Chiller Tonnage (Delta-T and GPM)
Cooling capacity (tons, BTU/hr, kW) from chilled-water flow and the entering/leaving temperature split.
Example
You enter
- Chilled-water flow (GPM) 240
- Entering water temp (°F) 54
- Leaving water temp (°F) 44
- Fluid water
You get
- Delta-T 10
- Q (Btu/hr) 1200000
- Cooling capacity 100
Checked against published worked examples from: ASHRAE.
Details, formula, and sources
ScopeRequired flow at a nameplate tonnage; water and 30/50% propylene-glycol factors. Q = GPM × 500 × delta-T (water); fluid factors per ASHRAE Fundamentals 2021 Ch. 31.
Formula or tableQ (BTU/hr) = GPM × factor × delta-T; tons = Q / 12000; kW = Q / 3412. Water factor 500 = 60 min/hr × 8.33 lb/gal × 1 BTU/lb-°F. Required flow at nameplate tons = tons × 12000 / (factor × delta-T).
Source and editionFirst-principles fluid energy balance; ASHRAE Fundamentals 2021 Chapter 31 (secondary coolants) by name for glycol factors.
Free accessASHRAE Handbook TOC free at ashrae.org; full handbook licensed.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field namesgpm, ewt_F, lwt_F, fluid, delta_T_F, q_btu_hr, tons
- Water factor 500 BTU/(hr · gpm · °F)60 min/hr × 8.33 lb/gal × 1 BTU/lb-°F (physical fact for water)
- 30% propylene glycol factor ≈ 475ASHRAE Fundamentals 2021 Ch. 31 property derivation
- 50% propylene glycol factor ≈ 449ASHRAE Fundamentals 2021 Ch. 31 property derivation
- Typical chiller delta-T 10-14 °FASHRAE engineering practice