Air source heat pumps

[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