Discussion on heating design of urban high-rise residential buildings?

With the rapid development of national economy and the advancement of urbanization, people's quality of life and working environment are constantly improving. Comfortable building heating has become a necessity for people's life and work, that is, daily necessities. People and related scholars have fully realized that the design of building heating system has great influence on urban environment and daily life. This paper discusses the heating design of high-rise residential buildings with the following engineering examples.

case study

Zhengzhou is located in the Central Plains, with relatively flat terrain. Taking a residential group consisting of 20 high-rise buildings as an example, this paper assumes that the basement of the high-rise building is a storage room and the first to tenth floors above ground are residential buildings, and briefly explains the heating mode selection and indoor and outdoor heating design of high-rise residential buildings.

First, the choice of heating mode for high-rise buildings

The heating of residential buildings in China mostly adopts cogeneration or central heating with regional boiler room as heat source. Because central heating can provide stable and reliable high-grade heat source, save energy and reduce urban pollution, it has remarkable economic and social benefits. Among them, the heating mode of regional boilers is safe, clean and convenient, and the heating time can be decided by the owners of residential quarters. But the disadvantage is that the cost is slightly higher than the urban central heating mode, and improper management will also cause pollution problems. Therefore, based on the strategic demand of urban environmental protection development, in recent years, with the change of energy composition, the heating system of residential buildings has also developed in a diversified direction, and the centralized household heating metering model of cogeneration has been vigorously developed. It has become the first choice of building heating mode in China in 2 1 century. The relevant regulations point out: "As long as it is possible to access the central heating pipe network of cogeneration, we will resolutely not adopt other heating methods".

For high-rise residential buildings, it is safe, clean and convenient to use municipal central heating network for cogeneration heating. Cogeneration is a heating technology that uses high-grade heat energy of fuel to generate electricity, and then comprehensively uses its low-grade heat energy. Relevant calculations show that this heating efficiency is about twice as high as that of small and medium-sized boiler rooms, and the air pollution caused by heat production is far less than that of small and medium-sized boiler rooms. However, there are also some shortcomings. For a long time, most of our buildings in the north use central heating, which also depends on the heating area of the room. This metering and charging method has brought great trouble to the heating charge, that is to say, users have to pay the heating fee regardless of whether they can't live, resulting in 30 ~ 40% heat waste. Secondly, for long-distance transportation, the initial investment of pipe network is high, and the maintenance and management costs are also high. However, with the discovery of problems, solutions have emerged. According to the large-scale experimental results of the former Soviet Union, adding adjustment means to this heating terminal and charging according to heat can save more than 30% of heat, thus avoiding the above inconvenience. Therefore, the heating mode of central heating and household metering has been widely used and has become a very advocated heating mode in China. Especially for high-rise residential building areas, cogeneration central heating and household metering should be the key development direction of heating methods in the future.

Second, the high-rise residential indoor heating design

2. 1 heat load design

The design and calculation of indoor heating heat load of high-rise residential buildings with household heat metering design include heat consumption of envelope, cold air infiltration and cold air when the external door is opened. Heat consumption of envelope: it consists of basic heat consumption and additional heat consumption, in which the basic heat consumption is calculated according to the formula q 1=afk(tn-twn); Additional heat consumption includes directional additional heat consumption, wind additional heat consumption and high additional heat consumption, and each additional heat consumption should be determined according to its percentage of basic heat consumption. Heat consumption of cold air infiltration: refers to the heat consumption of cold air penetrating into the room through the gap between doors and windows, and is calculated by formula q2=0.28cpρwnlln(tn-twn). When the outer door is opened, the heat consumption of cold air is changed from q3 = qj to? βkq。 The formula has been calculated.

It should be noted that: ① From the first point above, we can know that the high-rise building adopts household metering, and users can adjust their indoor temperature according to the different use time, while the household metering adopts a temperature control valve in the indoor system. In order to meet the needs of temperature adjustment after heat metering, the indoor design temperature of residential buildings should be increased by 2℃ according to the corresponding design standards as a design temperature calculation parameter instead of being added to the total heat load. ② When calculating the heat consumption of residential building envelope, it should be noted that the average heat transfer coefficient after considering thermal bridge should be adopted as the heat transfer coefficient of external wall; The light wall should be modified in combination with the heating system; When the floor of a room has a heating pipe trench along the external wall, the floor heat consumption of the room can not be calculated; If the basement does not heat the roof, insulation measures must be taken, and the temperature difference and heat transfer should be calculated. (3) When the temperature difference between adjacent rooms is greater than or equal to 5℃, attention should be paid to calculating the heat transfer through the partition wall or floor. Because this kind of house adopts household metering and temperature control in different rooms, if the adjacent rooms are uninhabited or intermittently heated, the heat transfer formed by the floor or partition wall will increase the load, so the heat load calculated conventionally should be multiplied by an appropriate coefficient to consider this part of the heat transfer problem. (4) For high-rise and super-high-rise buildings, due to the increase of building height, the comprehensive effect of hot pressing and wind pressure should be considered, and the outdoor wind speed increases with the increase of building height. Because convective heat transfer is related to outdoor wind speed, the greater the wind speed, the faster the heat transfer, so the influence of wind speed on heat consumption can not be ignored sometimes and must be determined by calculation.

2.2 Determine the number of radiators in indoor rooms.

To determine the number of radiators, first assume that the correction coefficient β 1 is 1. Firstly, the heat dissipation area is determined, and the heat dissipation area is calculated by the formula f=qβ 1β2β3/k(tpj-tn). Then according to the heat dissipation area f of each radiator, the number of radiators is calculated and multiplied by the correction coefficient β 1, which is the result.

2.3 Hydraulic calculation design

Usually, the hot water heating system of high-rise buildings is supplied by zones, but when the height is less than 50m, vertical zones are not necessary. The tenth floor of this high-rise building is less than 50 meters, and the indoor heating system adopts the same horizontal double-pipe system, so the hydraulic calculation method is the same as the conventional calculation method, the only difference is that the resistance of heat meter and temperature control valve is increased, and the parallel loop of riser is changed from the traditional radiator to a separate indoor heating system.

In the design and calculation, it should be noted that: ① This system adopts a double-tube system, and the branch pipes of each floor in the room are the same scheme, but the parallel circuits of double risers are different schemes. First, select the most unfavorable circuit, and determine its pipe diameter and pressure loss. Then the diameter and pressure loss of each parallel circuit are calculated in turn by the same method, and the imbalance rate of pressure loss of each parallel circuit is obtained. The allowable difference between two programs with the same program is 15%, and the allowable difference between two programs with different programs is 25%. (2) Pipe selection: Double risers are set in the pipeline shaft, which are made of hot-dip galvanized steel pipes and connected by threads; Pb pipes are used indoors buried in the cushion, and their outer diameter is not greater than de25. Because of flat terrain and no slope, the flow rate should not be less than 0.25m/s, and plastic pipes buried in the cushion should not have joints. ③ Heat meter setting: each resident user is provided with a household heat meter, water filter, etc. , one meter per household. There is a drainage device at the entrance of every household, and the drainage pipe leads to the next pipe well, and the indoor horizontal pipe also has drainage, which is convenient for decoration or maintenance. (4) When the directly buried geothermal pipeline passes through the bathroom, the waterproof layer is usually not used, that is, the main heating pipe does not enter the bathroom, and the branch pipe connected with the radiator is buried in the side wall (non-load-bearing wall) of the bathroom, and it turns up to the upper part of the waterproof rolled edge (generally 30cm) to enter the bathroom, and the radiator is connected as soon as it enters the bathroom (the radiator is 30cm above the ground), so as not to affect the high point deflation.

Third, outdoor heating design

High-rise residential buildings adopt environmental protection and energy-saving measures, and outdoor heating design includes: determination of total heat of residential buildings, flow and lift of circulating pump, flow and lift of make-up pump, and selection of outdoor pipes. The total heat load of the residential group is obtained by multiplying the comprehensive heating heat index of the residential area by the total construction area. Determination of flow and lift of circulating water pump: According to the flow calculation formula g=0.86q/△t, the flow value is obtained, and then the sum of resistance of outdoor pipe network and end users is obtained through hydraulic calculation, which is the meter of lift. Calculation of flow and lift of makeup pump: Generally speaking, makeup water is 5% of circulating water, and its lift is calculated according to the formula H = HB+HS-H. Selection of outdoor heating pipes: seamless steel pipes are usually used for outdoor heating pipes dn200 and below, and spiral steel pipes with live welds are used for heating pipes larger than dn200. No matter what kind of pipe is selected, polyurethane is used for thermal insulation and high-density polyethylene is used for external protection.

To sum up, combined with practical experience, the author obtained the indoor and outdoor heating design and calculation of high-rise buildings with unit housing as the main body, cogeneration as central heating mode and household metering. Of course, combining the characteristics of high-rise buildings, comprehensively analyzing various factors, and choosing the best heating mode to meet the needs of residents' comfortable life to the greatest extent are the best policies for building heating design.

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