1. The role of heating, ventilation and air conditioning

It is the technology to control the heat and humidity environment and indoor air quality of the building, and also includes the control of noise generated by the system itself.

2. Composition of HVAC

HVAC consists of three parts: heating, ventilation and air conditioning. Abbreviated as HVAC (Heating, Ventilating and Air Conditioning). Because of the different control objects and functions, they are:
(1) heating (Heating): also known as heating, is to supply heat to the building to maintain a certain indoor temperature. Such as kang, furnace, fire wall, fire and other heating methods and today's heating equipment and systems.
(2) Ventilation (Ventilating): the process of sending in outdoor air to a room or space and discharging air from a room or space by natural or mechanical means; the air sent in can be treated or untreated. In other words, ventilation is the use of outdoor air (called fresh air or fresh air) to replace the air inside the building (referred to as indoor air) to improve indoor air quality
(3) air conditioning (Air Conditioning): to achieve the temperature, humidity, cleanliness and air flow rate in a room or space to regulate and control, and provide a sufficient amount of fresh air. Air conditioning is referred to as air conditioning.



1.2 Working Principles of Heating, Ventilation and Air Conditioning (HVAC) Systems

Figure l-1 shows the basic methods of controlling the indoor environment of civil and industrial buildings, respectively.
1. Why the indoor environment regulation and control.
(1) in the summer, civil buildings, such as the figure (a) in the personnel, lighting fixtures, electrical and electronic equipment to the indoor heat and moisture; due to solar radiation and indoor and outdoor temperature difference and make the room to obtain heat, if not these indoor excess heat and moisture from the indoor removal, will inevitably lead to the indoor temperature and humidity rise.
(2) In winter, the building will transmit heat to the outdoors or infiltrate cold air, if not to the room to supplement the heat, will inevitably lead to a drop in indoor temperature.
(3) in civil buildings, the crowd is not only indoor "heat, humidity source", but also "source of pollution", they produce C02, body odor, smoke emitted when smoking; indoor furniture, decorative materials, equipment, etc. also emit a variety of pollutants, such as formaldehyde, toluene, Even radioactive substances, thus leading to the deterioration of indoor air quality.
(4) in industrial buildings, many process equipment disperses harmful gases, vapors, solid particles and other pollutants, in order to ensure the health of the staff, these pollutants must be managed.
2. Heating, ventilation and air conditioning tasks
Is to provide indoor cooling or heat, and dilution of indoor pollutants to ensure that the indoor has appropriate thermal comfort conditions and good air quality.
3. Indoor environmental control program in Figure 1-1
(1) Figure 1-1 (a) Setting up a fresh air system, fan coil system, indoor air seeps outside through the cracks of doors and windows, thus diluting pollutants. A fan coil unit (consisting of a fan and a water/air heat exchanger-coil) is used to supply cold (when there. is a cold load indoors) or heat (when there is a heat load indoors in winter) to the room; Fresh air delivered to the room is first passed through an air filter to remove dust particles and is treated with cooling and dehumidification (in summer) or heating and humidification (in winter)
(2) Figure 1-1(b) Provide an exhaust system that excludes pollutants, and a fresh air system, where the fresh air can be infiltrated through doors and windows or fed from the fresh air system, so that the concentration of pollutants in the plant reaches the concentrations permitted by the standards or codes. In cold areas, the fresh air is heated in winter and a heating system is provided in the workshop to maintain a certain temperature in the plant. The heat medium used for the in-plant heating system and fresh air heating can be hot water or steam.



Figure 1-1 Heating, Ventilation, and Air Conditioning (HVAC) Systems for Civil and Industrial Buildings
(a) Civil buildings (b) Industrial buildings
1-Air handling units for fresh air 2-Fan coil units 3-Electrical and electronic equipment
4-Lighting fixtures 5-Process equipment 6-Exhaust fans and exhaust systems 7-Radiator
4. The working principle of heating, ventilation and air conditioning
When the room gets heat or loses heat, then take out heat from the room or supplement heat to the room, so that the heat in and out of the room is equal, that is to say, to achieve thermal equilibrium, so as to maintain a certain temperature in the room; or to make the humidity in and out of the room balanced, in order to maintain a certain degree of humidity in the room; or to discharge polluted air from the room, while supplementing the same amount of clean air (processed or not), that is to say, to achieve air balance.

1.3 Classification of heating, ventilation and air conditioning systems

.1 According to the building environment control function
1. Building heat and humidity environment as the main control object of the system
The main control object for the building indoor temperature and humidity, such as air-conditioning system (such as Figure 1-1 (a) of the system) and heating system
2. To building pollutants as the main control object of the system The main control of indoor air quality in the building, such as ventilation systems (such as Figure 1-1 (b) of the system) and building smoke exhaust system. The control object and function of the above two categories are intersecting with each other. For example, the main task of ventilation to control the indoor air quality of the building, and sometimes can also have the function of heating, or to remove the residual heat and humidity; and to control the indoor heat and humidity environment of the air conditioning also has the function of controlling the quality of indoor air.
1.3.2 According to bear the indoor heat load, cold load and wet load of the medium
1. All-water system
All water is used to carry the indoor heat and cold loads. When the hot water, to provide heat to the indoor, bear the indoor heat load, such as the current common hot water heating system; when the cold water (often called chilled water), to provide cooling to the indoor, bear the indoor cold load and wet load.
2. Steam system
Steam is used as a medium to supply heat to the building. It can be directly used to bear the heat load of the building. For example, steam heating system, steam as the medium of the heater system, etc.; used in air-handling units to heat and humidify the air; used in all-water systems or other systems in the hot water preparation or hot water supply of hot water preparation.
3. Whole air system
Air as a medium to provide cold or heat to the room. For example, all-air air-conditioning system, which provides indoor treated cold air to remove the indoor sensible heat and latent heat cold load, indoor cooling is no longer required.

1.3.3 By concentration of air-handling equipment

11. Centralized system
The air is centralized in the machine room for processing (cooling, dehumidification, heating, humidification, etc.), and the room only air distribution device.
Characteristics: in the building occupies the machine room area, but control, management is more convenient.
2. Semi-centralized system
Indoor air treatment (heating or cooling, dehumidification) of the equipment is set up in each of the rooms being regulated and controlled, and centralized part of the processing equipment, such as chilled water or hot water centralized preparation or centralized treatment of fresh air, etc..
Characteristics: in the building occupies less area of the room, easy to meet the temperature and humidity control requirements of each room, but the room set up air-handling equipment, management and maintenance is inconvenient; when there is a fan, it will bring noise to the room.
3. Decentralized system
Heat and humidity treatment of indoor equipment all dispersed in the room, such as commonly used in the family room air conditioners, electric heaters and so on. Characteristics: in the building does not need a machine room, do not need to air distribution ducts, but management and maintenance is inconvenient; high energy consumption, low efficiency; refrigeration compressor, the fan will bring noise to the room.

1.3.4 According to the purpose of air-conditioning system

1. Comfort air-conditioning system Comfort air conditioning for short is an air conditioning system that creates a comfortable and healthy environment for indoor people. Air conditioners used in buildings such as office buildings, hotels, stores, theaters, libraries, restaurants, gymnasiums, entertainment venues, and airport or bus waiting halls are comfort air conditioners. Characteristics: As human comfort in a certain range of air parameters, so this type of air conditioning on the temperature and humidity fluctuations in the control, the requirements are not strict.
2. Process air-conditioning system Also known as industrial air conditioning, for the production process or equipment to create the necessary environmental conditions for the operation of the air conditioning system, staff comfort requirements can be taken into account when available.
Characteristics: Due to the different types of industrial production, a variety of high-precision equipment operating conditions are different, so the function of the process air conditioning, system form, etc. vary greatly.
For example, semiconductor component production is extremely sensitive to the concentration of dust in the air, requiring a high degree of air purification; cotton textile cloth workshop on the relative humidity requirements are very strict, generally controlled at 70% to 75%; measurement room requires a year-round benchmark temperature of 20 ℃, fluctuations ± 1 ℃, the length of the high-grade measurement room requirements of 20 ± 0.2 ℃, the I-level coordinate hammer bed requires the ambient temperature of 20 ± 1 ℃; Antimicrobial production requires sterile conditions, and so on.



1.3.5 Classification of pollutants in buildings as the main object of control

1.3.5.1 By use
1. Ventilation of industrial and civil buildings
Ventilation system aimed at controlling pollutants produced by people and their activities in industrial production processes and buildings.
2. Building smoke prevention and exhaust
Ventilation system aimed at controlling the flow of smoke from building fires and creating smoke-free evacuation routes or safety zones for people.
1. Accident ventilation
Ventilation system that removes a large amount of gases and vapors with combustion and explosion hazards or toxicity produced by emergencies.

1.3.5.2 According to the service scope of ventilation
1. General ventilation
Clean and fresh air is sent into a room to dilute the concentration of pollutants in the indoor air, and at the same time the pollutant-containing air is discharged to the outdoor area, so that the concentration of pollutants in the indoor air meets the requirements of health standards. Also known as dilution ventilation.
2. Localized ventilation
Control the spread of pollutants in local indoor areas or control the concentration of pollutants in local areas to meet the health standard requirements of ventilation. Local ventilation is also divided into local exhaust and local air supply.

1.3.5.3 Power of air flow
1. Natural ventilation
Relying on the wind pressure caused by outdoor wind or heat pressure caused by the difference in indoor and outdoor temperatures, fresh outdoor air enters the room, and indoor air is discharged into the room.
Fresh outdoor air enters into the room and indoor air is discharged to the outdoor. Characteristics: Economical, not energy-consuming, but greatly affected by outdoor meteorological parameters, poor reliability.
2. Mechanical ventilation
Relying on the power of the fan to send people indoors or exhaust air. Characteristics: The system is highly reliable, but requires a certain amount of energy consumption.

1.4 The development trend of heating, ventilation and air conditioning technology

In order to adapt to the change of people's concept of environmental control and the growth of demand, some traditional HVAC methods are accelerating the change, a large number of both energy-saving and environmentally friendly benefits of the new system type continues to be created; equipment to accelerate its upgrading and towards unitization, multi-functionality, intelligent direction.
The equipment is being upgraded and developed towards unitization, multifunctionality and intelligence.
The key technical support for the greening of building environmental control systems lies in building automation (BA), especially the automation of energy management of building equipment and systems such as HVAC.