Thermodynamics question

[Gilberdyke John]

We are being persuaded to replace boilers with heat pumps as a national policy. In fact when my old oil boiler approached the end of its life I took the step, encouraged by Renewable Heat Initiative grant towards the cost. As my system has an Air Source Heat Pump which delivers hot water to the radiators at a much lower temperature than the oil boiler did the project included changing the radiators to one's with appropriately larger heat emission areas.
After using the system for a while it became evident that comfort conditions in the house were vastly inferior to the oil system. Response time to attaining desired daytime temperature from night time setback indoors is very much slower plus the efficiency of the heat pump drops off as outside air temperature falls. The response from most industry sources is to run with a setback only a couple of degrees lower than daytime so maintaining very little difference in heat loss indoors to outdoors.
I'm by no means a thermodynamics guru but surely this in/out delta t is wasteful and has a significant negative effect on the efficiency? Increase in insulation may reduce the losses but heating a building when residents are either tucked up in bed or out at work seems wasteful.
If Derek M reads this perhaps he can comment?

 

[Murox]

I don't pretend to even understand the details yet many years ago I discovered the technology involved was never intended to be retrofitted to existing housing stocks for a range of reasons; though it could be an adjunct to traditional forms of heating. Only purpose built high spec. housing could truly benefit. Whilst the "rhetoric and spin" around heat pumps has changed I don't believe the basic issues and dare I say flaws have seriously been addressed at all.

 

[user 20297]

We are being persuaded to replace boilers with heat pumps as a national policy. In fact when my old oil boiler approached the end of its life I took the step, encouraged by Renewable Heat Initiative grant towards the cost. As my system has an Air Source Heat Pump which delivers hot water to the radiators at a much lower temperature than the oil boiler did the project included changing the radiators to one's with appropriately larger heat emission areas.
After using the system for a while it became evident that comfort conditions in the house were vastly inferior to the oil system. Response time to attaining desired daytime temperature from night time setback indoors is very much slower plus the efficiency of the heat pump drops off as outside air temperature falls. The response from most industry sources is to run with a setback only a couple of degrees lower than daytime so maintaining very little difference in heat loss indoors to outdoors.
I'm by no means a thermodynamics guru but surely this in/out delta t is wasteful and has a significant negative effect on the efficiency? Increase in insulation may reduce the losses but heating a building when residents are either tucked up in bed or out at work seems wasteful.
If Derek M reads this perhaps he can comment?

We live in a very well insulated, modern property with a ASHP and underfloor pipework. Even with the heating turned off during an inactive period, the house is rarely below 18C. But my partner hates the lack of that deep, radiant heat that you get from a conventional radiator, so a 5kw woodburner is fitted and intended for late evening use.
In an older house (pick a date...I would say pre 2016 in Scotland!), unless significant changes have been made to wall, roof and floor insulation and the house is extremely airtight and benefits from solar gain, I think air-source heating is a non-starter. "Setback" ,(usually meaning the heating effectively permanently activated to prevent the house going below 16C) is going to be really inefficient unless the house fulfils these conditions.

 

[philipm]

Years ago I looked into fitting ground or air source heating.After much research I found how inefficient it was and went with LPG.I found that to achieve the same temperatures as a traditional system you still need an electric or gas boiler to boost the heat.Sorry to say now we are all being conned that this will save the planet. One other thing nobody talks about is the noise from the air source heating fan,There is a chap living on the estate up the road that has loads of complaints from his neighbours.

 

[madasafish]

I did my sums on our house: 1820s built, solid stone floors: thick stone walls : We needed to spend £50k on a heat pump system. A new gas boiler plus insulation upgrades: £5k.

It is a load of politicians defying the basic laws of physics: and economics: and common sense.

 

[user 6228]

We are being persuaded to replace boilers with heat pumps as a national policy. In fact when my old oil boiler approached the end of its life I took the step, encouraged by Renewable Heat Initiative grant towards the cost. As my system has an Air Source Heat Pump which delivers hot water to the radiators at a much lower temperature than the oil boiler did the project included changing the radiators to one's with appropriately larger heat emission areas.
After using the system for a while it became evident that comfort conditions in the house were vastly inferior to the oil system. Response time to attaining desired daytime temperature from night time setback indoors is very much slower plus the efficiency of the heat pump drops off as outside air temperature falls. The response from most industry sources is to run with a setback only a couple of degrees lower than daytime so maintaining very little difference in heat loss indoors to outdoors.
I'm by no means a thermodynamics guru but surely this in/out delta t is wasteful and has a significant negative effect on the efficiency? Increase in insulation may reduce the losses but heating a building when residents are either tucked up in bed or out at work seems wasteful.
If Derek M reads this perhaps he can comment?

If your heating system had a efficiency that was constant regardless of loading you would switch it off not set it back. (set back is a reduced thermostat setting ) However, ASHP dont appear to be like that and in addition their performance is highly dependant on the boiling point and heat capacity of the refrigerant gas they use. So their efficiency curve may for some gases may go up as the outside temperature drops to some extent.
For your system you need to look at the efficiency curve.
Beware of taking "common knowledge" as always true, its a bit like bees

 

[user 6228]

....so a 5kw woodburner is fitted and intended for late evening use.
...

Alas woodburners have been found to be much more highly polluting of fine health damaging particles than Diesel engines...
Alas the info we have on these things does not stay still and make what seem like good decisions at time look very bad with later info.

 

[JamezF]

Alas woodburners have been found to be much more highly polluting of fine health damaging particles than Diesel engines...

And there are now laws allowing on-the-spot fines for anyone living in certain parts of the country who is using a woodburner that produces too much particulate matter, though I've no idea how it is expected to be enforced.

James

 

[Newbeeneil]

I have 50’s ex local authority house that was subject to a murder and fire that was ignited to destroy evidence before we bought it.
We purchased it in a sorry state but complete revamped the whole property including the insulation. Since I owned a company installing renewables I decided I would use my house as a testing ground so I could tell my clients that I believed in the technology. Due to upgraded insulation my house has total energy requirement of 5.5kw which is satisfied by a 9kw ASHP and for that cosy feel a 4.5kw log burner which enforces the need to open every door in the house to dissipate the heat!
At first my wife didn’t like the fact that we didn’t fling windows open at every opportunity but has grown to like the constant low level heat.
Living with heat pump does requires a different mind set due to long periods needed to recover heat in the building when it’s lost.
In the recent cold period I have taken to keeping the core temperature more constant overnight due long recovery in the morning and the fact I’ve had a problem with the auxiliary inline heater which has caused the pump to shut down on the coldest nights .
The difference in maintaining the temperature slightly higher overnight does not seem too costly according to my smart meter which I assume is due to closed doors and little air movement over night.

 

[user 20297]

Alas woodburners have been found to be much more highly polluting of fine health damaging particles than Diesel engines...
Alas the info we have on these things does not stay still and make what seem like good decisions at time look very bad with later info.

You're obviously correct on that, and the said partner very rarely allows me to light the woodburner because of microparticles.. The principle of having one was esablished by the house designers. The best I can say is that it is a model that is a very efficient and modern and for the last seven years we have burned entirely our own timber harvested from storm-damaged trees on our land. We live in the countryside, but are close to another property. The owner is a house-build joiner and kitchen-fitter and burns God only knows what sort of crap in his logburner. The toxic fumes drive me indoors very early in the afternoon in the winter.

 

[user 20297]

Years ago I looked into fitting ground or air source heating.After much research I found how inefficient it was and went with LPG.I found that to achieve the same temperatures as a traditional system you still need an electric or gas boiler to boost the heat.Sorry to say now we are all being conned that this will save the planet. One other thing nobody talks about is the noise from the air source heating fan,There is a chap living on the estate up the road that has loads of complaints from his neighbours.

Ground source is very efficient in terms of energy usage and better than air-source. Correctly installed there is no reason why a good external air-source unit should be noisy; they operate very smoothly and most times you would hardly know ours was running.

 

[user 20297]

And there are now laws allowing on-the-spot fines for anyone living in certain parts of the country who is using a woodburner that produces too much particulate matter, though I've no idea how it is expected to be enforced.

James

....good to know.

 

[user 20297]

I have 50’s ex local authority house that was subject to a murder and fire that was ignited to destroy evidence before we bought it.
We purchased it in a sorry state but complete revamped the whole property including the insulation. Since I owned a company installing renewables I decided I would use my house as a testing ground so I could tell my clients that I believed in the technology. Due to upgraded insulation my house has total energy requirement of 5.5kw which is satisfied by a 9kw ASHP and for that cosy feel a 4.5kw log burner which enforces the need to open every door in the house to dissipate the heat!
At first my wife didn’t like the fact that we didn’t fling windows open at every opportunity but has grown to like the constant low level heat.
Living with heat pump does requires a different mind set due to long periods needed to recover heat in the building when it’s lost.
In the recent cold period I have taken to keeping the core temperature more constant overnight due long recovery in the morning and the fact I’ve had a problem with the auxiliary inline heater which has caused the pump to shut down on the coldest nights .
The difference in maintaining the temperature slightly higher overnight does not seem too costly according to my smart meter which I assume is due to closed doors and little air movement over night.

That sounds similar to our experience with a 170m2 house being heated with a 8.5 kW ASHP. It's obviously going to be cheaper than our similar-sized, previous house that had a 14kW electric boiler. On the most simplistic analysis it's impossible for us to use as much electricity as previously. I was sceptical about heat pumps, but living with one has converted me. However, my partner hates the principle that be should be airtight and won't accept that a closed, heat recovery ventilation system is better than openng windows.

 

[user 6228]

You're obviously correct on that, and the said partner very rarely allows me to light the woodburner because of microparticles.. The principle of having one was esablished by the house designers. The best I can say is that it is a model that is a very efficient and modern and for the last seven years we have burned entirely our own timber harvested from storm-damaged trees on our land. We live in the countryside, but are close to another property. The owner is a house-build joiner and kitchen-fitter and burns God only knows what sort of crap in his logburner. The toxic fumes drive me indoors very early in the afternoon in the winter.

Just for the SchadenFreude

Electric cars also emit the same small particles, from their tyres. tyre particles

 

[philipm]

One downside of having to keep the wiindows closed to maintain the heat is more houses having black mold due to a build up of moist air.Years ago when I was a boy and in the winter we had frost inside the windows it wasnt a problem, but then we had to live with the cold.

 

[user 20297]

One downside of having to keep the wiindows closed to maintain the heat is more houses having black mold due to a build up of moist air.Years ago when I was a boy and in the winter we had frost inside the windows it wasnt a problem, but then we had to live with the cold.

Yes. The solution to that is that when your new house achieves the correct level of airtightness, Building Control (in Scotland) force you to design a dfor mechanical extraction. the cheap way is just to have special extractor fans (dMEV) that are permanently powered on and ensure that the house has regular air changes (thus removing heat).

The proper way is an expensive heat exchanger extraction system that uses electricity to recover the heat from stale and damp air before removing it.

Both approaches are an unplanned, complex and expensive side-effect of the drive towards reducing energy consumption and having warmer and more comfortable homes.

 

[Gilberdyke John]

Years ago I looked into fitting ground or air source heating.After much research I found how inefficient it was and went with LPG.I found that to achieve the same temperatures as a traditional system you still need an electric or gas boiler to boost the heat.Sorry to say now we are all being conned that this will save the planet. One other thing nobody talks about is the noise from the air source heating fan,There is a chap living on the estate up the road that has loads of complaints from his neighbours.

Being fair to the machine, noise is not a problem from my 15kW Vaillant unit. It's quieter than a hair dryer when standing close up in front of it.

 

[madasafish]

I am awaiting for the Government's long promised bonfire of EU regulations to provide an endless supply of red tape that I can burn for warmth.
I have ben holding my breath for it for three years.

 

[Gilberdyke John]

If your heating system had a efficiency that was constant regardless of loading you would switch it off not set it back. (set back is a reduced thermostat setting ) However, ASHP dont appear to be like that and in addition their performance is highly dependant on the boiling point and heat capacity of the refrigerant gas they use. So their efficiency curve may for some gases may go up as the outside temperature drops to some extent.
For your system you need to look at the efficiency curve.
Beware of taking "common knowledge" as always true, its a bit like bees

The ability of reasonably late model pressure jet oil boilers to produce circulating water at up to 80C (although usually somewhat lower to avoid contact burns) gave rapid air temperature rise within the habitable space. Hence on/off control during desired periods worked adequately and gave comfort.
Use of single thermostat control evolved into individual thermostatic radiator valves which became mandated by British Standards.Since the building losses were proportional to the difference from inside to out energy transfer fuel costs were restricted to heating "on periods". Even newer oil (and gas) boilers were operated in condensing mode with radiator circulation temperature lower so bigger radiators were required. A lot of condensing boilers were installed without adequate consideration to condensate pies freezing in icy weather. That was trivial if correctly routed/trace heated was condensate pipe was installed.
The heat pump efficiency does vary significantly as the source air temperature drops although it can produce hot(ish) water but with higher fuel (electricity) usage. Mine can perform an anti-legionella cycle once a week but it operates in the circulating water range 40 to 50 degrees C during heating periods between late autumn to spring. Running at those lower temperatures requires even bigger radiators than were required for condensing boilers. I have all radiator heating but underfloor heating is happy at low water temperature. Problems can arise if trying to combine the UFH function with radiators (say upstairs) unless means of individual temperature modulation for the UFH slab pipes are included.
My impression of the "campaigning" to persuade people to adopt heat pumps is that it approaches a religious crusade fuelled by climate worship. Once installed and dissatisfaction emerges proponents seem to miss what I feel is the whole point of having a heating system. The system should provide comfort to my expectations. NOT to require me adapt my lifestyle to the heat pump. Additionally individual rooms should have the ability to adjust to other factors - cooking, solar gain on Southern aspects etc.
On balance and with hindsight I would have been better to have simply renewed my oil boiler (no natural gas within reach here). Unfortunately the RHI grant deal requires continued use of the system for a number of years so I'm stuck with it until the cycle is completed, however I'm quite likely to make fundamental change once this is over.

 

[Anduril]

A report from the Energy Savings Trust suggests that 80% of heat pumps are underperforming in the UK because they have been poorly installed.