Air-cooled Condensing Units

September 4, 2006
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When installing walk-in coolers and freezers, the installing contractor will need to select the proper location of the condensing unit. Location is an important consideration for the overall success of the installation. There are several items to consider when selecting the location.

First, the location should be discussed with the customer. Be sure the customer is in agreement with the placement of the condensing unit. The customer may have a plan for the location different from where the installing contractor decides to place the unit. As retail space becomes more expensive, customers will want to take advantage of all their indoor space and may want the condensing unit located outdoors or in an indoor location that will not interfere with their operation.

If the condensing unit is to be placed indoors, make sure the location has adequate ventilation. Low-temperature condensing units will require approximately 200 cubic feet per minute (cfm) per 1,000 Btu, and medium-temperature units will require approximately 165 cfm per 1,000 Btu. Always check with the condensing unit manufacturer for ventilation requirements, as they may differ from these approximate values. Another consideration with air-cooled units located indoors is the heat they may add to the space. This additional heat may be objectionable to the equipment owner.

OUTDOOR CONSIDERATIONS

An alternative to locating the condensing unit indoors is to place it outdoors. When installed outdoors there are several components that should be added with the condensing unit. Some of these components may be ordered as installed options.

The condensing unit should have a crankcase heater installed. This will help to prevent refrigerant migration during the off-cycle when the condensing unit is exposed to temperatures that are colder than the evaporator. The condensing unit will also need some means of keeping the high side pressure above a minimum value during low outdoor temperatures. This is normally accomplished with either a fan-cycling control or a head-pressure controller.

The method of controlling the case temperature may also need to be modified. The system should use a pumpdown method to control the operation of the condensing unit. A standard air-sensing temperature controller should be used to control the operation of a liquid line solenoid. When the temperature controller is satisfied, it will close the liquid line solenoid, causing the refrigerant to be trapped in the condenser and receiver.

This will cause the low-side pressure to drop. The system's low-pressure control will then shut down the condensing unit as the low side pressure drops to an appropriate value. A defrost timer will also need to be added to the control system to ensure that the evaporator defrosts properly.

The outdoor unit should be covered to protect it from the outdoor environment. If the condensing unit is ordered for an outdoor application, it will normally come with some type of enclosure. When moving an indoor condensing unit to the outdoors, make sure an adequate enclosure is constructed to properly protect the unit.

One last consideration when installing either an indoor or outdoor condensing unit is to make sure the system can be easily serviced. Too often, service technicians encounter systems in which the condensing unit is located in an area where it is extremely difficult to access. Also, make sure there is an electrical disconnect available to shut off the electrical supply when needed.

Publication date: 09/04/2006

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