Troubleshooting Defrost Problems

When troubleshooting walk-in freezers, technicians often find a frozen evaporator coil. Although there are several possible causes, one common cause involves the defrost system. For some reason, the system is not properly defrosting the evaporator’s coil on a regular basis. In order to effectively troubleshoot this problem, a technician must understand the design and operation of the defrost systems typically used.

One popular method of defrosting walk-in freezers is the electric defrost system. This is comprised of several components, including a defrost timer, resistive heater(s), defrost termination switch, fan cycling control, and drain line heater. An electric resistance heater is placed on the outer surface of the evaporator’s coils. The energized heater supplies enough heat to completely defrost the coils.

The resistive heaters used on a typical electric defrost system are sized to provide sufficient heat to effectively defrost the coil’s surface. Their capacity is normally rated in watts per foot. They are shaped to fit snugly onto the coil surface, creating efficient heat transfer during defrosts.

Most heaters are manufactured for a specific coil, and when replacing these heaters it is best to obtain the OEM replacement. Universal defrost heaters are available, but matching their wattage and shape may be difficult.

A defrost timer controls the entire defrost operation. It initiates the defrost cycle, controls the operation of the compressor and defrost heaters, and is part of the defrost termination. Defrost timers can be adjusted to initiate defrost from just once a day to several times a day.

The actual number of defrosts per day depends upon the location of the walk-in. Walk-in freezers are usually designed to defrost once or twice a day. The more humid and warm a location, the more defrosts will be needed. If a system needs to be defrosted more frequently, add only one additional defrost period at a time and monitor the results. Adding too many defrost periods will not be beneficial to the system or the customer.

In a common wiring diagram for a time-initiated, temperature-terminated electric defrost system the time motor (TM) is energized continuously. Normally closed contacts 2-4 of the defrost timer are wired in series with the compressor and the evaporator fan motor (EFM). Normally open contacts 1-3 are wired in series with the electric defrost heaters and the timer release solenoid (TRS).

The timer motor controls the operation of contacts 2-4 and 1-3. They work opposite each other. When contacts 2-4 are closed, 1-3 are opened. When contacts 2-4 are opened, 1-3 are closed. When the timer motor initiates a defrost, contacts 2-4 will open and 1-3 will close. This stops the compressor and the evaporator fan motor, and energizes the defrost heaters. Read the rest of this entry »

Refrigeration Guidelines for Specific Applications

This article is courtesy of Austin Industrial Refrigeration.

Flowers do best with High Humidity and Low Velocity refrigeration

Aside from the box temperature, other considerations that are particular to medium temperature applications (walk-in coolers & refrigerators) are the air velocity and humidity of the refrigerated space. Below freezing, humidity is inherent (the moisture is mostly frozen out of the air), so low temp applications are easier to spec than medium temp.

The following are common design parameters and examples of their application:

• 35 degrees F / 90%+ relative humidity (low velocity coils) – high humidity – Used for: sensitive materials, floral – roses
• 35 degrees F / 85% – 90% relative humidity – general purpose – Used for: foodservice, fresh meats, packaged goods not sensitive to humidity, short-term mixed produce, thawing, and dry goods unaffected by humidity
• 35 degrees F / 60% – 75% humidity – low humidity – Used for: retail, beer and beverage coolers, packaged items, materials sensitive to humidity
•  45 degrees F / 55% – 70% humidity – low humidity – Used for: aging red wine
• 45 degrees F / 90%+ humidity (low velocity coils) -high humidity – Used for: sensitive materials, floral – general
• 55 degrees F / 55% – 70% humidity – low humidity – Used for: processing rooms occupied by personnel
• 55 degrees F / 60% – 75% humidity (low velocity coils) – low humidity – Used for: produce Read the rest of this entry »

Diagnosing Walk-in Coolers & Freezers Problems

A systematic approach to walk-in cooler and freezer maintenance is the technician’s best guide.

The ubiquitous walk-in cooler or freezer is an essential part of many cafeterias, restaurants and convenience stores. It is also a large energy user in these facilities but is rarely considered until problems emerge.

Problems include failure to maintain pressure and compressor failure, both of which can result in expensive losses to the products stored in the cooler. These problems, as well as unnecessarily high energy use, can be avoided by observing equipment and taking corrective action.

Evaporators
Moisture from the air freezes onto the evaporator coils (the cooling coils in the freezer) and forms an insulating barrier to heat transfer. Airflow also decreases as the passages narrow due to ice buildup. Each evaporator has a defrost cycle to melt frost/ice that has built up on the evaporator coils. Water from the melted ice is drained from the freezer . . . ideally. Read the rest of this entry »

Cutting Down On Cooler Costs

Whether your chain is gearing up for LEED certification or just hoping to save on the electric bill, instituting an energy management solution can pinpoint energy waste.

Energy reduction remains an ongoing quest for convenience store operators as they look for ways to cut costs in an effort to improve their bottom lines.

Building stores to LEED (Leadership in Energy and Environmental Design) standards and seeking LEED certification is something more chains are pursuing, including Kum & Go, Kwik Trip and Quick Chek, which just opened its first LEED-certified store last month in Bayonne, N.J.

LEED is an internationally operated program encompassing the design, construction and operation of high performance green buildings established by the U.S. Green Building Council and verified by the Green Building Certification Institute (GBCI). It provides third-party verification that a building was designed and built by implementing strategies aimed at improving performance in areas such as: energy savings, water efficiency, CO2 emissions reduction, improved indoor environmental quality and stewardship of resources and sensitivity to their impacts. Read the rest of this entry »

Preventative Maintenance for Refrigeration Systems

Suggested Refrigeration Systems Preventative Maintenance

Refrigeration systems are critical in the foodservice industry. It is very important to provide maintenance on your cooling systems to help prevent them from clogging or breaking down, which could lead to spoiled food, rotten food, etc. The following guidelines are provided from Heatcraft’s Operation & Instruction Manual.   By following these preventive maintenance steps, it does not guarantee your unit will not break down. However, by taking care and maintaining your refrigeration systems your unit is less likely to have problems.

Preventive Maintenance

Unit Coolers

At every six month interval, or sooner if local conditions cause clogging or fouling of air passages through the finned surface, the following items should be checked.

Read the rest of this entry »

New! Copeland Scroll Outdoor Condensing Unit

Copeland now carries outdoor condensing units for the food service industry. There new light weight, slim shaped units are available in medium and low temperatures ranging from 2 – 6 horsepower.

Copeland Scroll Outdoor Condensing Units are perfectly suited for walk-in cooler and freezer applications. All units integrate the many benefits of the Copeland Scroll compressor technology, fan speed control and Copeland Performance Alert™ diagnostic controls, and are available in 208/230 single-phase and 208/230 three-phase voltage applications.

Scroll compressors offer the highest energy efficiency levels to lower energy bills. With integrated controls that optimize fan motor speed to maximize the heat transfer through over-sized condenser coils, additional energy savings are achieved. The average energy savings for end-users is $350 per year for a 3HP medium temperature unit, however this number could be greater depending on the application.

Read the rest of this entry »

Types of Refrigeration Systems Used in Walk-ins

Refrigeration systems consist of a condensing unit and an evaporation coil. The condensing unit is located outside the walk-in and the evaporator is located inside the walk-in. The compressor compresses gas to a liquid. The liquid is then pumped through the condensing unit coil while a fan blows outside air through the coil. Gas is condensed to a liquid and is then pumped through a small copper pipe into the walk-in to the evaporator coil. There, through the expansion valve located in the evaporator coil the liquid is allowed to expand back into a gas. The expansion of the liquid to a gas causes a rapid chilling of the evaporator coil. Since heat always flows toward cold, inside the walk-in air is blown across the evaporation coil to let the coil absorb heat from inside the walk-in. The gas is then allowed to exit the walk-in through a larger copper pipe to the condensing unit where it is once again compressed and cooled to a liquid state and returned to the evaporator coil inside the walk-in. There the cycle is started over.

The new EISA law requires all new walk-ins be equipped with high efficiency motors to be compliant. These cost a little bit more but save you money in the long run. Some suppliers may try to sell you non EISA compliant refrigeration systems. To be compliant with the law and purchase the best lifetime value always ask for EISA compliant equipment.

1. Remote Systems - Remote systems are the least expensive systems to purchase. They consist of a condensing unit, evaporator unit and misc. parts such as expansion valve, site glass, dryer, pump down solenoid thermostat, and on freezers a timer and drain heater to install the system. They require the use of a licensed refrigeration installer since they are pumped down and charged with refrigerant gas on site. The installer will also charge for any other parts needed for the install such as copper pipe, pipe insulation, connectors, and electrical. They are less expensive systems to buy with the walk-in but may cost more over all depending on what the going hourly rate is with the installer and the cost of the parts he provides. They also provide an advantage by allowing the condensing unit to be located outside the building. There the condensing unit can dump its heat without adding extra heat to the building and air conditioning systems. Read the rest of this entry »

EC Motor Start-up

Interesting information about EC motors that could lead to an incorrect diagnosis.

As of January 1, 2009, all walk-in manufacturing companies must sell their refrigeration units with Electronically Commutated (EC) motors. EC motors lower energy costs and significantly improve the walk-in cooler or freezer performance. These energy efficient motors are offered as a complete unit or as a drop-in replacement. Whichever your use is, if you are not familiar with the EC motor it may seem odd when you initially start it up.
When starting an EC motor, the motor must know where the rotor is located in order to start and continue to run. When power is first applied to the motor, the controller will apply a gradually increasing amount of current to all three windings in the motor over a period of 2 seconds. This will cause the rotor to move to a known location. This move will range from no movement at all if the rotor has stopped in the location needed for the next start or may be a much larger movement if it was a longer distance  from where it needed to be. With a fan blade attached, it may even overshoot and move backwards to get to the right location. After that 2 second “positioning” period the controller will start applying power to different phases in a slow rotating pattern that increases in speed over the next 2 seconds until the rotor is moving fast enough for the controller to be able to detect its location. This second phase of the start cycle usually happens so quickly that you cannot really see what is happening. Within 3 to 5 seconds of applying power, the motor should appear to be running normally, but during those first 2 seconds the movements may seem as though the unit is having troubles starting or is broken.

Meeting 2009 EISA Walk-in Cooler & Freezer Standards

The federal government’s EISA (Energy Independence & Security Act) standards went into effect Jan. 1st, 2009. This act was intended to improve energy efficiency within the refrigeration industry as well as many other industries. AHRI reports there have been some concerns since there are no enforcement mechanism or standard testing methods built into the act; non-compliant walk-in manufacturers will stand to benefit. These manufacturers will be able to beat compliant competitors on price (due to the lower input costs of their non-regulation walk-ins). Be sure that when buying a walk-in, you check to make sure they are EISA compliant.

The AHRI (Air-Conditioning, Heating, and Refrigeration Institute) is trying to raise awareness about what this act mandates among distributors, installers, and consumers. They have created a checklist of the standards walk-in coolers & freezers are required to meet that can be found at ACHR The News. Use this checklist to ensure the walk-in unit you are about to purchase meets the EISA standards. Read the rest of this entry »

An energy saving experiment for your grocery store.

A research study at Kettering University in Michigan investigated how to make an open refrigerated display case (like those found in grocery stores) operate more efficiently.  The study concluded that raising the temperature setting while lowering the air velocity from the refrigeration would not only provide energy savings, but the food was actually kept cooler.

Lower infiltration [of warm air] means the air is coming out at a lower velocity, said Navaz. “Previously, air came out of the upper vent (or grille) of a specific display case at 90 feet per minute. We calculated the optimal speed as 65 feet per minute as an optimal discharge air velocity to yield lower infiltration rate,” he said.

By reducing the velocity by 30 percent, infiltration was reduced by 12 percent and the power required was reduced by 13 percent.

Increasing the temperature at the discharge air grille by about 1 degree (F) and lowering the velocity of air resulted in lower suction pressure at the compressor inlet which reduced the compressor usage and therefore less energy consumption.

Infiltration represents 83 percent of the cooling load and is the biggest draw on energy of refrigerated display cases. Less energy use translates into real cost savings to the tune of about $13 million for the state of California alone, according to Navaz.

In addition to energy savings, lowering the pressure on the compressor also extends the life of the compressor and creates more cost savings over the long term.

Click here to read the entire Kettering refrigeration study.