Browse Forums Eco Living Re: Thermal mass walls 41Feb 23, 2010 8:02 pm It is all about understanding the implication of this: Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ For more information: Passive Design Re: Thermal mass walls 42Feb 23, 2010 8:17 pm Oh I do understand that bit d-69! But thanks anyway! It's terms like earth berming and direct gain vs indirect gain and isolated system that have me looking to google! It's ok though, I'm catching up now .... Building on an acre in Macedon ......one day. Re: Thermal mass walls 45Apr 08, 2010 10:51 pm Hi all Very interested in this topic as we are have designed a house to build in southern victoria on a rural block , which we are trying to achieve high levels of energy efficiency and passive solar efficiency. Had a couple of questions for dynolite who seems to be very experienced and knowledable in this area. (or anyone else who knows this stuff) First off , the house is orientated North and we don't have space restrictions , so it is pretty much a long ,skinny rectangle in oberall basic shape. The mainly living /dining/kitchen is 15 X 7 , with a 400 mm rammed earth spine wall on the south side ,a rammed earth dividing wall , a concrete floor (polished) , with a skillion roof and a north wall of glass , which would roughly give a north glass to floor ratio of 35-40%, which is way higher than the recommendations in any of the manuals. So my questions for Dynolite are 1. Apart from the obvious heat loss at night from the windows are there any other practical disadvantages to having a higher ratio than recommended of north facing glass. (We are planning to cover the heat loss by double glazing and curtains). looking at a low E slightly tinted glass to cut down some of the glare 2. Will the high amount of thermal mass be likely "soak up" any overheating that occurs . The sun won't hit the rear wall much - only a little in the mornings , but it will hit the room divider wall 6 months of the year. 3. Have been agonizing over heating , current plan is to put hydronic pipe in the slab just in case , and install a large wood heater with 35kw wetback to drive the slab heating if we need to. You sound like you are in a similar climate - pros and cons of hydronic slab ? Will we need it ? We are coastal so we don't frost , and our low's only get down to 5. We are surrounded by water with an ambient low of about 12 in winter. My gut feel ( and its only gut) , is that our heat bank from solar gain would be wiped out by 2-3 overcast days. What has your experience been. (I'm basing this partly on a distant past experience with electric slab heating and I think the slab took about 2 days to cool down - the house was not at all solar efficient though). Will an efficient high output wood heater have a chance of replacing/maintaining the heat bank or will be walking around on freezing cold floors. Thats all I can think of for now , I'm sure there'll be more , any help would be much appreciated. Re: Thermal mass walls 46Apr 09, 2010 1:00 pm We have a similar open plan room with north glass to floor area around 37% with 450mm eaves. Floor is bamboo. No mass walls. Most of the time it is comfortable. Winter and shoulder season temp 21-22 (peak 24). Summer temp 23 (peak 28 ). Overheating in the cooler months easily addressed by cracking the window open slightly to let some cool air in.
In contrast another carpeted room with 33% glass:floor will more readily overheat but again opening windows addresses this. Glare is an issue with direct gain passive solar. A light shelf could help address this or having a row of high set windows instead of full height windows. I'd suspect with reasonable eaves that you have enough mass to absorb heat. Note that large exposed area of mass is more important than volume of mass. Also note that radiant heat reflects within the room and gets absorbed by mass but convected heat doesn't travel very well to non-sun exposed area of the house. It depends on how well insulated and how cold your climate is but our experience in middle of last winter was a 0.5 degree fall per hour after sunset. Currently our house in mid Autumn stays 20-21 degrees 24/7 with no auxiliary heating (night time temps low teens) My overall observation is that our passive solar building provides about at least an 8 degree gradient with ambient extremes. At least 8 degrees warmer than outside on cold winter nights. At least 8 degrees cooler than outside on hot summer days. Re: Thermal mass walls 47Apr 09, 2010 1:08 pm Personally I don't think hydronic heating is needed for a good passive solar design. The radiant system is a comfortable method of heating but the cost of heating is not cheaper i.e. gas fired hydronic heater costs the same as gas ducted heating to run. It is expensive 12K for the pipes and heater. There is no point in running solar hydronic because you would need a huge collector to get any useful heating in winter. Expect to pay > $18K for a full solar set up. Using a solar pool collector might make this cheaper. Current systems don't provide radiant cooling. Putting hydronic in the north-facing rooms is doubling up on solar gain and could lead to overheating. If you are using it then put it on the south side.. Re: Thermal mass walls 48Apr 09, 2010 2:17 pm We are LPG so gas space heating is not an option. The hydronic slab , decision , is do we put the pipes in the slab just in case - as it can't be retro fitted. What form of back up heating do you use for that room ? And in terms of Heat loss , did you double glaze , drape - or both ? Your average climate would be close enough to ours to make a comparision I think Thanks for the reply and information Re: Thermal mass walls 49Apr 09, 2010 2:57 pm We don't have town gas either and LPG is 3x the cost per MJ of energy here. A very expensive heating option. We opted for RCAC so we could have heating and cooling. Cooling requirements for summer was less than 5kWh per day. Most days it wasn't required. For heat waves we had it on for two one hour bursts before night time arrived. Ceiling fans usually were adequate. In the whole time we have lived here we did not require overnight heating or cooling. Lowest overnight temp is 15 degrees (single digit outside), highest O/N indoor temp was 23 degrees (usually around 20 degrees). Note that our nights cool down substantially during summer. The cheapest heater to run would be wood stove. Use an efficient one. Invest in a few heat transfer kits to move the hot air to other places in the house. We used DG in most areas + cellular blinds. The blinds make a huge difference. We didn't have any coverings for the first month of occupation during May (delivery issues). Re: Thermal mass walls 50Apr 09, 2010 9:20 pm One thing I would do if I built again is insulate the slab edge. I was given bad advice by our desiginer that it would be redundant. Although it is not a huge site of heat loss, it is a relatively cheap thing to do and will easily pay itself off in savings. Re: Thermal mass walls 51Apr 09, 2010 11:55 pm Haven't looked into whats required to insulate the edges - foam I imagine , but have read about it having some benefit You mentioned bamboo flooring , is that laid over the slab like a floating floor ? Does that stop the heat collection at all ? The only thing that worries me about the concrete is the hardness on the feet , we are coming off timber floors. Re: Thermal mass walls 52Apr 10, 2010 12:27 am Foam board buried 1 foot deep around the slab edge before pouring. There is no information in the literature about wood over concrete in passive solar. But note that wood (or grass in this case) has thermal mass properties. Our floor is direct stick. I have place my hand on it when it is in direct sun and it doesn't get overly warm (unlike carpet). Re: Thermal mass walls 54Apr 11, 2010 12:36 pm What do you mean by raised ? You can have a suspended slab, which would give you plenty of thermal mass. You would just insulate the bottom of the slab. Have seen people do suspended slabs by pouring into a spandeck (roofing tin ) base which is laid on top of brick or concrete footings. Can be used on a sloping site as an option to digging in to the slope. Render your bathroom walls, two opinions versus the one, makes you wonder. 3 6065 The spacing of the studs looks pretty large especially for a load bearing wall. 3 11122 Nope, only on the inside, I've literally has my ears to the brick outside and can't hear anything. I can sort of 'reset' the noise by pressing firmly on the studs. This… 10 11786 |