Insulating window glass essentially consists of two panes of glass fused
together at their edges. Before being joined, the individual glass panes must be
thoroughly washed and rinsed - they must be spotless. Once washed and rinsed,
the glass is immediately heated to reduce any potential thermal shock, joined
through a special electrical process, and annealed for strength. Finally, air is
evacuated from the welded unit, and an inert gas is pumped in its place.
A heat recovery system, using a closed-loop circulating water system, cools the plant's large air compressors. The warm water (up to about 115°F) is piped to the heat pump's evaporator, where the waste heat is removed, cooling the water to about 85°F and returning it to the air compressors for reuse. A second process hot water loop feeds the plant's needs and delivers return water to the heat pump condenser at about 120°F, where heat is added and the temperature is increased. This 140°F hot water returns to the plant.
The first priority use of the heated water is to provide the demineralized water needed for rinsing the glass panes before their edges are joined (or fused) together. The water is demineralized to eliminate any spots that might otherwise occur. The hot water from the heat pump condenser goes through a heat exchanger in the demineralized water loop to provide the 120°F hot rinse water.
Since excess heat is still available, the heated water then proceeds to the plant's hot water system, where it preheats city water used for both domestic purposes and for the soft water system connected to the process glass washer. At the washer, the water can be further heated by electric or steam heaters to the 160°F condition needed for detergent action. By preheating in this manner, much less heat is needed from the immersion heaters. In the winter, any excess heat is sent to a fan-coil unit to provide space heat for the maintenance area. In the summer, the fan-coil unit is bypassed. For these conditions, the heat pump operates at a 4.3 COP.
