How to ensure you don't spring a refrigerant leak
Julius Banks of the EPA reported that the goals of the agency’s National Recycling and Emissions Reduction Program include extending recycling and emissions reduction to HFCs and PFCs, and maximizing the effectiveness of the program for CFCs and HCFCs.
Hydrocarbons, ammonia, and chlorine are not part of the EPA program. “They’re already regulated by some other federal agency,” said Banks.
There are four options for defining leak rate:
1. Annualizing method;
2. Rolling average;
3. Choice of annualizing or rolling average; and
4. Stricter use of annualizing or rolling average.
Banks said the EPA “wants to force owners and operators to repair leaks in under one year.”
The agency has a refrigeration leak repair trigger rate of 35% currently. It would like to change that to 10% for new appliances since 1993, and to 15% for older appliances.
The comfort cooling trigger rate is presently 15%. The agency is looking at changing it to 5% for new appliances since 1993, and to 10% for older appliances.
Industrial process refrigeration will have its rate remain at 35% if it meets certain requirements.
Upcoming in 2000, the EPA will address refillable cylinder evacuation requirements for disposable cylinders. Also, the Substitutes Rule will be published by next winter.
Banks stressed that recordkeeping requirements will not become more stringent.
Make mine hermeticDermott Crombie of Thermo King Corp. then talked about hermetic transport refrigeration systems for marine transport.
In this application, “The big issue is reliability,” Crombie noted. Reefer boxes are mounted up on deck and are subjected to wide climate changes and salt water.
To make the system hermetic for marine transport, the compressor first is replaced with a hermetic compressor. A temperature sensor is used to monitor compressor discharge temperature and a right-angle tube is used for flanges and valves.
The expansion valve is non-adjustable so it can’t be changed to compensate for some other problem. A pair of process tubes are employed to evacuate and charge.
Crombie said that this hermetic system is now a standard product.
Glen Williams of Hill-Phoenix took on the subject of secondary coolant systems for refrigeration in supermarkets.
A supermarket normally uses direct expansion parallel racks. This involves thousands of feet of pipe, hundreds of devices, and thousands of braze joints, pointed out Williams. “This means tremendous potential for leakage.”
And since leaks aren’t detected very well, the amount of refrigerant lost can be substantial.
Efforts to reduce leakage include tighter regulations, tighter control, and better design. One alternative, said Williams, is a secondary cooling system.
Putting a secondary cooling system out in the store, while keeping all refrigerant in the mechanical room, “dramatically reduces the amount of refrigerant used,” Williams stated. It takes “85 to 90 percent less refrigerant.”
Secondary coolants include water, brine, and glycols. The coolant is chilled through a heat exchanger by the primary refrigeration circuit.
Initial secondary cooling systems cost more and use more energy, admitted Williams. But design improvements are being made.
“We see secondary coolants as the wave of the future,” he concluded.
Maintaining integrityPractical suggestions to reduce emissions were provided by Dennis Dorman of The Trane Company. He observed that manufacturers “used to think about design leak rates.” He asserted they need to think about product integrity to reduce leaks.
Passing along some lessons learned regarding product integrity, Dorman noted:
- Good designs eliminate 50% of joints.
- There’s a poor understanding of the shipping and handling environment, and the problems it introduces.
- Testing and analysis methods are poorly developed.
- Leaking hoses and fittings are a problem.
- Brazing is robust but extremely inconsistent.
- Rolled tube joints are robust, but threaded and flare joints are not robust.
- Teardowns due to gasket leaks are common.
- O-rings work well in the factory, but not in the field. (Compressive force is lost over time.)
- Flat gaskets work well in the field, but not in the factory. (Debris is a problem.)
He also noted that “bolted joints are not that easy.” For a bolted joint, tension is the key, not torque, to achieve proper clamping. Dorman recommended using a bolt rotation method to ensure the correct tension.
Denis Clodic of Armines Centre D’Energetique discussed advances in leak measurement techniques. Among his conclusions he stated that continuous measurement of refrigerant concentration permits calculation of reliable leak flow rates. He also emphasized that testing needs to be performed in real operating conditions.