anyone had any experience of the air heat pumps. seems a good energy saving method and easier than ground source.
air heat pumps
- Thread starter fitz1
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Direct experience is coming soon for us... big 33kW model is being specc'd for a job - needs a three phase supply though.
That is the issue as far as I can see - you need a good electrical supply to run some of them. It depends on the wattage.
For high density area like London I think it the way to go - ground source is too complicated/restrictive.
That is the issue as far as I can see - you need a good electrical supply to run some of them. It depends on the wattage.
For high density area like London I think it the way to go - ground source is too complicated/restrictive.
In many cases these things are a complete con and represent the height of greenwashing UNLESS your property is fully insulated to current building regulations AND you purchase genuine green sourced electricity (at higher cost) AND you install it with very closely spaced underfloor heating (to run to unit at a low output temperature).
Carefully read the tech. specs and then you'll see the catch
Carefully read the tech. specs and then you'll see the catch
Yes, these are a complete con so I will try to explain why.
Firstly the users cost! Electricity costs about 11p per unit on a good tariff. Under the BEST conditions 1 kw can produce 3+1 kw = 4 kW.
So you get 4 kW for the price of 11p. Thats about 2.7 p per kW.
However if you have a gas supply then the gas is about 2.7 pence per kW and burnt in a modern boiler is well over 90% efficient.
So the cost of using gas is about the same as the cost of using heat recovery!!!
Secondly, to produce 4 kW of heat you can use 1 kW of electricity. However electricity generation is about 30% efficient so it uses 3 kW of coal/gas/oil to produce that 1 kW of electricity.
So unless the electricity is nuclear or wind ( 18% + 0.02 ) there is a very small carbon advantage for heat recovery but thats only under the most efficient conditions.
Recovered heat is not modulatable yet so its either on or off! The efficiency falls dramatically as the air/heat source temperature falls towards zero. Its very difficult to recover heat from below 0°C as freezing on the heat exchanger is likely.
All in all its not of any significant advantage until we can generate most of our electricity from nuclear sources and as we have not progressed research that puts us about 10 years behind any significant improvement in green generation.
Tony
Firstly the users cost! Electricity costs about 11p per unit on a good tariff. Under the BEST conditions 1 kw can produce 3+1 kw = 4 kW.
So you get 4 kW for the price of 11p. Thats about 2.7 p per kW.
However if you have a gas supply then the gas is about 2.7 pence per kW and burnt in a modern boiler is well over 90% efficient.
So the cost of using gas is about the same as the cost of using heat recovery!!!
Secondly, to produce 4 kW of heat you can use 1 kW of electricity. However electricity generation is about 30% efficient so it uses 3 kW of coal/gas/oil to produce that 1 kW of electricity.
So unless the electricity is nuclear or wind ( 18% + 0.02 ) there is a very small carbon advantage for heat recovery but thats only under the most efficient conditions.
Recovered heat is not modulatable yet so its either on or off! The efficiency falls dramatically as the air/heat source temperature falls towards zero. Its very difficult to recover heat from below 0°C as freezing on the heat exchanger is likely.
All in all its not of any significant advantage until we can generate most of our electricity from nuclear sources and as we have not progressed research that puts us about 10 years behind any significant improvement in green generation.
Tony
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Interesting points Tony - I'll put them to the company man when I see him - fortunately I am just the gopher at this stage; but it is an extremely interesting avenue for me at the moment.
Dont forget that the customer knows what he wants and some just want to spend money because thats what they want to do.
Thats what I like about Viessmann, they are happy to tell it as it is without making any wild and unsubstanciated claims.
Solar has no living payback and if its serviced every year it almost loses money but its still green as it saves fossil fuel unlike heat pumps!
The other downside is the guarantee on the heat pump is usually relatively short for such an expensive part.
The growth industry with the ( usually ) hot weather is air-con and anyone entering the HVAC industry would be better getting involved with that. Not very green though! PV cells driving DC fans is good though.
Tony
Thats what I like about Viessmann, they are happy to tell it as it is without making any wild and unsubstanciated claims.
Solar has no living payback and if its serviced every year it almost loses money but its still green as it saves fossil fuel unlike heat pumps!
The other downside is the guarantee on the heat pump is usually relatively short for such an expensive part.
The growth industry with the ( usually ) hot weather is air-con and anyone entering the HVAC industry would be better getting involved with that. Not very green though! PV cells driving DC fans is good though.
Tony
This chap might well be getting six of 'em...
Gas-provided heat may well be around 2.7p / Kw NOW.
But it will soon be a lot more expensive than that!
With much of our natural gas coming from dodgy parts of the planet, in some cases via VERY expensive transport (refrigerated ships), I cannot see any path for gas prices except up! (Of course, problem is also that much of the mains electricity is currently gas-generated, so we're doubly-screwed!)
But it will soon be a lot more expensive than that!
With much of our natural gas coming from dodgy parts of the planet, in some cases via VERY expensive transport (refrigerated ships), I cannot see any path for gas prices except up! (Of course, problem is also that much of the mains electricity is currently gas-generated, so we're doubly-screwed!)
That may well be true!
However because electricity is inefficiently made from burning fossil fuel the price of electricity will also rise in line with the gas prices. So my example will still hold good.
As fuel prices rise, the benefits of solar will increase. Unfortunately as interest rates are climbing the potential return on a solar installation has become more negative. The only way this can be redressed would be if gas prices rise significantly AND if interest rates FALL significantly.
There is a way of making a heat pump worthwhile and I will post that as a seperate thread shortly.
Tony
However because electricity is inefficiently made from burning fossil fuel the price of electricity will also rise in line with the gas prices. So my example will still hold good.
As fuel prices rise, the benefits of solar will increase. Unfortunately as interest rates are climbing the potential return on a solar installation has become more negative. The only way this can be redressed would be if gas prices rise significantly AND if interest rates FALL significantly.
There is a way of making a heat pump worthwhile and I will post that as a seperate thread shortly.
Tony
Agile wrote
A split unit or ground source heat pump does not recover heat. In simple terms they raise the temperature of a process medium from a low to a high temperature level using additional energy.
Recovered heat on the other hand is utilised via that part of the latent heat in the extracted air, which cannot be used by the heat recovery of the ventilation system.
Commercial Air/Air systems have been modulatable for some time now.
The top brands are using digital invertors coupled with highly advanced microprocessors to monitor accurately the current for motor control.
Quite a few of the domestic ground-air/water systems incorporate advanced thermal stores like these -
in order to eliminate cycling.
And one of the above in an installation.
Modulatable domestic air/water systems are also becoming available though expensive at the moment.
The efficiency falls but air systems have a significant advantage over ground source due to being direct exchange.
The units go into a hot gas defrost cycle which prevents freeze ups on the heat exchanger.
A split unit or ground source heat pump does not recover heat. In simple terms they raise the temperature of a process medium from a low to a high temperature level using additional energy.
Recovered heat on the other hand is utilised via that part of the latent heat in the extracted air, which cannot be used by the heat recovery of the ventilation system.
Commercial Air/Air systems have been modulatable for some time now.
The top brands are using digital invertors coupled with highly advanced microprocessors to monitor accurately the current for motor control.
Quite a few of the domestic ground-air/water systems incorporate advanced thermal stores like these -
in order to eliminate cycling.
And one of the above in an installation.
Modulatable domestic air/water systems are also becoming available though expensive at the moment.
The efficiency falls but air systems have a significant advantage over ground source due to being direct exchange.
The units go into a hot gas defrost cycle which prevents freeze ups on the heat exchanger.
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