Tips for a successful refrigeration installation

June 1, 2000
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The best way to avoid problems with a refrigeration system is to get it right the first time, but that is not as easy as it may sound.

Whether you are new to the field or have been installing refrigeration systems for years, anyone can benefit from some installation refresher tips.

The employees at Heatcraft who field problem calls every day know where most problems tend to occur — and how to avoid them. They have compiled the following suggestions for a successful refrigeration system installation.

You have all seen it before — the booklet that comes shipped with every piece of equipment. You may have put it in a file or even thrown it out, but have you ever read it through?

It contains helpful information that can save you time and money. Instructions, drawings, charts, and diagrams help you get the most out of your equipment.

“A majority of the questions and problems I hear every day could be answered or prevented by consulting the installation manual,” says service engineer Galen Holzhausen.

It covers the basics, but it also provides specific guidelines for special situations that you may not have run across before. Look through it and chances are you will find something useful.

Expansion valve selection and adjustment

Whereas the nozzle is a distribution device, the expansion valve is a metering device. Proper thermostatic expansion valve adjustment for superheat can increase the efficiency of the evaporator, give you better system balance, and more efficient operation.

Sales engineer Steve Holmes explained, “The expansion valve basically controls the volume of refrigerant entering the evaporator coil. This is accomplished by controlling the superheat leaving the evaporator.

“A properly sized and adjusted expansion valve will adjust to the varying evaporator load and frosting conditions, allowing the evaporator to function at maximum capacity.”

An improperly adjusted expansion valve can reduce the capacity and the efficiency of the refrigeration system. “For example,” said Holmes, “if the system is operating with an expansion valve that is too small, the evaporator will be starved, lacking adequate refrigerant, preventing the system from cooling enough.”

That can also happen with a poorly adjusted expansion valve that allows high superheat to leave the evaporator. By contrast, if the expansion valve is too large, the valve will tend to “hunt,” or have large swings in superheat temperatures, leaving the system off balance and negatively affecting system capacity and efficiency.

“The expansion valve should be selected for the condensing unit capacity and not the evaporator capacity,” said Robert Thornton, application engineer. “The condensing unit is the dictator, that’s what is actually pumping this capacity and removing the heat.”

Service engineer Archie Nalbandian cautioned, “Many people believe that expansion valves are preset by the manufacturer. They are not, however, preset for your specific application.”

Make sure you know the capacity of your condensing unit and follow the tables for expansion valve selection found in the unit’s installation guide.

Evaporator placement

“Refrigeration equipment refrigerates air within an insulated space,” said Holmes. “The air in turn refrigerates the product, so proper air distribution and circulation is critical.”

Often times, poor product temperature is blamed on refrigeration equipment when the problem is actually poor air distribution and circulation. The best way to prevent this is by correctly configuring evaporator placement. From the evaporator, air must freely circulate in and around the product and return back to the evaporator.

You have two useful resources to help you get the best evaporator placement. First, the installation manual should outline minimum space requirements away from walls and between units, offering tips like, “Always avoid placement of unit coolers directly above doors and door openings.”

Second, talk to your end-user. Make sure you have complete understanding of where product will be stacked, where light fixtures will be placed, and where shelves and racks will be located. Once you know this, you can adjust equipment placement accordingly.

If there is a conflict between optimal unit placement and end-user use intentions, make sure you address this while compromises can still be made by both you and the end-user. Remember, the end-user will call you if the product is not holding temperature.

Also, take into consideration accessibility to the unit for future service and maintenance. It is not enough to get the unit in place; you must have access to end panels, drain pan, etc., to be able to work on it later.

Piping practices

Correct system piping is essential for proper system operation and adequate oil return to the compressor.

Select pipe sizes carefully. If the pipe size selected is too large, the refrigerant velocity becomes insufficient to carry oil vertically up to the compressor when the compressor is above the evaporator. The oil must pass freely through the entire system and reach a state of equilibrium to maintain stable oil levels in the compressor.

Equally important in system piping design is the use of traps in the suction line. Mike Jarrell, manager of application engineering, said, “Most people get the pipes properly pitched downhill so that the oil flows down toward the condensing unit, but you get into situations where the oil has to go up, so you can’t rely on gravity. You have to rely on a trap that will be a collection point for the oil and aids in moving that oil up through the coil.”

A p-trap should be used at the base of any suction riser greater than 3 to 4 ft in length. A suction riser is any vertical line that has an upward refrigerant flow. In long suction risers, p-traps should be used for each 20 ft of vertical rise.

In addition, it is good practice to install a p-trap at the outlet of the evaporator if the suction line rises above the bottom of the evaporator.

Without effective traps, you can log oil. “You don’t get the oil back to the system unless sometimes it’ll do it in a defrost, and it all comes back at one time,” said Jarrell. “This eventually leads to capacity problems or compressor breakdown.”

Setting defrost

Defrost must be adjusted to the usage of the refrigerated space. Again, this is something you need to discuss with the end-user.

Ask them how they use the space, what the busy times are, and when they stock it. Then you can make a good estimate as to what time of day you want the system to go into defrost and how many times a day it needs to do so.

You should never set the defrost to occur under the heaviest activity, like when stocking normally takes place.

“A good rule of thumb for starting out your defrost is four times a day, every six hours,” said Thornton. “Every time you open the door to a freezer, you let moisture in. The heavier the use, the more moisture you’re going to collect.

“You may end up having to go to six defrosts per day,” he added. “The contractor really needs to do a follow up check on that box and see how it’s doing.”

On the other hand, the box might be closed up and not opened for days. Overheating the evaporator is not a good situation either; it throws heat off into the refrigerated space, which can create steam and droplets on the ceiling and other surfaces. If the box isn’t getting much traffic, you might cut back to two or three defrosts a day, which will also save energy.

Another important consideration is defrost termination. Some systems require more manual operation. Many smaller evaporators come with fixed defrost, with adjustable defrost available as an option. The larger units generally come standard with adjustable defrost. Adjustable defrost units require fan delay setting.

“You need an idle time between when the compressor starts running, coming out of defrost, and when the fans come on,” said Thornton. “After the ice melts, a residue of water is left on the coil surface. If the fans come on immediately, it just sucks that water right through the fan and blows it all over the product, the ceiling, everywhere.”

The compressor needs to run long enough to refreeze any moisture left on the coil before the fans are energized.

A good rule for setting the defrost termination switch is to watch your coil in defrost. After all the ice has melted, give it one minute more, then start adjusting your defrost termination switch to kick it into refrigeration. “Just a minute or two after all that ice is melted is all it takes,” said Thornton.

(Next week: Topics covered include wiring, outdoor unit replacement, nozzle selection, and insulating lines.)

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