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Attic heat harvester system
An enormous amount of useable solar energy is wasted in the world every day, this energy is absorbed by and temporarily stored
in attics. On sunny days attic temperatures can exceed outdoor temperatures by 20°C (approx. 40°F). A new
Attic Heat Harvesting System has been invented which can move this free solar energy into
homes and measure and display the solar energy collected and the system efficiency.
Assuming that the efficiency of electric heat is 1, the Attic Heat Harvesting System can achieve an average efficiency of greater than 20
(2,000%). At this extraordinary high efficiency when you pay for 1 energy unit you get more than 19 free, few other home heating systems can
achieve even a tenth of this!
The temperature in an unheated home will typically be close to the average daily outdoor temperature. On days where there is some sun, attic
temperatures can be 10's of degrees higher. Solar heated attic air can optimally be harvested to heat your home when average daily outdoor
temperatures are below but generally within 15°C (30°F) of indoor temperatures.
The 'Attic Heat Harvesting System' uses solar energy in the form of solar heated attic air which can provide an extremely
efficient supplementary heating system reducing the use of far more costly conventional heating systems.
Late October Toledo Ohio temperatures
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The chart shows kitchen (the room being heated), attic and outside temperatures from October 22 to 27 2011 monitored using a
La Crosse data logger.
The prototype Attic Heat Harvester System controller was set to turn on the fan if the attic temperature exceeded the kitchen temperature by more than 3.5°F.
The solar energy collected increased the kitchen temperature.
On October 27th there was little sun, local electric radiant heat was used to heat the room.
The heating efficiency, as determined by the relative cost of one unit of heat, of a prototype Attic Heat Harvester System achieved during the period
was 18.3. Production Attic Heat Harvester systems will have an improved duct system which achieves an even higher relative heating efficiency level.
The relative heating efficiency of a number of conventional heating systems
is shown in the chart below. The chart is based on US 2009 average costs of heating sources.
US home heating system relative efficiency 2009
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Attic Heat Harvester System
The attic heat harvesting system comprises of:
- An electric fan mounted close to the roof apex on the sunny side of the attic
- A duct system that runs from the fan to the room being heated
- An automated damper valve which, when open, allows solar heated attic air to be blown into rooms below, and
when closed, stops warmer air from escaping into the cooler attic
- A custom differential temperature controller system. The system can also be used to cool attics that get too hot,
this requires one additional exhaust damper valve and ducting. When the attic temperature exceeds a preset maximum
the differential temperature controller turns on the attic fan and opens the exhaust damper, hot attic air is exhausted
at the attic eaves
At the heart of the Attic Heat Harvesting System is a microprocessor based differential temperature controller fitted in a
small enclosure. The differential temperature controller continually monitors both attic and room temperatures. The controller
only turns on the fan when the room temperature is below a preset maximum, and the attic temperature exceeds the room temperature
by a preset minimum.
During normal operation the differential temperature controller continually monitors and records system performance parameters, namely:
- Current room and attic temperatures
- Current power and efficiency
- Total power and efficiency
- Fan running hours and average 'attic - room' temperature
- Maximum and minimum attic temperatures
Push buttons are provided on the differential temperature controller to preset system parameters and to display system performance figures.
More details of the Attic Heat Harvesting System, it's features,
it's performance, where it and the other system components can be obtained from here.