As summer comes to an end and high energy bills have been paid in full, many manufacturers and processors are left wondering what they can do to increase energy efficiency and decrease costs. With rolling California blackouts, increasing gasoline costs and high energy bills, any words of wisdom seem to go a long way. Following is a short list of best practices for keeping your freezers energy efficient while also staying current on the latest technological advances.
1. Specify an Electric Expansion ValveOnly a few manufacturers offer refrigeration systems with an electronic expansion valve. One equipment manufacturer uses a valve with 1,600 steps that can efficiently maintain superheat from the pull-down cycle through the normal refrigeration mode. Conventional thermostatic expansion valves typically are less adjustable and efficient.
With a standard mechanical system, the head pressure must be maintained with a head pressure control valve or fan cycling because a thermostatic expansion valve requires about 100 lb across the valve to operate properly. Because the electric expansion valve does not require this high head pressure, the head pressure control can be eliminated, which allows for a lower head pressure and condensing temperature. A compressor operating at a lower condensing temperature yields higher capacity with less energy input.
2. Maintain Proper Defrost SchedulesFrost buildup reduces a refrigeration system's efficiency, so an efficient defrost system is a must. Some traditional refrigeration systems are preset to defrost about six to eight times during the day, regardless of the amount of frost buildup on the evaporator. However, frost accumulation is not always consistent; it is influenced by changeable conditions, such as ambient temperature, humidity and product load. Defrosting before a significant amount of frost accumulates is an energy-wasting process. Instead, defrosting should only take place when the coils need to be cleaned.
Demand defrost, which constantly checks for ice buildup on the evaporator to determine if defrosting is required, can be an efficient alternative to the conventional method and is a good way to minimize defrost time. Extensive laboratory tests indicate that many unnecessary defrosts can be eliminated with demand defrost technology. Electricity consumption is also dramatically reduced -- in some applications, up to a 26 percent energy savings is possible.
3. Consider Reverse Cycle DefrostAnother defrost option involves a reverse cycle valve added to the condensing unit and used with an electronic system that controls the entire refrigeration system.
The valve's primary function is to reverse the direction of refrigerant flow during defrost. When the master controller's demand defrost determines that a defrost is necessary, the reverse cycle valve is activated, and the high-temperature refrigerant flow is reversed. The refrigerant flows back through the evaporator coil, heating it along its entire length and eliminating frost buildup. When defrost heaters are used, sometimes only part of the coil is heated, leaving ice deposits that diminish the evaporator's performance.
For those freezers sized to use reverse cycle technology, the technology offers other benefits. It uses less energy than electric defrost heaters and can reduce defrost energy usage by 80 percent. It eliminates the need for defrost heaters, head pressure control valves, check valves and expansion valves at the condenser. Removing these components reduces the evaporator cost and the cost of installation and wiring. Defrost time also is lessened.