1, operation control design
1. 1 Determination of fresh air valve opening in summer dehumidification condition
In the case of dehumidification in summer, from the perspective of energy saving, the fresh air valve should be kept at the minimum opening on the premise of keeping the minimum air exchange times. According to China's HVAC code, in the air-conditioned area where the room temperature is allowed to fluctuate within the range of 65438 0.0℃, the number of air changes should be greater than or equal to 5 times/hour (minimum air supply). Ensure the minimum air exchange times and calculate the minimum opening of the return air valve: in order to obtain the value of fresh air volume, a wind speed detection port is set in the fresh air straight pipe section, which is shielded during daily operation, and an anemometer is inserted to measure the fresh air speed during detection. Parameter definition: air conditioning control area and volume -VN air conditioning fresh air volume-cross-sectional area of QX fresh air duct-wind speed measured by SX fresh air duct-then fresh air volume Qx=SxVx, and the following requirements must be met in order to make indoor air exchange times reach 5 times per hour: Vx=. By adjusting the opening of the fresh air valve, the wind speed vx can meet the above requirements, and the opening of the fresh air valve at this wind speed is confirmed and recorded. In order to meet the requirements of energy-saving operation of air conditioning, the opening value of fresh air valve can be maintained in summer dehumidification stage, and the wind speed can be tested regularly to correct the opening value of fresh air valve.
1.2 temperature and humidity independent control mode
When cooling and dehumidifying in summer, the original combined control program of temperature and humidity is adjusted to a separate control program of temperature and humidity, that is, the valve opening of the main surface cooler (dehumidifying channel) is controlled according to the difference between the moisture content of indoor return air (calculated and converted from the temperature and humidity of return air) and the moisture content of indoor set working conditions, or the humidity of indoor set working conditions is tracked and adjusted by PI according to the change of fresh air humidity; According to the difference between the indoor return air temperature and the indoor set temperature, control the valve opening of the auxiliary surface cooler (cooling channel). In the transitional season, it is still operated according to the original fresh air ratio or fresh air volume, but it is necessary to increase the switch control of the bypass fresh air valve. The specific logic is that when the outdoor working conditions enter the transitional season and the electric cold water valve for fresh air dehumidification is closed, the bypass fresh air valve should be opened at the same time. When outdoor is in summer dehumidification condition, the opening of electric cold water valve for fresh air dehumidification is not zero, and the bypass fresh air valve should be closed. The adjustment of fresh air volume in transition season is still the responsibility of the original fresh air and return air regulating valve.
2. Comparative analysis of thermal conditions between conventional control and dual-channel temperature and humidity independent control.
2. 1 parameter definition
G 1- fresh air volume n- indoor set point G2- return air volume w- summer outdoor state point G- total air volume (G 1+G2)c- mixed air state point I- enthalpy value L- machine dew point Q- cooling consumption O- summer air supply state point.
2.2 Reheat analysis of conventional air conditioning system under dehumidification conditions in summer
2.2. 1 conventional summer dehumidification air heat and humidity treatment process The air conditioning system of cigarette factory provides high-precision indoor temperature and humidity environment for cigarette production process, and the system is generally equipped with various heat and humidity treatment methods such as surface cooling, heating and humidification. The heat and humidity treatment process of conventional air conditioning system in summer is: fresh return air is mixed, cooled and dehumidified by surface cooler, reheated by heater, and then supplied to the room after reaching the air supply state point. Its corresponding enthalpy-humidity diagram of air treatment process expresses the enthalpy-humidity diagram of air treatment process of conventional air conditioning system under the condition of dehumidification in summer.
2.2.2 calculation of cooling consumption of conventional surface cooling treatment 1) calculation of enthalpy (c) of mixed air state point: according to:, iC=iN+(iW-iN)2) calculation of cooling consumption: q = (g1+G2) (IC-IL) =/.
2.3 Energy-saving analysis of dual-channel temperature and humidity independent treatment scheme
2.3. 1 Two-channel dehumidified air heat and humidity treatment process According to the above, the two-channel temperature and humidity independent treatment process of air conditioning system can be summarized as follows: fresh air (or mixed with part of return air) is cooled and dehumidified by the main surface cooler, and the return air is dried and cooled by the auxiliary surface cooler, and then the new return air is further mixed to supply air to the room after reaching the air supply state point.
2.3.2 Cooling consumption controlled by temperature and humidity respectively: 1) Calculation basis of enthalpy of mixed air state point (c): = obtained: iC=iN-(iN-iL). 2) calculation of cooling capacity (q): q = g1(iw-il)+(g1+G2) (IC-io) = (g1+G2) (in-io) indoor load+g/kloc-0.
3. Conclusion
The energy-saving points of the two air treatment methods are: the temperature and humidity control scheme saves the energy consumption of the reheating part; For a single chilled water pipe network system, it will not increase the operating energy consumption of refrigeration units, on the contrary, it will reduce the adjustment of supercooling load and reduce the energy consumption of refrigeration units due to the conventional cooling and dehumidification process. This scheme can completely solve the unreasonable phenomenon of summer cold and heat cancellation, save a lot of summer reheating and refrigeration, quickly recover the initial investment, and the energy saving efficiency is very obvious. At the same time, it does not affect the operation of fresh air or fresh air in transition season, and the hardware equipment of air conditioning unit has a small range of change and is not difficult to transform.
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