Editing 2009-009

From: Monica Kilpatrick <monicakilpatrick@hotmail.com> Date: 2009-02-01 (Sun) 16:42:18 AST Subject: flooring for passive solar home, roof pitch for solar panels I attended the passive solar home course in November 2007. I am building a house this spring and I had 2 queries. In regards to the information in the thermal mass in the booklet, could you tell me what ceramic,porcelain and slate flooring are similar to. Are they more similar to brick or stone? I assume the slate falls under the stone category, but I was not sure about porcelain and ceramic. 2.) Some literature recommends a 8/12 pitch roof for solar panels for hot water. My house is long and narrow , and is more suitable to a 4/12, or 5/12 pitch. Could you tell me the disadvantages to this. If the solar panels are adjusted to a more steep angle , does there tend to be disadvantages with regards to wind? Thankyou Monica Kilpatrick Proposed General Response (Jamie): Generally speaking the thermal mass of ceramic porcelain and slate will be similar to both brick and stone. The thermal mass you have in your design will depend greatly on the amount of these materials used and not just the type of material used. Like many design choices picking the best choice is a detailed question. Thermal mass is the product of the volume of the material and the material's density and specific heat. If you have multiple materials, such as ceramic tile over concrete, then you can calculate the solar mass of each material and add them together. Thermal Mass = Volume x Density x Specific Heat Volume = the calculated total volume of a particular material in cubic meters. Density = a material property, Density, in kilograms per cubic meter Specific Heat = a material property, Specific Heat, in Joules per kilogram) Searching the material properties can be difficult, but many tables are available on the internet or in refernce books at a library near you. Regarding roof slope and solar panels, Solar panels collect the most energy when they are pointed squarely at the sun. As the sun moves through the sky daily and rises and falls relative to the horizon yearly, they reap the maximum benefit when they are pointed at the sun. This can be accomplished with a mechanisim that controls their position. These mechanisims, called tracking mounts, are only practacble for solar photovoltaic panels in sunny climates. For a fixed solar collector, such as one for heating hot water, you will want to orient the panels as near to south as possible. The slope of the panel will depend on your latutude and the time of year you want the most benefit from your panels. For example, in Stewiacke Nova Scotia, at 45 degrees latitude, a 45 degree panel slope (12/12 pitch) will have peak output at the spring and fall equinox. This would make sense for hot water heating. If you are using the panels to provide home heating, you may want to tilt the panels higher to collect the most energy in the winter heating season. If you are heating water for the hot tub on the back deck, you may want them lower to hit the summer hot tub season. If your roof does not match the slope you want, you may use a frame to prop the panels up. This fram will have to be securely mounted to the roof and will have to comply with the panel manufacturers instructions. If you want a clean roof line, you will have to add an extra panels to make up for the lower solar gain from the installed panels or consider mounting the panels on a separate ground level frame or out building.

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