Many industrial processes in a variety of industries require cooling water in order for their equipment to achieve optimal performance.  These may include Automotive, Chemical, Pharmaceutical, Food, Paper and general manufacturing companies.  Cooling water needs may vary from very stable temperature and flow requirements for lasers to “just keep any kind of water flowing to my application” as is commonly the need for hydraulic fluid cooling.  Whatever cooling water your application requires there are occasions where your work may benefit from the use of a chiller.

There are a number of water sources typically available in a plant or industrial facility.  These include city water, well water, tower water, or building chilled water.  Each of these has its advantages and disadvantages.  City water is expensive.  You not only pay for the water itself but in most municipalities, you must pay a sewer charge also.  This can sometimes be more than the cost of water itself. But, the advantage of city water is it is easily obtainable.  Most plants have it and if it works for the process, great.

In addition to city water, well, tower, and building chilled water temperature, flow, and pressure can fluctuate greatly depending on the season and amount of use at one time.  Also, this water may contain harmful particulates that can damage certain types of equipment.  Lasers require stable temperatures to achieve a coherent beam and repeatable results.  Welder tip life can be extended greatly if water temperatures are kept below 70° F (21°C).  Machine tool spindles can have better results if the spindle is kept at a constant temperature and not allowed to heat up which will cause it to expand in size.  The result will be parts not uniform in size.

Building chilled water systems provide an excellent cold water source but also suffer from some of the same problems noted above.  Another potential issue with a building chilled water system is condensation.  Temperatures can typically range down to 45° F and can cause condensation on plumbing parts.  Damage to your equipment can occur if this condensation comes in contact with any electrical components.  

Some processes may not require cooling water but may benefit from its usage.  One example is hydraulic fluid drawn from a large tank.  The tank acts as a heat sink allowing the warm returning fluid to cool down using ambient air.  In some processes, the return temperature of the hydraulic fluid can be too great for the storage tank to cool sufficiently.

The solution to the above problems can be a refrigerated recirculating chiller.  A chiller is a compressor based cooling system that is similar to an air conditioner except it cools and temperature controls a fluid instead of air.  Also included in a chiller is a temperature controller and a recirculating pump.  Operation and setup is simple.  Fill the 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 the chiller’s controller, the chiller will provide a stable temperature, flow, and pressure as well as keep harmful particulates out of the system due to the fluid path being a closed loop.

Choosing which chiller is appropriate is simple but there are a number of factors which must be kept in mind in order to ensure proper performance.  The first thing you must know is how much heat needs to be removed from your application.  This is also known as the heat load.  This will determine the size of the chiller and the horsepower of the compressor.  Heat loads are typically stated in watts, BTU per hour, or tons.  Any of these are sufficient.  If you do not know your heat load, look in the operator’s manual or call the manufacturer of your equipment.  Most laser, machine tool, packaging equipment, and welder manufacturers have this information.  

If the information is not available, there is a method of calculating the heat load.  You will need a thermometer, a 5 gallon bucket, and a stop watch.  With your process running under normal conditions, measure the temperature of the cooling fluid entering and exiting your equipment.  Also, measure the flow rate of the cooling fluid to your application.  If you do not have a flow meter available, use the stop watch to determine how long it takes to fill the 5 gallon bucket.  Now, with this temperature difference and flow rate, you can apply these numbers to the heat load calculation formula in Chart 1.

Other information you will need from the equipment manufacturer or operator’s manual is the required flow rate, pressure, and recirculating temperature for the equipment.  If this is not available and your process is working sufficiently with the current source of water, you can use this flow, pressure, and temperature.  Now, you are ready to look at different manufacturers’ chillers.  Typically, a chiller’s heat removal capability is specified at a certain recirculating temperature, typically 68° F (20°C).  As you lower the setpoint of a chiller its heat removal capability will decrease because it has to 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.   

Now that the base chiller has been defined there are a number of configurations and options available depending on your specific requirements.  A chiller must rid itself of the waste heat it has removed from your application.  It can reject the heat into the ambient air (air cooled condenser) or into a secondary water source (water cooled condenser).  Air cooled condensers are advantageous because they are stand alone units that only require plumbing and source of power to operate.  The disadvantages are that they can be loud and the waste heat is rejected into the surrounding air.  This can cause worker discomfort or tax an air conditioning system.  If the chiller is to be placed in a plant type setting, this is usually the best choice as there is plenty of room around the chiller for heat rejection and noise should not be a problem due to surrounding equipment in operation.  

If the chiller is to be placed in a small room, a water cooled condenser may be a better choice.  Water cooled units are much quieter (no large fans needed) and they reject only a small amount of heat since the waste heat is removed by a secondary source of water recirculating through the chiller.  This can be city, tower, well or building chilled water.  The disadvantage is that you must use a secondary source of water to remove waste heat.  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.  

If you cannot use an air cooled chiller because of the noise and waste heat and cannot use a water cooled chiller due to a lack of secondary water availability or cost, there are two more options: a remote condenser (split system) or an outdoor unit.  In a remote condenser, the portion of the chiller that creates all of the noise and waste heat is placed in a separate unit which can be located in another area in the plant or outdoors.  Remote condensers are more expensive than a self contained chiller, however, and require an HVAC person for installation.  Outdoor units are another excellent method of keeping waste heat and noise away from plant workers.  Once again, these units are more expensive than a self contained chiller and in colder climates, require a non freezing fluid for circulation.    

Once your base chiller needs have been established there are a number of options which can further customize the chiller to meet your needs.  Fluid safeties or interlocks can be added to alarm or shut the chiller off should the recirculating temperature go out of range, the fluid in the reservoir get too low, or the flow to your equipment stop due to a blockage.  Also, chillers can be connected to process controllers or computers using RS232 or RS485 interfaces.  Another useful feature is a remote control box.  These are especially useful when using an outdoor chiller.  All of the chiller’s functions can be controlled indoors at your desk or at the equipment.

Overall, a chiller is the perfect replacement for city, tower, well, or building chilled water where tighter temperature, flow, and pressure control is essential.  Also, a chiller can typically pay for itself in less than a year when used to replace city water.  Check with your municipality for water and sewer costs to calculate the pay back time of a recirculating chiller.

Flow Rate (gallons/hour) x Cooling Fluid Weight (pounds/gallon) x Specific Heat of Cooling Fluid x  DT ° F (Temperature Out – Temperature In) = Heat Load (BTU/hr)

Notes:

Weight of water/gallon = 8.35 pounds/gallon 

Specific heat of water = 1 

12,000 BTU/hr = 1 ton

1 watt = 3.41 BTU/hr

(As seen in Process Cooling, June 1999)