HVAC Technology Paper 1 HVAC Technology and Energy Saving
Abstract: With the improvement of people's living standards, people's pace of life is gradually accelerating, and psychological pressure is increasing, which makes people's working and living environment should be paid attention to. Advocating environmental protection and energy-saving lifestyle is becoming more and more important in people's work and living environment. This paper mainly analyzes HVAC technology and energy saving.
Keywords: HVAC technology energy saving
On September 22, 2009, President Hu Jintao delivered an important speech at the opening ceremony of the United Nations Climate Change Summit entitled "Working Together to Meet the Challenges of Climate Change-Speech at the Opening Ceremony of the United Nations Climate Change Summit", and solemnly promised that China will further integrate climate change into its economic and social development plan and continue to take effective measures: First, strengthen energy conservation and improve energy efficiency; Second, vigorously develop renewable energy and nuclear energy; Third, vigorously increase forest carbon sinks; Fourth, vigorously develop green economy, actively develop low-carbon economy and circular economy, and develop and popularize climate-friendly technologies. Clearly put forward the major strategic task of building ecological civilization, and stressed the need to adhere to the basic national policy of saving resources and protecting the environment, adhere to the road of sustainable development, and accelerate the construction of a resource-saving country. It can be seen how important energy conservation is for a country and even the world. This paper mainly discusses HVAC technology from the perspective of energy saving.
1. Interior design parameters
Generally speaking, when heating in winter, the energy consumption will be reduced by about 5% ~ 10% for every decrease in indoor calculated temperature. When cooling in summer, the energy consumption will be reduced by about 8% ~ 10% for every increase of indoor calculated temperature. Interior design parameters must be within the specified parameters. In recent years, low-temperature floor radiant heating system has replaced radiator heating. The reason why this method is adopted is mainly because it has the advantages of low energy consumption, high comfort, convenient household metering and no occupation of room area.
2. Heating design
The heat load of heating and air conditioning is 12650KW, and the thermal index is. The heat source is provided by urban heating network, and the return water temperature of primary water is 95/70℃. The backwater temperature of high-temperature secondary water after heat exchange is 85/60℃, which is used for heating system and fresh air treatment unit. All kinds of machine rooms and bicycle garages are equipped with 5-8℃ on-duty heating. The heating design temperature of the civil air defense bunker is 18℃, and the design temperature of the toilet is 16℃. The return water temperature of low-temperature secondary water supply is 60/50℃, which is used for the deicing system of fan coil units and automobile ramps, or the deicing system is not used for some reason. In order to ensure a good indoor temperature environment on the first floor and resist the invasion of cold air at the gate, a hot air curtain is set at each gate.
Heating in cold areas with air as heat source of heat pump is the focus of current research. Because it has outstanding advantages in environmental protection, energy saving, safe use and even economy compared with previous heating methods such as coal burning, oil burning and direct electricity consumption, its popularity also exceeds that of water source and ground source heat pump.
2. 1 Selection of capacity of air heat pump unit for floor heating
Unit capacity (W)= local building heating design load () × user heating building area () ⊙( 1-)×0.85-0.9.
2.2 The outdoor unit is best installed on the downwind side of the prevailing wind in winter, and a snow shed should be set up. If the device is installed on a platform, the bottom surface should be raised at least 20 cm to avoid thawing and freezing. The air inlet of the unit is at least 25cm away from the obstacle, and the distance between the two machines is at least 20cm.
2.3 Design of buried pipes under the floor
When using air heat pump as heat source, the water supply temperature or the average temperature of water supply and return should be designed as low as possible to make the efficiency of the unit as high as possible. As the engineering practice proves that the temperature difference between supply and return water in this unit is only 2℃-3℃, please refer to Appendix E-65440 of Technical Specification for Application of Low Temperature Hot Water Floor Radiant Heating (DBJ/T0 1-49-2000) when selecting underground buried pipes.
3. Wind system design
3. 1 waste heat recovery of central air conditioning system
For a long time, people in the industry have only measured the advantages and disadvantages of heat recovery devices from an economic perspective, ignoring environmental protection and energy saving. Now the perspective of people in the industry has changed. Now, the advantages and disadvantages of heat recovery devices are measured from the perspective of environmental protection and energy saving.
There is a lot of heat energy in the air-conditioned area. If these heat energies are recycled, environmental protection and energy saving will be realized. If fresh air and exhaust air are transported by special independent pipes, it is beneficial to the setting of centralized heat recovery device. Fresh air and exhaust air exchange damp heat or total heat by heat recovery device, and the energy saving effect is very obvious.
3.2 Air conditioning air system
(1) According to the data, if the indoor design temperature decreases 1℃ in summer or increases 1℃ in winter, the project investment will increase by 6% and the energy consumption will increase by 8%. This data clearly shows that increasing the indoor air temperature in summer and reducing the indoor air temperature in winter will play a significant energy-saving effect. At the same time, in order to ensure the indoor air quality and people's demand for fresh air, the current Code for Design of Heating, Ventilation and Air Conditioning clearly stipulates the minimum fresh air volume, requiring buildings to meet the current relevant national health standards. The research shows that increasing the fresh air volume can solve the indoor air quality problem to some extent, but it increases the energy consumption of air conditioning. The fixed value of fresh air volume must be determined according to the specifications, because fresh air volume plays a very important role in energy consumption and human health. If the personnel density is high, it is very uneconomical to supply air according to the personnel density. China buildings adopt fresh air demand control (detecting indoor CO2 concentration). It is worth noting that the fresh air volume changes and the exhaust air volume also changes. Otherwise, it will cause negative pressure, which may be counterproductive.
(2) HVAC designers agree with the provisions of the specification for fresh air volume. HVAC designers believe that it is necessary to increase the fresh air volume under the background of irregular cleaning of central air conditioning. But they have reservations about the requirements of indoor design temperature. There is a saying in the industry: "If energy conservation is like a tree, there are many branches that can be used as creativity, then the owner's opinion is more like that one. Their attitude will become the fundamental factor that determines the HVAC profession and even building energy conservation. " According to industry insiders, the opinions of the builder are very important.
In order to increase the fresh air volume or enhance the ability of fan coil to handle indoor return air, the fresh air inlet of fan coil should be arranged separately or next to the coil outlet, rather than at the coil return air inlet.
(3) In air-conditioned areas with large room area or space, a large number of people or the need for centralized temperature control, the air conditioning system should adopt all-air air conditioning system instead of fan-coil system, so as to centralize treatment and adjustment, give play to favorable factors and make up for the problems that have occurred before.
(4) When the height of building space is greater than or equal to 10m, and the volume is greater than, layered air conditioning system should be adopted. Compared with the whole room air conditioning system, the layered air conditioning system can save energy by about 30% in summer, but not in winter. Usually, when designing, the air distribution in summer is as follows: nozzle side delivery, return air in large space and exhaust air in large space; In winter, the floor radiation or floor air supply heating system is generally set on the ground floor, and the overheated air in the upper part can also be sent to the lower part of the room through the air duct.
(5) Multiple air conditioning zones share 1 air conditioning air system, and the load of each zone is quite different, and the low-load operation time is long, so the indoor temperature needs to be adjusted separately. When economic conditions permit, all-air VAV air conditioning system should be adopted. It should be noted that fan speed regulation is required to change the air volume of the system, but constant speed fan cannot be used to change the resistance adjustment of the system; Secondly, measures should be taken to ensure the minimum fresh air volume, so as to avoid the consequences that the fresh air volume is reduced due to the reduction of air supply volume and does not meet the sanitary requirements; Furthermore, when adjusting the air volume of the terminal air supply outlet, it is suggested to use the terminal device driven by series fans to ensure the indoor air distribution.
(6) In some cases, such as large heat transfer on the roof, large heat generated in the ceiling and large ceiling space (at this time, the height from the ceiling to the floor bottom exceeds 1.0m), if return air is used in the ceiling, the air conditioning area will increase and the energy consumption of air conditioning will increase, which is very unfavorable for energy saving. Therefore, it is unreasonable to return air directly from the ceiling when there is a lot of heat on the top floor or ceiling of the building and the ceiling space is high.
4. Enclosure structure
Wu Desheng, former president of Beijing Architectural Design and Research Institute and consultant chief engineer of Beijing Architectural Design and Research Institute, thinks that since HVAC is the pillar force of building energy saving, we should not only focus on how to optimize the design of HVAC system, but also focus on the design of envelope.
Envelope plays an increasingly important role in energy saving. The so-called energy saving of building envelope usually refers to that buildings can isolate outdoor heat from entering the room in summer and prevent indoor heat from leaking out in winter by improving the thermal performance of building envelope, so as to make the room as close as possible to the comfortable temperature, and reduce the load of reaching a reasonable and comfortable room temperature through auxiliary equipment, and finally achieve the purpose of energy saving, such as energy saving through heating and refrigeration equipment.
The envelope structures of traditional residential buildings are ordinary clay bricks, simple overhead roofs and single-layer glass fiber reinforced plastic windows, and their heat transfer coefficients are 1.96, 1.66 and 6.4 respectively. In the envelope structure of "energy-saving residence", thermal insulation measures are adopted for the exterior wall and roof, and hollow plastic-steel windows or hollow heat-insulating aluminum alloy windows are used for the exterior windows, and their heat transfer coefficients are 1.5, 1.0 and 3.0 respectively, which makes the energy-saving contribution of the envelope structure account for about 25%. Adopt heating and air conditioning equipment with high energy efficiency ratio (according to national standards, energy efficiency ratio of room air conditioner: refrigeration >; 2.3, heating > 1.9), so that the energy-saving contribution of heating and air-conditioning equipment accounts for about 25%, and the goal of total energy saving is achieved.
According to reports, the energy-saving design of envelope should be considered from three aspects: wall, window and roof. For designers, how to deal with the problem of building glass curtain wall has always been controversial in the industry. Ordinary glass curtain wall is one of the factors that can't realize building energy saving. Statistics show that the sunlight heat passing through the glass window can account for 30% of the maximum load of the refrigerator in summer, and the heat loss of a single glass can account for about 20% of the boiler load in winter. The energy-saving technology of windows is mainly considered from three aspects: reducing penetration, reducing heat transfer and reducing solar radiation energy. In addition, under the premise of ensuring good indoor lighting, it is very important to determine the window-wall ratio reasonably. When the area ratio of window to wall exceeds 50%, the load will increase obviously. Not only the outer shell but also the inner shell is equally important in the design. HVAC designers know more about building energy-saving methods than ordinary architects, so it is better for HVAC designers and ordinary architects to communicate more.
Energy saving
When designing a scheme, HVAC designers should first have a deep understanding of the owner's energy situation, the use of air conditioners, and whether there is residual heat and waste gas, and then make a reasonable and comprehensive comparison of various energy schemes. Designers should focus on how to use renewable energy and low-grade energy when designing.
After the HVAC designer completes the basic work in the design stage, the most important thing is to realize environmental protection and energy saving, which is achieved by comprehensively utilizing various advanced technologies and renewable resources.
It is the most ideal way to meet people's demand for indoor temperature by using natural conditions. At present, the temperature adjustment through various devices is only to remedy human errors. Cold and heat sources are the most concerned points for designers, because their energy consumption often accounts for about 50% of the total energy consumption of air conditioning systems.
In this situation, the ground source heat pump system has developed rapidly, which uses the soil heat in the underground constant temperature layer to significantly improve the efficiency of the air conditioning system. At the same time, the supply mode of new energy utilization is adopted to realize the triple supply of cold, heat and electricity; Based on the energy conversion principle of gas, steam and electricity, the waste heat at the end of industrial process is collected and used for air conditioning chilled water of refrigeration system and domestic hot water of heating system. In this way, the utilization rate of energy can be improved to about 70% ~ 80%. All these provide a wide range of energy-saving design ideas for HVAC designers.
summary
With the emergence of global warming, air conditioning is now an indispensable part of people's lives. It makes people's work and life more comfortable, and people have a certain dependence on air conditioning. However, environmental protection and energy saving are very important issues today. Therefore, in HVAC design, environmental protection and energy saving of HVAC is the development direction of air conditioning technology at present, that is to say, environmental protection and energy saving of urban heating is a problem that needs to be strengthened and sustainable development at present.
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