CN100455920C - A district cooling system and its cooling capacity cascade utilization method - Google Patents

Abstract

The present invention relates to provides one kind of regional cold supply system, which includes one secondary refrigerated water pipeline with refrigerated water supplying pipe, refrigerated water returning pipe, fresh air cooler and returned air cooler. The fresh air cooler and the returned air cooler are independent, the returned air cooler has water inlet connected to the refrigerated water supplying pipe and water outlet connected to the water inlet of the fresh air cooler, and the fresh air cooler has water outlet connected to the refrigerated water returning pipe. The present invention has increased water supply and water return temperature difference of the secondary refrigerated water pipeline, lowered cold loss, lowered pump power consumption and lowered cost.

Description

A district cooling system and its cooling capacity cascade utilization method

technical field

The invention relates to an energy-saving technology for a district cooling system, in particular to a district cooling system and a cascaded utilization method for cooling capacity thereof.

Background technique

The per capita share of energy in my country is far below the world average level. At this stage, the demand for energy use in my country is growing rapidly, and the contradiction between supply and demand is acute. The only way to solve my country's current energy dilemma is to use energy scientifically and improve energy utilization efficiency. my country's building energy consumption accounts for 30% of the country's total energy consumption, and the unit energy consumption is much higher than that of developed countries; in building energy consumption, HVAC system energy accounts for 65%, and domestic hot water energy accounts for 15%. The energy saving of HVAC system is the key to building energy saving.

The district cooling system has the characteristics of high energy utilization efficiency, small installed capacity of refrigeration equipment, fewer operation and management personnel, environmental protection, favorable energy cascade utilization, architectural aesthetics and space utilization. District cooling systems have been widely used around the world since their inception in the 1960s. Especially since the early 1990s, the development of district cooling has been more rapid. my country's district cooling technology also presents a good development trend.

With the implementation of policies such as vigorously developing and introducing natural gas resources and optimizing my country's energy structure, the gas distributed energy system, which is the most efficient and economical use of natural gas, will surely develop rapidly. On the other hand, with the acceleration of my country's urbanization process, the improvement of people's living standards and global warming, the cooling load and demand have grown strongly, which will greatly promote the development of district cooling systems in my country. Gas distributed energy system + district cooling system is an effective way to solve the contradiction between energy supply and demand in my country, and both have good development prospects.

Although the district cooling system has many advantages, compared with the conventional central air-conditioning system, it has the following energy consumption and cost: the secondary chilled water pipeline of the district cooling system (that is, the chilled water between the central refrigeration station and the user) The cold loss of the transmission pipe network), the energy consumption of the secondary pump, the initial investment of the secondary pipeline and the construction cost. In addition, the economic transportation distance of chilled water is limited due to cold loss and pump energy consumption. At present, the general economic transportation distance is 1.6km. Therefore, for the district cooling system, the cold loss of the chilled water secondary pipeline, the energy consumption of the secondary pump and the initial investment of the secondary pipeline weaken its advantages. It is also a key issue related to whether the system can be promoted.

At present, the temperature difference between the supply and return water of the secondary pipeline of the chilled water in the district cooling supply is about 10°C at most. There are two cooling methods for the terminal equipment:

(1) Centralized air conditioning system

Centralized air conditioning systems are generally used in places with large spaces such as shopping malls, libraries, restaurants, and theaters. The cooling method of the terminal equipment of the system is as follows: fresh air and return air are mixed first, then processed by the surface cooler to the required temperature and humidity, and then sent to the air-conditioned room.

(2) Fan coil unit + fresh air air conditioning system

Fan coil unit + fresh air air conditioning system is used in hotels, office buildings and other places. The cooling method of the terminal equipment of the system is as follows: the return air in each room is cooled and dehumidified by the fan coil (surface cooler) installed in the room, and the fresh air is generally provided by one or several fresh air units ( Surface cooler) is sent to each room after centralized cooling and dehumidification, and the temperature of chilled water supply and return water of the surface cooler dealing with fresh air and return air is the same.

The cold loss of the secondary chilled water pipeline and the energy consumption of the secondary pump will decrease with the decrease of the chilled water flow. Therefore, by increasing the temperature difference between the supply and return water of the secondary pipeline, the cold loss of the secondary pipeline and the energy consumption of the secondary pump can be reduced. In order to increase the temperature difference between the supply and return water of the secondary pipeline, it is possible to improve the traditional terminal equipment by adopting a new technology and using a cold method.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the above-mentioned prior art, and provide a district cooling system, which can increase the temperature difference between the supply and return water of the secondary pipeline, thereby reducing the cold loss of the secondary pipeline and the secondary pump. energy consumption.

The object of the present invention is also to provide a cooling capacity cascade utilization method for the above-mentioned district cooling system.

The purpose of the present invention is achieved through the following technical solutions: the regional cooling system, which includes the chilled water supply pipe of the chilled water secondary pipeline, the chilled water return pipe, the fresh air surface cooler, and the return air surface cooler, the fresh air The surface cooler and the return air surface cooler are independent of each other, the chilled water supply pipe is connected to the water inlet of the return air surface cooler, the chilled water return pipe is connected to the water outlet of the fresh air surface cooler, and the return air surface cooler The chilled water outlet of the fresh air surface cooler is connected with the chilled water inlet.

The cooling capacity cascade utilization method of the above-mentioned district cooling system refers to cooling the fresh air and the return air through the fresh air surface cooler and the return air surface cooler which are independent of each other, and the chilled water in the secondary chilled water pipeline passes through the chilled water first. The water supply pipe enters the return air surface cooler to exchange heat with the return air with low temperature and low humidity content, then enters the fresh air surface cooler to exchange heat with fresh air with high temperature and high humidity content, and finally enters the chilled water return pipe. Therefore, on the premise of maintaining the same indoor heat and humidity load and maintaining the same comfort, the return temperature of chilled water can be increased and the flow rate can be reduced.

Compared with the prior art, the present invention has the following advantages and beneficial effects: From the perspective of scientific energy utilization, temperature matching, and cascade utilization, the present invention enlarges the secondary pipeline of chilled water through a new cooling method of terminal equipment The temperature difference between the supply and return water can reduce the cooling loss of the secondary pipeline of chilled water, the energy consumption of the pump and the initial investment of the pipeline. At the same time, it can also expand the economical transportation distance of chilled water and expand the cooling area of the district cooling system and scale, improve economic benefits and energy efficiency.

Description of drawings

Figure 1 is a schematic diagram of the end-use cooling method of a traditional centralized air-conditioning system;

Figure 2 is a schematic diagram of the cooling method at the end of the traditional fan coil unit + fresh air air conditioning system;

Fig. 3 is a schematic diagram of an end-use cooling mode of a district cooling system according to the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Embodiment one

Figure 1 is a schematic diagram of the end-use cooling method of a traditional centralized air-conditioning system;

Figure 2 is a schematic diagram of the cooling method at the end of the traditional fan coil unit + fresh air air conditioning system;

Fig. 3 is a schematic diagram of the terminal cooling mode of a district cooling system of the present invention;

As shown in Figure 3, the regional cooling system includes the chilled water supply pipe 1 of the chilled water secondary pipeline, the chilled water return pipe 2, the fresh air cooler 3, the return air cooler 4, and the fresh air cooler 3. The return air cooler 4 is independent of each other. The chilled water supply pipe 1 is connected to the water inlet of the return air cooler 4, the chilled water return pipe 2 is connected to the outlet of the fresh air cooler 3, and the return air cooler 4 The chilled water outlet of the fresh air surface cooler 3 communicates with the chilled water inlet of the fresh air surface cooler 3.

The cooling system in this area uses cascaded cooling capacity in this way: the fresh air and return air are cooled by the fresh air surface cooler 3 and the return air surface cooler 4, which are independent of each other, and the chilled water in the secondary chilled water pipeline passes through first. The chilled water supply pipe 1 enters the return air surface cooler 4 to exchange heat with the return air with low temperature and low humidity content, and then enters the fresh air surface cooler 3 to exchange heat with the fresh air with high temperature and high humidity content, and finally enters Chilled water return pipe 2. Therefore, on the premise of maintaining the same indoor heat and humidity load and maintaining the same comfort, the return temperature of chilled water can be increased and the flow rate can be reduced.

The specific design parameters and calculation process are as follows: The original design parameters of the chilled water secondary pipeline of the district cooling system: supply water temperature T _s1 = 3.5°C, return water temperature T _h1 = 13.5°C, supply and return water temperature difference ΔT ₁ = 10°C. The cooling capacity of the secondary pipeline is 30000kW, the inner diameter of the chilled water pipe is 600mm, the flow rate of water is 2.54m/s, and the thickness of the polyurethane is 90mm for insulation. The center of the buried pipe is 1.6m from the ground, and the horizontal distance between the center of the water supply and return pipe is 1m. Two secondary pumps, each with a flow rate of 1290m ³ /h, a lift of 30m, and a power of 140kW.

After adopting the terminal cooling mode of a district cooling system of the present invention, the supply water temperature remains unchanged (T _s2 =3.5°C), the return water temperature is increased to T _h2 =18.5°C, and the temperature difference between supply and return water is increased to ΔT ₂ = 15°C. Now calculate the changes in the diameter of the secondary pipeline, the power of the secondary pump, and the cold loss of the secondary pipeline after the temperature difference between the supply and return water of the secondary pipeline increases.

(1) The diameter of the secondary pipeline of chilled water

The local resistance of the chilled water secondary pipeline is 20% of the resistance along the way. When the flow rate of the secondary pipeline changes, the equivalent roughness of the steel pipe is assumed to be constant, and the total resistance of the pipeline is kept constant by adjusting the pipe diameter (ie ΔP ₁ =ΔP ₂ ). The relationship between the pipe diameter and the change of the flow rate can be deduced from the relevant formula of fluid mechanics: $\frac{d_2}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="C20061012279500081.png,C20061012279500082.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}={\left(\frac{L_2}{L_1}\right)}^{0.381}.$

Assuming that the volume flow rate of frozen water corresponding to ΔT ₁ =10°C is L ₁ (m ³ /s), then when ΔT ₂ =15°C, the volume flow rate is L ₂ =0.667L ₁ (m ³ /s) , d ₂ =0.857d ₁ =0.857×600=514mm. Therefore, when the temperature of the secondary chilled water pipeline increases from 10°C to 15°C, the flow rate decreases by 33.3%; by adjusting the pipe diameter to maintain the same total resistance, the pipe diameter decreases by 14.3%.

(2) Secondary pump power

When the temperature of the chilled water secondary pipeline increases from 10°C to 15°C, the head and efficiency of the secondary pump can be considered as unchanged because the total resistance of the pipeline is maintained by adjusting the pipe diameter. The changing law of the electric power of the secondary pump is: N ₂ =0.667N ₁ , that is, the power of the secondary pump is reduced by 33.3%. After the flow rate is changed, 2 secondary pumps are also used, and the parameters of each pump are changed to: flow rate 860m ³ /h, head 30m, power 93.4kW.

(3) Cold loss of the secondary pipeline

The cold loss of the secondary pipeline of the district cooling system includes two parts: the cold loss (ΔQ ₁ ) transmitted to the soil through the pipeline and the cold loss (ΔQ ₂ ) caused by the input power of the water pump.

The cold loss (ΔQ ₁ ) transmitted to the soil through the pipe decreases with the increase of the temperature difference of the frozen water in the pipe and the decrease of the pipe diameter.

When the calculated supply/return water temperature is 3/13°C (ΔT ₁ =10°C), ΔQ ₁ =202.6kW, when the return water temperature of the district cooling system increases to 18°C, the supply water temperature remains unchanged (ΔT ₂ = 15°C), ΔQ ₁ =152.7kW. After the temperature difference between the supply and return water of the secondary pipeline is increased, the cold loss ΔQ ₁ transmitted to the soil through the pipeline is reduced by 24.6%.

The cooling loss ΔQ ₂ caused by the input power of the water pump decreases with the decrease of the input power of the water pump. When the temperature difference between supply and return chilled water is 10°C, the total power of the secondary pump is 280kW; when the temperature difference between supply and return chilled water is 15°C, the total power of the secondary pump is 186.8kW, and ΔQ ₂ is reduced by 33.3%.

When the temperature of the secondary pipeline of chilled water increases from 10°C to 15°C, the total cooling loss of the secondary pipeline of the district cooling system decreases from 482.6kW to 339.5kW, a reduction of 29.6%.

As described above, the present invention can be preferably carried out.

Claims (2)

1. A district cooling system, which includes a chilled water supply pipe of a chilled water secondary pipeline, a chilled water return pipe, a fresh air surface cooler, and a return air surface cooler, characterized in that: the fresh air surface cooler, The return air surface coolers are independent of each other, the chilled water supply pipe is connected to the water inlet of the return air surface cooler, the chilled water return pipe is connected to the water outlet of the fresh air surface cooler, and the chilled water outlet of the return air surface cooler is The water port is connected with the chilled water inlet of the fresh air surface cooler. 2. A cooling cascade utilization method for a district cooling system as claimed in claim 1, characterized in that the fresh air and the return air are cooled by fresh air surface coolers and return air surface coolers that are independent of each other, and the chilled water The chilled water in the secondary pipeline first enters the return air surface cooler through the chilled water supply pipe to exchange heat with the return air with low temperature and low humidity content, and then enters the fresh air surface cooler to exchange heat with the fresh air with high temperature and high humidity content. Heat exchange, and finally enter the chilled water return pipe.

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