ACHRNEWS

Money leaking from the mechanical room: A practical guide to addressing chiller leaks

January 25, 1999
The U.S. Environmental Protection Agency published a proposed rule in Fall 1997 to reduce the emission limits for chillers and industrial process refrigerant equipment. This rule may become law under the U.S. Clean Air Act (CAA).

The ruling will reduce allowable emission rates from 5% to 15%, depending on the application (see Table 1).

There will be discussion on how to define new vs. existing chiller leak rates, and how to distinguish between leaks during system operation and repair.

This ruling refocuses the industry’s efforts on containment practices and improving refrigeration chiller designs for the future.

As demonstrated in Table 2, leak rates in the industry have dramatically improved in new designs.

In the past, leaking chillers were tolerated due to readily available supply and cost.

Today, if a refrigerant charge is lost, the cost can be substantial (see Table 3).

For example, a typical 500-ton CFC chiller that becomes overpressurized due to a system malfunction could result in a $29,000 R-12 replacement expense. Unlike the past, that incident could also cost building owners and managers downtime on a process, or downtime for the building itself — a cost that certainly would exceed the refrigerant cost.

This is money leaking from the mechanical room.

Also, under the Clean Air Act, if a leak occurs, building owners and managers have 30 days to correct the leak or develop a dated retrofit-retirement plan, and complete all actions detailed in the plan within one year from the plan date. Beyond that, if detected, they can be fined $25,000 per day per incident under the Clean Air Act regulations.

Not only is this costly, but embarrassing, as EPA has released examples of violations to the press.

What Actions Should Facility Owners Take?

Referring back to Table 2, leak rates can be reduced to 0.5% to 2% on new equipment. On older installed equipment, reducing the leak rates to 2% to 5% is possible with close attention to proper “containment.”

With a negative-pressure chiller (old CFC-11 or newer HCFC-123 chillers), as noted in Table 2, the leak rates historically have been high. Although these chillers operate below atmospheric pressure on the cooler side of the unit, they are operating well above atmospheric pressure in the condenser and compressor.

This results in a critical leak path of sucking air and moisture into the cooler, which adds to corrosion and loss of refrigerant from the condenser and compressor.

Why do manufacturers of these chillers allow a design of this type? Simply stated, the customer did not want to pay for upgraded containment in the past. For example, these negative-pressure chillers were supplied to the market with standard purge units to purge out the air and moisture that leaked into the cooler.

However, on these standard units, for every 1 lb of non-condensables (air and/or moisture) that was purged, between 3 to 20 lb of refrigerant were exhausted.

Today, very high-efficiency purge systems that significantly lower this emission, along with improved containment equipment (see Table 4), are available. Remote refrigerant storage tanks are available for serving negative-pressure chillers, as the construction of negative-pressure chillers does not allow for internal storage during service.

A special notation should be made that external storage and transfer pump units are required by the U.S. Clean Air Act during service. These storage and transfer units must meet the requirements of the U.S. Clean Air Act for evacuation levels in removing refrigerant, and also must comply with standard ARI-740 as a recycle-reclaim device.

Does this law require that an owner of equipment must purchase a storage-transfer unit? No. However, the agency servicing the chiller must supply certified equipment during the service.

It is highly recommended that if the chiller is larger than 300 tons of refrigeration, that the owner purchase a storage tank. Forcing a service agency to bring smaller, multiple tanks on-site to store the refrigerant results in increased risk of emissions during transfer, and increases the potential for a refrigerant spill.

Also, at that nominal level and above the refrigerant charge (approximately 720 lb), removal may result in a long transfer period and an increase in potential leaks.

More Accessories

Back-up relief valves are excellent devices that prevent the loss of refrigerant in a chiller.

The standard pressure-relief device on a negative-pressure CFC-11 or HCFC-123 chiller is a carbon disk with a 0.03-in. membrane, which shatters at 15 psig. Any overpressurization results in total loss of the refrigerant.

Back-up relief valves have been created to lower this loss during overpressurization. These back-up devices contain non-fragmenting disks with a reseating plunger that will relieve the pressure and then reseat. This saves a good portion of the refrigerant that was lost. These devices typically cost $3,800, which may vary with installation costs.

When you consider that a total loss of CFC-11 or HCFC-123 on a 500-ton chiller could result in a refrigerant bill of $5,028 (HCFC-123) to $16,836 (CFC-11), the $3,800 back-up valve is a good investment, especially when you consider the potential cost of chiller downtime.

Two other good containment products on the market are pressurizing systems and oil filter-isolation valves.

Pressurizing systems facilitate leak detection on negative-pressure chillers, to ensure the chiller remains below the leak rate requirements of the CAA. Isolation valves allow oil filters to be changed while isolating the main oil circuit, which typically has a considerable amount of entrapped refrigerant.

Piping all of the mentioned containment devices typically will cost an additional $3,000, for a total of $24,700.

This add-on containment is recommended when upgrading or purchasing new negative-pressure chillers. The added cost and installation was considered during the design of the new chillers using HCFC-22 or HFC-134a and, as can be noted in Table 4, was eliminated or built into these chillers.

A key feature of these positive-pressure certified-vessel chillers is the ability to charge the refrigerant into the equipment at the factory and ship them to the construction site. This greatly reduces the emissions, start-up time, and incidents of accidents that could result when charging a chiller on-site.

Also, with the use of isolation valves built into the chiller, refrigerant can be stored in the chiller during service. With best-in-class 0.1% annual leak rates and the ability to store refrigerant in the chiller, the equipment results in an emission-preventable design.

The compressor motor type should be considered in lowering emissions of refrigerants. The industry offers semi-hermetic sealed motors up through 2,000 tons of refrigeration. Above that level, the horsepower requirements dictate that open-drive or separate coupled motors are used. Where the semi-hermetic (hermetically sealed, but serviceable) prevent the loss of refrigerant, open-drive motors will lose approximately 2% of the chiller’s full charge annually.

As refrigerant and oil mix during the chiller operation, any loss of oil results in the loss of refrigerant entrapped in the oil.

On existing open-drive equipment, the placement of a refrigerant detection monitor close to the open-drive seal is an excellent method to indicate both the excessive loss of refrigerant, and as a warning that the seal between the motor and the compressor may have excessive wear and is in need of replacement.

This loss of refrigerant is addressed in ASHRAE Guideline 3-1996, “Shaft Seals are Required on Open Style Compressors and can be a Source of Refrigerant Leakage.” This standard is an excellent reference guide in reducing emissions in air conditioning equipment. Written by a committee of industry experts, the practices addressed in this guideline are the standard to reduce refrigerant emissions.

Stemming The Flow

The money leaking from the mechanical room is not only the loss of the expensive refrigerant, but also the loss of efficiency of the chiller.

In the use of negative-pressure chillers (CFC-11, HCFC-123 designs), this loss of efficiency is a result of the refrigerant leaks, both internally and externally. Negative-pressure chillers have a potential leak path that draws non-condensable air and moisture into the cooler section of the chiller.

For every 1 psi of air that leaks into a negative chiller, a 3% loss of efficiency occurs. As air is a non-condensable product in the chiller, the air will collect in the upper portion of the chiller’s condenser and reduce the effect of the heat exchanger — all the more reason to have a high-efficiency purge to remove these non-condensables.

Loss of refrigerant through condensers and compressors that operate above atmospheric pressure for all chiller equipment (CFC-11, HCFC-123, CFC-12, HFC-134a) can result in a shortage of refrigerant to provide the proper heat transfer in both the cooler and condenser as the optimum refrigerant charge is lowered.

Also, in negative-pressure chillers, the air and moisture leaking into the chiller can combine to produce oil foaming in the cooler, due to both the leaks and the migration of oil from the compressor during part-load capacity. This foaming of oil can result in an 8% loss in cooler efficiency as the foaming blankets the upper heat-transfer portion of the cooler.

When you consider that a negative-pressure chiller is purchased at a specific efficiency level and then can degrade by as much as 12% due to system leaks, prevention of these leaks will lower your power bill. A review of your refrigeration chiller equipment should be addressed.

The importance of leak prevention and specification of advanced designs is critical to ensuring that money is not leaking from the mechanical room.

Jim Parsnow is director of environmental systems marketing for Carrier Corp., and can be contacted at 315-433-4376; 315-432-7836 (fax); jim.pars now@carrier.utc.com (e-mail).