Chapter 53 Mechanical Refrigeration

Automatic crossover valves shall be provided to automatically relieve excess system pressure to a lower pressure zone if the pressure in a high or intermediate pressure zone rises to within 90 percent of the set point for emergency pressure relief devices.

Where required by the AHJ, automatic crossover valves shall be capable of manual operation.

Refrigeration system zones that are connected to a higher pressure zone by an automatic crossover valve shall be designed to safely contain the maximum pressure that can be achieved by interconnection of the two zones.

Operation of an automatic crossover valve shall cause all compressors on the affected system to immediately stop in accordance with the following:

1. Dedicated pressure-sensing devices located immediately adjacent to crossover valves shall be permitted as a means for determining operation of a valve.
2. To ensure that the automatic crossover valve system provides a redundant means of stopping compressors in an overpressure condition, high pressure cutout sensors associated with compressors shall not be used as a basis for determining operation of a crossover valve.

The lowest pressure zone in a refrigeration system shall be provided with a dedicated means of determining a rise in system pressure to within 90 percent of the set point for emergency pressure relief devices.

Activation of the overpressure sensing device shall cause all compressors on the affected system to immediately stop.

Systems containing toxic or highly toxic refrigerants shall discharge vapor to the atmosphere only through an approved treatment system in accordance with Chapter 63 or flaring system in accordance with 53.2.2.2.

Systems containing flammable refrigerants shall discharge vapor to the atmosphere in accordance with the following:

1. For refrigerants having a density equal to or greater than the density of air, discharge shall be through an approved treatment system in accordance with or flaring system in accordance with 53.2.2.2.
2. For refrigerants having a density less than the density of air, discharge to the atmosphere shall be permitted, provided that the point of discharge is located outside of the structure at not less than 15 ft (4.6 m) above the adjoining grade level and not less than 20 ft (6.1 m) from any window, ventilation opening, or exit.

Systems containing ammonia refrigerant shall discharge vapor to the atmosphere through a treatment system in accordance with 53.2.2.1, through a flaring system in accordance with 53.2.2.2, through an approved ammonia diffusion system in accordance with 53.2.2.3, or by other approved means except as follows:

1. Discharge through a treatment, flaring, or diffusion system shall not be required for ammonia-water absorption unit systems installed outdoors serving a dwelling unit, provided that the discharge is shielded and dispersed.
2. Discharge through a treatment, flaring, or diffusion system shall not be required for ammonia-water absorption unit systems containing less than 22 lb (10 kg) of ammonia and for which the ammonia circuit is located entirely outdoors.

Flaring systems for incineration of flammable, toxic, or highly toxic refrigerants or ammonia shall be designed to incinerate the entire discharge.

The products of refrigerant incineration shall not pose health or environmental hazards.

Incineration shall be automatic upon initiation of discharge, shall be designed to prevent blowback, and shall not expose structures or materials to threat of fire.

Standby fuel, such as LP-Gas, and standby power shall have the capacity to operate for one and one half the required time for complete incineration of refrigerant in the system.

Ammonia diffusion systems shall include a tank containing 1 gal of water for each pound of ammonia (4 L of water for each kg of ammonia) that will be released in 1 hour from the largest relief device connected to the discharge pipe.

The water used shall be prevented from freezing without the use of salt or chemicals by burial of the discharge pipe below frost depth or other approved means.

The discharge pipe from the pressure relief device shall distribute ammonia in the bottom of the tank, but no lower than 33 ft (10 m) below the maximum liquid level.

The tank shall contain the volume of water and ammonia, described in 53.2.2.3.1, without overflowing.

The tank shall be substantially constructed of not less than ¹/₈ in. (2.51 mm) (10 gauge) steel.

The horizontal dimensions of the tank shall be equal to or less than one half of the height.

The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top.

Pipe connections shall be through the top of the tank.

The refrigerant vapor detector shall activate approved visual and audible alarm signaling devices at one of the following refrigerant thresholds:

1. At a value not greater than the corresponding TLV-TWA (or toxicity measure consistent therewith); not to exceed 25 percent of the lower flammable limit (LFL)
2. For ammonia, at a concentration not exceeding 25 parts per million

Audible and visual alarm signaling devices shall be located inside the refrigeration machinery room and outside the room at each entrance into the room.

Audible alarm signaling devices shall provide a sound level of at least 15 dB above the operating ambient noise sound pressure level of the space in which they are installed and shall provide approved, distinctive audible and visual alarms.

Where the quantity of a Group A2, B2, A3, or B3 refrigerant, other than ammonia, in an independent circuit would exceed 25 percent of the LFL if released to the surrounding room, either of the following shall apply:

1. Electrical equipment shall comply with the requirements of NFPA 70 for Class I, Division 2.
2. The refrigerant vapor detection system required by 53.2.3.1 shall automatically de-energize all electrical power within the space at vapor concentrations at or above 25 percent of the LFL.

Refrigerant vapor detection and alarm systems shall be powered and supervised as required for fire alarm systems in accordance with NFPA 72.

Refrigerant vapor detection and alarm systems shall transmit a signal to an approved location.

Detection and alarm systems shall be installed and maintained in accordance with the equipment manufacturers' specifications. (Also see 53.3.2.1.)

Fans providing emergency purge ventilation for refrigerant escape from a refrigeration room shall have a clearly identified switch of the break-glass type providing on-only control immediately adjacent to, and outside of, each refrigerant machinery room means of egress.

An emergency purge control shall be provided with a manual reset only.

For systems using a refrigerant other than ammonia, purge fans shall also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at the threshold levels set forth in 53.2.3.1.1. For systems using ammonia, purge fans shall also respond automatically to the refrigerant concentration detection system set to activate the ventilation system at an ammonia concentration not exceeding 150 parts per million.

Mechanical ventilation systems serving refrigeration rooms shall have switches to control the power to each fan.

The switches shall be key-operated or within a locked glass-covered or tamper-resistant enclosure at an approved location adjacent to and outside of the principal entrance to the refrigeration machinery room.

Keys necessary for operation of ventilation systems shall be located in a single approved location.

Switches controlling fans providing continuous ventilation shall be of the two-position, on/off type.

Switches controlling fans providing intermittent or emergency ventilation shall be of the three-position, automatic on/off type.

Switches shall be labeled identifying both the function and the specific fan being controlled.

Two colored and labeled indicator lamps responding to the differential pressure created by airflow shall be provided for each switch.

One lamp shall indicate flow, and the other shall indicate no flow.

Exhaust from mechanical ventilation systems in refrigeration rooms shall be discharged 20 ft (6.1 m) or more from a property line or openings into buildings.

Discharges capable of exceeding 25 percent of the LFL or 50 percent of the immediately dangerous to life and health (IDLH) value shall be equipped with approved treatment systems to reduce the discharge concentrations to these values or lower, except as provided in 53.2.3.3.13.1 and 53.2.3.3.13.2. (Also see 53.2.2.1.)

The refrigeration machinery room shall not be required to be classified as a hazardous location for electrical equipment except as provided in the mechanical code or NFPA 70.

Refrigeration machinery rooms used exclusively for direct-fired absorption equipment shall be permitted not to be classified as a hazardous location for electrical equipment in accordance with NFPA 70.

Electrical equipment and electrical installations in refrigeration machinery rooms shall comply with Section 11.1.

Where treatment, detection, or alarm systems are required, such systems shall be connected to a secondary source of power to automatically supply electrical power in the event of loss of power from the primary source.

A clearly identified switch of the break-glass type or with an approved tamper-resistant cover shall provide off-only control of refrigerant compressors, refrigerant pumps, and normally closed, automatic refrigerant valves located in the machinery room. In addition, this equipment shall be automatically shut off whenever the refrigerant vapor concentration in the machinery room exceeds the vapor detector's upper detection limit or 25 percent of the LFL, whichever is lower.

Flammable and combustible materials shall not be stored in refrigeration machinery rooms except for incidental materials necessary for the safe and proper operation and maintenance of the system.

Storage of materials in a refrigeration machinery room, including reserve supplies of refrigerants or refrigerant oils, shall be in accordance with other applicable chapters of this Code.