Browse Forums Eco Living 1 Dec 06, 2008 9:22 pm In the course of my research, I have come across a number of glaring aberrations (committed particularly by so-called green-architects) in their passive solar house designs. These elements significantly deviate from standard passive solar principles potentially compromising the energy performance of the house or requiring more expensive components to compensate for them.
I assume the reason for some of this are concessions to architectural freedom but I also wonder if they are due to an insufficient understanding of thermodynamic principles. Just a recap on the important elements to consider in passive solar: * Orientation * Shading * Glazing * Insulation * Thermal Mass * Ventilation A fuller description can be found at websites as http://www.greenhouse.gov.au/yourhome/t ... l/fs10.htm or eere.energy.com or in a reputable Passive Solar book such as by Dan Chiras. Make a note of these potential flaws the next time you evaluate a purported passive solar house: Orientation * Excessive glazing on non-northern aspects e.g. Sunspace on the Eastern wall. Leading to excessive heat gain in summer or heat loss during winter. Shading * Inadequate overhangs for the lower storey on multi-storey buildings causing the lower floor to overheat in summer. Glazing * Employing Angled/tilted glass, traditional skylights or clerestory windows that are either difficult to shade during summer or become a site of unwanted heat loss during winter. * Excessive amounts of north-facing glazing which result in overheating during summer or heat losses at night during winter (see below - Thermal mass) NB glass is the most difficult building material to insulate effectively. A triple glazed, heavily curtained window still allows more heat transfer than a standard wall insulated with fibre-glass batt and radiant barrier. Insulation * Neglecting to use a radiant barrier in the roof and particularly on the western or eastern walls to reduce summer heat gain (bulk insulation is insufficient to reduce the intense solar radiation of a temperate or hot environment) * Neglecting to install appropriate window coverings to reduce heat losses during winter or at night-time Thermal mass * An over-reliance on expensive thermal mass (e.g. concrete, rammed earth) to store heat gain which has been generated from excessive glazing. * Using 'exposed' un-insulated thermal mass in a temperate environment. This strategy only works in a hot, arid climate where diurnal temperature variations are high. * Deploying large redundant portions of thermal mass in areas of low-solar gain e.g. South facing rooms (An inefficient strategy that has the potential to work only in hot, humid climates) (Beyond a certain point, additional glazing requires large amounts of thermal mass to allow the house to function effectively) Ventilation * Trying to use ventilation strategies to compensate for poor radiation control during summer i.e. not installing a radiant barrier, excessive glazing, inadequate overhangs, lack of shading * see 'Whirlybird' thread - roof ventilation is an insufficient solution to achieve summer cooling * Other fairly pointless ideas are wall cavity ventilation and under-eave vents. (The main objective of ventilation is to assist in human cooling through evaporation or remove convected/conducted heat - and not to address radiant heat gains) Re: Passive Solar Advice 2Dec 08, 2008 8:43 am Very well put.
Possibly a bit too technical and complicated for the average layman though. Synergy (WA electrical company) have a section in their website which very simplistically goes through some of the principles you have outlined, click on the 'how to design an energy efficent home' section. Its all interactive and pretty informative. http://www.synergy.net.au/Residential_S ... ohome.html Give it a go. Pat. Re: Passive Solar Advice 4Dec 24, 2008 1:43 am Do it dog
You might enjoy theese articles as well. http://www.sedo.energy.wa.gov.au/uploads/Energy_Eff_hous_8pg_49.pdf http://www.sedo.energy.wa.gov.au/pages/publications.asp Re: Passive Solar Advice 5Dec 30, 2008 6:28 am Yeah I like those articles a lot. Thanks.
Although they are specific to WA and I'm in NSW (and the equivalant NSW govt site isn't as good) - should it make any difference? We are on a similar latitude. Re: Passive Solar Advice 6Dec 30, 2008 10:32 am do-it-dog Yeah I like those articles a lot. Thanks. Although they are specific to WA and I'm in NSW (and the equivalant NSW govt site isn't as good) - should it make any difference? We are on a similar latitude. You can translate for the temperate/cool temperate climates. The sub-tropical areas need a different emphasis. If you understand the basic principles and whether your needs are mainly heating or cooling then you know which ideas to use. My 5 favourite sites are: http://www.yourhome.gov.au/technical/index.html http://www1.sedo.energy.wa.gov.au/pages ... _homes.asp http://www.sustainability.vic.gov.au/ww ... ystar.gov/ http://www1.eere.energy.gov/buildings/r ... build.html Note that these are all government based websites and free from commercial interests. The first three are Australian-based and the latter two are US-based. It is useful to verify the information with each other when doing your research. Other helpful sites include: http://www.heat.net.au/action-advice-page (ACT based government website) http://www.homeenergy.org/ (you usually need to purchase the articles but if you combine the terms 'Home Energy Magazine' with a topic of interest in a search engine, you can yield some interesting articles) http://www.ausdesign.com.au/index.html (a commercial website but contains good advice about archictectual conventions) Re: Passive Solar Advice 7Jan 03, 2009 1:56 pm do-it-dog Yeah I like those articles a lot. Thanks. Although they are specific to WA and I'm in NSW (and the equivalant NSW govt site isn't as good) - should it make any difference? We are on a similar latitude. A site from the NSW government: http://www.energysmart.com.au/les/Displ ... ?PageID=21 Re: Passive Solar Advice 8Jan 03, 2009 2:47 pm Quote: Possibly a bit too technical and complicated for the average layman though. Chris (one of them ) My father rode a camel, I drive a car, my son flies in a jetliner, his son will ride a camel.Saudi saying Re: Passive Solar Advice 9Jan 03, 2009 10:52 pm kristofw Quote: Possibly a bit too technical and complicated for the average layman though. Chris (one of them ) Or maybe a very good opinion of you! Re: Passive Solar Advice 10Jan 12, 2009 7:05 pm Dymo - do you reckon it's possible to insulate a house/cabin sufficiently using galv iron cladding and roof?
We'd really like to use straw bale but suspect we are in a potential flood zone - ie. we back on to a river. Re: Passive Solar Advice 11Jan 12, 2009 8:08 pm do-it-dog Dymo - do you reckon it's possible to insulate a house/cabin sufficiently using galv iron cladding and roof? We'd really like to use straw bale but suspect we are in a potential flood zone - ie. we back on to a river. I am not a builder but if you can have a comfortable building with strawbale and two faces of render than anything is possible. The theory is the same for houses as a commercial freezer. Make the construction air tight and have a thick layer of still air pockets sandwiched between the internal and external cladding. It is not uncommon for reverse BV constructions just to use metal cladding. Re: Passive Solar Advice 13Jan 13, 2009 9:49 am do-it-dog Thanks again dymo. Sorry for all the dumb questions. And should we use a radiant heat barrier in the roof and the walls? Radiant protection is really important during summer. The solar energy coming in is about 10x the convective losses going out. It does offer some insulation from the energy that is radiated outwards by the house structure and the objects within (and contributes a little to winter warmth) I would definitely under the roof (sun beats down all day) and especially western face (hot summer afternoon). I decided to cover our entire house in foil. One could argue that this reduces solar gain during winter. However, I should have enough north facing windows that gets the heat inside during winter, with enough shading to keep it out in summer. There is always a compromise. The ideal house should be airtight when it is cold and well-ventilated when it is hot. It needs to be invisible to solar radiation on a cold day (a glass house) but opaque on a hot one (a foil house) But don't forget bulk insulation. This is another discussion. Passive solar is about finding the optimal balance between the two. This is dictated by your particular location and climate. Re: Passive Solar Advice 14Jan 14, 2009 7:01 pm dymo - thanks for your great advice as always. I get more info from you experienced guys with first hand knowledge than any other resource. I guess that's what these forums are all about.
Think we'll go for a concertina double sided foil radient barrier - roof and walls - plus the highest rating batts. With that and taking advantage of all other passive solar principles, I think we'll be right. Re: Passive Solar Advice 15Jan 14, 2009 8:41 pm do-it-dog dymo - thanks for your great advice as always. I get more info from you experienced guys with first hand knowledge than any other resource. I guess that's what these forums are all about. Think we'll go for a concertina double sided foil radient barrier - roof and walls - plus the highest rating batts. With that and taking advantage of all other passive solar principles, I think we'll be right. If you are seriously considering RBV then the owner-builder-architect who used it reckons that his air gap/batt.air gap construction provides more insulation then just the batt alone. Moreover, if you use metal cladding you gain an additional advantage because you don't need to ventilate the cavity (which creates air currents and loss of insulation). Re: Passive Solar Advice 16Jun 23, 2009 6:50 pm OK - I'm finally ready to build. Wondering if you have any ideas what I should specilfy for the concertina radiant foil and batts (my builder not sure what I'm talking about). Anyone know any specific brands or suppliers I might research? Re: Passive Solar Advice 17Jun 24, 2009 12:04 am do-it-dog OK - I'm finally ready to build. Wondering if you have any ideas what I should specilfy for the concertina radiant foil and batts (my builder not sure what I'm talking about). Anyone know any specific brands or suppliers I might research? I can't see why you would use concertina batts in a new house construction. There is no advantage over a flat sheet. Concertinas would seems to only useful if you needed to squeeze it down a cavity when retrofitting to an existing house. There are pros and cons for different types of bulk insulation. Poly/Glass/Rockwool or loose fill all are compressible and can lose effect over time. Foam is less sucesptible to this but chasing services through it is problematic. There are other occ. health and handling issues with fibreglass or Rock wool. The type is usually less important than ensuring you have adequate amounts. As far as foil goes, the expense rise with the durability of the laminated backing. They all have the same thermal properties. Re: Passive Solar Advice 18Jun 26, 2009 7:32 pm Thanks again dymo By 'flat sheet' do you mean sarking - or is there another product I don't know about? You mentioned before that an air gap is important between the foil and the batts? Since I'm cladding walls and roof with galv iron and we have hot summers and sub zero winters I want to get this right. Re: Passive Solar Advice 19Jun 26, 2009 11:14 pm do-it-dog By 'flat sheet' do you mean sarking - or is there another product I don't know about? You mentioned before that an air gap is important between the foil and the batts? I mean that some foil products come as discrete sections such as concertina or foil covered board. They provide radiant protection not moisture control. Rolls of foil or wrap can be used as sarking. The air gap allows the foil to work properly. The shiny side should face a 25 mm gap otherwise anything it touches will draw the heat away by conduction. e.g. fill a stainless steel teapot with hot water and put your away near it (no discernible heat). Touch it and you will see the difference. Re: Passive Solar Advice 20Jun 26, 2009 11:20 pm Good to hear the knowlege is out there... Now to start implementing Where you are coming from is where you are going to... 0 4987 Versaloc is a mortarless besser block system that still needs a properly engineered footing. If you just do a 400x200 footing it will fail in time. At 17m long you need it… 1 18249 I looked into it a few years ago and my conclusion was to just build a carport that will support panels and get a system installed separately. The company I looked at had… 1 6484 |