In HVAC design, attention should be paid to improving the thermal performance of envelope and the thermal insulation performance of thermal equipment; The air conditioning system scheme should save energy, fully recover energy and make full use of natural gas energy as much as possible. At the same time, effective methods such as automatic control and energy saving should be adopted, and the energy-saving system combining HVAC should be reasonably selected in the design to effectively reduce the cold and heat loss of the building. Then, I will analyze the energy-saving design of HVAC system for you. Welcome to read and browse.
1. Overview
With the rapid development of urbanization in China and the improvement of people's living standards, the proportion of building energy consumption in the total energy consumption is increasing, reaching 40% in developed countries. For a long time, in our country, due to over-emphasis on building costs and personal interests, lack of standards and norms for building energy efficiency, there are repeated construction and quality problems, resulting in serious energy waste. Building energy consumption mainly includes building energy consumption in heating, ventilation, air conditioning, lighting, electrical appliances and hot water supply. In order to maintain the proper temperature and humidity of the air environment inside buildings, modern buildings usually use HVAC systems to ensure this demand, and the energy consumed is the energy consumption of HVAC systems. This part of energy consumption includes energy consumption caused by building cooling and heating load, energy consumption caused by fresh air load and energy consumption caused by pipe cooling. The main factors affecting the energy consumption of HVAC system are outdoor climate conditions, indoor design standards, envelope characteristics, lighting conditions of indoor personnel and equipment, and the setting of fresh air system. Some views on effective countermeasures for energy saving of HVAC system in China.
2. Energy-saving design ideas of HVAC system
2. 1 scheme design
At present, the popular air conditioning design schemes are: displacement air supply system with adjustable air volume, cold radiation ceiling system, low temperature air supply system combined with ice storage dehumidification air conditioning system on the premise of low energy consumption and high ieq. In order to balance the radiant heat generated by main heat sources such as equipment and lighting in high-rise office buildings, radiant cooling is adopted. Cold radiation ceiling should be combined with displacement air supply, and fresh air should be sent indoors by downward air supply, which not only ensures indoor air quality, but also ensures a good indoor thermal environment. The air conditioning dehumidification scheme can ensure the indoor air quality first, and then ensure that the indoor humidity of green buildings can be controlled below 60%.
2.2 Have a good ventilation system.
Green buildings should have a good ventilation system to achieve reasonable natural ventilation, but some buildings contain volatile and harmful substances in decoration materials, causing indoor air pollution, so the flow of indoor fresh air is very important to health.
2.3 evaporative cooling technology
Evaporative cooling air conditioning technology is a green bionic air conditioning technology, including indirect evaporative cooling (IEC) and direct evaporative cooling (DEC). The system uses water as refrigerant, which makes the air conditioner run pollution-free. In addition, the COP value of evaporative cooling system is much higher than that of mechanical refrigeration, and its refrigeration does not consume compression work, so it is an energy-saving and environmental-friendly green air conditioning technology.
2.4 Ground source heat pump air conditioning system
Ground source heat pump air conditioning system is an efficient air conditioning method which uses soil, groundwater or rivers and lakes as cold and heat sources. Soil is a very suitable heat source, with suitable and stable temperature, good heat storage performance and everywhere. The ground source heat pump runs stably all year round, and can realize heating in winter and cooling in summer without other auxiliary heat sources and refrigeration equipment. The COP value of ground source heat pump can reach above 4. 0. The water source heat pump for deep well reinjection pumps the groundwater and reinjects it into the ground through the heat exchanger, which belongs to the totally enclosed mode. Therefore, water resources are not used, and underground water sources will not be polluted.
3. Ways and methods of energy saving in HVAC field
3. 1 Improve the thermal insulation performance of the building envelope and reduce the cold and heat losses.
For HVAC systems, the thermal insulation performance of the envelope determines its heat transfer coefficient, and the heat transfer coefficient also determines the cooling and heating load of the envelope. Therefore, in the national building energy-saving design codes and standards, the primary requirement is to improve the thermal insulation performance of the envelope structure. Properly improving the thermal insulation performance of walls and roofs can reduce the cold and heat load generated by these envelope structures. For example, using new energy-saving wall)) Small concrete hollow block as wall can effectively reduce the building load, and its heat transfer coefficient K=0.54 W/m2, which is more than twice as energy-saving as traditional clay solid brick wall. According to the thermal test results of residential envelope by authoritative departments, it is proved that 40%~50% of the heat loss in residential buildings is due to the penetration of cold air from doors and windows and the intrusion of cold air from external doors. New plastic steel doors and windows with good sealing, heat preservation and energy saving should be adopted as far as possible.
3.2 The fresh air volume of air conditioning affects the energy consumption of air conditioning system.
The problem of fresh air in air conditioning is an important aspect that affects whether air conditioning can save energy. Too much fresh air will increase its load, and then increase power consumption. Too little fresh air volume will affect the quality of air conditioning environment, so adjusting the supply air temperature and fresh air ratio for a specific air conditioning environment is very beneficial to energy saving. For example, for air-conditioned rooms that need cooling in summer and heating in winter, the greater the outdoor fresh air volume, the greater the energy consumption of the system. In this case, outdoor fresh air should be controlled at the minimum required by hygiene. In the transitional season, air-conditioned rooms generally do not need cooling or heating, and all can use fresh air. This method is one of the most effective energy-saving measures in air conditioning system.
3.3 The air conditioning mode affects the energy consumption of the air conditioning system.
Choosing an appropriate air conditioning mode is an important aspect of air conditioning energy saving. In recent years, inverter air conditioning has developed rapidly because of its remarkable energy saving and comfortable environment. Up to now, inverter air conditioners in Japan account for more than 80% of the residential air conditioner market share. According to Japanese JRA404 standard, the seasonal energy efficiency ratio of inverter air conditioner is much higher than that of fixed frequency air conditioner. Under the same cooling load, the power consumption of inverter air conditioner is only 66% of that of fixed frequency air conditioner, that is, it saves electricity by 34%. Therefore, frequency conversion air conditioning should be a trend of air conditioning development, so that air conditioning can meet the energy-saving requirements as much as possible. In the central air conditioning system, frequency conversion technology should be adopted, mainly in two forms: replacing the regulating valve with variable speed pump and variable speed fan to reduce the internal friction of the system and improve the efficiency of the whole machine; Or use variable flow technology to change water flow or air flow according to air conditioning load to achieve energy-saving effect.
3.4 Adopting new energy-saving methods
There are many environmental parameters that affect human thermal comfort. Different combinations of environmental parameters can get the same thermal comfort effect, but different combinations of thermal and humid environmental parameters have different effects on the energy consumption of air conditioning systems. For example, in winter, if the whole indoor air is heated by traditional air conditioners, and the heat and moisture exchange between human body and environment is realized through air, higher air temperature is needed. At this time, the heat loss by maintaining the structure and heating fresh air is relatively large. If we change the traditional air conditioning mode and increase the radiant heat according to the research results of hot and humid environment, the required air temperature will drop obviously, generally reaching 65438 04℃, while the traditional air conditioning mode is generally 20℃. Obviously, the latter has a significant energy-saving effect than the former.
3.5 Research and apply cold and heat recovery to realize the maximum utilization of energy.
At present, many researches on the recovery and utilization of cold and heat in air-conditioning systems are also developing vigorously, such as the total heat recovery device for exhaust air of air-conditioning systems, and the use of condensed heat to supply sanitary hot water in summer, all of which recover the cold and heat of the system and significantly improve the energy utilization rate of air-conditioning systems. Considering energy saving, it is a trend to move the waste heat that needs to be discharged from the system to the place where heat is needed. The heat transfer efficiency of the total heat exchanger can now reach 75%~80%. There are also some commonly used heat recovery devices, such as heat pipe heat exchanger, plate heat exchanger and heat recovery loop. Relatively speaking, the recovery method of heat pump system is more common. The heat pump can recover the waste heat below 65,438+000e ~ 65,438+020e, and it can save a lot of heating fuel by using natural environment (such as air and water) and low-temperature heat sources (such as underground hot water, low-temperature solar heat and waste heat). It is a new energy-saving technology that uses low-temperature energy efficiently. If the heat pump is combined with direct contact heat recovery equipment, its heat recovery efficiency is much higher than that of a single equipment.
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