Air Source Heat Pump in Stone House

[saveasteading]

10 hours ago, Bemak said:

fan assisted radiators.

Using electricity to drive the fans?

I do favour fans in big spaces, especially on the ceiling to force the hot air down again.

 

[Bemak]

13 minutes ago, saveasteading said:

Using electricity to drive the fans?

I do favour fans in big spaces, especially on the ceiling to force the hot air down again.

 

 

something like this https://www.dimplex.co.uk/smartrad 

[saveasteading]

10 minutes ago, Bemak said:

Using electricity to drive the fans

That is very pretty but the price!.

 

40% less energy consumption to bring a room to 21°C from 10°C

 

How so? Energy in = Energy out.

40% quicker I could believe. Less energy, no.

The electric fan is heating the space too, of course.

[SteamyTea]

33 minutes ago, saveasteading said:

quicker I could believe. Less energy, no.

Tricky one.

As heating is exponential, time is important. But at the same time, the bigger the temperature difference, T₁-T_0, more energy is transferred at the start. So transfer efficiency is higher, because standing losses are lower.

Now if say all the heat, the old word for work, which is really just energy, leaks out the object in a fixed time, say 18 hours, then bring it up to T₁ quickly probably does use less, if you consider that below T₁ it is of no use, think DHW.

 

I have often wondered if, when using a ASHP, if it is better to start with a lower flow temperature, but higher efficiency, then ramp up the flow temperature, while taking a hit in the efficiency.

Or just keep the flow temperature the same.

 

Edited August 15, 2022 by SteamyTea

[Bemak]

43 minutes ago, saveasteading said:

That is very pretty but the price!.

 

Definitely pricey but I'd probably only be looking for 4 or 5 for bedrooms and corridors. The bathrooms will have towel rads and I don't mind the idea of larger rads in sitting room (behind couch, room will have a stove too) and a vertical rad in the kitchen. 

[SteamyTea]

13 minutes ago, Bemak said:

Definitely pricey

Have you considered Plinth Heaters.

https://www.screwfix.com/p/tcp-uph201ss-plinth-mounted-fan-heater-silver-2000w-500-x-100mm/348KR

Quick check, I meant to link to the plumbed in one's, not the electrical ones, but you get the idea.

https://kitchenheaters.co.uk/product/kph-1500-classic/

 

Maybe in conjunction with Skirting Radiators.

https://www.discreteheat.com/thermaskirt/products-and-information/overview.aspx

 

Edited August 15, 2022 by SteamyTea

[Bemak]

11 minutes ago, SteamyTea said:

Have you considered Plinth Heaters.

 

 

parents have one in the kitchen - they're decent alright but I think I'd rather a tall rad. I put one in my own kitchen recently, a merriott profile and I'm delighted with it.

 

 

[SteamyTea]

6 minutes ago, Bemak said:

think I'd rather a tall rad

All I see is a dust trap 

[Bemak]

10 minutes ago, SteamyTea said:

All I see is a dust trap 

 

nah - about 70mm between the fins, its actually quite easy to rub down

[AliG]

The numbers @saveasteadinghas listed are the numbers I have seen for the u-value of a solid stone wall i.e. roughly equivalent to a double glazed window. Imagine your whole house was a sun room, it would require a a similar amount of heating without upgraded insulation.

 

You can do the heat loss calculations and see how much heat output you need. The key to using an ASHP is keeping the heat output to a level where you can run the flow temperature as low as possible. This is where ASHP in badly insulated houses goes wrong, as flow temps rise, the COP of the ASHP falls and some houses designed for a gas boiler will need the ASHP to run at its max 55C output where the COP would be awful at low temperatures and costs would be high. Indeed radiator systems are often designed for 70C flow temps and just won't work with an ASHP that cannot provide this high a water temperature.

 

So if the calculation suggest you can run a flow temp of 45C or ideally less then an ASHP is OK. If not then I would stick to a boiler.

 

 

This would require digging up the floors and putting in insulation and UFH. Then you could have a low flow temperature with closely spaced pipework. It would not work with radiators.

 

Also in passing you said that you hoped to use ASHP and PV. PV provides as good as no output in the winter when you need heating. 80-90% of our output comes during the summer when the heating is off. It can help with hot water at that time of year.

[Bemak]

3 minutes ago, AliG said:

The numbers @saveasteadinghas listed are the numbers I have seen for the u-value of a solid stone wall i.e. roughly equivalent to a double glazed window. Imagine your whole house was a sun room, it would require a a similar amount of heating without upgraded insulation.

 

You can do the heat loss calculations and see how much heat output you need. The key to using an ASHP is keeping the heat output to a level where you can run the flow temperature as low as possible. This is where ASHP in badly insulated houses goes wrong, as flow temps rise, the COP of the ASHP falls and some houses designed for a gas boiler will need the ASHP to run at its max 55C output where the COP would be awful at low temperatures and costs would be high. Indeed radiator systems are often designed for 70C flow temps and just won't work with an ASHP that cannot provide this high a water temperature.

 

So if the calculation suggest you can run a flow temp of 45C or ideally less then an ASHP is OK. If not then I would stick to a boiler.

 

would you recommend using that heat loss calculator that was circulated around previously? think i have it. is it easy to work out?

[AliG]

Yes, I actually just brought it up and changed the wall u-value from the 0.11 I had in for my parent's house to 1, it roughly doubled the heat energy required. I then removed MVHR and it added another 50%.

 

You have to size the system to keep the house warm at a reasonably lively low temperature, say -5C.

 

At a guess you are looking at around 50W/sq metre of heat input which is 3-4x what a new well insulated house needs. This is doable with UFH or low temperature radiators, but I looked very quickly and don't have all the data on your insulation levels.

[Bemak]

9 minutes ago, AliG said:

Yes, I actually just brought it up and changed the wall u-value from the 0.11 I had in for my parent's house to 1, it roughly doubled the heat energy required. I then removed MVHR and it added another 50%.

 

You have to size the system to keep the house warm at a reasonably lively low temperature, say -5C.

 

At a guess you are looking at around 50W/sq metre of heat input which is 3-4x what a new well insulated house needs. This is doable with UFH or low temperature radiators, but I looked very quickly and don't have all the data on your insulation levels.

 

Thanks for that. I have no doubt it will require 3-4 times what a new build would need. At this point I'm only realistically going to get the attic insulated 300-400mm. The walls and floors will have to stay as is. The windows will be upgraded though and I might insulate the reveals around the windows to prevent that short route out for heat but other than that it will be what it will be. 

 

The floors are in good shape - so much so I can't justify the cost of new slabs etc. The low temperature rads are probably the way I'll go - fan assisted where possible in the bedrooms as mentioned previously. 

 

Regardless of whether its oil or heat pump - it's going to be 3-4 times more costly to heat the house than a new house. I suppose I just want to try and figure out what the most cost effective would between the two systems for this particular scenario. 

Edited August 15, 2022 by Bemak

[Bemak]

went through the calculator there myself - pretty quickly adding areas and volumes etc. End result, if I'm reading it correctly, is an average monthly heat energy input of circa 2300 kWh. what would a figure like that mean in terms of choosing the correct heating system?

[AliG]

The system has to be sized for the maximum heat input, not the average.

 

If you look at the January column, you will see a heat required at the minimum temperature in watts. Depending on the weather where you are I would suggest changing the minimum temperature to around -5C and seeing what heat input is required at this point. I would guess it is 4-5000W. I guess your floor area is quite small at around 100sq metres then.

 

You can divide this by your floor area to calculate the output per square metre required.

 

You would thus probably need at least a 5kW output heat pump for heating, but you also need to be able to heat hot water whilst heating the house so I would suggest 8-10kW (depends on that minimum figure)

 

Personally I always allow a decent amount over the spreadsheet number just in case real life is worse.

[SteamyTea]

7 minutes ago, Bemak said:

2300 kWh. what would a figure like that mean in terms of choosing the correct heating system?

A litre of heating oil has around 10 kWh of energy, add at least 20% for efficiency losses.

A kg of timber has about 4.5 kWh, but add 40%, but as it will shorten your life, maybe not so bad.

An ASHP at CoP 2.3 will use 1MWh of electrical energy.

So oil will use 2.8 MWh, timber 3.2 MWh.

Multiple them by the going rate if the source price.

[Bemak]

2 minutes ago, AliG said:

The system has to be sized for the maximum heat input, not the average.

 

If you look at the January column, you will see a heat required at the minimum temperature in watts. Depending on the weather where you are I would suggest changing the minimum temperature to around -5C and seeing what heat input is required at this point. I would guess it is 4-5000W. I guess your floor area is quite small at around 100sq metres then.

 

You can divide this by your floor area to calculate the output per square metre required.

 

You would thus probably need at least a 5kW output heat pump for heating, but you also need to be able to heat hot water whilst heating the house so I would suggest 8-10kW (depends on that minimum figure)

 

Personally I always allow a decent amount over the spreadsheet number just in case real life is worse.

 

 

hopefully thats legible. around 3600 kWh in Jan. The house is only 120sqm in size. I would agree with going for a larger unit just to have it rather than be looking for it. I'm thinking of an electric shower upstairs and then a normal shower downstairs to avail of hot water provided by the diverter from PV panels. 

[Bemak]

4 minutes ago, SteamyTea said:

A litre of heating oil has around 10 kWh of energy, add at least 20% for efficiency losses.

A kg of timber has about 4.5 kWh, but add 40%, but as it will shorten your life, maybe not so bad.

An ASHP at CoP 2.3 will use 1MWh of electrical energy.

So oil will use 2.8 MWh, timber 3.2 MWh.

Multiple them by the going rate if the source price.

 

Thanks - this is really useful!

[Bemak]

Quick calculation would suggest it could cost in the region of €200 a month to heat the house in the depth of winter. However this figure doesn't take the potential for zoned heating into account or any offset from PV. 

[Iceverge]

Unless you have a gigawatt array discount any sort of solar for space heating. It's been tried widely and if it is big enough to work it's typically very uneconomical. 

 

Do you have any idea of how much oil has been used to heat the house in the past?

 

 

[Bemak]

ah i just thought the pv might offset some of the electrical loading is all. i wouldn't say it could be used for space heating.

 

see the house never had heating - so i'm finding it hard to gauge it

 

 

[Roger440]

6 hours ago, Bemak said:

 

 

hopefully thats legible. around 3600 kWh in Jan. The house is only 120sqm in size. I would agree with going for a larger unit just to have it rather than be looking for it. I'm thinking of an electric shower upstairs and then a normal shower downstairs to avail of hot water provided by the diverter from PV panels. 

 

Thats a rather healthy consumption!

 

If im understanding this right and using steamys numbers, with oil that would be circa 450 litres!!

 

Or has my maths failed me again?

 

[saveasteading]

I think it was ProDave who pointed out that the summer PV is not a waste as it is needed for hot water.

[AliG]

21 hours ago, Bemak said:

 

 

hopefully thats legible. around 3600 kWh in Jan. The house is only 120sqm in size. I would agree with going for a larger unit just to have it rather than be looking for it. I'm thinking of an electric shower upstairs and then a normal shower downstairs to avail of hot water provided by the diverter from PV panels. 

 

3600kWh is the amount of energy you would need in January if the average temperature was 0.6C. It is calculated from the instantaneous consumption multiplied by the number of hours in the month.

 

The ventilation heat loss looks wrong, it should probably be around 1/3 of the fabric heat loss. Even a very airtight house with MVHR would struggle to get to the figure you have.

 

The number you have to look at is "Total daily heat loss power for minimum OAT (W). This is the instantaneous heat input your house will require at the minimum temp of 0.6C. The heating system has to be sized to keep your house warm at the minimum temp. So basically 5kW at just above 0C. I would change the minimum temp to -5C and see what the number is then, as well as fixing the ventilation heat loss, as you want the heating system to cope on a cold day.

[AliG]

16 hours ago, Iceverge said:

Do you have any idea of how much oil has been used to heat the house in the past?

I meant to ask this. Rather than the spreadsheet, the actual energy consumption in past winters would give you a good idea of how much you are going to need.