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.

Hmmmmm, Interesting

I think the earthen material stabilizes temperatures by absorbing and releasing atmospheric moisture, though I am not knowledgeable enough on it to say anything definitive.

My understanding is that as humidity rises at night, earthen walls absorb moisture.  Then, when it is warmer, that moisture evaporates out of the walls, adding a cooling effect.  Seems entirely non-applicable to high humidity situations.  

And I wonder, if it’s an enclosed space, if the increased humidity is significant, won’t that negate any benefit to warm blooded animals (like me) who rely on evaporative cooling of their skin.

It’s just an idea I heard some folks kicking around.

I have been taking down the cheapo 1/8 inch thick paneling in my hovel, at least it’s laminated wood with some faux wood grain on it.  I once lived in a building where the interior wallboard was actually compressed paper.  I am preparing for sheetrock installation.  Not that it’s thick enough to provide mass that retains its temperature, but the material is heavy!  I do think it will slow the temperature swings a bit.

As this is rather old ( 3 years) Please don't be shy, how has this worked out for you.  

So many threads start out  " this is what I am going to do and it is going to save this X amount"  and then we never hear from again.  So, where does this "great idea" fall into?

cheers
Scott

ps  I am a equal progress comment oriented Person!  Simply meaning, if it is a great idea and has worked out well, then all want to know, and if it didn't work out, that should be stated as well. Learning from dreams of others good or bad, is the basis of true learning.

I did find this:
The Effect of Thermal Mass on Annual Heat Load and Thermal Comfort in Cold Climate Construction | Journal of Cold Regions Engineering | Vol 30, No 1 https://share.google/tywi9WRREYXM6QeA9

But i didnt buy to see the full article. I read somewhere that most original far northern climate homes where built partly into the side of a hill with full log walls to increase thermal mass. When compared to the heat efficiency of a house made of the most effective insulation on the market the log house in a hill won hands down. I think it is less to do with direct thermal mass, and more to do with materials. Solid stone the same mass doesnt effectively trap the heat as well. Wood stores heat very well, but releases it faster than stone, at the same time meaning it needs less heating to begin with because it has a lower specific temperature. Being partially burried also helped, the geothermal heat supplemented the heating, while also making the home extraordinarily sealed, meaning less heat loss.

  I was thoroughly impressed and always thought if I was designing a home I would make it partially burried with full logs, with a green house on  the top "above ground"  floor to further trap heat in winter, and make a heated green house at the same time. The below ground portion would have a lower "basement" level that would be fairly deep for food storage. The below ground would also help keep cool in the summer, and you wouldn't need to haul your roof water to the garden because it would be piped in already. Ahh dream builds.

R Grier, have you come across wofatis yet?  Lots of discussion on advantages of earth sheltering of buildings.’

Stone in a buried structure will quickly transmit heat from interior to ground or vice versa, depending on which is warmer. The issue for modern civilization is that ground temperature in any place that needs serious heating in some part of the year is around 55 F at most, considerably cooler than comfortable. Dry sandy soils may allow heat to build up from a heated interior and eventually approach comfort levels, but wet soils will never get warm.

Wood as the underground structure will effectively insulate the interior from the ground, losing heat much more slowly than when exposed to the cold air and wind. Stone holds more heat per unit volume, and transmits it faster than wood. Soft, lightweight woods will be better insulators than dense woods, though they will most likely rot much faster if exposed to damp.