How Do I Choose the Best Heating And Air Conditioning?

Heating, Ventilation and Air Conditioning (HVAC) refers to the system or related equipment responsible for heating, ventilation and air conditioning indoors or in the car. The design and application of HVAC systems to thermodynamics, fluid mechanics, and fluid machinery are important branch disciplines in the field of mechanical engineering. Its purpose is to establish an indoor artificial environment that is beneficial to human survival.

Heating, Ventilation and Air Conditioning (HVAC) refers to the system or related equipment responsible for heating, ventilation and air conditioning indoors or in the car. The design and application of HVAC systems to thermodynamics, fluid mechanics, and fluid machinery are important branch disciplines in the field of mechanical engineering. Its purpose is to establish an indoor artificial environment that is beneficial to human survival.

Sometimes R is also added to the abbreviation HVAC, which stands for Refrigeration. The abbreviation becomes HVAC & R or HVACR, or R is added to the abbreviation, minus V for ventilation, and the abbreviation becomes HACR.

HVAC system can control the temperature and humidity of the air and improve indoor comfort. It is an important part of medium and large industrial buildings or office buildings (such as skyscrapers). In the pharmaceutical, electronics, mission-critical facilities, and oil and gas fields and industries, HVAC plays an important role.

Chinese name

HVAC

Foreign name

Heating, Ventilation and Air Conditioning

HVAC background

Heating, ventilation, and air conditioning were the result of inventions and discoveries by many scientists, including Nicholas Lviv, Michael Faraday, Willis Carrier, Ruben Trane, James Joule, William Rankin and Nicholas Kano and others.

Parts of HVAC systems were invented around the time of the Industrial Revolution. Companies and inventors around the world have also introduced various modern and efficient new methods. The three main functions of heating, ventilation, and air conditioning are related to heating, ventilation, and air conditioning. The purpose is to provide comfortable temperature and appropriate indoor air quality at reasonable installation, operation, and maintenance costs. The HVAC system provides ventilation, reduces air penetration, and maintains the pressure relationship between indoor and outdoor or different rooms. The characteristic of air flowing in or out of the room is called indoor air distribution. [1]

In modern buildings, the above functions (including its control system, and the design and installation of the system) are integrated into one or more HVAC systems. For small buildings, the contractor will directly select HVAC systems and equipment as required. If it is a large building, the building designer and mechanical and structural engineers will analyze, design and select the HVAC system, and then install it by a professional mechanical contractor.

HVAC system is an international industry, and its related work includes system operation, maintenance, design and architecture, equipment manufacturers and business, research and education promotion. The HVAC industry was previously managed by manufacturers of HVAC equipment. Now many international management and standardization organizations pay attention to this area, including the Air Conditioning Heating and Refrigeration Institute, the International HVAC Distributor Management Committee, the American Heating , Association of Refrigeration and Air Conditioning Engineers, American Sheet Metal and Air Conditioning Contractors Association, American Air Conditioning Contractors Association, Uniform Mechanical Code, and International Building Codes provide services and improve their level in the HVAC industry.

HVAC heating

Heating systems have been around since the days of the Roman Empire. At that time there was a duct system called hypocaust in the walls and floors of public baths.

There are many types of heating systems. In cold climates, central heating systems are often used to heat private homes and public buildings. The system will include a boiler or furnace that heats steam, water, or air. This system is typically placed in the building's machinery room. A system using water as a heat exchange medium is called a circulating water cooling and heating system. Heating systems also include pipes or pipelines that carry heated fluids, and radiators that use convection to transfer heat to the air. The radiator is usually buried in the wall or under the floor. Most heating systems have pumps to circulate the water in the system, so that the heat provided by each radiator will not be much different.

The air heating system uses air as a heat exchange medium, and the air pipe is used to transport hot air to the room. If the weather is warm or even hot, the same air duct can be used in the air conditioning system. Some systems filter hot air through a filter or air filter before sending it indoors.

The heating system can also use the heat emitted by the current flowing through the resistor as a heating source, which can be made into skirting board heaters and portable heaters, or it can be the main (or backup) heat source or backup heat source of the heat pump system.

The air outlet or radiator of the heating system needs to be placed in the coldest place in the room. If there are external windows in the room, the low temperature of the glass window will make the air cool, the density will increase and drop, and the glass window will easily condense water vapor. The air outlet or radiator is generally placed beside the window to reduce the formation of cold air and the window Water vapor. In addition to the design of the heating system itself, it is also necessary to minimize the amount of air that penetrates outdoors.

HVAC

Ventilation refers to the process of exhausting air from an area or flowing outside air into an area. Its purpose includes reducing humidity, odor, smoke, bacteria, and carbon dioxide in the area, and supplementing oxygen. Ventilation also includes air circulation in buildings, and avoiding stagnation of indoor air is one of the important factors in maintaining indoor air quality.

The ventilation methods of buildings can be divided into two types: mechanical ventilation (or forced ventilation) and natural ventilation.

Mechanical ventilation

Mechanical ventilation or forced ventilation is the use of mechanical equipment for ventilation, and the introduction of outside air to maintain indoor air quality and reduce moisture, odors and pollutants in the air, but if the outside humidity is high, additional energy is required to remove the introduction Moisture in the air. Exhaust fans can provide preliminary mechanical ventilation, while air handling units can provide more complete functions.

Mechanical ventilation is divided into three modes: positive pressure ventilation, negative pressure ventilation and balanced ventilation. Positive pressure ventilation is generally used in rooms that require protection or require high cleanliness; negative pressure ventilation is generally used in rooms that need to exclude odors or dangerous gases, such as kitchens, toilets, bathrooms, and factories or warehouses that produce dangerous gases. Equipped with a large amount of air for cooling, such as a transformer room.

Generally kitchens and bathrooms will have range hoods or exhaust fans to remove odors and moisture. The main considerations when designing such systems are air flow rate (related to fan speed and size) and noise. If the air pipe will pass through some areas with lower temperature, the air pipe needs to be insulated to prevent the water pipe from condensing due to the low temperature. Many applications use direct-drive fans, which reduces maintenance costs.

The electric fan in the room allows the air to flow, and the sweat on the skin evaporates, so people in the room will feel cooler. Hotter air will rise, and ceiling ceiling fans will be used in winter to circulate warmer air above the room and other locations. However, the indoor electric fan can only make the indoor air flow, and can not achieve the purpose of introducing outside air.

natural ventilation

Natural ventilation refers to the ventilation of a building without the use of fans or other mechanical devices. The windows that can be opened are the simplest natural ventilation equipment. It is suitable for situations where the area to be ventilated is not large and the building allows it. The more complex natural ventilation system will use the principle of warm air rising (ie, the chimney effect) to make the air in the building convection, the warm air is discharged from the opening above the building, and the cold air above will drop to a lower level. region. This type of system consumes very little energy, but care must be taken to ensure that the ventilation process does not cause discomfort to people in the building. In humid or hot weather, it is difficult to maintain comfortable indoor temperature only by natural ventilation, so it will still be used with traditional air conditioning systems. The function of the air-side energy-saving device is also natural ventilation, but it will pre-treat the external air to be introduced as needed, and adjust the temperature and humidity before entering the room.

HVAC air conditioning

Air conditioning in the broad sense refers to the adjustment of the temperature, humidity, and cleanliness of indoor air. Air conditioning in the narrow sense is cold air, that is, reducing the temperature of indoor air. The functions of the air conditioning system include air conditioning, ventilation and air humidity control.

The principle of an air-conditioning system is roughly similar, mainly through a heat pump to transfer heat from a low-temperature heat source to another higher-temperature heat sink. This procedure is called a refrigeration cycle. The medium that transfers energy in an air-conditioning system is called a working medium or a refrigerant. Water, air, ice, or other chemicals can be used as a refrigerant.

Schematic diagram of refrigeration cycle: 1) condensation coil, 2) expansion valve, 3) evaporation coil, 4) compressor

In the refrigeration cycle, the refrigerant is initially in a gaseous state. The refrigerant is turned into a high-temperature and high-pressure gas by a compressor, and then the high-temperature refrigerant flows to an outdoor heat exchanger (also known as a condensation coil). The refrigerant releases heat and condenses into liquid. The liquid refrigerant first controls the flow through the expansion valve, and then enters another indoor heat exchanger (also known as the evaporation coil). The refrigerant absorbs the heat of the indoor air, evaporates into a gaseous state in the evaporation coil, and then enters the compressor to repeat the process. A loop. The above cycle will absorb the heat in the room and then release the heat to the outside, so the temperature in the building can be reduced.

Many modern homes, offices, and public buildings are equipped with all-air central air-conditioning systems. All-air air-conditioning systems use air as a medium for transferring heat, and the outdoor unit absorbs the heat of the air (or provides heat) To the air), the treated air is sent directly to the room through the duct. However, the full-air air-conditioning system requires large air ducts. If such air-conditioning systems are not considered during the construction of the building, it is difficult to retrofit the full-air central air-conditioning system later. And the design of the duct needs to avoid the spread of bacteria. This type of air-conditioning system is mainly used in residences, and has recently been used in small commercial buildings.

The dehumidifier function in the air conditioning system is provided by the evaporation coil. The working temperature of the evaporation coil is below the dew point, so that water vapor in the air condenses on the outside of the evaporator coil. The condensed water is concentrated in the condensate pan below the evaporation coil, and then drained to the drainage system or directly to the ground outdoors. Dehumidifiers are appliances used to reduce indoor humidity, similar in principle to air conditioning systems. In the food retail industry, large-scale open-type ice water hosts have high dehumidification efficiency. The function of a humidifier is exactly the opposite of that of a dehumidifier. It is an electrical appliance used to increase the humidity in a room.

The windows of buildings with air-conditioning systems are mostly sealed windows, because open windows prevent the air-conditioning system from achieving the purpose of maintaining constant indoor air conditions.

Modern air conditioning systems are equipped with air filters inside. Generally, a light-weight air filter is used, and the air is sent to the evaporation coil after passing through the filter. Evaporation coils need to be cleaned or replaced regularly according to the conditions of use. For example, if the building is located in a high dust environment or there are pets such as cats and dogs in the room, the filter replacement frequency will be relatively high. If the air filter is not replaced late, it will cause a decrease in air flow, reduce heat exchange efficiency, waste energy on the one hand, increase electricity costs, and shorten the life of the equipment. If the air flow in the cold heading system is insufficient, the evaporation coil will freeze and the air flow will become less. If the air filter in the heating system is so dirty that it is blocked and the air flow is insufficient, it will cause the heating circulation system to overheat and even cause a fire.

The main role of the air conditioning system is to transfer heat from the indoor evaporation coils to the outdoor condensation coils. In addition to exhausting indoor heat to the outside, the condensing coil is also responsible for exhausting heat generated by the operation of the compressor. Therefore, it is also very important to keep the condensing coil clean, so as not to damage the system due to the poor heat dissipation of the compressor.

New technology and development direction of HVAC

(1) Energy-saving design of heating and air-conditioning systems;

(2) Development, testing and application of new energy-saving products in heating and air-conditioning systems;

(3) Application of air purification equipment;

(4) Development trend of air conditioning system applications;

(5) Air-conditioning mode and equipment selection of high-power density machine room;

(6) Optimize the organizational form of air supply and return air;

(7) New technologies in cold storage and heat storage;

(8) Application technologies such as water source heat pump, ground source heat pump, low temperature heat source for surface water;

(9) Research on thermal energy recovery and utilization in high power density machine rooms;

(10) Research on reasonable methods of system backup, equipment backup, and pipeline backup;

(11) Research on the optimal airflow organization method for dividing cold (hot) channels and closed cold (hot) channels;

(12) Research on the air-conditioning mode of the warehouse data room;

(13) Research on the application of air-conditioning natural cooling technology in cold regions.