This comes under the heading of there is no such thing as a dumb question.
I read/hear a lot about the benefits of thermal mass in a house for passive heating. No problem with that I can see that is fine in winter when you are trying to heat the house BUT doesn't that mean that come summer the house just heats up like an oven an can't cool down? The reason I ask is where we are at the moment is an old stone cottage with massive stone walls, lots of thermal mass. It takes awhile to heat up but once it does after 3-4 days of 40plus temps it then becomes an oven that takes at least that long to cool down again. You can really feel the heat in the walls
question about thermal mass
(73 posts) (20 voices)-
dreuky
MemberPosted Wednesday 3 Dec 2014 @ 9:11:23 pm from IP # -
Russell Moore
MemberYou are correct to a point, especially if the mass is not insulated from the outside heat in summer. I am guessing that your stone walls are solid, ie one whole piece? There is a reason why homes built like that are usually rendered and/or painted white, as they are in places like Mexico and Spain.
We have a lot of internal mass in our house (brick walls) but they sit behind insulated walls and ceilings. That said we have to vent as much as possible once the outside temps drop and attempt to cool the house overnight in summer. Constant days of high temps do cause a rise in the internal temperature, especially if we have hot nights and can't cool down the house overnight.
Posted Wednesday 3 Dec 2014 @ 10:05:31 pm from IP # -
As Russell said, you are half correct.I concur with his comments about insulating and shading the thermal mass, but would add...understanding the apparent path of the sun and how it changes from summer ( basically overhead at midday) to winter (lower in the northern sky depending on the latitude )is the key to successful solar passive design. Once you understand this you will see that thermal mass can be used very successfully or (conversely ) with appalling results if sun angles are not accounted for. Very simple explanation I know ,but the understanding path of the sun is the KEY.
Posted Wednesday 3 Dec 2014 @ 10:25:38 pm from IP # -
Etherealise
MemberYes, shading is very important as is ventilation. We live in a passive solar house with some design problems that we are slowly correcting, and in doing so learning more about all this (and from this excellent forum.)
I would say with good design thermal mass can help in summer as well by evening out temperature fluctuations, but it has to be appropriately placed as well as shaded. And you need good airflow (something we don't really have nailed yet) but in my experience if you have an isolated hot day followed by cool overnight conditions, thermal mass can make things more comfortable.
Our place has double brick walls, multilevel slab and all internal walls are brick (in one case double brick). I think where thermal mass becomes a liability is when you allow too much heat gain into the house in the first place, then the mass will absorb it and hold it. I wish our upstairs bedrooms were not so high in mass as they get too hot and stay hot. Part of that is bad design of course, allowing those rooms to get too hot in the first place, but heat always rises so it's maybe not ideal to have all that mass up there.
In heat wave conditions (like last summer in Melbourne) everything ends up the same temperature so heaps of mass is not great. But then not many houses will be comfortable anyway, they just might cool down quicker when a change comes in...
The Your Home website is a great resource for learning: http://www.yourhome.gov.au/passive-design/thermal-mass
Posted Thursday 4 Dec 2014 @ 2:53:33 am from IP # -
Greg C
MemberWe live in a passive solar house which we built in 1987. The internal walls are all 90mm concrete block, the outside walls are face brick. My wife lived in two houses in Sydney in her childhood, both old double brick homes. She likes this house because even though it might heat up sometimes it cools down a lot faster than those old homes did. Now I would suggest that it never gets as hot here as in the old houses but maybe having just the right amount of thermal mass helps. Also, being a standard passive solar it has very good cross ventilation, but being built in the '80s probably has too much north facing glass, the northern wall is virtually 100% glass, single glazed of course. The insulation level is well bellow what you would put in now. R2.5 in the roof and none in the walls. The single glazed windows are insulated with double skinned blinds in winter and really hot days. Theoretically this gives better insulation than double glazing at a fraction of the price in 1987. Shading is by a pergola on the north wall, that totally excludes the sun in summer, eves on the southern side which help but don't eliminate a little bit of sun coming in around the summer solstice, and no windows on the east or west walls. The secret is alignment, shading, insulation and cross ventilation. I'll bet the old stone house falls down on several of those measures.
In the last week in Sydney which has been warm, on a few days getting up to 35C, the house has topped out at 25C and with windows open at night we get the inside temp down to about 22 where outside temps have fallen to about 19C. The worst situation we have faced is 3 days over 40C in Sydney (2005?). On the last day interior temps got up to 35C when our outside thermometer was showing 45C. Still 10C better but it took 2 days to get the temp down below 25 inside.
If I had my time again we would have more insulation, and better sealing. Sliding doors are very hard (impossible?) to seal up. Then we could up the thermal mass by filling the blocks with concrete.
Posted Thursday 4 Dec 2014 @ 10:53:23 am from IP # -
Etherealise
MemberHere is a good article that talks about advantages and disadvantages: renew.org.au/cooling/
Posted Thursday 4 Dec 2014 @ 10:44:41 pm from IP # -
dreuky
I am surprised that, after the responses above, you still talk of "the downside of thermal mass". Provided that the thermal mass is insulated from the environment, which it MUST be, there is hardly any "downside" to it. In non-tropical parts of Australia that have heat waves, thermal mass has great value in keeping a house cool. A well-shaded and insulated massive house will hardly get warmer than the average weekly temperature, which will be some ten degrees cooler than the hottest daily maxima in a heat wave.
Due to the extreme heat load on all the surfaces of the house that are above ground, the house would tend to get hotter than the average weekly temperature but, to counter this, the thermal mass will be kept cooler by contact with the cold subsoil under the house.Posted Friday 5 Dec 2014 @ 2:26:39 am from IP # -
Benny
MemberDreuky - you say you are in an old stone cottage - so is it mainly the external walls which are getting hot and staying hot too long ? As others have said - shading these walls in summer is essential - how are yours shaded ?
Catopsilia - is there a downside to thermal mass ? What about in colder climates ? I'm sure the old castles of England were impossible to get warm with so much stone to heat up. I guess the starting point is "what is your local yearly average temperature - of air and ground". The thermal mass will tend to stay at this temp. If that temp is lower than a comfortable temperature (say 19-20C ?) then the thermal mass could cause problems in winter although it would help in summer. Unless of course the thermal mass is exposed to sun in winter and collects the days heat.
Our old house (double brick, Perth) is great in summer, but takes a lot of heating to get it warm in winter and would be very hard to retrofit to solar passive.Posted Friday 5 Dec 2014 @ 3:40:14 am from IP # -
d.darroch
MemberOne thing that hasn't been mentioned is the 'Diurnal temperature range'. Let me explain.
Thermal mass is like a thermal battery. It doesn't create heat, it only stores it & releases it later. As Etherealise said, it evens out the temperature fluctuations, knocking off the peaks of daytime highs & night time lows.
So for a high thermal mass building to be effective in summer, what you need, along with effective insulation, shading, appropriate internal placement, & cross ventilation, is a climate with a high diurnal temperature range. This is the difference in temperature between the daytime highs & night time lows. For coastal areas, particularly in the tropics, high thermal mass can have a negative impact on the comfort of a house. If the climate doesn't cool down enough at night time the house will remain uncomfortable for those trying to sleep.
So for the the tropics, low thermal mass is appropriate, for other coastal areas, low - moderate thermal mass is appropriate, while further inland, where the temperature cools off a lot more at night, thermal mass can usually be higher. Ie. The higher the diurnal temperature, the higher the thermal mass can be.
For winter passive heating, along with effective insulation & appropriate levels of glazing, placement is crucial. There's no point in having thermal mass in the southern side of a house if it doesn't receive sunlight. The thermal mass will absorb available heat, reducing the effectiveness of heat sources. An exception to this is a masonry heater. These are heaters made of high thermal mass. They produce a lot of heat very quickly & very efficiently, with low burn times. They absorb much of the heat produced, slowly releasing it throughout in the day. So, generally for winter, you want your thermal mass to be placed internally, on the north side of the house, where it will receive adequate sunlight in winter, & be shaded in summer.
Posted Friday 5 Dec 2014 @ 4:43:06 am from IP # -
Greg C
MemberOne thing I forgot in the thermal mass equation in our house is the floor. In our case a concrete slab on ground. This probably is the majority of the thermal mass in the house. As per a 1980's passive solar house it is not insulated in any way. The theory then was it would couple to the deep earth constant temp, in Sydney it is supposed to be 17C. I have never measured the temperature of the slab but it is normally slightly cool under foot, never cold and a little warmer when it has been warmed by the sun in winter. So in summer it acts as a heat soak to keep the house at a more constant temp, always pulling it down. Compared to older double brick homes with timber floors, the lack of a large mass referenced to a convenient constant temperature is probably the major reason they don't perform as well. Same with double story homes, the current fashion is madness if you are trying to build a passive home. It is very difficult to deal with the rising heat from below to make the bedrooms habitable. In a standard passive design, the bedrooms are usually on the southern side, where they could be a little colder, but no matter in bed you can use more blankets etc to stay warm.
Point taken about the diurnal temperature range. Luckily the places where most people live in Australia are very suitable for a high thermal mass passive solar house.
Posted Friday 5 Dec 2014 @ 7:14:58 am from IP # -
dreuky
MemberThe use of my words "downside of thermal mass" was maybe wrong. Maybe what I should have said was the other side. A lot I have read about thermal mass seems to totally disregard that in a lot of places in Australia you have to worry about cooling the house and this isn't mentioned, only heating. The cottage I am living in at the moment has a how lot of things not working as far as cooling once it heats up which takes time. Usually the gully breezes cool it nicely at night and so no probs it is just the heatwave conditions with no night breezes and then it does heat up and becomes an oven. I'm moving out of here next year so my question was about understanding both sides of thermal mass as far as my next house is concerned. Your answers have explained things thank you
Posted Friday 5 Dec 2014 @ 10:20:17 pm from IP # -
Morbo
Memberwell, my weatherboard becomes an oven faster and cools down faster. In heatspells over a few days when it does not cool down at night eventually it will be stuck at 35 or so degrees.
Summer shade, winter light in is a big help and maybe something that helps air movements in those days when there is no wind at night and eventually it gets down to 25 between 4 and 4:15 AM, but it does not come into the house.Posted Saturday 6 Dec 2014 @ 12:15:15 am from IP # -
In this graph, I have used my last twelve months of temperature data to show the benefit of thermal mass in summer as well as in winter.
Outdoor temperature in this year went as low as minus 4.0 degrees Celsius and as high as plus 43.7 degrees: a range of 47.7 degrees.
The total effect of orientation, glazing, insulation, shading and thermal mass was to reduce the range of room temperature to 16.4 degrees, and to make it agree closely with the adaptive comfort zone. At Manilla, the adaptive comfort zone goes down to 17.3 degrees in winter, and goes up to 29,3 degrees in summer. Room temperature went down only to 15.0 degrees, and went up only to 31.4 degrees. Not many hours in the year were beyond the comfort zone limits. As a result, practically nothing had to be spent on heating or cooling.
I observe subsoil temperature at 750 mm depth below the surface of the soil in the garden, and at the same depth in the footings below the floor slab. Clearly, the house protects the mass below the slab from much of the temperature variation that occurs below the garden. While the mean temperature is almost the same, the temperature range is reduced from 13.9 degrees to 5.8 degrees.
The fact that the subsoil at 750 mm below the floor slab did not get warmer than 23.3 degrees prevented the surface of the slab from getting warmer than 28.6 degrees, nearly 3 degrees cooler than the maximum room temperature.Posted Sunday 7 Dec 2014 @ 1:50:01 pm from IP # -
To MR2
I am citing the Adaptive Comfort Zone of de Dear and Brager (2001) which is now included in the de facto indoor climate Standards of ASHRAE (American society of Heating, Refrigeration and Air-conditioning Engineers).
http://forum.weatherzone.com.au/ubbthreads.php/topics/864290/Re_Indoor_Climate#Post864290
The Adaptive Comfort Zone limits vary with the mean temperature of the month at each place. They are fairly realistic limits.
They are NOT for comfort while sleeping. Sleeping comfort has hardly been studied at all. I have discussed sleeping comfort in a response to a question on my blog:
http://climatebysurly.com/2014/04/21/january-coolth-in-a-house-without-air-conditioning/#comments
"In this experiment (in Hong Kong), the authors kept the room and its surfaces at 22°C, the relative humidity 50% and the airflow below 0.15 m/s. These conditions may be near the ideal for sleeping with light sleepwear and bedding."Posted Monday 8 Dec 2014 @ 12:53:58 am from IP # -
Greg C
MemberThe temperature that is the upper limit for comfort do vary. I can vouch for the effect on that hot 3 day spell. it was about 45 outside, on walking inside the cool in the house was instantly felt, almost like walking into an air-conditioned space even though it was 35. However after a while you would start to feel warm, and that could be ameliorated by a fan to a certain degree. On the 3rd day we all thought to get some relief, go for a drive. The car was an old European machine noted for its poor air-conditioning and I thought this is going to be good. It was magnificent, it might have only got the car down to 30 or so inside but as everyone was normalised to a much higher temperature it felt very cool.
Humidity also has a huge effect, based on that I would say 27 is the top temp in Sydney, before my wife is searching for a bit of relief.
However much as I love the feeling that the design, architecture and siting of house will look after occupants comfort automatically, if building a new house today it would be prudent to look at another way. Design the house properly, insulate and then put lots of solar panels on the roof to run an efficient ducted heat pump system. If batteries were included in the mix so that you could heat and cool the house only from energy collected there we would have a solar house for the C21. There are a few designs out there already.
http://www.architectureanddesign.com.au/news/net-zero-energy-home-and-green-steel-project-trium
What level of thermal mass would be required, I don't know but I would suggest a little less than in an old school design like mine
Posted Monday 8 Dec 2014 @ 9:32:39 am from IP # -
Nat Vegan Green
MemberGreat to find this discussion on thermal mass. I was keen to build (hopefully in Tasmania) a hempcrete house with slab on ground but after reading the latest Renew magazine, I am reconsidering this amount of thermal mass being on the outside of the building. So wondered if there may be a way to do reverse hemp veneer walls ( aiming for R4.0 walls), and in light of the changing climate and small Diurnal temp range. Any thoughts?
Posted Monday 5 Jan 2015 @ 4:47:30 am from IP # -
Hi
For a different approach try the international passive house standard whereby you heat up the house naturally in cold climates without thermal mass!!
Interestingly our design which we are now testing does have a concrete floor but not so the sun can shine on it. The walls and roof are lightweight insulated panels.Benefit of thermal mass concrete? On hot days it feels cooler underfoot!
So I like it in our climate (Melbourne) for that reason...Posted Saturday 28 Feb 2015 @ 5:50:32 am from IP # -
David
Memberscipe said:
concrete (cement+) is one of the worst green house bandits on earth ???Your thinking about embodied energy from when it's produced, given enough time it's gets to neutral and beyond provided your building design is good enough and it's used wisely.
Posted Sunday 1 Mar 2015 @ 3:26:27 am from IP # -
d.darroch
MemberIt's a good idea to replace a proportion of the cement (which has extremely high embodied energy) with fly ash (or blast furnace slag). Fly ash is a waste product from power stations. Although it can take a little longer to reach strength, by 28 days (when most concrete testing is done) it will match the strength of Portland cement, & surpass it over time. More importantly it shrinks less than Portland cement, so shouldn't crack as much, & is more resistant to corrosive environments.
Posted Sunday 1 Mar 2015 @ 11:28:41 am from IP # -
Morbo
Memberbrick has higher embodied energy than concrete
http://www.yourhome.gov.au/materials/embodied-energyPosted Thursday 5 Mar 2015 @ 4:11:08 am from IP # -
scipe
Member"...since the 19th century, human induced CO2 emissions from fossil fuel
combustion, CEMENT MANUFACTURE and deforestation have disturbed the balance,
adding CO2 to the atmosphere faster than it can be taken up.." (emphasis added)Source - "The science of climate change".
Australian Academy of Science. Feb 2015. p12.
science.org.auMy reading of above suggests CEMENT is about as green as coal fired power and deforestation, i.e. it is a bloody climate menace! And anything employing great
lumps of its manufacture is NOT green, irrespective of how many stars are slavished upon it ? YES / NO ?Posted Thursday 5 Mar 2015 @ 8:35:22 am from IP # -
d.darroch
MemberHence why I'd be limiting my concrete use to a slab, where appropriate, & replacing as much of the cement as possible with supplementary cementitious materials. These materials, namely fly ash, blast furnace slag & silica fume are waste products from coal fired power stations & steel manufacture. While there's a source of this waste we may as well use it.
Posted Thursday 5 Mar 2015 @ 9:21:58 am from IP # -
Johnnojack
MemberI keep hearing about flyash yet in years of contact with concrete batching plants I never found one with a separate silo filled with flyash. Just how does one order concrete containing it? BTW my son is about to get a split level slab poured, estimated concrete quantity, 90m3. Lets hope the house lasts a good 100 years.
Posted Thursday 5 Mar 2015 @ 11:46:11 am from IP # -
Morbo
Memberthis is about as much as next doors complete concreted backyard?
Lifespan of an Australian house is 25 years? Residential highrises even less, but they are mainly made of postcard thin furring channels.
meanwhile:
http://theconversation.com/the-devaluing-dream-why-australian-suburbia-is-an-economic-disaster-4792Posted Thursday 5 Mar 2015 @ 11:09:58 pm from IP # -
Bushwalker
MemberMorbo said:
this is about as much as next doors complete concreted backyard?
Lifespan of an Australian house is 25 years? Residential highrises even less, but they are mainly made of postcard thin furring channels.
meanwhile:
http://theconversation.com/the-devaluing-dream-why-australian-suburbia-is-an-economic-disaster-4792So we should all live in multistorey boxes in high density rat nests?
It might delight a family to have a larger kitchen or a bedroom in the roof. The problem is that the house is in the wrong place and would need another four storeys on top of it to be sustainable in a contemporary metropolis.
[..]
We might ponder how the low-density suburbs damage the environment, first by instituting the least energy-efficient detached housing and second by forcing people into cars on our now strangled roads, which fill the air with carbon. But what is never contemplated is how the low-density pattern also has the effect of sucking Australian capital into a vacuum.
If that is the future of living in society, I'll pass thanks. I've lived in dormitory suburbs where everyone is a few metres from their neighbours. It might save some fuel for transport, but at the cost of the community's sanity. We moved out because we got sick and tired of listening to everyone else's domestic disharmony.
Posted Friday 6 Mar 2015 @ 12:30:19 am from IP # -
Morbo
Membercan listen to that as well since next doors walls are paper thin. Plus we got 9 split system condensers facing our wall. The only good thing is, we still have a garden that is not made of concrete/termac.
In European houses you would not hear your neighbour, because there is more than 20mm gypsponge between appartements.Posted Friday 6 Mar 2015 @ 4:08:54 am from IP #
