Scroll compressor technology reduces energy consumption and increases the reliability of air-cooled and water-cooled chillers.
As with all chillers, air-cooled chillers require cooling - the term 'air-cooled' simply refers to how the chiller dissipates heat. Air-cooled chillers transfer heat from one medium to another by using the surrounding air to cool a heat exchanger from the finned tube refrigerant to the air. For example, consider a plastic injection moulding machine. The hot plastic in the mould transfers heat to the process water. The process water then transfers the heat to the refrigerant, which distributes the heat to the surrounding air.
The design of air-cooled chillers varies depending on where the equipment is used. Some chillers are designed for outdoor or indoor applications. Other air-cooled designs, called split systems, allow the cooling part of the unit to be installed indoors and the hot air discharge part or condenser to be installed outdoors.
When considering your options, remember that air-cooled chillers generate more heat than they absorb. The total heat discharge is equal to the heat discharge rating of the chiller plus the electrical input of the compressor. If you are using an air-cooled chiller indoors, the room in which the chiller is installed must be well ventilated, have adequate operating space and a consistent ambient temperature of 65 to 95°F (18 to 35°C). If the room in which the chiller is to be installed is poorly ventilated, has limited operating space or is air-conditioned, the chiller should be installed outdoors or in a split system. Installing the cooling section indoors and the condenser outdoors has several advantages over installing the entire chiller outdoors. They include.
Air Cooled Scroll Chiller
Smaller space requirements. Without the air-cooled section, the chiller's footprint is much smaller.
Lower service costs. By placing the cooling section indoors, the unit is much easier to service.
Lower operating costs. Split systems installed in northern climates do not require antifreeze if the process water temperature is above 48°F (9°C).
Air-cooled chillers can operate all year round in all climates.
For any chiller application, understand the operating limitations of the chiller. Process cooling chillers must be able to operate at temperatures of -20°F (-29°C) in northern climates and 0°F (-18°C) in southern climates. These design constraints distinguish HVAC units from process cooling chillers: HVAC chillers do not normally operate at temperatures below 32°F (0°C), whereas process cooling chillers are expected to operate at a variety of temperatures throughout the year.
Process cooling coolers are provided with a separate baffled air section with horizontally mounted coils to prevent cold air from blowing through the unit. This design prevents air from being drawn through the fan which has been cycled off and helps to maintain a consistent cooling pressure. For temperatures below 0°F, this design will also regulate the speed of the last fan motor based on refrigerant pressure. This allows the chiller to operate at temperatures below 0°F.
Air Cooled Screw Chiller
When choosing an outdoor air-cooled chiller, look for a design that is less prone to refrigerant leakage. Refrigerant leaks are the main cause of chiller shutdowns. Air-cooled heat exchangers use copper tubes which are mechanically expanded into aluminium fins and tube plates. Often, leaks form in the tube plates that support the weight of the heat exchanger. A design was sought that would not expand the refrigeration tubes into the tube plates. This design uses a blind tube or non-refrigerant tube to support it through the tube plate. The copper tube circulating the refrigerant passes through a hole in the tube plate that is larger than the tube, thus eliminating any chance of wear caused by vibration.
Remember that the compressor or the pump that delivers and compresses the refrigerant is the heart of the chiller. Chillers that use rotary technology compressors have a lower probability of failure. These rotary technology units are called scroll or screw compressors and have no connecting rods, pistons or valves. Screw compressors are used above 40 hp, while scroll compressors are used below 30 hp.
When buying any type of equipment, being informed is key. These tips on indoor and outdoor air-cooled chillers will help ensure that the next air-cooled chiller you buy will be the right chiller for your situation.