High Relative Humidity (90-95%) is important in most applications dealing with perishables since %RH of cold storage rooms has a significant effect on the shelf life of the product and with the income derived from those products that are normally sold by weight.

Water vapor present in the air inside cold storages is normally condensed into liquid water by the evaporators during the cooling cycle. The quantity of water condensed by the evaporators would normally be evaporated from the stored products thus dehydrating the products and consequently reducing its shelf life and sales value. Humidifying Systems “make-up” for the water removed by the evaporators by supplying the water to be condensed thus reducing the weight loss by dehydration of the stored products.

Different Methods of humidity control

There are several methods of introducing “humidity” into cold storage rooms. Some the most common methods are as follows:

1. Various Methods of spinning water into very fine threads (Ligamentation) that eventually break into very small water particles which would then evaporate and increase the room %RH. These methods are recommended for rooms with temperatures 50ºF and above. At temperatures below 50ºF these minute water particles would not consistently evaporate and will float until they settle on a surface where they coalesce into water and wet the surface.

2. Atomizing Heads that work with High Pressure Water, produce minute water particles that will have success in evaporating at temperatures higher than 45ºF. However, this size particle will not evaporate consistently at temperatures below 45ºF making this system inadequate below this temperature range since it will have the wet surface effect described before.

3. Atomizing Heads that work simultaneously with High Pressure Water and High Pressure Air will produce water particles small enough to successfully evaporate at temperatures between 36ºF and45ºF thus providing levels between 90-95% RH typically recommended for the storage of perishables. This type of Atomizing Head equipped with Ultra Sonic Vibration is capable of producing particles so small that will successfully evaporate at temperatures below 36ºF.

We perform calculations to determine the quantity of water that is condensed by the evaporators in order to determine how much water is necessary to replenish the water removed. We then select the proper “Humidifying” equipment with which to accomplish the replenishing task.

In the design phase we carefully select the refrigeration equipment in order todiminish the amount of water removed by the equipment. Our %RH Controllers are properly selected to operate consistently and accurately at the high levels of %RH required by the perishables industry.

Our Data Acquisition, Control, Alarm, Diagnostics and Communications System is currently the most powerful, and yet flexible, instrument available to manage and control every aspect of refrigerated or other industrial processes.

Data Acquisition Systems– Physical parameters such as Temperature, Relative Humidity, Pressure, Flow, pH, etc. can be easily measured and monitored. An important by-product of Data Acquisition is the fact that every parameter that is measured, automatically generates a Real Time Graph that can be viewed in the PC Monitor, Printed to hard copy, E-mailed or saved to a file for future reference.

Control Systems– Every parameter that is measured as part of a process can be accurately controlled (Refrigeration Equipment turned ON & OFF to control Temperature, Atomizing Systems turned ON & OFF to control Relative Humidity). PID Control is also easily achieved. The System is also an extremely accurate Timing Device and can be used to control processes such as Pre-Cooling and Defrost Time without loosing synchronization.

Alarm Systems– The alarm features of the system are quite extensive and may be a simple local Buzzer to alert high temperature inside a cold storage room or may be sophisticated enough to Dial Out one or several beeper signals to inform the responsible party of pending problems.

Diagnostics Systems– In Refrigeration Systems, the vital system safeties and operating parameters (Oil Pressure Switch, Head Pressure Switch, Compressor Current, Under Voltage, Over Voltage, etc.) are routinely monitored. When any of these safeties or parameters fails or goes into an alarm condition the system will immediately alarm and inform the failure and its source. This is a very important safety feature since you will be informed that a current failure will result in future problems (temperature rise, for instance).

Communications System– Together with the Alarm and Diagnostics capabilities, the Communications forms a most unique and innovative concept in service. When the system Dials Out an alarm to our office, we can then Dial Into your system and remotely determine the source and nature of the cause of the alarm. Our Technician gets dispatched to solve a diagnosed problem not to look for a problem. We know you have a failure before the failure becomes a problem.

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.

Our 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”!

Some of the features incorporated into our control system are:

• Auto Suction Pressure Control
  
• Capacity Control
  
• Flexible Compressor Sequencing
  
• Alarm Conditions
  
• System Wide Approach

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.