Once-Through Cooling Equipment
Once-through cooling systems, also known as single-pass cooling systems, are expensive and waste large amounts of fresh drinking water. These systems remove heat by transferring it to a supply of clean, cold municipal drinking water that runs through the unit, and then by discharging the used water directly to the sewer. Equipment that may use OTC includes commercial and industrial air conditioners, refrigerators, coolers and ice machines.
Once-through cooling systems are often used for small commercial cooling loads because they are relatively inexpensive to install and require less maintenance. However, the cost of water to operate a small OTC system for two years is usually greater than the cost of installing an air cooled system that uses no water. For a 12,000 BTU/hour (or one ton, roughly equivalent to one horsepower) condensing unit, OTC systems millions of litres of water per year. A typical restaurant using several units can send thousands of dollars’ worth of clean water down the drain each year.
Options for replacing an OTC system include:
- Air-cooled equipment - install stand-alone air-cooled ice machines and condensing units
- Closed-loop piping - re-circulate cooling water to a remote air-cooled chiller or cooling tower, or connect to an existing closed-loop system serving another area of the building
- Split-system - use heat pumps with remote air-cooled condensers
Payback on Replacements
The actual cost to eliminate OTC in a facility can vary widely depending on numbers, sizes, and type of OTC systems currently operating, and conditions that may prevent or complicate direct replacement with equivalent air-cooled systems. Typical payback periods for small commercial systems are as low as two years.
Based on many retrofits that have been completed in recent years in Greater Victoria and Greater Vancouver, retrofit costs and utility cost savings are typically in the ranges shown in this Restaurant OTC Retrofit Fact Sheet. If you would like an estimated payback period for replacing the water cooled equipment, as well as realizing other potential savings for your business, please contact us at 250.360.3103.
How to identify OTC
Any refrigeration system may be positively identified as OTC where it has a coaxial tube condensing coil connected to a domestic cold water supply and a drain (for any appliance with an enclosed refrigeration system that does not otherwise require a water supply or drain connection). However, air-cooled ice makers with self-contained refrigeration systems do require a water supply and drain connection for the ice production process, and are therefore difficult to distinguish from water cooled ice makers. One simple tip is that if the ice maker is Energy Star approved, it is air-cooled. Stay tuned for more details on how to identify OTC.
OTC Best Practices
If you’ve identified OTC equipment in your business but cannot replace or retrofit the equipment, follow these tips to minimize water use:
- Install solenoid valves that shut off cooling water when the equipment is turned off.
- Regularly inspect exiting solenoid or water control valves to ensure water is only flowing when there is a heat load to be removed. Improperly functioning valves can cost thousands of dollars per year in wasted water.
- Use the minimum flow rate required to cool the system recommended by the manufacturer.
- Insulate the piping, chilller and storage tanks for maximum efficiency.
- Keep coil loops clean to maximize heat exchange.
- Consider reusing cooling water to preheat water for other applications.