Carrier 30GB060 - Manual (Page 3)

Application data (cont)
MINIMUM COOLER WATER FLOW RATES
AND MINIMUM LOOP VOLUME
MINIMUM PRESSURE MINIMUM
UNIT 30GB FLOW (1) DROP VOLUME (2)
Gpm ft of water Gallons
060 67 3.8 180
NOTES.
1 . Minimum flow based on 1 5 fps veiocity in cooier without special
cooler baffling
2. Minimum Loop Volumes:
Gallons = V X ARl Cap (tons)
APPLICATION
Normal Air Conditioning
Process Type Cooling
Low Ambient Unit Operation
Leaving water temperature reset
Accessory board* may be installed in 30GB chillers to
provide reset of LCWT in constant water flow systems.
Reset reduces compressor power usage at part load when
design LCWT is not necessary. Humidity control should
be considered since higher coil temperatures resulting
from reset will reduce latent heat capacity. Three reset
options are offered;
From return water temperature*
— Increases LCWT
temperature set point as return (or entering) water tem­
perature decreases (indicating load decrease). Option
may be used in any application where return water provides
accurate load indication. Limitation of return water reset is:
LCWT may only be reset to value of design return water
temperature. Return reset is the simplest of 3 reset acces­
sories available, as return water sensor is already installed.
From outdoor temperature*
— Increases LCWT as
outdoor ambient temperature decreases (indicating load
decrease). This reset should be applied only where outdoor
ambient is an accurate indication of load. An accessory
thermistor is required.
From space temperature*
— Increases LCWT as space
temperature decreases (indicating load decrease). This
reset should be applied only where space temperature is
an accurate indication of load.
For details on applying a reset option, refer to 30GB
Controls and Troubleshooting Instructions.
*Obtain ordering part numbers from current price pages.
Cooler flow range
Ratings and performance data in this publication are
for a cooling range of 10°F or 6°C. Flotronic^" chillers with
microprocessor control may be operated at a different
temperature range provided flow limits are not exceeded.
For minimum flow rates, see Table. High flow rate is limited
by pressure drop that can be tolerated. If another range is
used, apply LCWT correction as given in selection example.
Minimum cooler flow (maximum cooler temperature
range) for standard units is shown in Table. When gpm
(L/s) required is lower (or range higher), follow recom­
mendations below:
a. Multiple smaller chillers may be applied in series, each
providing a portion of the design temperature range.
b. Cooler water may be recirculated to raise flow rate.
However, mixed temperature entering cooler must
be maintained a minimum of at least 5°F (2.8°C) above
the leaving chilled water temperature.
c. Special cooler baffling is required to allow minimum
flow rate to be reduced 12%.
CHILLER COOLER
RECIRCULATION
SUPPLY RETURN
Maximum cooler flow
(> 5 gpm/ton or < 5 F range
[>0.09 L/s . kW or <2.7 C range]) results in practical
maximum pressure drop through cooler.
a. Return water may bypass the cooler to keep pressure
drop through cooler within acceptable limits. This
permits a higher AT with lower water flow through
cooler and mixing after the cooler.
b. Special cooler baffling is available by special order,
to permit a cooler flow rate increase of 10%.
CHILLER COOLER
BYPASS
SUPPLY RETURN
Variable cooler flow rates may be applied to a standard
30GB chiller. Unit will, however, attempt to maintain a
constant leaving chilled water temperature. In such cases,
minimum flow must be in excess of minimum flow given in
Table and flow rate must change in steps of less than 10%
per minute. Apply 6 gallons per ton (6.5 liters per kW) water
loop volume minimum if flow rate changes more rapidly.
Water loop volume — In circulation must equal or
exceed 3 gallons (11.4 liters) per nominal ton of cooling
(3.25 liters per kW) for temperature stability and accuracy
in normal air conditioning applications. (For example, a
30GB060 would require 180 gallons in circulation in system
loop — see Table.) For process jobs where accuracy is
vital or for operation at ambient below 32 F (0°C) with low
unit loading conditions, there should be from 6 to 10 gallons