48 replies to this topic

[mab01uk]

"Heat pumps explained. Roger Bisby rants about air source heat pump disadvantages, the green homes grant, types of heat pumps and asks are heat pumps worth it?"

Why Heat Pumps May NOT Be The Future:-

 

Edited by mab01uk, 26 October 2021 - 10:10 PM.

[nicklouse]

Fitted to many many houses in Scandinavia. They work and are cost effective. But then their houses are insulated and underfloor heated.

[xrocketengineer]

Well, this is interesting. I had heat pumps/air conditioning in my house in Florida for over 30 years. But the scheme is very different from what is presented in the video. During most of the year it works as an air conditioner to cool the house and control the humidity inside and in the winter (about one day a year lately), the unit reverses the operation and provides heat inside the house. Now, the unit is more efficient heating than cooling (to a point) because in simple terms, most of the work put in as compressing the refrigerant, moving fans and so on result in generating heat which in addition to the heat extracted from the outside air is all released inside the house. However, the efficiency of this process starts going down as the outside temperature approaches its freezing point or below. First, there is less and less heat that can be absorbed from the outside air as the temperature goes down. Second, the temperature of the outside coils of the heat pump get so cold that they can freeze up and no air from the outside fan can flow through them therefore no heat can be extracted from the outside air. Then the indoors emergency electric heater coils have to kick in on the furnace to provide some indoors heat. On top of that something has to be done with the frozen outside coils, so now the compressor is run in the air conditioning mode to defrost those coils needing even more electricity. Even here in Florida, I had seen that happen a few times when we had winters.  I am not sure how such a system would work efficiently in the UK with much colder temperatures in the winter. On the other hand, if the heat pump heat source is underground (a well or just deep in the soil) and not air, then it would be possible to heat a house efficiently all year long based on the stable temperatures underground. It was very common in the 60's in Florida to have a heat pump that used well water for its heat source. Not only the heat pump was more efficient heating but it was also more efficient as an air conditioner since there were no outside air coils trying to exchange heat in a sweltering day. All that went by the way side because so many wells were sucking the underground aquifer dry and contaminating the ground water with salty sea water.          

[Ethel]

Perhaps us Brits could use rain instead of a well 

 

We really ought to start with the insulation first.

 

 

 

Some interesting points there: we don't have much really cold weather, but night time temperatures can regularly drop to single figures (^oC)  for half the year & we have ample humidity. Doubtless it could be calculated, but roughly 3-4kw would be a typical heating requirement. Sounds a lot to get with maybe 3 or 4^oC headroom - then there's the week or two when it gets below freezing and we'll really want our heating to work.

 

The other option they're touting is piping hydrogen in place of natural gas, but as there's currently a stink over the sewage system not being fit for purpose, god knows if our ancient gas mains will be up to it - I'm guessing the pressure would have to increase substantially for the much lower density

[PoolGuy]

I’ve got over 20 years experience of heat pumps as they’re used for heating some pools. Ground source are very good but a big investment. Air source are ok for heating a pool to 28deg when the weather is favourable (think 20deg min), they’re next to useless for the the average outdoor pool in early and late summer. Yes, they’ll heat the pool but they use a huge amount of electricity to do so, at times you’d be getting less than 1:1 return on your electricity input.

So I find it laughable that Boris keeps mentioning air source heat pumps as a green solution for heating an average house in the average English winter. A possible solution would be for groups of residents to jointly fund ground source heat pumps. 

[DomCr250]

I’ve got over 20 years experience of heat pumps as they’re used for heating some pools. Ground source are very good but a big investment. Air source are ok for heating a pool to 28deg when the weather is favourable (think 20deg min), they’re next to useless for the the average outdoor pool in early and late summer. Yes, they’ll heat the pool but they use a huge amount of electricity to do so, at times you’d be getting less than 1:1 return on your electricity input.

So I find it laughable that Boris keeps mentioning air source heat pumps as a green solution for heating an average house in the average English winter. A possible solution would be for groups of residents to jointly fund ground source heat pumps. 

 

I agree, it's a bit of a joke to think they will actually help - but the great British press seems to want to promote them as the next saviour of the planet.

 

The other consideration which people fail to comprehend is that the current grid cannot provide that much electrical power if we switch to heat pumps - I think people are saying we'd need another 6 to 8 nuclear power stations just to keep up - considering that great French company EDF is currently X years late on Hinkley C and is charging an extra £1.5B its never going to happen.

 

I'm a Hydrogen fan, for both transport and heating - Bosch boilers are already being shipped that are compatible with a natural gas / hydrogen mix and its a simple and efficient way of storing wind and solar energy.

[MikeRotherham]

If only we had known about climate change 30 years ago we could have started to do something about it then instead of now. 

[KTS]

the green credentials are based simply on a case of where does the input energy come from; fossil fuel or renewable.

 

Heat pumps can use renewable energy sources, therefore they're a green solution, just like electric cars etc

 

how energy efficient they are, and how much of the energy they actually consume is generated from renewable sources is not necessarily a subject any politician is going to win any argument on at the moment, so no surprise they won't go there

[Ethel]

I think that would be the way to go - somebody will develop  a rig that'll take a plug out of your front lawn bore a deep hole, install a coil & back fill it in one, easy, operation - but not until the gov't has blown a couple of billion on a short sighted PR stunt than only benefits their chums that got the contract.

 

Even a 3:1 energy return would be a struggle for the electricity grid when it's also  recharging our cars.

[PoolGuy]

If only we had known about climate change 30 years ago we could have started to do something about it then instead of now. 

The people who knew were too busy trying to get nuclear power stations banned, look what a mess that’s left us in. We need to reassess what’s considered an expert.

[Itsaminithing]

Had an air sourced heat pump installed 2 years ago (not by choice).

Extremely noisy in operation.

Extortionately expensive to run.

Heat control is erratic at best.

Water temperature, the amount of hot water available, & the water pressure all vary enormously (& that's without anyone turning on a tap or flushing a toilet).

 

This system might be considered 'green' by some but unless you have an MPs salary & don't mind the inconvenience of there never being sufficient heat or hot water as required then don't even think about having on of these installed in your house.

 

(....& yes, i do know of many people who've had this installed & despise it as much as i do!).

[greenwheels]

The only answer in my view is the Small Modular reactors like the ones being developed by Rolls Royce - https://www.rolls-ro...reactors.aspx#/

One thing that puzzles me is when I look out my window I see lots of house roofs - why isn't it a building regulation saying these should be covered with solar panels on all new builds. I suspect that the raw materials in huge volumes are just not available.

[IronmanG]

I work in so many places now where heating is only a 500 or 750 watt wall mounted electric heater in each room. The insulation is that good. If they continued to insulate correctly and to a greater extent new builds don't even need gas. Air source heat pumps not good enough for the UK.
My house is 100 years old. I put 25mm batten on the walls and 20mm celotex with silver foil tape in 1 room. The radiator never comes on in that room. As previously mentioned insulation first. Then gas consumption would drop dramatically anyway

[Homersimpson]

I've worked with air to water heat pumps on various projects over the last 15-20 years and they do work but they have to be correctly designed and that means the entire system.

 

There is a lot of confusion about what these are, how they work and the different types and it was mentioned above about a unit that provides heating and cooling, although that uses the same basic principals that is a different system which doesn't use water as a heat transmission medium.

 

If using an air to water heat pump to heat a house you need to consider the following:

 

• The temperature that they produce is lower than a gas boiler, therefore the amount of heat you get out of the radiators reduces for a given size.  You therefore need bigger radiators.
• As mentioned above they are less efficent as the outside temperature drops and therefore they need to be sized to cope with this.

A lot of the problems that I have seen are caused by designers/manufacturers installing the wrong sized unit on the basis that it works when its 10^oC outside but when it drops to 0^oC or below it then has an electric immersion heater that comes in to boost it which increases running costs.  This is due in part to manufacturers all trying to make their units look comparable or better than their piers so they make misleading claims that inexperienced designers/installers don't pick up on.

 

They can be made to work successfully but insulation is important and its very difficult and expensive to insulate a lot of the older housing stock (anything with solid walls particuarlly).

 

The whole air to water heat pumps are rubbish arguement is not correct, they are reliable proven technology that tends to be badly designed and installed leading to the reported problems.

 

With the rising cost of gas and the increase in production of low carbon/renewable electricity the switch to a heat pump will soon make a lot more financial sense, however,at the momement i'm not rushing out to change my three year old boiler (came with the house when I bought it) but when the times come (probably sooner rather than later as its a Baxi boiler and its already failed once requiring replacement of most of its components) I will happily install a heat pump for my house.

Edited by Homersimpson, 27 October 2021 - 08:17 PM.

[sonikk4]

I've worked with air to water heat pumps on various projects over the last 15-20 years and they do work but they have to be correctly designed to cover the entire system.

 

There is a lot of confusion about what these are, how they work and the different types and it was mentioned above about a unit that provides heating and cooling, although that uses the same basic principals that is a different system which doesn't use water as a heat transmission medium.

 

If using an air to water heat pump to heat a house you need to consider the following:

 

• The temperature that they produce is lower than a gas boiler, therefore the amount of heat you get out of the radiators reduces for a given size.  You therefore need bigger radiators.
• As mentioned above they are less efficent as the outside temperature drops and therefore they need to be sized to cope with this.

A lot of the problems that I have seen are caused by designers/manufacturers installing the wrong sized unit on the basis that it works when its 10^oC outside but when it drops to 0^oC or below it then has an electric immersion heater that comes in to boost it which increases running costs.  This is due in part to manufacturers all trying to make their units look comparable or better than their piers so they make misleading claims that inexperienced designers/installers don't pick up on.

 

They can be made to work successfully but insulation is important and its very difficult and expensive to insulate a lot of the older housing stock (anything with solid walls particuarlly).

 

The whole air to water heat pumps are rubbish arguement is not correct, they are reliable proven technology that tends to be badly designed and installed leading to the reported problems.

 

With the rising cost of gas and the increase in low carbon/renewable electricity the switch to a heat pump will soon make a lot more financial sense, however,at the momement i'm not rushing out to change my three year old boiler (came with the house when I bought it) but when the times come (probably sooner rather than later as its a Baxi boiler and its already failed once requiring replacement of most of its components) I will happily install a heat pump for my house.

 

Just to add to this ref temps. We used to hire a converted Steading in the Highlands of Scotland for a sort of winter holiday (visiting wifey's family) It had a heat source pump and if memory serves me correctly it was a Air type.

 

Now this conversion was cracking, fully insulated, underfloor heating in the very large open plan kitchen area, log burner etc etc. So when the temp hovered about 0c and internal temp set to 20c it kept it nice and toastie. However the issues started to arise when it went below freezing. Even turned up to max chat it made the rads warm to the touch but not hot. The colder it got (it went down to -10c one evening) and extra clothing was worn and we fired up the wood burner for a while. However that was a like a blast furnace. Nice to start with but a pain to try and balance.

 

I had a look at the unit and there was ice hanging off the pipework going to the house. They were lagged but the pump was not a happy hector. Now this i believe was down to its position, east facing with no direct sunlight to come anywhere close to it. (There were trees very close to it adding even more shelter)

 

Is this a potential problem?? The other steadings had their individual pumps in more open areas but we never got to talk to the other occupants to see if they had the same issues.

Oh and there were large double rads, thermostatic valves etc fitted throughout all of the other rooms.