Potential efficiency improvements for refrigerated vending machines include improved lighting, better insulation, efficient or variable-speed compressors, improved condenser heat transfer, efficient fans and motors, and control changes to the refrigeration cycle (such as raising setpoints during late-night hours or other times of low use). The US Department of Energy (DOE) established the first national minimum efficiency standards for vending machines, which became effective in 2012. A new set of minimum efficiency standards will go into effect in 2019, bringing those standards in line with the current Energy Star specification. Standards may apply to Class A machines, which have transparent glass fronts, and to Class B machines, which have closed, opaque fronts. Within each class, a unit may also be known as a combination machine, in which only part of the total volume is refrigerated and the other part offers products that don’t require refrigeration.
Occupancy sensors. At least one retrofit device now on the market uses a passive infrared occupancy sensor to turn off the compressor and fluorescent lights in the vending machine when no one is nearby. A temperature sensor powers up the machine at appropriate intervals to keep the products cool (Figure 1).
Figure 1: Vending machines controlled by occupancy sensors
This soda machine sits between two others, each of which has its own occupancy sensor and controller. Sensors need to be mounted away from ceiling air ducts to prevent false triggering.
In typical occupancy sensor operation, power is cut to the vending machine after the area has been vacant for 15 minutes. A machine in a room that’s around 70° Fahrenheit (F) could be shut down for up to two hours if no one walks by. At that point, the machine turns 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 occupancy sensors range from 24 to 76 percent, depending on usage patterns, occupancy in the area, and ambient conditions. Occupancy sensors can be most cost-effective when the machine is located in such a way that people trigger the sensor only when they want to purchase something.
Favorable location. Vending machines located in cool and shaded areas tend to last longer, use less energy, and demand less power. Ambient conditions, such as high temperatures or direct solar gain, can make the compressor work harder to maintain the appropriate environment for snacks and beverages.
Improved lighting. A typical modern vending machine with a lighted front display panel uses two or three 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 cost of $190 at $0.12/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 is another option.
Another option is to use LEDs that are compatible with T8 and T12 fixtures. LEDs can save up to 65 percent of electricity use compared with fluorescent bulbs. LEDs also have 50,000-hour lifetimes, so service replacement costs are almost completely cut.
Energy Star models. Vending machines that comply with Energy Star specifications use efficient compressors, fan motors, and lighting systems, and are up to 50 percent more efficient than standard models. To receive the Energy Star label, a vending machine must incorporate software that can operate the machine in a low-power lighting state (where lights are off for an extended period), a low-power refrigeration state (where product temperature is allowed to rise to at least 40°F for an extended period), or both. Table 1 shows Energy Star standards calculated for machines with refrigerated volume sizes of 20 and 26 cubic feet.
Table 1: Energy Star standards
To qualify for Energy Star, vending machines must have a maximum daily energy consumption (MDEC)—measured in kilowatt-hours per day—below a certain threshold. MDEC values are shown for the two standard vending machine sizes in the US.
Refrigerant type. In 2015, the US Environmental Protection Agency (EPA) banned the use of the R-134a refrigerant for beverage vending machine applications and designated propane as an acceptable alternative, effective January 2019. The DOE conducted an analysis detailing life-cycle cost savings and payback periods of new Energy Star machines, for both carbon dioxide (Table 2) and propane (Table 3) refrigerant types, and found all payback periods to be under two years.
Table 2: Financial analysis of Energy Star standards—carbon dioxide refrigerant
Life-cycle cost savings and payback periods are shown for compliance with Energy Star standards for all four classes of vending machines. Combination machines see greater savings due to improvements in separating the refrigerated from nonrefrigerated segments.
Table 3: Financial analysis of Energy Star standards—propane refrigerant
Life-cycle cost savings and payback periods are shown for compliance with Energy Star standards for all four classes of vending machines.