Radiators in a ground scource heat pump heating system?

[mpooley]

Hi there

I have been looking into a Ground or air scource heat pump heating system.

My house has fairly undersized rads in my opinion as when the weather is cold we have a hard time keeping warm even though the boiler is oversized.

So I have been told by "salesmen" that normally rads are oversized for a house and that you can run them at a lower temp for longer and it will work ok.

I am sure that is right (or am I?) theoretically but what about in practice?

has anyone any experience of this please?

I will probably change quite a few rads anyway as I think they are inadequate but is there any formula I can use?
are there special high output rads designed for heat pump use?
does anyone want to quote me for a whole house system?

thanks

Mike

 

[DeltaT]

If you are using normal radiators on any heat pump, they should be double the size of any radiator used with a normal gas or oil boiler. So a heat-loss calc should be done for a normal 80*C flow temperature. Then double the size of emitters required.

Any HP is best with Underfloor Heating or fan convectors. Also you require a weather compensation control system.

 

[simond]

It's easier changing the rads than the house.

But, if your house is poorly insulated and there are reasons why this cannot be practically improved, a heat pump will not be the best option.

The heat pump is a low heat solution ideally suited for well insulated properties; there are some unscrupulous outfits recommending them in all instances, the projected savings will only be achieved if the conditions are right.

 

[mpooley]

It's easier changing the rads than the house.

But, if your house is poorly insulated and there are reasons why this cannot be practically improved, a heat pump will not be the best option.

The heat pump is a low heat solution ideally suited for well insulated properties; there are some unscrupulous outfits recommending them in all instances, the projected savings will only be achieved if the conditions are right.

Thank You for your advice.
The property is a large 1990's converted barn with mainly good brick / block insulated walls or stone and two block walls cavity filled.
The loft is 175mm insulation. the only bits which are poor are some old stone walls which are either not parts of the house used in winter or are going to be lined with 100mm insulation. also one room with lots of glass!

I have done a detailed analysis of all u values etc and hope this will be good enough - they calc that i need 18kw (two 9kw air scource pumps?)

 

[DeltaT]

Hmmmmmm.......that's 75amps single phase, what leccy supply have you got going into your house??

FFS go for ground source if you can, if you have a nearby spring that's even better. ASHP for a house of your size would be madness!!

If you are putting in a ground loop you are looking at a ground area twice the size of your house floor area.

As said, there's loads of cowboys doing HPs so be very, very careful.

 

[electronicsuk]

Hmmmmmm.......that's 75amps single phase, what leccy supply have you got going into your house??

FFS go for ground source if you can, if you have a nearby spring that's even better. ASHP for a house of your size would be madness!!

I agree that ASHP is a bad idea, it won't be able to provide a reasonable amount of heat nor particularly high efficiency in the dead of winter when the defrost coils are running all the time.

However, it will not consume 75 amps. A 9kW ASHP would be expected to have a COP of at least 3, so electrical power consumption will be 3kW. Multiply that for two units and you have 6kW, or 26A.

 

[mpooley]

Hmmmmmm.......that's 75amps single phase, what leccy supply have you got going into your house??

FFS go for ground source if you can, if you have a nearby spring that's even better. ASHP for a house of your size would be madness!!

I agree that ASHP is a bad idea, it won't be able to provide a reasonable amount of heat nor particularly high efficiency in the dead of winter when the defrost coils are running all the time.

However, it will not consume 75 amps. A 9kW ASHP would be expected to have a COP of at least 3, so electrical power consumption will be 3kW. Multiply that for two units and you have 6kW, or 26A.

Thanks
The guys that quoted said that as I needed 18KW it would be hard to supply a suitable GSHP whereas two 9kw ASHPs would be "just as good" and cheaper ??

Are they BSing me then?

I have the area to install Ground scource.

Mmike

 

[electronicsuk]

Thanks
The guys that quoted said that as I needed 18KW it would be hard to supply a suitable GSHP whereas two 9kw ASHPs would be "just as good" and cheaper ??

Air source heat pumps are relatively easy (and inexpensive) to install and have therefore historically been the most widely used heat pump type. However, they suffer limitations due to their use of the outside air as a heat source or sink. The higher temperature differential during periods of extreme cold or heat leads to declining efficiency, as explained above. In mild weather, COP may be around 4.0, while at temperatures below around −8 °C (17 °F) an air-source heat pump can achieve a COP of 2.5 or better, which is considerably more than the COP that may be achieved by conventional heating systems

With GSHP, assuming the installer is competent and buries the ground loop at the required depth, then the ground temperature will be constant all year round. This allows a high COP regardless of outdoor temperature.

If you have the choice of ground or air source, and you don't mind the additional expense of the former, then it would seem to be the better choice. It sounds to me as if the company that have quoted you either don't really know what they're talking about, or are after a quick and easy install. If there are the same guys who told you that your existing radiators will be large enough for use at much lower flow temps than the existing CH, then I'd stay well away from them.

 

[Agile]

I may be having a 7m x 30m roadway built which will mean raising the level by about 1m on average.

Does anyone suggest that I should take the opportunity of placing collection pipes underneath for a future GSHP ?

What size and loop lengths would anyone suggest?

Tony

 

[simond]

 

[Biggles..]

1KW = 25sqm @1m centres.sure you can do the maths.

those figures based on 40mm hdpe

 

[Agile]

Using those figures would give about 8 kW.

For a house which if all heated would lose about 24 kW it hardly seems worth the bother when I have a gas supply anyway?

Its just that being able to bury it for free seems an opportunity not to be lost.

I have also thought about letting the flue products heat up the ground as a kind of thermal store.

Tony

 

[Biggles..]

8KW would be about the average.

 

[DeltaT]

Hmmmmmm.......that's 75amps single phase, what leccy supply have you got going into your house??

FFS go for ground source if you can, if you have a nearby spring that's even better. ASHP for a house of your size would be madness!!

I agree that ASHP is a bad idea, it won't be able to provide a reasonable amount of heat nor particularly high efficiency in the dead of winter when the defrost coils are running all the time.

However, it will not consume 75 amps. A 9kW ASHP would be expected to have a COP of at least 3, so electrical power consumption will be 3kW. Multiply that for two units and you have 6kW, or 26A.

Thanks
The guys that quoted said that as I needed 18KW it would be hard to supply a suitable GSHP whereas two 9kw ASHPs would be "just as good" and cheaper ??

Are they BSing me then?

I have the area to install Ground scource.

Mmike

He certainly is talking complete shyte!! As for a ASHP doing a COP of 2.5 @ -8*C.....................

 

[DeltaT]

Using those figures would give about 8 kW.

For a house which if all heated would lose about 24 kW it hardly seems worth the bother when I have a gas supply anyway?

Its just that being able to bury it for free seems an opportunity not to be lost.

I have also thought about letting the flue products heat up the ground as a kind of thermal store.

Tony

For all the cost of the pipe Tony, I'd say it's worth doing & who knows what will happen with the technoligy in a few years? Or indeed what will happen with gas prices!!