[Greenbuilding] A solar air heater with a Scandinavian breathing wall deep mesh

[nick pine]

Deep Mesh Solar Air Heating Collector -- Test 1

      Nick Pine proposes a solar home heating concept using solar heating system that is aimed at producing a very high solar fraction with relatively inexpensive solar air heating collectors. In order to accomplish the high solar fraction, the system must include several days worth of heat storage for extended cloudy periods -- a large storage capacity.

      The physical size of this large heat storage depends on the maximum temperature that the storage can be raised to -- higher temperatures store more heat in less space. But, producing higher temperatures normally means that the solar air heating collectors would operate less efficiently as the losses out the collector glazing go up with collector temperature -- thus the desire for high storage temperatures can result in an undesirable increase in collector area.

      There is a potential collector design that may produce the desirable higher collector temperatures at good efficiency. This design uses several layers of mesh for the absorber. The advantages are said to be: 1) the pressure drop caused by the mesh spreads the airflow evenly over the full surface of the absorber, and 2) the first layer of mesh acts as a radiation shield to reduce the radiation from the hotter inner layers toward the glazing. The first layer of mesh runs relatively cool in part because in this heating scheme, the air introduced into the collector is relatively cool (70F) room air -- this cooler first layer of mesh thus reduces losses out the glazing.

      So, in an ideal design, 70 F room temperature air is introduced between the glazing and the first (south most) layer of mesh. This coolish air spreads evenly over the full mesh surface because of the mesh pressure drop. Even though the airflow rate is low (to achieve higher temperatures), the first layer of mesh runs at a low temperature because of the relatively cool 70F air, and the ability of the mesh absorbers to provide very even airflow over the full surface. As the air progresses through the layers of mesh, it heats up, and since flow rate is low, the residence time is long and the air heats up to high temperatures (say 140+F). This hot air is then passed through an air to water heat exchanger and the hot water produced goes to heating the heat storage. By using the hottest air to heat the storage, the max storage temperature can be higher and it can store more heat. The still warm air leaves the heat exchanger and is blown into the house for immediate space heating. 

      A key element in making this scheme work is the low flow, deep mesh collector that operates efficiently while producing high temperatures. This test is a starting point in trying to see if this can be accomplished in a collector that is straight forward and inexpensive to build. My standard air heating collector which has just 3 layers of aluminum screen mesh is the starting point. The idea is to see how well it does in achieving the high temperatures AND high efficiency, and to identify changes that might make it do better, and possibly test those.

      On this page: 

      - Collector Description 

      - Test Setup 

      - Results (temperatures, flow rates, heat out, efficiency, glazing temperature) 

      - Where to go from here? 

      - More detail in some areas 

      - A glazing temperature puzzle 

      First comments from Nick on this test...

     

http://www.builditsolar.com/Experimental/DeepMeshCol/120116Test.htm
Nick
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