It is important that technicians understand what happens inside an evaporator and how different evaporators affect different conditions. Following is a sample of the evaporator type and proper operating conditions a technician could expect in a medium-temperature walk-in refrigerator. A standard walk-in refrigerator designed for a 35°F box temperature would use a fan-coil unit designed [...]
The speed of air moving across an evaporator or the rate of liquid flow through tubing can change the rate of heat exchange. Readers familiar with AC are well aware of the effects air volume has on the system. In a standard AC system the evaporator absorbs about 12,000 Btu with approximately 400 cubic feet per [...]
Liquid is the most efficient heat exchange “ medium.” Because of its density, liquid provides better heat transfer than vapor. For example, heat the end of a 7∕8-inch piece of copper pipe until it is cherry red. What will cool it faster, blowing 70°F air over it or pouring 70°F water over it? The water, [...]
Hot pull-down refers to start-up of a new system, a freezer after defrost, or when there is warm product in the box. This means there is a tremendous load on the system initially, and it will not have proper temperatures and pressures until it is near its intended design conditions or normal operating conditions. However, the [...]
Refrigerant boils inside the evaporator, absorbing latent heat. The temperature at which the refrigerant boils is referred to in several different terms: • Evaporator temperature • Suction temperature • Saturation temperature • Saturated suction temperature (SST) Although these terms sound different, they all essentially mean the same thing. As the temperature of the air over [...]