SINGLE-PACKAGE ROOFTOP UNITS
Single rooftop units can be used for both heating and cooling for industrial and commercial installations. Figure 5.12 shows such a unit. It can provide up to 1.5 million Btu if water heat is used. It can also include optional equipment to supply heat, up to 546,000 Btu, using electricity. Such units can use oil, gas, or propane for heating fuels.
These units require large amounts of energy to operate. It is possible to conserve energy by using more sensitive controls.
Highly sensitive controls monitor supply air. They send signals to the control module. It, in turn, cycles the mechanical equipment to match the output to the load condition.
An optional device for conserving energy is available. It has a “no load” band thermostat that has a built- in differential of 6 degrees F (3.3 degrees C). This gives the system the ability to “coast” between the normal control points without consuming any primary energy within the recommended comfort-setting range.
Another feature that is prevalent is a refrigerant heat-reclaim coil. It can reduce supermarket heating costs significantly. A reheat coil can be factory-installed downstream from the evaporator coil. It will use the con- denser heat to control humidity and prevent overcooling. A unit of this size is designed for a large store or supermarket. Figure 5.13 shows how the rooftop model is mounted for efficient distribution of the cold air. Since cold air is heavy, it will settle quickly to floor level. Hot air rises and stays near the ceiling in a room. Thus it is possible for this warmer air to increase the temperature of the cold air from the conditioner be- fore it comes into contact with the room’s occupants.
