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Walk-In Cooler Heat Load
Box load = transmission (U x area x deltaT) + infiltration + product + internal, times a safety factor.
Example
You enter
- Panel U-factor (4 in styrene ~0.06, 4 in urethane ~0.04, Heatcraft) 0.05
- Envelope area (ft²) 800
- Ambient-to-box deltaT (°F) 60
- Infiltration/door load (Btu/hr) 3000
- Product load (Btu/hr) 5000
- Internal load: lights/motors/people (Btu/hr) 1500
- Safety factor (default 1.10) 1.1
You get
- Transmission load 2400 Btu/hr
- Total load (24-hr average) 13090
Checked against published worked examples from: Heatcraft Refrigeration Products.
Details, formula, and sources
ScopeU 0.05, 800 ft^2, 60 F, +3000/5000/1500, 1.10 -> 2,400 transmission, 13,090 Btu/hr (1.09 tons); a 6 in panel (U 0.03) cuts it to 12,034. That is a 24-hr average: the equipment removes it in 16 hr (no defrost timer) or 18 hr (timer), so 13,090 x 24/16 = 19,635 Btu/hr of equipment. The box-load method and equipment ratings govern.
Formula or tabletransmission = U x area x deltaT; total = (transmission + infiltration + product + internal) x safety; tons = total / 12000.
Source and editionThe walk-in cooler/freezer box heat-load method (transmission + infiltration + product + internal, with a safety factor), from ASHRAE Refrigeration, by name.
Free accessThe four-component box-load method is standard published refrigeration practice; the ASHRAE Handbook - Refrigeration covers it.
What governsEstimate. AHJ and licensed professional govern.
API field namesu_factor, area_ft2, delta_t_f, infiltration_btuh, product_btuh, internal_btuh, safety, transmission_btuh, total_btuh
- Four components transmission (U A deltaT) + infiltration + product + internal, x safetyASHRAE Refrigeration
- Insulation a lower U-factor cuts the transmission and the compressor directlyfirst principles
- Run time equipment capacity = box load x 24/16 (35 F room, no defrost timer) or 24/18 (with a timer)Heatcraft Engineering Manual H-ENGM0408 (2008), p. 5