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From your experience, which heater designs works the best?

posted Jul 25, 2014, 3:53 PM by Greenhill EnviroTechnologies Inc.   [ updated Jul 25, 2014, 4:08 PM ]
There are so many different designs out there! We have tried most of them ourselves. 

We found the pop-can designs labor intensive and the connections between the cans difficult to seal completely. They involved lots of silicon, glues and paints, which we found off-gassed a lot, even though they were rated for high-heat. We then tried aluminum baking pans, turkey baking pans and pie tins (inexpensive and easy to assemble) in open designs, meaning the air could go behind and in front of the tins (painted with high-heat black BBQ paint). They smelled until the paint cured, for a month or so. These designs were hotter and required little to no glues (we stapled the tins in place), but still needed some paint.

We have seen designs of snaking coiled drier-vent tubing, but it still requires paint and complicated manifolds. 

Building any manifolds for down-spouts or tubes or pop-can designs can lead to trouble with air-flow impedance. It is very important for good air-flow throughout the heater, and this is very difficult to achieve evenly and without a laboring fan, with any of these designs involving tubes. Often heat is lost to the outside because of poor air-flow distribution.

Mesh screen and flat panel designs are good for simplicity of construction. Aluminum is always better to use than steel because it has higher thermo-conductivity properties, meaning it transfers the heat to the passing air more quickly than steel.

Flat panels, with air flow in front and behind are better than flat-panel designs where there is just air-flow behind them. This is because of the greater surface area: the more surface area for the air to pass by, the more heat that can be transferred to the air. But again, these still involve paint and curing times, with off-gassing.

The insect/mesh aluminum screens designs are by far the best producers of heat: the air has so much more surface area to go around the woven wires, and thus more heat is transferred more quickly. The Okapi Systems work very well to accommodate any heat-to-air transfer rate, so they work well with any type of design, but we have seen the best heat harvest results from screen designs. However, all standard brands of aluminum insect screens will off-gas for a few weeks to months, just like most paints, even the high-heat kind of paints. This can be unpleasant or sickening for some people. 

We are making strides with a company, after almost a year of research, in developing a black coated aluminum mesh screen that is designed for these high heat conditions. 
Stay tuned: 
We will soon be offering this specialized solar heater aluminum mesh screen for sale on our website soon!