How to estimate cold storage refrigeration load
Refrigeration load for a walk-in or warehouse breaks into three pieces: transmission through the insulated panels, infiltration of outside air when doors open, and the product load of pulling incoming goods down to room temperature. Enter the inside dimensions, temperatures, and daily product volume, and this tool reports each piece, adds 10% for lights, fans, and people, applies your safety factor, and converts the result to tons of refrigeration.
Transmission is U-value x envelope area x temperature difference, where 0.035 BTU/hr·ft²·°F is typical of 4 in urethane panel. Infiltration is driven by enthalpy, not temperature alone, so the tool builds the psychrometric enthalpy of the outside air from your dry bulb and humidity and subtracts room air enthalpy at an assumed 90% relative humidity. Product load adds specific heat times temperature drop plus, when you are freezing below 32°F, the latent heat of fusion, about 108 BTU/lb for product that is roughly 75% water.
The answer is an average 24-hour load. Because defrost cycles interrupt running time, compressors are commonly selected on 16 to 18 hours of run time per day, so multiply the result by 24 divided by run hours before picking equipment. Specific heat changes above and below freezing, so blast freezers should be figured in three stages of chill, freeze, and subcool. One ton of refrigeration is 12,000 BTU/hr. Have the final selection verified with a refrigeration engineer or the manufacturer selection software.
Frequently Asked Questions
Storage rooms with infrequent traffic run about 1 to 2 changes per day, while small busy freezers can reach 4 to 8. Smaller rooms see more changes per unit volume, so base the number on actual door traffic.
Freezing releases latent heat that often exceeds the sensible cooling. Loading warm product into a freezer every day can dominate the total, which is why blast freezing is usually handled in a separate room from long-term storage.