passive house and ufh

[jonM]

On 10/02/2023 at 10:24, Iceverge said:

@jonM

 

Back on topic, you mentioned having different rooms at different temps which I can see some benefit in. 

 

Maybe bathrooms at 23, living room at 22, kitchen at 21, circulation spaces at 20 and bedrooms at 19. 

 

Have you actually done something like this in practice, does it create drafts?

 

 

Yes, we have used it to keep our bedroom at a cooler temperature. The house has a high level of air tightness so drafts aren't a problem. 

[ProDave]

In our house we often have to keep the bedroom door shut all day to keep it cool enough or too much heat convects up the stairwell.

[Iceverge]

On 12/02/2023 at 12:51, jonM said:

Yes, we have used it to keep our bedroom at a cooler temperature. The house has a high level of air tightness so drafts aren't a problem. 

 

I was of the notion that differential temps created drafts too. Mind you, I've not ever noticed any in our house, even when some rooms are warmer. 

 

Is there any handy way of comparing rads output to UFH, I haven't done any of the sums but would like to get stuck in. I'm also thinking that standard radiator TMV's wouldn't be appropriate for very low flow temps? 

 

I like the idea of very oversized rads, intelligently placed, running on a single circuit at very low flow temps. Balanced to achieve the stated above temps in each room for an ASHP, or even retrofit compatible for ASHP. No zoning to worry about, no pipes to lay during the initial stages of the build, similar cost to UFH. 

 

It would be good for suspended floors and floating OSB over insulation floors. Situations which avoiding screed, avoiding very hard floors and minimising height buildup was an issue. 

 

Also because you wouldn't be directly heating up the ground perhaps losses would lightly be lower than UFH? 

 

 

 

 

 

 

 

 

 

 

 

 

[IanR]

10 minutes ago, Iceverge said:

I was of the notion that differential temps created drafts too. Mind you, I've not ever noticed any in our house, even when some rooms are warmer. 

 

I do remember reading the PH principles of Thermal Comfort, and avoiding drafts through differential temps, but iirc that was with regards to convection currents caused by any of the inner surface of the thermal envelope being more than a few degrees lower than ambient (3.5°C is the delta I remember). As I remember the cooling air drops to the floor and moves away from the exterior wall, causing a draft. For a delta under 3.5°C the drafts should be imperceptible. I believe it's a key part of the PH Certification of windows, ie. not just their U values, but also the thermal bridge Psi values for the frame.

 

I don't believe rooms at different temps would cause the same issue, at least, not once temps are stable.

[SteamyTea]

42 minutes ago, Iceverge said:

 

Is there any handy way of comparing rads output to UFH

Calculate the power output and divide by the floor area to get the W/m².

[TerryE]

By way of an example we typically need around 30-40 kWh heat per day during the peak winter months, so that's around 1.5 kW on average. Our heated slab is around 75 m² so that's 20 W/m². Black body radiation is around 7  W/m²K so the UFH heating has to keep the floor around 3°C warmer than room temperature to provide this heat input.   Nice to walk barefoot on this.  🙂

[carou]

On 08/02/2023 at 09:41, Russdl said:

Actually, thinking about it (it’s been a while since I did my PHPP) a heating system isn’t specified. The PHPP just tells you what the heat requirement will be - you choose what to do with that information. 
 

Any other PHPP users confirm my recollection??

 

if you get the PHPP off your architect I’m happy to take a look at it. 

Really appreciate your help thank you. I’ll message you my contact. 

Edited February 15, 2023 by carou