Estimate the cooling load of a room by the simplified ASHRAE steady-state method. Transmission sensible load Q_trans = Σ(A_i·U_i·ΔT) over envelope surfaces entered one per line as 'area,U' (U in W/(m²·K)). Infiltration/ventilation sensible Q_s = 1.23·ACH·V·ΔT and latent Q_l = 3010·ACH·V·ΔW (W), where ΔW is the indoor-outdoor humidity-ratio difference derived from dry-bulb temperature and relative humidity via the Magnus saturation fit. Total cooling load = total sensible + total latent. Temperature in °C/K/°F (only differences matter), area in m²/ft².
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Key facts
Category
Math & Numbers
Input types
textarea, select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Estimate a room’s cooling load with a simplified steady-state ASHRAE method. Enter envelope surface areas and U-values, indoor and outdoor temperatures, relative humidity, room volume, and ACH to calculate transmission, sensible infiltration, latent infiltration, and total cooling load in watts.
When to use
Estimate preliminary air-conditioning capacity for a room or conditioned space.
Compare cooling loads for different envelope U-values, areas, or air-change rates.
Separate transmission, sensible infiltration, and latent infiltration contributions to the total load.
How it works
1Enter one envelope surface per line using the format `area, U-value`, such as `50, 0.5`.
2Choose square meters or square feet, then provide indoor and outdoor dry-bulb temperatures and their unit.
3Enter indoor and outdoor relative humidity, room volume, and air changes per hour; ACH defaults to 0.5.
4The calculator applies the simplified formulas and returns transmission load, sensible and latent infiltration loads, total sensible load, and total cooling load in watts.
Use cases
Preliminary HVAC sizing for residential rooms, offices, and other conditioned spaces.
Building-envelope comparisons using different surface areas and U-values.
Humidity-sensitive load checks that distinguish latent infiltration from sensible heat gain.
Examples
1. Estimate the load for a 120 m³ room
HVAC designer
Background
A designer needs a preliminary cooling-load estimate for a room with two envelope surfaces and moderate outdoor heat and humidity.
Problem
Calculate the transmission, infiltration, and total cooling loads from the room’s envelope and air-change conditions.
How to use
Enter `50, 0.5` and `10, 1.8` as the envelope surfaces. Use m², indoor 24 °C and 50% RH, outdoor 33 °C and 70% RH, volume 120 m³, and ACH 0.5.
After converting the entered areas internally, the result is approximately 387.46 W transmission, 664.2 W sensible infiltration, 2365.41 W latent infiltration, and 3417.08 W total cooling load.