Handbook of air conditioning and refrigeration / Shan K

(5.6 to 6.7°C) in temperature difference between condensing and evaporating temperature is
roughly 10 to 15 percent more power input to the compressor.
Second, during occupied heating mode at part-load operation, to maintain a preset T ret and let
T sup float results in a lower mean condenser water temperature T m,con; instead maintain a preset T sup
and let T ret float. A lower mean T m,con reduces the power input to the compressor.
Third, to be more energy-efficient, T cl should be reduced in part-load operation during winter
heating. Condenser water entering temperature T ce should be adjusted to provide an optimum hot
water supply temperature T cl at part-load operation.
Fourth, an air economizer reduces the heat recovery effect. This result is due to the reduction of
the refrigeration load, which also reduces the heat recovery from condensing heat.
Finally, for the same building with equal areas of conditioned space, the heating load is smaller
than the cooling load in many locations in the United States. For a refrigeration plant with multiple
centrifugal chillers, usually only some of them include heat recovery. The remainder are coolingonly
centrifugal chillers, which are more efficient.
13.4 AUTOMATIC BRUSH CLEANING FOR CONDENSERS
Principles and Operation
REFRIGERATION SYSTEMS: CENTRIFUGAL 13.13
The condenser water from the cooling tower is usually in an open-circuit system. As described in
Sec. 10.3, although many well-maintained cooling towers may have a long-term fouling factor for
condenser tube surfaces of 0.00025 h�ft 2 �°F/Btu (0.000044 m 2 �°C/W), the fouling factor for condenser
tubes may exceed 0.0005 h�ft 2 �°F/Btu (0.000088 m 2 �°C/W) when a significant amount of
suspended solids is contained in the condenser water. High fouling factors result in a high
condensing pressure and higher kW/ton. ARI Standard 550-88 specifies a field fouling allowance
of 0.00025 h�ft 2 �°F/Btu (0.000044 m 2 �°C/W) for condensers.
The purpose of an automatic brush cleaning system is to remove deposits and dirt from the
water-side tube surface of a condenser for which the fouling factor of the condenser tubes is higher
than 0.00025 h�ft 2 �°F/Btu (0.000044 m 2 �°C/W). Cleaning brushes in a condenser tube of a horizontal,
two-pass, and shell-and-tube condensers are illustrated in Fig. 13.7. Special nylon brushes
are inserted inside the tube, and catch baskets are attached to each end of the tube.
When condenser water flows through the condenser tubes, the difference in the pressure across
the brush, approximately 1 psi, causes the brush to move in the direction of water flow. As the
brushes in the condenser move, they remove deposit from the inner tube surfaces. The deposits are
carried away by the condenser water. The brushes are then caught by the baskets at one end. The
time taken for the brushes to travel the whole length of the tube is about 1 to 2 min.
FIGURE 13.7 Cleaning brushes in a condenser tube. (Source: Water Services of America. Reprinted with
permission.)