How do you actually work out the cooling tonnage for a space — can someone show a worked example?
From the how-many-tons thread I get that a "ton" is 12,000 BTU/h and that sizing is more than floor area. But I still can't picture how you'd actually estimate it for a real space.
- Can someone walk through a rough worked example — how you'd ballpark the tons for, say, a café or an office?
- Which factors move the number most?
- Enough to sanity-check a quote (so I know if I'm being sold way too much or too little)?
Not asking for a full engineering calc — just a realistic mental model with numbers, so a quote isn't a total black box. How would you rough it out?
3 answers
Short answer: a proper number comes from a full heat-load calc, but here's a realistic mental model. Start from a rough area-based ballpark, then ADJUST hard for the things that actually dominate a UAE load — glazing/sun, occupancy, equipment heat, and fresh-air. Two same-size spaces can differ 2-3x once you account for those, which is exactly why "X tons per 1000 sqft" alone is misleading. Use the rough number only to sanity-check a quote, not to buy from.
A rough worked example (café, illustrative — not a substitute for a real calc): 1. Start with area. A simple, well-insulated space might start around a rough rule of thumb per area — but in Dubai you treat that as a floor, not the answer. 2. Glazing & sun: a café with a big west/south glass frontage can add a large chunk — sun through glass is a major load. This alone can push the number up significantly. 3. Occupancy: people are heat sources. A busy café full of customers adds meaningful load an empty shop wouldn't. 4. Equipment: kitchen gear, ovens, coffee machines, display lighting, fridges throwing heat — F&B is equipment-heavy, so this is big. 5. Fresh-air (ventilation): conditioning the hot outside air you're required to bring in is often the single most underestimated chunk, especially for F&B/high-occupancy.
Add those up and a café can easily need several times what a bare area rule would suggest — which is the whole point: the adjustments dominate.
How to sanity-check a quote: - If someone sized it off floor area alone with no questions about your glass, occupancy, equipment or fresh-air → be sceptical (likely wrong in either direction). - A credible quote comes with a load calculation that names those factors. - Oversizing isn't "safe" — it short-cycles, wastes energy and under-dehumidifies; undersizing can't keep up.
So use the rough model to smell-test the quote, but insist the real number comes from a proper load calculation and sizing. Tell me the space's glazing/occupancy/kit and I'll point at what'll dominate its load.
The fresh-air point deserves the emphasis Sam gives it — for anything with high occupancy or F&B, the ventilation load is enormous and it's the bit cowboy quotes ignore entirely, because it's invisible on a floor-plan. I've seen spaces badly undersized purely because nobody accounted for conditioning the outdoor air being brought in. So when you sanity-check a quote, the question "did you include the fresh-air load?" separates the people who calculated from the people who guessed off square footage.
This is exactly the mental model I wanted — not a full calc, just enough to know what drives it and spot a lazy quote. The equipment and fresh-air points land for me; my kitchen throws off serious heat and we've got the doors opening all day. Makes sense a café needs a lot more than a shop of the same size. I'll be asking whoever quotes whether they've factored the kitchen load and the fresh air, not just measured the floor. Thanks — feel much less at the mercy of the numbers now.
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