How to use this calculator
- Sum the zone peaks. Each zone's individual design peak, added — the number terminal equipment is sized from.
- Establish the block. The simultaneous building peak from an hour-by-hour calculation or trend data at design conditions.
- Compute or apply DF. Compute mode documents the factor your numbers imply; apply mode sizes plant from a known factor.
- Document it. State the DF and any safety factor separately on the schedule — stacked invisible factors are how plants end up 40% oversized.
How it works
Add up every zone's design peak and you get a number the building never actually experiences — the sun cannot be east and west at once. The diversity factor is the honest correction:
DF = block (coincident) load / Σ zone peaks
It buys real capital savings on chillers, mains and pumps, but only when the block number is a true simultaneous peak. This page runs the arithmetic both directions and flags the impossible case (block above the sum) plus aggressive factors below ~0.6 that usually mean an average sneaked in where a peak belonged.
Companions: the CFM/ΔT load calculator for the zone sensible loads themselves, the BTU/GPM/ΔT calculator for the hydronic mains the block load sizes, and the mini-split sizing calculator where single zones make diversity moot.
Worked example
Verified against the live calculator
Twelve zones sum to 120,000 Btu/h (35.2 kW) of individual
peaks, while the hour-by-hour calculation shows a coincident block of
96,000 Btu/h (28.1 kW):
DF = 96,000 / 120,000 = 0.80 → 24,000 Btu/h (20%) of central capacity saved
The chiller and mains are sized near 96,000 Btu/h; every zone terminal still gets its own full peak. Two tons of plant capacity disappear from the purchase order because the math distinguished "all peaks added" from "the peak of the sum" — the entire content of the diversity concept.
Frequently asked questions
What is a diversity factor in cooling load calculations?
The ratio of the building's coincident (block) peak load to the sum of the individual zone peaks: DF = block ÷ Σ peaks, always ≤ 1. Zones peak at different hours — east glass in the morning, west in the afternoon — so the central plant never sees all the zone peaks at once.
What gets sized with diversity and what does not?
Central plant, mains and risers are sized to the coincident block load (with diversity). Each terminal unit, zone coil and branch duct is still sized to its OWN zone peak — applying diversity to terminals is how individual rooms end up undersized.
What is a typical cooling diversity factor?
Multi-zone buildings with mixed orientations commonly land around 0.7-0.9; a single-orientation or single-zone building approaches 1.0. The number must come from a coincident (hour-by-hour) load calculation, trend data or documented experience — not from a wish.
Can I use the same diversity factor for heating?
Usually not. Morning warm-up pulls most zones simultaneously, so heating diversity is often much closer to 1.0 than cooling diversity in the same building. Borrowing the cooling DF for boiler sizing is a classic under-sizing path.
Method & assumptions
- Arithmetic on your loads only — the DF value's justification (coincident calculation, trends, documented experience) lives outside this page.
- Applies to central plant and distribution mains; terminal equipment keeps zone peaks.
- Ventilation/outdoor-air loads may have their own (often higher) coincidence — handle them explicitly rather than inside one blended factor.
- Heating diversity differs (warm-up coincidence); compute it separately.