Empire Controls, LLC has helped numerous companies achieve drastic reductions in energy consumption, allowing them to be more competitive and profitable. The cost of implementing the energy efficiency measures is often subsidized by the electrical utility. The savings have been repeatedly verified and documented.
Variable Speed Control
Equipment is sized for peak capacity requirements, but it’s often oversized for the existing load. In that situation, fans, pumps, compressors, and other rotating equipment waste electrical energy. Dramatic savings can result from reducing motor speed to match the equipment’s capacity to the load. This is most often accomplished by installing a variable frequency drive (VFD) — an electrical device designed to operate standard AC induction motors over a 0–100% speed range.
In refrigeration applications, evaporator fans are often continuously operated at full speed even when the heat load is minimal. In this situation the fans produce approximately 70% of the refrigeration (heat) load. In addition to the negative impact on energy efficiency, product quality can also be adversely affected. Research has shown that excess evaporator capacity tends to result in less stable temperature control, which is detrimental to highly perishable products. The high air velocity that results from full-speed fan operation can seriously affect the rate of moisture loss, or transpiration, from the product — equating to as much as 2–5% weight loss and lower quality due to shrivel.
Variable-speed evaporator fan control typically operates the fans over a range of 40–100% of full speed. Because the power required to drive a fan varies as the cube of the speed, energy consumption drops off dramatically as the speed is reduced. The reduction in fan motor energy also results in less heat being added to the refrigerated space, reducing the load on compressors and condensers as well.
Variable-speed technology is well suited for refrigeration compressor and condenser fan applications too. The system uses intelligent control algorithms to operate these critical components at the speed required to match the refrigeration load — eliminating the need to continually start and stop motors to control capacity. The compressor slide valve can remain 100% loaded while the motor speed varies for maximum efficiency.
Some pump applications can also benefit from variable-speed control. In low static-head pressure installations, the pump speed can be varied with the flow requirement to achieve energy savings similar to fan applications.
If your plant isn’t benefiting from variable-speed control, you could probably earn some “hero buttons” by realizing significant energy savings through well-planned implementation of VFD technology.
Duty Cycling
Duty cycling is a low-cost method of reducing equipment capacity. Some industrial applications permit on/off cycling of equipment to achieve energy savings and match capacity to load. In refrigerated storage facilities, the control system can cycle zones off at regular intervals. An override feature restarts refrigeration if the zone temperature rises significantly. Adjustable on/off schedules are easily entered from a graphic screen. A typical schedule operates the evaporators only a small fraction of the time.
Does your facility have equipment that can be duty-cycled? How much could your efficiency be increased using this simple technique?
Demand Refrigeration
Demand refrigeration saves large amounts of energy in facilities that permit turning off the refrigeration system for several hours at a time. Different from duty cycling — where individual zones are shut off on scheduled intervals — demand refrigeration shuts down the entire facility’s refrigeration system when all zone temperatures are reasonably close to setpoint. The system stays off until any single zone requires refrigeration again, indicated by a rise in temperature. At that point, refrigeration resumes for the entire system until all zones are back to the desired temperatures. This cycle continuously repeats.
Intelligent Engine Room Control
You won’t believe how simple it is to select capacity control and compressor sequence parameters that fit your plant’s changing control needs. You decide which compressors will run under different load requirements, and define parameters for auto-suction-pressure reset control. Make sure that you have the capacity you need, when you need it, without wasting energy and without accumulating unnecessary run hours on compressors.
If you don’t use a wet-bulb approach to determine optimum discharge pressure, you are undoubtedly working your compressors harder than necessary. Efficient condenser control is as simple as tracking ambient wet-bulb temperature (the ideal limit of evaporative cooling) and continuously resetting the discharge pressure setpoint to utilize the currently available condensing capacity. Add variable-speed control of condenser fans and really achieve optimum energy efficiency.
Load Shedding
Load shedding is another energy feature offered by Empire Control Systems. Selected loads can be cycled off at a preset time of day and back on at a later time to reduce energy consumption and time-of-day demand charges. One set of times may be used for weekdays and another for weekends. The same scheme can be used to lower fan speeds — or whatever makes sense for your plant’s operation.
Demand Limiting
To reduce demand charges, the rate of kilowatt usage can be monitored by the system, with control algorithms implemented to keep the demand from exceeding a maximum limit. As the electrical demand approaches the limit, certain equipment can be inhibited from starting or further loading. If the demand rises above the limit, equipment will begin to be unloaded or cycled off. When the facility load returns to a normal level, the equipment will return to normal operation.
Intelligent Defrost Control
Refrigeration systems typically defrost evaporator coils at preset intervals. This often results in unnecessary defrosting, which actually adds heat to the refrigerated space and reduces the time available for product cooling. In some cases, defrost cycles have the effect of reducing the moisture content of highly perishable products. Automated on-demand defrost control can not only save energy but also improve product quality and weight.
On-demand defrost control is designed to hold off defrost cycles until they’re necessary, as indicated by the performance of the evaporator coil. A demand defrost condition is detected when the zone temperature is above setpoint and the temperature drop of the air passing through the coil is less than normal. If these conditions exist for a preset delay period, a defrost cycle is initiated.
Improving energy efficiency is our specialty — and we have a lot of tricks. Duty cycling, demand refrigeration, intelligent engine room control, load shedding, and variable-speed control will greatly reduce your energy costs. Many facilities have been using these techniques for years. How about your plant?