Project details printed on the A4 calculation sheet
Room & envelope transmission through insulated panels
Dry goods: 55–65%
Use 0 if under a shed
Product load daily intake pulled down over the pull-down period
Fresh goods? Use the blast tab
kJ/kg·K
kJ/kg·K
kJ/kg
Gunny/jute, cartons — Cp 1.6
For respiration heat
Fresh produce only
Internal & operating loads equipment, people, doors
0 = auto estimate 7%
50% credited to room
Sizing = 24 h load ÷ run h
Chamber & envelope usually inside a process hall
Batch & product the dominant load — typically 60–80% of total
Core to −18 °C
kJ/kg·K
kJ/kg·K
kJ/kg
Re-cooled every cycle
Fans, defrost & door fan heat is large at high air velocity
0 = auto estimate 10%
Loading + unloading
Fraction of chamber volume
For daily throughput only
Throughput continuous duty — steady-state, not batch
After pre-chiller, if any
kJ/kg·K
kJ/kg·K
kJ/kg
Moisture frozen onto the coil
Tunnel enclosure air temperature runs well below the product outlet temp
Belt inlet + outlet openings
Belt, drives & defrost
Full loops per hour
Warm-up on the return / wash leg
Hot-gas defrost: enter 0
Duty continuous flow or batch pull-down
Jacketed vessel, reactor etc.
Tank, piping & pumps
Shaft work ends up as heat
Process demand hours
Product thermal properties ASHRAE Ch. 19 · dry commodities from Siebel's correlation on moisture content
| Product | Moisture % | Cp above fr. kJ/kg·K | Cp below fr. kJ/kg·K | Latent heat kJ/kg | Freezing pt °C | Respiration W/tonne | Store temp °C | Store RH % |
|---|
Dry commodities carry too little free water to show a usable freezing plateau, so the freezing point reads “—” and the calculator treats them as sensible-heat only. Cp above freezing = 0.837 + 3.349·w, Cp below = 0.837 + 1.256·w, latent = 334·w, where w is the water mass fraction.
Indian dry-commodity storage practice controlled-atmosphere and low-RH rooms
| Commodity | Room °C | RH % | Safe moisture % | Typical storage life | Governing concern |
|---|---|---|---|---|---|
| Dry red chilli (whole, S4 / Teja) | 8–10 | 55–60 | 10–11 | 9–12 months | Colour (ASTA) loss, aflatoxin, cigarette beetle |
| Chilli powder / oleoresin feed | 5–8 | 50–55 | 8–9 | 12 months | Colour fade, caking |
| Turmeric finger / bulb | 10–12 | 60–65 | 10 | 12 months | Curcumin retention, mould |
| Coriander, cumin, fennel seed | 10–12 | 55–60 | 8–9 | 12 months | Volatile oil loss, insect |
| Black pepper, cardamom | 8–10 | 55–60 | 10–11 | 12 months | Piperine / oil loss, mould |
| Tamarind (deseeded block) | 8–10 | 60–65 | 18–20 | 10–12 months | Darkening, fermentation |
| Pulses — chana, tur, moong, urad | 12–15 | 55–60 | 9–10 | 12–18 months | Bruchid weevil, hardening |
| Rajma, dry peas, lentil | 10–15 | 55–60 | 10–12 | 12 months | Hard-to-cook defect |
| Paddy, rice, wheat, maize | 15–18 | 60–65 | 12–13 | 12 months | Insect, mould, germination loss |
| Sowing / vegetable seed | 4–8 | 35–45 | 6–8 | 24–36 months | Germination — low RH is critical |
| Cashew kernel, almond, dry fruit | 4–8 | 60–65 | 5–6 | 12 months | Rancidity, insect |
| Copra, groundnut kernel | 8–10 | 60–65 | 6–7 | 6–9 months | Aflatoxin, free fatty acid rise |
| Raisin, dry dates, dry figs | 2–5 | 60–65 | 15–20 | 9–12 months | Sugaring, fermentation, moth |
| Jaggery / gur block | 10–12 | 55–60 | 8–10 | 9–12 months | Moisture pickup, melting, inversion |
| Dehydrated onion / garlic flake | 8–10 | 45–55 | 5–6 | 12 months | Rehydration, browning |
| Areca nut, green coffee, tea | 12–15 | 55–60 | 10–11 | 12 months | Mould, flavour loss |
| Dry fish, dry prawn | 0–5 | 60–65 | 18–20 | 6–8 months | Rancidity, mite, halophilic mould |
Dry-commodity rooms are humidity-controlled, not just cooled. Product load is small — the duty is dominated by transmission and by latent load from infiltration, so the enthalpy-based infiltration term in this calculator matters more than the product term. Where the design RH is below about 50%, an air cooler alone cannot hold it and a desiccant dehumidifier is required; its reactivation heat then becomes an additional room load. Keep panel joints and door seals vapour-tight — moisture ingress, not heat ingress, is what fails these rooms.
Insulation conductivity & typical thickness
| Material | k (W/m·K) | Dry store +10 °C | Chill room +2 °C | Freezer −20 °C | Blast −35/−40 °C |
|---|---|---|---|---|---|
| PUF (polyurethane, 40 kg/m³) | 0.022 | 60–80 mm | 80–100 mm | 125–150 mm | 150–200 mm |
| PIR (polyisocyanurate) | 0.021 | 60–80 mm | 80–100 mm | 120–150 mm | 150–200 mm |
| EPS (expanded polystyrene) | 0.036 | 100 mm | 125–150 mm | 200–250 mm | 250–300 mm |
| XPS (extruded polystyrene) | 0.030 | 80–100 mm | 100–125 mm | 150–200 mm | 200–250 mm |
| Rockwool (fire-rated panel) | 0.040 | 100 mm | 150 mm | 250 mm | 300 mm |
| Spray PUF in situ | 0.025 | 75 mm | 100 mm | 150 mm | 200 mm |
U-value used here = 1 / (Rout + t/k + Rin) with surface films Rout = 0.04 and Rin = 0.13 m²·K/W. Floors on grade use the slab temperature, not ambient. Freezer floors also need under-floor heating against frost heave — that heater is a room load.
Air changes per 24 h — infiltration allowance
| Room volume m³ | Above 0 °C | Below 0 °C |
|---|
Follows the ASHRAE curve N = 13.5 × (V/100)−0.544, with a 0.8 factor below freezing, then multiplied by the door-usage factor and any curtain or vestibule credit. Heavy dock traffic can double the base figure — do not under-set it, infiltration is often the second-largest load in a freezer and the largest latent load in a dry store.
Method and formulas used
Transmission Q = U · A · ΔT [W] U = 1 / (0.04 + t/k + 0.13)
Infiltration Q = N · V · ρroom · (hamb − hroom) / 86400 [kW]
Product Q = m · [Cp₁(T₁−Tf) + Lf + Cp₂(Tf−T₂)] / (3600 · tpd) [kW]
Occupancy q = 272 − 6 · Troom [W per person]
Equipment Q = kWrated · (run hours / 24) · defrost credited 50% into the room
Chilled fluid Q = ṁ · Cp · ΔT [kW], ṁ in kg/s
Selection TR = (24 h load ÷ plant run hours) ÷ 3.517
- Moist-air enthalpy from h = 1.006·T + W·(2501 + 1.86·T), saturation pressure over water above 0 °C and over ice below it.
- Loads are averaged over 24 h (or over one cycle for blast freezing), then divided by compressor run hours for the selection capacity. Never select on the 24 h average alone.
- Setting evaporator fan kW to 0 triggers an estimate — 7% of subtotal for cold rooms, 10% for blast freezers. Replace it with the real fan kW once the unit cooler is picked.
- Latent heat applies only where the product crosses its freezing point. Goods arriving already frozen, and all dry commodities, are charged sensible heat only.
- Saturated suction normally runs 6–8 K below room temperature for freezers, 6–10 K for chill and dry stores. Read compressor capacity at that suction, not at room temperature.
Typical design values
| Application | Room °C | RH % | Suction °C | Pull-down | Run h/day | Air velocity |
|---|---|---|---|---|---|---|
| Dry commodity / spice store | +8 to +15 | 55–65 | 0 to +3 | 24–48 h | 14–16 | low |
| Seed store (low RH) | +4 to +8 | 35–45 | −2 | 48 h | 16 | low + desiccant |
| Banana / potato ripening-chill | +13 / +8 | 90 | +3 | 24 h | 16 | low |
| Fruit & vegetable cold store | +2 to +4 | 90–95 | −5 | 24 h | 16–18 | 0.3 m/s |
| Dairy / meat chill | 0 to +2 | 85–90 | −7 | 18–24 h | 18 | 0.5 m/s |
| Frozen store | −18 to −25 | 90 | −28 to −33 | 20–24 h | 18–20 | 0.3 m/s |
| Blast freezer (batch) | −35 to −40 | 85 | −40 to −45 | 8–12 h | 20 | 3–6 m/s |
| IQF spiral / fluidised bed | −35 to −40 | 85 | −40 to −45 | 6–40 min | 20–22 | 4–8 m/s |
| Chilled water (food / dairy) | +1 to +5 | — | −2 to −5 | — | 18–20 | — |
| Glycol / brine circuit | −5 to −10 | — | −12 to −18 | — | 20 | — |
Unit conversions
| From | To | Multiply by |
|---|---|---|
| kW | TR (tons of refrigeration) | 0.28435 |
| TR | kW | 3.51685 |
| kW | kcal/h | 860.0 |
| kW | BTU/h | 3412.1 |
| TR | kcal/h | 3024 |
| TR | BTU/h | 12000 |
| kJ | kcal | 0.2388 |
| m³/h water | kg/s | 0.2778 |
A design aid. Verify product properties, ambient design conditions and site operating patterns against project data and the relevant ASHRAE / ISHRAE standard before releasing equipment selections.