Insulation layer for shorter time constant?

[Alan Ambrose]

Is there an advantage to putting an intermediate thin-ish insulation layer under UFH screed in a PH-style house? We have 300mm XPS with a 150mm slab on top and we plan to have 100m screed with UFH. But I’m wondering whether, say, a 30mm insulation layer and then 70mm screed would provide a shorter time constant for more rapid heating & cooling. I know some peeps subscribe to always heating to 20/21 degrees and cooling to 25 degrees 24/365 using the slab as a big heat reservoir. But that assumes you never want to change the temperature any, and if ever you do, then it’s going to take days i.e. a v long time-constant.

[Mike]

Only if you think that more rapid heating and cooling is good. In which case why not use radiators?

[JohnMo]

 

2 hours ago, Alan Ambrose said:

70mm screed would provide a shorter tjme constant for more rapid heating & cooling.

If want a short time constant for some reason, you could use Jaga Strada fan radiators, so you can cool also. Cheaper than fan coils, and designed to provide above dew point cooling. Also way smaller than radiators.

 

Seems a strange design choice to do 150mm concrete then another 100mm screed on top.

[Nickfromwales]

5 hours ago, Alan Ambrose said:

Is there an advantage to putting an intermediate thin-ish insulation layer under UFH screed in a PH-style house? We have 300mm XPS with a 150mm slab on top and we plan to have 100m screed with UFH. But I’m wondering whether, say, a 30mm insulation layer and then 70mm screed would provide a shorter time constant for more rapid heating & cooling. I know some peeps subscribe to always heating to 20/21 degrees and cooling to 25 degrees 24/365 using the slab as a big heat reservoir. But that assumes you never want to change the temperature any, and if ever you do, then it’s going to take days i.e. a v long time-constant.

Ask yourself why and when you'd ACTUALLY want to change these temps  I doubt there's much practical / real world need to follow this route tbh.

[Alan Ambrose]

I remember working in a very air-condition building in Bahrain. I used to open the windows to warm the place up. Luckily we could. Sometimes, I think, you just want to control the temperature rather than living in a isolated machine-controlled cocoon. Maybe you're cooking Xmas dinner for the family and want to stop it getting too stifling. Yeah open the windows but you would like to stop heating the place too.

[-rick-]

34 minutes ago, Alan Ambrose said:

I remember working in a very air-condition building in Bahrain. I used to open the windows to warm the place up. Luckily we could.

 

Suggests the temp was set wrong on the place. With a home you get to choose the setpoint. With a well designed and insulated house (taking account of solar gains as well as heat loss) you should be able to find a temperature that just works and doesn't really require fiddling. Exceptions being if different family members have very different comfort temperatures (but that's at least as much of a pain if you have a more dynamic system, if not worse).

 

Nothing stopping you opening or closing windows as you desire.

34 minutes ago, Alan Ambrose said:

Sometimes, I think you, just want to control the temperature rather than living in a isolated machine-controlled cocoon. Maybe you're cooking Xmas dinner for the family and want to stop it getting too stifling. Yeah open the windows but you would like to stop heating the place too.

 

The heating would naturally switch off if it went about the setpoint. With the windows open the internal temp would relatively quickly return to normal and a low/slow system with lots of concrete likely helps speed up the return to 'normal' temperature.

 

Though on cooking, for my own future project I'm definitely leaning towards a directly vented solution (if I can get comfortable with air tight closable vents when not in use) despite what a lot of the advice for recirculating systems in an airtight house here. Reason being is if I am doing much cooking I'm likely batch cooking and that means heat output for hours that will likely overwhelm a well insulated airtight house. So replacing hot cooking air with direct outside air is a way of controlling heat gain more than anything else. Saw some Americans building custom cooker hood shrouds that directly push the make up air into the cooking area to then be sucked back out again from the stove.

 

With low and slow you are going to smooth out a lot of temperature variation that we experience in normal houses. Sharp changes caused by opening windows/cooking will still happen but the reversion to mean will be a lot stronger in a house built for low/slow.

 

The decision for a fast response system is in theory the safer choice, it's more like what we are all used to living with and moving away from a low/slow system once it's in is difficult/expensive. But going based on feedback from people who have low/slow, it is the way to go for many people if you can get comfortable with the idea.

 

I want to find a setpoint that I can just set and forget about (bedrooms being on a separate floor expected to be cooler/or directly zoned).