Refrigeration Load & Compressor Sizing
Sizes field heat
What size refrigeration unit do you need to cool and hold your produce? Enter the room, the crop and the duty — the calculator splits the load into product field-heat, respiration, transmission, infiltration and misc and gives the total kW, refrigeration tonnage (TR), pull-down duty and daily energy & cost.
Size your cold room
Next: specify a unit of 6.16 TR (round up to the next standard condensing unit) sized to run ~18 h/day. Provision the evaporator to deliver the 42.3 kW pull-down duty so a fresh 40 t batch reaches 4 °C within 24 h.
ASHRAE Refrigeration Handbook component method + USDA Handbook 66 respiration & specific-heat data. Treat as a sizing estimate; a refrigeration engineer should confirm evaporator/compressor selection and refrigerant circuit.
Refrigeration sizing — key facts
- 1 ton of refrigeration
- 3.517 kW (12,000 BTU/h)
- Total load
- product + respiration + transmission + infiltration + misc
- Field heat
- m × cp × ΔT ÷ pull-down seconds
- Respiration
- tonnes × W/tonne ÷ 1000 (rises with temp)
- Transmission
- U × area × ΔT ÷ 1000
- TR
- duty(W) ÷ 3516.85, duty = load × 24 ÷ run-hours
- Apple specific heat
- 3.81 kJ/kg·K above freezing
- Privacy
- Runs in your browser; nothing uploaded
Every watt the plant removes — broken out, not guessed
Sizing a cold room is an addition problem the rules-of-thumb get wrong. The refrigeration plant must remove five separate heat streams every day: the field heat in freshly harvested produce, the respiration heat the living crop keeps generating, the transmission conducted through the insulated walls and roof, the infiltration of warm humid air through the door, and the internal loads from lights, people and evaporator fans. Sum them, add a safety margin, divide by the compressor's daily run-hours and convert to refrigeration tons. Miss the respiration component for a leafy crop, or under-rate the field heat for a daily intake, and the plant will never hold temperature on a hot day.
This calculator follows the published ASHRAE Refrigeration Handbook component method and pulls respiration heat and specific-heat data from USDA Handbook 66, so the answer is defensible to a buyer or a financier — not a back-of-envelope guess. It also reports a separate pull-down duty so you size the evaporator to cool an incoming batch in time, and the daily energy and cost so you can compare a cheap low-COP unit's running bill against a better one.
Commodity respiration heat & storage data
Respiration heat in watts per tonne (near 0 °C and near 20 °C) and specific heat above freezing — USDA Handbook 66. The calculator interpolates respiration to your room temperature.
| Commodity | Group | Specific heat (kJ/kg·K) | Resp ~0 °C (W/t) | Resp ~20 °C (W/t) | Optimum °C | RH % |
|---|---|---|---|---|---|---|
| Apple | fruit | 3.81 | 10 | 60 | 0 | 92 |
| Pear | fruit | 3.80 | 9 | 55 | -1 | 92 |
| Grape | fruit | 3.71 | 5 | 30 | -0.5 | 92 |
| Strawberry | fruit | 4.00 | 35 | 280 | 0 | 92 |
| Orange | fruit | 3.81 | 9 | 60 | 4 | 87 |
| Banana | tropical | 3.35 | 30 | 130 | 13 | 90 |
| Mango | tropical | 3.74 | 25 | 130 | 13 | 87 |
| Tomato | vegetable | 3.98 | 15 | 80 | 12 | 90 |
| Potato | root | 3.43 | 10 | 35 | 5 | 95 |
| Onion | root | 3.77 | 8 | 35 | 0 | 70 |
| Carrot | root | 3.92 | 18 | 90 | 0 | 98 |
| Lettuce | leafy | 4.02 | 25 | 130 | 0 | 98 |
| Broccoli | leafy | 3.96 | 55 | 470 | 0 | 98 |
| Spinach | leafy | 4.02 | 50 | 420 | 0 | 98 |
| Cabbage | leafy | 3.94 | 12 | 70 | 0 | 98 |
| Bell pepper | vegetable | 3.94 | 18 | 95 | 8 | 95 |
| Cucumber | vegetable | 4.06 | 15 | 70 | 11 | 95 |
| Green peas | vegetable | 3.31 | 40 | 280 | 0 | 95 |
| Mushroom | vegetable | 3.89 | 35 | 280 | 0 | 95 |
| Cut flowers | leafy | 3.90 | 30 | 200 | 1 | 95 |
Insulation U-values
| Panel | U-value (W/m²·K) |
|---|---|
| PUF panel 60 mm | 0.36 |
| PUF panel 80 mm | 0.28 |
| PUF panel 100 mm | 0.23 |
| PUF panel 125 mm | 0.18 |
| PUF panel 150 mm | 0.15 |
| EPS/thermocol 100 mm | 0.34 |
How to size your cold room in 5 steps
- 1Describe the room. Pick the commodity and the wall insulation, then enter the internal length, width and height.
- 2Set the conditions. Enter the worst-case ambient temperature, the room set-point, and the tonnes you hold.
- 3Enter the duty. Give the tonnes loaded per day, their incoming field temperature and the pull-down time you want.
- 4Add internal loads. Enter lighting, number of people, fan/equipment watts, compressor run-hours, system COP and a safety factor.
- 5Read the size. Read the total kW load, refrigeration tonnage (TR), the separate pull-down duty, and the daily energy & cost.
Frequently Asked Questions
How many TR of refrigeration do I need for my cold room?+
Add every heat source the room must remove in 24 hours — product field-heat (cooling incoming produce), respiration heat of the stored crop, transmission through the walls and roof, air infiltration through the door, and internal loads from lights, people and fans — then add a safety margin. Divide that total kW load by the compressor's daily run-hours (a 24/18 scale-up if it runs 18 h) and convert: 1 ton of refrigeration (TR) = 3.517 kW. A typical 8×6×4 m fruit store works out near 3–4 TR.
What is the respiration-heat component and why does it matter?+
Living produce keeps respiring after harvest, releasing heat the refrigeration plant must remove continuously. The rate is given in watts per tonne and rises sharply with temperature — apple gives about 10 W/t near 0 °C but 60 W/t at 20 °C, while broccoli can exceed 400 W/t when warm. Most thin online calculators ignore this; for high-respiration leafy crops it can be the second-largest load after field heat, so we break it out by commodity from USDA Handbook 66.
What is product field heat?+
Field heat is the sensible heat you must pull out of freshly harvested produce to bring it from its incoming (field/pulp) temperature down to the room set-point. It equals mass × specific heat above freezing × temperature drop, spread over the pull-down window. Cooling 5 t of apple (specific heat 3.81 kJ/kg·K) from 25 °C to 4 °C over 24 h is about 4.6 kW — usually the single biggest load when fresh produce arrives daily.
What is pull-down time and how does it affect compressor size?+
Pull-down time is how fast you want a fresh batch cooled to the set-point. The shorter the window, the higher the instantaneous duty the evaporator must deliver: halving the pull-down hours doubles the field-heat kW. We report a separate pull-down duty so you can size the evaporator to cool the batch in time, not just hold the room.
How is wall transmission calculated?+
Transmission = U-value × envelope area × temperature difference, in watts. The U-value depends on the insulation — a 100 mm PUF panel is about 0.23 W/m²·K, a 150 mm panel 0.15. For a 94 m² envelope with a 31 °C pull (35 °C ambient to 4 °C room) at U 0.23, transmission is about 0.67 kW. Thicker panels and a smaller ambient-to-room gap cut this load.
How do I account for door openings and infiltration?+
Each door opening swaps cold room air for warm, humid outside air the plant must re-cool. We estimate it from an air-change rate that falls with room volume (about 70 ÷ √volume changes per day) times the enthalpy difference of the air. High air-change rates (small rooms, busy doors) flag a warning — strip curtains or an air-curtain are the cheapest fix.
Is 3 TR enough for a 50-tonne fruit cold store?+
It depends on how fast produce arrives and how warm. A 50 t store that only holds pre-cooled fruit may need 3–4 TR; the same store taking 10 t/day of field-warm fruit needing a 24 h pull-down can need 6–8 TR because field heat dominates. Enter your daily turnover and incoming temperature — the calculator separates the holding load from the pull-down load so you size for the worst case.
What COP and run-hours should I assume?+
A medium-temperature cold-room plant typically has a system COP of 2.2–2.8 (lower in hot ambients) and runs 16–20 hours a day, leaving time for defrost and idling. Daily energy = refrigeration duty ÷ COP × run-hours. The tool uses your figures so you can compare a cheaper low-COP unit's running cost against a better one.
Why add a safety factor?+
Real rooms have extra loads the textbook misses — door-seal leaks, frost on the evaporator, packaging mass, and ageing insulation. A 10–15% safety factor on the calculated load gives headroom so the plant holds temperature on the hottest day. We add it before converting to TR.
Does this work for ripening rooms and tropical produce?+
Yes. Set the room set-point to the ripening temperature (e.g. 13 °C for banana or mango) — the respiration heat is interpolated to that temperature, which is higher than in a near-freezing store, so the respiration load is correctly larger. Tropical produce should not be set below its chilling-injury temperature.
What is the formula the calculator uses?+
Total load = product field-heat + respiration + transmission + infiltration + misc, then × (1 + safety%). Product = m·cp·ΔT ÷ pull-down seconds; respiration = tonnes × W/tonne ÷ 1000; transmission = U·A·ΔT ÷ 1000; infiltration = air-changes × volume × air-enthalpy ÷ 86400. TR = duty(W) ÷ 3516.85, where duty scales the 24 h load by 24 ÷ run-hours.
How accurate is the result?+
It is a solid engineering estimate built from the published ASHRAE component method and USDA respiration/specific-heat data, good for sizing and quotation. Final equipment selection should be confirmed by a refrigeration engineer who will check the evaporator TD, refrigerant circuit, and local ambient design conditions.