Thermal mass

[Thedreamer]

What can I do to increase the thermal mass in a timber frame home?

 

The only high density material we will have within the inside of the house is some concrete blocks round the stove which is in centre of the house and in front of some south facing glazing.  

 

My idea was that this would act as a battery, storing heat during the day and gradually releasing this heat during the evening.

 

Are there particular blocks that you can buy that would work well here? Presumably dense ones.

 

Are there other materials we can utilise that would improve the thermal mass in the house? We are having a suspended timber floor, so no concrete slab/screed.

 

We have two young children, so our house is occupied during the day, but this will become less when they are both in school.

[PeterW]

I’m sure @JSHarris will be along shortly but just to be clear there is no such thing as “thermal mass”.... it’s a combination of the heat capacity of materials and their propensity to absorb and release heat ... oddly from memory, blocks are quite poor and plasterboard is quite good but there is a whole table of data that was put on here a while ago. 

 

What you’re looking for is a way to reduce the temperature swings - @TerryE has done it by creating a huge mass of concrete in his floor that acts as a buffer. 

[Nickfromwales]

I'd keep your head down for the next 15 mins  

 

It all begins here.....

[Alexphd1]

Just 15 minutes???

[Nickfromwales]

3 minutes ago, Alexphd1 said:

Just 15 minutes???

Ok, so I like a bit of entertainment.....sue me

 

[Ferdinand]

5 ... 4 ... 3 ... 2 ...

 

[ProDave]

I suspect you are wanting a timber framed house that behaves a bit like ours.

 

Well insulated so heat loss is low. It takes a very long time to heat up or cool down in response to changes in outside temperature, days usually.

 

Some may mistake this for "high thermal mass" but it is all down to the decrement delay of the insulation used, in our case a mixture of earthwool and wood fibre. Not a concrete block to be seen.

 

As has been mentioned, plasterboard has quite a high heat capacity so helps a lot. I am already noticing a difference in how the building responds since we have plasterboarded the big room downstairs.

[Trw144]

We re pretty safe st the moment as the thermal mass enforcer does nt seem to be around at present - I hope he’s ok??

[SteamyTea]

What are you trying to achieve and why do you think that adding mass will help?

 

You could try a simple experiment by getting some water butts/containers and filling them up.  Water is about the best energy storage medium you can get.

You would need to monitor the temperature before and after the experiment just so you are not kidding yourself that it has worked.

[MikeSharp01]

2 hours ago, PeterW said:

 

I’m sure @JSHarris will be along shortly....

 

 Me thinks the dragon snoozeth@

[Nickfromwales]

8 minutes ago, MikeSharp01 said:

 Me thinks the dragon snoozeth@

He'll be along in his own good time. . 

In the meantime, it looks like we need a distraction........

 

 

[Thedreamer]

Maybe one of the administrators should delete this and we can all pretend it never happened...

 

I noted a few articles on thermal mass recently and just wondered how our design compares to what they were discussing. 

 

Okay, I'll forget about thermal mass.

 

Considering insulation, I would be interested in your opinions as to what kind of standard this is. 

 

Crowntherm 34 between studs with 25mm continous kingspan over the top offer.

Crowntherm 90  between joists, 55mm Kingpspan between joists and 25mm Kingspan on top

2 x 80 Kingspan with 25mm Kingspan on top (trusses)

 

Windows, triple glazed average u value 1.0

[SteamyTea]

21 minutes ago, Thedreamer said:

I noted a few articles on thermal mass recently

All 'Thermal Mass' is, is the product of insulation and specific heat capacity of a material.

There is a lot of misunderstanding about how it can make a building thermally stable.  Nearly all the examples come from 10° South of the UK with much sunnier climates and much higher temperatures, especially in summer.

When I was studying the affect of solar radiation on mass (granite in fact), there was no real gain to be had with typical UK insolation levels.

Our old mate Ed Davies did some work on it and concluded that a sheet of 9mm plasterboard could absorb and release energy just as well as 4 inches of brick.

Don't fall into the trap that adding mass is all you need to do to store or stabilise thermal energy.

 

If you want to slow down the rate of change of the losses though a wall, look at cellulose insulation.  It has good insulation properties, good specific heat capacity and very good sound absorbing characteristics.

[Cpd]

It has been pointed out to me that kingspan and the like are great at insulating but have a very poor decrement delay, I have doubled and tripled up on plaster board in many areas to help with both noise reduction and to try and help even out temperature fluctuations...... out of interest I recently Ripped out a previously bricked up open fire, 1.2m x 1.2m it had been fully filled with brick and mortar with the flue from the wood burner going in at the top..... i insulated the cleaned up fire recess with kingspan and then built a block box  recess somewhat smaller than the original due to all the extra insulation and re instated the wood burner. It now performs much better as previously the heat from the fire was just being lost to an unisulated stone wall. The point though and trying to get back on topic is that even after the fire has been out all night the block work is still radiating heat out in the morning and the kitchen is noticeably warmer than before. Doing this experiment has highlighted the need to add in extra materials into my renovations to help store heat and to help minimise the heat fluctuations that would be found with just kingspan and a single layer of plaster board.... Using an insulation with good decrement delay would have solved this problem but hay ho you live and learn...... well I try. 

[Thedreamer]

8 minutes ago, SteamyTea said:

All 'Thermal Mass' is, is the product of insulation and specific heat capacity of a material.

There is a lot of misunderstanding about how it can make a building thermally stable.  Nearly all the examples come from 10° South of the UK with much sunnier climates and much higher temperatures, especially in summer.

When I was studying the affect of solar radiation on mass (granite in fact), there was no real gain to be had with typical UK insolation levels.

Our old mate Ed Davies did some work on it and concluded that a sheet of 9mm plasterboard could absorb and release energy just as well as 4 inches of brick.

Don't fall into the trap that adding mass is all you need to do to store or stabilise thermal energy.

 

If you want to slow down the rate of change of the losses though a wall, look at cellulose insulation.  It has good insulation properties, good specific heat capacity and very good sound absorbing characteristics.

 

Thanks for that. No, the thermal mass was some think I discovered after the finalisation of the design. 

 

 

 

 

 

[Cpd]

10 minutes ago, SteamyTea said:

Don't fall into the trap that adding mass is all you need to do to store or stabilise thermal energy.

 

If you want to slow down the rate of change of the losses though a wall, look at cellulose insulation.  It has good insulation properties, good specific heat capacity and very good sound absorbing characteristics.

 Could not agree more and would have used a different type of insulation had I known then what I know now.......

[Thedreamer]

8 minutes ago, Cpd said:

It has been pointed out to me that kingspan and the like are great at insulating but have a very poor decrement delay, I have doubled and tripled up on plaster board in many areas to help with both noise reduction and to try and help even out temperature fluctuations...... out of interest I recently Ripped out a previously bricked up open fire, 1.2m x 1.2m it had been fully filled with brick and mortar with the flue from the wood burner going in at the top..... i insulated the cleaned up fire recess with kingspan and then built a block box  recess somewhat smaller than the original due to all the extra insulation and re instated the wood burner. It now performs much better as previously the heat from the fire was just being lost to an unisulated stone wall. The point though and trying to get back on topic is that even after the fire has been out all night the block work is still radiating heat out in the morning and the kitchen is noticeably warmer than before. Doing this experiment has highlighted the need to add in extra materials into my renovations to help store heat and to help minimise the heat fluctuations that would be found with just kingspan and a single layer of plaster board.... Using an insulation with good decrement delay would have solved this problem but hay ho you live and learn...... well I try. 

 

So what's the scientific name/process for the blocks absorbing/retaining the heat from a fireplace/stove and then still being warm in the morning? Our stove as shown in our plan below will be in the middle of the house.

 

 

 

 

 

[PeterW]

It’s just the block heating up and then returning to room temperature. The same would happen if it was plasterboard, but as it’s only usually 15mm thick you don’t have the heat capacity that you do with a 100mm block. 

 

 

 

 

Just one observation on the plans - the right hand corridor headroom is very low. Can you move the chimney/stove over to the left ..??

[joe90]

Well I am a “ mass” advocate, my caravan that I have been living in on and off fir two years cools down very quickly but heats up quickly. My new build is block and brick ( not thermalite as I don’t like them) 200mm full fill cavity insulation ( rock wall). Ever since the doors and windows were installed people entering the build assumed the UFH was working and on, but it was not, and that was not warm weather. During this warm spell the inside remains cool and there is very little in the way of temperature swing. I am not saying there are not other ways of copying a heavy construction but mine works very well and I could not be more pleased with it. ( also I can hang anything I want from the walls)

 

p.S. I also have a wood stove in a heavyweight fireplace centrally within the house. Role on Christmas ? 

Edited June 3, 2018 by joe90

[pdf27]

Heat Capacity is the term you want (Specific Heat Capacity x Mass), which has units of Joules per Kelvin (i.e. the amount of energy absorbed by the material for every degree increase in temperature). It isn't a terribly useful term however - the rate at which that heat is released again (a function of surface area, thermal conductivity, emissivity of the surface, etc.) is critically important. Combined that gives you the time constant of the system, which should be matched to the time constant of the building as a whole (too short and you'll get overheating followed by no heat at all, too long and it won't do any good).

[Thedreamer]

4 minutes ago, PeterW said:

It’s just the block heating up and then returning to room temperature. The same would happen if it was plasterboard, but as it’s only usually 15mm thick you don’t have the heat capacity that you do with a 100mm block. 

 

 

 

 

Just one observation on the plans - the right hand corridor headroom is very low. Can you move the chimney/stove over to the left ..??

 

The right hand corridor is just a small room with a W/C and sink, it's only 1.3m wide. So I'm happy as long as there enough head height to take a ...... 

 

Perhaps my first question should have been, do certain blocks take longer to cool down? For example comparing aircrete block, to the ridiculous six inch solid blocks I busted my back lifting.

[PeterW]

3 minutes ago, Thedreamer said:

 

The right hand corridor is just a small room with a W/C and sink, it's only 1.3m wide. So I'm happy as long as there enough head height to take a ...... 

 

Perhaps my first question should have been, do certain blocks take longer to cool down? For example comparing aircrete block, to the ridiculous six inch solid blocks I busted my back lifting.

 

Thanks for that ..!

 

Aircrete is just that - air..! Very low heat capacity, whereas the dense blocks have more concrete and as @joe90 notes, they reduce the swing between temperatures. I’ve used them with plasterboard tight bonded using foam to them and have experienced the same long lag in temperature change. Those heavy 6” blocks have probably 6-8 times the concrete content than an aircrete block so have a similar multiple of heat capacity 

[Thedreamer]

 

I have quite a lot of south facing glazing and now I wonder if it will be too hot. I'm in Skye so usually temperatures are usually mild and midgey.

 

My initial thoughts when posting, was that light and solar gains would come in via the south and shine pretty much on where the blocked stove area would be. This would absorb the heat and then it would be released during the evening. 

 

In the winter, if necessary the stove would be lit and then the blocks would heat up gradually and then the heat would be gradually released from the centre of the house during the course of the night.

 

I didn't really plan my design around this, it just happens that my views to the south are of a loch, sea and mountains so wanted as much glazing as possible.

 

 

 

 

[Thedreamer]

5 minutes ago, PeterW said:

 

Thanks for that ..!

 

Aircrete is just that - air..! Very low heat capacity, whereas the dense blocks have more concrete and as @joe90 notes, they reduce the swing between temperatures. I’ve used them with plasterboard tight bonded using foam to them and have experienced the same long lag in temperature change. Those heavy 6” blocks have probably 6-8 times the concrete content than an aircrete block so have a similar multiple of heat capacity 

 

For blocks houses, does it make sense for external walls to be build with aircrete blocks (because these will be easier to handle and presumably quicker) and then use denser blocks for the internal walls and the inner leaf of cavity to improve heat capacity?

 

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

 

[TerryE]

5 hours ago, Thedreamer said:

What can I do to increase the thermal mass in a timber frame home?

 

This is probably the wrong Q anyway, but in our case we use cellulosic filler rather than PUR etc.  OK, this requires a deeper profile to get a decent U value, but it is also a lot denser so has a better decrement delay, we also have 15 tonne of slab and ring beams inside the thermal envelope.

 

The thing that so many self builders miss is the DD of acres of glass is zero, and this can play havoc with temperature stability for 9 months a year whenever you have a clear sunny day.  Architects seem to love designing in large areas of glass even where there is no real added value for the occupants.

 

This isn't to say that you shouldn't do this, if there it's genuine value to you as occupant, but don't kid yourself: your major thermal design challenge isn't going to be how to warm your house; it will be how to prevent it becoming a tropical hot house on a sunny day.

Edited June 3, 2018 by TerryE