Refrigeration glossary
Evaporator, condenser, superheat, GWP, blast freezing… Industrial refrigeration and cold room terms in plain English, with example figures and where each term comes up on the site.
Refrigeration glossary
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A5 terms
- Adiabatic coolingSystemsA method that pre-cools the air drawn in by an air-cooled condenser or gas cooler by passing it through a wet pad or spraying a water mist; it lowers the condensing temperature while using water only in the hot hours.
- Air changeBasic conceptsThe replacement of the air in the cold room by outside air; the unintended kind, through door openings, is a heat and moisture load, while the deliberate kind, carried out in fruit and vegetable stores to remove carbon dioxide and ethylene, is ventilation.
- Air curtainCold roomA measure that reduces the exchange of air in and out through an open door: a strong vertical air stream blown from above (air curtain) or clear PVC strips covering the door opening.
- Air flowBasic conceptsThe volume of air the evaporator fans circulate through the room per hour (m³/h); it determines air distribution, air throw and how fast the product cools.
- Air-cooled and water-cooled condenserSystemsAn air-cooled condenser gives its heat to outside air blown by fans, a water-cooled condenser to water from a cooling tower or a well; the choice depends on capacity, climate and water availability.
B4 terms
- Banana ripening roomCold roomA special room, with heating and cooling working together, in which bananas harvested green are ripened evenly in 4–8 days at 14–18 °C, 90–95% relative humidity and under controlled ethylene gas.
- Blast freezerCold roomA room that freezes product to below −18 °C within hours at an air temperature of −30/−40 °C and high air velocity; what sets it apart from a storage room is its speed and capacity.
- Blast freezing (quick freezing)Cold roomFreezing food in a short time with very cold air and high air velocity; because small ice crystals form, texture, flavour and nutritional value are preserved.
- BTU/hBasic conceptsThe unit of heat power used in American and British catalogs; 1 kW ≈ 3,412 BTU/h, 12,000 BTU/h = 1 ton of refrigeration.
C23 terms
- Capacity controlOperation and measurementMatching the capacity delivered by the refrigeration system to the heat load at that moment; it is done by on/off cycling, compressor staging, cylinder unloading, digital scroll or inverter, and it determines efficiency, temperature stability and compressor life.
- Cascade systemSystemsA system made up of two separate refrigeration circuits with different refrigerants, one of which cools the condenser of the other; it is used for temperatures between −50 and −80 °C that a single circuit cannot reach, and for industrial CO₂ plants.
- Central refrigeration system (rack)SystemsA refrigeration arrangement in which several compressors are connected in parallel on a common frame and feed many rooms and cabinets from one system; for supermarkets, large warehouses and food plants.
- Check valveComponentsA valve that lets the refrigerant pass in one direction only and closes by itself with its spring and disc when flow starts in the reverse direction; it prevents liquid or gas from escaping back to where it is not wanted.
- Chiller (water chiller)SystemsA refrigeration unit that cools water (or glycol-water) rather than air; the chilled water is piped to process lines, milk tanks, air-handling units and heat exchangers.
- Chilling injuryCold roomThe permanent tissue damage suffered by fruit and vegetables of tropical and warm-climate origin when they are held at a temperature above freezing point but below their own lower limit; the limit is around 13 °C for bananas and 10 °C for cucumbers.
- Cold chainCold roomKeeping perishable product within its own safe temperature range at every stage from production to the consumer; mostly 0–4 °C for fresh food, −18 °C and below for frozen food, 2–8 °C for pharmaceuticals.
- Cold roomCold roomAn insulated room built from sandwich panels, with a door and a refrigeration unit, in which product is stored; it can run at any temperature between +15 °C and −40 °C.
- Cold room doorCold roomA special door with an insulated leaf, gaskets and (in frozen rooms) a heated frame; hinged, sliding, swing and automatic types are chosen according to traffic and room temperature.
- Cold room floorCold roomThe layer that forms the base of the cold room, bringing together thermal insulation, the vapour barrier and the load-bearing surface; in small rooms it is a floor panel, in stores entered by forklifts it is reinforced concrete poured over insulation.
- Cold room lightingCold roomInterior lighting provided by water- and dust-tight luminaires resistant to low temperature and humidity; today it is almost entirely LED (light-emitting diode), and every watt it uses is also heat load for the room.
- Cold storage warehouseCold roomA facility built from insulated panels and equipped with a refrigeration system, where food and perishable goods are stored for long periods at a set temperature and humidity; it consists of one or many cold rooms.
- CompressorComponentsThe machine that compresses the low-pressure refrigerant vapour from the evaporator to high pressure and temperature, drives the cycle and consumes most of the electricity.
- Compressor oil (POE, mineral, PAG)RefrigerantsThe special oil that lubricates the moving parts of the compressor, provides sealing and carries heat; it is chosen according to the refrigerant: mineral oil with R22, POE with HFC and HFO refrigerants, PAG in vehicle air conditioning and some CO₂ systems.
- CondenserComponentsThe heat exchanger that turns the hot, high-pressure refrigerant vapour from the compressor back into liquid by giving its heat to the outside air; the place where the system rejects heat.
- Condensing temperatureOperation and measurementThe saturation temperature at which the refrigerant condenses in the condenser; it lies 10–15 K above the ambient temperature, and the lower it is, the less electricity the compressor uses.
- Condensing unitSystemsA ready-made outdoor unit in which the compressor, condenser, receiver and auxiliary components are assembled on a common frame; together with the evaporator inside the room it forms a split system.
- ContactorComponentsAn electromagnetic switch that pulls in its coil with a small control current and closes its main contacts, switching high-power loads such as a compressor, fan or heater on and off.
- Controlled atmosphere storage (CA)Cold roomA gas-tight cold store in which the oxygen in the room air is lowered to 1–3% and the carbon dioxide is held in the 1–5% range; it extends the storage time of products such as apples, pears and kiwifruit by several months compared with a normal cold store.
- Cooling capacityBasic conceptsThe amount of heat a refrigeration system or unit can remove from a space per unit of time; expressed in kW, kcal/h or BTU/h.
- Cooling towerSystemsA device that cools the water returning warm from a water-cooled condenser to a value close to the wet-bulb temperature of the outside air by evaporating a small part of it, and sends it back to the condenser.
- COP (coefficient of performance)Basic conceptsThe ratio of cooling capacity to electrical power consumed; a system with a COP of 3 removes 3 kW of heat for every 1 kW of electricity.
- Crankcase heaterComponentsA low-power electric heater that keeps the oil in the crankcase warm while the compressor is stopped; it prevents the refrigerant from migrating into the oil and condensing, the oil from foaming at start-up, the bearings from running without oil, and liquid slugging.
D5 terms
- DefrostOperation and measurementMelting the ice that builds up on the evaporator fins at set intervals; done with electric heaters, hot gas or (in rooms above 0 °C) fans alone, and managed by the controller.
- Defrost heaterComponentsA rod-shaped electric heater with a stainless steel sheath, placed between the evaporator fins and under the drip tray, which is energised during defrost and melts the frost on the tubes and fins; it is the most common defrost method in frozen storage rooms.
- Dew pointBasic conceptsThe temperature at which the water vapour in air begins to condense as the air is cooled; in a cold room it is the yardstick for sweating, icing and humidity control.
- Discharge temperatureOperation and measurementThe temperature of the superheated gas leaving the compressor; it is far higher than the condensing temperature and is measured at between 60 and 110 °C on the discharge pipe. If it goes above the limit it breaks down the oil and wears out the compressor in a short time.
- Drain line heaterComponentsA flexible, waterproof, silicone-sheathed heating cable laid inside or around the drain pipe that carries the evaporator’s defrost water out of frozen storage rooms, preventing the water from freezing in the pipe.
E11 terms
- EC fanComponentsA high-efficiency, quiet fan that runs directly from mains voltage with its brushless permanent-magnet motor and on-board electronics, and whose speed can be adjusted steplessly with a 0–10 V signal. EC stands for electronically commutated.
- EconomiserComponentsA circuit that gives the liquid refrigerant additional cooling before it enters the expansion valve and feeds the vapour produced to the compressor’s intermediate pressure port; it noticeably increases capacity and efficiency at low temperature.
- Electronic expansion valve (EEV)ComponentsAn expansion valve that measures superheat with sensors and meters the refrigerant precisely by driving a stepper motor on command from a controller; it saves energy and offers a wide operating range.
- Energy efficiency (SEPR, ecodesign)Operation and measurementHow much cooling a refrigeration system delivers for every kilowatt-hour of electricity it uses; its instantaneous measure is the COP, its measure that takes account of the outside air conditions changing through the year is the SEPR, and the ecodesign rules set the minimum values.
- EnthalpyBasic conceptsThe total heat content carried by a unit mass of a substance (kJ/kg); the enthalpy difference between two states gives the heat transferred.
- EthyleneCold roomA colourless plant hormone gas (C₂H₄) that fruit and vegetables produce by themselves and that triggers ripening and ageing; it is effective even at one part per million (1 ppm), is sometimes wanted in the store and is mostly removed.
- EvacuationOperation and measurementDrawing the air and moisture out of the system with a vacuum pump before charging, bringing the pressure below 500 microns (0.67 mbar); if skipped, acid, icing and high-pressure problems follow.
- Evaporating temperatureOperation and measurementThe saturation temperature at which the refrigerant boils in the evaporator; it lies TD below the room temperature and is the basic operating point that determines compressor capacity, efficiency and evaporator selection.
- Evaporative condenserComponentsA condenser in which water is sprayed over the condenser tubes and the refrigerant is condensed by the evaporative cooling of the water; it gives a much lower condensing temperature than an air-cooled condenser.
- EvaporatorComponentsThe finned-tube heat exchanger inside the cold room where the refrigerant evaporates and removes heat from the room air; its fans circulate the air.
- Expansion valve (TXV)ComponentsThe valve that throttles the high-pressure liquid refrigerant from the condenser before it enters the evaporator, lowering its pressure and feeding the evaporator exactly as much refrigerant as it needs.
F9 terms
- F-gas regulationRefrigerantsLegislation that limits the production, use and leakage of fluorinated greenhouse gases (HFCs); it phases out high-GWP refrigerants and makes leak checks and record keeping mandatory.
- Fan motorComponentsThe electric motor that turns the impeller which moves room air through the finned tubes of the evaporator and outside air through those of the condenser; it determines the unit’s air flow, its noise and a significant part of its electricity consumption.
- Fan speed controlComponentsAn arrangement that adjusts the speed of the condenser or evaporator fans according to pressure or temperature; it keeps the condensing pressure at an adequate and stable level in winter too, and reduces the fans’ electricity consumption and noise.
- Filter drierComponentsA cartridge filter in the liquid line that traps moisture, acid and dirt in the refrigerant; it prevents the expansion valve from freezing up and the compressor windings from breaking down.
- Fin spacingComponentsThe distance between the fins of an evaporator or condenser (mm); chosen by room temperature: close fins in warm rooms, wide fins in frozen rooms.
- Floating condensing controlOperation and measurementA control method that, instead of holding the condensing temperature at a fixed value, lets it fall along with the outside air as it cools; it reduces the compression work of the compressor and lowers annual electricity consumption by 10–20%.
- Free coolingSystemsCooling carried out, when the outside air is cold enough, without running the compressor, using the coldness of the outside air with fan and pump energy only; it greatly reduces electricity consumption in winter and the transitional seasons.
- FrostingOperation and measurementThe build-up of moisture from the air as a thin layer of hoar frost on evaporator fins or cold pipes whose surface temperature is below 0 °C; to a certain extent it is normal, but in excess it reduces capacity and points to a problem.
- Frozen storageCold roomKeeping frozen food for months at a constant temperature of −18 °C or lower; the room does not freeze the product, it keeps product that arrives frozen in that state, and it usually runs between −18 and −25 °C.
G3 terms
- Glide (temperature glide)RefrigerantsThe difference between the temperatures at which a zeotropic refrigerant blend starts to evaporate (bubble) and is fully evaporated (dew) at constant pressure; about 4.5 K for R449A.
- Glycol system (secondary loop)SystemsAn indirect refrigeration arrangement in which the refrigerant stays in the machinery room only and the cold is carried to the rooms and process points by a glycol–water mixture circulated by pump; it greatly reduces the refrigerant charge and the risk of leaks.
- GWP (global warming potential)RefrigerantsThe warming effect of one kilogram of a refrigerant released to the atmosphere over 100 years, relative to one kilogram of CO₂; 3,922 for R404A, 1,397 for R449A, 3 for R290, 1 for CO₂.
H11 terms
- HACCPCold roomA record-based food safety system (Hazard Analysis and Critical Control Points) that identifies hazards in food production in advance and controls them by measuring at critical points; cold room temperature is the most frequently encountered critical point.
- Heat exchangerSystemsA device that transfers heat between two fluids without mixing them; the evaporator and condenser are each heat exchangers; plate and shell-and-tube types are used in chillers and heat recovery.
- Heat loadBasic conceptsThe total heat entering a cold room that must be removed from it: the sum of heat passing through the panels, heat brought in with product, heat leaking through the door, and heat from people, lighting, fans and defrost.
- Heat of respirationBasic conceptsThe heat that fresh fruit and vegetables release during the respiration that continues after harvest; it is given in watts per tonne (W/tonne), rises rapidly with temperature and is the product-specific item of the cold store heat load.
- Heat pumpSystemsA device that uses the refrigeration cycle for heating: it draws heat from a low-temperature source (air, water, ground or waste heat) and delivers it at a higher temperature to where it is used.
- Heat recoverySystemsThe practice of reusing part or all of the heat that the refrigeration system rejects from the condenser to the outside air for domestic hot water, cleaning water, space heating or underfloor heating; it reduces fuel costs.
- Heat transfer coefficient (U-value)Basic conceptsThe heat flow passing through 1 square metre of a wall, panel or door for every 1 K of temperature difference between its two sides; its unit is W/m²K, and the smaller the value, the better the insulation.
- Hermetic and semi-hermetic compressorComponentsIn a hermetic compressor the motor and compression unit are inside a single welded shell and cannot be opened; in a semi-hermetic compressor the body is bolted and can be serviced and repaired.
- HFC, HFO and HCFC refrigerantsRefrigerantsThe chemical families of synthetic refrigerants: the chlorinated CFCs and HCFCs have been phased out because they damage ozone, the HFCs are being phased down because of their high GWP, and the double-bonded HFOs form the new generation with very low GWP.
- Hot gas defrostOperation and measurementA defrost method in which the hot refrigerant vapour leaving the compressor is temporarily sent to the evaporator and melts the ice from the inside; faster and cheaper than electric, with more complex pipework.
- Humidification (ultrasonic humidifier)Cold roomRaising the relative humidity by adding very fine water droplets to the cold room air; it reduces water loss and weight loss in fruit, vegetables and flowers, and its most common device is the ultrasonic humidifier, which turns water into fog by vibration.
I4 terms
- Ice bankSystemsA thermal storage system that builds up ice on the refrigeration tubes inside a tank full of water and, when needed, melts this ice to supply ice water at 0–1 °C; it meets large instantaneous loads with a small condensing unit.
- Icing (ice block on the evaporator)Operation and measurementThe transformation of frost on the evaporator into a hard, clear mass of ice when it does not melt completely in defrost and refreezes; it blocks the passage of air, warms the room and is almost always the result of a defrost or drainage fault.
- Inverter (variable frequency drive)ComponentsAn electronic device that changes the fixed 50 Hz frequency of the mains to adjust the speed of a compressor, fan or pump motor to the demand; it controls capacity steplessly and saves energy.
- IQF (individually quick frozen)Cold roomThe method by which small products such as peas, strawberries, shrimp and meatballs are frozen one by one without sticking together; in a fluidised bed tunnel the product is kept suspended by a stream of cold air.
K1 terms
L4 terms
- Latent heatBasic conceptsHeat absorbed or released while a substance changes state (freezing, melting, evaporating, condensing) without its temperature changing.
- Leak testOperation and measurementChecking whether the refrigeration circuit is leaking refrigerant, using an electronic detector, foam, pressure or vacuum methods; the F-gas regulation makes regular checks mandatory for charges of 5 tonnes CO₂ equivalent and above.
- Liquid receiverComponentsA pressure vessel at the condenser outlet that stores liquid refrigerant; it holds the surplus refrigerant as the load changes and collects the system’s charge during service.
- Liquid sluggingOperation and measurementThe compressor drawing in liquid refrigerant or oil instead of vapour; because liquid cannot be compressed it breaks the valves, connecting rods and scroll wraps. It is one of the most frequent and most expensive mechanical causes of compressor failure.
M1 terms
N2 terms
- Nitrogen pressure testOperation and measurementVerifying the tightness and strength of a newly installed or repaired refrigeration circuit by pressurising it with dry nitrogen and holding it for a set time before refrigerant is charged; evacuation follows.
- Non-condensable gasesOperation and measurementAir or nitrogen that has entered the refrigeration circuit and does not liquefy under condenser conditions; it collects in the condenser and blanks off surface, raises the discharge pressure and electricity consumption and lowers capacity. It is mostly the result of inadequate evacuation.
O3 terms
- ODP (ozone depletion potential)RefrigerantsThe damage a refrigerant does to the ozone layer relative to R11; chlorinated refrigerants (R12, R22) thin the ozone layer, while HFCs and natural refrigerants have an ODP of zero.
- Oil returnOperation and measurementThe return to the crankcase, by way of the suction line, of the oil carried from the compressor into the system with the refrigerant; it is ensured by pipe diameter, gas velocity, slope and oil traps, and if it is not ensured the compressor is left without oil.
- Oil separatorComponentsA device at the compressor outlet that traps the compressor oil carried along with the refrigerant vapour and returns it to the crankcase; it stops oil accumulating in the system on long lines and at low temperatures.
P12 terms
- Panel thicknessCold roomThe foam thickness of a cold room panel (mm); it increases as the room temperature falls: 80–100 mm for 0 °C, 120–150 mm for −20 °C, 150–200 mm for −35 °C.
- Periodic maintenanceOperation and measurementCleaning, measuring and adjusting the refrigeration system at set intervals, before a fault occurs; condenser cleaning, leak checks, electrical connections, defrost and oil checks are its main items. It lowers electricity consumption and extends equipment life.
- Phase monitoring relayComponentsAn electronic relay that detects phase loss, wrong phase sequence, voltage imbalance and excessively low or high voltage on a three-phase supply and protects the compressor by cutting the control circuit.
- Plate freezerSystemsA machine in which the product is frozen by direct contact, pressed between metal plates with refrigerant passing through them; it freezes regular-shaped block products faster and with less energy than air blast freezing.
- Polyurethane (PUR) and PIR foamCold roomThe closed-cell rigid foam that fills cold room panels; with a thermal conductivity of 0.022 W/mK it is one of the best insulators, and the PIR version is more fire resistant.
- Pre-coolingCold roomRapidly removing the field heat of harvested fruit and vegetables within hours, before they go into the store or onto the vehicle; it slows the product’s respiration, reduces water loss and decay, and noticeably extends shelf life.
- Pressure dropBasic conceptsThe pressure a fluid loses to friction as it passes through pipes, valves, filters and coils; in refrigeration lines it is expressed as its saturation temperature equivalent (K), and in the suction line it should not exceed 1–2 K.
- Pressure equalising valveCold roomA two-way flap vent fitted in the wall panel that automatically equalises the air pressure difference between the inside and outside of the cold room; it is heated in frozen rooms and prevents the panels from buckling inwards and the door from becoming impossible to open.
- Pressure switchComponentsA switch that monitors refrigerant pressure and opens or closes an electrical contact at a set limit; at low pressure it stops the compressor (pump-down, leak protection), at high pressure it protects the system.
- PsychrometricsBasic conceptsThe branch of science that studies the properties of moist air (temperature, relative humidity, dew point, moisture content, enthalpy) and how they change during heating, cooling and humidification; its basic tool is the psychrometric chart.
- Pump-downOperation and measurementWhen the room reaches the set temperature, the solenoid valve in the liquid line closes and the compressor collects the refrigerant from the evaporator into the receiver and stops on the low-pressure switch; it protects the compressor from drawing in liquid.
- PVC strip curtainCold roomA simple and cheap measure that covers the door opening with overlapping clear, flexible PVC (polyvinyl chloride) strips, allowing passage while largely cutting off the exchange of air when the door is open.
R23 terms
- R1234yfRefrigerantsAn HFO refrigerant with a GWP of 4 that breaks down in the atmosphere within days; it has replaced R134a in vehicle air conditioning, is mildly flammable (A2L) and is the main component of blends such as R449A, R448A, R513A and R454C.
- R134aRefrigerantsThe pure HFC refrigerant of medium and high temperature applications (chillers, milk cooling, car air conditioning, refrigerators); GWP 1,430; being replaced by lower-GWP alternatives such as R513A and R1234yf.
- R22RefrigerantsAn HCFC that was the main refrigerant of air conditioning and refrigeration for decades and that damages the ozone layer because it contains chlorine; ODP 0.055, GWP 1,810. Its new production and import are banned, and old systems are serviced only with reclaimed gas.
- R290 (propane)RefrigerantsA natural, highly efficient hydrocarbon refrigerant with a GWP of 3; because it is flammable (A3) its charge is limited and it is used in sealed, leak-tight appliances.
- R32RefrigerantsA single-component HFC that is the standard refrigerant of new air conditioners and heat pumps; GWP 675, it works at high pressures similar to R410A, and because it is mildly flammable (A2L) the charge quantity and installation rules are restricted.
- R404ARefrigerantsThe HFC blend that has been the standard refrigerant of commercial refrigeration for twenty years, used at low and medium temperature; with a GWP of 3,922 it is banned in new systems by the F-gas regulation and is being replaced by R449A/R448A.
- R407CRefrigerantsAn HFC blend of R32, R125 and R134a that replaced R22 in air conditioning, chillers and heat pumps; GWP 1,774, safety class A1, and with a glide of about 7 K one of the highest among common refrigerants.
- R410ARefrigerantsThe common refrigerant of air conditioners and heat pumps; high pressure (8 bar at 0 °C), almost no glide, GWP 2,088; being replaced by R32 and R454B.
- R448ARefrigerantsAn A1 class HFO/HFC blend with a GWP of 1,387, used in place of R404A; it works with the same compressor and POE oil, and because it has a temperature glide of about 5–6 K the settings are made according to the dew and bubble values.
- R449ARefrigerantsAn HFO/HFC blend with a GWP of 1,397 developed to replace R404A; it works with the same compressor and oil and has a temperature glide of about 4.5 K.
- R454CRefrigerantsA mildly flammable (A2L) HFO blend of R32 and R1234yf with a GWP of 148; it is the long-term alternative to R404A in cold rooms and frozen storage, and is used only in new systems designed for A2L.
- R507ARefrigerantsAn azeotropic HFC refrigerant with no glide, a half-and-half blend of R125 and R143a; at low temperature it does the same job as R404A, and because its GWP is 3,985 it is banned in new systems.
- R513ARefrigerantsAn azeotropic blend of R1234yf and R134a developed to replace R134a; GWP 631, safety class A1, no glide. In medium and high temperature applications it works with the same compressor and POE oil.
- R717 (ammonia)RefrigerantsThe most efficient natural refrigerant, with a GWP of 0, used by large industrial refrigeration plants for a century; because it is toxic and mildly flammable (B2L) it needs a separate machine room and expert operation.
- R744 (carbon dioxide, CO₂)RefrigerantsA non-flammable, non-toxic natural refrigerant with a GWP of 1; because it works at very high pressure (34 bar at 0 °C) it needs special equipment, and it is replacing HFCs in supermarket and large warehouse rack systems.
- Reciprocating compressorComponentsThe classic compressor type in which pistons moving back and forth in cylinders draw in and compress the refrigerant; the widest capacity and temperature range, and a repairable design.
- RefrigerantRefrigerantsThe working fluid that circulates in the refrigeration cycle, absorbing heat as it evaporates in the evaporator and releasing it as it condenses in the condenser; R404A, R449A, R134a, R290, CO₂ and ammonia are the main ones.
- Refrigerant chargeOperation and measurementFilling the system with the correct quantity of refrigerant, and the total quantity of refrigerant in the system; undercharge cuts capacity, overcharge raises pressure, and the correct charge is confirmed by superheat and subcooling.
- Refrigerant safety class (A1, A2L, A3, B2L)RefrigerantsThe classification of refrigerants by toxicity (A low, B high) and flammability (1 non-flammable, 2L mildly flammable, 2 flammable, 3 highly flammable); R404A is A1, R32 A2L, R290 A3, ammonia B2L.
- Refrigeration cycleBasic conceptsThe closed loop in which the refrigerant circulates between the compressor, condenser, expansion valve and evaporator, absorbing heat from the cold space and rejecting it to the outside.
- Relative humidityBasic conceptsThe ratio of the water vapour in the air to the maximum it could hold at that temperature; given as a percentage, and in a cold room it directly determines product quality.
- Remote monitoring systemSystemsA system that continuously records the temperature, humidity, door and equipment status of cold rooms with sensors, monitors them over the internet and sends an alarm to your phone on a deviation.
- Ripening roomCold roomA room in which fruit harvested green or firm is brought to ready-for-sale ripeness under control of temperature, humidity, ethylene and carbon dioxide; used for bananas, avocados, mangoes, tomatoes, kiwifruit and for degreening citrus.
S18 terms
- Safety valve (pressure relief valve)ComponentsA spring-loaded valve that opens by itself when the pressure in the system exceeds the maximum allowable value and discharges refrigerant, preventing the vessel or pipe from bursting; it is the last safety measure.
- Sandwich panelCold roomA ready-made building element with foam injected under pressure between two sheets of painted galvanised or stainless steel, serving as insulation and load-bearing structure at once; the walls, ceiling and floor of cold rooms are made from it.
- Saturation temperature and saturation pressureOperation and measurementThe temperature at which a refrigerant exists in equilibrium as liquid and vapour at a given pressure; every pressure has a corresponding saturation temperature, and this relationship is the refrigerant’s P–T chart.
- Screw compressorComponentsA compressor that compresses the refrigerant continuously between two meshing helical rotors; large capacity and suited to uninterrupted operation, for central systems and large warehouses.
- Scroll compressorComponentsA compressor type that compresses the refrigerant through the orbiting motion of one of two interleaved spiral plates; few parts, quiet and vibration-free, the most common type in commercial refrigeration.
- Sensible heatBasic conceptsHeat that changes the temperature of a substance without changing its state; the heat you see on a thermometer and feel by hand.
- Service valve (Rotalock)ComponentsA hand-operated shut-off valve with a stem, found at the suction and discharge ports of the compressor and at the receiver outlet, used to close the line, connect a gauge and remove a component without draining the refrigerant; every condensing unit has them.
- Shelf lifeCold roomThe time for which a food remains safe and of saleable quality under given storage conditions; it depends most on temperature and covers the sum of the time spent in the cold store and the time on the shelf.
- Short cyclingOperation and measurementThe compressor stopping and restarting every few minutes; it heats the motor winding, wears the contactor and carries oil into the system. Manufacturers mostly allow no more than 6–12 starts an hour and require a running time of at least a few minutes.
- Sight glassComponentsA glass-windowed fitting in the liquid line for checking the refrigerant flow and moisture condition by eye: bubbles show a lack of liquid, a colour change shows moisture.
- Solenoid valveComponentsAn automatic valve that opens when energised and closes when de-energised; in the liquid line it shuts off refrigerant flow to the evaporator, enabling pump-down and room control in multi-room systems.
- Specific heatBasic conceptsThe amount of heat that must be added to or removed from 1 kilogram of a substance to change its temperature by 1 K (1 °C); its unit is kJ/kg·K, and the value is 4.19 for water and about 2.1 for ice.
- Spiral freezerSystemsA compact freezer in which the product is frozen continuously by fast air at around −35 °C on a belt that rises or descends in a helix around a drum inside an insulated enclosure.
- Split refrigeration systemSystemsA system in which the evaporator is inside the room and the condensing unit (compressor + condenser) outside, connected by copper pipes; the most common cold room solution.
- SubcoolingOperation and measurementHow far the temperature of the liquid refrigerant at the condenser outlet is below the saturation (condensing) temperature at the same pressure; the normal value is 3–8 K, and it is the most reliable indicator of the charge quantity.
- Suction accumulatorComponentsAn upright pressure vessel located in the suction line just before the compressor, which holds back liquid refrigerant arriving unevaporated from the evaporator and lets only vapour go to the compressor; it protects the compressor from liquid slugging and oil foaming.
- Suction pressureOperation and measurementThe low-side pressure measured at the suction port of the compressor; it is converted to the evaporating temperature from the refrigerant’s P–T (pressure–temperature) chart and is the first measurement that shows how the evaporator is working; a value lower or higher than normal points to a problem.
- SuperheatOperation and measurementHow far the temperature of the refrigerant vapour at the evaporator outlet is above the saturation (evaporating) temperature at the same pressure; the normal value is 5–10 K, and it is the most important health indicator of the system.
T7 terms
- TD (temperature difference)Basic conceptsThe difference between the room air temperature and the evaporating temperature in the evaporator; the most important value in evaporator selection, determining both capacity and room humidity.
- Thermal bridgeBasic conceptsA zone that pierces or interrupts the insulation layer and conducts heat far more easily than its surroundings; in a cold room, steel columns, bolts, the door frame and the floor–wall junction are typical examples.
- Thermal overload relayComponentsA relay that, when the current drawn by the motor exceeds the set value for a time, opens the control circuit with its heated bimetal strips and drops out the contactor, protecting the motor windings from overload, phase loss and burning out.
- ThermostatComponentsThe control device that measures the room temperature and starts and stops cooling according to the set value; modern digital thermostats also manage defrost, fans and alarms.
- Ton of refrigerationBasic conceptsA cooling capacity unit of American origin: 1 ton of refrigeration is the heat removal equivalent to melting 1 ton of ice in 24 hours, about 3.52 kW.
- Transcritical CO₂ systemSystemsA system that uses carbon dioxide (R744) as the refrigerant and whose high-pressure side works above the critical point in hot weather; the heat is rejected to the outside air in a gas cooler, without condensation.
- Two-stage compressionSystemsAn arrangement in which the refrigerant is compressed from suction pressure to condensing pressure not in one go but in two steps, with cooling in between; at evaporating temperatures of −35 °C and below it raises efficiency and protects the compressor from overheating.