I have had a new courtyard attached to my house, and it is largely paved with concrete.
I intended the courtyard to ensure a better supply of cold night air to channel into the house in midsummer. To my disappointment, I found that the concrete gets as hot as hell during the day, several degrees warmer than the screen temperature. It also holds the heat all night, being still warmer than the screen at dawn. My supply of cooling air is reduced, not increased.
It has been suggested to me that I could prevent the concrete from getting so hot by covering it with matting. Several types of matting might be suitable. They are designed for other purposes, and I cannot find advice about what might be both cheap and suitable for my purpose: to reduce the temperature of a concrete path heated by the sun.
The mats go by different names, such as playground matting, soft-fall matting, anti-fatigue matting, and outdoor matting. Often they are made from old car tyres, a "sustainable" virtue.
It seems to me that a thickness of 10 mm would be ample for strength and for thermal insulation. Since thermal insulation is seldom intended, naturally there is no information about it.
In playgrounds, the coolness of the matting is probably seen as an advantage, in addition to the protection from injury.
I would be grateful for any advice or ideas on this topic. Can you recommend a particular type of product?
Outdoor matting for thermal insulation
(31 posts) (9 voices)-
Posted Thursday 11 Feb 2016 @ 7:48:28 am from IP #
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Annette, I am concerned to be practical. I might consider raising the matting in winter if that had an advantage, but shifting it daily would be too much hassle.
It seems to me that if I could get the maximum temperature a few degrees lower, the whole daily cycle would be lower, more like the temperature cycle in the thermometer screen.
I thought of erecting shade cloth, but I would definitely want that removed at night to allow out-radiation.To wlb. Are you sure the mats would not offer much insulation? I know that there are other factors to include, but concrete has a conductivity of 1.440 Watts per metre per degree, while I guess that these rubber-based materials might be a bit like "carpet plus underlay" at 0.050 or like "cork tiles" at 0.079. (Data in "Energy Efficient Building and Design Resource Book" by Holger Willrath and others, Brisbane Institute of TAFE, 1992.)
In that case they would have about 20 times the insulating effect of plain concrete. I don't yet know what thicknesses the mats come in.
They do come in different colours, and I would specify colours near to white for maximum solar reflectance.
Do people here have experience of walking on such mats in hot sunshine? In bare feet I can't walk on my concrete paths.Posted Thursday 11 Feb 2016 @ 11:56:08 am from IP # -
Bushwalker
MemberI'd try 90% shadecloth awning. It would reduce the temp of the concrete dramatically. We have a section on our verandah and the difference of the heat in the floor and walls is significant.
If you think that the shadecloth should be removed at night, then why wouldn't an insulating cover not need to be removed?
Posted Thursday 11 Feb 2016 @ 8:27:29 pm from IP # -
Morbo
Member"To my disappointment, I found that the concrete gets as hot as hell during the day"
glad you figured that out, how many years did it take you? 1st thing I got rid off as much as I could.
Plants/grass will be at ambient temperature. Or white paint.
Or maybe some shade structure. Can you make it so that it only gets winter sun, so then it would give out some warmth at night.Posted Thursday 11 Feb 2016 @ 9:37:56 pm from IP # -
To Bushwalker
I am still considering shade-cloth. It is more controllable than trees or shrubs.
(Deciduous plants don't let in enough sun in winter. They don't lose their leaves until winter is half over, and there is still a lot of shade from the wood.)
As to removing insulation (of any sort) at night, this needs a more thorough analysis than I can do. The day-time short-wave radiation gain is extreme, but lasts only an hour or two at any one spot; the night-time long-wave radiation loss is much slower and actually continues through all 24 hours.
I have never seen any analysis of the effect of shade cloth on long wave radiation. People don't ask about it, I suppose.To Morbo
The law of natural cussedness applies. I draw my cold air from the cooler south side of the house: the side that does NOT get winter sun. It gets plenty of summer sun though, because the shadow of the house is so short.I really would like to know more about the thermal effect of outdoor matting. My builder friend says that when it is laid it makes the area feel much cooler.
Posted Thursday 11 Feb 2016 @ 10:49:13 pm from IP # -
Bushwalker
MemberWouldn't it be easy to test?
Just get a few square metres of shadecloth and the same of the matting. Use your temperature measurement devices to work out the benefits over a 24 hr period.
Posted Friday 12 Feb 2016 @ 12:25:15 am from IP # -
Not so easy, Bushwalker.
My sensors can only detect the performance of the courtyard as a whole, (or of strata within it if I am lucky).
I would have to do the whole treatment. Then the results might not show up for weeks, as the weather changes.
Actually, I still have only provisional data, because I have not finished calibrating the new thermometers and screens.Posted Friday 12 Feb 2016 @ 1:28:21 am from IP # -
Thanks wlb.
Could you please refer me to numbers supporting that?Posted Friday 12 Feb 2016 @ 2:07:20 am from IP # -
Bushwalker
MemberCaptosilia,
You have a courtyard, you don't need to measure it all.
You could rig up a 1-2 square metre of shadecloth and a 1-2 square metre of matting and use an IR thermometer. You just need to measure the concrete surface temperature as well as the matting surface at regular intervals.
Sure, you need to do it on a sunny day.
Posted Friday 12 Feb 2016 @ 2:55:45 am from IP # -
To wlb
I was looking forward to reading data on the performance of shade cloths through the solar spectrum. Sales promotions give figures only for ultra-violet protection, not even for reduction in solar heating or visual glare, far less for reduction in infra-red transmission. Reducing infra-red transmission would generally be a disadvantage in that whatever heat is still generated below the cloth would not easily radiate away.
This is the very point at issue here.About the temperature difference under shade cloth at night:
"if you don't notice it, it probably doesn't really matter"
That is not the case. I am not aiming for night-time comfort in the courtyard, but for daily summer comfort in the house. The mean minimum overnight temperature in the courtyard through the summer determines the (higher) minimum overnight temperature in the house, and that is the main thing that stops the house from getting too hot during the day.
You are right: I would not feel warmer standing under shade cloth at night. I can barely detect a two degree temperature change unless it takes me past the limit of my comfort zone.
To keep the house within the comfort zone in summer calls for using every tiny bit of cooling in the incoming night air.To Bushwalker
I don't have a reliable infra-red thermometer yet.
Posted Friday 12 Feb 2016 @ 4:48:42 am from IP # -
wlb
MemberCatopsilia said:About the temperature difference under shade cloth at night:
Sorry, we seem to be at cross purposes here. I wasn't referring to the use of shade-cloth in general; only to your comment that if you did use it during the day, you would have to remove it each night.
Posted Friday 12 Feb 2016 @ 5:04:50 am from IP # -
Bushwalker
MemberIs $29.95 too much?
Also look on ebay, there are plenty.
If you were local I'd loan you ours.
Posted Friday 12 Feb 2016 @ 6:40:13 am from IP # -
Following up on shade sails (the technical term, I find), one of the best summaries is in this brochure:
http://www.sunsmart.com.au/downloads/resources/brochures/shade-for-everyone.pdf
I find this rather frustrating, in that my particular needs are not considered. I see now why UV protection, and only UV protection, is the quality of shade cloth that is covered in depth. That is what protects people from skin cancer.
In my proposed use, UV protection is beside the point: people will hardly ever be there. What I need to know is the reduction in received short-wave radiation (good) and the reduction in outgoing long-wave radiation (bad).
Reading the advice in the brochure, it seems that adding a shade sail to my courtyard could double its cost.
I'm going cold on that idea.Posted Friday 12 Feb 2016 @ 11:38:05 am from IP # -
johnmath
MemberI seriously doubt that a thin layer of insulation on the concrete would make any difference. What effect would you expect is that was the insulation in your roof?
You could possibly instal a retractable shade cloth that shades the concrete during the daytime, but can easily be retracted at night to allow the concrete to radiate its heat away. These structures can be not much more expensive than a fixed shade cloth and look somewhat like a horizontal roman blind. The material can be any grade/colour of shade cloth (in your case you would want white) or perforated membrane that allows air circulation yet provides protection from light showers.
For ideas have a look here (I am not endorsing this company) http://shadeformsails.com.au/shaderunnerretractablesails/
Posted Friday 12 Feb 2016 @ 9:05:59 pm from IP # -
Thanks for the suggestion, johnmath.
Unless the material is almost transparent to heat, I would want to retract it every night for three months of the year.
The courtyard is a tricky shape: not a rectangle but two triangles, both at the property boundary.Posted Friday 12 Feb 2016 @ 10:09:40 pm from IP # -
I have found a link to a new, very high-tech, material that achieves the result that I want.
http://www.kurzweilai.net/new-solar-structure-cools-buildings-in-full-sunlight-replacing-air-conditioners
This "nano" material acts as a mirror for sunlight, and also radiates away any heat that accumulates. It radiates selectively at the infra-red wavelengths that allow heat to escape through the "atmospheric window" (well-known through the "greenhouse effect").
The material has practically no absorptivity (i.e. complete reflectivity like a mirror) at the visible wavelengths of light, and almost 100% absorptivity (and therefore emissivity) at the infra-red wavelengths felt as "heat".
I would like to know if (quite low-tech) shade cloth has a high enough emissivity/absorptivity to ordinary "heat" to mean that it provides no barrier to radiative cooling at night.Posted Friday 12 Feb 2016 @ 11:29:08 pm from IP # -
Flying high
MemberI considered concrete for our courtyard however, in the summer it would bake the rest of the house, so ended up with a timber deck instead.
Timber of course has more maintenance issues but IMO it was the better choice, deck in our court yard is just shy of 100 square metres and we have glass windows looking onto the deck too.
Possible options;
Timber deck of sorts over the concrete?
90% rating Shade cloth hung overhead to keep the sun off during the day?
Cool off the concrete with tank water?
Paint with reflective paint?Not sure about the matting, could be a PIA job..
Posted Saturday 13 Feb 2016 @ 1:05:10 am from IP # -
scott drew
MemberWhat about a pool cover type thing? They are like bubble wrap for insulation purposes. Can come on a roller type arrangement for putting it away when required. Could be cut to correct shape as required. I dont know about people walking on it though, if people walking pops the bubbles you lose insulation.
Posted Saturday 13 Feb 2016 @ 1:14:47 am from IP # -
johnmath
MemberI have sandstone pavers on the north side of a wall of glass, with a pergola that slopes up away from the house. The pergola is clad with clear polycarbonate to allow winter heating, which works fantastically. The pavers also help by absorbing heat and reradiating it through the glass.
In summer (usually November) I sling a shade sale under the pergola to block the sun from heating the pavers. The eave keeps the sun off the glass. The pergola sloping upwards away has two purpose: we can see the sky and the trees of the neighbours; and it stops hot air pooling near the house. The shade sale usually comes down in April.
In relation to the 'high tech' solution, anything that absorbs UV and stores it into heat will reradiate the heat as IR (long wavelength) because the wavelength of reradiating is a function of the temperature of the reradiating surface. Nothing special about that. So all you need to fulfil your requirement is something that is opaque to IF and opaque to VL (visible light) to the extent that you want to block VL. Most of the polycarb sheets have this data. If the cladding slopes up away from the house it will convect any stored heat away.
I had intended to have the 'roman blind' shade sail under the pergola, but released I didn't have enough space under the eave to store it tidily. Hence I bought a pre-made shade sail for $50 which is still perfectly good after 5 years.
Posted Saturday 13 Feb 2016 @ 1:35:01 am from IP # -
Thanks for the detail about your set-up, johnmath.
As you know, from material I have posted in the "Low Energy Houses" thread, my house uses standard features such as north-facing windows, with shading by eaves and by vegetation.
http://www.ata.org.au/forums/topic/3
This new south-side courtyard is the first time I have struck a shading problem.
I don't quite follow your paragraph: "In relation to the 'high tech' solution..." In my case I have a concrete slab with behaviour that is an obvious problem. One proposal is to shield it with a shade sail. It is the properties of the shade cloth, not the concrete, that are at issue. At night, the concrete and the shade cloth will be at similar temperatures (say 15 degrees). Will the concrete "see through" the shade cloth to the sky, which is nearly 300 degrees colder, and radiate heat like crazy? Or will the concrete "see" only the shade cloth, and get as much heat back from it as it sends out?Posted Saturday 13 Feb 2016 @ 2:35:48 am from IP # -
Thanks, Flying high.
About some of your suggestions:
The concrete is, in fact, painted already. Within minutes of the final trowelling, rain poured down and destroyed the finish. It was repaired with paint loaded with sand. I asked for the lightest possible colour, but it turned out to be about the average colour for concrete.
I am experimenting with using tank water for cooling. However, I don't apply it to the concrete paths, where it will quickly evaporate. I apply it to areas of ornamental gravel, where the gravel acts as a mulch.Posted Saturday 13 Feb 2016 @ 2:51:20 am from IP # -
Flying high
MemberHi Catopsilia,
What about retractable overhead blinds?
Any photos of the area?
Posted Saturday 13 Feb 2016 @ 3:04:09 am from IP # -
Phil A
MemberCatopsilia said:
Thanks, Flying high.
About some of your suggestions:
The concrete is, in fact, painted already. Within minutes of the final trowelling, rain poured down and destroyed the finish. It was repaired with paint loaded with sand. I asked for the lightest possible colour, but it turned out to be about the average colour for concrete.
I am experimenting with using tank water for cooling. However, I don't apply it to the concrete paths, where it will quickly evaporate. I apply it to areas of ornamental gravel, where the gravel acts as a mulch.We had a similar dilemma here. As per johnmath, we went with a sloping polycarbonate covered pergola with pavers below, the pavers are also sloping away from the building. In our case we have the pergola sloping towards the building with a gap at the top so that the airflow is greater alongside the building removing heat from the building as it rises. The pavers are patterned from white alongside the building to darker at the extreme outside (like a faded effect) away from the building. They are also laid in a semi chequered effect to give airflow effect similar to the striping on a zebra. The pavers don't transfer the heat in the same way a slab does as each paver is its own individual heat block. When needed we water the pavers. The water is stored between them in the medium (this gives evaporation from all sides as well as the top of the paver) and evaporates to remove the heat energy. This enhances air flow up the slope. This complimented by a microspray curtain at the outer wall of the pergola which also enhances the airflow which is created by the sloping pergola and the sloping pavers.
In your case, the water that is evaporating from the path is giving you the desired cooling effect. If the water didn't evaporate then there is no temperature change. It is the change of state of the water that is indicating the removal of heat energy. The water that stays in the gravel would evaporate at a much slower rate. This is counter intuitive to most I guess. I imagine that the cost of cooling the concrete with conventional water would far outweigh the benefit of the cooling.
I have followed your posts over time with much interest. I cannot believe that you don't have an IR thermometer! Do yourself a favour and get a good quality fluke or similar model. For someone with your interest in this subject (energy transfer)it will begin to pay for itself the minute you start using it. It certainly did for me. My next item will be a thermal imaging camera, so I don't need to graph it all in my head.Posted Saturday 13 Feb 2016 @ 4:30:22 am from IP # -
Thanks, Phil A
You have pin-pointed the evaporative cooling strategy.
If I needed to live in the courtyard during summer days, I could water the hot paths, costing a lot of money and precious water (Memories of a Port Moresby pub!).
Since I am not trying to beat the extreme heat of the day, I hope to economise on water by having it soak into areas of soil that are protected by a gravel mulch. It will cool the courtyard by evaporating very slowly from under the gravel.I am well on with my experiment in keeping these areas moist. It has rained quite often, and when there is no rain for several weeks I add a tonne or two of tank water.
You say that you have a microspray curtain. Is that like a misting nozzle system? I considered that, but it was hard to organise and expensive. It needs continuous high water pressure. Since I use tank water with medium-high pressure pumped up only on demand, I would have had to install a dedicated pump. For nocturnal cooling, that would have meant pump noise at night.
I am a little puzzled by your description. Is the higher edge of the pergola, and of the area of pavers, the edge that is against the house wall? You mention air cooled by evaporation flowing UP the slope. Cooled air is expected to flow down a slope (katabatic flow).
Posted Saturday 13 Feb 2016 @ 6:35:21 am from IP # -
johnmath
MemberCatopsilia said:
I don't quite follow your paragraph: "In relation to the 'high tech' solution..."Will the concrete "see through" the shade cloth to the sky, which is nearly 300 degrees colder, and radiate heat like crazy? Or will the concrete "see" only the shade cloth, and get as much heat back from it as it sends out?
1. The reference was to the 'magic' material for which you posted 'data'. I was trying to point out that the 'magic' material (your reference: http://www.kurzweilai.net/new-solar-structure-cools-buildings-in-full-sunlight-replacing-air-conditioners) must still conform to the laws of thermodynamics and conservation of energy.
2. The energy absorbed by the shade cloth from the concrete will be re-radiated ~50% up to the sky and ~50% back down to the concrete.
The amount of heat absorbed by the concrete during the daytime will be a function of the shade factor. 80% shade cloth will reject 80% of the incident heat. 50% shade cloth will reject 50% of the incident heat. At night both shade cloths will re-radiate in the same way, namely 50% of the heat captured will be re-radiated upwards and 50% downwards. Of course the 80% shade cloth will capture more of the upward radiant heat from the concrete than the 50% will, however a LOT of the heat stored by the concrete will be convected, so the best option by far is to reduce the amount of heat stored in the first place, namely by increasing the shading factor.
Posted Saturday 13 Feb 2016 @ 11:09:46 am from IP # -
Phil A
MemberYes, the high part of the pavers and the pergola are against the house wall. When the micro sprays are not on, the air flow just flows in under the pergola in general and makes its way out the top against the building or at the top at the ends. When the micro sprays are on, as you say, the outside air is cooled and falls to the floor area where it absorbs heat from the pavers and then flows up the slope and then the wall to the top. It is as if the air is flowing underneath a curtain. Of course the pavers are evaporating water or not as the case may be or just radiating heat and creating airflow up the slope aided by the heat from the wall. At the moment the ends of the pergola are open but we are considering filling them in to get better "draw" up the wall surface without contamination from the side entry airflow. I would like to get the thermal imaging camera to work out exactly is happening and to aid fine tuning. I have used pieces of cotton and paper on string to get a basic picture of air flow.
We needed a clear roof area to maximise light into the building, this of course gave us the heat issue. The building cladding is colour-bond.(a converted barn) We have considered replacing some of the clear laser-light with tinted but the light is important to us and the cooling system is working effectively now.Posted Saturday 13 Feb 2016 @ 11:28:43 am from IP #
