Walk-In Cooler & Cold Room Load Calculator

Envelope heat is $Q=UA\Delta T$, with the doorway removed from opaque wall area and its closed-door transmission added separately. Wall and ceiling U-values share one input; floor temperature and U-value are separate.

Door exchange follows Gosney and Olama (1975), as reproduced by Foster et al., Reducing energy consumption in cold stores using a freely available mathematical model, author manuscript PDF p. 15, Eqs. 16–17:

This is fully developed, single-door buoyancy exchange. Divide moist-air mass flow by $1+w_w$ before multiplying by the enthalpy difference per kilogram of dry air. Multiply by total door-open time divided by 24 hours and by $(1-\eta)$. Moisture freezing adds $333.5\,\mathrm{kJ/kg}$ when the evaporator is below freezing. Condensate sensible heat is neglected conservatively. Moist-air saturation pressure, humidity ratio, density and enthalpy use the equations documented in PsychroLib 2.5 (2017 ASHRAE Fundamentals psychrometric equations, not refrigeration load tables); the liquid-water saturation equation is used over 0–55 °C.

Daily product sensible heat is $E_p=mc_p(T_p-T_r)$. The target curve is derived here from Newton cooling:

The whole sensible energy to the room setpoint enters the daily budget, including the residual after seven-eighths cooling.

Respiration uses USDA Agriculture Handbook 66 (2016), printed p. 265 / PDF p. 275: upper topped-carrot rates of 20, 26, 42, 54 and 95 mg CO₂/(kg h) at 0, 5, 10, 15 and 20 °C, linearly interpolated. Custom rates can replace these. The USDA conversion of 61 kcal/(tonne day) per mg CO₂/(kg h), with its 4.186 kJ/kcal convention, is equivalent to 10.6394 kJ/g CO₂.

People, lights and fans are time-weighted over 24 hours. Defrost heat is heater power × cycle count × duration × retained fraction; operating hours exclude defrost downtime. The selected capacity is $(1+f_m)\max(E_{day}/t_{run},Q_{active}+Q_{p,0})$. Active background uses simultaneous people, lighting and fans, daily-average door exchange, design respiration and additional heat. Defrost is recovered through the daily energy criterion. One US refrigeration ton is 12,000 Btu/h.

• One rectangular, unfrozen-product room and one door; steady design ambient and room conditions. Envelope dimensions approximate panel mid-plane dimensions.
• One incoming batch per day. Already-cold mass excludes that batch. For a holding-only calculation set incoming mass to zero.
• Warm-batch respiration is evaluated at incoming temperature and held for the entire day. This intentionally overestimates its respiration as it cools; custom rates must cover the actual product and condition.
• The seven-eighths curve is a sizing target derived here, not a product-core simulation. It assumes adequate airflow and heat transfer, continuous cooling through the specified period, and a maintained room air setpoint.
• Fans run for the entered refrigeration hours. People and lights are included simultaneously in peak background even if their entered daily durations are short.
• Carrot specific heat defaults to a nominal 3.9 kJ/(kg K), within FAO's reported approximate range; it is editable and independent of the respiration preset. The 15% allowance and 50% retained defrost heat are editable design assumptions.
• Closed-door leakage, deliberate ventilation, evaporating product moisture, packaging, pumps and other equipment are omitted unless included in additional continuous heat. Closed-door conduction is conservatively retained during openings.

Use for preliminary engineering selection of walk-in coolers with room temperatures 0–20 °C and unfrozen incoming product. The carrot preset is restricted to 0–20 °C; use measured or published custom respiration rates for other produce and warmer batches. U-values must represent the installed construction.

For door traffic, incoming-air enthalpy must be at least room-air enthalpy. Drier incoming states that would imply an evaporative cooling credit are rejected; humidity balance and heating demand are outside this cooling-only model.

Gosney–Olama predicts established buoyancy exchange, without wind, cross-drafts, fan pressure or short-opening transients. It can overpredict narrow-door exchange (Foster et al., 2003, DOI 10.1016/S0140-7007(03)00097-5). Long openings can invalidate the fixed room-temperature assumption; the conditional warning begins at a 10% daily open fraction as an engineering screening threshold.

Daily-average door heat does not guarantee recovery during a traffic rush. Check defrost heat-source capacity and timing against the reported moisture ingress; this model adds the specified retained defrost heat but does not design the defrost system. Defrost recovery timing, hot-gas defrost, simultaneous batch arrivals, changing ambient, freeze/thaw loads, initial room construction pull-down and solar power interruptions need a separate transient or schedule-based study. Product storage suitability and RH control are outside the model.

Select equipment at its actual evaporating and condensing conditions and confirm low-load operation, control, airflow, drainage and defrost with the supplier. Thermal kWh is not electrical kWh or a photovoltaic array size. Installation work belongs to a qualified person.

Reference checks verify USDA worked-example components, a USDA respiration rate and the Ontario seven-eighths endpoint. USDA PDF p. 30 has an inconsistent transmission total (519,149 versus 591,149 kJ/day); the calc does not fit its aggregate total.

The cooling curve is idealized and does not show food safety: check the product's time–temperature limits with measured core temperatures, not room air.