Rik - any more news on your experience with air source heat pumps?

[Matthew Sharp]

I'm now beginning to look at these seriously, any idea on their effectiveness when the outside air temp is low?

[Rik Smith]

Matthew

i can aggregate some information from a variety of people / source into one place for you - without going into too much detail.


some background reading from the Chief Scientific Advisor to DECC (David Mackay)
http://www.inference.phy.cam.ac.uk/withouthotair/c21/page_140.shtml

Performance:

the graph attached below shows a variety of information:
Outdoor air temp - left hand vertical axis
heating demand - right hand axis
airsource heat pump capacity - right hand axis
COP (coefficient of Performance) - right hand axis

what this suggests is that for the average year it is possible that the heat output of the air source heat pump (ASHP form now) will fall below demand - the very exceptionally cold days - based on traditional sizing techniques. i believe a number of ASHP can provide an electric heating boost from the unit. you will also notice the the COP falls with falling outside air temperature, this is to be expected - i don't believe this graph factors in the additional energy required to prevent freezing of condensation (an electric heating coil is used to prevent the exhaust heat exchange elements from cooling - resulting in anti-cycling modes [it stop heating your house to look after itself - 5 minutes at a time]). A similar line can be drawn for temperature demanded from unit.


Case study (large Isle of Wight Victorian property renovation - including insulation)

Air source heatpump Mitsubishi - Ecodan 14 Kw (w140 ecodan) (£9,600 installed + cost of radiators etc) - 200 m2 being heating based on needing 70 w/m2 of floor area (modern building regulations)

this is the largest domestic unit i believe Mitsubishi do at the moment (recently released)

General Advice:

go with a large, established manufacturer - Mitsubishi, Fujitsu - and have them install it, not your 'builder mate who saw it on Grand Designs'

Good practice = Insulate before heating - insulate before sizing heat demand.

Good controls are a must! - room thermostats etc.

i previously made a comment about Victorian floors, this is because ASHP prefer traditional 'low loads' ie output of 40 Deg C (not 70 for water radiators) as a result underfloor heating is normally the best output for the ASHP. also an hot water tank with an immersion heater is a must!


i hope that provides a bit more information, let me know any more questions you may have an i'll try to answer them.


Rik

[Matthew Sharp]

Rik

thanks for your very full reply. Are you using ASHP for radiators, or under floor? I wonder if it would be sensible to have a separate one for Hot Water just to supplement the solar, and a dedicated one for under floor. Do you think that architects could advise on questions like this, or perhaps the ASHP suppliers? I'm talking to a number of architects at the mo to see if I can find one who will do our project.

Matthew

Rik Smith said:

Matthew

i can aggregate some information from a variety of people / source into one place for you - without going into too much detail.


some background reading from the Chief Scientific Advisor to DECC (David Mackay)
http://www.inference.phy.cam.ac.uk/withouthotair/c21/page_140.shtml

Performance:

the graph attached below shows a variety of information:
Outdoor air temp - left hand vertical axis
heating demand - right hand axis
airsource heat pump capacity - right hand axis
COP (coefficient of Performance) - right hand axis

what this suggests is that for the average year it is possible that the heat output of the air source heat pump (ASHP form now) will fall below demand - the very exceptionally cold days - based on traditional sizing techniques. i believe a number of ASHP can provide an electric heating boost from the unit. you will also notice the the COP falls with falling outside air temperature, this is to be expected - i don't believe this graph factors in the additional energy required to prevent freezing of condensation (an electric heating coil is used to prevent the exhaust heat exchange elements from cooling - resulting in anti-cycling modes [it stop heating your house to look after itself - 5 minutes at a time]). A similar line can be drawn for temperature demanded from unit.


Case study (large Isle of Wight Victorian property renovation - including insulation)

Air source heatpump Mitsubishi - Ecodan 14 Kw (w140 ecodan) (£9,600 installed + cost of radiators etc) - 200 m2 being heating based on needing 70 w/m2 of floor area (modern building regulations)

this is the largest domestic unit i believe Mitsubishi do at the moment (recently released)

General Advice:

go with a large, established manufacturer - Mitsubishi, Fujitsu - and have them install it, not your 'builder mate who saw it on Grand Designs'

Good practice = Insulate before heating - insulate before sizing heat demand.

Good controls are a must! - room thermostats etc.

i previously made a comment about Victorian floors, this is because ASHP prefer traditional 'low loads' ie output of 40 Deg C (not 70 for water radiators) as a result underfloor heating is normally the best output for the ASHP. also an hot water tank with an immersion heater is a must!


i hope that provides a bit more information, let me know any more questions you may have an i'll try to answer them.


Rik

[Rik Smith]

The ASHP is being used with underfloor heating and a hot water tank (there is a reserve oil boiler - off gas network) . To me, having multiple units would seem a bit like over kill, 1 gas boiler can do both heating and hot water - only for very short periods do their demands overlap.

the experience with architects has been very poor, numerous firms will nod and say approving things, but when it come to actually implementing it, they have very little clue about this new technology (unless they have a resident expert on the subject).

you also need to be careful with suppliers - or at least the sales men. for the isle of Wight, a guarantee / corrosion resistance (to salt air) was fundamental - nearly all the sales people were ready and willing to say 13... 15... 20 year guarantee, but the paper work / details can be very different ( guarantee only on pump and pips, not on the heat exchange etc.)

so in terms of getting advice, i would recommend either getting heavily involved in the detail yourself, or you contract a consultant / contractor that can spell out the options and choices from models and installation types.

Numerous colleagues have told me stories of friends having builders install solar hot water units on the roof, only to find their gas bill go through the roof the next winter. REASON: the builder had installed the solar collector 'backwards' and had in effect installed a radiator on their roof!

one last thought - my understanding is that solar hot water collectors are utilised by having a secondary (dedicated) coil in the hot water tank, as a result you could get a tank with 2 coils in but only use 1 of them ever - leaving the potential to plumb in the additional capacity (oil, gas, ASHP, etc) without replacing the tank....

hope this helps.

Rik

[Matthew Sharp]

Rik

thanks for the extra info. I'll do some more reading and talking to a number of architects to suss out their actual understanding of the principles and experience of the technologies. Your warning is taken! If you like I can update you/the TK2K site on progress.

thanks

Matthew

Rik Smith said:

The ASHP is being used with underfloor heating and a hot water tank (there is a reserve oil boiler - off gas network) . To me, having multiple units would seem a bit like over kill, 1 gas boiler can do both heating and hot water - only for very short periods do their demands overlap.

the experience with architects has been very poor, numerous firms will nod and say approving things, but when it come to actually implementing it, they have very little clue about this new technology (unless they have a resident expert on the subject).

you also need to be careful with suppliers - or at least the sales men. for the isle of Wight, a guarantee / corrosion resistance (to salt air) was fundamental - nearly all the sales people were ready and willing to say 13... 15... 20 year guarantee, but the paper work / details can be very different ( guarantee only on pump and pips, not on the heat exchange etc.)

so in terms of getting advice, i would recommend either getting heavily involved in the detail yourself, or you contract a consultant / contractor that can spell out the options and choices from models and installation types.

Numerous colleagues have told me stories of friends having builders install solar hot water units on the roof, only to find their gas bill go through the roof the next winter. REASON: the builder had installed the solar collector 'backwards' and had in effect installed a radiator on their roof!

one last thought - my understanding is that solar hot water collectors are utilised by having a secondary (dedicated) coil in the hot water tank, as a result you could get a tank with 2 coils in but only use 1 of them ever - leaving the potential to plumb in the additional capacity (oil, gas, ASHP, etc) without replacing the tank....

hope this helps.

Rik

[George Latham]

Matthew
We are going through some similar discussions and decisions to you. Our architect has brought in a separate energy consultant called Roger Kelly, who is going to advise on the the best way to tackle all the energy issues.
Roger is local and his email is [e-mail]
Regards
George

[Matthew Sharp]

George

thanks very much for the contact - I'll email Roger and see if he is interested.

Matthew

George Latham said:

Matthew
We are going through some similar discussions and decisions to you. Our architect has brought in a separate energy consultant called Roger Kelly, who is going to advise on the the best way to tackle all the energy issues.
Roger is local and his email is [e-mail]
Regards
George