Cold Rooms: a Summary

Use this list to learn what goes into making an efficient cold room.

- Friday, July 21, 2017 By Danfoss

Types of Cold Rooms
    • There are three kinds of cold rooms:
         1. self-contained
         2. remote condensing
         3. multiplex condensing

    • Cold rooms walls are constructed with insulated walls, floors, and ceilings
    • The insulation material, typically some type of foam, is sandwiched between thin walls usually made from steel or aluminum
         — insulating the cold room keeps the temperatures inside and out separated, requiring less work from the     evaporators and condensers to maintain the temperature and conserving electricity.
    • If a cold room is properly insulated, the internal temperature will be better stabilized while also lightening the load placed on the compressor, evaporator, and condenser

Door Curtains
    • There are generally two kinds of door curtains:
         1. strip curtains are made up of thick plastic sheets cut into strips
         2. air curtains are made up of walls of air, blasted at a high velocity from directly above the door
    • Both designs help keep the temperature of the cold room low and its efficiency high

    • For smaller cold rooms, small reciprocating compressors with capacities of up to 1 hp are recommended
    • For larger cold rooms, scroll compressors with capacities starting at 1 hp are recommended
         — scroll compressors have fewer moving parts than reciprocating compressors, which results in fewer opportunities for break downs and a long-lived, reliable unit
         — scroll compressors are incredibly energy efficient, with some models showing 35% lower energy consumption compared to reciprocating compressors under laboratory conditions

Heat exchangers
    • Heat exchangers efficiently and reliably transfer heat out of the cold room
    • The design of the heat exchanger, from the materials used to its shape and structure, are crucial in determining its performance

Filter Driers
    • Filter driers extend the lifetime and reduce the maintenance costs of the refrigeration system
    • There are typically two kinds of filter driers: loose desiccant with spun copper tubing and solid core molecular sieve with steel housing
         1. spun copper filter driers use loose desiccant beads coated with a binder enclosed in a thin copper casing tube and with a built-in wire mesh or fiberglass mat for solid particulate filtration; the binder coating slows absorption
        2. solid core filter driers use an integrated process when the refrigerant passes through molecular sieve material and polyester felt mats; solid core filter driers can be delivered with a moisture level up to three times lower than that of spun copper

Sight Glasses
    • Sight glasses are great for detecting moisture present in a cold room’s refrigeration system.
         — bubbles in the refrigerant may indicate a pressure drop after passing through the filter drier (which can usually be fixed by replacing the filter drier)
         — bubbles may also mean that not enough refrigerant is present (likely caused by a leak)
         — bubbles may be a signal that subcooling is not being achieved, which is a critical step in the refrigeration cycle

Pressure Switches
    • A pressure switch has two main functions: protection and control.
         1. protective: the pressure switch limits refrigeration pressure by stopping the flow of refrigerant if pressures exceed a safe operating limit or if pressures drop too low (e.g., the system has a leak)
        2. control: controlling the pressure also controls other aspects in the cooling cycle (e.g., compressor cycling, fan cycling, pump-down, etc.)

Ball Valves
    • Ball valves can block refrigerant off in one section of the cold room system, i.e., requiring less refrigerant to be recovered during servicing, saving time and money
Fan Speed Controllers
    • Fan speed controllers can be used to:
        — reduce noise
        — stabilize condensing pressures under different climatic conditions
        — stabilize temperatures over the course of the refrigeration cycle
        — increase a cold rooms energy efficiency, by maintaining a constant low speed
    • Depending on the application, two speed fan motors may be used for special areas like preparation rooms for food processing

Thermostatic Expansion Valves
    • TXVs regulate the flow of refrigerants based on the needs of the system, ensuring that the cold room will operate as efficiently and with as little refrigerant as possible

Solenoid Valves
    • Solenoids work well for a multitude of cold room applications, including hot gas defrost and humidity control
Electromechanical Thermostats
    • Most cold rooms use an electromechanical thermostat consisting of a sensor and an electric contactor
    • These types of thermostats are switches in that they operate on an on/off basis
        — when the interior temperature climbs too high, the thermostat sends a signal to the compressor to turn on, activating the refrigeration cycle
        — once the desired temperature has been reached, the thermostat will signal the compressor to shut off, interrupting the cycle
    • Correctly adjusting the temperature differential is vital in achieving optimal energy efficiency
        — if the differential is too small, the refrigeration cycles will be too short, starting and stopping frequently, negatively impacting the working life of the equipment
        — if the differential is too large, the refrigeration cycles will be too long, resulting in large temperature fluctuations, risking product freshness

Electronic Controllers
    • By using an electronic thermostat or controller, the entire system can better work together, offering better energy efficiency and a more stable internal temperature
    • Electronic controllers can be programmed to meet the specific needs of each cold room, depending on patterns of use, ambient temperatures, air humidity, and other factors
    • Depending on the model used, electronic controllers can reduce power consumption, save money, and collect usage data (e.g., the number of times the door opens, fluctuations in temperature levels, fan and compressor cycles during the day and night, etc.)



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