The user's indoor temperature control is realized through the thermostatic radiator valve. The thermostatic radiator valve consists of a thermostatic controller, a flow regulating valve and a pair of connectors, in which the core component of the thermostatic controller is the sensor unit, that is, the temperature bag. Temperature bag can induce the change of ambient temperature to produce volume change, drive the valve core to move, and then adjust the water quantity of radiator and change the heat dissipation of radiator. The temperature set in thermostatic valve can be adjusted artificially, and thermostatic valve will automatically control and adjust the water quantity of the radiator according to the set requirements, so as to achieve the purpose of controlling the indoor temperature.
2. The regulation characteristics of the radiator are determined by the thermal characteristics of the radiator, the flow characteristics of the temperature control valve and the valve weight.
The ratio G/Gmax between the flow rate of the temperature control valve at a certain opening and the fully opened flow rate is called relative flow rate; The ratio L between the stroke and the full stroke of the temperature control valve at a certain opening is called relative stroke. The relationship between the relative stroke and the relative flow is called the flow characteristic of the temperature control valve, that is, G/Gmax=f(l). The relationship between them presents several characteristic curves, such as linear characteristics, fast opening characteristics, equal percentage characteristics and parabolic characteristics.
For radiators, from the perspective of water conservancy stability and thermal power dispatching, the relationship between heat dissipation and flow presents a cluster of upward-throwing curves. With the increase of flow rate g, the heat dissipation q gradually tends to be saturated. In order to make the system have good regulation characteristics, it is easy to use the regulating valve with equal percentage flow characteristics to compensate the nonlinear influence of the radiator itself (1).
Influence of valve weight on regulation characteristics. The adjustable ratio r is the ratio of the maximum flow rate and the minimum flow rate that can be controlled by the temperature control valve:
R=Gmax/Gmin
Gmax is the flow rate when the temperature control valve is fully opened, which can also be regarded as the design flow rate of radiator; Gmin varies with the valve weight of the temperature control valve. In the radiator system, because the temperature control valve and the radiator are connected in series, the relationship between the adjustable ratio R and the valve weight is: R=Rmax (2).
Taking a certain type of thermostat valve and radiator as an example, the circulating capacity of radiator is 5m3/h, the valve weight of thermostat valve is 88%, the actual adjustable ratio is 28, and the corresponding flow adjustable range is 100%-4%. See table for the actual adjustable range of radiator heat dissipation under different inlet and outlet temperature differences.
As can be seen from the table, when the temperature difference between the inlet and outlet of the radiator is small, the actual adjustable heat dissipation range is also small. However, when the temperature difference between the inlet and outlet of the radiator is less than 10℃, 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 temperature control valve is determined by the adjustment characteristics of the radiator, and this characteristic of the temperature control valve must be considered in the design to avoid insufficient capital pressure.
3 Installation position of temperature control valve
3. 1 Radiator thermostatic valve is generally installed on the water inlet pipe of each radiator or the main water inlet pipe of household heating system. Especially for the built-in sensor, vertical installation is not recommended, because the thermal effect of the valve body and the surface pipeline may lead to the wrong action of the thermostat controller. It is necessary to ensure that the sensors in thermostatic valve can sense the temperature of the circulating air in the city and cannot be covered by curtain boxes, heating covers, etc.
3.2 In order to reduce investment, it is suggested that only one temperature control valve should be installed in the indoor system (one heating system for each household).
Under normal circumstances, each radiator (that is, each room) should be equipped with a temperature control valve. In order to reduce the investment, a scheme of installing only one temperature control valve on the indoor system (one heating system for one household) is put forward. Firstly, the thermal characteristics of single pipe system, that is, the variation law of flow rate and room temperature, are analyzed, and the installation method of temperature control valve is pointed out.
3.2. 1 Single-pipe indoor system only installs one temperature control valve in the terminal room. A five-story upper-divided single-pipe downstream system (also applicable to indoor single-pipe downstream system) is calculated by using the simulation analysis software of heating network working conditions. The results are shown in table 1. Table 1 is a constant water supply temperature, which is more in line with the actual working condition of uneven flow distribution in large heating systems, so it is representative. At the design outside temperature, when the actual flow is less than the design flow (the relative flow is less than 1), the upper layer is hot and the lower layer is cold. Where the actual flow is greater than the design flow (the relative flow is greater than 1.0), the upper layer is cold and the lower layer is hot.
Table 1: Flow and room temperature changes of upgraded single-pipe downstream system at constant water supply temperature
Room temperature (℃)
Relative flow (%) 5 layers, 4 layers, 3 layers, 2 layers, 1 layer
The above-mentioned variation law between room temperature and flow rate is universal. When the outdoor temperature is not equal to the design outdoor temperature. This change law still exists, the only difference is that the vertical imbalance of the system is the most serious when the design outside temperature is the coldest, that is, the room temperature deviation between the highest floor and the lowest floor is the largest; As the temperature gets warmer, the vertical imbalance gradually slows down. This vertical misalignment of single-tube system is mainly caused by the inconsistency between the change of flow rate and the change of radiator surface temperature. Generally speaking, the heat dissipation of radiator mainly depends on the average surface temperature of radiator. In the design state, the selection of heat transfer area of radiator is calculated according to the average design surface temperature of each layer of radiator under the design condition.
However, in actual operation, due to the uneven flow distribution, the change rate of the average surface temperature of each layer of radiator will be different from the design condition. When the actual flow of the riser is less than the design flow (that is, the relative flow is less than 1.0), the temperature difference between the supply and return water of the riser is greater than the design temperature difference. At this time, the average surface temperature of the upper radiator is more conducive to heat dissipation than that of the lower radiator, so there is a phenomenon of heating up and cooling down. When the relative flow is greater than 1.0, the situation is just the opposite.
The vertical imbalance of single pipe system shows that the greater the flow rate, the higher the room temperature in the terminal room; The smaller the flow rate, the lower the room temperature in the terminal room. According to this thermal characteristic, for a single-pipe system, each household should install a temperature control valve according to the following principles: (1) For a single-pipe downstream indoor system, a temperature control valve should be installed on the radiator in the room at the end of the indoor system;
(2) For a single-pipe indoor system with cross pipes, a temperature control valve should be installed on the water inlet pipe or return pipe of the indoor system, and the remote temperature sensor of the temperature control valve should be placed in the last room of the indoor system;
(3) For the upward-divided single-pipe downward system of the old building, the temperature control valve of each riser should be installed on the radiator of the lowest floor room, and the heat should be metered by the heat distributor at this time. It should be pointed out that the advantages of using this temperature control valve are: not only improving the regulation performance of heating system, but also reducing the initial investment of the project; Its disadvantage is that the room temperature of every household is the same standard and cannot be adjusted at will.
3.2.2 The temperature control valve of the double-tube indoor system is installed at the indoor entrance. The vertical maladjustment of double-pipe system is caused by the change of system flow caused by the change of pressure head under natural circulation. The most ideal scheme of this system is to install a temperature control valve on each radiator. Some real estate developers are reluctant to increase investment and cancel all temperature control valves. Although there will be no serious imbalance in the indoor system, it will inevitably lead to vertical imbalance between floors in the building. This has also been proved in engineering practice. In order to reduce the cost without affecting the adjustment function of the heating system, a temperature control valve is installed at the indoor entrance of the double-pipe indoor system, and its remote temperature sensor can be placed in any room. Although the room temperature adjustment of each room lacks flexibility, this scheme improves the uneven cold and heat between floors in the building, which is more in line with the current domestic economic situation.
4. The energy-saving function of radiator thermostatic valve in heating system.
The radiator thermostatic valve is correctly installed in the heating system, and users can adjust and set the temperature according to the requirements of room temperature. In this way, the room temperature of each room is guaranteed to be constant, and the problems of uneven water flow in the riser of single-pipe system and uneven room temperature on the upper and lower floors are avoided. At the same time, constant temperature control, free heating and economical operation can not only improve the comfort of indoor thermal environment, but also realize energy saving.
Constant temperature control-dynamically adjust the output with the climate change, control the room temperature to be constant, and achieve the purpose of energy saving. At the same time, eliminating the horizontal and vertical misalignment of temperature can also reduce the energy waste in the favorable circuit and make the unfavorable circuit meet the requirements of flow and temperature.
Free heat-sunlight, human activities, cooking, electrical appliances and other heat is called heating free heat. Because of uncertainty, it is not fully considered in design and operation, and only considered as a safety factor. After the room temperature control is realized, this part of energy can replace part of heat dissipation, and at the same time, it can eliminate the temperature difference between rooms with different orientations, which not only improves the comfort of urban thermal environment, but also saves energy.
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