Cold Room Refrigeration Load Calculator

Estimate the cooling capacity a walk-in cooler or freezer needs in kW, BTU/h and tons from insulation, air changes, product, people, lights and run time.

Inside length (m)

Inside width (m)

Inside height (m)

Room temperature (°C)

Room relative humidity (%)

Outside air temperature (°C)Design temperature of the space around the room (a hot warehouse or outdoor summer air).

Outside relative humidity (%)

Temperature under the floor (°C)Ground or slab temperature below an insulated floor.

Panel insulation

Insulation thickness (mm)Chill rooms commonly use 75–100 mm PUR panels; freezers 125–200 mm.

Air changes per dayFrom door openings and leakage. Small, busy rooms can see 20+ a day; large stores with strip curtains under 5.

Product loaded per day (kg)

Product entering temperature (°C)

Product water content (%)Fruit and vegetables about 80–95%, meat 60–75%, fish 70–80%.

Product freezing point (°C)Only used when the room is colder than this.

Pull-down time (hours)Time allowed to bring the product down to room temperature.

People working inside

Hours per person per day (h)

Lighting power (W/m² of floor)

Lighting hours per day (h)

Evaporator fans and other equipment (W)Assumed to run 24 hours a day.

Safety factor (%)

Compressor run time (hours per day)Leaves time for defrost: about 16–18 h for chill rooms, 18–20 h for freezers.

Estimate a cold room’s refrigeration design load from panels, infiltration, product cooling, occupants, lighting and equipment. The result is a preliminary capacity allowance in kW, BTU/h and refrigeration tons. It is heat-removal capacity, not electrical input, and does not by itself select equipment.

How to use this tool

Enter the inside dimensions, the room temperature and humidity, and the outside and under-floor temperatures.
Pick the panel insulation and its thickness.
Enter air changes per day and the product loaded each day, with its entering temperature, water content and freezing point.
Add people, lighting and fan loads, then set the safety factor and compressor run time.

Formula

Capacity (kW) = (Q walls + Q floor + Q air + Q product + Q internal) × (1 + safety factor) ÷ (run hours × 3,600)

All terms are equivalent kJ per 24 hours. Transmission is U × area × temperature difference × 86.4, with U = 1/(thickness/k + 0.17). Infiltration uses dry-air mass at room conditions and the moist-air enthalpy difference at 101.325 kPa. Product energy uses approximate sensible/latent heat terms, then a 24/pull-down-hours design factor. People use the approximate 272 − 6T watts/person model. The daily design total can exceed actual daily heat when pull-down time is shortened.

Example

For a 5 × 4 × 3 m room, walls, ceiling and floor total 94 m². With 100 mm insulation at k = 0.022, U = 1/(0.1/0.022 + 0.17) ≈ 0.21207 W/m²·K. Room air at 2 °C and both ambient and floor at 32 °C give 94 × 30 × U ≈ 598 W. Set air changes, product, people, lights, equipment and margin to zero, and runtime to 24 hours: the capacity is 0.598 kW.

Frequently asked questions

Why divide by 16–18 hours instead of 24?

Select an operating allowance appropriate to the actual defrost and duty schedule. Dividing the design load by fewer operating hours increases required capacity. The product pull-down correction is a separate sizing assumption.

Which load is usually the biggest?

In a busy chill room, product cooling and air infiltration often outweigh the panels. Strip curtains and pre-cooled product cut the required capacity sharply.

Is this enough to order equipment?

A refrigeration designer must verify airflow, product properties, packaging, defrost, respiration and the equipment capacity at actual evaporating/condensing temperatures. A generic safety margin cannot replace missing material heat loads or guarantee pull-down time.

Sources

Heatcraft — Engineering Manual, load components and pull-down correction

Last updated: 2026-10-30