Air Source Heat Pumps

lovesgshp

richardc1983 wrote: »

I echo Albyota's comments above

No problem, we only install heat pumps and have done for the last 15 years, so I will not comment any further.

Cardew

Doesn't 8.5kW seem small for a 4 bed house and to heat the hot water tank? Especially as it is unlikely to be a very modern highly insulated property if a replacement heating system is to be fitted.

If they haven't up-rated the radiators, perhaps the idea(of the installers) would be to run the ASHP at a higher water temperature to compensate?

OP. ASHP's are at their most efficient with water temperatures as low as possible 30C to 35C. For this temperature water to heat a house adequately you need(ideally) under-floor heating or huge radiators. If you have to turn up the water temperature to provide adequate heating, then the ASHP will operate at a lower efficiency.

albyota

lovesgshp wrote: »

A heatpump should never be oversized, it is meant to be operated at peak efficiency levels.
Albyota, we don't even know the make of the pump the poster has. The Ecodan is only built for the UK, as far as I can see, so hope he can supply more info.

I agree, to a certain extent, however under MCS rules we have to design systems to cover 100% of the space heating requirements at design temperature, so if a house requires 9.2kW at minus 4 and the nearest heat pump is 11kW output, you have to see what it can output at minus 4, and an 11kW heat pump would only deliver 8kW so you look at the next size up, i.e 14kW.

richardc1983

lovesgshp wrote: »

No problem, we only install heat pumps and have done for the last 15 years, so I will not comment any further.

Why would you not comment? Surely this is a place to debate and discuss things? No one asked you not to comment and more so not sure why you would say that.

lovesgshp

richardc1983 wrote: »

Why would you not comment? Surely this is a place to debate and discuss things? No one asked you not to comment and more so not sure why you would say that.

Ok. We know that a heat pump should be sized to the house requirements. The normal standard is for ASHP to 7C, which is what most manufacturers quote on their specs, so fair enough.
The design allows for additional heat to be supplied as required when the temperature gets below the parameter that the pump can supply. Normally through a countdown timer of about 60 mins.
Yes, you can put a 14Kw in to resolve this, but the extra expense is not worth it in the end.
Have a look at this link for the new IVT AIRX it even shows outputs for -7C. Sorry it is in Swedish but think it is fairly clear if you look on the data pdf.

http://www.ivt.se/produkter/luftvattenvarme/ivt-airx/oversikt/

richardc1983

Yes but there isn't much diff in price between a 8kw or a 14kw and an inverter is more efficient when it isn't running flat out. Appreciate your points but the guidance isn't always the best way of doing it.

captainhindsight_2

I don't know what heat pump you have gone for, but heat pumps have different outputs at different outside temperatures.

The heat pump should be designed to meet the heat demand of the house with an outside temperature of -5. (This is what the mcs approved heat loss calculation software uses)

Different manufactures use different outside temperatures to label the heat output of the heat pump.

So heat pump A May be labeled as 15kw, heat pump B maybe labeled at 10kw, but at -5 they are the same heat output.

Hope that makes sense, it would be usefull if all manufactures used to same out side temperature to label their heat pumps.

You should be able to get access to a chart, which shows the heat output of the heat pump at different outside temperatures. The premium heat pumps manufactures such as vaillant have this information on their websites for their heat pumps.

So you may have a heat pump which is 8.5kW at -5 but is just labeled as 14kw, it's a minefield and it is important you have used an installer who knows what they are doing.

lovesgshp

There is a european standard for air/water heat pump output measurement. It is +7/35C and -7/35C. EN14511. Vaillant only show to -5C, so presume this is to do with the RHI.
Here is the AIRX data to -7C:
http://ivt.se/produkter/luftvattenvarme/ivt-airx/tekniska-fakta/
I actualy have the data for all of the IVT Air units down to -20C, with output temperatures of 35/45/55/65C.

Cardew

captainhindsight wrote: »

it is important you have used an installer who knows what they are doing.

Absolutely!


How does Mr and Mrs Average find such an installer.


From all the reports we get, not to mention the EST trials, it is quite clear that many installers do not 'know what they are doing'.


To make matters worse customers do not know if they have a good installation until they start getting huge bills(or not) a year or two down the line.


Although more complicated, look at the troubles technically minded posters have with their installations in the GSHP thread, and 'lovesgshp' sadly isn't available to help out all with a faulty installation of an ASHP system.

lovesgshp

Thanks for your confidence with me regarding gshp Cardew. We do also install ASHP systems, though not so many, but I will always try to help with any problems.