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


Jeremy Harris

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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 by SteamyTea
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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.

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  • 3 years later...

It’s too late to wind Jeremy up, he left ages ago, but his “Dr Sidekick” will be along shortly to explain the science and maths 😴

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31 minutes ago, joe90 said:

It’s too late to wind Jeremy up, he left ages ago, but his “Dr Sidekick” will be along shortly to explain the science and maths 😴

Didn't everyone just loose the will to live on this thread, to resurrect it again.  @Pocster is just having fun with you.

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2 hours ago, JohnMo said:

Didn't everyone just loose the will to live on this thread, to resurrect it again.  @Pocster is just having fun with you.

(I still call it thermal mass, but not in front of steamy tea) 🤣. However I did learn stuff from that thread like decrement delay.

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Posted (edited)

But I feel this thread hasn’t resolved the great thermal mass myth . Discuss ! 😊 ( slow day for me ) 

Edited by Pocster
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4 hours ago, Pocster said:

But I feel this thread hasn’t resolved the great thermal mass myth

Has is my mind.

Even if there was a measurable advantage, it would be swammed by normal activity.

 

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Posted (edited)

to add my two pence  worth 

 my house has 6-700mm  granite stone walls ,then 50mm air gap then 150mm t/f and insulation 

I can say now that mass matters to making a stable temp 

even now with still no bifolds fitted --but just blanked off with ill fitting osb -no heating as yet 

the temp inside is stable and in rooms that are finshed that get sun -and bear in mind these are not huge windows in old stone house the temp goes up  noticably 

so much there have been days when joiners and plasters have complained of it being colder inside than out  and upsatairs where it is all plasetered etc it is much warmer .

but yes i agree with others that spending on insulation and stopping air leaks sghould be top priority   on any house--

 

 

Edited by scottishjohn
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I have a suspicion that "thermal mass" induced temperature stability has an awful lot more to do with the tiny windows in old buildings rather than any other imaginary benefits. 

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1 hour ago, Iceverge said:

I have a suspicion that "thermal mass" induced temperature stability has an awful lot more to do with the tiny windows in old buildings rather than any other imaginary benefits. 

I thought that also ( I didn’t , but felt as I had resurrected this zombie thread I should attempt to comment )

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Yes if feels right to feed a Zombie - it just keeps shuffling along with with its limp hands on the ends of outstretched arms emitting a constant moaning noise. I wonder if Simon Pegg is on the forum, he would know what to do.

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1 hour ago, MikeSharp01 said:

Sans Zombies one presumes!

Yes, was all peaceful and very civilised today.

The shit happens come the next bank holiday, then the relentless months till November.

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