Air Source Heat Pumps

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roubaixtuesday
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Joined: 18 Aug 2015, 7:05pm

Re: Air Source Heat Pumps

Postby roubaixtuesday » 12 Aug 2020, 8:01am

irc wrote:
roubaixtuesday wrote:
irc wrote: Only a few years ago we had a winter with sub zero temps for days on end. No heat to exchange.


This is a fundamental misunderstanding of thermodynamics.



An over simplification. But plenty reliable sources say air source heat pumps are less efficient as it gets colder. If back up electric heating needs to be used it will get expensive.

The amount of heat that can be transferred to you home by an air source heat pump is massively reliant on the outdoor temperature. As the temperature outside drops, so does the overall heat output of the air source heat pump.

The heating capacity of the air source heat pump also tends to drop as the outside temperature decreases. The air source heat pump is typically sized to be able to produce heat for 80-90% of your annual load, and when the temperatures are above freezing, it should be able to fill 100% of the heating requirements for your home.

As a result of this, it is recommended that you have a backup source of heating available for when the outside temperature drops. This way, it is able to pick up the slack when your air source heat pump starts to decline in efficiency.


https://www.renewableenergyhub.co.uk/ma ... d-weather/

as the thermometer fell, the bills went up. He was getting about 100 kilowatt hours of heat for each 100 kilowatt hours of electricity he used. This means that in cold weather the unlucky householder is spending eight or nine pounds a day on electricity (multiplied up, £250 a month) but, even more strikingly, he would be better off if he simply installed a few electric heaters in the main rooms. In fact, if I were advising him, I’d say he should turn off the pump whenever outside temperatures fall below about 7 degrees.


https://www.carboncommentary.com/blog/2 ... ld-weather


Yes, heat pumps become less efficient as the temperature difference becomes larger. The efficiency is defined as "coefficient of performance", COP.

This is not the same as "no heat".

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Paulatic
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Location: 24 Hours from Lands End

Re: Air Source Heat Pumps

Postby Paulatic » 12 Aug 2020, 8:17am

We’ve a ASHP in its 9th year and still working well without ever having a service.
It’s air to air and heats the whole house. The heat is fine if you are active and and it’s above freezing outside.
However if you are sitting on an evening it is not radiant heat and I will get a cold nose. So we still need to light the stove at night and I will sometimes light stove through day of below freezing outside.
A larger unit might address those issues. From memory I think ours is about 5Kw. Fujitsu.
We have larger 3 phase units installed in my squash club. They definitely Give out a lot more noticeable warmth
Edit: should have said it was £1200 fitted back then. Costs around £12/week in winter running g 24/7
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KFT
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Joined: 28 Jan 2015, 8:53pm

Re: Air Source Heat Pumps

Postby KFT » 12 Aug 2020, 9:43am

Thanks for all the replies - plenty to look into there.
I'm off work for the next 2 days so will hopefully get time to have a look and digest the information.

@Paulatic - do you use yours for cooling in the summer as well ?

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Paulatic
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Location: 24 Hours from Lands End

Re: Air Source Heat Pumps

Postby Paulatic » 12 Aug 2020, 9:49am

KFT wrote:Thanks for all the replies - plenty to look into there.
I'm off work for the next 2 days so will hopefully get time to have a look and digest the information.

@Paulatic - do you use yours for cooling in the summer as well ?

Very occasionally it’s rarely that hot in Scotland
When we have it has been very appreciated
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squeaker
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Location: Sussex

Re: Air Source Heat Pumps

Postby squeaker » 12 Aug 2020, 2:15pm

freeflow wrote:Our neighbour has fitted Air source heating. The plant for the heat exchangers/fans is bout 75 yards from our house. You can hear it working at night which is annoying.
My primary concern, too, followed by switching a gravity fed primary system to 'pressurised' with old radiators :?
"42"

Shreds
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Joined: 19 Dec 2010, 4:43am

Re: Air Source Heat Pumps

Postby Shreds » 12 Aug 2020, 7:41pm

squeaker wrote:
freeflow wrote:Our neighbour has fitted Air source heating. The plant for the heat exchangers/fans is bout 75 yards from our house. You can hear it working at night which is annoying.
My primary concern, too, followed by switching a gravity fed primary system to 'pressurised' with old radiators :?


Your concern in that case should probably the effect of the magnetite black sludge in the internally corroded raditors. This will impact particularly on the impeller in the circulating pump, plus valves as well as boiler life. Very occasionally power flushing should remove it but may also high light any defects or potential defects in the system. Occasionally pub prick holes in radiators may show up in which case they will then need replacing, although this is relatively rare.
Last edited by Shreds on 12 Aug 2020, 8:21pm, edited 2 times in total.

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squeaker
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Location: Sussex

Re: Air Source Heat Pumps

Postby squeaker » 12 Aug 2020, 7:48pm

Shreds wrote:Your concern in that case should probably the effect of the magnetite black sludge in the internally corroded raditors. This will impact particularly on the impeller in the circulating pump, plus valves as well as boiler life. Very occasionally power flushing should remove it but may also high light any defects or potential defects in the system. Occasionally pin prick holes in radiators may show up in which case they will then need replacing, ut this is relatively rare.
Some reassurance then, especially as the system has had Fernox in it from day 1.
"42"

Jdsk
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Re: Air Source Heat Pumps

Postby Jdsk » 13 Aug 2020, 2:10pm

as the thermometer fell, the bills went up. He was getting about 100 kilowatt hours of heat for each 100 kilowatt hours of electricity he used. This means that in cold weather the unlucky householder is spending eight or nine pounds a day on electricity (multiplied up, £250 a month) but, even more strikingly, he would be better off if he simply installed a few electric heaters in the main rooms.

Would those electric heaters give more than 100 kW h of heat for each kW h of electricity?

Jonathan

halfpenny
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Joined: 11 Aug 2020, 3:07pm

Re: Air Source Heat Pumps

Postby halfpenny » 13 Aug 2020, 4:11pm

We have 10 years with a Mitsubishi air source heat pump in a well insulated new build. Noise is low, and only when fan is running -can't hear it indoors. Electricity costs are fine with low temp. underfloor heating, and maintenance cost is zero, much lower overall than gas or oil. Wouldn't switch back