October 1988
Energy Resource Center
A Service for commercial / industrial professionals from Portland General Electric

LPA Pump Boosts Refrigeration Efficiency

The remarkable science of refrigeration chills our foods and cools our buildings even in a heat wave. Although a relatively simple system, it is not always a smooth one. One phenomenon - known as "flash gas" - creeps into most cooling systems, stealing power and crippling efficiency.

Now, a simple, low horsepower pump added to a refrigerant line can eliminate flash gas and cut energy use up to 40 percent. The product id the "Liquid Pressure Amplification" (LPA) pump and it can be applied wherever a refrigeration system is present - frozen food case, meat cooler, air conditioner or chiller.

Figure 1: Normal system.

 Figure 2: System with LPA Pump Added

Back to Refrigeration Basics
The LPA pump intervenes in the basic refrigeration cycle. If you have studied refrigeration, you know that the main components of the system are the compressor, the condenser, the thermal expansion valve (TXV) and the evaporator.

Each of these parts accomplishes what its name suggest. When refrigeration gas or refrigerant, enters the compressor, it is compressed into a smaller space. The gas becomes increasingly hot as the pressure builds.

The gas moves to the condenser where it is condensed into a liquid, and in the process gives off heat. This heat is captured or released into the air. Since heat moves towards cold, the refrigerant in the condenser must be hotter (at least 15 to 20 degrees) than its surroundings in order to convert the hot gas into a liquid.

The thermal expansion valve regulates the flow of refrigerant into the evaporator. As the refrigerant evaporates, the liquid is reconverted to gas. The gas returns to the compressor and the cycle is repeated over and over again.

How the LPA Pump Works
Flash gas occurs when an undesirable mix of liquid and gas is triggered by pressure losses in the liquid line from the condenser. The result is similar to the bicarbonate discharge from a soft drink bottle popped after a vigorous shaking.

The LPA pump, developed and patented by Hy-Save, Inc. a West Linn, Oregon company, eliminates flash gas by slightly increasing pressure to the liquid refrigerant, which eliminates losses in the line. Only 1/5 horsepower, the pump is placed between the condenser and the thermal expansion valve.

The figure above illustrates the reduction of energy used by the compressor when and LPA pump is added to the refrigeration system. "Work" refers to the energy required by a compressor to lift the refrigerant temperature high enough to efficiently release heat to the air or water-cooled condenser. Note that the higher the condensing temperature, the more energy required to operate the compressor. The LPA pump reduces the lift requirement and less horsepower is needed to pump the refrigerant in the liquid line.

Multiple Benefits

In addition to eliminating flash gas, the LPA pump takes a load off the compressor, allowing it to work easier, last longer and use less energy. There is also an increase in the net refrigeration effect of the evaporator creating a significant increase in evaporator capacity.

Lower condenser temperatures result in reduced maintenance costs because windings, valves and cylinders operate cooler.

The LPA pump works well in refrigeration cases and coolers and standard commercial air conditioning systems in conjunction with reciprocating chillers, package units and various types of built-up units.

For further information, contact Energy Resource Center Mechanical Applications Specialist Bruce Dobbs, 691-3969. To contact Hy-Save, call 667-5091.

For more information about the Energy Resource Center call 503/692-48008 7895 SW Mohawk Street Tualatin, Oregon 97602.