HVAC knowledge

Central air conditioning: central air conditioning is a kind of air conditioning system which controls different rooms by a host through air duct or connecting cold and hot water pipes to multiple terminals to achieve the purpose of indoor air conditioning. That is to say, all rooms are supplied with cold and warm air. There are only forced draft fans in each room, and the original external cooling units are all integrated into a box.

Central air conditioning system: there are mainframe and terminal system. According to the media used to bear the indoor heat and humidity load, it can be divided into all air system, all water system, air water system and refrigerant system. According to the concentration degree of air treatment equipment, it can be divided into centralized and semi centralized. According to the source of treated air, it can be divided into closed type, direct flow type and mixed type (primary return air and secondary return air). The main components of the equipment are air conditioning host (cold and heat source) air cabinet, fan coil unit and so on.

Refrigerant: refrigerant is the refrigerant, which is the working medium to complete the refrigeration cycle in the refrigeration system. The refrigerant absorbs the heat of the object to be cooled in the evaporator and evaporates. In the condenser, the heat is transferred to the surrounding air or water and is condensed into a liquid body. With the help of the state change of refrigerant, the refrigerator achieves the purpose of refrigeration.

Cooling capacity: the heat absorbed by the refrigerant at the low pressure side in the evaporator per unit time during the refrigeration operation of the air conditioner. The commonly used unit is w or kW.

Heat pump heating capacity: the heat input into the confined space, room or area in unit time during the heat pump heating operation of air conditioner (the auxiliary electric heater of heat pump shall operate at the same time).

The ratio of heat to power of the cycle. Refrigeration is called energy efficiency ratio, expressed by eer; heating is called coefficient of performance, expressed by cop.

Carrier refrigerant: it refers to the intermediate medium used to transfer cooling capacity in indirect refrigeration system. After being cooled by refrigerant in the evaporator, the refrigerant is sent to the cooling equipment for cooling, absorbing the heat of the object or environment being cooled, and then returning to the evaporator to be re cooled by the refrigerant, so as to achieve the purpose of continuous cooling.

Fan coil unit: set the heat exchange equipment commonly used in central air conditioning system, which is composed of finned tube and fan. When the refrigerant flows through the fan coil unit (inside the pipe), it exchanges heat with the air at the pipe to cool the air. Fan coil unit belongs to air cooling equipment.

Water cooled chiller: the water-cooled chiller belongs to the refrigeration unit part of the central air-conditioning system. Its refrigerant is water, which is called water chiller. The cooling of condenser is realized by the heat exchange and cooling of normal temperature water, so it is called water chiller. The condenser of air-cooled unit is called air-cooled unit opposite to water-cooled machine. The condenser of air-cooled unit achieves cooling purpose by forced ventilation and heat exchange with air in the room.

Cooling tower: special equipment for cooling water with the help of air, usually installed on the top of a building. In many industries such as refrigeration, electric power and chemical industry. The hot cooling water discharged from condenser and other equipment is recycled after cooling by cooling tower.

Modular unit: it changes the traditional Freon pipeline into water system, combines indoor and outdoor units into refrigeration units, and changes indoor units into fan coil units. Using the heat transfer of refrigerant water to realize the refrigeration process, the modular machine is named because it can automatically adjust the number of starting units according to the requirements of cooling load and realize flexible combination.

Multi split: the multi split unit is not the traditional central air conditioning. The traditional central air conditioning system is to supply water to the fan coil unit, while the multi split unit is to direct the fluorine into the fan coil unit. Therefore, it is doomed that the pipeline of the multi split is not too long, and the energy loss on the pipeline of the multi split is larger than that of the whole machine. If the pipeline of the multi split machine leaks, it is often impossible to repair.

Not all compressors are variable frequency, generally only one compressor is variable frequency, the others are fixed frequency. The pipeline system is more complex and the control system is more complex.

The difference between modular machine and screw machine, multi split machine: both modular machine and screw machine are water systems, that is, the chilled water comes out from the main engine and is supplied to the indoor terminal air disc and other equipment for refrigeration.

The multi split machine is a fluorine system. The refrigerant (R22 or R410A refrigerant, etc.) comes out of the main engine. The end of the room is also the internal unit of the fluorine pipeline. It is similar to the one driven one air conditioning unit for household use, but it has changed into one for many, and frequency conversion (DC frequency conversion or digital vortex frequency conversion) technology is added.

The difference between air cooler and water cooler: air cooler means that the main engine dissipates heat by fan, while the water cooler only dissipates heat by water. The air cooler has a compact structure, does not need a special machine room, and is easy to maintain. The disadvantage is that the refrigeration and heating are greatly affected by the climate, and the energy efficiency ratio is slightly lower than that of the water cooler. Water chillers generally need special machine rooms with cooling towers. The system is slightly complex and maintenance is slightly cumbersome. Most of them can not make heat. The advantages are that the cost of water chillers is lower than that of air coolers, and the energy efficiency ratio is slightly higher than that of air coolers.

Energy efficiency ratio: the energy efficiency ratio of air conditioner is the ratio of nominal cooling capacity (heating capacity) to operating power, namely EER and cop. The mathematical expression is: eer = refrigerating capacity / cooling consumption power, cop = heating capacity / heating consumption power. The higher EER and cop, the lower the energy consumption and the higher the performance ratio. 5, 2.8-3.0, 3.0-3.2, 3.2-3.4, 3.2-3.4, 3.4 and above. Grade 1 * energy saving, grade 5 energy efficiency * low, and products below grade 5 are not allowed to be sold on the market. Air conditioning enterprises need to attach energy efficiency labels on their products to inform consumers of their energy efficiency level.

Vertical imbalance: in the hot water double pipe system, due to the different height difference between the radiator and the boiler, although the supply and return water temperatures of the radiators entering and leaving each layer are the same (without considering the influence of cooling along the pipeline), the action pressure with larger vertical distance from the boiler is larger, and the action pressure with smaller distance is smaller. Even if different pipe diameters are selected, the resistance balance of each layer can not be achieved. The phenomenon of uneven flow distribution between upper and lower layers and uneven cooling and heating will appear, which is usually called vertical imbalance. Moreover, the more the number of building floors, the greater the difference of pressure between the upper and lower layers, the more serious the vertical imbalance will be.

Design heat load of heating system: the designed heat load of heating system is the heat supplied to the building per unit time in order to meet the requirements of indoor temperature and maintain the heat balance of the room under a certain outdoor temperature. The design heat load Q 'of the heating system includes two parts: one is the heat consumption of the maintenance structure Q1 ', that is, the heat lost from indoor to outdoor through the maintenance structure of building doors, windows, floors, roofs and other maintenance structures; the other part is the heat consumption Q' of cold air infiltration into the room by heating the gap between doors and windows, and the heat consumption Q 'of cold air entering the room due to the opening of doors and windows.

Indoor air calculation temperature: the calculated indoor air temperature generally refers to the average ambient temperature within 2.0m away from the ground in people's activity area, which should meet the technological requirements of people's life and production.

Outdoor calculation temperature for heating: the daily average temperature over the years which does not guarantee 5 days per year shall be adopted for the outdoor calculation temperature of heating.

Low limit thermal resistance (* small heat transfer resistance): it refers to the lower limit value of heat transfer resistance of enclosure structure allowed in design calculation. The purpose of * small heat transfer resistance is to limit the excessive heat transfer through the enclosure structure, prevent condensation of the internal surface, and limit the excessive radiation heat transfer between the internal surface and the human body, which may cause the human body to catch cold.

Economic heat transfer resistance (economic thermal resistance): the heat transfer resistance when the sum of construction cost (depreciation cost of initial investment) and use cost (heating operation cost and equipment depreciation cost shared by unit area of enclosure structure) reaches * small value.

Comprehensive ventilation: comprehensive ventilation is to ventilate the whole room. The concentration of harmful gases in the room is diluted to below the allowable range of health standards with the fresh air sent into the room. At the same time, the indoor polluted air is directly or purified before being put into the outdoor atmosphere.

Accident ventilation: accident ventilation is an exhaust system set up to prevent large amount of harmful gas or explosive gas which may be released suddenly in the production workshop when the production equipment has an accidental accident or fault, which is a necessary measure to ensure the safety of production and the safety of workers.

Ventilation rate: ventilation rate n refers to the ratio of ventilation rate L (m3 / h) to room volume V (m), i.e., n = L / v.

Air quality balance: in a ventilated room, no matter which ventilation mode is adopted, the air quality entering the room per unit time should be equal to the air quality discharged at the same time. That is, the air quality of the ventilated room should be kept in balance, which is the air quality balance.

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

Fan air volume: refers to the volume of gas transported in unit time when the fan works under standard conditions, which is called fan air volume, expressed by the symbol L, and the unit is m3 / h.

Fan wind pressure: refers to the sum of dynamic pressure and static pressure per m of air passing through the fan, expressed by symbol P, unit: PA.

Partial pressure of water vapor PQ: the partial pressure of water vapor in wet air is called the partial pressure of water vapor in wet air when it occupies the volume of wet air alone and has the same temperature as the wet air. The partial pressure of water vapor reflects the content of water vapor in the air. The more water vapor content in the air, the greater the partial pressure of water vapor.

Saturated steam partial pressure PQ. B: at a certain temperature, when the water vapor content in the wet air reaches the * limit, the wet air is said to be in saturated state, and the corresponding partial pressure of water vapor is called the saturated steam partial pressure.

Moisture content: moisture content (d) is defined as the amount of water vapor contained in wet air corresponding to one kilogram of dry air. Its unit is g / kg. The moisture content changes with the amount of water vapor in the air, which can accurately reflect the amount of water vapor content in the air.

Total pressure: the sum of dynamic pressure and static pressure.

Heat exchanger: equipment in which fluids of different temperatures exchange heat, also known as heat exchanger.

Expansion water tank: in hot water system, it can adjust and compensate the expansion and contraction of water volume.

Radiator: a device that releases heat to a heating room by convection and radiation.

Hot air curtain: the air curtain that can eject hot air, also known as hot air curtain.

Water mixer: in a hot water system, the inlet device for mixing the supply and return water to meet the required parameters.

Dirt remover: in water system, it is used to remove the impurities in the circulating water.

Water distributor: in water system, it is used to distribute water to each branch system with large section.

Water collector: in the water system, it is used to collect the backwater of each branch system.

Check valve: only allow fluid flow in one direction, can automatically prevent backflow valve, also known as check valve.

Globe valve: a valve whose plug moves perpendicular to the seat to shut off and regulate flow.

Gate valve: gate valve used to cut off and regulate flow.

Angle valve: used to close and regulate the flow and the inlet direction and outlet direction into a certain angle valve.