Every senior MEP consultant carries a mental table of sqm/TR ratios. They are not a substitute for a real calc — but they are how you sanity-check a number in a tender review meeting, validate a third-party submission, or call out a junior engineer’s calc that runs 30 % off. Indian numbers run differently from ASHRAE-published US norms because our climate, glazing fraction, and equipment density don’t match.
What sqm/TR actually means
Sqm/TR = floor area cooled per ton of refrigeration. Higher sqm/TR = more area per TR = a more efficient envelope. The number conflates a lot of things: glazing fraction, SHGC, U-values, internal load density, OA rate, occupancy density. Two buildings at the same sqm/TR may have very different load drivers — one envelope-dominated, one internal-gain-dominated. Use sqm/TR as a sanity check, not a design driver.
Indian baseline numbers by climate zone
These ranges are calibrated against MEPCON Design Studio’s project portfolio (~340 projects, 2010-2025) plus ASHRAE / ISHRAE published benchmarks adjusted for Indian construction practice (230 mm brick exterior wall, RCC slab, double-glazed reflective on commercial, single-pane on residential).
Office (8 hr occupancy, ECBC compliant)
| Climate zone | Sqm/TR (good envelope) | Sqm/TR (typical) | Sqm/TR (poor envelope) |
|---|---|---|---|
| Hot & Dry (Ahmedabad, Jaipur) | 18-21 | 14-17 | 10-13 |
| Warm & Humid (Mumbai, Chennai) | 20-23 | 16-19 | 11-14 |
| Composite (Delhi, Pune) | 19-22 | 15-18 | 11-14 |
| Temperate (Bengaluru) | 23-27 | 19-22 | 14-17 |
| Cold (Shimla — cooling) | 30+ | 25-28 | 20-23 |
Hospitality (24 hr occupancy)
| Space | Sqm/TR (typical Indian) |
|---|---|
| 5-star hotel guestroom | 12-15 |
| 5-star hotel public area (lobby, banquet) | 8-11 |
| 3-star hotel guestroom | 14-17 |
| Restaurant (high-occupancy peak) | 6-9 |
| Hotel banquet (peak event load) | 5-8 |
Hospitality runs lower sqm/TR than office because of higher OA per person, latent load from people + kitchen, and occupancy intensity at peak.
Retail
| Space | Sqm/TR (typical Indian) |
|---|---|
| Retail mall common area | 14-17 |
| Anchor retail store | 10-13 |
| Jewelry / display retail (high lighting LPD) | 7-10 |
| Cinema multiplex auditorium | 6-9 (peak occupancy) |
Healthcare + Lab
| Space | Sqm/TR (typical Indian) |
|---|---|
| Hospital ward (general) | 14-17 |
| ICU | 8-11 |
| Operation theatre | 5-8 (high air change rate dominates) |
| Lab (Class 100,000) | 6-9 |
| Pharma cleanroom (Class 10,000) | 4-6 |
Data centre / IT
| Space | Sqm/TR (typical Indian) |
|---|---|
| Data hall (high density) | 1.5-2.5 |
| Server room (medium density) | 3-5 |
| BMS room | 8-12 |
Data centres are equipment-driven: nameplate W/m² maps almost 1:1 to TR/m².
How to use these numbers
Step 1: Compute your design TR using a real method (CLTD, RTS, or HBM).
Step 2: Divide floor area by design TR to get your sqm/TR.
Step 3: Cross-check against this table. If you’re outside the typical band, ask why:
- Below typical: confirm your envelope inputs are not understating load (low U, low SHGC, no infiltration?)
- Above typical: check for missed gains (kitchen exhaust make-up, equipment underestimated, top floor combined with middle floors?)
Step 4: Document the sqm/TR figure prominently in your design report. It’s the single number a project director looks at before reading anything else.
What pushes the number up or down
Up (more area per TR, lower TR/m²):
- Tight envelope — ECBC compliant U-values + SHGC ≤ 0.27
- Good shading — overhangs, light shelves, internal blinds
- LED lighting (LPD ≤ 9 W/m² for office)
- Heat recovery on OA (sensible + enthalpy wheel)
- Demand-control ventilation (CO2 sensors)
- Daylight-linked dimming
- Cool roof or vegetative roof on top floor
Down (less area per TR, higher TR/m²):
- Single-glazed or non-reflective glass
- High glazing fraction (> 40 % WWR)
- West/south-west façade dominance without shading
- Top floor without insulated roof
- High occupancy density (< 8 m²/person)
- Restaurant/kitchen with high latent load
- 100 % OA system without heat recovery
- 24/7 IT/data load mixed with normal office
From the Field — Engineer’s Notebook
On the Marriott Lonavala project (2023 design, opened 2025), the architect proposed a single-pane non-reflective skylight over the lobby atrium for daylighting effect. Our first-pass cooling load came in at 6.5 sqm/TR for the atrium — outside any reasonable hospitality benchmark. We ran the calc against a reflective double-pane spec and the number moved to 9.5 sqm/TR. The architect kept the daylighting intent but switched to spectrally-selective low-iron double-glazed with internal motorized blinds. Final figure: 10.2 sqm/TR. Reading the sqm/TR table early in DD prevented a 60 TR oversize.
5 common mistakes
1. Treating sqm/TR as a design target instead of a check. You don’t size a chiller to hit a sqm/TR — you compute the load and the sqm/TR falls out.
2. Comparing across building types. A 14 sqm/TR office and a 14 sqm/TR retail anchor mean very different things. Compare within type.
3. Forgetting top floor effects. A 50,000 m² IT park with 30 m floor plate and 20 floors will have a 25 % higher TR on the top floor than the middle. Average sqm/TR hides this.
4. Quoting US-published sqm/TR. ASHRAE 90.1 baseline numbers (often quoted as 25-30 sqm/TR for office) do not transfer to India. The Indian base load is 30-40 % higher because of OA + climate + equipment density.
5. Ignoring occupancy mode in the ratio. A 24-hour data centre at 2 sqm/TR is normal; an 8-hour office at 2 sqm/TR is over-loaded. Match the ratio to the operating profile.
Designer’s checklist
- [ ] Compute design TR using CLTD/RTS, not a sqm/TR back-calc
- [ ] Cross-check the result against this rules-of-thumb table for the building type + climate zone
- [ ] Investigate any deviation > 20 % from the typical-band midpoint
- [ ] Report sqm/TR prominently in the design summary
- [ ] Top floor sized separately from middle floors
- [ ] Hospitality + healthcare loads include latent peak hour
- [ ] Document the envelope assumption that drives the sqm/TR
- [ ] Show the client the chart of where the gains come from (this is the conversation that gets architects to upgrade glazing)
Pairs with: Cooling Load Calculator, Cooling Load Methods Compared