Major Equipment Retrofit Concepts

Owners and operators must first determine whether a retrofit makes more sense than replacement. This involves an evaluation of the facility plans, and the age, efficiency, and general condition of the chiller. Reviewing service, efficiency, and refrigerant-use records will also help. "Stopgap" conversions typically use the existing compressor, cooler and condenser. A typical stopgap conversion might include the following steps:

1. An evaluation of the system's performance and condition, along with a projection of the likely performance after conversion

2. Changing the CFC refrigerant in the system to an acceptable HCFC or HFC alternative

3. Converting the hardware and other components including controls, refrigerant flow devices, and relief valves

4. Recharging, with new refrigerant

5. Recycling, reclaiming or disposing of the old CFC refrigerant

6. Start-up services including operator training.

Converting low-pressure chiller CFC-11 to HCFC-123 requires new seals, O-rings, gaskets, and elastomers. Hermetic motors exposed to the refrigerant may have to be rewound or replaced because HCFC-123 is not compatible with some motor winding insulation. Open-driven chiller motors are not affected because they are not exposed to the refrigerant.

Medium-pressure chiller CFC-12 and R-500 conversions to HFC-134a require a new lubricant because the conventional mineral oils are not compatible with HFC-134a. The system is typically flushed several times to remove all traces of mineral oil and then replaced with the new ester-based oils.

This work should be done by certified technicians only. None of these conversions are "Drop In". They all require significant equipment modifications. Some loss of capacity and efficiency may occur in some conversions. Conversion should be performed by the original equipment supplier if possible, or an experienced service agency following the original manufacturer's explicit recommendations. Realize that some chillers will simply not accommodate conversion. Carefully investigate each situation and make decisions accordingly.

Optimized conversions go one or more steps beyond the stopgap conversion to compensate for any anticipated efficiency and capacity losses. These conversions may include changes to the compressor impeller, gear-set, operating speed, and drive.

Low-pressure refrigerant conversions may involve an impeller change or modifications. Gear set replacement is not uncommon in medium-pressure refrigerant conversion. Conversion results can range anywhere from a moderate loss to a moderate gain in performance capacity and efficiency.

Other conversion issues include upgrading the chiller machinery room to comply with the forced ventilation requirements of ASHRAE Standard 15-94. Mechanical rooms which contain refrigerants such as HCFC-123 require refrigerant monitors. Refrigerants such as HFC-134a require oxygen sensors.

Retrofit costs will vary widely. A rule of thumb is that they will run from 20 to 60 percent of the installed cost of a new chiller.