Design method of parallel return water tank for multiple cooling towers in air conditioning system

Abstract

The present invention discloses a design method for a multi-cooling tower parallel return water tank of an air-conditioning system. The return main pipe supplies water from the return water tank to the condensers of each chiller; the water flow state in the return water tank is designed according to the non-uniform gradually varied flow in an open channel; the outlet pipes of the water collection trays of each cooling tower are respectively connected to the return water tank from the cover plate of the return water tank, and the outflow state of each outlet pipe is designed according to the free outflow at the end, that is: according to the water level difference between the water collection tray of each cooling tower and the return water tank, the water inflow and outflow of each cooling tower are respectively calculated to balance the water inflow and outflow, so as to avoid the overflow of the water collection tray of each cooling tower; the return water tank is laid with a slope of 2-3%, and the water passing capacity of the return water tank is calculated by the Manning formula. According to the design method of the present invention, even if there are differences in the water inflow of each cooling tower, since the water flow state in the return water tank has no influence on the water flow state in the outlet pipe of the water collection tray of the cooling tower, the overflow problem of the water collection tray of the cooling tower is fundamentally eliminated.

Description

Technical Field

[0001] The invention relates to the design of a return water tank of a cooling tower of an air-conditioning system, in particular to a design method of parallel return water tanks of multiple cooling towers of an air-conditioning system. Background Art

[0002] In the early design of air conditioning cooling water or industrial cooling water systems, due to the small scale of buildings, the scale of refrigeration stations and the number of chillers, a "single-pipe" cooling water supply and return solution was mostly used, that is, each chiller corresponded to a cooling tower, and each had independent cooling water supply and return pipes.

[0003] As the scale of buildings becomes larger and larger, the scale of refrigeration stations and the number of chillers increase accordingly. If the "single-pipe" cooling water supply and return solution is still adopted, the number of supply and return pipes will be relatively large, and the area of ​​the floor occupied will also be relatively large (the pipe well area is larger). Therefore, the "mother pipe" cooling water supply and return solution has gradually emerged, that is: the cooling water outlet pipes of multiple chillers are merged into a water supply mother pipe after the cooling circulation pump and supplied to the roof cooling tower; the cooling water after being cooled by multiple cooling towers is merged into a return mother pipe on the roof of the building and supplied to the condenser of each chiller.

[0004] Using "mother pipe control", from the basic principles of hydraulics, even if a ring pipe network is used to supply water to multiple cooling towers of the same model, it is impossible to strictly and evenly distribute water to each cooling tower. The water intake of each cooling tower can only be adjusted to be roughly consistent through the subsequent valve adjustment. In addition, with the changes in climate and outdoor wet-bulb temperature, in order to save energy in the air-conditioning system, it is necessary to shut down some chillers and link up to shut down some cooling towers and cooling circulation pumps. When the number of cooling towers open changes, the pipeline characteristic coefficient of the cooling water system distribution pipeline changes accordingly. It is necessary to adjust the opening of the water inlet valve of the cooling tower that continues to work to change its local resistance coefficient, which is very difficult to achieve.

[0005] like Figure 2 As shown in the figure, there are four cooling towers using "main pipe control". The water collecting pan outlet pipes 1.1, 1.2, 1.3, and 1.4 of each cooling tower converge into a return water main pipe 1.5 (the main pipe does not change diameter). From the basic principle of hydraulics (pressure continuity), even if the water intake of each cooling tower is exactly the same, when the valve of the cooling tower outlet pipe is fully open, the water output must be inconsistent. The farther the cooling tower is from the cooling water return riser 1.6, the smaller the water output q1 of the cooling tower water collecting pan outlet pipe 1.1; the closer the cooling tower is to the cooling water return riser 1.6, the larger the water output q4 of the cooling tower water collecting pan outlet pipe 1.4, that is, q4>q3>q2>q1 (this is similar to the hydraulic state of the multi-bucket suspended roof rainwater system).

[0006] From the above analysis, it is not difficult to see that due to the imbalance of the water inflow and outflow of each cooling tower, water overflow in the water collecting tray of the cooling tower occurs from time to time, resulting in unnecessary waste of water resources.

[0007] Regarding the problem of water overflow in the water collecting tray of the cooling tower, Article 3.11.13, Paragraph 2 of the national standard GB 50015-2019 "Design Standard for Building Water Supply and Drainage" stipulates that "when multiple cooling towers without a collecting pool are used in parallel, a connecting pipe should be provided for the water collecting trays of each tower." For the same problem, Article 2, Paragraph 3 of Section 26.10.7 (Cooling Water System Design) of the "Practical Heating, Ventilation and Air Conditioning Design Manual" (Second Edition) in the HVAC specialty states that "the water levels of each cooling tower should be controlled at the same height, and the height difference should not be greater than 30 mm. When designing, the height of the base of different-capacity cooling towers should be considered based on the height of the water collecting tray. Install a balance pipe between the chassis of each tower and increase the diameter of the common section of the outlet pipe. Generally, the balance pipe can be one size larger than the diameter of the total return pipe." (Although the connecting pipe and the balance pipe are expressed differently, they are both pipes added between the water collecting trays of each cooling tower to balance the water levels of the water collecting trays of each tower.) However, when the models of each cooling tower are the same, it is relatively easy to add a connecting pipe (balance pipe). For cooling towers of different models, the depths of the water collecting trays are different, and the heights of the tower body supports are also different. To ensure that the water levels of the water collecting trays of each cooling tower are basically the same, it is also necessary to adjust the concrete foundation implemented by the civil engineering specialty in the later stage, and then consider adding a connecting pipe (balance pipe); therefore, it is difficult to implement and the infrastructure cost is high. Summary of the Invention

[0008] The purpose of the present invention is to provide a design method for the parallel return water tank of multiple cooling towers in an air-conditioning system, aiming to redescribe the return water method when multiple cooling towers in the air-conditioning cooling water circulation system are connected in parallel based on the basic principles of hydraulics and in combination with the actual operation needs of the cooling water system, and completely eliminate the problem of water overflow in the water collecting trays of the rooftop cooling towers.

[0009] To achieve the above purpose, the present invention can adopt the following technical solutions:

[0010] In the design method for the parallel return water tank of multiple cooling towers in the air-conditioning system of the present invention, in the air-conditioning cooling water circulation system where multiple cooling towers are connected in parallel, the return main pipe supplies water to the condensers of each refrigerating machine through the return water tank; the water flow state in the return water tank is designed according to the non-uniform gradually varied flow in an open channel; the outlet pipes of the water collecting trays of each cooling tower are respectively connected to the return water tank from the cover plate of the return water tank, and the outflow state of each outlet pipe is designed as free outflow at the end, that is: according to the water level difference between the water collecting tray of each cooling tower and the return water tank, calculate the water inflow and outflow of each cooling tower respectively, so that the water inflow and outflow are balanced, and the water overflow in the water collecting tray of each cooling tower is avoided; the return water tank is laid with a slope of 2-3%, and the water passing capacity of the return water tank is calculated using the Manning formula.

[0011] When the water return tank needs to be converted downward into a water return riser at the position corresponding to the pipe well on the building roof, a transition water collection tank is added at the conversion position to facilitate the connection between the water return tank and the water return riser.

[0012] The advantages of the present invention are reflected in the following aspects:

[0013] 1. The main water return pipe of the cooling water system of multiple parallel cooling towers is designed as a water return tank. Even if there are differences in the water intake of each cooling tower, since the water flow state in the water return tank has no influence on the water flow state in the outlet pipe of the cooling tower water collection tray, the overflow problem of the cooling tower water collection tray is fundamentally eliminated.

[0014] 2. By adopting the water return tank design, there is no need to additionally support a connecting pipe (balance pipe) and drill holes additionally on the cooling tower water collection tray; compared with the traditional design method, it reduces material consumption, reduces the project cost, and at the same time shortens the construction period.

[0015] 3. When some refrigerating machines, cooling circulation pumps and cooling towers need to be shut down, there is no need to adjust the inlet and outlet valves of the cooling tower anymore. While eliminating the overflow of the cooling tower water collection tray, it realizes the non-adjustment of the inlet and outlet valves of the cooling tower, and reduces the workload of system operation and maintenance.

[0016] 4. Even if the models of the cooling towers are different, as long as the water level difference between the cooling tower water collection tray and the water return tank is calculated well, the normal operation of each cooling tower can be ensured. Brief Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the water return tank design of four parallel cooling towers in the embodiment of the present invention.

[0018] Figure 2 It is a schematic diagram of the main water return pipe design of four parallel existing cooling towers.

[0019] Figure 3 It is a schematic diagram of the hydraulic radius R when the main water return pipe design is adopted in the present invention.

[0020] Figure 4 It is a schematic diagram of the hydraulic radius R when the water return tank design is adopted in the present invention. Detailed Embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The design method of the parallel return water tank of multiple cooling towers in the air conditioning system of the present invention is based on the Manning formula, that is, when draining in an open channel, under the same pipeline slope, the greater the hydraulic radius, the greater the water passing capacity.

[0023] As Figure 3 shown, when the main return water pipe 3.1 is designed, its hydraulic radius R is half of the pipe radius r, that is, R = r / 2; as Figure 4 shown, when the return water tank 4.1 is used as the return water pipe of the condenser of each refrigerating machine, its hydraulic radius R increases by 50%, that is, R = 3r / 4.

[0024] Therefore, for the parallel air conditioning cooling water circulation system of four cooling towers of the present invention, as Figure 1 shown, the main return water pipe supplies the condenser of each refrigerating machine through the return water tank 2.1; the water flow state in the return water tank 2.1 is designed according to the non-uniform gradually varied flow in the open channel; the outlet pipes 2.2 of the water collecting trays of each cooling tower are respectively connected to the return water tank 2.1 from the cover plate 2.3 of the return water tank, and the outflow state of the outlet pipes 2.2 of the water collecting trays of each cooling tower is designed according to the free outflow at the end, that is: according to the water level difference between the water collecting trays of each cooling tower and the return water tank 2.1, calculate the water inflow and outflow of each cooling tower respectively to make the water inflow and outflow balanced, so as to avoid the overflow of the water collecting trays of each cooling tower; the return water tank 2.1 is laid at a slope of 2-3%, and the water passing capacity of the return water tank 2.1 is calculated by the Manning formula.

[0025] When the return water tank 2.1 needs to be converted into a return water riser 2.4 downward at the position corresponding to the pipeline well on the building roof, a transition water collecting tank 2.5 is added at the conversion place to facilitate the connection between the return water tank 2.1 and the return water riser 2.4.

Claims

1. A design method for the parallel return water tank of multiple cooling towers in an air conditioning system, characterized in that: For an air-conditioning cooling circulating water system with multiple cooling towers in parallel, the return main pipe supplies water to the condensers of each chiller through a return water tank; the water flow state in the return water tank is designed according to the non-uniform gradually varied flow in an open channel; the outlet pipes of the water collecting trays of each cooling tower are respectively connected to the return water tank from the cover plate of the return water tank, and the outflow state of each outlet pipe is designed as free outflow at the end, that is: according to the water level difference between the water collecting trays of each cooling tower and the return water tank, calculate the water inflow and outflow of each cooling tower respectively to balance the water inflow and outflow and avoid water overflow in the water collecting tray of each cooling tower; the return water tank is laid with a slope of 2-3%, and the water passing capacity of the return water tank is calculated by Manning's formula.

2. The design method of the parallel return water tank of multiple cooling towers of the air conditioning system according to claim 1, characterized in that: When the return water tank needs to be converted into a return water riser downward at the position corresponding to the pipe well on the building roof, a transition water collecting tank is added at the conversion place to facilitate the connection between the return water tank and the return water riser.

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