Are your door heaters robbing you?
If you already have door heater controls for supermarket refrigerated cases, you need to check your wallet. Imagine a shoplifter walking through the aisles of your grocery store sticking candy bars, fruit snacks, baked beans and Slim Jims in his/her pockets. Would you approach them and make them pay for the items, or would you let them walk out the front door? You’d stop them – of course! If you let them walk out the door, they are taking money directly from your bottom line. If you wouldn’t let a shoplifter take your money, then why would you be willing to throw it away on overuse of reach-in door heaters?
Back in the day, door heaters were energized 100% of the time, just to make sure there was no condensation. But if humidity levels are low, there is no reason to run the door heaters all the time.
In recent years, anti-sweat heater controls have been added in many stores to modulate the power to the electric anti-sweat heaters in doors and frames of reach-in refrigeration cases. This maintains doors and frames just above the temperature at which condensation or sweating will occur. Thus, anti-sweat heater controls can save energy/money.
Anti-sweat heater controls can be installed on frozen food/ice cream, and medium temperature reach-in cases. The installation is simple and does not require any case downtime.
If controls are already installed, chances are they are not working as intended, and are not saving the maximum amount of energy. Sensors drift and are frequently out of calibration, and most contractors don’t check them as often as necessary. They’re thinking; just keep the fog off, baby. I don’t want to be called back, so I’m playing it safe — way safe. There is almost always potential to optimize the control settings and parameters.
The graph of an actual anti-sweat heater control in a recently retro-commissioned supermarket shows the percent time the heaters are on (yellow line), a measure of the rate at which energy is consumed. In this store, the humidity sensor was reading 10% points higher than actual, causing the heaters to run more than necessary.
The dew point, the temperature at which a surface will show condensation (navy line), shows a steep drop at the start of the retro-commissioning. The controls were also made smoother and more efficient by optimizing settings and parameters. Note that the ice cream (red line) and frozen food (green line) cases are now controlled independently, given that they are set at different temperatures, which gives the control the ability to run the heaters in each case type only as much as necessary.
Installation of anti-sweat heater controls on the reach-in cases for frozen food/ice cream should provide savings of about 50% to 70%; this translates to annual savings of about 625 to 875 kWh/door. In a supermarket with 100 reach-in doors, it represents an annual dollar savings of approximately $5,000 to $7,000 (at $ 0.08/kWh) – just for a little time spent tuning the controls!