The Great Thermal Mass Myth................

[SteamyTea]

36 minutes ago, stubiff said:

Would the room with wood fibre boards use less energy to maintain a certain room temp,

Yes, or No, depends on the 'something else'.

Energy cannot be created, it can only change its form.

So, stored energy has to be created first, and this is where the confusion comes in.  If, for instance, you need to raise the temperature of the building by 2° C, and you have 10 tonnes to heat, assuming brick/concrete, with a specific heat capacity of 0.8 kJ/kg.K, then you need 16,000 kJ (4.44 kWh), while at the same time as heating say 100 kg of air, that has a SHC of 1 kJ/kg.K, so an extra 200 kJ (0.056 kWh).

But if you have a timber/insulation combination, you may be reducing the 10 tonnes to 2 tonnes, but the SHC may be higher, say 1.3 kJ/kg.K, then that initial heating load is reduced to 5,200 kJ (1.44 kWh), while the air heating load is the same.

Now people argue that you get that difference (3 kWh) back when you turn the heating off, except some of it has leaked out to the atmosphere/ground.  So by having a larger store of energy, you have a larger amount to loose, and as heat loss is non proportional, the larger the temperature differences, the larger the losses, and the faster those losses happen.

Controlling losses, and gains, is the key to temperature stability, this is why people put blinds on oversized windows and have MVHR fitted.  In the UK it is a rare day that the weather conditions are idea of stable passive heating, or cooling for that matter.

Spend your time and money on insulation and airtightness, not on large windows, tonnes of concrete and aftermarket fixes.

Edited March 29, 2021 by SteamyTea

[stubiff]

Sorry, should have added.

U value of 0.15 say, airtight, timber frame.

'Something else' could be PUR or similar. I.e. something a lot less dense.

 

Edited March 29, 2021 by stubiff

[SteamyTea]

Just now, stubiff said:

Sorry, should have added.

U value of 0.15 say, airtight.

The U-Value is of little consequence when looking at energy storage, it is, in effect, just the speed at which the losses happen (why it is measured in watts, not joules).

Realistically, the U-Value will be similar i.e. your 1.5 W/m².K, just that you have a larger amount to loose when you have a larger store.

 

Better off spending your cash to get the U-Value down, you only spend that money once and it is a marginal increase in cost for the extra material, the fitting is about the same cost.

[stubiff]

@SteamyTea Thanks very much