1112.2 Positive Displacement Compressor. A positive

displacement compressor with a stop valve in the discharge connection shall be equipped with a pressure-relief device that is sized, and with a pressure setting, in accordance with the compressor manufacturer to prevent rupture of the compressor or to prevent the pressure from increasing to more than 10 percent above the maximum allowable working pressure of components located in the discharge line between the compressor and the stop valve or in accordance with Section 1113.5, whichever is larger. The pressure-relief device shall discharge into the low-pressure side of the system or in accordance with Section 1112.10. Exception: Hermetic refrigerant motor-compressors that are listed and have a displacement not more than 50 cubic feet per minute (1.42 m ³ /min).

Section 1112.10. The pressure relief device shall be connected at the highest possible location of the heat exchanger or piping between the heat exchanger and its manual isolation valves. Exceptions: (1) Relief valves shall not be required on heat exchanger

coils that have a design pressure more than 110 percent

(1) Relief valves shall not be required on heat exchanger

coils that have a design pressure more than 110 percent of refrigerant saturation pressure when exposed to the maximum heating source temperature. (2) A relief valve shall not be required on self-contained or

unit systems where the volume of the lowside of the sys

The relief device(s) shall be sized based on compressor flow at the following conditions: (1) For compressors in single-stage systems and high-stage

compressors of other systems, the flow shall be calcu

A relief valve shall not be required on self-contained or

unit systems where the volume of the lowside of the system, which is shut off by valves, is more than the specific volume of the refrigerant at critical conditions of temperature and pressure, as determined in accordance with Equation 1112.4.

(1) For compressors in single-stage systems and high-stage

compressors of other systems, the flow shall be calculated based on 50°F (10°C) saturated suction temperature at the compressor suction. (2) For low-stage or booster compressors in compound sys tems, the compressors that are capable of running only

(2) For low-stage or booster compressors in compound sys tems, the compressors that are capable of running only where discharging to the suction of a high-stage compressor, the flow shall be calculated based on the saturated suction temperature equal to the design operating intermediate temperature. (3) For low-stage compressors in cascade systems, the com pressors that are located in the lower-temperature

V1 / [ W1 – (V2 – V1) /Vgt ] (Equation 1112.4) Shall be more than Vgc

Where: V1 = Lowside volume, cubic foot (m ³ ). V2 = Total volume of system, cubic foot (m ³ ). W1 = Total weight of refrigerant in system, pounds (kg). Vgt = Specific volume of refrigerant vapor at 110°F

(43°C), cubic feet per pound (m ³ /kg).

(3) For low-stage compressors in cascade systems, the com pressors that are located in the lower-temperature stage(s) of cascade systems, the flow shall be calculated based on the suction pressure being equal to the pressure setpoint of the pressure-relieving devices that protect the lowside of the stage against overpressure. Exceptions: For Section 1112.2(1), Section 1112.2(2), and Section 1112.2(3), the discharge capacity of the relief device shall be permitted to be the minimum regulated flow rate of the compressor where the following conditions are met: (1) The compressor is equipped with capacity regulation. (2) Capacity regulation actuates to a flow at not less than 90

percent of the pressure-relief device setting.

Vgt = Specific volume of refrigerant vapor at 110°F

(43°C), cubic feet per pound (m ³ /kg). Vgc = Specific volume at critical temperature and pressure,

cubic feet per pound (m ³ /kg). [ASHRAE 15:9.4.4]

(2) Capacity regulation actuates to a flow at not less than 90

percent of the pressure-relief device setting. (3) A pressure-limiting device is installed and set in accor dance with the requirements of Section 1111.0.

(1) Pressure relief device to relieve hydrostatic pressure

to another part of the system. (2) Reseating pressure relief valve to relieve the hydro static pressure to an approved treatment system.

Vgc = Specific volume at critical temperature and pressure,

cubic feet per pound (m ³ /kg). [ASHRAE 15:9.4.4]