Equipment - Refrigeration - Refrigeration Control Guide
This article will guide through refrigeration controls for the KE2 Therm and Masterbilt V 1 refrigation units. This guide includes information about refrigeration cycle and defrost cycle.
Table of Contents
Data Points
KE2 Therm
- Internal Temperature: internal ambient freezer temperature
- Temperature Setpoint: internal ambient freezer temperature setpoint
- Coil Temperature: temperature of evaporator coil in the freezer (not applicable for refrigerator)
- Compressor runtime: call for compressor runtime (cooling mode)
- Defrost runtime: call for defrost runtime (electric defrost for freezers, air defrost for coolers – reducing ice buildup on evaporator coils)
- Cooler: 6x/day for 15 minutes
- Freezer: 4x/day for 30 minutes
Masterbilt V1
- Internal Temperature: internal ambient freezer temperature
- Temperature Setpoint: internal ambient freezer temperature setpoint
- Max Defrost Temp SP: Defrost termination setpoint
- Max Temp Last Defrost: Trend is very similar to coil temp
- Saturated temp: the temp at which the refrigerant changes state from liquid to vapor (ie boils) – saturation temperature increases and decreases in direct response to pressure
- Suction temp: temperature of refrigerant entering the compressor – suction temperature also increases and decreases in direct response to pressure (suction pressure). Usually about -20 degF
- Suction pressure: the pressure of the refrigerant at the compressor This means that when we see compressor runtime, suction pressure goes down because it is measured at the intake. The refrigerant is pulled into the compressor and compressed meaning the discharge pressure will be higher.
- Superheat SP: 10 degF
- Superheat: Difference between the saturation temperature and the actual temperature of the This is a result of the refrigerant absorbing ambient heat as the refrigerant moves along the coil.
- ( Ta – Ts ) = Tsh
- Compressor runtime: KE2/MBV1 call for compressor runtime
- Defrost runtime: KE2/MVB1 call for defrost runtime
- Cooler: 4x/day for 30 minutes
- Freezer: Demand defrost – based on coil temp
- Freezer valve position: TXV (Thermostatic Expansion Valve). Restricts the flow of refrigerant to the As flow is restricted, liquid refrigerant pressure and temperature drop allowing it to absorb heat inside the refrigeration unit. This also helps to protect the compressor by evaporating any liquid refrigerant before the liquid makes it to the compressor.
Note
- For KE2 we are only controlling the flow of refrigerant via the liquid line solenoid – the compressor only engages when the pressure rises far enough (~20 psi “cut in” for low pressure switch on the suction side).
KE2 shuts off liquid line solenoid when in defrost
Compressor short cycling occurs if the internal temperature sensor is installed too close to the coil - Example: Unit cycles frequently, may struggle to keep up with setpoint and defrost runtime is very low
Defrost short cycling occurs if the coil temp sensor is installed too close to the heating element. - Example: WAG2142 Paul
Refrigeration Heat Pump Cycle Explained (Masterbilt V1)
Refrigeration Cycle
- Low pressure, low temperature vapor refrigerant enters the compressor
- Refrigerant exits compressor as a high pressure, high temperature vapor refrigerant
- Vapor goes through reversing valve
- Vapor enters outdoor condenser coil and rejects The fan blows air across the coils allowing that heat to sink to outdoor. Temperature decreases until the refrigerant enters saturated state where liquid and vapor exist (state change from vapor to liquid).
- The high pressure, high temperature liquid then enters the thermostatic expansion valve (TXV). TXV maintains superheat across the evaporator coil.
- When the high pressure, high temperature liquid refrigerant enters the TXV, pressure drops (80% liquid, 20% flash gas due to pressure drop).
- From the TXV, the refrigerant enters the evaporator coil where heat is absorbed by the refrigerant until it becomes saturated (state change from liquid to vapor)
- Delta T of refrigerant from liquid to vapor in the evaporator coil is called superheat.
- Refer to Figure 5 from the Master Controller Manual below
Defrost Cycle
- High pressure, high temperature vapor enters the reversing valve and, instead of heading to the outdoor condenser coil, is sent to the indoor evaporator coil.
- The high pressure, high temperature refrigerant heats the evaporator coil defrosting it from the inside out.
- Then the refrigerant enters the TXV where is expands and drops in pressure and temperature
- From there, the refrigerant is sent to the outdoor condenser coils where heat is absorbed, and the refrigerant enters saturated (state change from liquid to vapor)
- Next, the refrigerant is sent back to the compressor to begin the cycle again.
- Refer to Figure 5 from the Master Controller Manual below
