Types of Walk-in Coolers and Freezers
There are three kinds of walk-in coolers and freezers:
- self-contained
- remote condensing
- multiplex condensing
Insulation
Walk-in 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 walk-in 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:
- strip curtains are made up of thick plastic sheets cut into strips
- 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
Compressors
For smaller walk-ins, small reciprocating compressors with capacities of up to 1 hp are recommended
For larger walk-ins, 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 walk-in
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
- 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
- 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 walk-in’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.
- 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)
- 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 walk-in 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 walk-in 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 walk-ins 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 walk-in, 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.)
Part 1 - Walk-in coolers: an introduction
Part 2 - Walk-in coolers: compressors and heat exchangers
Part 3 - Walk-in coolers: filter driers and sight glasses
Part 4 - Walk-in coolers: pressure switches, ball valves, and fan speed controllers
Part 5 - Walk-in coolers: thermostatic expansion valves and solenoid valves