Dwell on the working principle of temperature control valve
First, the radiator thermostatic valve structure and working principle The user's indoor temperature control is through the radiator thermostatic control valve to achieve. Radiator thermostatic control valve is a thermostat controller, flow control valve and a pair of connectors, of which the thermostat is the core component of the sensor unit, that temperature package. Temperature package can sense changes in the ambient temperature and volume changes, drive the valve spool displacement, and then adjust the radiator water to change the radiator heat dissipation. Thermostatic valve set temperature can be artificially adjusted, thermostatic valve will be set according to the requirements of automatic control and adjust the radiator water, in order to achieve the purpose of controlling the indoor temperature. Second, the adjustment of the radiator characteristics by the thermal characteristics of the radiator, temperature control valve flow characteristics and valve authority jointly determine. Temperature valve in an opening under the flow and the ratio of full-flow G / Gmax is called the relative flow; temperature control valve in an opening of the trip and the whole trip ratio l is called relative travel. Relative stroke and relative flow between the relationship known as the flow control valve temperature characteristics, namely: G / Gmax = f (l). The relationship between them shows linear characteristics, quick opening characteristics, such as percentage characteristics, parabolic characteristics of several characteristics. For the radiator, from the point of view of water conservancy stability and heat regulation, the relationship between heat output and flow rate is a curve on a cluster. As the flow rate G increases, the heat dissipation Q becomes gradually saturated. In order to make the system have good regulation characteristics, it is easy to adopt the control valve with equal percentage flow characteristics to compensate the influence of the radiator's own non-linearity (1). The effect of valve authority on regulatory characteristics. The adjustable ratio R is the ratio between the maximum flow rate and the minimum flow rate that the temperature control valve can control: R = Gmax / Gmin Gmax is the flow rate when the thermostatic valve is fully open and can also be regarded as the design flow of the radiator; Gmin Temperature control valve valve size changes. In the radiator system, the thermostatic valve and the radiator are connected in series, so the relation between the adjustable ratio R and the valve power is as follows: R = RmaxKV0.5 (2) Taking a certain type of temperature control valve and radiator as an example, Radiator flow capacity of 5m3 / h, valve temperature valve is 88%, the actual adjustable ratio of 28, the corresponding flow adjustable range of 100% -4%. Radiator temperature difference in different import and export of heat under the actual adjustable range in the table below. Import and export temperature difference (℃) 25 20 15 10 5 Adjustable range (%) 100 ~ 11.6 100 ~ 13.5 100 ~ 16.1 100 ~ 20.2 100 ~ 28 Table shows that when the radiator inlet and outlet temperature is small, the actual amount of heat dissipation Adjustable range is also small. However, when the temperature difference between the inlet and outlet of the radiator is less than 10 ° C, the minimum adjustable heat dissipation of the temperature control valve is about 20% of the standard heat dissipation, and the effective working range of the temperature control valve is reduced. In addition, it is worth noting that the high resistance of the thermostatic valve is determined by the adjustment characteristics of the radiator, and the design of the thermostatic valve must take this characteristic into account to avoid the situation of insufficient capital pressure. Third, the installation position of the temperature control valve 1, the radiator thermostatic valve is generally installed on each radiator inlet pipe or sub-household heating system on the inlet pipe. In particular, the built-in sensor does not advocate vertical installation because the thermal effects of the body and surface piping may cause the thermostatic controller to malfunction. Make sure that the thermostatic sensor senses the temperature of the circulating air in the city, Heating cover and other coverage. 2, in order to reduce investment, put forward in the indoor system (one for each heating system) only installed a temperature control valve program. Under normal circumstances, you should install a thermostatic valve for each set of radiators (that is, each room). In order to reduce the investment, proposed in the indoor system (one for each heating system) only installed a temperature control valve program. The following first analysis of the thermal characteristics of single-tube system, that is, the variation of flow and room temperature, and pointed out that the installation of temperature control valve. 2.1 single-tube indoor system only installed in the terminal room temperature control valve. The calculation of a five-storey upper monopole single-pipe downstream system (also applicable to indoor single-pipe downstream system) is carried out by using the heat net operating simulation software. The results are shown in Table 1. Table 1 shows the situation where the water supply temperature is constant. This situation is more representative of the fact that a large heating system has actual conditions of uneven distribution of flow rate. In the design of the external temperature, where the actual flow is less than the design flow (relative flow less than 1), were the upper heat, the lower the phenomenon of cold; where the actual flow is greater than the design flow (relative flow greater than 1.0) occurred in the upper cold, lower heat The situation. Table 1: Flow rate and room temperature when constant water supply temperature is constant on upper fractional single-tube system 5-story 4-story 3-story 2-story 1-story Relative flow rate (%) 1.80 18.5 18.7 18.9 19.3 19.6 1.00 18.6 18.3 18.2 17.7 17.5 , 0.48 17.8 16.8 15.8 14.8 13.5 0.24 17.3 15.3 12.3 9.9 8.6 Note: The water supply temperature 81 ℃ above room temperature and the flow between the rules of change, is universal. When the outdoor temperature is not equal to the design of the external temperature. This variation still exists, but the difference is only in the design of the external temperature, that is, the coldest temperature, the system vertical imbalance is the most serious, that is, between the highest and lowest floor temperature deviation; with the warming, vertical imbalance Also gradually slow down. Single-tube system occurs this vertical imbalance phenomenon, mainly due to changes in flow and radiator surface temperature caused by inconsistencies. In general, the radiator heat dissipation depends on the average surface temperature of the radiator. In the design state, the radiator heat transfer area selection, are based on design conditions, the design of the radiator surface layer average temperature calculated. However, in actual operation, due to the uneven distribution of the flow rate, the ratio of the change of the average surface temperature of the radiators on all the layers will be different from the design conditions. When the actual flow of the riser is less than the design flow (ie, the relative flow rate is less than 1.0), the temperature difference between the riser and the return water is greater than the design temperature difference. At this time, the average surface temperature of the upper radiator is lower than the average surface temperature of the radiator More conducive to heat dissipation, which appeared on the heat under the cold; relative flow greater than 1.0, the situation is the opposite. The vertical imbalance of single-tube system is characterized by the larger the flow rate and the higher the room temperature at the end of the room. The smaller the flow rate, the lower the room temperature of the end room. According to this thermal characteristics, for a single-tube system, Pressing: (1) For single-pipe downstream indoor systems, a thermostatic valve shall be mounted on the radiator of the end-of-the-home system; (2) For single tube indoor systems with spanning tubes, Control valve should be installed in the indoor system inlet pipe or return pipe, the temperature control valve remote temperature sensor to be placed in the indoor system at the end of the room; (3) The system, a thermostatic valve for each riser pipe, shall be installed on the radiator of the lowest floor, at which time the heat supply shall be metered using a heat distributor. It should be noted: The use of such a temperature control valve, which has the advantage of not only improving the regulatory performance of the heating system, but also reduce the initial investment of the project; the disadvantage is that each room in each room at the same standard temperature can not be arbitrarily adjusted . 2.2 double tube indoor system A temperature control valve installed in the indoor entrance. The vertical imbalance of a two-pipe system is due to changes in system flow due to changes in the indenter of the natural circulation. The ideal solution for this type of system is to have a temperature control valve on each radiator. Some real estate developers are reluctant to increase their investment and have canceled all thermostatic valves. Although no serious imbalances will occur in indoor systems, they will inevitably lead to vertical imbalance between floors in the building. In engineering practice, also proved this point. In order to reduce the cost without influencing the regulation function of the heating system, a thermostatic valve is installed at the indoor entrance in the two-pipe indoor system, and the remote temperature sensor can store any room. This solution, although lacking flexibility in room temperature regulation per room, has improved uneven heating and cooling between floors and is more in line with the current domestic economic conditions. Fourth, the radiator thermostatic valve heating system in the role of energy-saving radiator thermostat valve installed correctly in the heating system, the user according to the requirements of the room temperature, adjust and set the temperature. This ensures that the room temperature is constant, to avoid the riser imbalance in water volume and single-tube system uneven temperature at the upper and lower floors. At the same time, through the thermostat control, free heat, economic operation and other effects can not only improve indoor thermal environment comfort, but also to achieve energy saving. Thermostatic control - with the climate changes dynamically adjust the output, control the room temperature is constant, you can save energy. At the same time, the elimination of horizontal and vertical temperature offsets can also be advantageous in reducing the energy waste in the loop, while at the same time adversely affecting the loop flow and temperature requirements. Free heat - sunlight incident, human activities, cooking, electrical appliances and other heat known as the heating of free heat, this part of the heat due to uncertainty and not in the design operation to be fully considered, only as a safety factor to consider. Realization of room temperature control, this part of the energy can replace part of the heat, at the same time, different orientations of the room temperature can be eliminated, both to improve the thermal comfort of the city, but also save energy. Economic operation - office buildings, public buildings at night, rest days without heating at full capacity. Residential users try to do as far as possible without heat, in order to save energy and heat costs. Even in different rooms can be implemented in different temperature control mode: When the staff is concentrated in the living room, the bedroom temperature can be set lower, the living room temperature can be increased set; sleeping time, the bedroom temperature can be increased set, the living room temperature Can reduce the setting and so on. These measures can be achieved through the radiator thermostatic valve has reached the energy-saving purposes.
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