Fan Cycling Head Pressure Controls
Condenser fans are cycled to maintain adequate head pressure. . Ambient and pressure fan cycling are available as optional equipment...
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Ambient fan cycling cycles fans in response to the ambient air temperature. .This control is ideal for
3 for minimum ambient temperatures for fan cycling. .Set points for thermostats will vary depending on the number of fans and condenser design T..D. .See table 4 for recommended set points...
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Pressure fan cycling cycles fans in response to condenser pressure. .This style of control is more appropriate where the load on the condenser will vary due to multiple compressor operation or stages of unloading or systems incorporating heat reclaim or hot gas defrost..
Flooding Head Pressure Controls
Another means of head pressure control is to change the condenser capacity by filling the inside of the condenser with liquid refrigerant. .Flooding controls are ideal for condensers operating in low ambient conditions (beyond the limits of fan cycling controls) or under partial load conditions. .These controls require additional refrigerant charge to flood the condenser. . This additional refrigerant charge can often be reduced by incorporating the flooded control with one of the fan cycle controls previously described...
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Several styles of flooding valves or combinations of valves are available. .Contact the valve manufacturer for specific recommendations..
Variable Speed
Condenser head pressure control is provided by varying the air flow through the condenser by changing the RPM of the condenser fan. .This control package is offered in combination with ambient fan cycling. .The fan motor next to the header end of the condenser is the variable speed fan...
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The remainder of the fans are constant speed and are cycled separately using ambient sensing thermostats. .On condensers with two rows of fans, two variable speed fans are provided (one per unit) and the remainder of the fans are constant speed and are cycled in pairs..
Refrigerant Charge
The refrigerant charge for summer operation can be found in table 8. .This table also contains the additional charge required by flooding style controls...
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Table 7 contains the recommended flooding charge required when combining fan cycling with flooding valves..
Splitting Controls
Additional head pressure can be provided by valving off a portion of the condenser circuit and removing that portion from the refrigeration circuit. .This is often referred to as splitting a condenser. .In addition to providing a means of head pressure control, this control will reduce the amount of refrigerant required to operate the condenser with a flooded head pressure control...
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Condenser splitting is recommended as a seasonal adjustment controlled by ambient temperature. .An initial setting of 50° to 55° F with a 20° F differential is recommended. .A pressure switch is also provided as a backup control to prevent high head pressures
from occurring during heavy load conditions...
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On condensers with a single row of fans the control package consists of an ambient sensing thermostat, a pressure switch sensing condensing pressure and a splitting relay. .The splitting relay provides a set of dry contacts to control the valves required to split the condenser (valves supplied by others)...
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On condensers with double rows of fans, additional controls and contactors are provided to cycle all of the fans on the side of the condenser which has been split off...
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Except as noted above, the splitting packages do not control fan cycling. .It is recommended that fan cycling be controlled by combining the splitting package with pressure fan cycling..
