tjo o tjim Posted October 9, 2019 Share Posted October 9, 2019 5 hours ago, GarryP said: I want a comfortable house in which I can sit in the living room and watch TV without the need for aircon, but my fear is that this would be so much more difficult in a bungalow than a two storey house. So, you need natural ventilation for the un-conditioned spaces, which would tend to require low thermal mass, good overhangs, and a way to bring air in low and exhaust high. There are several ways to do that; the traditional Thai stilt house with high open ceiling and gable vents (possibly augmented with fans) works pretty well with a radiant barrier. If you want a 2-story concrete box, you will be forced to have the bedrooms upstairs and the “un-conditioned” spaces below. But, in reality the cooling upstairs is also cooling the lower floor. Personally I am not a fan of the ground-coupled style @willi2006 is looking at; I think the ground temperature is optimistically closer to 26-27C, and that will end up with too much thermal mass at the wrong temperature. However, the wrap-around veranda makes tremendous sense here; normally the biggest pain point is really the solar heat gain especially when that continues to radiate back into the space at night. Humidity is seasonally painful, and is most economical to address with air conditioning and transfer-exhaust or direct ventilation of latent heat sources. Link to comment Share on other sites More sharing options...
willi2006 Posted October 10, 2019 Share Posted October 10, 2019 8 hours ago, tjo o tjim said: ... Personally I am not a fan of the ground-coupled style @willi2006 is looking at; I think the ground temperature is optimistically closer to 26-27C, and that will end up with too much thermal mass at the wrong temperature. ... Completely agree. I meant a suspended slab as it is used here, not a slab-on-grade, but didn't make it clear in my posting. As far as I know the average ground temperature here is 27 °C or even higher. But EnergyPlus doesn't accept a value higher then 25 °C. So I used that. Also not made clear in my posting as many other details. Link to comment Share on other sites More sharing options...
willi2006 Posted October 10, 2019 Share Posted October 10, 2019 11 hours ago, sometimewoodworker said: There are 3 recommend ways (US department of energy) of fitting a radiant barrier in a new build. They are equally effective. The choice of fitting method is dependent on the construction process. Please give a reference, preferable an internet link. Link to comment Share on other sites More sharing options...
GarryP Posted October 10, 2019 Share Posted October 10, 2019 2 hours ago, willi2006 said: Completely agree. I meant a suspended slab as it is used here, not a slab-on-grade, but didn't make it clear in my posting. As far as I know the average ground temperature here is 27 °C or even higher. But EnergyPlus doesn't accept a value higher then 25 °C. So I used that. Also not made clear in my posting as many other details. We will be building our house between 1 to 2 meters off the ground. Link to comment Share on other sites More sharing options...
tjo o tjim Posted October 10, 2019 Share Posted October 10, 2019 4 hours ago, willi2006 said: But EnergyPlus doesn't accept a value higher then 25 °C. I’ll see if I can get someone to talk to Martyn. I don’t think EnergyPro has the same limitation, and it is the same code base IIRC. Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 10, 2019 Share Posted October 10, 2019 5 hours ago, willi2006 said: Please give a reference, preferable an internet link. Why? You can do your own research, as I did. The information is there if you want it. The graphic I posted is from the US DoE I highlighted no. 3 Link to comment Share on other sites More sharing options...
willi2006 Posted October 10, 2019 Share Posted October 10, 2019 1 hour ago, sometimewoodworker said: Why? You can do your own research, as I did. The information is there if you want it. The graphic I posted is from the US DoE I highlighted no. 3 Because I did my research before already and did it again to be sure. The sources tell a different story. E.g. U.S. DOE: "To be effective, the reflective surface must face an air space." https://www.energy.gov/energysaver/weatherize/insulation/radiant-barriers Or Wikipedia: "Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid or gas)." https://en.wikipedia.org/wiki/Heat_transfer#Radiation I would be glad to learn how radiation from the roof deck to the attic is reflected with "METHOD 3" where the "radiant barrier" is clued to the roof deck, as shown in posting #30. Or is this just a thin foam insulation:https://forum.thaivisa.com/topic/1123874-ceiling-insulation-types-recommendations-please/?do=findComment&comment=14651293 Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 10, 2019 Share Posted October 10, 2019 1 hour ago, willi2006 said: Because I did my research before already and did it again to be sure. The sources tell a different story. No they do not, you have just misinterpreted the information. Or it explained poorly, unfortunately a not unusual case, which is confusing you. 1 hour ago, willi2006 said: To be effective, the reflective surface must face an air space. If you are using a REFLECTIVE barrier yes However Quote All materials give off, or emit, energy by thermal radiation as a result of their temperature. The amount of energy emitted depends on the surface temperature and a property called the "emissivity" (also called the "emittance"). The emissivity is a number between zero (0) and one (1). The higher the emissivity, the greater the emitted radiation. Silver foil has a very low number around 0.02 ~ 0.05 Reflective, reflects heat Radiant, does not radiate much Quote A closely related material property is the "reflectivity" (also called the "reflectance"). This is a measure of how much radiant heat is reflected by a material. The reflectivity is also a number between 0 and 1 (sometimes, it is given as a percentage, and then it is between 0 and 100%). Silver foil is about 0.95~0.98 Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 10, 2019 Share Posted October 10, 2019 1 hour ago, willi2006 said: I would be glad to learn how radiation from the roof deck to the attic is reflected with "METHOD 3" where the "radiant barrier" is clued to the roof deck, as shown in posting #30. It is not reflected of course neither is there any reflection in methods 1 and 2 if single sided radiant barrier is used neither is it reflected in the pictures I show of my back kitchen. it is not the reflectivity that is important. The hint is in the name RADIANT BARRIER it is the radiation that is poor the emissivity!!! Quote A radiant barrier reduces the amount of heat radiated across an air space that is adjacent to the radiant barrier. So there must be an air space on the silver side for the radiant barrier to function, it emits (Radiates) very little heat. do this demonstration at home. Heat a black frying pan to around 400 degrees C put your hand as close as you can, note the distance. Put a layer of silver foil in contact with the surface, shiny side up (no air gap between the foil and pan) repeat the test. The second time you will be able to get hour hand very much closer because the foil is a bad emitter. Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 10, 2019 Share Posted October 10, 2019 Does this help? single sided foil or foil in contact with the roofing materials Link to comment Share on other sites More sharing options...
willi2006 Posted October 11, 2019 Share Posted October 11, 2019 15 hours ago, sometimewoodworker said: It is not reflected of course neither is there any reflection in methods 1 and 2 if single sided radiant barrier is used neither is it reflected in the pictures I show of my back kitchen. it is not the reflectivity that is important. The hint is in the name RADIANT BARRIER it is the radiation that is poor the emissivity!!! Okay, guess now I understand there's a misunderstanding. Or better misleading use of terms. Radiant barrier is, e.g. Wikipedia: "A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer." https://en.wikipedia.org/wiki/Radiant_barrier Emissivity is e.g. Wikipedia: "The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation." https://en.wikipedia.org/wiki/Emissivity In method 3 the bottom surface of the roof deck is covered with material that has a lower emissivity than the roof deck. Searching for information about this method I found: Thermal Proof That Foil Radiant Barriers Don’t Work Directly Under Roofing Shingles Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 11, 2019 Share Posted October 11, 2019 1 hour ago, willi2006 said: Okay, guess now I understand there's a misunderstanding. Or better misleading use of terms. Radiant barrier is, e.g. Wikipedia: "A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer." https://en.wikipedia.org/wiki/Radiant_barrier Emissivity is e.g. Wikipedia: "The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation." https://en.wikipedia.org/wiki/Emissivity In method 3 the bottom surface of the roof deck is covered with material that has a lower emissivity than the roof deck. Searching for information about this method I found: Thermal Proof That Foil Radiant Barriers Don’t Work Directly Under Roofing Shingles OK you seem to understand that there are 2 different, but related, properties of silver (aluminium) foil. Both of them require an air space to function. (No airspace no radiated heat, as the example video explains) Both can function without an airspace on the reverse side. If you have double sided foil you can employ both properties. If you have the cheaper single sided then the most effective way (because of dust) is to use the low emissive property. All factory installed foam insulation with foil uses the low emissive property of the foil. No factory installed insulation (in Thailand) uses the reflective properties. It all works, some better than others. None/few of the explanations use terms that make clear which properties are functioning as they mix the terms (possibly scientifically correctly but leading to immense confusion) . Yes radiation can be reflected (95%~98%), so technically you can term that function as a radiant barrier. However if you term that function as a reflective barrier (it is) and the low emissive function (0.02~0.05) as a radiant barrier NOT emitting radiation, things begin to be more understandable and less confusing, maybe ???? . You could also use the accurate but cumbersome terms "reflective radiant barrier" and "emissive radiant barrier" but good luck with that. None of this is helped by marketing speak, ceiling insulation is often sold in foil bags. These have a single main benefit, to keep the insulation dust and moisture free. A secondary function is to reflect heat radiation back to the roof this will be compromised over time by dust. The fact that the bag is completely silvered just eliminates the chance of installing it the wrong way up In conclusion due to the materials use in roofing in Thailand with a well vented roof space double sided foil may have a slight advantage if fitted in type 1 & 2 ways. This is borderline as you will have heated air being produced by the hot (hotter because of the reflected radiation) underside of the roof. [I postulate that where bitumen roof shingles are used you may cause them to fail due to overheating, I have no data and little interest in that as it's not a roofing material used in Thailand] A not insignificant benefit is that you have 2 shiny sides so you will always have one effective side down however incompetent (or good) the people installing the foil are. Link to comment Share on other sites More sharing options...
sometimewoodworker Posted October 11, 2019 Share Posted October 11, 2019 2 hours ago, willi2006 said: In method 3 the bottom surface of the roof deck is covered with material that has a lower emissivity than the roof deck. In all methods that is correct and a rather massive understatement, as shown under. You did note that single sided foil is acceptable in 1 & 2 didn't you? Link to comment Share on other sites More sharing options...
GarryP Posted October 28, 2019 Share Posted October 28, 2019 As my house is in the very early planning stages, I was wondering whether it would be worthwhile pouring a concrete floor/ceiling instead of using gypsum or concrete ceiling panels hung from the roof framework. I will only be building a bungalow but it would allow me to store heavy stuff under the roof. I am just concerned that it may not be good from an insulation perspective. Link to comment Share on other sites More sharing options...
CharlieH Posted October 28, 2019 Share Posted October 28, 2019 2 minutes ago, GarryP said: As my house is in the very early planning stages, I was wondering whether it would be worthwhile pouring a concrete floor/ceiling instead of using gypsum or concrete ceiling panels hung from the roof framework. I will only be building a bungalow but it would allow me to store heavy stuff under the roof. I am just concerned that it may not be good from an insulation perspective. I would think it would make things a lot cooler and be a more useful space to develop or use later. If you add the reflective film etc to the roof frame prior to fitting the roof tiles on etc you will tick all the boxes in my opinion. Link to comment Share on other sites More sharing options...
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