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Engineers LLP

Cold chain · Guide

How a CA store gets built.

The stages, in order, from land in possession to the first season of fruit. Written for a promoter planning one, with the portfolio as the worked example.

  1. 01

    Land, access and services

    A CA store needs a site the promoter holds, road access for trucks in the harvest weeks, a power sanction that will cover the refrigeration load at peak, and water for the condensers. Ground conditions decide the foundation; at Dekevada and Halol the portfolio has buildings and walls on pile foundations where the ground demanded it. We ask whether the land is in your possession first, because everything else waits on it.

  2. 02

    Capacity and the chamber plan

    Capacity in MT, then chambers. NHB norms allow chambers from 50 to 250 MT. Smaller chambers cost more per MT to build and earn more per MT in use, because each can be opened, loaded and run on its own regime and let separately. The chamber plan fixes the column grid, the door positions and the plant sizing, so it is settled before the structural design.

  3. 03

    The structure: RCC or PEB

    The insulated box sits inside a shell that carries the roof, the wind and, in the hills, the snow. RCC or PEB is decided by span, height, ground and programme; the RCC or PEB guide sets out the trade-offs. The shell has to be built to tolerance: a panel envelope will not seal against a frame that is out of line.

  4. 04

    The floor

    The floor of a cold chamber is insulated and, where freezing is planned, heated below to stop frost heave. The slab is laid flat enough for stacked bins and forklifts and is finished before the envelope closes. It is the one element that cannot be fixed later without emptying the store.

  5. 05

    The envelope

    Insulated panels for walls and ceiling, a continuous vapour barrier on the warm side, and doors with gaskets that seal. India's NHB standard sets the reference thicknesses and densities for CA chambers; the specification for a given store follows the commodity, the regime and the climate. Panel joints are where most stores fail. They are sealed as they go up, not afterwards.

  6. 06

    Penetrations

    Every cable, pipe, sensor line and duct that passes through the envelope is a leak path. Each goes through a sleeve, sealed on both sides, and the number is kept to what the plant needs. The electrical and refrigeration crews work to the same penetration schedule as the envelope crew, which is the practical reason for having them on one contract.

  7. 07

    Refrigeration and CA plant

    Evaporators in each chamber, the refrigeration racks and condensers outside, a nitrogen generator to pull oxygen down, CO2 scrubbers to hold carbon dioxide, ethylene control where the commodity needs it, and sensors per chamber feeding a monitoring system. On turnkey contracts SAI BA installs this plant; on the FHEL contract at Rai it maintains a 12,000 MT plant of exactly this kind.

  8. 08

    Electrical

    Transformer and HT/LT panels sized for the plant, DG backup for the storage season, motor control and the monitoring network. The founding partner on the electrical side has practised since 1994; electrical work appears on the CA stores at Lassipora, Rangreth, Rai, Thane and Kumarsain.

  9. 09

    Testing

    Before any chamber is loaded, it is tested for gas-tightness. The NHB and NCCD standard references ISO 6949:1988(E) Type-2, a pressure-decay test with a defined pass rate. A chamber that fails is fixed before commissioning, not compensated for by running the nitrogen plant harder. Why gas-tightness is a civil problem explains what the test finds and who is responsible for it.

  10. 10

    Commissioning and handover

    The plant is run through its regime on empty chambers, sensors are calibrated, the monitoring system is proven and the operators are trained. The handover file records the chamber plan, the envelope specification, the plant schedule and the test results. Public clients ask for this as a matter of course: the HPMC and Uttarakhand pack house contracts are recorded as supply, installation, testing and commissioning.

  11. 11

    The first season, and after

    The store is loaded chamber by chamber as fruit arrives. Through the season the plant is watched for gas consumption and energy, which is how a leaking chamber first shows itself. An annual maintenance contract, of the kind SAI BA holds for HPMC at four stores, keeps the plant and envelope inspected before every season. See operation and maintenance.

Stores built this way

Cold chain

Cold store

Shiva Agri Fresh

Digadhaar, Himachal Pradesh

Cold store

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