Heat your home for the cost of running a light bulb
Traditionally roofs were designed to protect homes from nature - most importantly preventing water damage to the property and it's contents, and to keep wildlife at bay. Until now roofs have not been considered as a potential source of cheap heat, the Attic Heat Harvester System changes that.
Attics with sunny roofs can contain many free kilo-watt hours of heat. On sunny and even cloudy days infrared electromagnetic solar energy is absorbed by attic roofs heating attic air. When room temperatures are too low this free heat can now be transferred to your home extremely efficiently.
Attic heat harvesting systems are incredibly efficient, inexpensive to buy, relatively easy to install (especially in a new build), cheap to operate, simple to maintain, and very reliable - no other heating system can compete in any of these criteria.
Attic heat harvesting efficiency, and energy transfer is directly proportional to: a) the temperature difference between the the attic apex air and the area receiving the solar heated attic air, and b) the air flow rate. The greater the temperature difference the greater the power harvested, the more efficient the system is
Solar heated attics have hot and cool sides, the temperature difference between them can exceed 10°C, heat escaping from the cool side reduces the attic temperature and the system efficiency.
This heat loss can be considerably reduced by adding reflective insulation on non sunny attic sides. The foil reflects radiated energy, the insulation reduces conducted energy, and the sealed surface reduces convection air flow beneath the cool roof, all three keep attics warmer.
During early tests carried out on the two prototype attic heat harvester systems.
Attic roof with no reflective insulation
Attic roof with reflective insulation
Reflective insulation has now been added to both the Balerno and Ohio homes on the internal north roof slope. Care was taken to ensure that ventilating air is able to flow between the insulation and the attic roof by leaving gaps in the insulation at both the bottom and top of the slope.
Reflective insulation will increase attic heat harvesting system efficiency and both day time and night time attic temperatures. Increasing night time attic temperatures reduces house cooling and also reduces the delay before the attic heat harvesting system begins operating.
Attic heat harvester efficiency and performance data will continue to be collected in the coming months and this web site will be updated with the results.
Hot attic air can increase home cooling costs. For locations where attic temperatures can get excessive the Attic Heat Harvester system can be supplied with a facility to control a separate 'low power' attic cooling fan. If the attic temperature exceeds a user pre-settable maximum value the system Controller turns on the attic cooling fan. The attic cooling fan can be fitted to an soffit or eave, a gable end, or in the roof. If the attic cooling fan is fitted to a soffit the fan should be mounted to draw in cool air pushing hot air out of roof vents. If the attic cooling fan is fitted to a gable end or in the roof the fan should such out hot air drawing in cool air from soffit vents The small cost of operating the attic cooling fan will be more than offset by savings in home cooling costs. The attic and the home will also benefit from the additional ventilation.
Attic roof with no foil wrapped insulation
Attic roof with foil wrapped insulation
When attics are to be used as a solar heat source roof design will evolve to optimize the heat available increasing both the heat available and attic heat harvester efficiency. Most roofs are constructed of waterproof material supported by wood, this delays attic air warm up by 2 to 3 hours, but retains heat for later use. Low sections of the roof that receive morning sun will be made from highly heat conductive material, that will reduce the attic air warm up time and increase the heat transmitted through the roof.