Page 347 - HVAC Pump Handbook

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Open Cooling Tower Pumps

344 Pumps for Open HVAC Cooling Systems

Figure 11.9 Tanden arrangement for free cooling.

outdoor temperatures of 55°F or less. Valves V and V modulate the
1 2
water through the heat exchanger when the condenser water supply
temperature is less than the temperature of the return chilled water
from the chilled water system. If the condenser water is too cold for the
chiller, it can be modulated by valve V , which is controlled by the refrig-
3
erant head pressure in the chiller.
Free cooling and heat recovery have become important subjects in
the HVAC industry. Chapter 32 provides information on advanced
heat recovery and proven methods of reclaiming part of the great
amount of heat discharged by cooling towers.
Refrigerant migration. Another method of free cooling is by refrigerant
migration, which is used on larger chillers when they are shut down.
Valves are opened on these machines that allow refrigerant vapor to
pass from the evaporator to the condenser and liquid refrigerant to
flow from the condenser to the evaporator. This process requires fairly
cold water from the cooling tower, below 50°F. With this type of free
cooling, there is no effect on the condenser pump performance.

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