The heart of a refrigeration system is the compression equipment. Refrigeration compressors are very critical to proper operation of the system, and therefore require special attention to ensure that they are efficiently servicing the load.

Crude pressure switch and/or manual control are often the means used to determine which compressors run, and how much of their full capacity is utilized. While these methods may get the job done, they are almost always inefficient in terms of energy usage and equipment wear.

Although most screw compressor packages incorporate precision microprocessor control features, they are typically limited to control of just one compressor. Since they are not able to “see the big picture” of what other compressors and the entire plant are doing, they also tend to be operated inefficiently at the largest anticipated capacity requirement.

Techni-Systems, LLC control systems integrate extensive logic to coordinate individual compressor operation with other compressors and the rest of the refrigeration system. In other words, we “look at the big picture”!

Auto Suction Pressure Control

Every refrigeration system has specific requirements for suction pressure. However, these requirements may change significantly depending on the season, product, ambient temperature, etc. If the suction pressure is too high, the zone temperatures will not be maintained at the desired setpoints. If the suction pressure is lower than necessary, energy efficiency and compressor capacity are unnecessarily degraded. Auto suction pressure control optimizes the compressor operation by automatically determining the best suction pressure for existing conditions.

Capacity Control

Whatever the suction pressure setpoint, operating compressors will efficiently load or unload in a coordinated pattern as the pressure varies. Generally, the largest compressor loads first, followed by the next largest compressor, etc. Unloading follows the reverse order.

Screw compressors load or unload as determined by a Proportional, Integral, Derivative (PID) algorithm that considers a number of factors to calculate the rate that the capacity is changed. In order to minimize slide valve position “hunting”, the control system suspends capacity control adjustments when the pressure is within the user determined deadband setpoints.

Variable speed technology is very well suited for capacity control as well. The system uses intelligent control algorithms to operate the compressor at the speed required to match the refrigeration load, eliminating the need to continually adjust the slide valve. The slide valve can remain 100% loaded while the motor speed varies for maximum efficiency.

Flexible Compressor Sequencing

An important function of intelligent compressor control is to determine which compressors will be operated for a given refrigeration load. We provide the user with an easily configured matrix that allows complete flexibility in selecting the compressors that will operate at each sequence step. If a compressor is out of service or the facility load pattern changes, the sequence steps can be re-defined with a few clicks of the mouse.

The sequencer steps up when the suction pressure is above setpoint, and steps down when the system detects that the load on the operating compressors is small enough to be handled by the next lower sequence step. All sequencer parameters such as pressure deviation, tonnage differential, and time delays are user adjustable to enable customized tuning of the system.

Alarm Conditions

The system continuously monitors the compressors for a fail to start condition, or a slide valve fail to load condition. If either of these alarms occur, the operator is immediately notified in order to prevent out-of-spec conditions in the facility.

System Wide Approach

Look at the “big picture” and control your compressors as part of the overall system, not as individual pieces of equipment. Keep the heart of your system operating at maximum efficiency and reliability. You won't believe how simple it is to select capacity control and compressor sequence parameters to fit your plants changing control needs. Make sure that you have the capacity you need, when you need it, without wasting energy and without accumulating unnecessary run hours on compressors.

One of our compressor control screens from a freezer storage facility in Woodland, Washington. This particular plant has two engine rooms, one of which has four suction headers.

One of our engine room monitoring screens from a fruit storage facility in Hood River, Oregon. This facility has two independent engine rooms, both of which can be monitored from this screen.