Ventilation Chillers Flashcards
What is the basic flow path through the refrigeration cycle?
Evaporator —> Compressor —> Condenser —> Expansion Valve
What portions of the refrigeration cycle are on the low pressure side?
- The outlet of the expansion valve is a low pressure liquid
- The Evaporator
- The outlet of the Evaporator leading to the Compressor is a low pressure vapor
What portions of the refrigeration cycle are on the high pressure side?
- The outlet of the Compressor is a high pressure gas
- The Condenser
- The outlet of the Condenser leading to the inlet of the Expansion Valve is a high pressure liquid
What is the purpose of the Evaporator?
The Evaporator transfers the heat from the medium being cooled(air or chilled water) to the refrigerant. The refrigerant is converted from a low pressure liquid to a low pressure vapor.
What is the purpose of the Compressor?
The Compressor raises the pressure of the low pressure gas to a high pressure gas. The pressure/temperature of the gas is raised to ensure that heat transfer is maximized in the Condenser.
What is the purpose of the Condenser?
The Condenser rejects the heat from the refrigerant to the heat sink. The high pressure gas is converted into a high pressure liquid.
What is the purpose of the Expansion Valve?
The Expansion Valve lowers the pressure/temperature of the high pressure liquid and controls the amount of refrigerant flowing to the evaporator.
What are the two parameters that most chiller packages work to control?
- Evaporator pressure
2. Refrigerant temperature
What is unique about the Economizer Chamber, and which chiller(s) have this component?
- The Economizer Chamber controls refrigerant flow to the Evaporator/Cooler, and returns some of the refrigerant that flashes to a vapor in this section to the second stage of the Compressor.
- The Control Room Chillers and the Containment Chillers have this component.
What type of control system does the Control Room Chiller have?
- The Control Room Chiller uses chilled water outlet temperature to control chiller load.
- The chilled water temperature sensor sends a signal to the guide vane actuator at the suction of the compressor opening and closing the vanes. If chiller load is low the vanes will close lowering vapor flow to the compressor thus lower refrigerant flow through the chiller.
What type of control system does the Containment Chiller have?
- The Control Room Chiller uses chilled water outlet temperature to control chiller load.
- The chilled water temperature sensor sends a signal to the guide vane actuator at the suction of the compressor opening and closing the vanes. If chiller load is low the vanes will close lowering vapor flow to the compressor thus lower refrigerant flow through the chiller.
What type of control system does the Computer Room Chiller use?
- Chilled water temperature is the parameter maintained by the Computer Room Chillers
- Flow through the expansion valve is controlled to match the flow through the Compressor using a stepper motor.
- Flow through the Compressor is controlled by means of a Female Step Load Control Valve and a Male Step Load Control Valve. The capacity of the compressor is dictated by the position of the loading valves relative to the compressor rotors.
What is the purpose of the Hot Gas Bypass, and which chiller package utilizes this function?
The Containment Chiller has a Hot Gas Bypass function that allows some of the refrigerant in the Condenser to be siphoned into the evaporator. This creates an artificial load and prevents erratic operation of the chiller in low load conditions such as outages when the Containment is cool.
What is the heat sink for the Control Room Chiller and how is it controlled?
- Nuclear Service Water(RN) is the heat sink for the Control Room Chiller
- RN flow is controlled by the chiller to control Condenser pressure
What is the heat sink for the Containment Chiller, and how is it controlled?
- Low Pressure Service Water(RL) is the heat sink for the Containment Chiller
- RL flow is controlled by the chiller to control Condenser pressure
