【 Weak current College 】 Central air conditioner cold water system design and configuration

1. introduction

As China's economy maintained rapid development, the building industry has taken a flourishing of prosperity, central air conditioning system in hotels, office buildings, business centres, hospitals and other buildings of a wide range of applications. Central air conditioning system will not only involve a high initial investment of funds, but also the building's energy consumption. Most of the engineering design, most concerned about is the air-conditioning cold source programme economics and run a comparison of energy consumption. But we know that choosing the ideal cold source programme is a good basis for central air conditioning system, air conditioning and cold water system effective operational management and energy consumption is not enough, central air-conditioning system saving energy depends to a large extent on effective air conditioning cold water system, design reasonable, debugging improvement, management and technical measures in place in the central air conditioner cold water system is the most powerful protection.

2. room side of the design configuration

Chiller capacity is big problem is the existence of central air conditioning system is more prevalent, the bulk of idle is undoubtedly the most significant waste, on the one hand, to a large extent, the increased investment at the beginning of the construction, on the other hand, it contributed to the system's energy consumption. Chiller capacity is large and determines the frozen, cooling water pump capacity, if the hydraulic air conditioning water system and the lack of detailed calculations, design engineers in the heart of countless, pump selection head inevitably partial, further increasing the pump power consumption (N and Q * H proportional), this is even worse. This phenomenon is due to the air conditioning cooling load calculation is not careful, instead of "racking our brains", this phenomenon is more common, on the one hand, the design engineers lack sufficient time to do the tedious calculations, on the other hand is the industry's lack of air conditioning system effect is good and bad judgement criteria, we know that the air conditioning system of "ability" to play depends on many aspects, in addition to the design of the factors which also includes the construction quality is good or bad, the completion of the debugging level, these are often due to a lack of effective management and monitoring, it can influence the effectiveness of air conditioning system formation and give full play to the decisive factor. Especially in the design of the total cooling capacity configuration less well-off, if the system lacks a careful debugging, it is easy to cause objectively between rich and poor, and thus produce air conditioning effect caused by bad or total cooling capacity is insufficient for the misunderstanding. Based on this concern, the design engineers will increase insurance coefficient, 174, it caused water chiller capacity for excessive waste, investment, building energy consumption stools are inevitable. So careful air-conditioning cooling load calculation is lower and the initial investment, achieving energy conservation's most fundamental, is also the most valid method, while improving the quality and completion of the installation of the debug level is the most direct safeguards.

2.2 room side unit effective operation and management of design solutions

For large buildings, central air conditioning system cooler source with the chiller, often more than one, there is 2 ~ 4, some even more than four units. Because of limitations in computer room area chillers and cooling water circulation pump cannot use one-to-one principle, most of the multiple chillers and multiple independent chilled water pumps in parallel settings. This arrangement has it more obvious advantages of a simple, convenient, but if the lack of funds or other reasons, the design of the air-conditioning system is unable to configure BAS Management system, in part air-conditioning cooling load, on the part of the chiller is the closure of the State, if the management operations management oversight, not to the closure of chiller pipeline valve closes, the frozen water by-pass flow occurs. Through the analysis it is not difficult to come to the conclusion that the cold water by-pass flow affects the play of the chiller efficiency, reduces chiller COP value. On the other hand if the Terminal air-conditioning cooling load demands increase, the need for the additional number of cold water unit, which requires the managers in place in time, timely open additional chiller pipe on valve. This operation management obviously is not feasible, in the most works of practical management, more is a kind of "laissez-faire" State, this will not only lead to increase of energy consumption for cooling water unit, and chilled water pumps operating point deviation from the nominal operating point, power consumption increases, the air conditioning cooling water system operation and management of effective energy-saving seems to be impossible. Resolve this to contradictory economic measures is chiller pipe considering additional electric butterfly valve, electric butterfly valve and water chillers one-to-one, both for the chain run control so that it can effectively facilitate the control of chilled water access, solve frozen water by-pass flow phenomena. If appropriate additional capital investment allows, you can also consider only the room side parts into small intelligent monitoring system (the part of the investment for medium-sized air conditioning water system according to the valuation of approximately 10 million RMB) so we can put air conditioning energy consumption is the most most energy most potential area into intelligent control, achieve the most economical investment, most energy-efficient and convenient management.

2.3 low load runtime frozen water pump overload problem design solutionbr>
Large central air conditioner cold water system, with the air conditioning zone cooling load changes in use of chillers, air conditioning in the number of the chilled water pumps are also with the change, while air conditioning cooling water system pipe flow also changed, this change in water resistance of pipe network. In low load situation, especially the air conditioning cooling water pump only need a single run-time, from the R (air cooling system for water resistance) = & Q2 (pipeline through traffic), it is not difficult to find, the air conditioning cooling system at full load and low load operation water resistance considerably, resulting in low load air cooling-water pump-flow operation, the operation point may jump out of the economic region, thereby causing motor efficiency decreases, while the increase in power consumption of pump operation, so only a single pump running condition, extremely prone to motor overload destroyed by accident. For the more large central air conditioner cold water system, the number of units in parallel, the more low load overload problem, the more serious cases, motor burned down, the more likely to occur. So the design does not only pay attention to the multiple pump rated status points can meet the requirements of pipeline calculation, you must pay attention to the air conditioning when running at low load point changesProblems and take the necessary measures to draw to the water-cooled centrifugal chillers shedding of design ideas, there are two solutions, one is frozen water pump adopts frequency conversion technology, i.e. in parallel operation of the pump, a pump adopts frequency conversion pump that acts as a low-load a single pump operation of fixed pump, flow-in system, the pump reduces operating frequency, the system of flow with reduced visible frozen water pump adopts frequency conversion technology is a system variable flow of energy-saving technology. Another solution is to air conditioning water dry pipe added additional bypass channel, non-low load operation, chilled water supply main pipe on the main path and by-pass road valve is opened, chilled water flow through two channels, while a low load on the main path of electric butterfly valve closed, frozen water only flows through the bypass road, under no load cases by-pass valve gate is always a close angle. We can use the following equation qualitative analysis of the pipe to the resistance changes before and after: R1 (non-single pump run time the pipe resistance) = 1/(1/R main + 1/R), R2 (single pumping the pipe resistance) = R, obviously R1 R2 gravity(25℃) >. From an intuitive, it is not difficult to know when a single pump operation, because the main path of electric butterfly valve closes, the bypass road in the sudden increase in resistance, dry pipe increase additional bypass channel actually is by changing the low load of piping water resistance, to solve the problem of overloading chilled water pumps, obviously this way non-energy-saving measures.

2.4 differential pressure setting of the by-pass difference

In General, the backwater dry pipe pressure differential bypass valve set on, is the end side variable flow and room side will flow the contradictions of the most commonly used method. The pressure differential system bypass valve work's basic principle: the system is in design mode, all devices running at full capacity, pressure differential bypass valve from opening is zero, then the pressure differential controller at both ends of the connector of the pressure differential that is the difference between the controller setting. But most have been put into use in engineering, pressure controller settings and functions are frequently used in construction units and units are ignored, pressure control system and the terminal equipment of electric second pass will exist in name only. From the hydraulic analysis, we are not difficult to come to the conclusion that the pressure value isset too low, the bypass valve is extremely easy to open and flow increases, next to the Terminal side of cooling cannot be met, while the pressure value is set too large, the bypass valve door open easily, bypass flow is small, this effect chillers normal run number required, this invisible increased air conditioning cooling system power consumption. So the design shall pay attention to pressure differential bypass control system on the whole system, properly define its parameters to meet users ' traffic, while according to actual needs to adjust the unit number of runs

2.5 room side of the pipeline control accessories set

Air conditioner cooling systems installed, before it is put into use, the system must be carefully, complete debugging. System debug pipeline without pressure gauges and thermometers. Pressure gauge, thermometer settings for air conditioning cooling water system in the engine room side part is very important, with pressure gauge readings to determine the portion of the initial water system of hydraulic condition is normal, with the thermometers preliminary judgment of settings can be flowing through the pipe run water meets the requirements. Pressure gauge set in these parts is essential: pump export and import and export, chiller, set water separator, with pressure gauge readings of the instruction, can adequately determine along the fluent direction of pressure distribution is normal, the pipeline valve closes, the reasonableness of the break. For example the author participate in an air conditioner works found in the first debugging: air-conditioned area on the terminal equipment into the outlet pressure difference generally is small, the indoor temperature fundamental to the design requirements, the system of water separator for pressure gauge readings clearly is small, sets, water separator pressure difference between the left and right, but only 80KPa chilled water pumps and export pressure difference clearly exceed the designof the lift, and chiller inlet pressure than the pump outlet pressure low 120Kpa, this section of the pipeline only 15 meters, it is clear that the pressure loss is not normal. Checked: pump export butterfly valve is construction units to two-thirds, off the valve to open degree smaller, consume a large part of the pressure drop. Full open the valve, the pressure distribution in the aforementioned sites, the air conditioning basically normal regional temperature up design requirements.

According to the in and out of the water temperature to determine the system's operating state, the thermometer settings in these areas is essential: chiller into and out of the tube and sets, water separator. Water separator and set water is part of the total brake air conditioning, this author recommends that each branch of the backwater stem manifold into sets of water before you should install a thermometer, temperature thermometer through observation, you can accurately grasp the cooling load distribution. Large temperature difference between the valve on the slip road to turn up the temperature difference between small tributary, the valve to open degree can reduce smaller. Only each return water pipes installed thermometers, operations management personnel to visually acquire system cooling load distribution.

3. configure the end side of design

3.1 pipeline layout with the use of different leg of the strategy

Reverse return system than with hydraulic lift system more stable, more uniform flow distribution, air conditioning water system of hydraulic balance, but the reverse return system and the more obvious downside, hoses, pipes, tubes and pipes to consume, so for all system pipeline layout is not possible to use reverse return. Through analysis, it is not difficult to find air conditioning water system does not require the use of reverse return hoses. Types of terminal equipment, there are fan-coil and air-conditioning hood, combined air-conditioning unit, at the end of the cold air flow rate, and a difference of more, on the other hand table of cold dishes may be three drainage pipe hose, four pipe or six pipes, so the difference between the water resistance of the device itself is relatively large, fan-coil water resistance mostly 1 ~ 3Kpa, air hood resistance mostly 4 ~ 6Kpa, fan-coil and air-conditioning wind tank mixed within one system layout using reverse return is clearly laid out for reverse return a "firmly," not only to the advantage of reverse return arrangement, but detrimental to the system of water regulating air hood. We know that the use of fan coil water system water points, with balancing valve and ordinary water conditioning valves are clearlyNot possible, the air-conditioning system design, fan-coil and air-conditioning hood set in different air conditioning water system, fan-coil layout using reverse return layout, use of different leg of the air conditioning hood, air-conditioning end pipeline configuration boxes of electric valve and the valve can make up different path layout negative, achieve the hydraulic balance. The author is a gymnasium in the design of the air-conditioning system using the same layout strategy, game Hall surrounding ancillary rooms with fan coil system, the portion of the water system piping layout using reverse return to the game Hall, the lobby lounge, and other services of high winds combined air conditioner, air conditioning, between the end of the hood is far, using reverse return layout clearly economical unreasonable, the author takes a different path layout and the end of the pipeline configuration balance valve and electric 2-way valve, the first regulation good individual air-conditioning hood balance valve on the pipeline, and each branch of the hydraulic balance through regulation freezing room set water separator on various branches of the valve, it can be successfully implemented.

3.2 terminal equipment pipeline accessories set

For air conditioning Terminal side cold water system, terminal equipment piping is very critical. Terminal equipment services in different regions, water air conditioning system is free to decide whether the end device has sufficient cooling output, so the end device pipeline set the necessary filter, thermometers, pressure gauge, the electric valve, balance valve, etc. as a secondary protection or determine the fault of measures to ensure the smooth flow of the waterway. For example, fan-coil inlet pipeline of proposals setting filters, because fan coil itself upon the small pipe section, blocked, flush is often will not solve the problem of the lack of filter block, the installation of irrigation, welding slag or refuse extremely easy to plug the fan coil pipe coolers. For air conditioning hood frozen fles should set water filters, at the inlet and outlet should be located on the pressure gauge, thermometer, electric control valves, etc., while the return duct testing hole on the reserve, with the help of these valves accessories to air conditioning system debugging. Such as a gymnasium of combined air-conditioning units in the debugging process, the wind out of the Hall there is wind, but in the empty field of indoor air temperature is always maintained at 26 degrees, is unable to further to fall. Total air tube through the test hole, measuring air temperature found air temperature is 23 degrees centigrade, it is clear that the supply air temperature differential is not up to the original design of the 10-degree temperature difference. Enter the air conditioning room inspection revealed: cold water pipe on valve fully open, chilled water inlet temperature 7.5 degrees, and back it up to temperature of 20 degrees, into the return pipe pressure readings on the poor only 1kpa, consequently, it is projected through the air conditioning unit of cold water and cooling tubes, the estimated amount of deviation less air conditioning unit table near the cold control zone in ducts obstruction, take apart and wash the filters, or cannot be resolved, issue a final concentration in the air cooler tubes, after a more complete removal, discover the pipe coolers are blocked, after construction waste more comprehensive washing problems before receiving the final solution.

4. concluding remarks

From the above analysis, we can further the understanding of the following:

4.1 chillers and refrigeration pump capacity allocation, air conditioning and cold water system running on the most effective energy saving and consumption reduction at source;

4.2 air-conditioning cooling system design should consider the room side of the effective operation and management of design solutions, so that the system is in energy saving, high efficiency, economy of operation; and the system design should consider non-design conditions, especially for single unit runs a chilled water pump overload resolution measures;

4.3 pressure differential bypass is a control unit operation number of the important means reasonable set pressure value, in order to give full play to the unit's effectiveness;

4.4 room side of the pipeline-related location should be set the necessary control accessories to enhance debugging ease of operation and management of work;

4.5 chilled water system piping layout using reverse return or ISO range must be considered terminal equipment itself water resistance characteristics, taking into account how to adapt to future commissioning work cold water system piping should take the necessary measures.