Vending Machine Energy Savings

Occupancy sensing. At least one device now on the market uses a passive infrared occupancy sensor (PIR) to turn off the compressor and fluorescent lights in the vending machine when no one is around. In addition, a temperature sensor powers up the machine at appropriate intervals to keep the products cool enough (see Figure 1).

In typical operation, power is cut to the vending machine after the area has been vacant for 15 minutes. The device is designed so that a machine in a room that's around 70 degrees Fahrenheit will be shut down for up to two hours if no one walks by. At that point, the machine is turned back on to run a compressor cycle, after which it turns back off if the occupancy sensor still indicates that no one is in the area. When someone approaches, the sensor sends a signal to turn the lights and other electronic components back on, and the compressor runs a cooling cycle if needed.

The control logic ensures that after the machine is repowered, the compressor is allowed to run a complete cooling cycle before it is powered down again. A sensor also determines whether the compressor is running and prevents the machine from shutting down until the cycle has been completed. Both of these features ensure that a high-head-pressure start, which would strain the compressor, never occurs. An indicator light goes on if the compressor has been running for more than two hours—a signal that maintenance may be required. Savings for vending machines equipped with these devices range from 24 to 76 percent, depending on usage patterns, occupancy in the area, and ambient conditions.

Improved lighting. A typical modern vending machine with a lighted front display panel uses two 4- or 5-foot high-output T12 fluorescent lamps powered by conventional magnetic ballasts, drawing as much as 180 watts of power. This continuous load consumes 1,580 kWh per year (for an annual total of $126 at 8¢ per kWh). The heat from the lights also increases the machine's refrigeration load.

Instead, look for machines that use low-temperature electronic ballasts paired with T8 lamps, which could reduce lamp power to about 80 watts. In addition, high-color-rendering T8s can significantly improve the appearance of the translucent front panel.

In one test, disconnecting a vending machine's lights cut energy use by 35 percent. However, users' attempts to get operators to disconnect the lights don't always meet with success. Adding a simple timing mechanism to turn the lights off in the late evening would be another option.

Energy savings from using an occupancy sensor and temperature sensor (to only cool product when necessary) are correlated with occupancy, the temperature of the space where the machine is located, and, to some degree, the frequency of product restocking. Additional savings may also come from a reduced need for maintenance and space conditioning.

Focus on occupancy. The parameter that has the greatest impact on energy savings is occupancy: the higher the traffic, the lower the savings. For example, in one test, when occupancy sensors were added to a machine located in a busy hotel lobby, relatively low energy savings resulted—roughly 25 percent. Generally speaking, locations that are unoccupied during nights and on weekends present the best opportunities for savings, although some energy can be saved as long as the area is unoccupied for more than 15 minutes at a time. Teachers' lounges, break rooms, office buildings, and school cafeterias all are good potential sites for saving energy with occupant sensing.

Assess how often the compressor runs. Other factors that affect energy savings relate to how often the compressor needs to turn on to keep the products cool. If a room's temperature is warmer than normal, the compressor will have to turn on more frequently. Likewise, if one machine has a product that is highly popular, that machine will be stocked with room-temperature products more often, causing the compressor to work harder to cool the product.

Because vending machines, like refrigerators, emit heat during operation, reducing "on" time will also reduce total air-conditioning loads when the vending machine is located in an air-conditioned space. It is unlikely, however, that occupancy sensing will reduce peak air-conditioning loads, as those loads generally correspond with peak occupancy rates.

Vending machines typically cool less than half the volume of a home refrigerator, yet may use more than five times as much energy. So the potential for improvements by manufacturers is huge. In addition to better lighting, potential efficiency improvements for beverage venders include more or better insulation, more-efficient compressors, improved condenser heat transfer, more-efficient fans, and control changes to the refrigeration cycle (such as raising setpoints during late-night hours or other times of low use). One study that evaluated these options concluded that the combination of lighting upgrades, turning lights off for nine hours per day, reducing cabinet heat gain by 40 percent, and using permanent split-capacitor fan motors with duty cycling could reduce energy consumption by 46 percent. Redesigning the machines to use LEDs instead of fluorescent lighting could also lead to energy savings. An Energy Star specification for vending machines is scheduled to become effective in early 2004.

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