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pcatterall said:
Yes, heating is quite another matter. my current understanding is that a ground source pump requires a kw of electricity for every 4kw of heat produced. My current gas usage is 17000kwh /year so 4000kw of electricity to
find from somewhere. That's about my current electricity usage so a 'simple' doubling up exercise!
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From actually installed systems Nottingham Energy Partnership suggest the annual efficiency of GSHPs are 3.5:1. ASHP average 2.7:1.
A friend of mine was involved with a study of actually installed system. His house was included in the study of 80 properties. His house is a barn conversion with lots of thermal mass, well insulated walls, roof and floor, underfloor heating throughout and simple controls. His installation was one of the highest efficiency systems in the study. Retrofitting heatpumps to existing properties without extensive high performance insulation and ideally underfloor heating will make running costs prohibitive in my opinion.
 
geem said:
From actually installed systems Nottingham Energy Partnership suggest the annual efficiency of GSHPs are 3.5:1. ASHP average 2.7:1.
A friend of mine was involved with a study of actually installed system. His house was included in the study of 80 properties. His house is a barn conversion with lots of thermal mass, well insulated walls, roof and floor, underfloor heating throughout and simple controls. His installation was one of the highest efficiency systems in the study. Retrofitting heatpumps to existing properties without extensive high performance insulation and ideally underfloor heating will make running costs prohibitive in my opinion.
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Ties up with what I've heard from a friend and a guy who installed ASHPs for houses and a hotel. I think they both mentioned 2.7 - 2,8. People seem to remember a factor of 4 but that's probably from an ideally sited system with high ambient and low internal temperatures (i.e. Lab. conditions :D).
 
geem said:
From actually installed systems Nottingham Energy Partnership suggest the annual efficiency of GSHPs are 3.5:1. ASHP average 2.7:1.
A friend of mine was involved with a study of actually installed system. His house was included in the study of 80 properties. His house is a barn conversion with lots of thermal mass, well insulated walls, roof and floor, underfloor heating throughout and simple controls. His installation was one of the highest efficiency systems in the study. Retrofitting heatpumps to existing properties without extensive high performance insulation and ideally underfloor heating will make running costs prohibitive in my opinion.
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Thanks Geem and also Mistroma. Again its good to have solid evidence rather that theory! Using my current gas heating requirement of 17000kwh Currently costing ( gas at 9p kwh) £1530
Once I have broke the bank by installing a ground source heat pump and using your figure of 3.5:1 rather than my 4:1 the cost with my current electricity at 29p /kwh becomes £1457
If I go for the air source pump and use the 2.7:1 factor then the cost becomes £1888
so about £400 /annum difference set against the cost of installing air versus ground !!
 
pcatterall said:
Thanks Geem and also Mistroma. Again its good to have solid evidence rather that theory! Using my current gas heating requirement of 17000kwh Currently costing ( gas at 9p kwh) £1530
Once I have broke the bank by installing a ground source heat pump and using your figure of 3.5:1 rather than my 4:1 the cost with my current electricity at 29p /kwh becomes £1457
If I go for the air source pump and use the 2.7:1 factor then the cost becomes £1888
so about £400 /annum difference set against the cost of installing air versus ground !!
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Air source ( and to an certain extent Ground Source ) heat pumps act like a refrigerator in reverse. And as such they produce less heat per kw of energy used when the outside temperatures are low. So your figures may need adjusting according to your location and outside temp.
Ground source when using a bore hole ( such as they do in Scandinavia ), reaches into a stable temperature deep in the rocks, so is less influenced by outside temperature.
 
KevinT1 said:
Air source ( and to an certain extent Ground Source ) heat pumps act like a refrigerator in reverse. And as such they produce less heat per kw of energy used when the outside temperatures are low. So your figures may need adjusting according to your location and outside temp.
Ground source when using a bore hole ( such as they do in Scandinavia ), reaches into a stable temperature deep in the rocks, so is less influenced by outside temperature.
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Bore holes are also used in the UK where insufficient land is available for a ground source trenched system. The down side is capital cost. Circa £20k for a pair of bore holes depending on ground conditions and depth needed, last time I was involved with such a system
 
An air source heat pump is here known as reverse cycle air conditioning. I have 2 units that work well. However the concept is that the compressor feeds to the condensor in the room with fan feeding warmth into room. The gas then is allowed to expand gets cold and goes to the outside evaporator. Here the gas is warmed by ambient air to start the cycle again. You are in effect trying to refrigerate the outside air. Obviously if outside air is near or below zero temperature you can't get much warmth from it.
Hence I think the system is popular here in west Oz where we don't get frosts but I think would be hopeless in UK. (might be wrong) However if you can use ground water or heat from deep in the ground you can use warmth to work the system.
Of course we have a similar problem if you want cooling where evaporator and condensor are swapped around if outside air temp is very hot 40 plus then it is hard to get cooling of the hot compressed gas. Powerful fan needed. But it does seem to work. ol'will
 
William_H said:
An air source heat pump is here known as reverse cycle air conditioning. I have 2 units that work well. However the concept is that the compressor feeds to the condensor in the room with fan feeding warmth into room. The gas then is allowed to expand gets cold and goes to the outside evaporator. Here the gas is warmed by ambient air to start the cycle again. You are in effect trying to refrigerate the outside air. Obviously if outside air is near or below zero temperature you can't get much warmth from it.
Hence I think the system is popular here in west Oz where we don't get frosts but I think would be hopeless in UK. (might be wrong) However if you can use ground water or heat from deep in the ground you can use warmth to work the system.
Of course we have a similar problem if you want cooling where evaporator and condensor are swapped around if outside air temp is very hot 40 plus then it is hard to get cooling of the hot compressed gas. Powerful fan needed. But it does seem to work. ol'will
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Yes Will, in Uk we need that heat in winter when extraction from air is most difficult. ground source is more effective but expensive especially where shortage of land necessitates bore holes.
 
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