Many institutional buildings have large industrial dryers with air intake from a conditioned space. These dryers consume great volumes of air, often the equivalent of many room air changes an hour. As such, during summertime operation in a conditioned space, the dryer draws in cooled air, heats it up to dry the linens, then immediately exhausts the air to the outside. Energy is wasted in two ways:
1. Conditioned air is exhausted and not recirculated, and
2. Cool air is drawn into the dryer instead of the much warmer (and perhaps dryer) outside air that is available in unlimited quantities.
Most large dryers have duct connections that can be connected to a short run of duct to draw outside air directly to the clothes dryer. An in-line filter prevents debris or contaminants from being introduced to the airstream. This is an inexpensive project that can realize considerable savings, especially for dryers with electric heating elements.
Arrangements can even be made to use the waste heat from commercial dryers. The warm air can be used to supplement heating to an adjacent space such as a gymnasium, lobby, or storeroom. The zone must be noncritical, however, since the dryers are not in constant use. These spaces must also have heating provided by another source that is only augmented by the discharge heat from the clothes dryers. Also, the supply air must be well filtered of lint.
The hot-air discharge can also be used in a waste-heat recovery mechanism. It can be ducted across a finned heat exchanger with water flowing through the coils to preheat the water before it enters the hot- water heater serving the laundry. The energy spent drying the clothes is recycled before it is finally discharged to the atmosphere.