37
APPENDIX B: SenTech Room Volume Considerations
(English)
Normal industry practice has been to
thin about refrigerant leans 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 feet/hour
FA – fresh air into the room in cubic
feet/hour
VOL – room volume in cubic feet
t – time in hours
R – volume of refrigerant in cubic
feet
LRmin – minimum leak rate that will
result in a given ppm
RD – refrigerant density in lbs/cubic
foot
To be able to convert between ppm
and leak rate in cubic feet/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(lb)/454(g)]
x [28.32(l)/1(cuft)] x [273(K)/293(K)] = RD(lb/cuft)
Calculating for R-22, 86.48(g/mole),
RD22 = .22 lb/cuft and
1/RD22 = 4.46 cuft/lb
Other densities are as follows:
R-22
RD22 = .22 lb/cuft
R-12
RD12 = .31 lb/cuft
R-11
RD11 = .36 lb/cuft
R-502
RD502 = .29 lb/cuft
R-123
RD123 = .41 lb/cuft
Summary of Contents for IR-SNIF-1
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