Solar Heating & Cooling An Above Sheathing Ventilation (ASV) System provides year round usage with winter heating and summer cooling.
AVS utilizes the most efficient and proven solar technology, the SolarWall® collector, in an unique configuration to also take advantage of nocturnal radiation cooling, a previously ignored cooling phenomena. This unique design has additional benefits as it ventilates and shades the roof covering the main roof in darkness all day long and preventing unwanted summer heat from reaching and conducting through the roof. With most roofs responsible for half of the cooling load, an AVS system in many cases can reduce the cooling equipment size in half and the associated energy costs.
Roof shading Roofs can reach 160°F (71°C) in the summer sun and that heat will conduct through the roof at the rate of 160°F (roof temp) – 75°F (indoor temp) x U factor (heat transfer rate which is inverse of R insulation value) = Btu/h.ft2 of roof area. Covering the roof with AVS panels shades the roof and lowers the roof temperature to within a few degrees of ambient which means the heat transfer rate through the roof and corresponding daytime cooling demand is now reduced by as much as 70°F.
Above Sheathing Ventilation (ASV) Oak Ridge National Laboratory (ORNL) states “we serendipitously discovered the second major advance in roofs for our century: We found that elevating the roof cover from the roof deck to induce above-sheathing ventilation is as important as increasing solar reflectance and may be the stronger player in reducing heat gain into the attic. The two combined can reduce heat gain through the roof by 50% compared to nailed asphalt shingle roofs.”
AVS ventilated roofs prevent unwanted solar gain reaching the building and the solar heat dries any condensation or moisture that may have accumulated on the roof. Take ASV one step further by not only ventilating the roof but doing it in a manner that either collects or expels the heat depending on the season and time of day. It incorporates a ventilated roof design which has precision micro perforations to collect or discharge the heat or cold boundary layer. A recent field monitored project in Europe is reporting as much as a 50% overall cooling savings on telecom buildings using existing fans and economizers.
Ventilated steep slope roofs rely on thermal stack effect to remove heat. Low slope roofs with long roof runs have insufficient height to remove heat whereas the AVS system is vented over the entire surface which eliminates the problem associated with low slope roofs.
Free Night Cooling Nocturnal radiation cools roofs as much as 18°F (10°C) below ambient on clear nights and the chilled air adjacent to the roof has the ability to reduce or even displace conventional air conditioning from sunset to sunrise. As warm night air touches the cooler surface of the collector, it transfers its heat to that surface and the cooled air is then drawn in through the perforated surface.