Room Gain Calculator

Room Gain Input Form

Room Length (m)

Room Width (m)

Room Height (m)

Indoor Design Temperature (°C)

Outdoor Design Temperature (°C)

Window Area (m²)

Wall U-Value (W/m²·K)

Roof U-Value (W/m²·K)

Window U-Value (W/m²·K)

Solar Heat Gain Factor (W/m²)

Shading Coefficient (0 to 1)

Number of Occupants

Sensible Gain per Person (W)

Latent Gain per Person (W)

Lighting Density (W/m²)

Lighting Usage (%)

Equipment Density (W/m²)

Equipment Usage (%)

Fresh Air per Person (L/s·person)

Humidity Ratio Difference (g/kg)

Infiltration Rate, ACH

Safety Factor (%)

Reset

This cooling-focused model estimates sensible and latent room gain from envelope, solar, occupancy, lighting, equipment, ventilation, and infiltration inputs.

Formula Used

Floor Area = Length × Width

Room Volume = Length × Width × Height

Gross Wall Area = 2 × (Length + Width) × Height

Net Wall Area = Gross Wall Area − Window Area

Transmission Gain = U × Area × ΔT

Solar Gain = Window Area × Solar Factor × Shading Coefficient

Lighting Gain = Floor Area × Lighting Density × Usage Factor

Equipment Gain = Floor Area × Equipment Density × Usage Factor

Ventilation Sensible = 1.206 × Fresh Air Flow (L/s) × ΔT

Ventilation Latent = 3.0 × Fresh Air Flow (L/s) × Humidity Difference

Infiltration Flow (L/s) = Room Volume × ACH ÷ 3.6

Total Sensible = Envelope + Solar + People + Lighting + Equipment + Ventilation Sensible + Infiltration Sensible

Total Latent = People Latent + Ventilation Latent + Infiltration Latent

Design Total = (Total Sensible + Total Latent) × (1 + Safety Factor)

BTU/h = Watts × 3.412142

Tons of Refrigeration = BTU/h ÷ 12000

This page is intended for early engineering estimates of room cooling gain. Real projects should also review orientation, occupancy schedule, equipment diversity, duct losses, exact psychrometrics, and local design conditions.

How to Use This Calculator

Enter room length, width, and height in meters.
Set indoor and outdoor design temperatures for the cooling case.
Enter window area, U-values, solar factor, and shading coefficient.
Add people count and sensible and latent heat per person.
Provide lighting and equipment load densities plus their operating percentages.
Set ventilation rate per person, humidity ratio difference, infiltration ACH, and safety factor.
Press Calculate Room Gain to show results above the form.
Review watts, BTU/h, refrigeration tons, and the recommended rounded AC size.
Use the CSV and PDF buttons to export the result summary.

Example Data Table

Length (m)	Width (m)	Height (m)	Occupants	Window Area (m²)	Outdoor / Indoor (°C)	Estimated Design Gain (W)	Suggested Size (TR)
6.0	5.0	3.0	4	4.0	35 / 24	Approx. 4,500 to 5,500	1.5
8.0	6.0	3.2	6	6.5	38 / 24	Approx. 7,500 to 9,000	2.5

FAQs

1. What is room gain?

Room gain is the heat entering or generated inside a room. It combines sensible and latent loads from walls, roof, glass, occupants, lights, equipment, ventilation, and infiltration. Engineers use it to estimate cooling demand.

2. Why are sensible and latent loads separated?

Sensible load changes dry-bulb temperature. Latent load changes moisture content. Cooling equipment must handle both, so separating them helps size coils, airflow, and dehumidification capacity more accurately.

3. What does the shading coefficient do?

The shading coefficient reduces solar heat entering through windows. Lower values mean better shading performance. Use it to reflect blinds, films, overhangs, or stronger glazing control.

4. Why is outdoor temperature important?

Outdoor temperature affects transmission through the envelope and sensible ventilation or infiltration gain. A higher outdoor design value usually increases cooling load and required system capacity.

5. Can I use this for final HVAC design?

This tool is best for preliminary engineering checks. Final design should include climate data, orientation, solar geometry, exact schedules, psychrometric analysis, duct effects, and code requirements.

6. What is ACH in this calculator?

ACH means air changes per hour. It estimates infiltration airflow through leakage paths or openings. Higher ACH adds sensible and latent load because more outdoor air enters the space.

7. Why does the calculator round the AC size?

The tool shows a calculated refrigeration tonnage and then rounds upward to a common practical selection step. This helps convert the raw result into a more usable equipment size.

8. What if outdoor temperature is below indoor temperature?

This page focuses on cooling gain. If outdoor temperature is lower, conductive sensible gain becomes zero in the model, though latent load from ventilation or infiltration may still remain.