1. Energy consumption analysis of central air-conditioning
(1) The equipment with the largest energy consumption in the water-cooled central air-conditioning system belongs to the chiller. The chiller is divided into reciprocating (also called piston) unit, screw unit and centrifugal unit according to the type of compressor. The power source is Electricity and heat, according to their rated cooling capacity and cooling efficiency, generally rated input power from 100KW to 1000KW. The purpose of the chiller is to produce low temperature (7°C) chilled water, so the temperature of the water supply directly affects the load of the chiller. The start of the terminal air handler will also affect the return temperature of the chilled water. The higher the return water temperature, the greater the load on the unit.
(2) The chilled water circulating pump (referred to as the refrigerating pump) mainly provides the power of the chilled water circulating. Its input power is generally from 11KW to 132KW. The traditional design of the refrigerating pump is a fixed quantity pump with a constant output power; the cooling water circulating pump (referred to as the cooling pump) It mainly provides the power of cooling water circulation, and its input power is generally from 11KW to 132KW. The traditional design cooling pump is a fixed quantity pump, and the output power is constant.
(3) The cooling tower fan mainly provides wind power for cooling the cooling water. Its input power is generally from 3KW to 15KW. The traditional design cooling tower fan is a constant speed fan, and the output power is constant.
(4) The air handler is the terminal equipment for indoor air temperature adjustment. The fan provides the power required for indoor air circulation. A constant speed and constant air volume fan is usually used. The rated power ranges from 0.5KW to 15KW, but the number is large.
(5) The design of central air-conditioning is often designed in accordance with local meteorological data and the characteristics of the building, and taking into account the maximum energy demand, a design margin of 10% to 20% is also reserved. Therefore, the main engine, water pump, and fan All have a large margin.
(6) Due to seasonal rotation and time changes, the central air conditioner runs at maximum power for a short period of time throughout the year, generally less than 1%, so a large number of constant speed motors have great energy-saving potential.
(7) The user's weak maintenance awareness is also one of the reasons for the reduction in the efficiency of the central air-conditioning.
2. Central air-conditioning energy-saving measures
(1) Energy saving of refrigeration host
In the central air-conditioning system, the energy consumption of the main engine accounts for more than 60% of the total energy consumption, so the energy-saving operation of the main engine is an important part of the energy saving of the entire system. Common energy-saving control methods are:
1. The best control for start and stop. The electrical energy consumed by the air-conditioning device is equal to the product of the operating time of the device and the capacity of the device. If the operating time is reduced, the electrical energy consumed will decrease proportionally. A detailed investigation and analysis of the air-conditioning load in different places of the building is carried out to find the best start and stop control method.
2. Slowly increase or decrease the number of mainframes or adjust mainframe operating power according to the load.
3. Parameter selection. In the central air-conditioning design, set the indoor design calculation temperature and humidity reasonably, avoid using too low temperature in summer and too high temperature in winter, avoid low air supply temperature in the design, and the lower the calculated temperature and humidity of indoor air in summer, the room The greater the cooling load of the calculation, the greater the energy consumption of the system.
(2) Energy saving of water pump
Since most of the water pump has a margin when selecting equipment, the outlet valve of the water pump will not be fully opened, and some can only be opened to 1/2, which causes the throttling loss of the valve, and at the same time, the valve restricts the water volume. , So that the cooling effect of the main engine is not ideal, often resulting in insufficient cooling of a single machine, but working under partial load when two or multiple machines cause a lot of waste of electric energy. Here, the frequency conversion speed regulation technology can make the valve fully open, and its throttling effect is good.
(3) Energy saving of cooling tower
Although the proportion of cooling tower energy consumption in the air conditioning system is not large, the cumulative energy consumption is still very large due to its high frequency of use.
1. Temperature control. Use the thermistor to connect the temperature regulator to control the on and off of the cooling tower fan power supply. When the thermal load changes, through the thermistor detection, send a signal to the thermometer to control the on and off of the fan. The thermal load is below a certain level, and the command is The fan stops running, the heat load increases, and then the fan is started, so as to achieve the purpose of energy saving.
2. Control of the number of fans. For cooling towers configured in parallel, the adjustment of the air volume can be achieved by controlling the number of fans, and the number of fans to be turned on is determined according to actual needs.
(4) Energy saving of water system
1. Energy saving of chilled water system. The higher the chilled water temperature, the higher the cooling efficiency of the chiller. First of all, don't set the chilled water set temperature too low. Secondly, you must close the water valve of the chiller that is out of operation to prevent part of the chilled water from passing through the bypass line. Otherwise, the amount of water passing through the chiller in operation will be reduced, causing the chilled water temperature to be too low by the chiller Level.
2. Energy saving of cooling water. As the cooling water temperature is lower, the refrigeration coefficient of the chiller is higher. First of all, for the cooling tower that is out of service, the valves of the water inlet and outlet pipes should be closed. Otherwise, because the water temperature from the stopped cooling tower is higher, the temperature of the mixed cooling water will increase, and the refrigeration coefficient of the chiller will be reduced. Secondly, the cooling tower should be overhauled in time after a period of use, otherwise the efficiency of the cooling tower will decrease.
(5) Selection and improvement of enclosure structure
For the central air-conditioning system, the air-conditioning load through the maintenance structure occupies a large proportion. Studies have shown that increasing the thermal insulation performance of the envelope structure can reduce the design load of the central air-conditioning. First of all, rationally design the structure of windows. For buildings with relatively large window areas, consider using heat-absorbing glass, heat-reflecting glass or shading measures, such as sun visors, eaves, shutters, curtains, etc. Second, improve the airtightness of doors and windows. The frequency of room air changes can be reduced from 0.8h to 0.5h, and the cooling consumption of the building can be reduced by about 8%. Therefore, doors and windows with good airtightness should be used in the design, which can effectively reduce the energy consumption of air conditioning. Third, the use of energy-saving building materials can effectively reduce heat dissipation through the enclosure structure, thereby reducing the capacity of major equipment and achieving significant energy-saving effects. In addition, by coating light-colored, high-reflectivity materials on the surface of ordinary roofs, the solar reflectivity of the roof is increased, and the absorption of solar heat is reduced, so as to reduce the cooling load of the air conditioner and save the energy consumption of the air conditioner.
(6) Reduce the impact of dirt, corrosion and moss on the water side
The water circulation system of the central air-conditioning system is prone to form dirt, corrosion and moss on the water side, which seriously affects the thermal conductivity and is an important reason for the high energy consumption of the central air-conditioning system. In order to reduce these phenomena, in addition to the installation of water softening equipment for chilled water pipelines and the installation of water treatment devices such as electronic water treatment devices in the cooling water pipelines, the water circulation system pipelines should be descaled, cleaned and cleaned after every two refrigeration operation periods. maintenance.
(7) Cleaning and maintenance of the ventilation system
The impact of pollutants in the ventilation system on energy consumption is reflected in the return air system. A large amount of dust and particles accumulate on the inner wall of the return air duct, which reduces the performance of the air valve and duct; at the same time, it reduces the delivery and return. The wind speed and the air supply and return volume increase the energy consumption of the fan, so it must be cleaned frequently. Check and clean up and replace filters regularly to keep the air-conditioning system clean, clean the air-conditioning box and wind box frequently, and clean and replace the muffler.
Third, the problems that should be paid attention to in the construction of central air-conditioning
The construction quality of the central air conditioner directly affects the operation effect of the system, and even affects the long-term stable and reliable operation of the system. In combination with the working characteristics of the air-conditioning system, the following aspects should be paid attention to during the construction.
(1) Insulation of pipelines. The parts with cold and heat loss during the transmission of cold and hot media should be insulated. The insulation material should have the characteristics of low thermal conductivity, low moisture absorption, good frost resistance, and safe use. The minimum insulation thickness should meet the temperature ratio of its outer surface. The average dew point of the outdoor temperature in the hottest month is 3°C higher to prevent condensation on the outer surface of the insulation layer. In the heat preservation process, the heat preservation pipe shell should be sealed and bonded, and the penetration of air is strictly prohibited. Between the pipe and the bracket, the heat preservation should not be interrupted when the pipe passes through the wall or the floor, and try to avoid the occurrence of "cold bridge" and "hot bridge".
(2) The tightness of ventilation ducts. During the construction of ventilation pipes, the airtightness of the pipes should be considered in the first place. There are gaps in the joints of the air pipe flanges or the air pipe bites, which will cause air leakage and cause the cold energy to be wasted in the halfway of the cold energy transportation. Increase in consumption.
(3) The tightness of the connection between the tuyere and the duct. In most central air-conditioning systems, when the tuyere is installed, the wind pipe only extends to the neck of the tuyere, without any sealing treatment, causing a large amount of air leakage at the connection between the tuyere and the wind pipe, and the cooling capacity is consumed in the ceiling. In order to reduce air leakage, it should be properly sealed, or the connection between the tuyere and the air duct should be soft-jointed with canvas, the length is 10-15mm, and the soft-jointed canvas should not be too long.
(4) Treatment of the return air from the air conditioner. The return air of air handlers and fan coils, most central air-conditioning systems use ductless return air, that is, the air in the air-conditioned room first returns to the air-conditioning machine room or ceiling before reaching the air handlers or fan trays. This method will cause the air in the air-conditioned room to passively increase the temperature when it returns to the air processor or fan tray, resulting in a loss of cooling capacity. The air in the air-conditioned room should be sent directly to the air handler or fan disk through ducts to reduce losses along the road.