Heat Exchanger Basics
The flat plate heat exchanger concept takes advantage of the direct proportional contribution from surface area in heat exchange principles. The general equation for overall heat exchange in any context is Q = U * A * delta T. Q is amount of heat, U is the heat transfer coefficient, A is the surface area of the realm of exchange and delta T is the temperature difference between the two flowing materials. In layman’s terms, the heat transfer coefficient will be higher for copper plate than urethane insulation; greater surface area provides greater heat transfer opportunity; and a higher temperature difference provides greater driving force for the movement of heat.
Home Air Exchange Unit
It is possible to build a large air-exchange heat exchanger for a residential home. It can be mounted along a side wall in a basement, or horizontally suspended right under the floor joists.
Purchase nine 4-by-4-foot galvanized steel sheets from a metals supplier. You will also require two 4-by-8-foot sheets of 1-inch-thick urethane foam with foil on one side, several tubes of silicone caulking, a large roll of duct tape and two 6-inch duct fans.
Cut one of the pieces of insulation into 27 2-inch-wide, 4-foot-long strips. Take three pieces, lay a single bead of caulking along each piece, and cement one along the left edge of one of the pieces of galvanized sheet. Likewise, cement a piece in the middle and another on the right edge. Do this to all nine sheets. Then alternatively rotate them and cement together so that one opening level is north-south and the next is east-west. Cement a 4-by-4-foot piece of insulation on both flat sides of the stack. Construct plenums for two of the sides with three 1-by-4-foot pieces of insulation, and 1-by-1-foot sections for end-caps. Make a hole in each plenum to fit the 8-inch ducting. Cement the edges with silicone, and bind all 90 degree corners with duct tape.
Installation and Use
Cut holes for the duct fans in a piece of plywood to insert in a basement window opening. Duct with soft ducting to each of the two plenums. One fan should blow out the window, and the other should blow in. Baffle the outside of the ducts using outward-facing elbows to prevent recirculation. The fans can be placed on a circuit with the home heater to only flow when the heater is on.