Handbook of air conditioning and refrigeration / Shan K

Selection and Installation
REFRIGERATION SYSTEMS: COMPONENTS 10.33
The evaporative condenser should be located as near to the compressor as possible. If it is located at
a distance from the compressor, the discharge refrigerant pipe should be selected to have a pressure
drop of 2°F (1.1°C) of saturated temperature difference of the refrigerant between the compressor
and the condenser.
If an evaporative condenser is located outdoors and will be operated during winter, its water
basin and pump can be located indoors in a heated space. A water heater can be installed in the
water basin, and the water should be drained back to the water basin as soon as the pump ceases to
operate, to prevent freezing.
To prevent the condensing pressure from falling below a certain value at which the expansion
valve or other system components are difficult to operate, the capacity of the evaporative condenser
is reduced by means of fan cycling, dampers, and fan speed modulation at low ambient temperatures,
as in air-cooled condensers.
The procedure for selecting and installing an evaporative condenser is as follows:
1. Before selecting an evaporative condenser, calculate the total heat rejection of the refrigerating
system Qrej, MBtu/h (kW).
2. According to the refrigerant used in the system, select the appropriate material for the condenser
coil. Copper tubes should be used for halocarbon refrigerants, and stainless steel or galvanized
steel should be used for ammonia.
3. Select a condenser coil that can provide a lower condensing temperature—below 95°F (35°C),
if possible. This will save a lot of energy and reduce scale accumulation on the outer surface of
the condenser coil significantly compared with Tcon � 100 or 105°F (37.8 or 40.6°C).
4. Based on the location of the evaporative condenser and the sound control requirement, it is often
best to select a centrifugal fan. Check the volume flow rate and the fan total pressure that can be
provided by the fan to overcome the pressure drop of the condenser coil and eliminator or air
duct, if any.
5. Check the flow rate of the water spray of the circulating pump.
6. For outdoor installation, select a casing and other system components that are weatherproof and
corrosion-resistant.
7. Install the evaporative condenser in a location where there is ample space for outdoor air intake
and discharge. The influence of nearby exhaust systems should be avoided.
Evaporative condensers have the advantage of lower condensing temperature and lower installation
and energy costs. They are widely used in industrial applications and have been adopted more
and more frequently in commercial buildings recently. The following reasons may explain why they
were not previously popular in commercial and institutional applications:
● Monthly maintenance, inspection, and cleaning are required to prevent buildup of scale on the
condenser coil.
● Water basin and water spraying system must be regularly inspected and cleaned to prevent the
growth of Legionella bacteria and other microbiological growth. Water treatments with chemicals
are often required. Mazurkiewicz (1996) reported that between the end of September and the beginning
of October, 1996, there was a recent outbreak of Legionnaires’ disease in a food market’s
evaporative condenser, in Farmington, Michigan.
● Designers and operators have less experience with evaporative condensers.
● Heat rejected from the evaporative condenser is more difficult to use in winter heating for energy
conservation than that from a water-cooled condenser.