Ceiling Panel Systems
A ceiling panel system is a forced-warm-air heating system in which the heated air is delivered through ducts to an enclosed space above a false ceiling. There are no air supply outlets in the ceiling, and the heated air is therefore blocked from direct penetration of the occupied spaces below. Because its downward path is blocked, the heated air spreads over the entire surface area of the false ceiling. The ceiling eventually absorbs the heat, and the cooler air is returned to the furnace for reheating and recirculation. The heat is transferred from the ceiling to the occupied spaces by radiation. A more appropriate name for this type of panel heating system might be “ceiling space panel system.” Other ceiling panel systems are described in Chapter 1 of Volume 3, “Radiant Heating.”
A ceiling panel system of this type does not differ from the standard forced-warm-air heating system except in the design of the heat-emitting unit. Instead of using compact (individual heat- emitting units) a ceiling panel system uses a portion of the structure itself. As a result, considerable experience is necessary for installing this type of heating system. It is recommended only for new construction, and never as a conversion from an existing heating system.
Crawl Space Plenum Systems
A crawl space plenum system uses the entire underfloor crawl space as a sealed plenum chamber to distribute warm or cool air. The use of the crawl space under the house as a plenum was first investigated and developed in the 1970s with funds provided by several wood technology organizations. This system is called the Plen Wood System.
In most conventionally shaped structures, air distribution is achieved without using ducts. In large, irregularly shaped structures, stub ducts are added to provide uniform air distribution. The conditioned air is supplied to the plenum by a forced-warm-air furnace, a downflow (or counterflow) furnace and cooling unit, or a heat pump with an air handler. No modifications are required to the HVAC heating and cooling unit.
The sealed underfloor crawl space in the Plen-Wood System is used as a plenum for the air supply in the winter and an air return during the summer (Figure 6-8). A damper in the HVAC unit is used to switch from one to the other. By using only the fan of the HVAC unit, comfortable temperatures can be maintained most of the year by circulating air from the plenum throughout the house.
Check your local building code before deciding on a Plen-Wood System. Although the Plen-Wood System is accepted by the major building codes, local building codes may place special restrictions on it. In many areas these local codes require the use of fully ducted heating supply runs. They will not permit the use of an open crawl space plenum. This system also requires the construction of a closed, tightly sealed crawl space.
Contact the American Plywood Association (P.O. Box 11700, Tacoma, WA 98411) for additional information about the Plenood System. See also the appropriate section in Chapter 7 of Volume 3, “Ducts and Duct Systems.”