Often an afterthought, chiller technology can be essential for good operating performance with specific laser types, especially since the units require stable temperatures to achieve a coherent beam and repeatable results. The technology also can be critical for other machining systems in your shop.

Chiller operation is usually simple. Fill its reservoir with the fluid to be recirculated, typically water or an ethylene glycol/water mix. Install plumbing between the chiller and the application and provide power to the chiller. Once the temperature is set on its controller, the unit will provide a stable temperature, flow, and pressure, in addition to keeping harmful particulates out of the system.

Even though equipment is both simple to set up and operate, you must still evaluate a number of factors to ensure its proper performance. For example, the application's heat load (how much heat needs to be removed) will determine both the size of the chiller and the horsepower of the compressor. A laser system's heat' loads can either be found in the operator's manual or through a cal to the machine's vendor.

You can also run a simple experiment, using a thermometer, 5 gallon bucket, and a stopwatch With the process running under normal conditions, measure the temperature of the cooling fluid entering and exiting the equipment. Also, measure the flow rate of the cooling fluid to the application. If you do not have a flow meter available, use the stopwatch to determine how long it takes to fill the bucket. Apply these numbers to this heat load calculator formula:

Heat Load (BTU/hr) - Flow Rate (gallons/hour) x Cooling Fluid Weight (pounds/gallon) x Specific Heat of Cooling Fluid x AF (Temperature Out - Temperature In).

Other key information that you will need includes the required flow rate, pressure, and recirculating temperature for the equipment. If these are not available and your process is working sufficiently with the current source of water, you can use the current flow, pressure, and temperature.

Typically, a chiller's heat removal capability is specified at a certain recirculating temperature, usually 68° F (20° C). Lower its setpoint and its heat removal capability will decrease because the unit must work harder to maintain a lower setpoint. The converse is also true. The higher the recirculating temperature, the more heat removal capability the chiller will have. The chiller manufacturer should be able to tell you what the cooling capacity is at a specific recirculating temperature.

Once you've defined the base chiller requirements, there are several configurations and options to choose from. A chiller can reject the heat into the ambient air (air-cooled condenser) or into a secondary water source (water-cooled condenser). Air-cooled condensers are standalone units that only require plumbing and a source of power. The disadvantages are that they can be loud and the waste heat is rejected into the surrounding air. If the chiller is to be placed in a plant type setting, though, this is usually the best choice as there is plenty of room around the chiller for heat rejection, and noise should not be as much of a problem.

If the chiller is to be placed in a small room, though, you may need a water-cooled condenser. This type of unit is quieter (no large fans needed) and gives off only a small amount of heat since the waste heat is removed by a secondary source of water-city, tower, well or building chilled water recirculating through the chiller. If this is city water, it will be dumped down the drain. If the reason for using a chiller is to stop using city water, this does defeat the purpose.

Once your base chiller needs have been established, you can further customize the equipment. Fluid safeties or interlocks can be added to alarm or shut off the chiller if the recirculating temperature goes out of range, the fluid in the reservoir gets too low, or the flow to your equipment stops due to a blockage. Also, chillers can be connected to process controllers or computers using RS232 or RS485 interfaces.

(As seen in Industrial Laser Solutions May 2000)