Refrigeration Systems Controls

A method to control the capacity of a refrigeration compressor where the compressor starts and stops based on temperature needs.

The compressor is stopped when the desired low temperature is reached, and then started up again once the temperature increases.

A method to control the capacity of a refrigeration compressor where the compressor runs continuously but with reduced output.

A method to control the capacity of a refrigeration compressor by reducing the number of cylinders working.

A method to control the capacity of a refrigeration compressor by bypassing some refrigerant from the compressor.

A method to control the capacity of a refrigeration compressor by returning some hot gas to the suction line.

Adjusts the speed of the compressor to change the amount of refrigerant circulated.

Reduces the amount of refrigerant entering the compressor by restricting its flow.

A method of controlling evaporator capacity where the evaporator is divided into sections, each with a refrigerant flow control valve. Sections can be shut off as the cooling load decreases.

A device that controls the amount of air passing over the evaporator coils by opening and closing to meet the changing cooling load.

The amount of cooling that can be achieved by the evaporator, which is directly proportional to the amount of refrigerant flowing through it.

A valve that controls the flow of refrigerant through a section of the evaporator.

A type of valve that is operated by an electrical signal, typically used in sectional evaporators to open or close sections as needed.

A device that positions the face damper in response to a control signal.

The total amount of refrigerant in the system, usually stored in a separate container.

Any event or situation that causes a reduction in the cooling load, such as a decrease in the temperature of the space being cooled.

A safety mechanism that prevents a compressor from starting when lube oil temperature is below a specific threshold.

A device that heats the lube oil in the compressor crankcase, ensuring optimal lubrication and preventing damage.

A type of safety device designed to stop the compressor in case of low oil pressure.

The amount of refrigerant that flows through a refrigeration system per unit of time.

The ability of a refrigeration system to remove heat, measured in units of power (kW or tons).

The process where refrigerant dissolves into the compressor oil at lower temperatures, diluting its viscosity and potentially causing wear.

The formation of refrigerant vapor bubbles within the lube oil, disrupting the oil flow and potentially causing problems.

The process of maintaining constant pressures and temperatures within a refrigeration system.

Limits the amount of electrical current drawn by the compressor motor during startup, preventing overload and minimizing electrical demand.

A control strategy that gradually increases the compressor's capacity during startup, preventing sudden temperature drops and potential low temperature trips.

A sensor that detects excessive vibration in a compressor bearing and triggers an alarm or shutdown if a certain threshold is exceeded.

A safety feature that monitors the liquid level in the suction scrubber. If the level rises beyond a set point, an alarm is activated and, if the level continues to rise, the compressor is shut down to prevent liquid from entering the compressor.

A sensor that monitors bearing temperature. If the temperature rises above a set point, an alarm is triggered and, if the temperature continues to rise, the compressor is shut down to prevent damage from overheating.

The amount of refrigerant flow into the compressor is controlled by the inlet vanes.

The power consumed by the compressor motor is directly related to the amount of refrigerant moved.

Variable speed drives can adjust the compressor speed, reducing electrical demand and ensuring optimal performance.

This safety device prevents the compressor from starting if the water flow is below a safe minimum level. Ensures safe operation by preventing compressor start when there is insufficient water flow.

A proximity switch that closes when the chiller capacity control vanes are closed. This is crucial for starting a centrifugal compressor as it ensures the compressor starts under a 'no-load' condition, protecting it from strain.

This safety device shuts down the compressor when the lube oil pressure drops below a safe minimum value. This prevents catastrophic damage to the compressor and potential refrigerant leaks.

This safety switch acts as a high limit thermostat and shuts down the compressor if the condenser pressure becomes too high. This prevents overheating and potential damage to the system.

This low limit thermostat senses the refrigerant temperature, shutting down the compressor if the temperature drops low enough to freeze water. This protects the cooling system from damage.

Most centrifugal chillers have a motor demand limiter to limit the maximum current flow to the compressor drive motor. This control overrides the water temperature sensor if necessary to prevent overloading the motor.

Typically, the chilled water temperature is higher than set point at startup. The motor demand limiter prevents high current flow during this initial stage, ensuring safe operation.

The capacity of a refrigeration system is determined by the amount of refrigerant flow through the evaporator. This flow is influenced by factors like the evaporator size, the refrigerant pressure, and the operating temperature.

When a hand-operated expansion valve flows more refrigerant than the evaporator needs to meet the cooling load, the evaporator will become flooded with liquid refrigerant. This can lead to reduced cooling efficiency and even damage to the system, as the liquid refrigerant can block the flow of air through the evaporator.

If a hand-operated expansion valve flows less refrigerant than the evaporator needs to meet the cooling load, the evaporator will not be able to absorb enough heat from the surrounding air. This will result in reduced cooling capacity and the evaporator may freeze up.

Thermostatic expansion valves (TEVs) are designed to maintain a constant superheat in the evaporator, regardless of changes in the load. This is achieved by using a sensing bulb that measures the temperature of the refrigerant leaving the evaporator, and then adjusts the flow of refrigerant accordingly.

TEVs use external equalizer piping for several reasons. One reason is to ensure that the sensing bulb senses the actual temperature of the refrigerant leaving the evaporator, even if the evaporator is located some distance away. Another reason is to improve the response time of the valve to changes in the load.

Low-pressure float valves are used with evaporators that operate at low pressures. This is because they are designed to maintain a constant level of liquid refrigerant in the evaporator, regardless of changes in the load.

Controlling the capacity of an evaporator is important to ensure that the system operates efficiently and provides the required cooling. If the evaporator is too large, it may operate at a lower efficiency, while if it is too small, it may not be able to meet the cooling demand.

Face dampers are not used in HVAC applications to control evaporator capacity because they are not very effective and can create uneven airflow distribution.