Understand These 50 Refrigeration and HVAC Terms to Make You More Professional

Central Air Conditioning:
Central air conditioning is an air conditioning system that controls different rooms to achieve the purpose of indoor air conditioning by having one main unit supply air through air ducts or connect multiple terminals via chilled water or hot water pipes. That is to say, it supplies both cooling and heating for all rooms. There are only air blowers in each room, and all the original outdoor refrigeration units are integrated into one casing.

Central Air Conditioning System:
It consists of a main unit and a terminal system. According to the medium used to bear the indoor heat and moisture load, it can be divided into all-air system, all-water system, air-water system, and refrigerant system. According to the degree of concentration of air handling equipment, it can be divided into centralized and semi-centralized types. According to the source of the processed air, it can be divided into closed type, direct current type, and mixed type (primary return air, secondary return air). The main equipment includes the air conditioning main unit (cooling and heating source), air cabinet, fan coil unit, etc.

Refrigerant:
A refrigerant, also known as a refrigeration working medium, is the working medium that completes the refrigeration cycle in a refrigeration system. The refrigerant absorbs the heat of the object to be cooled in the evaporator and evaporates, and transfers the heat to the surrounding air or water in the condenser and is condensed into a liquid. The refrigerator achieves the purpose of refrigeration by means of the state change of the refrigerant.

Refrigerating Capacity:
When the air conditioner is operating for refrigeration, the heat absorbed by the refrigerant on the low-pressure side in the evaporator per unit time. The commonly used units are W or KW.

Heat Output of Heat Pump:
When the air conditioner is operating for heat pump heating (the heat pump auxiliary electric heater should operate simultaneously), the amount of heat delivered into a closed space, room or area per unit time.

Coefficient of Performance:
The ratio of the refrigerating (heating) capacity generated in the refrigerating (heating) cycle to the power consumption for refrigerating (heating) is the coefficient of performance. When it is for refrigeration, it is called the energy efficiency ratio, represented by EER; when it is for heating, it is called the coefficient of performance, represented by COP.

Coolant:
A coolant refers to the intermediate medium used to transfer the cooling capacity in an indirect refrigeration system. After being cooled by the refrigerant in the evaporator, the coolant is sent to the cooling equipment for cooling, absorbs the heat of the object or environment to be cooled, and then returns to the evaporator to be cooled by the refrigerant again. In this way, it circulates continuously to achieve the purpose of continuous refrigeration.

Fan Coil Unit:
It is a commonly used heat exchange device in the central air conditioning system, composed of finned tubes, fans, etc. When the coolant flows through the fan coil unit (inside the tubes), it exchanges heat with the air outside the tubes, cooling the air. The fan coil unit belongs to an air cooling device.

Water-cooled Chiller:
The water-cooled chiller belongs to the refrigeration unit part of the central air conditioning system. Its coolant is water, so it is called a chiller. The cooling of the condenser is achieved by exchanging heat with normal temperature water to reduce the temperature, so it is called a water-cooled unit. In contrast to the water-cooled unit is the air-cooled unit. The condenser of the air-cooled unit achieves the cooling purpose by forced ventilation and heat exchange with the outdoor air.

Cooling Tower:
It is a special device that cools water with the help of air, generally installed on the top of a building. In many industries such as refrigeration, power, and chemical engineering, the hot cooling water discharged from equipment such as condensers is cooled by the cooling tower and then recycled.

Modular Unit:
It changes the traditional Freon pipeline into a water circuit system, combines the indoor and outdoor units into a refrigeration unit, and changes the indoor unit into a fan coil unit. It realizes the refrigeration process by the heat exchange of the coolant water. The modular unit gets its name because it can automatically adjust the number of starting units according to the cooling load requirements and achieve flexible combination. The modular unit is a combined central air conditioning system. The single unit has a small volume and light weight, and the occupied area is small after splicing. As long as the selection is correct, due to the large number of units, the relative reliability is high. In many places with high reliability requirements, there are often 10 units or even 50 units. When the load fluctuates greatly, the modular unit is energy-saving.

Multi-split Unit:
The multi-split unit is not really a central air conditioning system in the traditional sense. In the traditional central air conditioning system, water is sent into the fan coil unit, while in the multi-split unit, the refrigerant is directly sent into the fan coil unit. So it is doomed that the pipeline of the multi-split unit cannot be too long, and the energy loss in the pipeline of the multi-split unit is larger than that of the split unit. If there is a leakage in the pipeline of the multi-split unit, it is often impossible to repair it. In the variable frequency multi-split unit, not all compressors are variable frequency. Generally, only one compressor is variable frequency, and the others are fixed frequency. The pipeline system and control system of the multi-split unit are relatively complex.

Differences between Modular Unit, Screw Unit and Multi-split Unit:
Both the modular unit and the screw unit are water systems, that is, the chilled water comes out from the main unit and is supplied to indoor terminal equipment such as air coils for refrigeration.
The multi-split unit is a refrigerant system. The refrigerant (such as R22 or R410a refrigerant) comes out from the main unit, and the indoor terminal is also an indoor unit connected to the refrigerant pipeline. It is similar to a home single-unit air conditioner, but it becomes a multi-unit system, and variable frequency (DC variable frequency or digital scroll variable frequency) technology is added.

Differences between Air-cooled Unit and Water-cooled Unit:
The air-cooled unit means that the main unit dissipates heat by a fan, while the water-cooled unit means that the main unit dissipates heat by water.

The air-cooled unit has a compact structure, does not require a special machine room, and is easy to maintain. Its disadvantage is that the cooling and heating are greatly affected by the climate, and the energy efficiency ratio is slightly lower than that of the water-cooled unit. The water-cooled unit generally requires a special machine room and is equipped with a cooling tower. The system is slightly more complex and the maintenance is a bit more cumbersome. Most of them cannot provide heating. Its advantage is that the cost is lower than that of the air-cooled unit, and the energy efficiency ratio is slightly higher than that of the air-cooled unit.
Energy Efficiency Ratio:
The energy efficiency ratio of an air conditioner is the ratio of the nominal cooling capacity (heating capacity) to the operating power. That is, the mathematical expressions of EER and COP are: EER = cooling capacity / cooling power consumption, COP = heating capacity / heating power consumption. The higher the EER and COP, the lower the energy consumption of the air conditioner and the higher the performance ratio.

Fresh Air System:
The fresh air system is a part of the air conditioning system. It cannot adjust the indoor temperature and is specially used for the exchange of indoor and outdoor air, keeping the indoor air fresh all the time. (This system is usually used, but it should be closed during a fire to avoid supplying oxygen to fuel the fire.)

Vertical Imbalance:
In a hot water double-pipe system, due to the different height differences between the radiators on each floor and the boiler, although the supply and return water temperatures entering and leaving the radiators on each floor are the same (without considering the influence of pipeline cooling along the way), the acting pressure of the radiators with a larger vertical distance from the boiler is greater, and that with a smaller distance is smaller. Even if different pipe diameters are selected, the resistance balance of each floor cannot be achieved, resulting in uneven flow distribution and uneven heating and cooling between the upper and lower floors. This phenomenon is usually called vertical imbalance. Moreover, the more floors a building has, the greater the difference in acting pressure between the upper and lower floors, and the more serious the vertical imbalance will be.

Design Heat Load of Heating System:
The design heat load of a heating system is the amount of heat supplied to a building per unit time at a certain outdoor temperature to meet the indoor temperature requirements and maintain the heat balance of the room. The design heat load Q′ of the heating system includes two parts: one part is the heat loss Q1′ through the building envelope due to heat transfer, that is, the heat dissipated from the interior to the exterior through the building envelope such as doors, windows, floors, and roofs; the other part is the heat loss Q′ due to the infiltration of cold air, which is used to heat the cold air infiltrated into the room through the gaps of doors and windows, and the heat loss Q′ due to the intrusion of cold air, which is used to heat the cold air entering the room due to the opening of doors and windows.

Calculated Indoor Air Temperature:
The calculated indoor air temperature generally refers to the average environmental temperature in the area where people are active within 2.0m from the ground, which should meet the requirements of people's living and production processes.

Calculated Outdoor Temperature for Heating:
The calculated outdoor temperature for heating should be the daily average temperature that is not guaranteed for 5 days on average each year over the years.

Minimum Thermal Resistance (Minimum Heat Transfer Resistance):
It specifically refers to the lower limit value of the heat transfer resistance of the building envelope allowed in the design calculation. The purpose of specifying the minimum heat transfer resistance is to limit the excessive heat transfer through the building envelope, prevent the condensation on the inner surface, and limit the excessive radiation heat transfer between the inner surface and the human body to avoid the human body getting cold.

Economic Heat Transfer Resistance (Economic Thermal Resistance):
The heat transfer resistance when the sum of the construction cost per unit area of the building envelope (the depreciation cost of the initial investment) and the usage cost (the heating operation cost and equipment depreciation cost apportioned per unit area of the building envelope) reaches the minimum value.

General Ventilation:
General ventilation is to ventilate and exchange air in the whole room. The fresh air sent into the room dilutes the concentration of harmful gases in the room to below the allowable range of the hygiene standard. At the same time, the polluted indoor air is directly or after purification treatment and discharged into the outdoor atmosphere.

Emergency Ventilation:
Emergency ventilation is an exhaust system set up to prevent greater losses of personnel or property caused by the sudden release of a large amount of harmful gases or explosive gases when production equipment has accidental accidents or failures in the production workshop.

It is a necessary measure to ensure safe production and protect the lives of workers.

Air Exchange Rate:
The air exchange rate n refers to the ratio of the ventilation volume L (m3/h) to the room volume V (m3), that is, n = L/V.

Air Quality Balance:
In a ventilated room, no matter which ventilation method is adopted, the mass of air entering the room per unit time should be equal to the mass of air discharged within the same time. That is, the air quality in the ventilated room should be kept in balance, which is the air quality balance.

Heat Balance:
Heat balance means that the total heat gain and total heat loss in the room are equal to keep the indoor temperature stable.

Fan Air Volume:
It refers to the volume of gas transported by the fan per unit time when the fan is working under standard conditions, which is called the fan air volume, represented by the symbol L, and the unit is m3/h.

Fan Air Pressure:
It refers to the sum of the dynamic pressure and static pressure that each cubic meter of air should obtain when passing through the fan, represented by the symbol P, and the unit is Pa.

Partial Pressure of Water Vapor Pq:
The pressure generated when water vapor in moist air occupies the volume of the moist air alone and has the same temperature as the moist air is called the partial pressure of water vapor in the moist air. The magnitude of the partial pressure of water vapor reflects the amount of water vapor in the air. The more water vapor there is in the air, the greater the partial pressure of water vapor.

Partial Pressure of Saturated Water Vapor Pq.b:
At a certain temperature, when the content of water vapor in moist air reaches the maximum limit, the moist air is said to be in a saturated state.

At this time, the corresponding partial pressure of water vapor is called the partial pressure of saturated water vapor.

Moisture Content:
The definition of moisture content (d) is the amount of water vapor contained in the moist air corresponding to one kilogram of dry air. Its unit is expressed in g/kg. The magnitude of the moisture content changes with the amount of water vapor in the air, and it can accurately reflect the amount of water vapor in the air.
Relative Humidity:
Relative humidity (φ) is defined as the ratio of the partial pressure of water vapor in moist air to the partial pressure of water vapor in saturated moist air at the same temperature. Relative humidity reflects the degree to which the water vapor in moist air approaches the saturated content, and also reflects the humidity of the air. When the relative humidity φ = 0, it is dry air; when the relative humidity φ = 100%, it is saturated moist air.

Enthalpy h:
The sum of the enthalpy of each kilogram of dry air and the enthalpy of d kilograms of water vapor coexisting with it is called the enthalpy of (1 + d) kilograms of moist air, and its unit is kJ/kg(a). In air conditioning, the pressure change of air is generally very small, which can be approximately regarded as a constant pressure process. Therefore, the enthalpy difference between the initial and final states when the moist air changes reflects the heat change in the process of state change.

Dew Point Temperature tl:
Under the condition that the moisture content remains unchanged, the temperature at which the moist air reaches the saturated state is called the dew point temperature of the air. When the moist air is cooled, as long as the temperature of the moist air is greater than or equal to its dew point temperature, there will be no condensation phenomenon. Therefore, the dew point temperature of the moist air is the criterion for judging whether condensation occurs.

Wet Bulb Temperature ts:
Theoretically, the wet bulb temperature is the adiabatic saturation temperature when the air is in direct contact with water and reaches a stable thermal and moisture equilibrium under constant pressure and adiabatic conditions. In reality, a thermometer's temperature sensing bulb is wrapped with gauze, and the lower end of the gauze is immersed in a container filled with water. Under the action of capillary phenomenon, the gauze is in a wet state. This thermometer is called a wet bulb thermometer, and the measured temperature is called the wet bulb temperature of the air.

Thermal Moisture Ratio:
In order to illustrate the direction and characteristics of the change in air state, the ratio of the enthalpy difference to the moisture content difference before and after the change in air state is often used to characterize it. This ratio is called the thermal moisture ratio.

Heat Gain and Cooling Load:
Heat gain refers to the sum of the heat entering the air-conditioned room from the outside and the heat generated inside the air-conditioned room at a certain moment; Cooling load refers to the amount of cooling that needs to be supplied to the room at a certain moment in order to maintain a constant indoor temperature. Heat gain and cooling load are sometimes equal and sometimes not. The nature of the heat gain and the heat storage characteristics of the building envelope determine the relationship between the two.

Cooling Load of Air Conditioning System:
It is composed of the cooling loads of each air-conditioned area served by the system and the additional cooling load. 24. Additional Cooling Load: It refers to the cooling load of fresh air, the cooling load caused by the temperature rise of air passing through the fan and air duct, the cooling load caused by the temperature rise of cold water passing through the water pump, water pipe and water tank, and the additional cooling load caused by the phenomenon of heat and cold offset in the air treatment process, etc.

Air Handling Equipment:
Air handling equipment is a combination of air thermal and moisture treatment and purification equipment such as filters, surface air coolers, air heaters and air humidifiers. It is the core of the air conditioning system. Indoor air and outdoor fresh air are sent here for thermal and moisture treatment and purification to reach the required air state parameters such as temperature and humidity, and then sent back to the room.

Air Distribution System:
The air distribution system is composed of supply fans, supply air ducts, air supply outlets, air return inlets, air return ducts, etc. It sends the treated air to the air-conditioned room and sends the indoor air to the air handling equipment for treatment or discharge to the outside.

Air Distribution:
It refers to some technical measures taken in the air-conditioned room to achieve a specific air flow pattern in order to ensure the air conditioning effect and improve the economy of the air conditioning system.

Resistive Muffler:
The resistive muffler is to fix the sound-absorbing material on the inner wall of the pipeline where the air flow flows, or arrange it in the pipeline in a certain way, so as to reduce the noise. Its main feature is that it has a good noise reduction effect on medium and high frequency noise, but a poor noise reduction effect on low frequency noise.

Reactive Muffler:
The reactive muffler is composed of some small chambers and air ducts, and is also known as an expansion muffler. Its noise reduction principle is to use the sudden change of the cross-section in the pipeline to make the sound wave propagating along the air duct reflect in the direction of the sound source, so as to play a role in noise reduction. The characteristic is that it has a good noise reduction effect on medium and low frequency noise, but the noise reduction frequency range is relatively narrow.

Evaporation Capacity:
It refers to the evaporation capacity of the steam boiler per hour. The size of this value characterizes the size of the boiler capacity. It is generally represented by the symbol D, and the unit is t/h.

Boiler Efficiency:
It refers to the ratio of the heat of steam or hot water generated by the boiler to the total heat released when the fuel is completely burned in the boiler. It is usually represented by the symbol η, and the unit is %. The size of η directly indicates the economy of the boiler operation.

Heat Pump:
The so-called heat pump is a device that consumes a certain amount of energy by the refrigeration unit to extract heat from the low-temperature heat source and supply more heat to the heat-requiring object. Using a set of heat pump units can not only cool in summer but also heat in winter.

Natural Smoke Exhaust:
Natural smoke exhaust uses the buoyancy, thermal pressure or other natural forces generated by hot smoke to discharge the smoke outdoors. There are two ways of natural smoke exhaust: 1) Natural smoke exhaust using external windows or specially designed smoke exhaust openings; 2) Natural smoke exhaust using shafts.

Mechanical Pressurized Smoke Prevention:
Mechanical pressurized smoke prevention is to rely on the pressurization of the fan to send fresh outdoor air into the evacuation areas that should be protected, such as the front room, staircase, closed refuge floor (room), etc., to increase the indoor pressure in this area and block the intrusion of smoke.

Positive Pressure Air Supply:
Positive pressure air supply is to supply air to the escape corridor in case of an accident, which is conducive to escape. At the same time, when the air is supplied, the corridor is under positive pressure, that is, the air pressure in the corridor is higher than that in other places, and the smoke will not seep in and cause people to suffocate, so as to ensure safety. (This system is not used in normal times, but only in case of fire. It is a setting for escape.)