Solar Heat Collectors |
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This page provides information regarding the Collector Array in use on my Solar Heated home. The collector array consists of 6 double units, or a total of 12 individual collectors. They cover a total of 384 square feet of active surface area, and are supplemented by a reflector area with an additional 200 square feet located on the access ledge at the base of the array.
Collectors
The collector array is located on the south side of the house and the collectors are set at a 65 degree pitch. Calculations set this as the optimum angle at this latitude with the reflector surface, average mean temperature, and hours of sunlight factored in. The collectors are built directly onto the roof; that is they are a part of the house rather than added on later. Duct work from each collector connects to a feeder and return trunk in the attic through the roof. A dual blower assembly in the attic provides for a varied recovery rate. This is set by the amount of solar radiation being received and the storage unit temperature at a given time. The digital control unit will determine the optimum speed to run the blowers using the temperatures measured.
The collectors themselves were home built. The figure below shows the basic components of a typical collector. The air flow is from bottom to top and moves both above and below the absorber plate. An air diverter is placed in the lower air intake. This provides for a uniform air flow across the entire width of the collector.
Collector Detail
The detail drawing on the right of the figure above shows a cross section of the collector. The backing board shown is actually the roof sheeting and provides a solid surface to mount the collector components. Each collector box is fitted with a 1 inch thick sheet of aluminum faced insulating board pressed tightly into the box. This both seals the back of the collector and provides a reflective surface to confine the heat recovered to inside the collector.
The absorber plate itself is consists of 8 aluminum sheets which were obtained from the local newspaper where they were used in the printing operation. They were bent to the angles as shown and painted flat black with a high temperature paint. The blue box in the drawing illustrates how the angles react to solar radiation to reflect incoming energy from one to the other. This technique also increases the absorber plate surface area to maximize heat transfer to the air as it is blown across the plate.
The glazing panels used on this system are fiberglass re-inforced plastic sheets. The design life expectancy of the panels is 15 - 20 years. Some deterioration has been noted to date, however it has not seriously impacted the system performance. It appears the panels will meet the design specification. The panels are sealed to the face of the collectors and held in place by aluminum angle which is bolted to the collector box. In 15+ years, only one collector has experienced any weather related damage; that due to high winds estimated in excess of 80 mph.
One additional feature located near the collectors is the Heat Dump. This is used in summer to prevent overheating of the collectors when the summer sun is shining. A vent located in the main collector output duct allows the air to be exhausted through the roof. An intake is located in the attic near the collector blower. When the Heat Dump is active, air is taken from the attic, blown through the collectors, and vented to the outside. This serves two purposes. First, the air keeps the collectors from overheating. Second, since air is taken from the attic, it serves as a power vent by removing warm attic air and drawing in cool outside air. This lowers the demand on the air conditioner by lessening the heat radiating through the ceiling into the rooms below.
