42
SenTech Room Volume Considerations
(Metric)
Normal industry practice has been to think
about refrigerant leaks in terms of pounds
of refrigerant per unit time, such as lbs/hr or
oz/yr. This is a natural and logical way of
looking at it. The system monitors the
amount of refrigerant present in the air in
parts per million (ppm) by volume or
refrigerant molecules as compared to air
molecules. In order to develop a correlation
between the leak rate in weight per unit
time and parts per million, there are a
number of items that need to be
considered. These are:
1. Room volume.
2. The weight of refrigerant per unit
volume at ambient temperature and
pressure.
3. The amount of time the refrigerant
has been leaking.
4. The rate at which fresh air enters the
room and existing air is exhausted.
5. The location of the inlet, relative to
the leak, airflow in the room and the
rate at which the refrigerant expands
to fill the room.
For a specific application, items 1 through 4
can be calculated, or estimated. Item 5 is
virtually unpredictable, therefore in all
calculations, it is assumed that the leaking
refrigerant will expand to fill the room with
an even distribution of refrigerant. This
assumption will yield safer, conservative
calculations. If the monitor sample and
reference locations have been appropriately
chosen, the monitor will see a higher
concentration than calculated from the ideal
formulas.
Formula Definitions:
ppm – refrigerant concentration
LR – leak rate in cubic meter/hour
FA – fresh air into the room in cubic
meter/hour
VOL – room volume in cubic meter
t – time in hours
R – volume of refrigerant in cubic
meter
LRmin – minimum leak rate that will
result in a given ppm
RD – refrigerant density in kg/cubic
meter
To be able to convert between ppm and
leak rate in cubic meter/hour, the refrigerant
density must be calculated. If the molecular
weight of the refrigerant is known, the
refrigerant density can be calculated.
[MolWt(gms)/1(mole)] x [1(mole)/22.4(l)] x [1(kg)/1000(g)] x
[273(K)/293(K)] = RD(kg/cubic meter)
Calculating for R-22, 86.48(g/mole), RD22
= 3.59 kg/cubic meter and
1/RD22 = .28 cubic meter/kg
Other densities are as follows:
R-22 RD22 = 3.59 kg/cubic meter
R-12 RD12 = 4.96 kg/cubic meter
R-11 RD11 = 5.76 kg/cubic meter
R-502 RD502 = 4.64 kg/cubic meter
R-123 RD123 = 6.56 kg/cubic meter
Summary of Contents for IR-SNIF-MC-1
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