Heat load is the rate at which heat enters the room and must be removed by the refrigeration system.
In short: room size is only one input. Doors, products, people, equipment and ambient conditions can matter just as much.
The main sources are:
- heat passing through walls, ceiling and floor;
- warm, humid air entering when doors open;
- warm products being cooled or frozen;
- lighting, evaporator fans, people and machinery;
- defrost heaters and other operating loads.
A busy small room may need more cooling than a larger room that is rarely opened. A freezer also has a larger temperature difference and may need to remove latent heat when products are frozen.
The Frostbox size calculator estimates storage volume. It does not collect every input required for a full heat-load calculation or select an exact unit for all site conditions.
The four heat loads
Sizing a unit means adding up every source of heat it must remove. There are four, and they must be summed at peak, not average, conditions.
- Transmission load — heat conducting through walls, ceiling, and floor. Constant; rises with hotter ambient, colder setpoint, and thinner panels.
- Infiltration load — warm, humid air entering at every door opening. In a busy kitchen this can be 30–50 % of the total. Strip curtains, air curtains, and ante-rooms exist specifically to cut it.
- Product load — goods loaded above storage temperature carry heat in. The unit must pull it out before the product reaches equilibrium; warm or fast-throughput product dominates the sizing.
- Internal loads — lights, evaporator fans, people working inside, and the defrost cycle all add heat that must be counted.
Size for the spike, not the average
Size for the spike, not the average. If a door opens fifty times during a lunch rush, the system has to hold temperature through that surge. A unit sized to the daily average will fall behind exactly when it matters most.
This is why infiltration control matters so much: cutting the warm-air ingress with strip curtains or an ante-room directly lowers the peak the unit must meet. Reducing transmission load — by stepping up panel thickness — does the same on the constant side. Both let you specify a smaller, cheaper-to-run unit. See How insulated panels keep heat out for the envelope side of the equation.
For a guided estimate of these loads, see Heat load calculation and the Frostbox size calculator.
Related articles
- How Cold Rooms Work
- The refrigeration cycle explained
- How insulated panels keep heat out
- Using the Frostbox size calculator
- Heat load calculation
Recommendations reflect the MTH Algor panel system and Daikin refrigeration supplied by Frostbox. For help sizing a room to your peak load, contact [email protected].
