Where the electrical installation does not conform to Section 2.6.6 the minimum
ventilation rate is defined by equation 2.6.4.a.
V
min =
(Equation 2.6.4.a)
M
r
t
r
· (SF) · (LFL)
Where:
V
min
= minimum volume flow rate of extract fan, m/hr (ft/hr).
M
r
= largest mass of refrigerant within any single circuit of any refrigerating system, kg
(lb).
t
r
= minimum release time of refrigerant following a catastrophic leak, typically 0.17
hr.
SF = safety factor, 0.5.
LFL = Lower Flammability Limit of refrigerant, kg/m (lb/ft) from Table 2.3.
In all cases a refrigerant detector should be linked into the initiation of mechanical
ventilation. The location of the sampling point should be at low level (where heavier than
air refrigerants are used). The ventilation must either be running continuously or use a
refrigerant detector starting device set at 20% of the Lower Flammability Level (LFL).
Lower ventilation rates can be initiated upon detection of lower refrigerant
concentrations.
The inlet of the extract ventilation should be located at floor level, and ducted to a safe
location. Discharge points for vented air or openings for fresh air shall be positioned so
as to avoid discharged air being drawn back in the building such as ventilation system
inlets, opening windows and doors and sources of ignition. The rejection of flammable
materials shall not present a hazard externally, such as entering a building or being in
contact with sources of ignition. The mechanical ventilation system should be designed
to maintain the room at a lower pressure than surrounding areas so that there will be no
escape of leaked refrigerants to other areas. Fans for mechanical ventilation should use
motors of non-sparking type and the fan blades and cowling should be designed so as to
avoid sparking as a result of metal-to-metal contact. Mechanical ventilation equipment
should be installed with independent emergency control located outside-of and near to
the machinery room.
NOTE:
To obtain a reduced airflow under non-emergency conditions, multi-speed fans may
be used.
Machinery rooms can also use natural ventilation provided that it is designed
adequately.
As always, regional guidelines and standards should be consulted.
2.6.5 Refrigerant Detection
Refrigerant vapor detectors should be provided in machinery rooms to activate an alarm and to
automatically switch on ventilation fans if the concentration of refrigerant release exceeds the Practical
Limit. Detectors should be used to isolate electrical equipment that does not conform to the electrical
requirements detailed in Section 2.6.6, and to warn persons that a release has occurred. Sampling points
should be installed at strategic points within machinery rooms. Points should be located so that they
provide rapid signals in the event of a leak, and that the effect of air movement does not inhibit their
effectiveness. Refrigerant leak detectors shall be calibrated for the specific refrigerant they are intended to
detect. Where the refrigerant is heavier than air, sampling points shall be located at floor level.
The
European Standard EN 378 should be consulted to identify the type of systems, size and location for
detection where relevant Provincial, Municipal or State Standards have not been legislated in your region.
Duracool Refrigerants Inc. 16
