I don't care about U values

[bassanclan]

I am planning an extension and was looking at options for different wall construction and their various u values.

 

Then I realised I don't care about U values.

I am interested in the heat transmission out of the room, not out of thee room, potentially through a cavity and more bricks.

 

Is there a way of measuring this?

 

Anecdotally my father in law's house of solid brick wall and 50mm "kingspan" drylining feels warmer than my 100mm kingspan filled cavity wall. The U value of my wall will be better, but because his insulation is nearer the inside of the house it feels warmer.

 

Over an extended period of time of heating a room my house would lose less heat, but often the desire is to heat a room quickly for a short time. E.g before going to work etc. How can this be modelled?

 

 

 

 

 

 

[SteamyTea]

2 minutes ago, bassanclan said:

Anecdotally my father in law's house of solid brick wall and 50mm "kingspan" drylining feels warmer than my 100mm kingspan filled cavity wall.

Anecdotally is an partial anagram of No Data.

 

Without knowing the energy inputs, air leakage and temperature variation, it is not possible to compare the two.

 

Building Regs will tell you a minimum standard anyway, so you cannot go below that.

6 minutes ago, bassanclan said:

the desire is to heat a room quickly for a short time. E.g before going to work etc. How can this be modelled

If you know the power losses and the power inputs, the sized of the room, you can calculate the energy needed to heat it

[RobLe]

If a house is continuously occupied, then insulation is best placed externally.  Or in a very wide brick cavity.  Either way, you'll end up with a high thermal capacity.  Thermal capacity is then desirable - fewer overheating events, easier to "ride through" a cold snap.

 

On the flip side - if you only use the house 10% of the time, high thermal capacity is wasteful - it's cold at first, it costs money to heat it all up, and that's all wasted if later you're not there!  IWI is then more appropriate.

 

[Marvin]

36 minutes ago, bassanclan said:

I am planning an extension and was looking at options for different wall construction and their various u values.

 

Then I realised I don't care about U values.

Well, good luck with that!

 

 

42 minutes ago, bassanclan said:

I am interested in the heat transmission out of the room, not out of thee room, potentially through a cavity and more bricks.

 

Is there a way of measuring this?

Yes. 

 

These are the main factors I see you have to take into account when calculating.

If the extension looks like a cube then there are 6 sides you will have to take into account all 6 sides thermal resistance, identified for each type of surface (windows, roof or what ever) and the air flow, all related to the temperature the other sides of the 6 sides, including any shading and or wind exposure, over the extremes of your local climate, all against the temperature required inside over various times of the day, as well as the room use and occupancy.

 

Good luck

 

Marvin

[jayc89]

I can't answer how to model this, but insulation is only part of the solution. Thermal bypass, thermal bridging, airtightness or all factors to consider. If done well, a solid wall insulated with PIR could mitigate certainly 2 out of 3 of those areas quite well.

 

This is exactly what I'm doing in my house. I've done one room, in the north west corner of the house (50mm PIR direct to the internal face of the brickwork), and it's made a massive difference, I've also taken the time to fully foam around the perimeter of each board, to try ensure any thermal bypass is limited to a single board area, and both taped and ran a VCL to airtightness and to restrict the risk of condensation. Whilst on-paper, it will still have a worse u-value than our last house (2000's mass-built detached), my expectation is that it will feel massively better to live in. 

"feel" is also hard to quantify... 

[ProDave]

When you get to a really well insulated house, the concept of "heat a room quickly for a short time" does not work, because once heated, it takes hours or even days to cool down again.  and it becomes near impossible to even have rooms at different temperatures, e.g our unheated upstairs was only 2 degrees lower than the heated downstairs when it was -10 outside.

[SteamyTea]

11 minutes ago, ProDave said:

concept of "heat a room quickly for a short time" does not work

I think in really it does not work anywhere.

There is a disproportionate I crease I energy usage when there is a change in temperature.

Bit like driving. You will soon notice the change in MPG if you only accelerate hard, when going up a hill.

 

Edited February 2, 2023 by SteamyTea

[Temp]

4 hours ago, bassanclan said:

Anecdotally my father in law's house of solid brick wall and 50mm "kingspan" drylining feels warmer than my 100mm kingspan filled cavity wall.

 

How well installed was your insulation? The remaining cavity is normally ventilated so gaps between insulation panels are bad news.

 

Any gaps in IWI is less critical as there is a brick wall stoping airflow to them.

[jayc89]

35 minutes ago, Temp said:

 

How well installed was your insulation? The remaining cavity is normally ventilated so gaps between insulation panels are bad news.

 

Any gaps in IWI is less critical as there is a brick wall stoping airflow to them.

 

I'd suggest gaps in IWI is actually worse for the fabric of the house as warm moist air will be able to condensate through those gaps to the cold side of the insulation.