Carrier 5H - Manual (Page 31)

Condenser Duty - The capacity of a given com­
pressor is greatest at high saturated suction
temperatures. Because of this, the compressor
normally requires the largest condenser at these
conditions, or for air conditioning duty.
On refrigeration or low temperature applica­
tions, the same compressor displacement results
in a lower refrigeration capacity and,consequently,
less heat rejection. Thus, the condenser size is
smaller than would normally be required with the
same compressor on air conditioning duty.
Condenser size is also affected by the refrig­
erant used, since compressor capacities (and
thus heat rejection) differ with Refrigerants 12,
22, 500, and 502.
Pulldown - Condensers for systems subject to
pulldown periods, especially low temperature or
multi-stage systems, should be oversized to some
extent beyond the capacity required at the final
balanced
load condition. The condenser must
adequately handle the load during the first stages
of pulldown, when the system capacity is substan­
tially greater than at the final condition.
There are a few general rules that can be
followed to determine the amount of oversizing
that is required. Much depends, of course, on job
conditions and how often pulldown will be required.
If the pulldown load is sizable, such as in most
water or brine cooling applications, check con­
denser performance when it is handling the total
heat rejection at the maximum rated suction tem­
perature (50 F for most compressors). The con­
denser size and water quantity must be adequate
to handle this start-up load without resulting in
excessive head pressure or excessive water pres­
sure drop. As a rough guide, condenser selected
should have a maximum total heat rejection rating
which is equal to or greater than the compressor
heat rejection at the pulldown conditions.
If this pulldown occurs very infrequenctly, then
it may be possible to select the condenser for the
design conditions and on each start-up limit the
compressor
capacity by manually throttling the
suction gas flow. This can be done by partially
closing the suction valve but this will extend the
time required to reach design conditions.
If the pulldown is of short duration, such as on
a direct expansion coil, the suction temperature
will drop very rapidly and more than likely design
conditions will be reached before the compressor
would cut out on high pressure. No oversizing of
the condenser would be required.
Whenever possible the selected condenser
should never be of a larger size than the largest
that will match the compressor used and still be
a standard combination. This should be considered
especially
when the condensers are to be used
with the 5 Series open reciprocating compressors.
Fouling Factors - The 5F and 09RH condenser
capacity ratings in the 5F,09RH-1XR are given
for water side fouling factors of 0.0005, 0.0001
and 0.0002. These fouling factors are the resist­
ance to heat flow introduced by scale and other
water impurities.
Condensers should not be normally selected
for less than 0.0005 fouling factor, even when
high quality water is available. For lower quality
water,
use the larger fouling factors from the
condenser ratings, but temper the factor accord­
ing to the operating conditions.
The following items affect the magnitude of
the fouling factor selected:
1. Percentage of yearly operating time.
2. Frequency of tube cleaning.
3. Condensing temperature.
4. Type of water treatment.
For instance, reduce the fouling factor when
the operating time is less than 4000 hours per
year, when frequent cleaning of tubes takes place,
or when low condensing temperatures exist.
Water Circuiting Arrangements - The water cir­
cuiting arrangement selected for the 5F and 09RH
condensers
depends on the available condenser
water pressure, temperature, quantity and source.
Refer to Table 25.
Piping - On the 5F shell and tube and the 09RH
condensers, excluding those with 14- and 18-inch
diameter shells, it is possible to interchange the
condenser
heads. This, however, should not be­
come a common practice but done only when
absolutely necessary. When it has to be done
extreme caution and care should be taken to not
ruin or dislocate the microbaffling.
The hot gas discharge line from the compres­
sor to the condenser should be as short as pos­
sible to reduce the hot gas pressure drop.
Refer to the Carrier System Design Manual
for specific information and recommendations
for refrigerant and water piping.
Economics - The selection of a condenser re­
quires the balancing of certain economic var­
iables, including:
1. First cost of compressor-condenser combina­
tion.
2. Operating costs.
3. Ratio between power costs and water costs.
Where first cost is the most important consid­
eration, the best combination of compressor and
condensers is the one which has the lowest total
equipment cost.
If owning and operating costs are both impor­
tant, the combination must be selected on the
basis of both considerations.
S U P E R S E D E S
SECTION
5F,H-1X
PAGES 1-42
DATE 11-63
SECTION
PAGE
DATE 5F,H-1XA
31
10-66