Air Source Heat Pumps

[roubaixtuesday]

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".

[Paulatic]

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

[KFT]

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 ?

[Paulatic]

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

[squeaker]

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

[Shreds]

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.

[squeaker]

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.

[Jdsk]

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]

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

[mjr]

I have friends who fitted a system about ten years ago. Replacing an oil fired boiler. [...]

So that's about three generations ago if it was a Mitsubishi.

So quite noisy, relatively complex, running costs can be higher than the sales(wo)man said.

Noisy depends on the unit. Some are designed for domestic uses and emit a slight whooshing when speeding up and slowing down and almost nothing otherwise. Quieter than a similar capacity oil boiler. But some are really made to be stuck behind a barn or stables at a big house and output lots of heat quickly but lots of noise.

I suspect running cost problems are mainly when they are set up by boiler installers to operate like a boiler, with relatively high fixed radiator temperatures and on-off thermostat(s) "calling for heat". Smart controllers can do so much better than that, ranging from the basic weather compensation, through factoring in weather forecasts (is it getting colder? Then extract more heat now when it's cheaper and store it in the building for later. Is it getting warmer? Do the reverse. What's the "feels like" temperature? Use that to tweak the plan to please the humans), up to learning how the building reacts to heating and what times of day the humans tend to adjust the target room temperature.

Rough calculations suggests air-source heat pumps should beat electric easily, oil if installed at boiler or tank replacement time, and be competitive with gas after April. When the climate change levy is moved from renewable electricity more onto gas and oil (especially gas, which currently underpays), it will all get easier.

But picking a good installer is both difficult and critical.

Ground source is better (and more difficult) IMV.

It depends. If you're using it for heating only and have solar or cheap overnight grid electric heating your water, especially in summer, then ground source definitely comes out well ahead. Otherwise, it's closer and depends what % of your annual heat demand is for hot water and whether the difference is enough to offset the extra cost of ground-source equipment.

In the right place may be worth considering though.
However it's not, in my experience, "plug and play" trouble free, for decades.

I'll let you know in a few decades

We chose a heat recovery ventilation system instead.

Which one, please? And how has that worked out for you?

Hate to think what electric heating would have cost or if the grid could cope with every home heating full blast after gas was gone.

The grid should develop to support it, probably including incentives for local power storage to smooth demand, in electric vehicles or otherwise.

[Jdsk]

We chose a heat recovery ventilation system instead.

Which one, please? And how has that worked out for you?

Villavent.

Mixed feelings. We'd certainly fit something similar again in the same situation.

Jonathan

[axel_knutt]

If it doesn’t work at reasonable negative temperatures then can someone please explain the freezer to me? Pretty sure freezers can go down to -20 or so without putting up a fight in the refrigerant unit.

Freezers aren't designed to pump more energy than they consume, they're designed to reduce the temperature inside a well-insulated cabinet. They don't have to make any design compromises to accommodate a wide range of temperatures, either.

This example of a domestic heat pump never exceeds a CoP of 3.3, so it will never be competitive running off electricity that's four times more expensive than gas. Neither will this one unless it's a very mild day.

[ANTONISH]

The grid should develop to support it, probably including incentives for local power storage to smooth demand, in electric vehicles or otherwise.

I see this trotted out a great deal.
Electric vehicles may be able to support a very short time boost - and of course they will need to be recharged - I can't see people plugging in their vehicle at night with the expectation of having a fully charged vehicle for use in the morning only to find it has been drained of charge and not recharged.

With extensive use of renewables storage is going to be the Achilles heel of the system. I have never heard any proponent of renewable energy put forward a solution to the storage problem - I listened to Caroline Lucas recently extolling the benefits of renewables but not a word on storage.
I don't foresee any storage solution which will be able to store and deliver the massive amounts of energy we will require.

IMO we should stop this game playing and go for nuclear power. Maybe build a number of mini nukes to get us over the period required to build large nuclear facilities.

[Jdsk]

,,, I listened to Caroline Lucas recently extolling the benefits of renewables but not a word on storage.

Lucas, 7 January 2022:

"Investment in renewable energy should be accelerated.  Wind energy, both onshore and offshore, is cheaper for electricity generation than gas, as is solar. The UK is now home to the world’s largest offshore windfarm.  We urgently need investment in a smarter, more flexible grid and better energy storage to tide us through periods of low wind speeds. "

https://www.newstatesman.com/spotlight/ ... ergy-bills

Jonathan

[ANTONISH]

,,, I listened to Caroline Lucas recently extolling the benefits of renewables but not a word on storage.

Lucas, 7 January 2022:

"Investment in renewable energy should be accelerated.  Wind energy, both onshore and offshore, is cheaper for electricity generation than gas, as is solar. The UK is now home to the world’s largest offshore windfarm.  We urgently need investment in a smarter, more flexible grid and better energy storage to tide us through periods of low wind speeds. "

https://www.newstatesman.com/spotlight/ ... ergy-bills

Jonathan

OK there was a word just no specifics