Why "so many BTU per square metre" fails
Floor area is only one input to a cooling load, and using it alone is why so many Kenyan rooms end up either freezing and humid or unable to cope on a hot afternoon. The heat an air conditioner must remove comes from many sources, and two rooms of identical size can have very different loads.
Sensible vs latent heat
A cooling load has two parts:
- Sensible heat changes air temperature: sun through glass, people, lights, computers, hot outside air leaking in.
- Latent heat removes moisture: from occupants, open doors, and humid outside air (a big factor at the coast).
An air conditioner sized for sensible heat alone leaves a space cold but clammy, because it has not been sized to dehumidify. A proper calculation totals both.
What actually drives the load
- Solar gain: glazing area and orientation. A west-facing glass wall takes the full afternoon sun.
- Occupancy: each person adds sensible and latent heat; a packed boardroom is a big load.
- Equipment and lighting: servers, kitchen equipment and old lighting all add heat.
- Ventilation: fresh air for health (per ASHRAE 62.1) must be cooled too.
- Climate: Nairobi highland conditions differ greatly from humid coastal Mombasa.
The reference unit
Cooling capacity is quoted in tons of refrigeration (TR) or kW: 1 TR is about 3.517 kW (12,000 BTU/h). Sizing matches the equipment capacity to the calculated load — not to a rule of thumb.
The oversizing trap: bigger is worse
It is tempting to "buy a size up to be safe." For air conditioning that is the wrong instinct. An oversized unit cools to setpoint so fast that it switches off before it dehumidifies, so it short-cycles — leaving the room cold and damp, wearing the compressor with constant stop-start, and costing more to buy and run. A correctly sized inverter (variable-speed) unit modulates to match the load, holding temperature and humidity steady while using far less energy.
Nairobi vs Mombasa: same room, different machine
Because climate is a major input, the same room needs a different unit in different cities. A humid coastal location carries a far larger latent (dehumidification) load than the dry highlands, so a Mombasa installation must be sized and selected with that in mind. This is exactly why a calculated load, not a generic chart, gives a comfortable, efficient result.
The bottom line
Air conditioning is sized by physics, not floor area. Calculate the sensible and latent load for the worst design hour, size the equipment to it (ideally an efficient inverter unit), and you get comfort, humidity control and a lower bill. Guess it, and you get a cold, clammy, expensive room.
Send us your room or building details, glazing, occupancy and city and we will calculate the cooling load and recommend the right, efficient system. Call +254 768 860 665 or +254 782 914 717.