Heating/Cooling - best combo to go for?

[Indy]

Pertinent details of our build

• 260sq m masonry build to BR standards and emphasis on airtightness.
• U Values
  • Floor: 0.14
  • Walls: 0.15
  • Roof: 0.11
  • Doors/windows: 1.2

 

• Wet UFH heating on both floors – ground and first. 22mm system for the first floor due to height restrictions. Missus likes feeling extra warm all the time - wants temperatures of upto 22C in the rooms. 
• No carpets through the property. Tiles in the living/hallway etc and then engineered wood in the bedrooms
• Digital thermostats for each bedroom, study, living/dining area (8 in total)
• ASHP – most likely 10kW
• 3-400l UVC
• MVHR
• Solar PV – 16 panels (7.1kW)
• Solar battery storage – maybe, depending on price but 5-10kWH battery to be added later.

 

This is generally straightforward and easily speccable. Where things start to get confusing is my desire to add some sort of cooling to the property. This would be in 5 rooms (4 bedrooms + living/dining area) or 8 rooms (adding studies) if we can find a system big enough.

 

Plan A – add a separate air con system using a 5-8way multi split system. One big external unit that sits outside and wall mounted units within the rooms – both to be added in 2 years time when we regenerate funds. Part of the build would be to have power and ducting/pipework to allow the external and internal units to be connected so that we’re not ripping open walls again. Rough cost of £10-£15k for a system like this.

 

Plan B – get a heat hump that runs cooling as well. Not eligible for grant but price difference won’t be that much. Dissuaded against this as running heat pump in reverse means issues with condensation.

 

Plan C – get an MVHR system that also does cooling. BPC quote for standard MVHR parts is £5k for Zehnder Q600(parts only) and £20k for 2 x Q600s with Enthalpy exchanger and ductwork for cooling option. Not going to be as good as active air con but the price differential is quite significant.

 

Plan D – get a Fan Convector unit/Fan coil unit. I’ve picked this up reading these forums and had no idea of the existence of these. But it seems that this look like radiators and can be floor or wall mounted and can do heating as well as cooling? Does this mean I only get the standard MVHR unit, wet UFH heating on ground floor and then install these FCUs in the bedrooms on the 1^st floor? Do they work like air con in the summer and radiators in the winter? What additional pipework do I have to get done for these – if I decide only to get the pipework done now and the actual units added later?

 

Make it make sense please! Would really appreciate some guidance as trying to find a company that pulls this all together in a simple package has been an exercise in futility mostly. They all want to quote or sell products that they stock and not really looking at what would be the most effective option – both in terms of installation and running costs.

 

Thanks in advance.

Edited Friday at 14:04 by Indy

[JohnMo]

57 minutes ago, Indy said:

Digital thermostats for each bedroom, study, living/dining area (8 in total)

Be careful here. Most thermostats are really rubbish with with UFH as the hysteresis is huge and you end up with big under and overshoot of room temp. When we first build I had loads of issues and found it unmanageable, and uncomfortable. Running weather compensation without thermostats works best for us.

 

1 hour ago, Indy said:

ASHP – most likely 10kW

That sound huge with MVHR and your U values are you sure, have you calculated the heat loss.

 

1 hour ago, Indy said:

UFH heating on both floors

I am not impressed with UFH in bedrooms, would do fan coils, way better cooling also, plus response time is good. Hate hot bedrooms, once the bedroom is warm its staying that way with UFH.

 

1 hour ago, Indy said:

Plan A – add a separate air con system using a 5-8way multi split system. One big external unit that sits outside and wall mounted units within the rooms – both to be added in 2 years time when we regenerate funds. Part of the build would be to have power and ducting/pipework to allow the external and internal units to be connected so that we’re not ripping open walls again. Rough cost of £10-£15k for a system like this.

Sounds a waste of good money

 

1 hour ago, Indy said:

Plan B – get a heat hump that runs cooling as well. Not eligible for grant but price difference won’t be that much. Dissuaded against this as running heat pump in reverse means issues with condensation.

No restriction come with grant that says you cannot cool.  It is related to permitted development, but you will have express planning permission with a new build so, make sense to go with option for heat and cool.

 

1 hour ago, Indy said:

Plan C – get an MVHR system that also does cooling.

Another waste of cash, it doesn't do much in the UK, check the datasheets for you flow rates you will get about 0.5kW max at super low flow temps.

 

1 hour ago, Indy said:

Plan D – get a Fan Convector unit/Fan coil unit. I’ve picked this up reading these forums and had no idea of the existence of these. But it seems that this look like radiators and can be floor or wall mounted and can do heating as well as cooling? Does this mean I only get the standard MVHR unit, wet UFH heating on ground floor and then install these FCUs in the bedrooms on the 1^st floor? Do they work like air con in the summer and radiators in the winter? What additional pipework do I have to get done for these – if I decide only to get the pipework done now and the actual units added later?

Install in bedroom instead of UFH. Fun UFH and fan coils on same WC flow rates for heating and cooling. No additional piping needed.

 

So standard MVHR (its ventilation only)

ASHP with cooling ability

Heat pump cylinder

Fan coils in bedrooms, they will manage room temps in auto mode or you can run in manual fan mode on WC

UFH on ground floor and upstairs wet room. Electric towel rads in wet rooms also.

 

If you can add more insulation to floor.

Keep ventilation separate from heating - different suppliers, installers, they are vey different things

 

Think simple not complex, simple is easier to run, cheaper to buy and run

[Indy]

Thanks for the detailed reply. Just to make sure I understand, I'm going to break it down step by step - and please correct me if I've got this wrong.

 

1. Standard MVHR - no cooling added

2. ASHP with cooling function - may or may not be eligible for grant but if we have only 1 unit, then we can put this outside without going back to planning and do it under PD rules. 

3. Heat pump cylinder - 300 to 400l for 3 bathrooms and 1 cloak room. 

4. Wet UFH heating on the ground floor

5. Can I also put fan coils in certain rooms on the ground floor with the wet UFH? This will make them work as air con units in the summer when we run the ASHP in reverse. 

6. Any modifications needed to the ASHP to make sure running in reverse doesn't cause issues?

7. Wet UFH only in bathrooms upstairs, and not bedrooms? Will the fan coils work enough on their own to provide heating up to say 22-23C to keep the rooms at that temp? And what temp can they cool down to in the summer?

8. I currently have towel rads that run off the ASHP and then an immersion element that can be turned off or on. I assume this is the equivalent of electric towel rads?

9. Stupid question: the fan coil units will have plumbing connections to them I assume - i.e. a pipe coming in and a pipe going out?

10. Why not have thermostats in the rooms? Or can we replace the thermostat with the fan coil unit which I assume will have some sort of manual control on it rather than running of a central system?

 

With regards to floor insulation - we did speak to the architect about adding more but his opinion is that BR regs are pretty good these days, and coming from my baseline of a 1930s semi with no cavity walls at all - it's going to be a massive step up. This is what I have so far

 

Floor construction: U Value = 0.14 W/m².K

• 65mm. sand: cement screed
• 500g. Polythene separation layer
• 120mm. Celotex XR4000 insulation
• Polythene DPM
• Concrete beam & block floor to manufacturer's design

Wall construction: U Value = 0.15 W/m².K

• Render
• 100mm. Thermalite Hi Strength 7 blockwork
• 50mm. clear cavity
• 100mm. Celotex CW4000 insulation
• 100mm. Thermalite Hi Strength 7 blockwork
• 12.5mm. plasterboard on dabs dry lining, plus skim

Pitched roof construction (insulation at rafter level): U Value = 0.11 W/m².K

• Roof tiles
• 25x46mm. treated tiling battens
• 25x46mm. treated counterbattens
• LR Breathable roofing membrane
• 150mm. rafters fully filled with 150mm. Celotex XR4000 insulation
• 25x47mm. battened services void beneath rafters
• Celotex PL4060 (60+12.5) insulated plasterboard plus skim
• Proprietary felt support tray

Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K

• Roof tiles
• 25x46mm. treated tiling battens
• 25x46mm. treated counterbattens
• LR Breathable roofing membrane
• 150mm. rafters
• Unventilated loft space
• 19mm. plywood decking or flooring plywood for loft storage
• 75mm. Celotex GA4000 insulation above ceiling joists
• 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation
• Visqueen High Performance vapour barrier
• 12.5mm. plasterboard plus skim

COLD Flat roof construction: U Value = 0.11 W/m².K

• GRP weather surface
• 18mm. plywood deck
• Firrings to give 1:40 fall
• 195mm. joists with 150mm. Celotex XR4000 between joists
• 90mm. Celotex GA4000 insulation below joists
• 12.5mm. plasterboad plus skim

[JohnMo]

2. Permitted development does not exist under planning permission. So if doing a new build permitted development only come after build control sign off.

 

5. Yes

6. Some need a widget adding such as Valiant, most will do it out the box, Daikin some will cool some will not. So be careful with choice.

7. You need to size for heat pump flow temps.

9. Yes

10. Thermostats mean you need a buffer, because you restricted flow from heat pump. Buffers unless very big are useless.

 

Floor insulation, the more the better with UFH. Your floor is hotter than the room, so downwards heat loss can be high.

 

 

[G and J]

2 hours ago, Indy said:

7. Wet UFH only in bathrooms upstairs

It’s a personal thing I guess but I’ve read on here many times that electric mat UFH in bathrooms gives warm wet toes even when the rest of the house doesn’t need heating.  
 

Zoning ASHP based UFH appears to be bad news.  My history is boiler and wet rads with zines which works well in my wind tunnel house.  So it took me a while to get my head round heated slab, slow reaction time, different control methodology entirely.  Talking of which…..

[G and J]

2 hours ago, Indy said:

Floor construction: U Value = 0.14 W/m².K

• 65mm. sand: cement screed
• 500g. Polythene separation layer
• 120mm. Celotex XR4000 insulation
• Polythene DPM
• Concrete beam & block floor to manufacturer's design

I think you may benefit from a bigger slab to benefit from more thermal mass.  (To the pedants, I know that there is scientifically no such thing but it is a useful concept in such debates.  So there.).  Now I appreciate that someone with letters after their name has decreed stuff but you are the client, so actually, what you want tops their sometimes odd preferences.  And remember sometimes the guys doing the drawing are driven more by how quickly they can get onto the next job than they are by your long term happiness.  
 

I’m looking at slightly lowering our bnb and increasing our screed to 100mm (75mm in drawings) and maybe upping the insulation from the 150mm PIR as drawn.  Might use an insulated bnb to help that.

[G and J]

2 hours ago, Indy said:

Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K

• Roof tiles
• 25x46mm. treated tiling battens
• 25x46mm. treated counterbattens
• LR Breathable roofing membrane
• 150mm. rafters
• Unventilated loft space
• 19mm. plywood decking or flooring plywood for loft storage
• 75mm. Celotex GA4000 insulation above ceiling joists
• 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation
• Visqueen High Performance vapour barrier
• 12.5mm. plasterboard plus skim

We’ve not had our as designed SAP done yet but we’ve designed out lots of PIR on the basis that it gives a more echoey house and is bad for the planet (and our carbon score).  So we are going for loads of soft fluffy stuff in the loft that will take me no time at all to deploy (c.f. many miserable hours trimming PIR to fit between trusses) and a raised walkway so as not to compress the fluff.  I’m hoping it will mean the rooms are quieter and feel nicer.  Certainly PIR is not the most popular stuff in here with everyone.

[G and J]

On 22/11/2024 at 14:02, Indy said:

Solar battery storage – maybe, depending on price but 5-10kWH battery to be added later

I’ll be wiring to make adding a battery later easy, but I can’t for the life of me build a case for it right now.  There appears to be no eco benefit and there won’t be a financial one for us.  But prices will come down….

[jfb]

On 22/11/2024 at 15:19, JohnMo said:

No restriction come with grant that says you cannot cool

Are you sure about that?

I was under the impression that if you are including cooling with the ashp you can’t get the grant

[G and J]

10 minutes ago, jfb said:

Are you sure about that?

I was under the impression that if you are including cooling with the ashp you can’t get the grant

I’ll let you know if and when I get the grant, for my ASHP that cools too!  (Perhaps sometime next summer).

[JohnMo]

9 minutes ago, jfb said:

Are you sure about that?

Yes.

 

You need to split some of thought processes out.

 

New build is covered by express planning permission, a retrofit is normally covered by permitted development. Permitted development does not allow cooling. Permitted development is not applicable to a new build until sign off is complete. Also permitted development is not applicable if you want cooling, you need planning permission.

 

None of the above has anything to do with grant. For grant applicability read up of Ofgem website. You need to read source information. If you find cooling isn't allowed I will happily eat my hat.