Advice on Cooling and Heating

[wcavanagh]

Hi all,

Been looking at so many posts and information here I am still confused as what is best.  I am renovating a large house in Spain and looking, to install UFH and some kind of cooling that does not involve blowing cold air using AC units.  I was thinking maybe using cooling in the UFH circuit and maybe even a cooling ceiling?  I will be based in Servile where 40C is not uncommon and trying to get the house comfortable.  I am an engineer and have experience with UFH here in UK.  I read so much about worries of condensation, etc I can deal with that via smart controls etc.  But was looking for some feedback on people with these cooling systems in place and do they really work?  I will be using MHVR systems also, to circulate and dump air out.

[Redbeard]

What inherent 'cooling measures' does it have already? Large roof oversails on the 'hot side(s)', smaller windows ditto, external shading, exposed masonry as 'leveller' There, I avoided saying Thermal Mass - Oops!

 

As I understand it quiet, slow-running MVHR systems rarely shift enough air to have a serious cooling effect, and systems which do may be too loud.

 

Stating the blindingly obvious (sorry!) the main effort should be to stop excessive solar gain, rather than to get rid of it once it's inside.

 

I agree with 'passive' measures where possible, but air-to-air HPs do have the advantage of being a winter heating system as well as a cooling system. I think if it were mine I'd do all the passive measures I could (including IWI) *and* fit a/a HP

[JohnMo]

UFH and condensation isn't an issue, as long as you control flow temperature. You manage the dew point inside the house envelope (what it's doing outside that envelope doesn't matter). But the way UFH cooling seems to work on the person is floor is cooler and pulls heat from the body, so actually room temperature feels cooler than it actually is. On the room temperature it pulls heat to the colder floor zone. Adding ceiling (or wall if easier) cooling into the mix should work well as cold air would continually fall.

[wcavanagh]

Thanks guys, the house has no heating or cooling just now.  So fresh start.  I will have to see how the building responds once I get out, etc.  I am a a real automation geek, so will employ all the automatic closing of shades, auto dimming glass, etc, to reduce solar gain as much as possible.  But very keen to make a comfortable environment as 35 - 45 C is normal in the summer.  I will have a PV system also of course to run the ASHP.

[-rick-]

I've not personal experience related to this so take this with a pinch of salt but I think you need to be very careful here - do a proper heatgain analysis. There are a lot of success stories here of using ufh cooling in the UK climate in airtight, very well insulated homes. You are adapting an existing building and with the general style of building in Spain I very much doubt your building has been built to those standards. Additionally, the climate in Spain is just much hotter so heat gain will be higher than we are used to here (both in terms of instant load but also daily demand - higher heat for a longer time during each day).

 

In-slab cooling is limited by the dew point and whether you will be able to get enough cooling capacity from it within that limitation is a big concern. If you are comfortable targeting an internal temperature of 26-30C then it's easier than targetting 20C but still this might be a challenge.

 

If your building is well insulated, airtight and has plenty of exterior shading to stop direct sunlight through the windows then this is all probably doable but likely still comes with conditions that you would need to maintain the internal temperature constantly, ie, not opening doors/windows until the outside temperature/humidity is similar the internal temperature/humidity. So a common situation of sitting outside in the cooler evenings with people going in out of the house would be more difficult.

 

The other thing to highlight is humidity. Because of the dew point issue there is no dehumidification ability with in-slab cooling. Therefore, if you want to control humidity at all you will need an alternative way of doing it. I suspect the outcome of all this is that you will need to install fan-coils in addition to ufh cooling (could all be run from the same ASHP or seperately). Maybe you only use the fan-coils intermittently with the ufh being used for maintaining the environment outside of the hottest hours/dehumidification cycles.

 

Anyway an interesting project and I'm very curious of the outcome. Good luck.

[Conor]

We use our ASHP to cool our house now and again on the rare occasions temps are in the high 20s. It takes the edge off. Maybe 5c after a couole of days constsnt running?  It's would not work at all in 35-45c. you need an air flow based system.

[Thorfun]

2 hours ago, Conor said:

We use our ASHP to cool our house now and again on the rare occasions temps are in the high 20s. It takes the edge off. Maybe 5c after a couole of days constsnt running?  It's would not work at all in 35-45c. you need an air flow based system.

Just out of interest, what’s the flow temp you use for your slab cooling?

[Nick Laslett]

1 hour ago, Thorfun said:

Just out of interest, what’s the flow temp you use for your slab cooling?

This is my first year, where I have been interested in the slab cooling at my place. We are still fermacell boarding at the moment. 
 

I don’t have the weather compensation dialled in for cooling, but currently running with a flow temp of 11°C, with room temp of 20°C. 
 

There is a thread here somewhere, with lots of useful info about dew point and automating the ASHP temp to track above the dew point. 
 

I have just lagged all my pipes, and at the moment 11°C flow temp seems to be working to keep the house cool. The only visible dew is on the manifold, but it is not dripping. 
 

We have UFH pipes in our concrete first floor, which does increase the area we have for cooling. 

Edited June 15 by Nick Laslett

[JohnMo]

4 minutes ago, Nick Laslett said:

but currently running with a flow temp of 11°C, with room temp of 20°C

11 degs is very close to dew point, if your heat runs at that temp all the time.

 

We suffer more from solar gain than hot outside temperature, being in NE Scotland.

 

Ours is set up to effectively manage return temp, so heat pump restarts when return temp hits 19 degs and heat pump will run down to about 12 degs. WC curve is very simple it reduces flow 1 Deg when outside temp is above 25 (pretty rare), I also have a double set point set, so if battery is nearly full the target temp is dropped 1 Deg. 

[Conor]

2 hours ago, Thorfun said:

Just out of interest, what’s the flow temp you use for your slab cooling?

12c I think. Not used it yet this year.

[SteamyTea]

Just had a quick look at your local weather, you are at about 35% RH and 35°C.

So I suspect condensation is not a real problem. Dewpoint is around 18°C.

 

Your main problem will be having enough air movement from convection, to make a real difference.

If there is not enough density change in the room air, then there will be hardly any power being transferred. This could also be easily swapped by ventilation.

 

You may find that using mechanical ventilation with fan coils for cooling, and heating, which need not be noisy, but can be easily boosted for exceptional circumstances, is by far the easiest solution.

Edited June 16 by SteamyTea

[MikeSharp01]

On 15/06/2025 at 13:52, Conor said:

We use our ASHP to cool our house now and again on the rare occasions temps are in the high 20s.

Is that via the UFH only then?

[Conor]

10 hours ago, MikeSharp01 said:

Is that via the UFH only then?

Yes, UFH on both ground and first floor.

[saveasteading]

The answer in Spain is to adopt Spanish habits.

Up early in the morning. Rest  12 to 4.

Work /shop 4 til 8.

Stay up late.

Use shade and air, shutters, blinds and fans, and purge the house of heat after dusk.

 

I'm in Spain now. 35°C max. Overnight min 23.

I was observing a construction worker digging a trench yesterday. With all the safety gear on too. I wouldn't fancy that but is it preferable to a UK frozen trench in February? At a restaurant we were leaving at 10.30 and families were still arriving. 

 

Chilling equipment is cheap to buy  (from €250) but expensive to run. Perhaps just have one room kept cool?

[JohnMo]

10 minutes ago, saveasteading said:

expensive to run

Coupled with PV not really, I actually spend less on electricity when it's blazing sun. ASHP runs a long time, powered by PV, battery needs less charge so less electricity imported. A dull day I might spend a pound or more on electric a sunny day 30p.

[MikeSharp01]

7 minutes ago, JohnMo said:

A dull day I might spend a pound or more on electric a sunny day 30p

Plus the standing charges naturally.

[JohnMo]

5 minutes ago, MikeSharp01 said:

Plus the standing charges naturally.

Can't not pay that, so plus 60p per day

[SteamyTea]

1 hour ago, saveasteading said:

With all the safety gear on too.

They take their H&S very seriously in Spain. Our maintenance guy went to our Spanish site and hated all the rules they had to comply with.

 

[JohnMo]

12 minutes ago, SteamyTea said:

They take their H&S very seriously in Spain. Our maintenance guy went to our Spanish site and hated all the rules they had to comply with.

 

Something like minimum 27 for summer cooling setting and 19 in winter heating mode. Would have most the soft folk in this country crying in their cornflakes, either too cold in winter or too hot in the summer.

[mk1_man]

We find the cool slab on ground floor great when it gets hot, definitely takes the edge of the room temp.  Our Vaillant flows around 13 degrees, no issues with any condensation.  Although upstairs has overlay ufh the cooling is not that effective so looking to install a couple of traditional air con units whilst we still have the access to run the pipework ( build ongoing ! )