Door Heat Loss Calculator

Estimate sensible and latent heat infiltration through doorways into refrigerated spaces using the Gosney & Olama (1975) air exchange equation for fully established flow (ASHRAE Equation 15).

Door Dimensions

Width and height of the doorway opening.

Width (ft)

Height, H (ft)

Doorway area A = 32.0 ft²

Air Conditions

Temperature and relative humidity for both sides of the doorway.

Outdoor / Infiltration Air

Temperature (F)

Relative Humidity (%)

Cold Space / Refrigerated Air

Temperature (F)

Relative Humidity (%)

ASHRAE Table 9 values are based on 90% RH in the cold room.

Door Usage

Frequency, duration of openings, and any protective devices.

Times Opened / Hour

Avg. Open Duration (sec)

Door Flow Factor, Df

1.0 = no protection, 0.15 = strip curtains, 0.10 = air curtain

Door open time fraction D_t = 16.7% (10.0 min/hr)

Shut-Door Leakage

Heat loss through door gaps when closed (Gosney & Olama convective leakage).

Shut Leak Gap, SLG

h_c (Btu/hr·ft²·°F)

Free convection: 0.88-1.761

Perimeter L = 2(h+w) = 24.0 ft, ΔT = 95.0°F

Air Curtain

Reduces infiltration heat load when door is open.

Air Curtain Performance

Heat Loss Result

Fully Open Heat Load591,388 Btu/h49.28 tons

Adjusted Heat Load98,565 Btu/h8.21 tons of refrigeration

D_t16.7%

D_f1.00

Shut-Door Leakage107 Btu/h0.0089 tons

Total Heat Load98,672 Btu/h8.22 tons of refrigeration

Heat Load Comparison by Door Type

Total heat load across different door/protection types and opening frequencies.

Hard Door - Tight (SLG: 0.0625, Df: 0.8)

Hard Door - Worn (SLG: 0.125, Df: 0.9)

Roll-up Door - Good (SLG: 0.25, Df: 0.95)

Roll-up Door - Worn (SLG: 1, Df: 1)

Air Curtain (75% eff.)

Current usage: 20 openings/hour

Annual Cost Savings: Air Curtain vs Door Types

Savings by switching from each door type to an air curtain(0% effectiveness)

Electricity Rate:

$/kWh

(US avg: ~$0.12/kWh)

Hard Door - Tight

Hard Door - Worn

Roll-up Door - Good

Roll-up Door - Worn

Based on 24h/day, 365 days/year operation. Conversion: 1 BTU/h = 0.000293 kW.

Calculated Air Properties

Intermediate psychrometric values used in Equation 15.

Property	Infiltration	Refrigerated
Enthalpy, h	42.40 Btu/lb	0.75 Btu/lb
Density, ρ	0.0708 lb/ft³	0.0863 lb/ft³
Humidity Ratio, W	0.01776 lb/lb	0.00071 lb/lb

F_m0.9509

Area32.0 ft²

Equation Reference

Gosney & Olama (1975) — ASHRAE Eq. 15

q = 795.6 · A · (h_i − h_r) · ρ_r · (1 − ρ_i/ρ_r)^0.5 · (g·H)^0.5 · F_m

With Your Values

q = 795.6 × 32.0 × (42.40 − 0.75) × 0.0863 × (1 − 0.0708/0.0863)^0.5 × (32.174 × 8.0)^0.5 × 0.9509

Step-by-step

A=4.0 x 8.0=32.0 ft²

h_i − h_r=42.40 - 0.75=41.65 Btu/lb

1 − ρ_i/ρ_r=1 - 0.0708/0.0863=0.1796

(g·H)^0.5=(32.174 x 8.0)^0.5=16.0434 ft/s

F_m=[2 / (1 + (0.0863/0.0708)^(1/3))]^1.5=0.9509

q=product of all terms=591,388 Btu/h

q_adj=591,388 x 0.1667 x 1.00=98,565 Btu/h

F_m = [ 2 / (1 + (ρ_r/ρ_i)^1/3) ]^1.5

q: Sensible + latent load, Btu/h
A: Doorway area, ft²
h_i, h_r: Enthalpy of infiltration / refrigerated air, Btu/lb
ρ_i, ρ_r: Density of infiltration / refrigerated air, lb/ft³
g: 32.174 ft/s²
H: Doorway height, ft
F_m: Density factor

Shut-Door Leakage Equation

Convective heat transfer through door gaps when closed.

q_leak,shut = h_c · (h + w) · SLG · ΔT

Derived from: q = h_c · A · ΔT

Where A = ½ · L · SLG and L = 2(h + w)

Simplifies to: q = h_c · (h + w) · SLG · ΔT

With Your Values

q = 1.00 × (8.0 + 4.0) × 0.0938 × 95.0

h + w=8.0 + 4.0=12.0 ft

ΔT=|95.0 - 0.0|=95.0°F

q_shut=1.00 × 12.0 × 0.0938 × 95.0=107 Btu/h

q_shut: Shut-door leakage heat load, Btu/h
h_c: Convection coefficient, Btu/hr·ft²·°F (free convection: 0.88-1.761)
h, w: Door height and width, ft
SLG: Shut leak gap, ft per linear ft
ΔT: Temperature difference, °F

Typical SLG Values:

Hard door: 0.0625 to 0.125 ft/ft
Roll-up door: 0.25 to 1.0 ft/ft