ASHP AND ELECTRICITY COST

[SteamyTea]

4 minutes ago, IanR said:

The MVHR has too low a flow rate to transmit 6.5kW to the house

I often think that if MVHR had 200mm diametre ducts, a lot more could be made if it.

 

[Dan F]

1 hour ago, pdf27 said:

15 kWh/m²/year for heating, or 10W/m² peak load - in reality the two are usually pretty close so let's assume that the notional "well insulated" new house hits both standards.

 

@Kesoolhe Our house is has design values of 12 kWh/m2/year for heating and 10W/m2 with 0.6ACH.  But, if I adjust aritigtness from 0.6 to 6 in the PHPP spreadsheet then these figures jumps to 33 kWh/m2/year for heating and 27W/m2 heating load.  With a 280m2 house and assuming COP of 3 that difference would be around something like £460/yr vs. £170/yr.  Of course you house isn't the same as ours, but it gives you an idea of the impact airtighness improvements could have on the heating element of this cost.   

 

You do have MVHR don't you?

[Thedreamer]

Interesting responses to my post earlier.

 

55 minutes ago, IanR said:

But I still need a 6.5kW heat source at times to maintain 21 degrees. ie. when it's been overcast for several days and the average temperature hasn't got above 0 degrees.

 

Would you rather have no heating system, then have a house that drops down to say 19 degrees when you have a cold overcast day? For us if it's exceptionally cold I wheel out an electric heater and then it's away as needed. Takes a matter of seconds.

 

 When you consider the capital and running cost it's very cheap way of providing that exceptional on demand heating needed in a modern self build house.  

 

1 hour ago, pdf27 said:

If you have a more efficient or smaller house - and particularly if you can use less hot water - then the payback time will get longer. I'm really struggling to see a heat pump not making sense though.

 

I hear what you are saying, if you are building a large property then perhaps a external air source heat pump has a place. But if we are wanting to get serious about climate change then we should consider whether we need to build such large properties. 

 

1 hour ago, SteamyTea said:

2 hours ago, Thedreamer said:

just don't get why they are needed in a recent self build for space heating and if installed in a earlier built properties then they will struggle to fight against lack of insulation and airtightness issues.

That is true for any heating system though. This is such a misunderstood point that it has become binary. 

 

Yes, that is correct. But if you have inefficient system you have high running costs, but replacing with another system you may have higher potential running costs and the capital cost of installing the system. Often people misunderstand how air source heat pumps work and their benefits.

 

They may also have place in fairly new built social housing schemes. In my local area this is typically where you see them installed.

 

1 hour ago, Pete said:

So for us a heat pump was necessary to be able to have a really warm house which needs heating from November to March (I think as we only moved in December) but yet still have very large windows and live as exactly as we would like to without the house dictating how we live.  

 

Again is it necessary to have a really warm house? That's your personal preference, which is none of my business, but generally can we live with slightly lower temperatures during the odd occasion of the year? 

 

2 hours ago, pdf27 said:

Assuming you did go for a 5kW unit, it would be running at full power for 600 hours/year to provide sufficient heating - just under 7% of the time - and the same amount again to provide hot water.

 

To me this is the bottom line, why pay for a system that operates at full capacity for only 7% of the year in heating the home? Is it really worth the capital cost to the customer and tax payer. As mentioned earlier much better to invest in insulation and airtightness and keep heating to exceptional times of the year.

[SteamyTea]

25 minutes ago, Thedreamer said:

why pay for a system that operates at full capacity for only 7% of the year in heating the home?

That is possibly the mean run time.

It is the power distribution that is important, generally the lower power output, the higher the CoP. This is why HPs are oversized by peak power output. 70% if the time they will be running well below capacity, only a few percent at maximum, then auxillary heating may be needed.

This is the same as most heating systems, except will some thermal ones, as they modulate downwards, the efficiency follows.

It is all a numbers game.

 

As always, if you can reduce the power losses, the problem becomes easier to solve.

I often think two ASHPs are needed, a basic one for water heating, and a more sophisticated one for space heating. They could share a box and many of the parts inside i.e radiator and fan, electrical and electronic interfaces. Only the actual compressors and pipework need to be separate so they can run two output circuits, a high and a low temp.

[joe90]

10 minutes ago, SteamyTea said:

I often think two ASHPs are needed, a basic one for water heating, and a more sophisticated one for space heating.

why, my small (5kW) heat pump does both (well, only water heating 9 months of the year) but copes with the heating as well during the other 3 months! Seems a shame to have a heating heat pump sat there fir 9 months not being used!

[IanR]

1 hour ago, Thedreamer said:

Would you rather have no heating system, then have a house that drops down to say 19 degrees when you have a cold overcast day? For us if it's exceptionally cold I wheel out an electric heater and then it's away as needed. Takes a matter of seconds.

 

Takes a matter of seconds, yes, but it is very local, so as you move around the house, you need to take it with you and plug it in. That's not how I personally wish to live, and not suitable for a family.

Even if I took the hot water requirement out of the equation I would want a heating system. I personally want the convenience, plus the house I built needs to be saleable, and I don't believe the general public are ready for a house without a heating system.

 

You can't however take the hot water requirement out of the equation. So with a heat source needed, it's there for space heating too.

 

1 hour ago, Thedreamer said:

I hear what you are saying, if you are building a large property then perhaps a external air source heat pump has a place. But if we are wanting to get serious about climate change then we should consider whether we need to build such large properties. 

 

A carbon neutral large property has no more impact on climate change than a carbon neutral small house. Any democratically elected government is going to find it very difficult to legislate on house size. 

Edited May 16, 2021 by IanR

[SteamyTea]

17 minutes ago, joe90 said:

why, my small (5kW) heat pump does both

Because for very little extra manufacturing costs, you could get a system that is more efficient.

Basically a normal HP is being asked to do two things, at different temperatures, and for different times. Combi boilers are the same.

It is akin to asking a car to be small, economic, high speed and spacious. Easy to do with a 2 seater (small heat loads), just put a box on the back and call it a van, not so easy to do with a 6 seater (high heat load), they end up like the Fiat Multipla, which was rubbish at everything.

[joe90]

14 minutes ago, SteamyTea said:

Basically a normal HP is being asked to do two things, at different temperatures,

Well mine is not normal then, it produces water at one set temp, 48’ in my case. When called to do heating it heats a buffer tank, this is then blended down at the manifold for the UFH at 24’.

[Pete]

1 hour ago, Thedreamer said:

Interesting responses to my post earlier.

 

 

Would you rather have no heating system, then have a house that drops down to say 19 degrees when you have a cold overcast day? For us if it's exceptionally cold I wheel out an electric heater and then it's away as needed. Takes a matter of seconds.

 

 When you consider the capital and running cost it's very cheap way of providing that exceptional on demand heating needed in a modern self build house.  

 

 

I hear what you are saying, if you are building a large property then perhaps a external air source heat pump has a place. But if we are wanting to get serious about climate change then we should consider whether we need to build such large properties. 

 

 

Yes, that is correct. But if you have inefficient system you have high running costs, but replacing with another system you may have higher potential running costs and the capital cost of installing the system. Often people misunderstand how air source heat pumps work and their benefits.

 

They may also have place in fairly new built social housing schemes. In my local area this is typically where you see them installed.

 

 

Again is it necessary to have a really warm house? That's your personal preference, which is none of my business, but generally can we live with slightly lower temperatures during the odd occasion of the year? 

 

 

To me this is the bottom line, why pay for a system that operates at full capacity for only 7% of the year in heating the home? Is it really worth the capital cost to the customer and tax payer. As mentioned earlier much better to invest in insulation and airtightness and keep heating to exceptional times of the year.

Previous house we always had the thermostat set to 18 but as I get older I feel the cold more and when you are sat we found 21 was a more comfortable temp. To be fair solar gain works really well for us and this means we have not had the heating on since March. It is touch and go sometimes if we had a cold spell whether to put the heating on but because the house takes a while to adjust to external temps then we found looking at the incoming weather (if it was going to be sunny) helps us decide to hang on a bit so it is free!!

[SteamyTea]

38 minutes ago, joe90 said:

Well mine is not normal then

It is quite normal.

All I am saying is that we can build better systems at not too much extra cost.

I could probably modify ab Ecocent type system and run both my water and space heating from it. But that is because, like you, we have very low energy needs.

In a larger, not so efficient, household, water heating may dominate, a system designed purely to heat just hot water may well be much more efficient i.e it would not have to modulate, could use a different refrigerant, run at higher temp with a larger radiator.

The UK is only at the start of the HP journey and there is a lot of friction to overcome. Imagine asking a plumber that is used to fitting gas boilers for the last 30 years that they now have to think differently. They have all the skills, but they will struggle to overcome their old prejudices, let alone explain to a customer that they have to be left on all the time. Not mentioning any names here, but we all know the kind of customer I am talking about.

1kW for 24 hours is the same energy as 2 kW for 12 hours, except the efficiency loses are greater at elevated temperatures.

(If thermal boilers were so (expletive deleted)ing great, why is CoP less than 1, when I was a kid we had a gas powered fridge in the caravan, why is there not a gas powered heat pump. I know the answer)

Edited May 16, 2021 by SteamyTea

[Thedreamer]

1 hour ago, IanR said:

Takes a matter of seconds, yes, but it is very local, so as you move around the house, you need to take it with you and plug it in. That's not how I personally wish to live, and not suitable for a family.

Even if I took the hot water requirement out of the equation I would want a heating system. I personally want the convenience, plus the house I built needs to be saleable, and I don't believe the general public are ready for a house without a heating system.

 

You can't however take the hot water requirement out of the equation. So with a heat source needed, it's there for space heating too.

 

Our heater moves a matter of meters. In the first year we have been in the house it was on a handful of times.

 

I do agree that the general public is not ready for a no heating situation.

 

The surveyor who valued the property at the end said that to be the case. I'm not sure how it affected the value as we were £40k above what they said it would be at the start. 

 

I heat my water with a joule aero heat pump. This can be set-up to work as an exhaust heat pump or extract colder air from the outside.

 

The bulk of my house heating in the winter evening is provided by our wood burner with rare quick heat provided by an electric oil radiator.

 

1 hour ago, IanR said:

A carbon neutral large property has no more impact on climate change than a carbon neutral small house. Any democratically elected government is going to find it very difficult to legislate on house size. 

 

What do you class as carbon neutral? You could build a massive house and get a good energy rating but in reality this does not take into account the environmental impact from the construction or how many people actually live in the house in the end.

 

45 minutes ago, Pete said:

To be fair solar gain works really well for us and this means we have not had the heating on since March.

 

That's great. I have a fair amount of south facing glazing as well, which provides the bulk of the heating.

 

1 hour ago, SteamyTea said:

The UK is only at the start of the HP journey and there is a lot of friction to overcome.

 

I agree with this.  

 

[pdf27]

2 hours ago, Thedreamer said:

Would you rather have no heating system, then have a house that drops down to say 19 degrees when you have a cold overcast day? For us if it's exceptionally cold I wheel out an electric heater and then it's away as needed. Takes a matter of seconds.

Allowing the temperature to drop and riding through a cold snap only works for intermittent cold days, although it's worth noting that a very well insulated and airtight house is likely to be significantly more comfortable if you try to do that than one built to building regulations. If that's your general plan however it just adds up to to using resistance heat - and there are ways to make it even easier than pulling out a fan heater (duct heater in MVHR, etc.).

 

2 hours ago, Thedreamer said:

When you consider the capital and running cost it's very cheap way of providing that exceptional on demand heating needed in a modern self build house.  

Capital cost is very low indeed. Running cost, not so much: a bill of £1200/year for heating and hot water in an exceptionally well insulated house is distinctly mediocre. With a heat pump that goes down to £400/year which is much better.

It's also worth noting that fitting a heat pump is equivalent to reducing the heat losses in the house by a factor of 3. If you account for the cost of building to the much higher standard required to achieve this in other ways, then achieving any given energy consumption standard will almost certainly be cheaper if a heat pump is used rather than any other form of heating.

 

2 hours ago, Thedreamer said:

I hear what you are saying, if you are building a large property then perhaps a external air source heat pump has a place. But if we are wanting to get serious about climate change then we should consider whether we need to build such large properties. 

I don't disagree with that. It doesn't make a huge difference to the maths though - for anything but the very smallest flats, it is much more efficient (both financially and in terms of lifetime energy use) to use a heat pump rather than resistive heat. It's also worth noting that I used Passivhaus numbers - it's still pretty rare for houses to be built to that standard, even most self-builds miss it and the volume housebuilders are miles off. That's deliberate on my part - if the numbers are clear for a Passivhaus, it's a no-brainer for 99% of the housing stock.

 

2 hours ago, Thedreamer said:

To me this is the bottom line, why pay for a system that operates at full capacity for only 7% of the year in heating the home? Is it really worth the capital cost to the customer and tax payer. As mentioned earlier much better to invest in insulation and airtightness and keep heating to exceptional times of the year.

The obvious parallel is a car. The average car drives 10,000 miles per year, and the average speed across the whole road network is 60 mph. That means the average car is driving for 167 hours per year - 1.9% of the year. Getting a taxi every time would have a much lower capital cost, but the running cost is significantly higher and in the vast majority of cases having your own car is considered more cost-effective.

[Thedreamer]

8 minutes ago, pdf27 said:

Capital cost is very low indeed. Running cost, not so much: a bill of £1200/year for heating and hot water in an exceptionally well insulated house is distinctly mediocre. With a heat pump that goes down to £400/year which is much better.

 

I only made a handful of taxi journeys with the electric heater and kept my eye on the meter.

 

My electricity bill all in was £67 in January and that was with the children being at home during lock down.

 

13 minutes ago, pdf27 said:

t's also worth noting that fitting a heat pump is equivalent to reducing the heat losses in the house by a factor of 3

 

Not against heat pump for water heating. My exhaust system is currently extracting the moist bath heat into the system for tomorrow. 

 

[NSS]

Haven't read every word in the thread, but not seen any mention of the other consideration that will increasingly need to be made - cooling. Our heat pump is primarily there to heat water and space, but can also cool the space and would be used to do so far more but for the fact that we have SageGlass.

[kxi]

How about this topical method of resistance heating:

https://heatbit.com/

(not an endorsement...)

 

Current UK kWh and BTC prices suggest about 50% pay back. Could be different tomorrow.

I suppose if you lived in a cold, sunny place and had excess PV you might be tempted.

[ProDave]

1 hour ago, kxi said:

How about this topical method of resistance heating:

https://heatbit.com/

(not an endorsement...)

 

Current UK kWh and BTC prices suggest about 50% pay back. Could be different tomorrow.

I suppose if you lived in a cold, sunny place and had excess PV you might be tempted.

At least someone is thinking about ow to usefully use the heat generated by mining BTC rater than just paying to remove the waste heat from a building.

[kxi]

2 hours ago, kxi said:

https://heatbit.com/

 

Industry secret that since 2016 this is how a Tesla's AC heating works. Sure they say the data connection is for OTA updates, but really it's sending the satoshis back to papa.

 

Edited May 18, 2021 by kxi
Dramatisation. May not have happened.

[SteamyTea]

5 hours ago, kxi said:

How about this topical method of resistance heating:

https://heatbit.com/

(not an endorsement...)

I shall just put on my thicker socks.

[gascar]

Sorry to go off-topic, but can anyone point me to a decent article on ASHPs such as might be useful to ordinary drafty houses with solid walls?

If I need 10kW with -5°C outside. Cop is what, 1.3? I think they'd be enormous and use more electrc power than is available.

?

[SteamyTea]

10 hours ago, gascar said:

Sorry to go off-topic, but can anyone point me to a decent article on ASHPs such as might be useful to ordinary drafty houses with solid walls?

If I need 10kW with -5°C outside. Cop is what, 1.3? I think they'd be enormous and use more electrc power than is available.

?

For some background stuff, read this (all of it).  A bit dated now as he never saw how cheap PV and Wind Power became before he died.

https://withouthotair.com/download.html

[PeterW]

10 hours ago, gascar said:

If I need 10kW with -5°C outside. Cop is what, 1.3? I think they'd be enormous and use more electrc power than is available.

?

CoP will only be that low if you’re trying to push the ASHP up to gas rad temperatures. A 10kW ASHP is pretty small, single phase ones go up to 16kW and usually run a max 32A breaker so you’re well within the usage boundaries. Some new R32 gas ASHP can get up to 67°C plus but CoP does suffer. Samsung make a 12kW and 16kW ASHP for change of £3,500, installation isn’t complex

 

 

 

 

[gascar]

Thanks Steamy & Peter - I thought this thread might be productive having read (most of) it! Time will tell if the prices really do crash now.

Edited May 30, 2021 by gascar

[SteamyTea]

On 18/05/2021 at 19:48, kxi said:

 

Industry secret that since 2016 this is how a Tesla's AC heating works. Sure they say the data connection is for OTA updates, but really it's sending the satoshis back to papa.

 

Missed this when you posted it.

I like that idea, better get working on it, I have a few graphics cards kicking about in a box in the loft.

 

I think there may be a radio play in the concept, how all our connected lives are really just making shitcoins, for no real purpose, with the side affect that the world's energy is all used up.

Similar to Harry Harrison's Bill the Galactic Hero. Which was about a pointless war (written in the Vietnam War era).

[Ronny]

My house was built in 1937 ex council and was used for many years by miners. It has cavity wall and attic insulation, double glazing and nothing much else. Small 2 bed with 2 pensioners. House is all electric and heat pump was installed just before last Christmas. 17 Feb to 8 may 81 days, total bill 203.42. This is comparable with the combi boiler we had. I am far from being an expert on heat pumps, but it works fine for me. At no time has the house been cold always around 20 / 21 deg. The heat pump is a LG Therma V 7 kw. 

[Kesoolhe]

On 16/05/2021 at 13:31, Dan F said:

 

@Kesoolhe Our house is has design values of 12 kWh/m2/year for heating and 10W/m2 with 0.6ACH.  But, if I adjust aritigtness from 0.6 to 6 in the PHPP spreadsheet then these figures jumps to 33 kWh/m2/year for heating and 27W/m2 heating load.  With a 280m2 house and assuming COP of 3 that difference would be around something like £460/yr vs. £170/yr.  Of course you house isn't the same as ours, but it gives you an idea of the impact airtighness improvements could have on the heating element of this cost.   

 

You do have MVHR don't you?

No MVHR, I just couldn’t justify it as we often have the windows and doors open. I have two young boys that are in and out plus we like to open our sliding doors that look across the adjacent ridge and furrow. I’ll work on then airtightness, I’m sure that will help no end