Why colder costs more
Two things happen when you lower a set point. More heat leaks into the cabinet, because the gap between inside and outside is larger. And the evaporator has to run colder, which lowers the suction pressure and makes the compressor work harder for each unit of cooling. Both effects increase energy use, and the second also tends to increase frost on the coil.
The extra energy per degree varies by unit and site, but the direction is always the same: a chiller held at 1 °C when 4 °C would do is paying for cold it does not need.
Commonly used temperature targets
| Application | Common target | Notes |
|---|---|---|
| Chilled food storage | 5 °C or below; often set around 3–4 °C | Leaves a margin for door openings |
| Beverage coolers | Typically a few degrees above freezing | Drinks do not need food-safety limits, but customers expect them cold |
| Frozen food | −18 °C or colder | Ice cream display may run at different temperatures for scooping |
| Vaccines and many medicines | Typically +2 to +8 °C | Follow the programme or manufacturer's guidance |
Air temperature is not product temperature
Most controllers read air temperature near the evaporator. Air swings quickly with door openings and defrost cycles, while food changes temperature slowly. Staff who see a brief rise on the display often turn the set point down to compensate, which then over-cools the product the rest of the time.
Check product temperature with a calibrated probe thermometer in a sample item, or use a probe placed in a small bottle of glycol or water to simulate product. Set the controller so that the product, not the air, sits where you want it.
Understand the differential
A controller switches the compressor on and off around the set point, using a differential or hysteresis. A very tight differential makes the compressor start and stop too often, wasting energy on starts and wearing the motor. A very wide one lets the cabinet swing too far. Manufacturers set sensible defaults; changes should be made only by someone who understands the controller.
Lock it and check it
- Use the controller's keypad lock or password so set points cannot be changed during a busy shift.
- Write the agreed set point on a label on each unit.
- Check product temperatures at least daily and record them.
- Verify thermometers against a reference, such as an ice-water bath, from time to time.
- Review set points when the use of a unit changes, for example from meat to drinks.
Night and eco modes
Some controllers offer an eco or night mode that raises the set point slightly, dims lights or slows fans when the shop is closed. For beverage coolers this can save energy without any food-safety concern. For food storage, only use modes that keep the product within its safe range, and confirm with temperature records that it does.
Frequently asked questions
- Will setting my fridge colder help it cope with a hot day?
- Usually not. If the cabinet is struggling, the cause is typically heat load, a dirty condenser or a fault. Lowering the set point just makes the compressor run longer and may freeze produce. Find the cause instead.
- Should a deep freezer be set as cold as it will go?
- No. Food-safety guidance commonly uses −18 °C or colder for frozen storage. Running far below what your product needs adds energy use and run time without a matching benefit, unless a specific product such as some seafood or a medicine requires a lower temperature.
- What does the number on the controller dial mean on older units?
- On many older mechanical thermostats, the dial numbers are relative settings, not degrees. Use a thermometer to find which setting gives the temperature you need.
- How often should I check fridge temperatures?
- Many food businesses check at least once a day, and more often for high-risk food. Follow your food-safety plan and any FSSAI or licensing requirements that apply to you.
