[GSBN] Fwd: Heat storage capacity of wall systems.

Thu May 2 15:55:58 UTC 2019

Thank you very much for your thoughts Derek.

I think the three answers I have received by now all agree on the
theoretical charateristics.
And then there is the practical application of how the theories apply in
the real world.
Very interesting.

I got this reply from a colleague on another list:

“Hi Lars,

you can take a look at this table. It’s in french but easy to translate.
You have to take a look at the « chaleur spécifique » and you can see how
much energy can be stored by each materials. You can search as well on
google "specific heat capacity » and compare. That’s true that cellulose is
one of the best because it’s from wood (see wood fiber panels). Solid oak
wood is up to 2300 J/kgK.
It’s not particularly related to weight, granite has only capacity of 774
J/kgK and hydrogen 14300 J/kgK.
In France now they start to take into account the capacity and « déphasage
» which is the time that is needed for an insulation material to start to
transfer the heat to the inside of the building.
On a roof, if you install the same thickness of insulation, one with glass
wool and one with wood fiber boards, even if the the lambda is better for
glass wool the thermic capacity is 2 time higher for wood fiber boards. It
means that the material can absorb 2 time more energy before it starts to
transmit it inside. It’s like a sponge that can absorb 2 times more water
than an other one that will be full 2 time later and start to let water go
2 time later.
Ideal is to have a « dephasage » of 12 hours, so in summer while the sun
heats the roof during whole day, the heat will start only to arrive inside
when night comes and already cools down the outside. 20 cm of wood fiber is
enough while you need 40 cm of glass wool to reach the same cycle and
prevent over-heating during summer. This works for summer but not for
winter. Energy streams are different. Having 40 cm of wood fiber wouldn’t
be the best because it means that heat would start to come inside the day
after when sun rise again and heat the inside of the room. Calculation of
insulation have to take into account local climate on 24 hour cycle and
seasonal as well to find the best ratio and equilibrium between summer and
winter comfort.
Other aspect is as well regulation of vapor that has a very high thermic
capacity (over 2000 J/kgK) so straw or wood again have a big advantage on
mineral wool that don’t deal well with this.
You can find on the web some studies or calculation about the time
releasing for each material and straw.
I don’t remember density of EC panels but it should not be too difficult to
calculate the whole capacity of a panel. This capacity cycle is
particularly important for the roof because it receive direct sun heat.
It’s less important for a wall and big capacity can be interesting to
maintain higher inertia of the building.

Have a good day,

Denis

Materiaux densité [kg/m3] conductivité thermique λ [W/mK] chaleur
spécifique [J/kgK] energie grise [kWh/m3] Ouate de cellulose soufflé 24
0.042 1900 15 Ouate de cellulose injecté 45 0.042 1900 100 Ouate de
cellulose panneaux 70 0.042 1900 150 Fibre de bois panneaux 50 0.039 2100
60 Polystyrène expansé 15 0.039 1450 500 Laine de verre panneaux 35 0.039
1030 470 Laine de roche panneaux 70 0.042 1030 430 Laine de chanvre
panneaux 40 0.040 1700 40 Liège expansé panneaux 125 0.049 1560 450 Paille
80 0.050 1330 0 Perlite en vrac 70 0.060 900 330

Densité ou masse volumique ρ [kg/m3]”

Best, Lars

- - -

tor. 2. maj 2019 kl. 16.50 skrev Derek Roff <derek at unm.edu>:

> Perhaps I am misunderstanding the scenario, but I’m skeptical, Lars, that
> the difference in heat storage capacity of different kinds of insulation is
> very important to the building performance question.  In the example that
> you quote, of wall insulation absorbing heat from solar influx when
> available, and later releasing that heat to the room, an important
> distinction is whether the scenario assumes sunlight falling on the outside
> of an insulated wall, or on the inside of an insulated wall.
>
> When sunlight heats the outside of an outside wall, we need enough
> insulation that very little of that heat ever makes it inside the
> building.  Super-insulated buildings are designed to prevent heat movement
> from outside to in or inside to out.  Therefore, we can’t expect useful
> heat transfer into the living space from sun shining on the outside of an
> insulated wall.  The wall is designed to prevent precisely that.
>
> If sunlight is coming trough a window or skylight and shining on the
> inside of an insulated wall, then there is some hope that this solar energy
> will help thermal performance of the house.  The surface of the wall being
> struck by the sunlight will heat up to above the average ambient
> temperature in the room, and then (immediately) begin to release that heat
> through radiation, conduction, and convection back into the room, tending
> toward temperature equilibrium.
>
> Several problems come to my mind in considering trying to store useful
> solar heat in an insulated wall.  The first is that I wouldn’t expect very
> much sunlight to strike the inside surface of an insulated wall.  Light
> coming in through windows and skylights will mostly strike the floor,
> furniture, and interior (uninsulated) walls.  As I imagine a normal house,
> I wouldn’t think that even ten percent of the sunlight entering the
> building envelope during the course of a day would touch the inside of an
> insulated wall.  For a larger, commercial building, the percentage would be
> even smaller.
>
> Next, the insulated wall is coated with something.  Clay, I hope, but
> certainly something less insulating and of higher density than the
> insulation itself.  Assuming a clay coating, for the moment, it will heat
> up above average room temperatures when the sun strikes it.  As a dense,
> fairly conductive material, it will store a fair amount of heat, and change
> relatively little in temperature.  That is what we want it to do.
> Therefore, the clay plaster will ‘protect’ both the air in the room and the
> insulation behind it from experiencing the higher temperatures that might
> otherwise occur from the solar influx.  That’s a good thing for comfort in
> the room, since it moderates temperature swings.  So now we have a slightly
> heated clay surface in contact with the room air on one side and with the
> insulation on the other side.  Certainly, the clay will conduct some heat
> into the insulation that it touches.  But temperature differential (delta
> T) is small, and the insulation wants to resist that heat flow.  Therefore,
> we can’t move very much heat very far into the low-mass insulation.  This
> gives us a small temperature change in a small amount of mass within the
> insulation, which equals low heat storage.  On the room side, the slightly
> heated clay wall surface will give up some heat to the room through
> radiation, conduction, and convection.  That is what we want, and that is
> where most of the heat will go.  So, what percentage of the heat stored in
> the clay plaster is transferred first to the insulation behind it, and then
> later, re-transferred to the clay plaster and returned to the room?  I’d be
> surprised if it was over one percent.
>
> If these guestimates are anywhere close, then the difference in heat
> storage capacity of different kinds of insulation won’t make any
> significant difference.  To summarize:  1) We can’t get much solar influx
> to heat the insulation, because little sunlight strike the inside of an
> insulated wall; 2) The surface coating of the wall will have more mass and
> greater conductivity than the insulation, and it will be the surface that
> is struck by the sunlight, therefore, it will do almost all of heat storage
> that might happen in the insulated wall; 3) Delta T will be low between the
> wall surface and the insulation behind it, minimizing the heat transfer to
> the insulation, and therefore minimizing the contribution to heat storage
> made by the insulation; 4) Differences between heat storage by different
> types of insulation will be insignificant in overall effect, because of all
> the preceding factors.
>
> Am I missing something important?
>
> Derek
>
> Derek Roff
> derek at unm.edu
>
>
>
>
>
> On May 2, 2019, at 6:37 AM, Lars Keller <larskeller at gmail.com> wrote:
>
> We have a discussion in Denmark where some people argue, that if you
> compare two walls with similar insulation values, one being insulated with
> mineralwool, and one with wood cellulose or paper cellulose, then the wood
> cellulose option can retain / contain more heat thatn the mineralwool
> solution.
>
> The advantage of this for the wood cellulose is, that this solution is
> then capable of absorbing more heat when there is eg more solar influx, and
> later release the heat into the room again, thus creating more comfort. I
> assume that this is a result of the cellulose option being heavier than the
> mineralwool option.
>
> I would like to hear thoughts about whether my understanding is correct.
>
> I assume straw would share the benefit of the cellulose option.
>
> Does anyone know if we have / there is numbers to back this up ?
>
> Best, Lars
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Small Planet
Om vores firma ~ link
Om vores masseovne ~ link
Om vores workshops ~ link
Kontakt-info
skype
jomorandin
lars.friland
jomorandin at gmail.com
larskeller at gmail.com

Home +45 8668 0505
Jo      +45 2390 0924 (mobile/handy)
Lars   +45 2024 0505 (mobile/handy)

Jo Morandin, Jamilla, Asger & Lars Keller
Friland 12 B
8410 Rønde
Danmark
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Small Planet
Om vores firma ~ link
Om vores masseovne ~ link
Om vores workshops ~ link
Kontakt-info
skype
jomorandin
lars.friland
jomorandin at gmail.com
larskeller at gmail.com

Home +45 8668 0505
Jo      +45 2390 0924 (mobile/handy)
Lars   +45 2024 0505 (mobile/handy)

Jo Morandin, Jamilla, Asger & Lars Keller
Friland 12 B
8410 Rønde
Danmark
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