ASHP Sizing

[LA3222]

I am trying to decide on ASHP sizing. Using the heat loss spreadsheet I believe I can get by with an 8.5kW ASHP.

 

The problem is that I want a 300l DHW tank. All the sellers i find with the Ecodan seem to pair the 8.5kW version with maximum 210l tank. I am considering to go up to the 11kW ASHP so I can get the larger tank - is there any reason 'not' to go ahead and oversize the ASHP?

 

The UFH will run off a buffer so there shouldn't be cycling issues with that part of the system?

[SuperJohnG]

I'm planning on getting the 400L gledhill or similar. I was planning on still getting the 8.5kW, but come closer to the time, I was going to run some calcs on reheat times for an 8.5 vs 11kW. 

 

I believe the 8.5kW is absolutely fine for the 300l tank. @Stones fitted an 8.5 witha 300l pre plumbed cylinder. 

 

 

You'll have read the same thing as me that I believe the COP is better when they aren't working hard hence in theory it should be fine. But I do wonder how much power an ASHP will use in the real world. 

[PeterW]

29 minutes ago, SuperJohnG said:

You'll have read the same thing as me that I believe the COP is better when they aren't working hard hence in theory it should be fine.

 CoP has little to do with working hard, and more to do with temperature differentials which is why they work better at 7/35 than they do at -5/55 and produce much better CoP. 

[SuperJohnG]

8 hours ago, PeterW said:

CoP has little to do with working hard, and more to do with temperature differentials which is why they work better at 7/35 than they do at -5/55 and produce much better CoP.

Well surely if you are trying to bridge a bigger temperature delta then you're working harder.

Edited February 15, 2021 by SuperJohnG

[Diy]

We just had an echo dan installed and it cost about 50quid a week to run and it's very complicated to use so make sure you look into them befor purchase

[SteamyTea]

8 hours ago, PeterW said:

 CoP has little to do with working hard, and more to do with temperature differentials which is why they work better at 7/35 than they do at -5/55 and produce much better CoP. 

 

8 minutes ago, SuperJohnG said:

Well surely if you are trying to bridge a bigger temperature delta then you're working harder.

I think the problem is language.

it is hard to describe in words how it varies with time.

But you know what, there is a second language that we all speak, with varying degrees of understanding.

Mathematics, use it.

[LA3222]

22 minutes ago, Diy said:

We just had an echo dan installed and it cost about 50quid a week to run and it's very complicated to use so make sure you look into them befor purchase

Do you run it from the grid or do you have solar to help with costs?

[Diy]

We run it from the grid but also when temperatures are low it defrost alot and cost even more to run hope this helps

[TonyT]

£50 a week to heat what?

floor area?

heating only?

Hot water too?

internal temp set point?

location in the uk?

house construction?

UFH/Rads?

air tightness?

insulation levels?

large family/working from home?

 

 

 

[SteamyTea]

31 minutes ago, TonyT said:

£50 a week to heat what

I shall add to that.

Is it 50 quid every single week.

 

I just put £40 of fuel in my car today. So now have free motoring for about 400 miles.

[SuperJohnG]

1 hour ago, Diy said:

We just had an echo dan installed and it cost about 50quid a week to run and it's very complicated to use so make sure you look into them befor purchase

Potentially you might be one of the people who have been supplied a system that just isn't set up and designed correctly. It would be worth providing more context as per @tonyshouse mentions to help everyone understand your 50 quid a week comment. 

[SteamyTea]

Back in the 1980s I lived up country in Aylesbury. One very cold winter I thought my gas heating had gone wrong. House was chilly and the boiler was alight.

Turned out it was undersized for those conditions.

That is when I found that 10 quid fan heaters are brilliant for warming a place up quickly.

(My original one has just packed up after 35 years, but it was my fault, opened a door into it and stopped the airflow)

[Pete]

13 hours ago, LA3222 said:

I am trying to decide on ASHP sizing. Using the heat loss spreadsheet I believe I can get by with an 8.5kW ASHP.

 

The problem is that I want a 300l DHW tank. All the sellers i find with the Ecodan seem to pair the 8.5kW version with maximum 210l tank. I am considering to go up to the 11kW ASHP so I can get the larger tank - is there any reason 'not' to go ahead and oversize the ASHP?

 

The UFH will run off a buffer so there shouldn't be cycling issues with that part of the system?

My Panasonic 9kw keeps my 300l Panasonic cylinder topped up nicely. The controller is very easy to understand and Luke at Panasonic is the most helpful person you can come across. 

I am not spending £50 a week on my unit but its horses for courses. I have a passive build and my floor tiles where still lovely and warm at 11pm last night when the unit turned off at midday. The house dropped half a degree overnight and the heat pump is still not coming on as it is still lovely and warm. There are only two of us most of the time so I appreciate HW usage will be lower. As I have said before it takes a while to get used to your house and it will/will not perform. 

[LA3222]

I suspect there is going to be a surge of people complaining about ASHP in the very near future. The Government creating artificial drives to encourage uptake of renewables tends to lead to homeowners switching over with little understanding of what they are and to what homes/circumstances they are suited to. Unscrupulous installers don't care about the aftermath!

 

Most people on here are focused on airtightness and insulation levels. In these circumstances I fail to see how they are nothing but a good option for providing both DHW and heating. I expect they are no different in terms of peaks and troughs in power usage than any other source when considered across the full 12 month weather cycle.

 

With Solar PV you can then get around 3:1 output from any energy generated by panels and use the ASHP throughout the day rather than trying to confine yourself to off peak energy usage?

 

Yes the initial infrastructure can require some capital outlay which some may balk at. Myself, I tend to take the line of it costs what it costs, I see the work I do know as putting in the infrastructure and then over the lifetime of me living there it will work out very cost effective, even taking ASHP lifetimes/ PV panel lifetimes into consideration. If any of them require changing it will not cost so much as the 'infrastructure' is there, its just parts change.

 

I am in an all electric situation, with 280m2 to heat and DHW for 2 kids who like long showers to consider. An ASHP and PV makes sense to me.

[LA3222]

9 minutes ago, Pete said:

My Panasonic 9kw keeps my 300l Panasonic cylinder topped up nicely. The controller is very easy to understand and Luke at Panasonic is the most helpful person you can come across. 

I am not spending £50 a week on my unit but its horses for courses. I have a passive build and my floor tiles where still lovely and warm at 11pm last night when the unit turned off at midday. The house dropped half a degree overnight and the heat pump is still not coming on as it is still lovely and warm. There are only two of us most of the time so I appreciate HW usage will be lower. As I have said before it takes a while to get used to your house and it will/will not perform. 

I am fixed on Ecodan in my head, no logical rhyme or reason other than I have spent a lot of spare time reading pams, installation manuals etc and have mentally committed myself there. I think I will go for the 11kW version with the 300l tank. I assume the benefit of higher power output would be reduced reheat times for DHW which can't be a bad thing.

 

I will have a quick look at the Panasonic though!

[TonyT]

22 minutes ago, SteamyTea said:

Back in the 1980s I lived up country in Aylesbury. One very cold winter I thought my gas heating had gone wrong. House was chilly and the boiler was alight.

Turned out it was undersized for those conditions.

That is when I found that 10 quid fan heaters are brilliant for warming a place up quickly.

(My original one has just packed up after 35 years, but it was my fault, opened a door into it and stopped the airflow)

Yes, I’m also a fan of cheap and cheerful fan heaters and keep a few in the garage for emergencies, used them initially  when doing the house up when it had no heating to start with.dragged out a few times when gas main was replaced and no gas supply for the day and guys in and out the front door all day.

very useful.

 

 

[Pete]

8 minutes ago, LA3222 said:

I suspect there is going to be a surge of people complaining about ASHP in the very near future. The Government creating artificial drives to encourage uptake of renewables tends to lead to homeowners switching over with little understanding of what they are and to what homes/circumstances they are suited to. Unscrupulous installers don't care about the aftermath!

 

Most people on here are focused on airtightness and insulation levels. In these circumstances I fail to see how they are nothing but a good option for providing both DHW and heating. I expect they are no different in terms of peaks and troughs in power usage than any other source when considered across the full 12 month weather cycle.

 

With Solar PV you can then get around 3:1 output from any energy generated by panels and use the ASHP throughout the day rather than trying to confine yourself to off peak energy usage?

 

Yes the initial infrastructure can require some capital outlay which some may balk at. Myself, I tend to take the line of it costs what it costs, I see the work I do know as putting in the infrastructure and then over the lifetime of me living there it will work out very cost effective, even taking ASHP lifetimes/ PV panel lifetimes into consideration. If any of them require changing it will not cost so much as the 'infrastructure' is there, its just parts change.

 

I am in an all electric situation, with 280m2 to heat and DHW for 2 kids who like long showers to consider. An ASHP and PV makes sense to me.

I totally agree about them not being set up properly but then again when you look at people on here most are really keen on understanding most things about their build and some are not!! Plus I think you need a month or so of tweaking the settings and getting to know how the house responds to the heat pump and vicky very.

Last week my cop was pretty poor as it was cold but now it is running at 4. The cost of heating the house is significantly less than it was last week. As we all keep saying put your money in the fabric of the building. I am really happy we put our ufh pipes in a slab rather than a screed imo.

[ProDave]

16 minutes ago, LA3222 said:

I suspect there is going to be a surge of people complaining about ASHP in the very near future. The Government creating artificial drives to encourage uptake of renewables tends to lead to homeowners switching over with little understanding of what they are and to what homes/circumstances they are suited to. Unscrupulous installers don't care about the aftermath!

Nail hit firmly on the head.

 

So we have to reduce CO2 emissions.  That we all understand, but don't let anyone kid you that ripping out a perfectly good working modern mains gas boiler and replacing it with an ASHP is going to reduce your fuel bills. IT IS NOT.

 

I think a lot of companies are going to scare home owners into believing their mains gas is about to be shut off very soon and they have to change for an alternative.  There is going to be a lot of grant money sloshing around which the cynic in me says (largely from previous history) that most of that will just end up lining the pockets of the companies offering to rip out your gas boiler and replace it with an ASHP and very little will benefit the end user.

 

An ASHP makes perfect sense for a modern well insulated low energy house in a location where mains gas is not available, and ours is performing well for that application, but I am yet to be convinced they are a viable option for an old poorly insulated house without huge upgrades to the buildings fabric. And a huge percentage of the UK's housing stock falls into that category.

[SteamyTea]

1 hour ago, ProDave said:

An ASHP makes perfect sense for a modern well insulated low energy house in a location where mains gas is not available, and ours is performing well for that application, but I am yet to be convinced they are a viable option for an old poorly insulated house without huge upgrades to the buildings fabric. And a huge percentage of the UK's housing stock falls into that category.

You can argue, on that basis, that night storage heaters are a viable option.

And is electricity really that expensive for a low enthalpy fuel, it is less than gasoline at the pumps, and look at the taxes on that.

[ProDave]

21 minutes ago, SteamyTea said:

You can argue, on that basis, that night storage heaters are a viable option.

And is electricity really that expensive for a low enthalpy fuel, it is less than gasoline at the pumps, and look at the taxes on that.

Yes or the Willis heater heating a concrete slab at cheap rate electricity periods.

 

But the fact is a heat pump will consume less electricity to deliver the same kWh of heat as a storage heater or willis heater.

[SteamyTea]

10 minutes ago, ProDave said:

But the fact is a heat pump will consume less electricity to deliver the same kWh of heat as a storage heater or willis heater.

Yes, and that is why they are used.

Over a year, they will still stave energy/money, compared to resistance heating, even when the outside temperatures are so low they fail to 'work'.

I don't think there is much difference in running costs compared to gas, assuming both system are working as designed.

[JamesP]

3 hours ago, LA3222 said:

I am fixed on Ecodan in my head, no logical rhyme or reason other than I have spent a lot of spare time reading pams, installation manuals etc and have mentally committed myself there. I think I will go for the 11kW version with the 300l tank. I assume the benefit of higher power output would be reduced reheat times for DHW which can't be a bad thing.

 

I will have a quick look at the Panasonic though!

We have an 8.5kW Ecodan with 300L UVC.  3.74kW of PV and a solar diverter. 285sqm / 750m3 new self build, ugh, air tight with MVHR.

The ASHP has used 4100kWh in the last year to provide heating and hot water for a family of 4 adults. 4 + showers a day, occasional bath, daily washing up and have had heating on in only 3 out of 14 rooms.

Homeowners being encouraged to adopt the new (old) technology are in for cost shock but that is probably due to the quality of the build and the price for that specific unit of energy.

But maybe that is part of the plan...still using lots of gas at the CCGT plant.

Edited February 15, 2021 by JamesP

[LA3222]

17 minutes ago, JamesP said:

We have an 8.5kW Ecodan with 300L UVC.  3.74kW of PV and a solar diverter. 285sqm / 750m3 new self build, ugh, air tight with MVHR.

The ASHP has used 4100kWh in the last year to provide heating and hot water for a family of 4 adults. 4 + showers a day, occasional bath, daily washing up and have had heating on in only 3 out of 14 rooms.

Homeowners being encouraged to adopt the new (old) technology are in for cost shock but that is probably due to the quality of the build and the price for that specific unit of energy.

But maybe that is part of the plan...still using lots of gas at the CCGT plant.

So about £600 of electricity then for heating and hot water in a house that size and with your occupancy looks like good value to me.

[Temp]

Do ASHP come with the sensors needed to monitor the actual COP achieved? 

[JamesP]

31 minutes ago, LA3222 said:

So about £600 of electricity then for heating and hot water in a house that size and with your occupancy looks like good value to me.

We were spending the same amount on oil in our old 100 sqm bungalow, damp and mouldy and very cold in the winter.