Calculate cooling capacity in BTU/hr, kW, and tons for room AC, general room loads, or water cooling from flow and temperature difference.
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Cooling Capacity Formula
The calculator uses different formulas depending on the selected tab: room air conditioner sizing, general heating or cooling BTU sizing, or water cooling heat transfer.
Room AC BTU Formula
- BTU/hr = estimated cooling capacity in British thermal units per hour
- B = base cooling capacity from the room area table
- M_h = ceiling height multiplier, based on ceiling height divided by 8 ft, with a minimum of 0.85
- P_a = people adjustment, equal to 600 BTU/hr for each person above 2 people
- R_a = room load adjustment, such as kitchen or high equipment load
- M_i = insulation multiplier
- M_s = sun exposure multiplier
- M_c = climate multiplier
- kW = equivalent cooling power in kilowatts
- Tons = refrigeration tons
In the Room AC BTU tab, the calculator starts with a standard room-size BTU estimate, adjusts it for ceiling height, adds extra load from people or room type, then applies insulation, sun, and climate multipliers.
General BTU Formula
- V = room or house volume in cubic feet
- W = width in feet
- L = length in feet
- H = ceiling height in feet
- DeltaT = desired temperature change in degrees Fahrenheit
- F_i = insulation factor
- M_u = use-case multiplier, 1.10 for cooling and 1.00 for heating
- CFM = approximate air conditioning airflow
In the General BTU tab, the calculator estimates capacity from the volume of air, the desired temperature change, the insulation condition, and whether the result is for heating or cooling.
Water Cooling Formula
- Q = cooling capacity in kW
- m_dot = mass flow rate in kg/s
- Cp = specific heat capacity in kJ/kg·K
- DeltaT = absolute temperature difference between inlet and outlet in K or °C
- BTU/hr = heat transfer rate in British thermal units per hour
- Tons = refrigeration tons
In the Water Cooling tab, the calculator converts the entered flow rate to mass flow, finds the inlet-to-outlet temperature difference, then applies the heat transfer formula.
Typical Cooling Capacity Reference Values
Use these values as a quick check against the result. Actual sizing can change with insulation, windows, sun exposure, occupancy, and equipment heat.
| Room area | Typical base capacity | Approximate tons |
|---|---|---|
| 100 to 150 sq ft | 5,000 BTU/hr | 0.42 tons |
| 250 to 300 sq ft | 7,000 BTU/hr | 0.58 tons |
| 350 to 400 sq ft | 9,000 BTU/hr | 0.75 tons |
| 450 to 550 sq ft | 12,000 BTU/hr | 1.00 ton |
| 700 to 1,000 sq ft | 18,000 BTU/hr | 1.50 tons |
| 1,000 to 1,200 sq ft | 21,000 BTU/hr | 1.75 tons |
| Conversion | Value | Use |
|---|---|---|
| 1 refrigeration ton | 12,000 BTU/hr | Common air conditioner sizing |
| 1 kW | 3,412.142 BTU/hr | Power and heat transfer conversion |
| Typical AC airflow | About 400 CFM per ton | General airflow estimate |
| Water specific heat | 4.186 kJ/kg·K | Water cooling calculation |
| Water density | About 1000 kg/m³ | Flow-to-mass-flow conversion |
Cooling Capacity Examples
Example 1: Room AC cooling capacity
You have a 400 sq ft room with an 8 ft ceiling, 2 regular occupants, average insulation, average sun exposure, and an average climate.
The estimated cooling capacity is 9,000 BTU/hr, which is 0.75 tons or about 2.64 kW.
Example 2: Water cooling capacity
You have water flowing at 1 L/s, with an inlet temperature of 20°C and an outlet temperature of 15°C. Use water properties of 4.186 kJ/kg·K and 1000 kg/m³.
The cooling capacity is about 20.93 kW, or about 71,419 BTU/hr.
FAQ
What is cooling capacity?
Cooling capacity is the rate at which a cooling system removes heat. It is commonly shown in BTU/hr, kW, or refrigeration tons. A larger value means the system can remove more heat per hour.
Is a bigger cooling capacity always better?
No. An oversized air conditioner may cool the space too quickly without running long enough to remove humidity well. It can also cycle on and off more often. An undersized unit may run continuously and still not reach the desired temperature. The best size is close to the actual load, with reasonable allowance for sun, insulation, occupancy, and equipment heat.
Why does water cooling use inlet and outlet temperature difference?
Water cooling is based on how much heat the water gains or loses as it flows through the system. The larger the flow rate or temperature difference, the larger the heat transfer. That is why the formula uses mass flow rate, specific heat capacity, and the inlet-to-outlet temperature difference.
