The resistance of the heating cycle system mainly comes from two aspects. First, the resistance produced by the flow of hot water in the conveying pipe is called resistance along the way; the two is the resistance produced by various water elements and heating equipment to the flow of water, which is called local resistance. The resistance along the way, according to the specifications: the frictional resistance of the most unfavorable loop in 30-60Pa/m, the other loop friction resistance should be less than or equal to 300 Pa/m, while the flow rate of circulating water is less than or equal to 3m/s. For the local resistance of various heating equipment, different products have different standards. The most unfavorable local resistance heating system in the loop and the resistance determines the size of the circulating pump head size, circulating pump head directly affects the size of the electricity consumption of the pump size, therefore, it is necessary for the heating system, a careful analysis of all kinds of resistance to the most unfavorable loop.

1. Resistance of a thermal station

There are two main forms of the heating station in the heating system, one is the form of the direct heating of the hot water boiler, the other is the form of heat exchanger heat transfer indirect heating.

1. Boiler

The boiler heating system using most of the hot water boiler, according to the rated heat output is divided into 7Mw, 14 Mw, 29 Mw, 58 Mw and other specifications, according to the heat medium parameters can be divided into 95/70° C, 115/70° C, 150/90° C, 95/70° C, 115/70° boiler application the two parameter C more. In the case of the boiler through the rated amount of water, the resistance of the boiler should be between 40-80Kpa. In the practice of heating, the cause of increasing the resistance of the boiler is that the actual amount of water passed by the boiler is greater than the rated circulating amount of water.

In the parameters of the nameplate of the boiler, no data of the rated circulating water is provided. What is the specific circulating amount of water to a boiler? It can be calculated by the following formula:

G = 860*Q/ (Tgth)

G: rated circulating water of a boiler, unit m3/h

Q: the rated heat of the boiler, unit Mw.

Tgth: Boiler rated inlet temperature and outlet temperature difference, ° C.

The circulating amount of water in the boiler is allowed to fluctuate, and the range of fluctuation should be less than 20%. When the actual flow exceeds the rated flow over time, greatly increased the resistance of the boiler; when the actual flow is lower than the rated flow too much, can make partial flow of boiler in the drift tube, causing partial vaporization or pipe explosion.

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