Energy-efficient walk-in refrigeration: There are ways to save energy and money in refrigeration
This is a challenge when your customers generally don’t know what they need. You are the professional; therefore, educating your customers becomes part of satisfying their needs.
Assisting them in choosing the right equipment if you build or sell, and showing them how their equipment can run as efficiently as possible if you repair and maintain, certainly helps satisfy customers.
There are several types of walk-in refrigerators. There is that new, clean, well-engineered box with the condenser, compressor, and evaporator sized properly for efficiency. There is the old workhorse, perhaps 10 years old, but still doing its job reasonably well.
If you are a technician, you aren’t called too often to service it but when you are, you know it’s going to really need you. Then there is the older, poorly engineered system that constantly needs work, but often does not receive even normal maintenance.
All of these boxes can benefit from various simple, cost-effective, energy-saving actions and equipment. According to several industry sources, refrigeration in grocery stores can be responsible for 40% to 50% of the total energy cost for the store. Refrigeration costs in restaurants can easily reach 15% or more of total energy usage.
In other words, any appreciable energy saving that can be done in the refrigeration system in many businesses can mean a lot on the bottom line.
There are a number of “free” energy efficiency measures that can be taken: Keep the doors closed (in a DOE-sponsored test, one walk-in in a large supermarket was found to be open six hours out of every 24); clean the equipment, especially the evaporator and condenser coils; fix any leaks in the system; and lubricate the fan motors at least twice a year.
New products help save energyThere are several energy efficiency products that can be added to a good or fairly good system, which can make a big difference in the cost to run the box, with payback periods of a year or less in many cases. These products will help a poor box as well, but may have a longer payback period.
Some of these products have been around for years, while others are relatively new. They can be used individually or together to make your customers’ boxes more efficient and their businesses more profitable.
One product is not new: Strip doors or strip curtains keep the cold air in, the warm air out, and let people and product move in and out of the box with as little disturbance to the temperature as possible. They are an excellent energy efficiency add-on for almost any box.
A very good upgrade for many evaporators in either new construction or as a replacement in existing boxes is to install energy-efficient PSC-type (permanent split capacitor) fan motors.
Another product is ART’s evaporator fan controller, which is applicable in most walk-in refrigerators and freezers with an on-off cycle.
It is the first product to be widely usable that saves energy by controlling the evaporator fans. The controllers can be implemented in new construction, in oem usage, and in retrofitting of existing boxes.
The evaporator fan controllers are a series of fan motor controllers that can decrease the electric power consumption of a walk-in refrigeration box by up to 40%.
The original model, the “ART4000,” employs the basic concept of controlling the fan motors efficiently to save electricity. The new models use this same concept and add monitoring and communications capability as well, the “ART5000” through a PC and the “ART6000” by using a modem.
The basic principle that is used in the evaporator fan controller is similar to “turn the light off when you leave the room.”
This idea is becoming the most accepted method of cutting energy waste, as long as you can easily determine when you need to “turn the lights back on,” such as when someone is in the room. This principle can work for almost every type of energy-using system.
With evaporators, “no one is in the room” when the compressor is off and/or refrigerant is not flowing through the system, so the need is to determine when this is true.
The ART controller has temperature sensors on each side of the expansion valve to determine when the refrigerant is not flowing; when it isn’t, voltage to the fan motors is reduced and they go to slow speed. When refrigerant begins to flow again, the controller puts the fan motors back on the normal full speed.
Controllers bring big benefitsIn a standard walk-in box, the fans run at full speed 24 hrs a day every day. This is not necessary, as it consumes a lot of unnecessary energy and generates extra heat that then has to be removed by the system.
When you reduce the voltage to the motors, you reduce their current need and also reduce the heat they generate.
This can mean that the system will gradually run less as a whole, depending on box loading and usage patterns, of course. Overall, this can save up to 40% of the total cost of energy used by the refrigeration system. Using average electricity rates, the payback period can be less than a year.
Added benefits with a fan controller installed are increased productivity and increased product life. The personnel who need to work in the box tend to keep the door closed much more when the fans are running on slow speed than they do when the fans are blowing harder on them.
Open perishable product in the box, such as meat or produce, maintains its natural moisture longer with a fan controller installed, because of the slower air speed and less heat generated in the box. This may mean a florist can buy flowers in larger amounts less often for a greater discount, or that produce “throw away” in a grocery is less.
These benefits also add to the customer’s profitability.
The concept of slowing motors to reduce energy usage has been around for a long time, but the ART controller is the first widely applicable product to embody the concept. Several years have been spent developing and testing the technology, with the aid of a United States Department of Energy grant, in order to prove conclusively that slowing the subject motors does not damage the motors themselves, the fans or the refrigeration system.
Stratification of temperatures in the box has been found to actually lessen with the controller installed. Suitable motors for the controller are single-phase induction types, including the energy-efficient PSC motors mentioned earlier. The controllers are available for both 110- to 115-vac and 208- to 220-vac motors.
The nuts and boltsHow does it work? The unit consists of a set of temperature sensors and associated electronics. The logic circuit determines whether the motor should be at high or low speed and selects the prescribed speed. The controller will save appreciable energy if the compressor is off and refrigerant is not flowing at least 35% of the time.
The longer the off time, the more energy that can be saved. The unit is designed in a fail-safe manner: If it ever fails, it will always fail in the high-speed mode so it cannot damage the compressor.
How is it installed? The product is designed to be installed by a refrigeration technician in less than an hour. The refrigerant lines are not opened or disturbed in any way. The unit can be mounted inside or outside the walk-in box.
The temperature sensors are clamped to both sides of the expansion valve with hose clamps. The controller is connected into the evaporator fan motor’s power line between the power source and the motors.
Energy efficiency is beneficial to everyone in the long run.
Energy providers and energy services companies (ESCOs) are encouraging energy efficiency by developing rebate and incentive programs to help business owners, as well as institutions such as schools and hospitals, to save energy. An important part of these programs is the need to monitor and record the energy usage of the equipment involved.
Additionally, owners and site managers want to know what their various efficiency measures are actually doing for them and how well their equipment is running. In refrigeration, it is extremely important to know if your box is icing, or the system has a bad leak.
ART has developed three controllers to answer these needs. The ART4000 is the basic energy-saving controller unit. The ART5000 also has current- and voltage-measuring components that allow the unit to monitor the power drawn by the fan motors.
The unit keeps track of the amount of energy used in low speed operation and the amount used at the normal high speed. The total time of high-speed operation tells the microprocessor how long the compressor is running.
By monitoring compressor run time compared to an established base line, the unit can warn the operator of a problem before the compressor is damaged. With the energy information from the fan motors, it can be determined if a motor has failed.
The inside box temperature can be monitored, which allows detection of icing in the evaporator, and also can give warning if the box is going out of its normal temperature range. On the ART5000, these warnings are given by a blinking red light. The model also has a serial port for local data downloading to a PC for recordkeeping of energy savings and alarms given.
In addition to the above features, the ART6000 can also communicate by modem over a standard telephone line. The unit can be telephoned remotely to check on the refrigeration system conditions, including power consumption and warnings of system problems.
ART also offers a reporting service in which ART calls the unit and reports to the operator whatever data is requested.