Selection of alternate heating system

[GlynM]

Hello,

 

I'm progressing well with the frame installation of my project, with windows in and cladding next on the list I've turned to trying to finalise the heating system. When I set out I thought I was clear that I was going to install a ASHP (circa 5 - 8 kW), cylinder with immersion back up and distribute through UFH downstairs and rads upstairs with a separate MVHR throughout. Now I've come to gather quotes I've been offered various alternatives to this that I'm considering.

 

The house is designed with the following u values and I'm targeting achieving around 1m3/m2/h air permeability, so low energy, without achieving passive house. 

Roof - 0.1
Walls - 0.127
Floor - 0.171
Windows - between 0.68 to 0.78
Rooflights between - 0.8 to 1.09
Front door 0.8 and back door 1.2 

 

The UFH is already installed so certainly using this as the emitter on the ground floor. 

 

The alternatives I'm being presented with are:

1. as I originally planned, but with a cooling option through MVHR 

2. a Ecocent for DHW linked to the MVHR system and separate ASHP for heating with UFH installed upstairs as well

3. as option 2 but with electric panel rad option upstairs as the heat demand is low for bedrooms

4. a single combined MVHR and cylinder unit (Nilan) with external ASHP to provide heating, dhw, cooling and ventilation in one (the most expensive option) 

 

Whilst there is gas within the nearby road, I am keen not to use it and to install a non fossil fuel solution, I don't have the space for GSH but wouldn't be against solar thermal if it was best.

I'd like to keep install costs under control and then use any spare cash in the future to put towards a PV array with battery storage, but think this may be phase 2 as the budget can't stretch that far and I need to move in as soon as practical.

 

I must admit whilst only having a relatively rudimentary understanding of heating systems I am getting confused by all the different 'expert' opinions who all appear to be convinced their solution is far superior to others. I'd appreciate some non-bias advice as to people's opinion the best solutions? 

 

[ProDave]

With your wall and roof U values (a bit better than mine) I think I can say with reasonable confidence, you won't need heating upstairs.  I am one of several here who installed electric heater points in the bedrooms to fit small panel heaters, and have never used them.

 

I went with ASHP to run both the UFH and DHW for sheer simplicity.  Solar PV supliments that nicely.

 

[joe90]

I too don’t have heating upstairs apart from electric UFH in the en suite and electric towel radiators, IF the weather is very cold which would be fir a very short time I would plug a fan heater into a 13amp socket, didn’t bother with outlets fir heaters and like @ProDave they would have not been used anyway. We have a 4kW ASHP Fir heating and DHW which works very well (and my u values are not as good as yours!).

[Mr Punter]

I think your original plan was fine, but you can ditch the heating upstairs.  Maybe an electric towel radiator or 2.

 

I am not sure why you need cooling at all.  If you have solar gain issues, try to design these out.  If there is a problem room, you could install a split a/c unit.  They are cheap and pretty efficient.

[Jeremy Harris]

Another one that put in connection points for panel heaters upstairs but didn't fit them.  All we have are towel rails in the bathrooms, on a timer so they come on morning and evening for an hour or two.  We did find that our bedroom got a bit too warm, so I installed a split aircon unit last year.  This works well, and has been in use a fair bit to cool the bedroom down over the past couple of weeks or so.

[SteamyTea]

You have stated the U-values for each element, but not the areas of them. 

I believe that separating space heating and domestic hot water us best, but not always the cheapest. Until one part of it fails, then the other but is still working. Also you need hot water all year, heating (and cooling) not so often.

MVHR is not really designed for heating/cooling, if you want to do that, then oversize the ductwork, that way you can shift more air closer to the temperatures you want.

PV is always good to have, ST, once the water is up to temperature, just sits there doing nothing.

[Gone West]

3 hours ago, GlynM said:

I'd appreciate some non-bias advice as to people's opinion the best solutions? 

It depends on where you live. There's a big difference between Cornwall and The Shetland Isles.

[Hobbiniho]

2 hours ago, PeterStarck said:

It depends on where you live. There's a big difference between Cornwall and The Shetland Isles.

 Its been a nice day here 4 degrees  or -1 with the windchill factored in 

[Jeremy Harris]

Just now, Hobbiniho said:

 Its been a nice day here 4 degrees  or -1 with the windchill factored in 

 

It's only been up to 17°C here today, but plenty of sun, so the house is currently sitting at 23.5° with all three cooling systems running . . .

[ProDave]

Just reached a high of +10 just now but sharp frost forecast tonight.  It was a lovely sunny afternoon for our walk with light wind.

[GlynM]

Thank you all for your feedback, very useful.

 

18 hours ago, PeterStarck said:

It depends on where you live. There's a big difference between Cornwall and The Shetland Isles.

Peter, I am located in west Hertfordshire in the Cilterns so a nice intermediate location between Cornwall and The Shetland Isles.

 

20 hours ago, SteamyTea said:

You have stated the U-values for each element, but not the areas of them. 

I believe that separating space heating and domestic hot water us best, but not always the cheapest. Until one part of it fails, then the other but is still working. Also you need hot water all year, heating (and cooling) not so often.

MVHR is not really designed for heating/cooling, if you want to do that, then oversize the ductwork, that way you can shift more air closer to the temperatures you want.

PV is always good to have, ST, once the water is up to temperature, just sits there doing nothing.

Approximate areas below;

Roof - 0.1 - 97.5m2
Walls - 0.127 - 137m2
Floor - 0.171 - 104m2
Windows - between 0.68 to 0.78 = 87m2
Rooflights between - 0.8 to 1.09 = 6.5m2
 

I've set all windows that face vaguely south back within the reveal as far as they will go and whilst I have 1 larger sliding door (6.5m2) that faces south, I am planning an external pergola to keep solar gain down, plus the rooflights will have blinds.

 

Sounds like its not worth the money to add the cooling function to the MVHR which is good news, or heat the upstairs bedrooms, I've left a void next to the stairs in the centre of the house so hopeful that this will aid the movement of heat from the UFH upstairs in winter months. I might still put the future connection in for the upstairs rads, but not connect them (apart from towel rads in the bathrooms).

 

Just need to decide on whether to combine the DHW with ASHP or look at a Ecocent as a separate system. As I understand it, the advantage of keeping them separate is that you wont need to run the ASHP in the summer months or in warmer spring/ summer times. If they were combined then DHW demand in the summer would rely on the ASHP kicking in, if the ASHP modulates, is this a big issue or not to its performance? 

 

 

 

[SteamyTea]

13 minutes ago, GlynM said:

Just need to decide on whether to combine the DHW with ASHP or look at a Ecocent as a separate system. As I understand it, the advantage of keeping them separate is that you wont need to run the ASHP in the summer months or in warmer spring/ summer times. If they were combined then DHW demand in the summer would rely on the ASHP kicking in, if the ASHP modulates, is this a big issue or not to its performance? 

 

Generally speaking, the less stressed an ASHP is the more efficient it is.

 

 

 

13 minutes ago, GlynM said:

Roof - 0.1 - 97.5m2

 

13 minutes ago, GlynM said:

Floor - 0.171 - 104m2

Why the difference?  The roof lights?

Edited April 14, 2020 by SteamyTea

[Jeremy Harris]

We have 500mm overhangs on our South facing glazing, totally useless, as the problem seasons are Spring and, to a lesser extent, Autumn, when the low sun projects deeply into the house.  We fitted reflective film to the windows that made a big difference, but hasn't completely fixed the solar gain problem.  With hindsight I should have opted for something far more effective at shutting out the heat.  Ideally I'd have liked to fit external blinds, as these can be very effective at controlling solar gain, but it would have created yet more hassle with the planners.  The other option we really should have looked at is Sage glass, as, despite the cost, that seems to work very well at reducing solar gain, too.

 

Our ASHP runs a lot more in Spring and Summer than it does in winter, not heating the house, but cooling it.  We run it in reverse so it pumps cool water around the underfloor heating pipes, something that is very effective.  As we have PV panels in the roof, there is no cost associated with running the ASHP in cooling mode.  Our ASHP rarely runs at anything other than it's very lowest speed.

 

We also have a heat pump built in to the MVHR (a Genvex) and that makes a useful contribution to cooling the house.  It's been running in cooling mode every day for the past few weeks, in this sunny weather.

 

Finally, I fitted an additional split aircon system in our bedroom last year, and that's invaluable at keeping the bedroom cool.  That's also been run every day for the past couple of weeks.

[GlynM]

1 minute ago, SteamyTea said:

Generally speaking, the less stressed an ASHP is the more efficient it is.

 

Why the difference?  The roof lights?

 

Correct 6.5m2 of rooflights, one large and 3 small.

[SteamyTea]

Have you run your build though @Jeremy Harris heat loss spreadsheet?

[Gone West]

2 hours ago, GlynM said:

I've set all windows that face vaguely south back within the reveal as far as they will go and whilst I have 1 larger sliding door (6.5m2) that faces south, I am planning an external pergola to keep solar gain down, plus the rooflights will have blinds.

It's a good idea having a pergola to reduce solar gain. For our roof window glazing we have a G factor of 0.3 IIRC, which keeps solar gain very low.

[JFDIY]

5 hours ago, Jeremy Harris said:

 

Finally, I fitted an additional split aircon system in our bedroom last year, and that's invaluable at keeping the bedroom cool.  That's also been run every day for the past couple of weeks.

 

Jeremy,

Can the mini-splits be used for heating? I'm Considering forgoing upstairs heating as I don't think we'll use it, air con would be nice, and great if could be used as back-up heating.

 

All that said my build is nowhere n at passive house, but better than a traditional build.

[Jeremy Harris]

Just now, JFDIY said:

 

Jeremy,

Can the mini-splits be used for heating? I'm Considering forgoing upstairs heating as I don't think we'll use it, air con would be nice, and great if could be used as back-up heating.

 

All that said my build is nowhere n at passive house, but better than a traditional build.

 

 

Yes, some of them can, just need to check the spec.  They have the big advantage of a rapid response time, as they really chuck out a lot of air initially, when the difference between the set point and the room temperature is a degree or two.  Ours slows right down once it's got the room to temperature, and is quiet enough that it doesn't disturb sleep on the few nights last year we kept it on.  They are also pretty cheap, I detailed the cost of ours in this thread:

 

[Conor]

On 13/04/2020 at 15:37, PeterStarck said:

It depends on where you live. There's a big difference between Cornwall and The Shetland Isles.

Agreed. @Jeremy Harris was actively cooling his house the other day  (Wiltshire?) and we had our heating on (Belfast).

 

But from those U values, space heating demands will be absolutely minimal. Hot water will be a bigger energy demand. I might wing it with off peak immersion heating of water and just have UFH loops for a future ASHP if it's ever required. I'll also get a gas connection put in (usually free here as long as have an appliance e.g. hob, tumble drier etc) to make resale easier.

[Jeremy Harris]

2 minutes ago, Conor said:

Agreed. @Jeremy Harris was actively cooling his house the other day  (Wiltshire?) and we had our heating on (Belfast).

 

As I type this all three cooling systems are running again, the aircon in the bedroom, the floor cooling from the ASHP and the air cooling via the heat pump in the MVHR.  It was sub-zero here last night, too, with a hard frost.  Solar gain can be a real bugger at times.

[SteamyTea]

55 minutes ago, Jeremy Harris said:

As I type this all three cooling systems are running again

I have my small (500W) fan heater on.

Been decorating most of the day, left the back door (NE facing) open.

Bloody freezing in my kitchen now.

Edited April 14, 2020 by SteamyTea

[Jeremy Harris]

20 minutes ago, SteamyTea said:

I have my small (500W) fan heater on.

Been decorating most of the day, left the back door (NE facing) open.

Bloody freezing in my kitchen now.

 

 

23.4°C in the house right now, and we've had no heating on for at least the past couple of weeks.

[ProDave]

I have just light the stove. Proving it was a little too early to turn the heating off completely.  At least wood is free.

[joe90]

We have had no heating on fir many weeks, the sunspace heats the house very well, in fact we have had to shut the bifolds today to stop the house overheating. Can’t remember the last time we lit the wood stove.

[coconutsaregood]

On 13/04/2020 at 12:35, GlynM said:

Windows - between 0.68 to 0.78

 

Super efficient windows you have there. Are you using Perspex of something? That range is half of those made with coated mineral glass and inert gas cavities.