Thermal mass as a design factor

The use of high thermal mass in studied buildings reduced the demand for cooling energy by 67–75% depending on assumed temperature threshold.
More later
A special forum would be great

John C Daley wrote:The use of high thermal mass in studied buildings reduced the demand for cooling energy by 67–75% depending on assumed temperature threshold.
More later
A special forum would be great

Please post a link.

David, here is the link I explained I would " more later"
https://www.sciencedirect.com/science/article/pii/S0360544220300918

John C Daley wrote:David, here is the link I explained I would " more later"
https://www.sciencedirect.com/science/article/pii/S0360544220300918

Lots to chew on in that article. A few things i noticed 1)they only studied the effect of mass on cooling while heating would represent a major load in Poland and I would expect that would penalize a mass structure 2) the study was an either or type traditional masonry versus wood frame no hybrid option 3) The structures did not use any kind of window blinds or overhangs because they are not common in Poland which would penalize the framed structure.  Hopefully with more testing they will come to the conclusion most high efficiency builders are coming to that a combination of smaller spaces, a well insulated shell AND mass on the inside offers a great structure.

Very interesting study. I hope they do more with window shading and ventilation in the two structures.

I can say that internal thermal mass combined with insulated walls, overhanging eaves to limit sun in summer, and night ventilation work extremely well for us. Our house has a concrete slab first floor and insulated concrete walls. We don't use or need air conditioning in summer, and use fairly small amount of wood (1.5-2 cords apx.) to heat in winter. Yesterday was 94F and inside was 70F.

During the heat dome weather event a couple of years ago I measured the outside wall temperature on the steel siding that was in full afternoon sun on a 105F day, and it was at 185F (I couldn't touch it for more than a split second) and the same spot on the inside was at 74F. The magic of combined insulation and thermal mass of the wall.

Now, if someone can figure out a way to retrofit existing houses to increase thermal mass and insulation, they could make a ton of money and save people a lot of heat stress.

Here is an interesting excerpt from this document:

The climate has the greatest impact on the efficiency of thermal mass utilization in reducing the energy demand for heating and cooling [42]. Increasing the thermal mass of the building reduced the annual cooling load from 53% to 82% and 85%–100% in Los Angeles and San Francisco respectively, depending on the PCM volume fraction used [43], did not have a significant effect on the cooling load in Hong Kong [44], and slightly increased demand for cooling energy in Las Vegas, USA [45]. Similarly, simulation tests carried out in New Zealand climate conditions and theoretical considerations have shown that the increase in the thermal mass of the building should not lead to a significant changes in heating demand [46,47].

Cristobal Cristo wrote:Here is an interesting excerpt from this document:

The climate has the greatest impact on the efficiency of thermal mass utilization in reducing the energy demand for heating and cooling [42]. Increasing the thermal mass of the building reduced the annual cooling load from 53% to 82% and 85%–100% in Los Angeles and San Francisco respectively, depending on the PCM volume fraction used [43], did not have a significant effect on the cooling load in Hong Kong [44], and slightly increased demand for cooling energy in Las Vegas, USA [45]. Similarly, simulation tests carried out in New Zealand climate conditions and theoretical considerations have shown that the increase in the thermal mass of the building should not lead to a significant changes in heating demand [46,47].

So hot arid area with cool nights benefit from mass buildings the most, humid and hot not so much. For winter time sunny and cool mass buildings works well cold and dark not so well.

Robin, I have a solution for your 185F deg. walls.
I design Safari roofs, which provide shade and cooling to iron rooves.
It works on walls also.
Install vertical battens on wall at 1.5M.
Cover with a good quality sisalation
Now install cross battens at 1M intervals.
Attach roofing iron vertically to the last battens.

I use metal battens 50 to 65mm thick.
Note; this wall or roof cover is not weather proof, the original design covers that aspect.
In Australia it lowers the surface temp. 38 deg. C

Anecdotal experience from builds on my property supports high thermal mass significantly reduces the need for cooling:

In mid summer in central Texas (Low temps: high 70° F; Highs: low to mid 100° F) our (very low thermal mass) 384 square foot pier and beam cabin with light clay straw infilled walls needs continual cooling where our (hjgh thermal mass) 216 square foot rubble trench foundation partially earth bermed cottage with cob infilled walls and continuous rockwool exterior insulation needs only a fraction of the cooling. For the latter, I have the air conditioner programmed to run at 76° F from 10 am to 4 pm and then 80° F the rest of time. If I don't run the A/C outside of the 10-4 window it creeps up to about 81° F. I had hoped to not to have to use A/C in the cottage but without it currently the inside temperate ranges from 84-86 ° F.

Here's a video where I talking about designing the cottage to take advantage of the thermal mass of cob:


I have the equipment installed to measure the comparative energy usage of the two buildings but haven't collected any data yet. Currently, the two buildings use a total of 14-16 kWh a day mostly for HVAC but I estimate the cottage only uses 2-3 kWh of that.  

I have a background in Earth Engineering.
I am not convinced the 4 inches of cob inside the stud wall will improve resistance to the weight of the berm on the other side
by a significant amount.
You effectively have a 4 inch wall of cob pushing back on a 6 ft high and 6ft thick earth berm.
I can see the benefit of its use as thermal mass, the insulation behind the stud wall will ensure any heat will stay within the cottage.

From my architectural education, I would agree that the cob infill will have little structural effect. A 4" thickness of it probably would not be enough to solidly brace the studs where a foot probably would, and more importantly, the buckling effect mentioned would occur at the outer edges of the studs, where the plywood sheathing assuming it is well fastened to the studs will massively reinforce the studs from moving or twisting sideways. The only likely failure mode for these studs is bending or shear strain, which the cob is irrelevant for. The mass of the cob infill is balanced on the stud sill plate and has zero effect at countering the inward force of the berm. Likewise, the 4" thick -non-continuous- cob infill will have little to no effect in resisting shear force from the back wall; that will be entirely taken by the plywood diaphragm stiffened by the studs, and possibly by the retaining walls at the front.

That said, the cob infill will definitely add considerable mass to the inside of the structure and when well insulated from the outside will dampen temperature swings on a daily basis.

John and Glenn, sorry, I didn't get a notification that you had commented. Yes, the primary purpose of the cob infill was to provide thermal mass inside the building envelope which is working really well.

Structurally, I agree the plywood sheathing, drainage and bracing are doing the heavy lifting.

John C Daley wrote:Robin, I have a solution for your 185F deg. walls.
I design Safari roofs, which provide shade and cooling to iron rooves.
It works on walls also.
Install vertical battens on wall at 1.5M.
Cover with a good quality sisalation
Now install cross battens at 1M intervals.
Attach roofing iron vertically to the last battens.

I use metal battens 50 to 65mm thick.
Note; this wall or roof cover is not weather proof, the original design covers that aspect.
In Australia it lowers the surface temp. 38 deg. C

I had to look up sisalation. Very interesting material. A 38C temperature reduction is impressive. We get heavy snow loads in winter and very little sun so now I wonder about setting up temporary panels in summer with this material. I definitely don't want to block what sun we get in winter. Thank you for the information.