Thermal mass

[SteamyTea]

6 hours ago, Thedreamer said:

Should people just refer to the whole thermal mass concept, as thermal heat capacity

Just heat capacity would do.

If you have a look at this page you can see the thermal properties of materials.

Some may surprise you.

http://www.kayelaby.npl.co.uk/general_physics/#2_3

[joe90]

Like some others, I don’t like aircrete blocks for either skin, yes, they insulate a little better than concrete block but I have come across so many cracking problems with them in the past. Like you I have fairly large windows facing south but so far ( we have only had a couple of weeks of sun) it’s not been a problem. I am putting a large conservatory across the whole back of the house and frankly on the odd hot day it will overheat ( we are having solar glass in the roof) but this we will cope with as it means it’s a usable space fir many months of the year.

[SteamyTea]

2 minutes ago, joe90 said:

( we have only had a couple of weeks of sun)

That much, I wish

[TerryE]

@joe90, my main point is that if you do want to maintain a comfortable environment then it is a good idea to design in your cooling temperature control as part of the build, as this will be cheaper than doing a retrofit. In the case of what looks like a near south facing conservatory, then your should consider opening lights in the roof, preferably servo controlled, and internal shading.  Internal shading will work fine so long as you have opening lights to let out the baking air.  If you want to keep plants in the conservatory you should think of temperature controlled windows and blinds.

[SteamyTea]

Or grow cacti.

 

I may have a go at modelling a wall that is being hit by the sun, just to see how much energy it can absorb and loose.

I ma have enough data from the last month to do that.

[joe90]

2 hours ago, TerryE said:

@joe90, my main point is that if you do want to maintain a comfortable environment then it is a good idea to design in your cooling temperature control as part of the build, as this will be cheaper than doing a retrofit. In the case of what looks like a near south facing conservatory, then your should consider opening lights in the roof, preferably servo controlled, and internal shading.  Internal shading will work fine so long as you have opening lights to let out the baking air.  If you want to keep plants in the conservatory you should think of temperature controlled windows and blinds.

 

Yes, the conservatory faces due south ( almost) the roof, as explained, will have solar glass which is very good at deflecting some solar gain, very large pairs of double doors and large opening windows in both East and West ends ( winds here are almost always westerlies) so the wind will blow through and out the other side. Like my heating strategy for the house ( no heating upstairs apart from towel radiators and en suite UFH) and if it’s very cold for a few weeks a couple of electric heaters will suffice) . Yes we may get overheated once or twice but I can live with that if it enables me to use it in the shoulder months. Internal blinds will be looked at if required! It’s a bit like the house, a question of suck it and see. Jeremy did lots of calcs for his build but they did not take into account his micro climate which meant cooling was reqd moor than he thought, we are very open here so don’t think we will suffer the same ?

[SteamyTea]

Done a quick 'first draught' of different materials (got to look up more material properties).

But if my house was made of brick, it would have had a mean response time of 35 hours over the 11°C mean temperature differences that I have good data for.  35 hours is greater than one day, so not much use.

If it was just OSB the mean response time would be 3.8 hours over the same mean 11°C, so a bit more useful.

Just got to find some more material data until I can find something that would give 12 hours, which would be best on average, but as this time of year the days are long, gentle overall warming would happen.

I shall see if I can get some more data.

But as an aside, I have been pretty happy with the temperature inside my house the last 4 weeks or so.

[joe90]

ST, this info will be helpfull but at the risk of confusion ( not difficult for me?) but how does decrement delay fit with a response time for a nominal material?

[SteamyTea]

It is the same thing really.

Decrement delay is time.K^-1, or temperature drop/raise

Thermal Inertia is energy.m^-2.K^-1.s^0.5

So you can think of it as as the difference between R-Values and U-Values.  You know they are related with R-Value being measured in m².K.W^-1 and U-Value being measured in W.m^-2.K

Just arithmetic juggling really.

The interesting thing is that for any given mass, to get a timeshift, there is a narrow temperature difference band it can work in.

Below is a chart that modelled a 1m² section of wall made from brick.

To get a 12 timshift, you need a temperature difference between inside and outside (called the energy forcings) of 1.8°C.  To get a more useful 8 hours temperature release the temperature difference will be 1.2°C, which is basically parity with external temperatures once internal energy forcings have been taken into account.

For OSB you can have a temperature difference of 19°C and have any absorbed energy released over a period of 8 hours.

I have to put in a caveat that this is just working with my house and my temperatures over the last 4 weeks.  I am sure those figures above will change when I have more data, and it is just a basic model, does not take into account air changes (they are kind of built in as it is real temperature data) and window area (again kind of built in).