The compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps before the overload trips. Some compressor manufacturers, such as Copeland, use a different factor. They divide the MCC by 1. For example a kW rated centrifugal type water cooled chiller has an RLA of Amps but the chiller will cut the power to the motor if it reaches amps.
This limit and value varies between all chillers. There are three different types of chillers: 1 air, 2 water, and 3 evaporative condensed chiller. There are four subcategories in each of the above categories for industrial chillers: 1 reciprocating, 2 centrifugal, 3 screw driven 4 and absorption chillers.
Chilled-water temperature reset adjusts the leaving chilled water set point to improve the efficiency of the chiller and thereby reducing the energy consumption. Generally, a chilled-water-reset raises the set-point temperature when the building load is at less-than-design conditions. Contractors each represent their own brands of commercial HVAC equipment so they like to stay consistent with their brand as much as possible.
Ammonia R is a type of refrigerant that belongs to the class of halogen-free chemicals. This is the most popular refrigerant used in chiller plants. It has the highest heat absorption rating which makes it ideal for use in smaller, portable chiller units negating the need for large cooling plants. A chiller works on the principle of vapor compression or vapor absorption. As the heat-transfer takes place, the refrigerant evaporates, changing from a low-pressure liquid into vapor, while the temperature of the process coolant reduces.
Example: A RLA of 20 amps should not exceed 23 amps. In most cases, I've found that properly sized and operating refrigeration equipment rarely reaches this maximum. On low temp refrigeration equipment the compressor can over amp, if the evaporator is warm or hot. The compressor is sized to pump the lower pressures you'll find on lower temperature evaporators. Higher pressures from a warm evaporator exceed the design capacity. The compressor motor must work harder. FLA is a rating for motors.
RLA is a calculated rating for hermetic compressors and is only useful for sizing the circuit wiring, not for the technician to use for running characteristics. Most compressor manufacturers will stamp an amperage rating on their compressors. However, the technician cannot use this value to determine the correct operating amperage. Also, trying to determine if a compressor is good or bad using RLA is not correct.
It has nothing to do with what the correct amperage draw should be under its various load conditions. The compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps MCA before the overload trips.
Some compressor manufacturers, such as Copeland and Carlyle, use a different factor. They divide the MCA by 1. If you REALLY want to know what the amperage should be on a given compressor at a given set of operating conditions, the manufacturer publishes compressor performance curves or publishes software to predict the amperage given suction, discharge, and other conditions.
It has been quite accurate in my experience. Im taking notes on this topic and thank you to all the contributors who explained and have given their ideas and links, again , additional knowledge gained on this forum. Hi there, I'm sure we got the book definitions, but let me hash out what they mean.
A properly designed and working compressor must not exceed this value under stabilized conditions. You can't make it match real life conditions unless you're pumping between almost non-variable temperatures such as making ice from near freezing water and dumping heat into a condenser with near infinite heat sink such as free flowing sea water aboard a ship. If you're exceeding FLA with normal line voltage, its a malfunction or a mismatch. Inrush is a bit more complex.
It's useful for evaluating if the power source can handle it.
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