Air conditioning hot and cold water system design and configuration

With the rapid development of China’s iron and steel industry, central air conditioning system in steel plant has been widely used, central air condition relative to the split air conditioner has the following advantages:

① Central air conditioning operation management flexibility, and running costs than split air conditioners, central air conditioning refrigeration station can directly control the start and stop time of refrigerator and cooling capacity size can be adjusted according to climate change to reduce operating cost.

II central air conditioning can guarantee deliveries to the room, and keep the room empty with the rapid development of China’s iron and steel industry, central air conditioning system in steel plant has been more widely used.

Central air conditioning in relation to split air conditioner has the following advantages:

① Central air conditioning operation management flexibility, and running costs than split air conditioners, central air conditioning refrigeration station can directly control the start and stop time of refrigerator and cooling capacity size can be adjusted according to climate change to reduce operating cost.

II central air conditioning can guarantee deliveries to the room, and keep the room air clean and sanitary. Split air conditioning only through doors, Windows, ventilation and fresh air ventilators, cooling capacity loss, which affects not only the room temperature, and a waste of energy.

③ Central air-conditioning fault less maintenance. Central air conditioning both for air conditioning units and air duct system or room fan-coil and fresh air system, were prone to failure, and refrigeration equipment are located within the cooling station, easy to repair. Split air conditioner split unit air conditioner all over everywhere, refrigeration compressors are not only plentiful but dispersed, a fault can hardly begin to repair their good.

④ air conditioning noise less than split air conditioning. Central air-conditioning retro-fitting noise reduction device to reduce noise, and split air conditioning compressor air conditioning rooms close, it is difficult to achieve noise reduction measures.

⑤ Central air conditioning ends form beautiful diverse, can and decoration construction close tie, pipeline and equipment are can hidden in ceiling within, guarantee building of beautiful, save indoor of using space; but points body air conditioning of wind cold type outdoor machine must scattered of hanging outside wall Shang or loaded Yu outdoor ground Shang, effects outside decoration effect, and indoor machine is must hanging in within wall Shang or placed in ground, and occupy has indoor space, this virtually reduced has room of area.

⑥ Central air conditioning air-conditioning condensation water can be concentrated at the end of discharge, but split air conditioner air conditioner layout scattered, condensate discharge is not easy to deal with.

For these reasons, using central air conditioning system is feasible in the steel mills, steel mills in the central air-conditioning system in relation to civil architecture has the following characteristics: ① steel mill air conditioner users scattered within air conditioning comparison many types of user, how to design air conditioning pipes to solve hydraulic maladjustment of air conditioning user, it is especially important to meet the needs of different users. ② steel pipes are quite complex, criss-crossing the network configuration as much as possible the economic compact is worth exploring, including outdoor insulation for hot and cold water piping practices is important, improper practices will directly affect the results. ③ Mills within the air conditioner user input to use at different times, air conditioning load change is big, take fully into account the unit automatically adjusts to changes in load.

Here two aspects from air conditioning machine rooms and air conditioning line to discuss steel plants in the air conditioning design should pay attention to the problem in order for your reference.

1, room design configurations

1.1 selection and configuration of chillers

Mills central air conditioning cold water unit of select should full considered factory within of energy configuration situation, for most Mills,, steelmaking and other process process will produced large of steam, from energy of angle for, in air conditioning cold water unit of select Shang should as considered using this part steam, so for has extra steam of mills, in cold water unit of select Shang should priority selection steam type bromide of lithium cold water unit, for same refrigeration volume of steam type bromide of lithium refrigerator group and electric refrigerator group,, Lithium bromide unit can be saving around 98%.

For chiller number option should try to avoid using a single machine, and in cases where conditions allow, can choose two or more of the chiller, which does not take into account the standby unit, and in the case of load changes, you can turn off some chillers, saving on running costs, you can make the unit run at a higher COP values. Chillers and chilled water pumps in ways corresponding to one by one can be used, such as limited by room size, more than one may be used independent chillers and chilled water pumps arranged in parallel. This arrangement has its obvious advantages in simplicity, and convenience, but should pay attention to in this way in the case of partial air-conditioning cooling load, part of the chiller in a closed state, if management operational management negligence, no chiller stopped running the pipeline valve closes, then freezing water bypass flow phenomenon occurs. Bypass flow will affect the efficiency of water chillers in cold water, reduce the COP values of chillers. If air-conditioning cooling load demand ends on the other hand, require an additional number of chillers, managers are required to timely, timely and open an additional pipeline valve in water chiller, the operations management is clearly in trouble. Most economic measures to resolve this conflict is introduced in the chiller piping electric butterfly valve. Electric butterfly valve, water chillers and chilled water pumps, cooling water pump designed to operate the chain controls, so you can in the largest energy-consuming air conditioning system part is saving the most promising region in the control of intelligent, most economic investment, the most energy-efficient and convenient management.

1.2 refrigeration pump selection and configuration

Large central air conditioning chilled water system, with the change of air conditioning cooling load, use cold water units, number of air conditioning chilled water pumps in the wake of changes in and flow of air conditioning cooling water system pipe network has changed, which caused water pipe network resistance to change. In low load run situation Xia, especially air conditioning cold pumps only needs single Taiwan run Shi, air conditioning cold water system full load and low load run Shi water resistance difference is big, this led to low load Shi air conditioning cold pumps Super flow run, its run work points may jumped out of economic regional, then caused motor efficiency of reduced, while pumps run power consumption of increased, so in only single Taiwan pumps run of workers condition Xia, very easy occurred motor overload burned of accident. So design in the cannot only note has more Taiwan pumps of rated State points can meet pipeline calculation requirements, also must attention air conditioning low load Shi run State points changes by raised of problem, and take necessary of solution measures, solution method has two species, a is frozen pumps used frequency technology, that parallel run of each pump in the, a Taiwan pump used frequency pump, it as low load Shi single Taiwan pumps run of fixed pump, in system Super flow Shi, the pump reduced running frequency, system of flow also with reduced, Chilled water pump by using frequency conversion technology is a system variable flow of energy-saving technologies. Another solution is to export of each pump fitted with a current-limiting valve, it can pump to prevent the backflow, replacing the traditional non-return valve, and can play a role in limiting flow of the working pump. The valve head can set a control, when the pump head is below the control valve closing motion lift so that actual working head increase, prevent motor in low-lift pump, high flow, low efficiency occurs when overload. This way for the first way, energy-saving effect is poor, but it would reduce investment, the system is easier to manage.

1.3 side pipeline control room accessories set

Pressure gauges, and thermometers are set for air conditioning water system in the engine room of the side part is particularly important, with pressure gauge readings can judge the hydraulic conditions of the water system is normal, with the thermometer settings can initially determines if the water flows through the pipeline to meet the requirements. Recommended in the backwater dry pipe into each set water separator should be installed until a thermometer, by observing the temperature thermometer can accurately grasp the distribution of cooling load. Large temperature difference between the way the valves can be opened, small temperature difference branch of the valve opening can be adjusted smaller. Each water tube thermometer, operation managers to cooling load distribution of intuitive control system.
1.4 system with constant pressure and water

Setting system pressure device to enable the system to the operating voltage to ensure the system does not empty, no vaporization. General central air conditioning system pressure points are located at the entrance to chilled water pumps on the backwater dry pipe, so you can make the pump produces pressure in the system has been an appropriate distribution. Current heating and air-conditioning system with constant pressure supply water main expansion tank water at constant pressure, filling pumps constant pressure supply water, gas constant pressure tank with fill water pumps constant pressure supply water, and so on. Expansion tank pressure water is most economical and easiest way, so now heavily used in civil construction, but the expansion tank must be located at the highest point of the system, iron, air conditioner users scattered, distance from maximum air conditioning facilities tend to be long, the expansion tank is difficult to decorate, management is not convenient, high limits the application of the water tank. Small pump pressure continuous make-up water system, its pressure is formed by filling the tank, fill the pump and the regulator, while the system is running, through the pressure regulator function, make small pump continuous replenishment of water leakage is compatible with the system so as to maintain the system of hydrodynamic curve, but this constant pressure, which normally takes continuous operation, low power consumption. Using pressure tank combines fill pumps of set pressure fill water device in steel industry in the was large using, it main by fill pumps, and diaphragm type pressure jug, and safety valve, and electric contact pressure table and electromagnetic valve composition, it of work principle following: Dang system prepared run Shi, opened fill pumps, water was sent to tube network of while also was sent to pressure jug of water room, water room expanded and will tank within of gas compression, tank within of pressure with of increased, Dang pressure increased to Supreme work pressure Shi (System Supreme points and set pressure points Zhijian of high poor plus 3~5mH2O), pumps stopped turned, system has full water, using pressure tank within of pressure to maintained tube network of pressure, dang system run process in the, due to system leaking or water temperature change led to system water volume reduced Shi, pressure tank within of water room narrowed, tank within gas expansion, pressure reduced, dang pressure reduced to system minimum work pressure Shi (System Supreme points and set pressure points Zhijian of high poor plus 1mH2O), pumps opened, System for filling water. Installations in the pressure gauge and the solenoid valve is a safety device, when overpressure, and through the pressure gauge and solenoid valve the excess water out of the system. Pressure tanks with pumps constant pressure supply water compensation device device selection and calculation procedure is as follows:

1.5 fill pump selection

System within of water, dang for hot or hot and cold dual-use Shi, should used softening water, dang softening water pressure cannot directly for into tank Shi, should another set pumps fill water, fill pumps of automatically fill water can by system cycle water of 1% considered, accident fill water by system cycle water of 3% considered, directly fill into cycle pumps of entrance, fill pumps of head should by fill water points and system Supreme points of high poor plus 3~5mH2O of rich volume considered.

1.6 selection of pressure tank

Maximum working pressure of the pressure tank should be greater than the small pump head.

Volume of the tank tank water volume should be selected, the tank water volume should be selected according to the volume of the expansion tank, and that the volume of water inside the tank should be able to accommodate the expansion of the water system.

Indoor machine loop heat pipe (temperature 25℃) 7.8

Outdoor mechanical loop heat pipe (temperature 25℃) 5.8

Internal machinery for cold (temperature 5 ℃) or cool-31.2

Outdoor mechanical circulatory cooling system (temperature 5 ℃) or cool-23.2

Boiler 2~5

Refrigeration of shell-and-tube evaporator 1

Steam-water or water-water heat exchanger 1

Cooling coil (hot and cold coil 1)

2, air-conditioning piping design configurations

2.1 main steelmaking plant in air-conditioning pipe configuration

With drive system than ISO drive system hydraulic workers condition more stable, flow distribution also more uniform, conducive to air conditioning water system of hydraulic balance, steel plant within of air conditioning competent line more is along plant column column line layout, so is easy take with program system (as figure by shows), but each air conditioning user due to distance air conditioning competent line of distance different, indoor layout situation different, hard used with program of layout (as Figure user 1~4 of indoor pipeline), Best solution for this is pressing economic specific frictional resistance determine the one farthest from the air conditioning in the mainline pressure loss pressure loss of the largest user, according to pressure loss to determine the other loops of pipe diameter, this allows flow of air conditioning in each user’s assigned demand, decreased workload. The pipeline inside the air conditioner users such as unconditional direct return scheme can be used, the terminal can be adjusted using a manual valve balancing valve.

2.2 main steelmaking workshop air conditioning pipeline configuration

General outdoor insulation pipe overhead laying trench for laying, laying three, overhead laying enterprise application often works in a factory, but some users relatively far from air conditioning facilities, as a good chunk of overhead piping, tends to affect the plant’s overall layout and affect the plant’s appearance. Addition regional heating for cold engineering often due to outdoor underground pipeline staggered and to set, common of underground pipeline has strong, and weak, and to drainage, and gas,, national specification on species pipeline set spacing has specific requirements, various outdoor pipeline should as reduced respective underground occupies space and will respective relationship straighten out, regional underground tube network party can effective implementation, this aspects straight buried than trench laying superior. Simple and sophisticated technology on engineering practice of application of polyurethane direct-buried pipes were analyzed and compared.

2.2.1 the structure and characteristics of thermal insulation direct-buried pipe

Prefabricated directly buried insulating pipe caused by the medium of steel pipes, coats, tube and pipe, and the outer casing is filled between the hydrophobic and made of non-combustible insulation layer of polyurethane combined prefabrication of pipe, insulation foam keep it closely together and the outer casing. Because direct-buried pipes, insulation and floor live loads directly under the pipeline and at the same time affected by ground moisture and groundwater, so insulation direct-buried pipes in waterproofing, anti-corrosion and high performance in terms of mechanical strength requirements and, therefore, only a buried pipe construction cost is high. But because of its comprehensive low cost, simple construction and trench laying compared savings volume of earthwork, concrete, brick works, construction schedule shortened by more than half. And actually not only directly buried insulating pipeline insulation effect, lower total cost, and in the case of strictly according to the requirements, thermal insulation of the physical Anatomy after six years service life analysis and artificial ageing tests confirmed in more than 15 years, and trench laying pipe insulation insulation material rock wool or cotton centrifugal 3-5 generally needs to be replaced again. To sum up, directly buried insulating pipe in heat preservation performance, investment, construction, maintenance and day-to-day running costs were a big lead.

2.2.2 design of directly buried insulating pipe

Because of the air conditioning with the maximum hot water temperature of 60 degrees centigrade, the lowest temperature was 7 degrees centigrade, so direct-buried under too much stress will not. General direct-buried pipes, seamless steel tubes or Q235 tube, material for the 20th, at 15 ° c above the temperature when installed directly buried heat-supply pipeline (<100 degrees) do not need to take any measures without installing pipelines buried underground in the form of compensation (without fixed bearing and compensator), the safe operation of the pipeline can be achieved. Therefore, for district heating and cooling (<100 ℃ water systems) installed without compensation is in the form of convenience, safety and economy. No-compensate directly-buried is friction between the soil and the outer sleeve fixed pipe. Piping finish laying should be preheated before covering pipe and pipelines without having to set compensator, usually don’t need fixed bracket. In order to reduce costs, while preheating water test. Of regional cooling and heating pipeline features tubes medium temperature is not high (<100), working pressure <1.0MPa, but the pipeline is long, straight sections are often hundreds of meters long. Friction is much larger than the thermal stress of the soil, occurred in the middle of the straight section “anchoring”, anchorage-side critical sections to stress checking so that it meets the allowable stress of steel. Use without compensation installation of directly buried heat-supply pipeline’s horizontal elbows, tees, stress concentration. At design time, and should stress calculation, select the appropriate pressure level of elbows and tees. In General, the supply and return water pipes for air conditioning, for safety’s sake, the choice of elbows and tees can be taken into account when using a pressure rating higher than the pipeline.

3, conclusion

1, central air conditioning system for steel mill hosts option, configuration should take full account of the plant’s energy situation, where there are rich steam, preference should be given-steam lithium bromide unit;

Air conditioner users within 2, for steel mills are scattered with expandable tank constant pressure supply water is more difficult, can be combined with pressure tank fill pump with constant pressure water supply equipment

3, factory air-conditioning in main line layout should be used with the program. Air conditioning design of user should be established in accordance with economic specific frictional resistance a farthest from the air conditioning in the mainline pressure loss is the largest user of pressure loss, according to pressure loss to determine the other loops of pipe diameter;

4, for district heating and cooling pipe of directly buried insulating pipeline can be used without compensation, it should be noted the “anchoring, and elbows, tees and other stress-calculation of stress concentration.

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