How to calculate the load of a chiller room
What the load is made of
A chiller-room heat load is the sum of five parts: heat transmitted through the panels (walls, ceiling, floor), the pull-down load on the product, respiration heat for fresh produce, air exchanges through the door, and internal gains from people, lights and fans. Defrost heat is added as a duty margin on the evaporator, not to the room load.
Worked example — 13.2 m³ at +2…+8 °C
- Transmission: 80 mm PIR panels, U ≈ 0.23 W/m²K, ΔT 25 K against a +30 °C ambient — roughly 150–180 W for a 3.2 × 2.2 × 1.9 m box.
- Product pull-down: 300 kg of dairy entering at +12 °C, leaving at +4 °C over 24 h — about 300–350 W average.
- Door and person gains: two staff, four door openings per hour in summer — 150–250 W depending on the air curtain.
- Fans and lights: evaporator fans 120–200 W, LED lighting 30–60 W.
Add a safety margin of 10–15 % and size the unit for the resulting duty at the design ambient, not at the sales-catalogue condition. A unit chosen on catalogue numbers alone will short-cycle in July and ice its evaporator in winter.
Why it matters
An oversized unit short-cycles and dehumidifies the room too fast; an undersized one never leaves the critical zone during loading. Both fail HACCP checks that a correctly sized unit passes.