.
Have a read of some manufacturers data, e.g. Mitsubishi Ecodan, Dimplex, Hitachi and Daikin etc.

 

[jason121]

I have one installed on my house 9kw TCAP using existing radiators no buffer tank yet (Buffer being done in summer). I am on mains gas. Coped during this winter and i am missing a radiator.

 

[SRE]

I have one installed on my house 9kw TCAP using existing radiators no buffer tank yet (Buffer being done in summer). I am on mains gas. Coped during this winter and i am missing a radiator.

What size/age house is yours Jason? We put an 8kw into 105m2 house in 2005 (ours) and it failed miserably because we had a 12kw heat load.

 

[jason121]

200 sq m built 1995

- - - Updated - - -

was that 8kw at -5

 

[Greenday]

Heat pumps work very well but only with careful design and installation.

Throwing one into a retrofit situation without considering the building structure and u values is a recipe for disaster . Heat losses of 50 W/m2 is preferable and look at what the heat pump is actually putting out at -3 or whatever your design temperature is. Panansonic T cap is a great unit as it maintains constant output down to -15. COP is important at this point too.

A two day course is not going to give you the heating engineer knowledge or experience that's needed for heating design at this level.

 

[SRE]

I assume it was 8kw @ 7 degrees, it was one of the first out in the UK, there wasn't any backup with it so when it failed we froze. The installers were supposed to know what they were doing but after freezing for 2 months I worked out our heat loss and discovered a massive mismatch. At the time nothing bigger than 8kw was being manufactured.

 

[The Mud Mouse]

Thanks everyone, the heat loss calculations say that I need under 12kW. I am able to link it directly into my UFH manifolds so should not have any mismatch issues with a 12kW unit but I would really like to know what COP is genuinely achievable in the winter (based in the South West) to justify the replacement of my LPG boiler (A rated). As the house is so well insulated the heating is only used 6 months/yr max. as hot water is from wet solar panels which so far have not let us down in the summer. We also have a back boiler on our wood burner in the lounge which provides hot water as well.

Is a COP average of 3.0 possible?

 

[Earthstore]

In my opinion, yes it is, many will tell you that it is not though.

When EST give out the specifics of their trials it would be helpful to understand which type of house is the best, which make of heatpump etc.

Just one small point, with your underfloor heating heatpumps work better with 100mm centers, as they run at lower temperatures, the lower they can run the higher the COP.

The standard for underfloor heating is 150mm, do you know what you have?

 

[somersetsparks]

Recently spoke to a couple loacal authority tennants who have had them fitted 6 months or so, they reckon they have cut there electricity bills in half literally, possibly by as much as 2/3rds, this is compared to storage heating. these were mitsubishi systems.

 

[The Mud Mouse]

Earthstore, yes we are at 150mm centres but we have 100mm of extratherm underneath the UFH with all external walls having 140mm of insulation and 240mm on 1st floor ceilings.

When achieving an average of 3.0 with the COP what is the flow water temp?

 

[Earthstore]

I am not a total expert on this, but I do have an understanding and some knowledge,
The room temp you are trying to achieve is around 20 degrees, so the lower temp you can run a heatpump the better really,
If I remember correctly 45 to 50 degrees, a heatpump can rack it up to 60-65 but the COP drops like a stone.

By the sounds of you insulation, your house will be ideal, do you have PV, as that would help to reduce your running costs also, daylight hours only of course.

 

[Greenday]

The house sounds ideal for a heat pump. How many square meters is it? I guess the heat loss would be something in the region of 50W/m2 so 160m2 house would need a 8kW heat pump. Do not add in the hot water load as it is usual to heat the water first then switch over to heating. A heat pump works better if it operates on a 24/7 basis with set back temperatures at night and in the day if you are out. Higher COPs will be achieved operating like this.

 

[Earthstore]

Just to add, heatpumps run better on longer cycles, rather than stop start, this is why you may have heard of "buffer tanks",
these help a pump to cycle for longer, they are not always necessary, it is all down to good system design and install.
There again that is the difference between an average PV system and an excellent performing one.

 

[Greenday]

Agreed earth store and we try to fit a buffer if the customer will agree whether the manufacturer specifies or not.

Dimplex do a combined unvented cylinder with buffer that is a convenient way of installing it.

Bad installs have done a lot of damage for heat pumps and this can only get worse if misguided sales and marketing companies get involved as the RHI looms. Bull***t sales techniques and sell at all costs is not the right approach. We walk away from a job if the heat pump won't work for that particular application. Would a salesman on commission only?

 

[jason121]

Samsung have buffer on there 210 litre tank its only 75litres. I thought for every 1kw for heat pump, 20litres is needed for buffer. I am right or wrong