Must-know: Advantages and Disadvantages of 14 Heating and Cooling Solutions!
2025-03-30
1. Conventional Electric Refrigeration Air Conditioning System
This is a commonly used air conditioning form at present. After more than a century of development, there are various forms of refrigeration host machines, which have the advantages of high refrigeration efficiency, etc. The characteristics are as follows:
Advantages:
① The system is simple and occupies a slightly smaller area than other forms.
② High efficiency, with the COP (Coefficient of Performance for refrigeration) generally greater than 5.3.
③ The equipment investment is less than that of other systems.
Disadvantages:
① The number and capacity of the chiller units are large, and the number and capacity of other electrical equipment also increase, increasing the workload of maintenance and repair.
② The total power consumption load is large, increasing the transformer's power distribution capacity and the cost of power distribution facilities.
③ All the electricity used is peak-hour electricity, and it does not enjoy the peak-valley electricity price policy, resulting in high operating costs.
④ The air conditioner cannot be used during power rationing. For example, in the summers of 2003/2004, the air conditioning host machines operated at half capacity, and most central air conditioners could not achieve the desired effect.
⑤ The operation mode is inflexible. During the transitional season, holidays, or rest periods, if cooling is required in individual areas, the host machine needs to be turned on, which wastes the unit's configuration capacity and increases operating costs.
⑥ It is difficult to achieve good cooling in a large-scale district cooling system (the water supply temperature cannot be lowered), with large investment in the pipeline network, high transportation energy consumption, and poor air conditioning quality.
2. Ice Storage Air Conditioning System
The ice storage air conditioner reduces the capacity of the refrigeration host machine and adds an ice storage device on the basis of the conventional water-cooled chiller unit system.
The central air conditioning system with ice storage represents the advanced level of central air conditioning in the world and indicates the development direction. The characteristics are as follows:
Advantages:
① Reduces the capacity of the chiller units (reduces the one-time investment in the host machine), with a lower total power consumption load, and reduces the transformer's power distribution capacity and the cost of power distribution facilities.
② The refrigeration host machine has high refrigeration efficiency (COP > 5.3). By taking advantage of the price difference between peak and off-peak electricity, the annual operating cost of the air conditioner can be greatly reduced, and the operating cost can be saved by more than 35% (more than 40% compared with heat pump and lithium bromide air conditioning forms).
③ Reduces the building's power distribution capacity, saves the investment in power transformation and distribution, and saves about 30% (the power distribution investment for the air conditioner); exempts from the high reliability cost of the dual-circuit system, saving investment.
④ Flexible to use. The air conditioning in some areas can be provided by ice melting without turning on the host machine, with obvious energy-saving effects.
⑤ Can provide quantitative cooling by melting ice for a smaller load without turning on the host machine.
⑥ During the transitional season, it can provide quantitative cooling by melting ice, avoiding the situation of "using a big horse to pull a small cart", and the operation is more reasonable with obvious cost savings.
⑦ Has an emergency function, improving the reliability of the air conditioning system. During power rationing, as long as there is electricity to drive the water pump, the ice can be melted to provide cooling. For example, in the summers of 2003/2004, the effect of the ice storage air conditioning was not affected.
⑧ The refrigeration temperature is low and stable, the air conditioning effect is good, and it improves the comfort and grade of the building.
⑨ With a low-temperature cold source, the refrigeration speed is fast, and the start-up time before going to work is short. If the start-up time is long, the air conditioner will have a lot of ineffective operations, resulting in great waste.
⑩ The driving energy is clean, environmentally friendly, stable, simple and reliable, and the price difference between peak and off-peak electricity will be more favorable in the future.
⑪ For large-scale district cooling of multiple buildings, it can supply water at a low temperature, reducing the energy consumption for water supply and the investment in the pipeline network; compared with a cooling station for each building, it can save investment, reduce management costs, and reduce the area of the machine room.
⑫ Provides low-temperature chilled water for the terminals, reducing the terminal investment; enhances the dehumidification ability, greatly improving the comfort of the air conditioning; using a low-temperature air supply system can save the energy consumption of the terminal fans, improve the air conditioning quality, and reduce the size and investment of the air ducts.
⑬ The air conditioning system has a high degree of intelligence, can achieve fully automatic operation, has an interface with the building's BAS, and is a world-advanced air conditioning system.
Disadvantages:
① When the host machine and the ice storage device and other equipment are arranged in the refrigeration machine room, the ice storage device needs to occupy a certain space (it can be buried under the green belt, arranged under the car ramp and other unused spaces).
② The investment in the machine room equipment is slightly higher than that of the conventional water-cooled electric refrigeration and lithium bromide unit systems.
③ Ice storage can only provide cooling in summer and requires a heating system (heat exchange heating through the heating network can be used, and the capacity of the heating network is about 50% of that required by the lithium bromide unit).
3. Water Source Heat Pump Air Conditioning System
1) It belongs to the renewable energy utilization technology.
The water source heat pump uses the solar energy resources stored in the earth's water bodies as the cold and heat sources for an energy conversion heating and air conditioning system. The available water bodies include groundwater, rivers, some surface rivers and lakes, and the ocean. The surface soil and water bodies are huge collectors and dynamic energy balance systems, making it possible to use geothermal energy, which is a clean renewable energy technology.
2) Convenient for metering and charging.
The power consumption load of the air conditioner is at the user's location, which is convenient for air conditioner metering and charging, and is conducive to users' rational use of the air conditioning system, energy conservation, and the fair distribution of air conditioning operation management.
3) Safe and reliable operation.
The air conditioning system of the water source heat pump unit can basically ensure that it is turned on according to the user's needs throughout the year and can also operate in the spring and autumn transitional seasons, which is equivalent to a four-pipe air conditioning system. The supply and return water temperatures of the water source heat pump are relatively stable throughout the four seasons, and the fluctuation range is much smaller than the change in air temperature. The water body serves as a cold source in summer and a heat source in winter, and the unit operates more reliably and stably, ensuring the high efficiency and economy of the system. There is no problem of defrosting in winter for the air source heat pump.
4) High efficiency and energy saving.
In winter, the temperature of the water body that can be used by the water source heat pump unit is higher than the ambient air temperature, the evaporation temperature of the heat pump cycle is increased, and the energy efficiency ratio is increased; in summer, the water body temperature is lower than the ambient temperature, the refrigeration condensation temperature is reduced, and the unit efficiency is increased.
5) Flexible application.
In some buildings, during the transitional season, some areas need cooling and some areas need heating. The water source heat pump can provide both cooling and heating at the same time, realizing the transfer and balance of cooling and heating in the building, and the system uses less energy.
The water and ground source air conditioning has been widely recognized for its energy conservation and environmental protection. The relevant technologies have been listed as scientific research projects and are developing rapidly in large and medium-sized cities. Demonstration projects have been established everywhere, and the government encourages the selection of such systems. With the climate warming, energy conservation has become an indicator for measuring the quality of buildings, and "low carbon emissions" have received attention. Energy conservation and emission reduction of central air conditioners are necessary. The state advocates relevant heat pump technologies and recommends the water source heat pump and ice storage technologies.
4. Electric Heat Storage Air Conditioning System
The electric heat storage air conditioner uses an electric boiler to generate heat with the low-cost electricity during the night off-peak period, stores the heat in the form of hot water in the heat storage device, and releases it to the air conditioning terminals for heating during the daytime.
The characteristics are as follows:
① Uses energy storage technology to shift the peak and fill the valley, balance the power grid load, improve the utilization rate of the power generation equipment in the power plant, reduce the operating costs of the power plant and the power grid, and save the investment in infrastructure construction.
② Takes advantage of the price difference between peak and off-peak electricity to greatly reduce the annual operating cost of the air conditioner.
③ Flexible to use. During the transitional season, holidays, or after work, the air conditioning in some offices can be provided quantitatively by the heat storage without turning on the unit, with obvious energy-saving effects and greatly reduced operating costs.
④ Has an emergency function, improving the reliability of the air conditioning system.
⑤ High degree of automation, can operate without on-site attendance, can track in real time according to the changes of the air conditioner, and provide cooling as needed, with obvious energy-saving effects.
5. Air-cooled Heat Pump Air Conditioning System
The air-cooled heat pump is cooled by outdoor air, and its refrigeration and heating performance is closely related to the outdoor environmental temperature. The characteristics are as follows:
Advantages:
① Integrates cooling and heating, and there is no need to configure an additional heat source.
② When the impact on the building's appearance and the vibration of the unit operation is not considered, it can be placed on the roof without a dedicated air conditioning machine room, which is suitable for buildings with a small area and no refrigeration machine room.
③ Air cooling, so there is no need to configure a cooling tower.
Disadvantages:
① Relying on air cooling, its refrigeration and heating performance is greatly affected by the outdoor environmental temperature, and the performance is unstable. In summer, when the outdoor temperature is high and the cooling demand is large, the refrigeration capacity deteriorates; in winter, when the outdoor temperature is low and the heating demand is large, the heating capacity deteriorates. Defrosting in winter affects the heating effect, the heating temperature is low, and the indoor temperature cannot reach the required level when it is cold.
② Low refrigeration efficiency (the nominal COP is lower than 3.2, and the actual operation is about 2.5), resulting in high operating costs.
③ The unit is placed outdoors and cooled by the wind. Over time, the condenser will be covered with dust, which affects the heat exchange efficiency, reduces the operating efficiency of the unit, and causes a sharp decline in the refrigeration capacity. Generally, after 3 years, the refrigeration capacity needs to be re-evaluated and dealt with, and sometimes additional units need to be added.
④ The unit selection needs to consider the environmental impact, which increases the configuration and investment. The investment is the highest among several air conditioning forms.
⑤ Low efficiency and large total power consumption load increase the transformer's power distribution capacity in the conventional air conditioning system. The cost of power distribution facilities is high, and more power connection fees and power construction fees need to be paid.
⑥ The unit is placed outdoors, making operation, management, and maintenance difficult. The unit is easily damaged, and the maintenance workload is large.
⑦ During the transitional season, when the cooling or heating demand decreases, the refrigeration or heating capacity reaches its maximum level, resulting in a wasteful situation like "using a big horse to pull a small cart", increasing operating costs.
6. Lithium Bromide Air Conditioning System
The lithium bromide unit uses thermal energy as the energy source. Through the absorption and release of lithium bromide and water, water is used as the refrigerant for cyclic refrigeration. According to the way of supplying thermal energy, it is divided into direct-fired type, steam type, and hot water type.
Advantages are as follows:
① The main energy source of the system is thermal energy, and the power distribution capacity is small (about 1/3 of that of the conventional electric refrigeration system and 1/2 of that of the ice storage system), resulting in low power consumption during operation. However, it cannot operate during a power outage. The self-provided generator can only ensure the operation of some water pumps, unlike the ice storage system, which can fully melt the ice to provide cooling by turning on the water pump; for example, in the summer of 2003, when the power was rationed and only half of the units were operating, the air conditioning effect could not be achieved, while the ice storage system could ensure the effect.
② Suitable for applications in places where waste heat is generated, such as steel mills and textile factories. It is applied in developed countries in Europe and America in such situations.
③ The direct-fired type integrates cooling and heating, and there is no need to configure additional heating equipment (it is like a gas boiler during heating, but the thermal efficiency is lower than that of a single gas boiler).
④ The floor area of the machine room is slightly smaller than that of the ice storage system.
Disadvantages:
① The refrigeration capacity decreases (the annual decrease is about 3% - 8%), and the capacity design is configured with a 15% margin.
② The outlet water temperature of the refrigeration host machine is high, and the actual operation is above 8°C. The air conditioning effect is poor, the refrigeration speed is slow, and the start-up time before going to work is long, reducing the grade of the building; due to the high water supply temperature, the capacity of the terminal equipment needs to be increased, increasing the investment.
③ Lithium bromide is corrosive, which is likely to cause corrosion of the unit and a decrease in the refrigeration capacity.
④ Low efficiency, with an energy efficiency ratio (COP) of about 0.8 - 1.2. It is a product that saves electricity but not energy, with high operating energy consumption and costs. In developed countries, it is not advocated to use it during energy shortages (unless there is waste heat).
⑤ Using water as the refrigerant requires ensuring the vacuum degree of the system. In actual operation, non-condensable gases are generated, which leads to a decrease in the vacuum degree and a decrease in the refrigeration capacity.
⑥ Poor unloading capacity during part-load operation, which is likely to cause the situation of "using a big horse to pull a small cart", wasting operating costs; when the cooling load in some areas is small, the unit may not be able to start (it cannot operate below 40% of the load); it cannot provide cooling when the cooling demand is very small; if the part-load operation is not well adjusted, lithium bromide is likely to crystallize, and the system is difficult to operate.
⑦ The cooling water system is larger than that of the conventional electric refrigeration system. The cooling tower is twice the size of that in the ice storage system, with a large amount of make-up water. It is difficult to arrange on the roof; the cooling water pipes are large, and the pipeline wells are large.
⑧ Complex operation and maintenance. Daily maintenance is important. If the maintenance is not good, the refrigeration capacity will decrease rapidly. The maintenance and management personnel need a high professional level, and the cost is much higher than that of the electric refrigeration system.
⑨ The lithium bromide solution needs to be maintained and replaced every year, which is costly. On-site replacement is likely to make the system unclean and reduce the refrigeration effect.
⑩ The unit is large in size and requires a larger maintenance space and passage.
⑪ The prices of oil and gas are rising, and the supply is tight, resulting in high operating costs.
⑫ Fire protection factors need to be considered for oil and gas, making management inconvenient.
7. VRV Air Conditioning System
Characteristics:
① It is not a central air conditioning system, and the air conditioning quality is poor.
② The system is relatively simple, integrates cooling and heating, and does not require a dedicated air conditioning machine room.
③ The system design is flexible, and an independent system can be configured for a small cooling area.
④ High investment.
⑤ Using air cooling, the cooling effect is worse than that of water cooling. The energy efficiency ratio (COP) of the unit is low (the sample calibration is generally less than 3, and the actual operation is much lower than 2.5). The air conditioning effect is poor, and the operating cost is high. The COP is even lower on the hottest days, resulting in higher operating costs; the efficiency is also low during winter heating, and the heating capacity decreases as the environmental temperature drops.
⑥ The unit is placed outdoors and cooled by the air. Over time, the condenser will be covered with dust, which affects the heat exchange efficiency, reduces the operating efficiency of the unit, and causes a sharp decline in the refrigeration capacity. After 3 years, it basically cannot meet the cooling demand, and additional units need to be added.
⑦ One outdoor unit is connected to multiple indoor units through copper pipes, and the refrigerant is in the pipes. During installation, it is necessary to ensure no leakage. If there is a leakage at one connection point, the air conditioning of the entire system will fail.
⑧ If the distance between the indoor unit and the outdoor unit is too large, it is difficult to return the oil, which affects the operation and service life of the compressor and also affects the heat exchange capacity of the unit.
⑨ Inconvenient for maintenance. Indoor maintenance will damage the decoration.
⑩ The number and capacity of the units are relatively large, resulting in a large maintenance workload.
⑪ The total power consumption load is large, which increases the transformer's power distribution capacity and the cost of power distribution facilities.
⑫ Additional water chiller units are required to solve the fresh air problem.
8. Ground Source Heat Pump Air Conditioning System
Heat naturally flows from a high-temperature area to a low-temperature area. A heat pump is a device that can draw heat from a low-temperature source to a high-temperature source, and it is energy-saving. The ground-source heat pump uses the heat exchange between water and geothermal energy (groundwater, soil, or surface water) as the cold and heat sources. In winter, it extracts heat from the ground, and the ground serves as a "cold source". The ground-source heat pump heating and air-conditioning system is composed of an outdoor geothermal energy exchange system, a water-source heat pump unit, and an indoor heating and air-conditioning terminal system. There are two forms of the unit: water-to-water or water-to-air, and the three systems exchange heat through water or air.
Advantages of the ground-source heat pump compared with the air-source heat pump:
① The temperature fluctuates less throughout the year. In winter, the ground temperature is higher than the air temperature, and in summer, it is lower. The heating and cooling coefficients are about 40% higher than those of the air-source heat pump, which can save about 40% in energy and costs.
② There is no need for defrosting during winter operation, reducing the losses caused by frosting and defrosting.
③ The ground has a good energy storage function.
9. Air-source Heat Pump Air-conditioning System
The air-source heat pump water heater combines the advantages of electric water heaters and solar water heaters. It is safe, energy-saving, environmentally friendly, and can operate 365 days a year. The cost of producing the same amount of hot water is low.
Working principle: Inside, there is a refrigerant as the heat-absorbing medium. In the liquefied state, its temperature is below minus 20°C. It absorbs external heat energy, and then its temperature is raised by the compressor. In the condenser, it liquefies and releases heat to heat the water in the water tank.
System composition: It consists of a compressor, a condenser, an evaporator, a throttling device, a filter, a liquid storage tank, a one-way valve, a solenoid valve, a condensing pressure regulating water valve, a water storage tank, etc.
Working principle:
① After the low-temperature and low-pressure refrigerant is throttled and depressurized, it evaporates and absorbs heat in the air exchanger, absorbing a large amount of heat Q1 from the air.
② The gaseous refrigerant is compressed into high-temperature and high-pressure by the compressor. At this time, the heat includes Q1 and the heat Q2 converted from the electrical energy of the compressor.
③ The high-temperature and high-pressure refrigerant releases the heat (Q1 + Q2) to the cold water in the heat exchanger. The cold water is heated to 55°C (maximum 65°C) and then enters the insulated water tank. The liquid refrigerant is throttled and depressurized for circulation.
Characteristics of the air-source heat pump water heater:
① Large water volume: The capacity of the water tank can be customized according to demand, with sufficient water to meet the needs of different customers at different times.
② Economical: It obtains a large amount of energy from the air, with an energy efficiency ratio as high as 300% - 400%. The cost can be saved by setting the automatic operation time according to the usage rules.
③ Wide application range: It is not affected by the climate and can work normally at -10°C to 43°C. It is widely used for centralized heating in various places.
④ Constant temperature: It uses an automated intelligent control system. After the power is turned on for the first time, it will automatically stop and start according to the specified water temperature, providing hot water 24 hours a day.
⑤ Safe and environmentally friendly: It separates water and electricity, has no harmful or toxic gas emissions or combustion, and is not affected by typhoons, etc., so it is safe.
⑥ Anti-freezing function: It has an intelligent defrosting function, which can intelligently judge defrosting according to parameters such as the outdoor environment temperature.
⑦ Easy to install: It is small in size and can be installed indoors or outdoors. It can be remotely monitored, occupies a small area, is simple to install, and does not require a separate machine room.
⑧ Long service life: The maintenance cost is low, the equipment performance is stable, and the service life can reach more than 15 years.
Advantages compared with conventional solar water heaters:
① In terms of investment: To achieve the same water supply effect, the investment is less than that of conventional solar products. It can produce and store hot water during off-peak electricity hours.
② In terms of usage: It is not affected by the weather and can provide hot water all day long, while conventional solar water heaters are greatly affected by the weather.
③ In terms of operating cost: The annual power consumption of the auxiliary system of conventional solar water heaters is 1.5 times higher than that of air-source heat pump water heaters.
④ In terms of other functions: It is not restricted by location, occupies a small area, has a long service life, low maintenance cost, and stable equipment performance.
Advantages compared with boilers:
① High thermal efficiency: The annual average thermal efficiency of the product is over 300%, while the thermal efficiency of boilers does not exceed 100%.
② Low operating cost: Compared with fuel-oil and gas-fired boilers, it can save about 70% of energy annually on average. As the electricity price decreases and the fuel price rises, the advantage becomes more prominent.
③ Environmentally friendly: There are no combustion emissions, and the refrigerant is environmentally friendly, with zero pollution to the ozone layer.
④ Safe operation and no need for on-site attendance: It operates safely, is fully automatically controlled, and does not require personnel on-site attendance, saving labor costs.
High-temperature air-source heat pump technology: It is an energy-saving and environmentally friendly heating technology based on the reverse Carnot cycle principle. It obtains a low-temperature heat source from natural energy and integrates the heat collection into a high-temperature heat source for heating or hot water supply, with high heat collection efficiency. Heat pumps have the advantages of energy conservation, environmental friendliness, combination of cooling and heating, and convenient regulation. They can improve energy efficiency utilization, reduce greenhouse gas emissions, and solve the problem of high-altitude power loads.
Characteristics of the air-source heat pump:
High-efficiency and energy-saving: High heat collection efficiency and low operating cost (the electricity consumption is 1/5 of that of an electric water heater).
Green and environmentally friendly: It represents the future development direction.
Safe and cost-saving: Low initial installation cost.
Heating throughout the four seasons: It can synthesize a high-temperature heat source all day long on rainy days or in cold winters.
Stylish and durable: The service life is over 18 years.
Well-designed: Fully automatically controlled and maintenance-free operation.
Compact size: It can be placed in many places and integrated with the building.
10. Low-temperature Air-supply Air Conditioning System
Characteristics:
1. Improve indoor air quality
The low-temperature air-supply system has a low chilled water supply temperature and a large dehumidification capacity, which reduces the relative humidity in the room and improves the thermal comfort. Reducing the relative humidity by 15% has the same thermal comfort effect as reducing the dry-bulb temperature by 1°C. It can inhibit the reproduction of "Legionella" and reduce the possibility of "air-conditioning syndrome".
2. Save building space
By using the low-temperature air-supply technology, the air-supply temperature is reduced, the air-supply temperature difference is increased, the air-supply volume is reduced, the size of the air duct is decreased, the height above the ceiling is reduced, and the building space is saved.
3. Reduce the cost of the mechanical system
The primary air supply temperature difference and the chilled water supply-return temperature difference of the low-temperature air-supply system are larger than those of the conventional system. When delivering the same cooling capacity, the air-supply volume and the chilled water flow are significantly reduced. The investment in pumps, fans, water pipes, air ducts, and insulation materials can be reduced by 30% - 40%.
4. Reduce the operating energy consumption of the air-conditioning system
To achieve the same comfort effect, the low-temperature air-supply system can increase the indoor dry-bulb temperature, reduce the heat transfer through the building envelope, and reduce the cooling load of the building. Compared with the constant-air-volume system at normal temperature, the energy consumption of the fans and pumps can be reduced by about 30%.
11. Variable-air-volume (VAV) Air Conditioning System
The variable-air-volume (VAV) system was introduced by foreign countries in the early 1970s. It is the mainstream air-conditioning system in developed countries such as those in Europe and America. It automatically adjusts the air-supply volume of the terminal and the air-handling unit according to the changes in the air-conditioning load and indoor parameters to ensure comfort and reduce operating energy consumption. The characteristics are as follows:
① Comfort: It can flexibly control each air-conditioned area and set the ambient temperature according to the load changes or individual requirements.
② Energy-saving: The air-conditioning system mostly operates under part-load conditions. The VAV system adjusts the room temperature by changing the air-supply volume, reasonably distributes the air volume, reduces the energy consumption of the fans, and lowers the operating electricity cost and the total installed capacity.
③ No over-cooling or over-heating: The temperature control is flexible and effective, avoiding over-cooling or over-heating in local areas, improving comfort, and saving energy.
④ Low system noise: The reduction of the air volume is achieved by reducing the fan speed, and the system noise is significantly reduced.
⑤ No worry about condensed water: It is an all-air system, and the chilled water pipes do not pass through the ceiling space, avoiding the dripping of condensed water to contaminate the ceiling.
⑥ Good system flexibility: A flexible hose is used between the air-supply duct and the air outlet. The position of the air outlet can be changed according to the changes in the room, and the number of air outlets can also be increased or decreased.
12. Absorption Chiller Air Conditioning System
Absorption chillers use heat energy as the driving force, usually steam, hot water, or natural gas, to drive the refrigeration cycle. They use a refrigerant and an absorbent (such as water and lithium bromide) to achieve refrigeration.
Advantages:
① Can make use of waste heat resources, such as the waste heat from industrial processes, exhaust gas of power plants, etc., improving energy utilization efficiency.
② The power consumption for operation is relatively small compared to compression refrigeration systems, which is beneficial for energy conservation in places where electricity is relatively expensive or in industrial areas with abundant waste heat.
③ In some cases, it can provide both cooling and heating functions, especially for some industrial enterprises or buildings with certain heat sources, which can meet different energy needs.
Disadvantages:
① The overall efficiency is relatively low compared to compression refrigeration systems. The coefficient of performance (COP) is usually lower, resulting in higher energy consumption for the same cooling capacity when using primary energy sources.
② The initial investment is relatively large. The absorption chiller system is more complex in structure, including components such as generators, absorbers, condensers, and evaporators, and requires higher costs for equipment procurement, installation, and commissioning.
③ Maintenance is relatively complex. The system involves the use of special refrigerants and absorbents, and the maintenance process needs to ensure the proper operation of each component and the stability of the solution concentration, etc. Regular maintenance and replacement of related media are required, increasing maintenance costs.
④ The system is more sensitive to the quality and stability of heat sources. If the heat source parameters change, it may affect the normal operation and performance of the absorption chiller, and the adjustment ability is relatively limited.
13. Evaporative Cooling Air Conditioning System
Evaporative cooling uses the principle of water evaporation to absorb heat to cool the air. There are two main types: direct evaporative cooling and indirect evaporative cooling.
Advantages:
① High energy efficiency. It mainly uses the latent heat of water evaporation, and the energy consumption for operation is very low, which is an energy-saving cooling method.
② Environmentally friendly. It does not use refrigerants that are harmful to the environment, reducing environmental pollution.
③ Low cost. The equipment is relatively simple, and the investment cost is lower compared to some traditional air conditioning systems. In addition, the operating cost is also low due to low energy consumption.
④ Suitable for arid and semi-arid regions. In areas with low humidity, the cooling effect is obvious, and it can effectively improve the indoor thermal environment.
Disadvantages:
① Limited by humidity. In areas with high humidity, the evaporation rate of water is low, and the cooling effect will be significantly reduced, so it is not suitable for use in humid climates.
② Can increase indoor humidity. Direct evaporative cooling will increase the humidity of the air, which may not be suitable for some places with strict requirements for humidity, such as some workshops for producing precision instruments or storage rooms for moisture-sensitive items.
③ The cooling temperature has limitations. It is difficult to achieve very low cooling temperatures, and it is usually suitable for occasions where the required cooling temperature is not extremely low.
14. Induction Air Conditioning System
The induction air conditioning system consists of an induction unit and a central air handling unit. The central air handling unit processes the primary air and supplies it to the induction unit, and the induction unit induces the indoor air to mix with the primary air and then supplies it to the room.
Advantages:
① Good air distribution performance. It can achieve a more uniform air distribution in the room, improving indoor comfort and air quality.
② Flexible system design. It can be adjusted according to different room layouts and usage requirements, and is suitable for various types of buildings.
③ Energy-saving potential. By reasonably designing the induction ratio and the operation mode of the central air handling unit, it can reduce the energy consumption of the air conditioning system to a certain extent.
Disadvantages:
① High initial investment. The system requires the installation of induction units in each room or area, increasing the equipment cost and installation cost.
② Relatively complex maintenance. Each induction unit needs regular inspection and maintenance, and the maintenance workload is relatively large. In addition, if there are problems with the induction unit, it may affect the normal operation of the entire room's air conditioning.
③ Noise issues. During the operation of the induction unit, there may be certain noise, which may have an impact on the indoor acoustic environment, especially in some places with high requirements for quietness.
This is a commonly used air conditioning form at present. After more than a century of development, there are various forms of refrigeration host machines, which have the advantages of high refrigeration efficiency, etc. The characteristics are as follows:
Advantages:
① The system is simple and occupies a slightly smaller area than other forms.
② High efficiency, with the COP (Coefficient of Performance for refrigeration) generally greater than 5.3.
③ The equipment investment is less than that of other systems.
Disadvantages:
① The number and capacity of the chiller units are large, and the number and capacity of other electrical equipment also increase, increasing the workload of maintenance and repair.
② The total power consumption load is large, increasing the transformer's power distribution capacity and the cost of power distribution facilities.
③ All the electricity used is peak-hour electricity, and it does not enjoy the peak-valley electricity price policy, resulting in high operating costs.
④ The air conditioner cannot be used during power rationing. For example, in the summers of 2003/2004, the air conditioning host machines operated at half capacity, and most central air conditioners could not achieve the desired effect.
⑤ The operation mode is inflexible. During the transitional season, holidays, or rest periods, if cooling is required in individual areas, the host machine needs to be turned on, which wastes the unit's configuration capacity and increases operating costs.
⑥ It is difficult to achieve good cooling in a large-scale district cooling system (the water supply temperature cannot be lowered), with large investment in the pipeline network, high transportation energy consumption, and poor air conditioning quality.
2. Ice Storage Air Conditioning System
The ice storage air conditioner reduces the capacity of the refrigeration host machine and adds an ice storage device on the basis of the conventional water-cooled chiller unit system.
The central air conditioning system with ice storage represents the advanced level of central air conditioning in the world and indicates the development direction. The characteristics are as follows:
Advantages:
① Reduces the capacity of the chiller units (reduces the one-time investment in the host machine), with a lower total power consumption load, and reduces the transformer's power distribution capacity and the cost of power distribution facilities.
② The refrigeration host machine has high refrigeration efficiency (COP > 5.3). By taking advantage of the price difference between peak and off-peak electricity, the annual operating cost of the air conditioner can be greatly reduced, and the operating cost can be saved by more than 35% (more than 40% compared with heat pump and lithium bromide air conditioning forms).
③ Reduces the building's power distribution capacity, saves the investment in power transformation and distribution, and saves about 30% (the power distribution investment for the air conditioner); exempts from the high reliability cost of the dual-circuit system, saving investment.
④ Flexible to use. The air conditioning in some areas can be provided by ice melting without turning on the host machine, with obvious energy-saving effects.
⑤ Can provide quantitative cooling by melting ice for a smaller load without turning on the host machine.
⑥ During the transitional season, it can provide quantitative cooling by melting ice, avoiding the situation of "using a big horse to pull a small cart", and the operation is more reasonable with obvious cost savings.
⑦ Has an emergency function, improving the reliability of the air conditioning system. During power rationing, as long as there is electricity to drive the water pump, the ice can be melted to provide cooling. For example, in the summers of 2003/2004, the effect of the ice storage air conditioning was not affected.
⑧ The refrigeration temperature is low and stable, the air conditioning effect is good, and it improves the comfort and grade of the building.
⑨ With a low-temperature cold source, the refrigeration speed is fast, and the start-up time before going to work is short. If the start-up time is long, the air conditioner will have a lot of ineffective operations, resulting in great waste.
⑩ The driving energy is clean, environmentally friendly, stable, simple and reliable, and the price difference between peak and off-peak electricity will be more favorable in the future.
⑪ For large-scale district cooling of multiple buildings, it can supply water at a low temperature, reducing the energy consumption for water supply and the investment in the pipeline network; compared with a cooling station for each building, it can save investment, reduce management costs, and reduce the area of the machine room.
⑫ Provides low-temperature chilled water for the terminals, reducing the terminal investment; enhances the dehumidification ability, greatly improving the comfort of the air conditioning; using a low-temperature air supply system can save the energy consumption of the terminal fans, improve the air conditioning quality, and reduce the size and investment of the air ducts.
⑬ The air conditioning system has a high degree of intelligence, can achieve fully automatic operation, has an interface with the building's BAS, and is a world-advanced air conditioning system.
Disadvantages:
① When the host machine and the ice storage device and other equipment are arranged in the refrigeration machine room, the ice storage device needs to occupy a certain space (it can be buried under the green belt, arranged under the car ramp and other unused spaces).
② The investment in the machine room equipment is slightly higher than that of the conventional water-cooled electric refrigeration and lithium bromide unit systems.
③ Ice storage can only provide cooling in summer and requires a heating system (heat exchange heating through the heating network can be used, and the capacity of the heating network is about 50% of that required by the lithium bromide unit).
3. Water Source Heat Pump Air Conditioning System
1) It belongs to the renewable energy utilization technology.
The water source heat pump uses the solar energy resources stored in the earth's water bodies as the cold and heat sources for an energy conversion heating and air conditioning system. The available water bodies include groundwater, rivers, some surface rivers and lakes, and the ocean. The surface soil and water bodies are huge collectors and dynamic energy balance systems, making it possible to use geothermal energy, which is a clean renewable energy technology.
2) Convenient for metering and charging.
The power consumption load of the air conditioner is at the user's location, which is convenient for air conditioner metering and charging, and is conducive to users' rational use of the air conditioning system, energy conservation, and the fair distribution of air conditioning operation management.
3) Safe and reliable operation.
The air conditioning system of the water source heat pump unit can basically ensure that it is turned on according to the user's needs throughout the year and can also operate in the spring and autumn transitional seasons, which is equivalent to a four-pipe air conditioning system. The supply and return water temperatures of the water source heat pump are relatively stable throughout the four seasons, and the fluctuation range is much smaller than the change in air temperature. The water body serves as a cold source in summer and a heat source in winter, and the unit operates more reliably and stably, ensuring the high efficiency and economy of the system. There is no problem of defrosting in winter for the air source heat pump.
4) High efficiency and energy saving.
In winter, the temperature of the water body that can be used by the water source heat pump unit is higher than the ambient air temperature, the evaporation temperature of the heat pump cycle is increased, and the energy efficiency ratio is increased; in summer, the water body temperature is lower than the ambient temperature, the refrigeration condensation temperature is reduced, and the unit efficiency is increased.
5) Flexible application.
In some buildings, during the transitional season, some areas need cooling and some areas need heating. The water source heat pump can provide both cooling and heating at the same time, realizing the transfer and balance of cooling and heating in the building, and the system uses less energy.
The water and ground source air conditioning has been widely recognized for its energy conservation and environmental protection. The relevant technologies have been listed as scientific research projects and are developing rapidly in large and medium-sized cities. Demonstration projects have been established everywhere, and the government encourages the selection of such systems. With the climate warming, energy conservation has become an indicator for measuring the quality of buildings, and "low carbon emissions" have received attention. Energy conservation and emission reduction of central air conditioners are necessary. The state advocates relevant heat pump technologies and recommends the water source heat pump and ice storage technologies.
4. Electric Heat Storage Air Conditioning System
The electric heat storage air conditioner uses an electric boiler to generate heat with the low-cost electricity during the night off-peak period, stores the heat in the form of hot water in the heat storage device, and releases it to the air conditioning terminals for heating during the daytime.
The characteristics are as follows:
① Uses energy storage technology to shift the peak and fill the valley, balance the power grid load, improve the utilization rate of the power generation equipment in the power plant, reduce the operating costs of the power plant and the power grid, and save the investment in infrastructure construction.
② Takes advantage of the price difference between peak and off-peak electricity to greatly reduce the annual operating cost of the air conditioner.
③ Flexible to use. During the transitional season, holidays, or after work, the air conditioning in some offices can be provided quantitatively by the heat storage without turning on the unit, with obvious energy-saving effects and greatly reduced operating costs.
④ Has an emergency function, improving the reliability of the air conditioning system.
⑤ High degree of automation, can operate without on-site attendance, can track in real time according to the changes of the air conditioner, and provide cooling as needed, with obvious energy-saving effects.
5. Air-cooled Heat Pump Air Conditioning System
The air-cooled heat pump is cooled by outdoor air, and its refrigeration and heating performance is closely related to the outdoor environmental temperature. The characteristics are as follows:
Advantages:
① Integrates cooling and heating, and there is no need to configure an additional heat source.
② When the impact on the building's appearance and the vibration of the unit operation is not considered, it can be placed on the roof without a dedicated air conditioning machine room, which is suitable for buildings with a small area and no refrigeration machine room.
③ Air cooling, so there is no need to configure a cooling tower.
Disadvantages:
① Relying on air cooling, its refrigeration and heating performance is greatly affected by the outdoor environmental temperature, and the performance is unstable. In summer, when the outdoor temperature is high and the cooling demand is large, the refrigeration capacity deteriorates; in winter, when the outdoor temperature is low and the heating demand is large, the heating capacity deteriorates. Defrosting in winter affects the heating effect, the heating temperature is low, and the indoor temperature cannot reach the required level when it is cold.
② Low refrigeration efficiency (the nominal COP is lower than 3.2, and the actual operation is about 2.5), resulting in high operating costs.
③ The unit is placed outdoors and cooled by the wind. Over time, the condenser will be covered with dust, which affects the heat exchange efficiency, reduces the operating efficiency of the unit, and causes a sharp decline in the refrigeration capacity. Generally, after 3 years, the refrigeration capacity needs to be re-evaluated and dealt with, and sometimes additional units need to be added.
④ The unit selection needs to consider the environmental impact, which increases the configuration and investment. The investment is the highest among several air conditioning forms.
⑤ Low efficiency and large total power consumption load increase the transformer's power distribution capacity in the conventional air conditioning system. The cost of power distribution facilities is high, and more power connection fees and power construction fees need to be paid.
⑥ The unit is placed outdoors, making operation, management, and maintenance difficult. The unit is easily damaged, and the maintenance workload is large.
⑦ During the transitional season, when the cooling or heating demand decreases, the refrigeration or heating capacity reaches its maximum level, resulting in a wasteful situation like "using a big horse to pull a small cart", increasing operating costs.
6. Lithium Bromide Air Conditioning System
The lithium bromide unit uses thermal energy as the energy source. Through the absorption and release of lithium bromide and water, water is used as the refrigerant for cyclic refrigeration. According to the way of supplying thermal energy, it is divided into direct-fired type, steam type, and hot water type.
Advantages are as follows:
① The main energy source of the system is thermal energy, and the power distribution capacity is small (about 1/3 of that of the conventional electric refrigeration system and 1/2 of that of the ice storage system), resulting in low power consumption during operation. However, it cannot operate during a power outage. The self-provided generator can only ensure the operation of some water pumps, unlike the ice storage system, which can fully melt the ice to provide cooling by turning on the water pump; for example, in the summer of 2003, when the power was rationed and only half of the units were operating, the air conditioning effect could not be achieved, while the ice storage system could ensure the effect.
② Suitable for applications in places where waste heat is generated, such as steel mills and textile factories. It is applied in developed countries in Europe and America in such situations.
③ The direct-fired type integrates cooling and heating, and there is no need to configure additional heating equipment (it is like a gas boiler during heating, but the thermal efficiency is lower than that of a single gas boiler).
④ The floor area of the machine room is slightly smaller than that of the ice storage system.
Disadvantages:
① The refrigeration capacity decreases (the annual decrease is about 3% - 8%), and the capacity design is configured with a 15% margin.
② The outlet water temperature of the refrigeration host machine is high, and the actual operation is above 8°C. The air conditioning effect is poor, the refrigeration speed is slow, and the start-up time before going to work is long, reducing the grade of the building; due to the high water supply temperature, the capacity of the terminal equipment needs to be increased, increasing the investment.
③ Lithium bromide is corrosive, which is likely to cause corrosion of the unit and a decrease in the refrigeration capacity.
④ Low efficiency, with an energy efficiency ratio (COP) of about 0.8 - 1.2. It is a product that saves electricity but not energy, with high operating energy consumption and costs. In developed countries, it is not advocated to use it during energy shortages (unless there is waste heat).
⑤ Using water as the refrigerant requires ensuring the vacuum degree of the system. In actual operation, non-condensable gases are generated, which leads to a decrease in the vacuum degree and a decrease in the refrigeration capacity.
⑥ Poor unloading capacity during part-load operation, which is likely to cause the situation of "using a big horse to pull a small cart", wasting operating costs; when the cooling load in some areas is small, the unit may not be able to start (it cannot operate below 40% of the load); it cannot provide cooling when the cooling demand is very small; if the part-load operation is not well adjusted, lithium bromide is likely to crystallize, and the system is difficult to operate.
⑦ The cooling water system is larger than that of the conventional electric refrigeration system. The cooling tower is twice the size of that in the ice storage system, with a large amount of make-up water. It is difficult to arrange on the roof; the cooling water pipes are large, and the pipeline wells are large.
⑧ Complex operation and maintenance. Daily maintenance is important. If the maintenance is not good, the refrigeration capacity will decrease rapidly. The maintenance and management personnel need a high professional level, and the cost is much higher than that of the electric refrigeration system.
⑨ The lithium bromide solution needs to be maintained and replaced every year, which is costly. On-site replacement is likely to make the system unclean and reduce the refrigeration effect.
⑩ The unit is large in size and requires a larger maintenance space and passage.
⑪ The prices of oil and gas are rising, and the supply is tight, resulting in high operating costs.
⑫ Fire protection factors need to be considered for oil and gas, making management inconvenient.
7. VRV Air Conditioning System
Characteristics:
① It is not a central air conditioning system, and the air conditioning quality is poor.
② The system is relatively simple, integrates cooling and heating, and does not require a dedicated air conditioning machine room.
③ The system design is flexible, and an independent system can be configured for a small cooling area.
④ High investment.
⑤ Using air cooling, the cooling effect is worse than that of water cooling. The energy efficiency ratio (COP) of the unit is low (the sample calibration is generally less than 3, and the actual operation is much lower than 2.5). The air conditioning effect is poor, and the operating cost is high. The COP is even lower on the hottest days, resulting in higher operating costs; the efficiency is also low during winter heating, and the heating capacity decreases as the environmental temperature drops.
⑥ The unit is placed outdoors and cooled by the air. Over time, the condenser will be covered with dust, which affects the heat exchange efficiency, reduces the operating efficiency of the unit, and causes a sharp decline in the refrigeration capacity. After 3 years, it basically cannot meet the cooling demand, and additional units need to be added.
⑦ One outdoor unit is connected to multiple indoor units through copper pipes, and the refrigerant is in the pipes. During installation, it is necessary to ensure no leakage. If there is a leakage at one connection point, the air conditioning of the entire system will fail.
⑧ If the distance between the indoor unit and the outdoor unit is too large, it is difficult to return the oil, which affects the operation and service life of the compressor and also affects the heat exchange capacity of the unit.
⑨ Inconvenient for maintenance. Indoor maintenance will damage the decoration.
⑩ The number and capacity of the units are relatively large, resulting in a large maintenance workload.
⑪ The total power consumption load is large, which increases the transformer's power distribution capacity and the cost of power distribution facilities.
⑫ Additional water chiller units are required to solve the fresh air problem.
8. Ground Source Heat Pump Air Conditioning System
Heat naturally flows from a high-temperature area to a low-temperature area. A heat pump is a device that can draw heat from a low-temperature source to a high-temperature source, and it is energy-saving. The ground-source heat pump uses the heat exchange between water and geothermal energy (groundwater, soil, or surface water) as the cold and heat sources. In winter, it extracts heat from the ground, and the ground serves as a "cold source". The ground-source heat pump heating and air-conditioning system is composed of an outdoor geothermal energy exchange system, a water-source heat pump unit, and an indoor heating and air-conditioning terminal system. There are two forms of the unit: water-to-water or water-to-air, and the three systems exchange heat through water or air.
Advantages of the ground-source heat pump compared with the air-source heat pump:
① The temperature fluctuates less throughout the year. In winter, the ground temperature is higher than the air temperature, and in summer, it is lower. The heating and cooling coefficients are about 40% higher than those of the air-source heat pump, which can save about 40% in energy and costs.
② There is no need for defrosting during winter operation, reducing the losses caused by frosting and defrosting.
③ The ground has a good energy storage function.
9. Air-source Heat Pump Air-conditioning System
The air-source heat pump water heater combines the advantages of electric water heaters and solar water heaters. It is safe, energy-saving, environmentally friendly, and can operate 365 days a year. The cost of producing the same amount of hot water is low.
Working principle: Inside, there is a refrigerant as the heat-absorbing medium. In the liquefied state, its temperature is below minus 20°C. It absorbs external heat energy, and then its temperature is raised by the compressor. In the condenser, it liquefies and releases heat to heat the water in the water tank.
System composition: It consists of a compressor, a condenser, an evaporator, a throttling device, a filter, a liquid storage tank, a one-way valve, a solenoid valve, a condensing pressure regulating water valve, a water storage tank, etc.
Working principle:
① After the low-temperature and low-pressure refrigerant is throttled and depressurized, it evaporates and absorbs heat in the air exchanger, absorbing a large amount of heat Q1 from the air.
② The gaseous refrigerant is compressed into high-temperature and high-pressure by the compressor. At this time, the heat includes Q1 and the heat Q2 converted from the electrical energy of the compressor.
③ The high-temperature and high-pressure refrigerant releases the heat (Q1 + Q2) to the cold water in the heat exchanger. The cold water is heated to 55°C (maximum 65°C) and then enters the insulated water tank. The liquid refrigerant is throttled and depressurized for circulation.
Characteristics of the air-source heat pump water heater:
① Large water volume: The capacity of the water tank can be customized according to demand, with sufficient water to meet the needs of different customers at different times.
② Economical: It obtains a large amount of energy from the air, with an energy efficiency ratio as high as 300% - 400%. The cost can be saved by setting the automatic operation time according to the usage rules.
③ Wide application range: It is not affected by the climate and can work normally at -10°C to 43°C. It is widely used for centralized heating in various places.
④ Constant temperature: It uses an automated intelligent control system. After the power is turned on for the first time, it will automatically stop and start according to the specified water temperature, providing hot water 24 hours a day.
⑤ Safe and environmentally friendly: It separates water and electricity, has no harmful or toxic gas emissions or combustion, and is not affected by typhoons, etc., so it is safe.
⑥ Anti-freezing function: It has an intelligent defrosting function, which can intelligently judge defrosting according to parameters such as the outdoor environment temperature.
⑦ Easy to install: It is small in size and can be installed indoors or outdoors. It can be remotely monitored, occupies a small area, is simple to install, and does not require a separate machine room.
⑧ Long service life: The maintenance cost is low, the equipment performance is stable, and the service life can reach more than 15 years.
Advantages compared with conventional solar water heaters:
① In terms of investment: To achieve the same water supply effect, the investment is less than that of conventional solar products. It can produce and store hot water during off-peak electricity hours.
② In terms of usage: It is not affected by the weather and can provide hot water all day long, while conventional solar water heaters are greatly affected by the weather.
③ In terms of operating cost: The annual power consumption of the auxiliary system of conventional solar water heaters is 1.5 times higher than that of air-source heat pump water heaters.
④ In terms of other functions: It is not restricted by location, occupies a small area, has a long service life, low maintenance cost, and stable equipment performance.
Advantages compared with boilers:
① High thermal efficiency: The annual average thermal efficiency of the product is over 300%, while the thermal efficiency of boilers does not exceed 100%.
② Low operating cost: Compared with fuel-oil and gas-fired boilers, it can save about 70% of energy annually on average. As the electricity price decreases and the fuel price rises, the advantage becomes more prominent.
③ Environmentally friendly: There are no combustion emissions, and the refrigerant is environmentally friendly, with zero pollution to the ozone layer.
④ Safe operation and no need for on-site attendance: It operates safely, is fully automatically controlled, and does not require personnel on-site attendance, saving labor costs.
High-temperature air-source heat pump technology: It is an energy-saving and environmentally friendly heating technology based on the reverse Carnot cycle principle. It obtains a low-temperature heat source from natural energy and integrates the heat collection into a high-temperature heat source for heating or hot water supply, with high heat collection efficiency. Heat pumps have the advantages of energy conservation, environmental friendliness, combination of cooling and heating, and convenient regulation. They can improve energy efficiency utilization, reduce greenhouse gas emissions, and solve the problem of high-altitude power loads.
Characteristics of the air-source heat pump:
High-efficiency and energy-saving: High heat collection efficiency and low operating cost (the electricity consumption is 1/5 of that of an electric water heater).
Green and environmentally friendly: It represents the future development direction.
Safe and cost-saving: Low initial installation cost.
Heating throughout the four seasons: It can synthesize a high-temperature heat source all day long on rainy days or in cold winters.
Stylish and durable: The service life is over 18 years.
Well-designed: Fully automatically controlled and maintenance-free operation.
Compact size: It can be placed in many places and integrated with the building.
10. Low-temperature Air-supply Air Conditioning System
Characteristics:
1. Improve indoor air quality
The low-temperature air-supply system has a low chilled water supply temperature and a large dehumidification capacity, which reduces the relative humidity in the room and improves the thermal comfort. Reducing the relative humidity by 15% has the same thermal comfort effect as reducing the dry-bulb temperature by 1°C. It can inhibit the reproduction of "Legionella" and reduce the possibility of "air-conditioning syndrome".
2. Save building space
By using the low-temperature air-supply technology, the air-supply temperature is reduced, the air-supply temperature difference is increased, the air-supply volume is reduced, the size of the air duct is decreased, the height above the ceiling is reduced, and the building space is saved.
3. Reduce the cost of the mechanical system
The primary air supply temperature difference and the chilled water supply-return temperature difference of the low-temperature air-supply system are larger than those of the conventional system. When delivering the same cooling capacity, the air-supply volume and the chilled water flow are significantly reduced. The investment in pumps, fans, water pipes, air ducts, and insulation materials can be reduced by 30% - 40%.
4. Reduce the operating energy consumption of the air-conditioning system
To achieve the same comfort effect, the low-temperature air-supply system can increase the indoor dry-bulb temperature, reduce the heat transfer through the building envelope, and reduce the cooling load of the building. Compared with the constant-air-volume system at normal temperature, the energy consumption of the fans and pumps can be reduced by about 30%.
11. Variable-air-volume (VAV) Air Conditioning System
The variable-air-volume (VAV) system was introduced by foreign countries in the early 1970s. It is the mainstream air-conditioning system in developed countries such as those in Europe and America. It automatically adjusts the air-supply volume of the terminal and the air-handling unit according to the changes in the air-conditioning load and indoor parameters to ensure comfort and reduce operating energy consumption. The characteristics are as follows:
① Comfort: It can flexibly control each air-conditioned area and set the ambient temperature according to the load changes or individual requirements.
② Energy-saving: The air-conditioning system mostly operates under part-load conditions. The VAV system adjusts the room temperature by changing the air-supply volume, reasonably distributes the air volume, reduces the energy consumption of the fans, and lowers the operating electricity cost and the total installed capacity.
③ No over-cooling or over-heating: The temperature control is flexible and effective, avoiding over-cooling or over-heating in local areas, improving comfort, and saving energy.
④ Low system noise: The reduction of the air volume is achieved by reducing the fan speed, and the system noise is significantly reduced.
⑤ No worry about condensed water: It is an all-air system, and the chilled water pipes do not pass through the ceiling space, avoiding the dripping of condensed water to contaminate the ceiling.
⑥ Good system flexibility: A flexible hose is used between the air-supply duct and the air outlet. The position of the air outlet can be changed according to the changes in the room, and the number of air outlets can also be increased or decreased.
12. Absorption Chiller Air Conditioning System
Absorption chillers use heat energy as the driving force, usually steam, hot water, or natural gas, to drive the refrigeration cycle. They use a refrigerant and an absorbent (such as water and lithium bromide) to achieve refrigeration.
Advantages:
① Can make use of waste heat resources, such as the waste heat from industrial processes, exhaust gas of power plants, etc., improving energy utilization efficiency.
② The power consumption for operation is relatively small compared to compression refrigeration systems, which is beneficial for energy conservation in places where electricity is relatively expensive or in industrial areas with abundant waste heat.
③ In some cases, it can provide both cooling and heating functions, especially for some industrial enterprises or buildings with certain heat sources, which can meet different energy needs.
Disadvantages:
① The overall efficiency is relatively low compared to compression refrigeration systems. The coefficient of performance (COP) is usually lower, resulting in higher energy consumption for the same cooling capacity when using primary energy sources.
② The initial investment is relatively large. The absorption chiller system is more complex in structure, including components such as generators, absorbers, condensers, and evaporators, and requires higher costs for equipment procurement, installation, and commissioning.
③ Maintenance is relatively complex. The system involves the use of special refrigerants and absorbents, and the maintenance process needs to ensure the proper operation of each component and the stability of the solution concentration, etc. Regular maintenance and replacement of related media are required, increasing maintenance costs.
④ The system is more sensitive to the quality and stability of heat sources. If the heat source parameters change, it may affect the normal operation and performance of the absorption chiller, and the adjustment ability is relatively limited.
13. Evaporative Cooling Air Conditioning System
Evaporative cooling uses the principle of water evaporation to absorb heat to cool the air. There are two main types: direct evaporative cooling and indirect evaporative cooling.
Advantages:
① High energy efficiency. It mainly uses the latent heat of water evaporation, and the energy consumption for operation is very low, which is an energy-saving cooling method.
② Environmentally friendly. It does not use refrigerants that are harmful to the environment, reducing environmental pollution.
③ Low cost. The equipment is relatively simple, and the investment cost is lower compared to some traditional air conditioning systems. In addition, the operating cost is also low due to low energy consumption.
④ Suitable for arid and semi-arid regions. In areas with low humidity, the cooling effect is obvious, and it can effectively improve the indoor thermal environment.
Disadvantages:
① Limited by humidity. In areas with high humidity, the evaporation rate of water is low, and the cooling effect will be significantly reduced, so it is not suitable for use in humid climates.
② Can increase indoor humidity. Direct evaporative cooling will increase the humidity of the air, which may not be suitable for some places with strict requirements for humidity, such as some workshops for producing precision instruments or storage rooms for moisture-sensitive items.
③ The cooling temperature has limitations. It is difficult to achieve very low cooling temperatures, and it is usually suitable for occasions where the required cooling temperature is not extremely low.
14. Induction Air Conditioning System
The induction air conditioning system consists of an induction unit and a central air handling unit. The central air handling unit processes the primary air and supplies it to the induction unit, and the induction unit induces the indoor air to mix with the primary air and then supplies it to the room.
Advantages:
① Good air distribution performance. It can achieve a more uniform air distribution in the room, improving indoor comfort and air quality.
② Flexible system design. It can be adjusted according to different room layouts and usage requirements, and is suitable for various types of buildings.
③ Energy-saving potential. By reasonably designing the induction ratio and the operation mode of the central air handling unit, it can reduce the energy consumption of the air conditioning system to a certain extent.
Disadvantages:
① High initial investment. The system requires the installation of induction units in each room or area, increasing the equipment cost and installation cost.
② Relatively complex maintenance. Each induction unit needs regular inspection and maintenance, and the maintenance workload is relatively large. In addition, if there are problems with the induction unit, it may affect the normal operation of the entire room's air conditioning.
③ Noise issues. During the operation of the induction unit, there may be certain noise, which may have an impact on the indoor acoustic environment, especially in some places with high requirements for quietness.
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