Refrigerant pumps Circulation factor

Refrigerant pumps Circulation factor

1st task of a refrigerant pump

The task of the refrigerant pumps is to draw the liquid refrigerant, which is under evaporation pressure, out of the separator and to convey it to the consumers. The pressure at the pump outlet depends on the resistances to be overcome in the system. In order to avoid cavitation during the suction process, the pump's NPSH value must be strictly adhered to.

They are used in refrigeration systems with pump forced circulation such as:

• Facilities with many cold rooms and cold stores, slaughterhouses, meat processing plants
• Plates freezer
• Spiral Froster
• Tunnel freezer
• breweries
• Liquid coolers and ice storage systems, among others

2. Calculation of the flow rate

The required flow rate of a refrigerant pump results from the calculation of the evaporating refrigerant in the evaporator multiplied by a predetermined circulation factor.

The following circulation factors and volume flows can serve as a guideline:

(* including circulating factor)

3. Factors in the design of the delivery height

The following resistances must be considered when selecting / calculating the refrigerant pump:

• geodetic height difference between consumer and separator
• Resistors of individual consumers in the pipe network
• Resistors of the valves (shut-off valves, solenoid valves, etc.) in the supply line
• Resistors in the return line

All these resistances result in the sum of the required equivalent head of the pump in m.

4. NPSH value of the pump

The Net Positive Suction Head (NPSH) value indicates the net positive suction height or total head of the pump. The NPSH is linked to cavitation and represents one of the most important operating parameters of the pump in addition to flow rate, delivery head and power requirement. The NPSH of the system must always be greater than the NPSH of the pump.

NPSH system > NPSH pump

This requirement must be met throughout the entire pump delivery range. In practice, a safety margin (usually 0.5 m) is included for NPSH.

The minimum distance between bottom edge of separator and pump center or top edge min. Fill level in the separator to pump center are specified by the manufacturers of the refrigerant pumps. Enlarging improves the behavior of the pump.