An Underfloor Plenum System for Heating and Cooling

The underfloor plenum concept has been used in various forms for heating since the days of ancient Rome. It is a feasible method of heating single-family homes as has been proven by several relatively recent tests by other scientists in the United States and current use by builders. To evaluate the feasibility of the underfloor plenum for both heating and cooling in single-family home construction, a test house with 1,850 square feet of living area was built in Gainesville, Florida in 1966. It was equipped with wood moisture probes and thermocouples in the floor system. The house was also equipped to monitor air temperatures and air distribution patterns in the plenum and in the rooms. A standard central air-conditioning system was installed. With the central air-conditioning system in operation, the moisture content of the wood in the floor and floor framing stabilized between approximately 6 and 14 percent with the highest moisture content recorded during the cooling cycle and the lowest moisture content recorded during the heating cycle. Under these very desirable moisture content conditions, no wood moisture problem occurred when the plenum was used to distribute both cool and warm air to the rooms in the house. Air pressure was found to be constant throughout the plenum space. Air speed decreased with distance away from the central air-conditioning unit. however, air distribution in the rooms was good for both cooling and heating. Temperatures in the rooms were easily regulated during both heating and cooling seasons. Temperature readings were taken at 6-, 30-, and 60-inch heights at several locations in all rooms. The maximum was recorded during the cooling cycle in the kitchen which was purposely set up as a difficult area to cool with its orientation to the south, large glass area and high ceiling. In the other rooms the average temperature differential was approximately 2-1/2?F. During the heating cycle the average temperature spread was about 1?F vertically. The temperatures were easily balanced in the rooms during all seasons of the year.

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