Air Source Heat Pump

[Pheo]

Danns said:

ASHP owner here, 14kw mitsi unit it a 1920 non cavity wall property.

Completely the wrong install for the house IMHO. Was installed before we purchased and outdoor unit replaced day before sale. Previous unit lasted 10 years, installed price £15k, replacement cost was £6k.

I’ve seen the PO’s bills and for a 1750sqft property, the electricity bill... £4.5k pa! House was vacant for 9 months and still racked up £2.6k in elec.

There were a few issues and I’ve got it running more efficiently now... god knows how long one of the rad zone valves had been stuck open for. 2nd zone had no stat so was permanently on.

Unfortunately UF heating out of the question atm (might do when we extend)

I’ve been replacing rads with larger units, have split the system into 3 zones and installed nests.

Last month (it was cold) still managed to use £320 (can’t remember exact kwh) and that was with 2 log burners also going!

Given longevity, running cost and practicalities of insulating an older property to a high enough standard, if it went again I think I’d be looking for another solution (no main gas here)

Great watching the defrost cycle out of the office window on a cold day though

Edited by Danns on Sunday 28th February 22:28

Isn't part of the problem that ultimately the system is trying to run at higher than ideal temperatures because of the radiators? My floor UFH circuit is set to stop the floor getting to more than what, 27C? This is massively lower than even a bigger radiator surely? The bigger the temp differential the harder it has to work.

Regardless, swapping them for something like storage heaters surely not going to cost any less? Given even at -7 my ASHP is 200% efficient (vs 100% on the storage heaters?

[eliot]

Evanivitch said:

Whilst I agree the economics of batteries are slim, even on a Agile tariff, they do offer significant CO2 benefits if used properly. The evening peak is met by a clusters of OCGT and diesel units, often quite close to homes.

8-10 years on agile the last time i checked.

[Danns]

Pheo said:

Isn't part of the problem that ultimately the system is trying to run at higher than ideal temperatures because of the radiators? My floor UFH circuit is set to stop the floor getting to more than what, 27C? This is massively lower than even a bigger radiator surely? The bigger the temp differential the harder it has to work.

Regardless, swapping them for something like storage heaters surely not going to cost any less? Given even at -7 my ASHP is 200% efficient (vs 100% on the storage heaters?

I’m no heating engineer so take the below with a large pinch of salt.

System doesn’t know what thermostat target temp is. It’s weather compensated and varies flow temp based on outside temp for the CH. It knows that it’s got to be on or off and what the flow/return temps are.

I’m trying to get the best I can out of my 38 -44 degree flow temp to reach the stat temperature and let the unit switch off. Hopefully storing a bit of that heat in the mass of the rad when it does so.

The larger the heat emitter, the quicker this will be. I’m sure there’s a lovely graph with a sweet spot for run time vs return temp/energy required.

There will be a few more variables and losses thrown into the mix I’m sure,

Standing by for someone knowledgable to show me where the above is incorrect.

[gangzoom]

Danns said:

Last month (it was cold) still managed to use £320 (can’t remember exact kwh) and that was with 2 log burners also going!

That's about 2000kWh + log costs. For a property that size its crazy high energy costs.

We used 5500kWh of gas last month at a cost of £150. Our electricity usage was only 500kWh including charging an EV, solar contributed 120kWh.

ASHP may be more efficient but interms of cost makes zero sense if you can get gas.

If everyone was to get ASHP than the electricity grid might actually collapse, the electricity demand to run them is much higher (and constant) compared to EVs.

14KW drain is 64amps, do you have a 100amp main fuse? Add in an EV charging at 32amps, you will actually need a 3 phase supply to keep the lights on in the house if you are heating the home and charging the EV at the same time!

[mfmman]

dvs_dave said:

They’ll also still run at 80% capacity down to -25C, and will remain at 100% at any temperature the UK climate can throw at it.

Those are performance figures way above anything I have ever seen (although I'm happy to admit I'm not as close to the trade as I used to be) got a source please?

[bazza white]

gangzoom said:

Danns said:

Last month (it was cold) still managed to use £320 (can’t remember exact kwh) and that was with 2 log burners also going!

That's about 2000kWh + log costs. For a property that size its crazy high energy costs.

We used 5500kWh of gas last month at a cost of £150. Our electricity usage was only 500kWh including charging an EV, solar contributed 120kWh.

ASHP may be more efficient but interms of cost makes zero sense if you can get gas.

If everyone was to get ASHP than the electricity grid might actually collapse, the electricity demand to run them is much higher (and constant) compared to EVs.

14KW drain is 64amps, do you have a 100amp main fuse? Add in an EV charging at 32amps, you will actually need a 3 phase supply to keep the lights on in the house if you are heating the home and charging the EV at the same time!

Isn't the 14kw output not input though, I think it's about a 3rd for consumption. Valliants 22kw version uses a 20amp fuse.

[Danns]

gangzoom said:

That's about 2000kWh + log costs. For a property that size its crazy high energy costs.

We used 5500kWh of gas last month at a cost of £150. Our electricity usage was only 500kWh including charging an EV, solar contributed 120kWh.

ASHP may be more efficient but interms of cost makes zero sense if you can get gas.

If everyone was to get ASHP than the electricity grid might actually collapse, the electricity demand to run them is much higher (and constant) compared to EVs.

14KW drain is 64amps, do you have a 100amp main fuse? Add in an EV charging at 32amps, you will actually need a 3 phase supply to keep the lights on in the house if you are heating the home and charging the EV at the same time!

Agreed it is high! Did just have a check, 14kw is the heat output, so it’s around 15A nominal /32A peak draw.

100A single phase cutout (haven’t inspected fuse size)

My understanding on older properties is they need to breathe / need ventilation. Sealing the house up a goodun like a newbuild in my mind will create more issues than it solves.

Got down to 25% humidity in the house last month, I understand that dry air holds less heat which also probably made the system struggle to get to target stat temperature.

I’ve rectified a few causes of draft but do still have 3 x open (albeit restricted) chimneys, I’m sure sealing those up would increase heat retention at a cost of restricted ventilation.

I’ve currently got all 3 nests set to a fixed 17-18 degree temp, my thinking is, takes so long to heat with low flow temp, I better off go with a lower stat temp and keep it stable (and get the other half used to it not being 22 degrees with windows open!)

[dvs_dave]

Danns said:

Agreed it is high! Did just have a check, 14kw is the heat output, so it’s around 15A nominal /32A peak draw.

100A single phase cutout (haven’t inspected fuse size)

My understanding on older properties is they need to breathe / need ventilation. Sealing the house up a goodun like a newbuild in my mind will create more issues than it solves.

Got down to 25% humidity in the house last month, I understand that dry air holds less heat which also probably made the system struggle to get to target stat temperature.

I’ve rectified a few causes of draft but do still have 3 x open (albeit restricted) chimneys, I’m sure sealing those up would increase heat retention at a cost of restricted ventilation.

I’ve currently got all 3 nests set to a fixed 17-18 degree temp, my thinking is, takes so long to heat with low flow temp, I better off go with a lower stat temp and keep it stable (and get the other half used to it not being 22 degrees with windows open!)

Relative humidity (Rh) affects your perception of how cold it is, not the air temperature or “heat”. Dryer air (low Rh) feels colder because the evaporative cooling effect on your skin is greater, even though the air temperature remains the same.

Bump up the humidity and it’ll feel much warmer at the same air temperature as the evaporative cooling effect on your skin drops as humidity increases. In winter in the UK you should aim to keep Rh 40-45%, and it’ll feel much warmer at lower actual air temperatures. Nest is able to control a whole home humidifier, and it could be a good investment for you as it’ll make it much more comfortable at lower air temperatures.

A few standalone ones will do the trick too, although a bit of a pain as you have fill them up.

[Danns]

dvs_dave said:

Relative humidity (Rh) affects your perception of how cold it is, not the air temperature or “heat”. Dryer air (low Rh) feels colder because the evaporative cooling effect on your skin is greater, even though the air temperature remains the same.

Bump up the humidity and it’ll feel much warmer at the same air temperature as the evaporative cooling effect on your skin drops as humidity increases. In winter in the UK you should aim to keep Rh 40-45%, and it’ll feel much warmer at lower actual air temperatures. Nest is able to control a whole home humidifier, and it could be a good investment for you as it’ll make it much more comfortable at lower air temperatures.

A few standalone ones will do the trick too, although a bit of a pain as you have fill them up.

I didn’t know they made such a thing!
Right off to google I go, thanks!

Also, ah yes that makes sense RE RH not changing actual temp just perceived temp, thanks.

Edited by Danns on Monday 1st March 14:08

[LaurasOtherHalf]

Planning through for my plot, starting the proper drawings this week;





It'll be my first ASHP instillation and I'm keen to get into it to be honest. It'll be a selling point and I really want to use this one as a learning curve but seeing as it's my first I'll be using the suppliers for back-up/guarantee.

I must admit I'm really concerned about some of the problems you can get with it. Construction will be as standard as you can get with block cavity and a block and beam ground floor, then insulation and UFH with a specific screed on top. Rads upstairs.

Looking forward to learning all about it but not going to lie, there's nerves as well!

[Trustmeimadoctor]

Thing is with heat pump it's not new technology we have been using them for years since 1855 for the first one says Wikipedia

America have had them in the home for a long long time but just for cooling.

https://youtu.be/7J52mDjZzto

Get to the end for the cold issues

I think the difference for us is we dont use central air we use pumped hot water and big emitters

Maybe we should start using the American method

But untill they artificially increase the price of gas to the point it makes electricity cheaper then it's not much use to us as we don't get the cooling affect to use during the summer

[JuanCarlosFandango]

That looks great.

Any reason for choosing air source over ground source? It seems like the conventional wisdom is ground source for a new build where possible.

[Trustmeimadoctor]

Groundsource doesn't have the winter issues of high energy usage as it doesn't get anywhere near as cold

But it does need a big bit of land to stick the piping in

[Evanivitch]

LaurasOtherHalf said:

Planning through for my plot, starting the proper drawings this week;





It'll be my first ASHP instillation and I'm keen to get into it to be honest. It'll be a selling point and I really want to use this one as a learning curve but seeing as it's my first I'll be using the suppliers for back-up/guarantee.

I must admit I'm really concerned about some of the problems you can get with it. Construction will be as standard as you can get with block cavity and a block and beam ground floor, then insulation and UFH with a specific screed on top. Rads upstairs.

Looking forward to learning all about it but not going to lie, there's nerves as well!

Why Rads upstairs?

[LaurasOtherHalf]

Conventional wisdom of rads upstairs due to simplicity/cost. No need to put in a screed floor and general lower heat requirements.

[Trustmeimadoctor]

Why not the insulation backed boards for suspended floors for ufh for upstairs

[LaurasOtherHalf]

Cost for benefit. I’m a developer after all!

[A chubby fishwife]

Trustmeimadoctor said:

Groundsource doesn't have the winter issues of high energy usage as it doesn't get anywhere near as cold

But it does need a big bit of land to stick the piping in

You can do boreholes instead (if the ground is suitable), but they come in at about £13k a pop, and you need a geotech fella who also sucks up money.

[Trustmeimadoctor]

Could live next to a lake and use water source heat pump

[Chloroform chic]

Trustmeimadoctor said:

Could live next to a lake and use water source heat pump

I designed a system for an office right on the shore of Lough Erne, using the lake. Works a treat and saves digging or drilling!