New scroll systems help lower refrigerant charges

July 12, 2000
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Reducing the refrigerant charge in supermarket systems has always been a goal of the supermarket refrigeration engineer. Less refrigerant means lower costs.

Tyler’s patented “Enviroguard” parallel refrigerant control system requires less refrigerant during start up, cuts refrigerant leaks, saves compressor energy, and provides subcooled liquid to improve evaporator coil efficiency.

The Enviroguard parallel refrigerant control systems are piped similar to conventional parallel systems with the exception of a mechanical SPR (system pressure regulating valve) on Enviroguard and a standard solenoid valve with an electronic I/O board on “Enviroguard II.”

In the mid-1990s, Tyler customers were requesting a refrigeration system that had simple technology to help reduce refrigerant costs.

The move toward HFCs had changed customers’ views on refrigerant costs, with R-404A and R-507 costing as much as $8 per pound at that time. Any new system had to be simple to understand and operate.

How it works

Enviroguard controls refrigerant in the system, using the receiver only as a bypass storage device. Without the requirement of charging the receiver with surplus liquid refrigerant, the refrigerant charge is reduced by up to 45% over standard parallel systems.

Enviroguard II utilizes an electronic board that receives information from an ambient temperature sensor, a liquid drop leg temperature sensor, and a liquid pressure transducer to control condenser fans (system head pressure). The electronic solenoid valve (SPR) controls the amount of liquid refrigerant being used in the system. A mechanical version of the system’s pressure regulating valve uses a gas- or liquid-filled bulb to sense ambient temperature to control liquid refrigerant in the system.

During installation of an Enviroguard system, the condenser is charged to a specific amount with liquid refrigerant; however, minimal refrigerant is charged in the receiver (hence the up to 45% refrigerant savings at start up).

During summer design conditions, almost all the condenser tube surface is required to condense the high-temperature, high-pressure refrigerant gas to a liquid state; the excess liquid refrigerant charged in the condenser flows to the receiver for excess storage.

Therefore, during the two to four weeks of the summer design condition, some refrigerant will be present in the bottom of the receiver.

Summer condition is described as the time during the year where the outdoor ambient air temperature rises to the design condition specified by ASHRAE. This design temperature occurs in locations throughout the U.S. approximately two to four weeks out of the entire year (disregarding any extraordinary conditions such as heat waves or cool spells).

During the other 48 to 50 weeks of the year, the customer is experiencing energy savings from the efficient operation of the Enviroguard refrigeration system.

During the non-design or winter condition, as the outdoor ambient temperature falls, the liquid refrigerant will stack in the condenser. The amount of condenser tube surface required to condense the high-temperature high-pressure gas to a liquid state decreases as the ambient temperature falls.

The additional liquid stacking in the condenser subcools to the ambient temperature, increasing the efficiency of the overall refrigeration system. During the winter condition, refrigerant will not be stored in the bottom of the receiver.

The Enviroguard refrigeration management system adjusts the refrigerant level during the year to provide high quality, subcooled liquid to the display fixtures and maintain a high efficiency rating.

The piping diagram on page 19 shows the non-design day temperature conditions and refrigerant flows in Enviroguard II systems with electric defrost. In hot gas defrost systems, a hot gas return manifold is used to keep hot gas separate from the subcooled liquid.

Enviroguard works with both electric and hot gas defrost.

A receiver is mounted on Enviroguard parallel systems to handle service pump-down refrigerant charges, manage refrigerant overflow to the receiver during alarming conditions (refrigerant leaks, condenser fan motor failures, sensor bulb failure, excess and minimal refrigerant charge, and other cautionary alarming conditions), and manage refrigerant flow in the system from summer to winter conditions.

Scroll systems and Enviroguard

Scroll parallel systems offer simple advantages. Scrolls offer fewer components and increased reliability over semi-hermetic compressors. Fewer moving parts mean fewer potential problems. If a problem occurs with the scroll compressor it’s replaced, not repaired.

Many supermarket refrigeration departments see this feature as an advantage over reciprocating compressors.

Enviroguard can be applied to scroll compressors as well as reciprocating compressors. Shown in Figure 2 is a two-tier scroll rack with Enviroguard piping and control for a supermarket in the Northwest U.S.

The Copeland scroll compressor systems are placed near the refrigerant loads to minimize the piping runs. The scroll compressors shown are 10- and 13-hp “ZF” Series scrolls. Combined with the refrigerant savings gained from using Enviroguard technology, it’s a big improvement from the traditional parallel rack in one machine room at the rear of the store.

Compared to constant head pressure systems, Enviroguard provides substantial energy savings. In the table on page 18, a typical 50,000-sq-ft supermarket is charted with four racks. Energy savings amounts are shown at $0.01/kWh.

Lowering the total amount of lost refrigerant also reduces annual operating costs. The less refrigerant in the system, the less you can lose during a leak.

Detecting refrigerant loss

Early detection of refrigerant leaks and excessively high condensing pressure are determined easily as well.

For example, if a condenser becomes fouled or malfunctions and the head pressure rises, the SPR valve would bypass into the receiver, resulting in a shortage of liquid to feed the evaporators. This would cause the evaporators to warm, simulating a refrigerant-starved system.

This fail-safe design principle immediately alerts you to a problem before equipment fails. If a refrigerant leak occurs in the system it will be noticed earlier by higher evaporator temperatures; consequently, less refrigerant would be lost to the atmosphere than with a conventional system.

By minimizing primary refrigerant charges and facilitating the early detection of leaks, Tyler Refrigeration Corp. contributes to a healthy environment by minimizing the release of ozone-depleting refrigerant and minimizing global warming potential. New technology has got to be simple to use and maintain to be accepted.

With over 1,500 installations, Enviroguard is a proven success.

For more information, contact Keith Glasch at Tyler’s Mechanical Systems Division in Waxahachie, Texas, at 972-923-6335.

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