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How to choose the instrument for measuring the chilled water cooling quantity

How to choose the instrument for measuring the chilled water cooling capacity? (1) Selection of platinum thermal resistance
1 Design to prevent condensation from forming in the platinum thermal resistance sleeve. Due to the respiration between the gas and the atmosphere in the thermal resistance casing, the water vapor content in the atmosphere is high in the summer, and is condensed into water by the suction casing. If ordinary platinum thermal resistance is used, the platinum resistance wire and its lead wire are easily replaced by the long-term platinum wire. The water is submerged and causes a malfunction. In order to avoid such problems, an armored platinum thermal resistor must be used. The structure of the junction box is shown in Figure 4.8. Since the space in the casing of the armored platinum thermal resistance is filled with the sintered magnesium oxide powder, the upper part of the casing is sealed with epoxy resin, and the residual gas in the casing is completely isolated from the outside of the pipe, thereby eliminating the The invasion of water.
Figure 4.8 Armored platinum thermal resistance junction box structure
2 The moisture-proof problem of the terminal block in the junction box. Since the chilled water temperature may be 20-40 °C lower than the ambient temperature, if the junction box is too close to the chilled water pipe, the junction box temperature may be much lower than the ambient temperature due to the heat conduction, causing condensation between the terminals, resulting in insulation degradation or even short circuit. Causes the temperature indication to be low. In order to avoid this problem, the junction box should at least leave the insulation layer 100mm. Make the junction box temperature close to the ambient temperature.
3 Reduce the temperature measurement error caused by the heat conduction of the temperature measuring sleeve. Since the accuracy of temperature measurement in chilled water cooling is particularly high, the temperature measurement caused by the heat conduction of the temperature measuring sleeve should be considered (assuming the ambient temperature is higher than the chilled water temperature). The armored platinum thermal resistance should be selected. Due to the thin casing and thin wall, the measurement error caused by heat conduction is negligible.
4 tube external platinum thermal resistance. There are some measurement objects that have no chance to stop all year round. They can't open the meter on the pipe. They can only use the temperature measurement method of platinum thermal resistance. The attached platinum thermal resistance must be waterproof and moisture-proof because the outer wall of the chilled water pipe is always wet. There should be good heat conduction between the thermal resistance and the pipe wall. The thermal resistance placement and the surrounding area should be strengthened by thermal insulation. After such treatment, the temperature measured by the platinum thermal resistance is higher than the water temperature inside the pipe is limited to 0.1. - Within 0.2 ° C is entirely possible.

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