Important Safety Factors in Refrigeration System Design

by / Tuesday, 18 April 2017 / Published in HVAC Design, Technical Expert

A refrigeration system is a combination of equipment connected in a closed circuit. A refrigerant is cycled through this circuit absorbing heat in one space and rejecting it to another. Many different compounds are used as refrigerants, but unfortunately many compounds that make excellent refrigerants can be harmful if leaked into an occupied space. As refrigerants have low boiling points, leaked refrigerant changes to a vapour state and can accumulate to create a potentially dangerous environment.

The Canadian Standards Association published B52 Mechanical refrigeration code, which limits the mass of refrigerant deemed safe in a volume of occupied space. Depending on the refrigerant, the permitted mass per volume of space varies. Mass may be limited to maintain a minimum oxygen concentration level of 19.5%. As some refrigerants are tasteless and odourless, their vapours can create an oxygen deprived environment without any signs to the occupants.  Some are limited by cardiac sensation level where inhalation can cause heart irregularities. Whereas others are limited by the lower flammability level or may be immediately dangerous to life and health.

When designing a refrigeration system, the designer must determine the worst case scenario in the event of a refrigerant leak. This involves identifying the smallest enclosed space where refrigerant containing parts are located. It may be a single room or an entire floor, depending on whether the refrigerant circuit physically passes through a space or if it passes through duct work supplying air to many spaces. Next, the total mass of the largest refrigerant circuit is calculated because when a leak occurs there is potential for the entire contents of the circuit to vapourize into one space. Knowing the largest mass of refrigerant and the smallest enclosed space, the designer can determine system compliance with B52 code.

If a refrigeration system contains more refrigerant in it than permitted, it may be an option to install the system in a dedicated machinery room. Due to the same risks of refrigerant leakage in the machinery room, there must be a refrigerant vapour detector with an audible alarm and it must initiate properly sized mechanical ventilation to exhaust any accumulated vapour.

Scott Sweiger

Scott is a Mechanical Designer with Efficiency Engineering Inc. He has a Bachelor of Mechanical Engineering & Management from McMaster University and is working towards his P.Eng.

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