1. Introduction

The central air-conditioning system has widely applied to the industry and the civil domain, in the guesthouse, the hotel, the office, the market, the in-patient department building, the industry workshop central air-conditioning system, its refrigeration compression unit, the freezing circulating water system, the cooling circulating water system, the cooling tower air blower system and so on the capacity mostly is defers to the building biggest refrigeration, the system hot load designation, also again remains has the sufficient remainder. In does not have the use to have in the load 随动 adjustment characteristic control system, regardless of the season, how the day and night and the user load does change, various electrical machinery all for a long time fix under the labor frequency condition the full speed movement, has created the energy huge waste. In recent years as a result of the electrovalence unceasing rise, caused the central air-conditioning system operating cost suddenly to rise, causes it to occupy the more and more great proportion in the entire building transport business cost expense, adds present each production, service industry competition intensely, the most enterprises profit space insufficiently is ideal. Therefore the electrical energy expense control obviously already became manages the superintendent matter of concern to be at. Statistics have indicated, the central air conditioning occupies each kind of building with the electric quantity always to use the electric quantity above 70%, central air conditioning water pump power consumption approximately composes the total air-conditioning system power consumption 20~40%, when saves the low load the compressor system and the aqueous system consumption energy, has the very vital significance. Therefore, but the automatic control change variable current quantity frequency conversion air conditioning aqueous system and the auto-adapted intelligent load adjustment compressor system arises at the historic moment along with the load change, and gradually demonstrates its huge superiority, moreover obtains more and more many is widely promoted and the application. Uses the frequency conversion velocity modulation technology not only to be able to enable the air-conditioning system to display the more ideal active status, more importantly the usual its energy conservation effect reaches as high as above 30%, the energy band comes the good economic efficiency.

2. Central air-conditioning system general structure and principle of work

The central air-conditioning system generally mainly by the refrigeration compressor system, the cold intermediary (freezing and cold is hot) the circulating water system, the cooling circulating water system, the plate tube air blower system, the cooling tower air blower system and so on is composed. Its craft structure flow chart like attempts A to show, in attempts in A to refrigerate the compression unit through the compressor the refrigerant (cold intermediary medium like R134a, R22 and so on) compresses the fluid queen mother to deliver in the evaporator, the freezing circulation aqueous system through freezes the water pump to enter the normal temperature water pump in the evaporator plate tube to carry on with the cold intermediary the indirect heat exchange, such original often the lukewarm water turned the low temperature freezing water, the freezing water has been delivered various air blowers gusty area in the cooling coil to attract around the closing tube the air quantity of heat, produced the low temperature air wafted each room from the plate tube air blower, thus achieved the temperature decrease the goal. Leng Mei fully reduces after the evaporator and follows the thermal absorption process to complete, again is delivered in the condenser to restore the atmospheric pressure condition, in order to Leng Mei releases the quantity of heat in the condenser, its release quantity of heat is precisely carries off through the recirculated cooling water system cooling water. The cooling circulating water system often the lukewarm water will pump into the condenser heat change plate tube after the cooling water pump, again has changed this the hot cooling water to deliver in the cooling tower, will carry on the natural cooling or by the cooling tower to it carries on through the cooling tower air blower to it sprays the type force forced-air cooling, will carry on the full heat change with the atmosphere between, will cause the cooling water to change the normal temperature, in order to again will circulate the use. Needs to make the heat when the winter, the central air-conditioning system only needs (to be called through the cold hot water pump in summer freezes water pump) to enter the normal temperature water pump the steam heat interchanger the plate tube, through delivers again after the steam full heat change the hot water various floors in the air blower plate tube, then realizes to the user provides the heating hot blast.
Understood the central air-conditioning system technical process is very important regarding the energy conservation transformation realization, looked from the causal relation angle, the freezing aqueous system, the cooling water system, the cooling tower air blower system is the host compressor system servosystem. When the host compressor system load changes, to freezes the water, the cooling water demand quantity and the cooling tower demand cooling amount of wind also has the corresponding change, because of so, we only then is having the energy conservation transformation the prerequisite condition, only then has the realization "the distribution according to need" the control plan possibility.

3. Central air-conditioning system energy conservation principle

The central air-conditioning system may divide into two big kinds according to the load type, (1) changes the torque loading: If air blower, water pump class load and so on cooling water system, freezing aqueous system, cooling tower air blower system; (2) Permanent torque loading: If host refrigeration compressor system. The different torque type has the completely different torque power relations characteristic, we knew the air blower, the water pump class change the torque loading characteristic to satisfy the hydrodynamics relations theory, namely following mathematical relation establishment:
N1/N2 �?Q1/Q2 H1/H2 �?(N1/N2) 2 P1/P2 �?(N1/N2) 3 (1)

Among them, N, H, Q, P separately expressed the rotational speed, the current capacity, lift, the shaft power.
May know by type 1, if rpm drop to rated speed 70%, then, will lift drops to the rated value 50%, simultaneously, the axis output will drop to the rated value 35%. May see from chart 2, the pipe network damping along with lifts reduces reduces. In satisfies the system basically to lift the demand under the situation, if the system current capacity demand reduces to time fixed current capacity 50%, under frequency conversion control mode, its correspondence output only approximately for rated power 13%. This has provided mathematics theoretically feasibility safeguard space for the implementation frequency conversion energy conservation technological transformations.

By the above fluid transmission facility water pump, the air blower principle of work may know: The water pump, the air blower current capacity (amount of wind) if transfers the intensive direct ratio; The water pump, the air blower pressure (lifts) if the rotational speed square to have the direct ratio, but the water pump, the air blower shaft power is equal to the current capacity and the pressure product, therefore the water pump, the air blower shaft power if the rotational speed cubic (cubicly has the direct ratio namely to have direct ratio with supply frequency) to act according to the above principle to be possible to know: Changes the water pump, the air blower rotational speed may change the water pump, the air blower power. For example: Will supply power the frequency to reduce to 45Hz by 50Hz, then P45/P50=453/503=0.729, namely P45=0.729P50 (P will be electrical machinery shaft power); Will supply power the frequency to reduce to 40Hz by 50Hz, then P40/P50=403/503=0.512, namely P40=0.512P50 (P will be electrical machinery shaft power).
May see by the above content, carries on with the frequency changer when the current capacity (amount of wind) controls, may save the massive electrical energies. Central air-conditioning system when design is, its cooling which considered according to the scene most greatly cold quantity demand quantity pumps, the freezing pumps, in the actual use which considered according to the single equipment biggest operating mode has 90% much time, cooling pumps, the freezing pumps all works under the non- full-load conditions. But with the valve, the self acting valve adjustment not only increased the system to reduce expenses to lose, moreover because to the air conditioning adjustment was gradual, created the entire air-conditioning system work in the undulation condition; But through pumps, the freezing in cooling pumps installs the frequency changer to be possible to solve this problem once and for all, but also may realize the automatic control, and the passable frequency conversion energy conservation has recouped the outlay of capital. Simultaneously the frequency changer soft start function and the smooth velocity modulation characteristic may realize to the system steady adjustment, causes the system active status to be stable, and lengthens the unit and the network management service life.

4. Under we mainly discuss the implementation plan and the application effect which the cooling tower air blower use frequency conversion conserves energy

4.1 cooling towers air blowers frequency conversion control implementation plan

Plan one: Fixed frequency conversion control mode.

Because of cooling tower pattern: Has the single tower pattern, and the multi- towers pattern; Therefore, fixed frequency conversion control mode: May divide into the single fixed frequency conversion control and many fixed frequency conversion control. Under take many fixed frequency conversion control as the example, makes the following explanation.
This system is composed by the frequency conversion return route and the labor frequency return route two parts:

Frequency conversion return route: By a frequency changer, air switch QF2, exchanges contact device KM02 and the frequency conversion operating control return route and the signal reports to the police the return route to be composed the frequency conversion shuttle service return route. Labor frequency return route: By air switch QF1, QF3, QF4, QF5, exchange contact device KM01, KM03, KM04, KM05, and thermal relay FR1, FR2, FR3, FR4, as well as constitution labor frequency and so on manual operating control return route (50Hz) moves the return route.

Movement way:

When labor frequency movement: The air blower assigns the air blower according to the labor frequency control loop choice to start, and by 50HZ full speed movement.

When frequency conversion movement: The air blower by the sensor measured the actual water temperature, passes through the warm controlling transformation standard electric current signal or the voltage signal, delivers the frequency changer to trace draws up the input end, when the first frequency conversion electrical machinery achieves the full load movement, but also cannot satisfy the actual operating mode then second Taiwan Telegraphic Transmission machine can start by the labor frequency, first Taiwan Telegraphic Transmission machine still frequency conversion movement; Same principle, after if second Taiwan Telegraphic Transmission machine starting, but also cannot satisfy the operating mode then third Taiwan Telegraphic Transmission machine can by the labor frequency starting; This time, three Taiwan Telegraphic Transmission machine all moves: First Taiwan Telegraphic Transmission machine frequency conversion movement, second Taiwan Telegraphic Transmission mechanic frequency movement, third Taiwan Telegraphic Transmission mechanic frequency movement.

Plan two: Circulation frequency conversion control mode.

May know by P �?n3: The air blower conserves energy the preferred plan controls the air blower rotational speed, the passable change electrical machinery control system has adjusted the electrical machinery movement the rotational speed, thus achieved the control air blower rotational speed the goal, under take three same powers electrical machinery cooling tower as an example, makes the following explanation: Three typhoons machine for identical power the electrical machinery, may use a frequency changer cyclic control the way movement, the system electricity principle survey chart, as follows shows:
This control system is composed by the frequency conversion return route and the labor frequency return route two parts:

Frequency conversion return route: By a frequency changer, air switch Q1, exchanges contact device KM1, KM3, KM5 and the automatic operating control return route and the signal reports to the police the return route to be composed the frequency conversion shuttle service return route. Labor frequency return route: Air switch QF2, QF3, QF4, exchange contact device KM2, KM4, KM6 and thermal relay FR1, FR2, FR3 as well as constitution labor frequency and so on manual operating control return route (5 this control system is composed by the frequency conversion return route and the labor frequency return route two parts:

Frequency conversion return route: By a frequency changer, air switch QF3, exchanges contact device KM4, KM5, KM6 and the automatic operating control return route and the signal reports to the police the return route to be composed the frequency conversion shuttle service return route. Labor frequency return route: Air switch QF0, QF1, QF2, exchange contact device KM1, KM2, KM3 and thermal relay FR1, FR2, FR3 as well as constitution labor frequency and so on manual operating control return route (50Hz) moves the return route.

Movement way:

The normal state, the change-over switch cuts to the automatic movement return route, determines the cooling tower water leakage temperature by the temperature sensor, passes through the warm controlling transformation standard electric current signal or the voltage signal, delivers the frequency changer to trace draws up the input end to control the frequency changer the rotational speed, changes the air blower the amount of wind, thus changes the cooling tower the water leakage temperature; When a typhoon machine movement still could not answer the purpose, changed this frequency conversion movement air blower the labor frequency movement, again the frequency conversion started another typhoon machine, until satisfied the circulating water temperature which the production installment needed to achieve the technological requirement (namely water temperature <= 32°C). The entire control system is a closed loop governing system. According to the equipment technological requirement, automatically determined the air blower is the frequency conversion movement fortunately labor frequency movement. And achieves the air blower which first moves first to excise, various electrical machinery shuttle service, thus lengthens the useful life of equipment the goal. When the frequency conversion systems control return route or the frequency changer crash, the change-over switch will cut the manual condition, three Taiwan Telegraphic Transmission machine movement still might satisfy the installment technological requirement in the labor frequency condition.

4.2 take circulates the frequency conversion control mode to explain the circulating water cooling tower frequency conversion energy conservation as the example the effect:
4.2.1 circulating waters cooling towers movement survey

Some company altogether has 3 serial numbers for the water works respectively is 1#, 2# and the 3# circulating water cooling tower. Each production installment returns the circulation hot water with the pump delivery to these towers in, through the tower in padding increase hot water and the air contacted area and the time, the promotion hot water and the air carries on the heat change, causes circulating water cooling. Thus obtains each production installment to need the circulating water temperature <= 32 �?cold water.

When the ambient temperature elevates, starts in the cooling tower the axis customs handed down from past generation machine implementation forced draft, speeds up on the cooling tower padding to circulate the moisture to deal with the liquid phase the heat change. In each cooling tower installs 1 axis customs handed down from past generation machine, its diameter is 8500mm, by the voltage is 380V, the rated power is the 160kW 4 extremely asynchronous machines actuates. Between the electrical machinery gentle breeze machine uses the constant 减��?speed reducer straight association, in the tower does not install the throttle valve. Therefore the axis customs handed down from past generation machine rotational speed and the amount of wind are cannot move. 3 towers total handling abilities reach 8000m3/h, far is bigger than each production installment biggest demand quantity sum total 6600m3/h, 2002 year various towers movement parameter for details sees table 1 and table 2.

4.2.2 cooling towers air blowers use the frequency conversion velocity modulation energy conservation plan

4.2.2.1 air blowers energy conservation feasibility analysis:
Table 1 various towers movement parameter statistical table
The tower serial number handling ability (m3/h) the electrical machinery electric current (A) the electrical machinery voltage (V) the power factor (cos phi) the electrical machinery power input (kw) the electric power only consumes (kW/m3)
1 2,000 250 380 0.87 143 0.0715
2 3,000 200 380 0.87 115 0.0383
3 3,000 220 380 0.87 128 0.042
Data knowledge shows which by table 1: 2002 year cooling towers air blower all moves the period, the cooling tower enters the water temperature the maximum temperature mean value to distribute in 34.5 �?~ 38 �?in; After circulates Water Classic to cool, the cooling tower water leakage temperature maximum temperature mean value distributes in 27.6 �?~ 28.8 �?in, it compares each production installment to need the cooling water temperature 32 �?to be low 3.2 �?~ 4.4 �? And may know simultaneously is satisfying the cooling tower to enter the water temperature to be lower than the most high fever water temperature mean value and the cooling tower water leakage temperature is lower than 高冷 under water temperature mean value this condition, the single typhoon machine whole year running time is 2705h. If uses the frequency conversion controller adjustment air blower rotational speed, changes the air blower amount of wind, may make the cooling tower water leakage temperature to enhance in 2 �?~ 3 �? situations, still could satisfy the cooling tower water leakage temperature <= 32 �?technological requirements, this obviously might save the electrical energy. Provides according to the factory: A. The water leakage and the air wet-bulb temperature and the cooling tower enter the water temperature relations diagram of curves; B. Turnover water temperature difference and air wet-bulb temperature and air blower shaft power percentage relations diagram of curves; As well as table 2 related data, result in the air blower through the process design the different month of energy conservation potential and income value like table 3.
Table when 22,002 year different month of air blower movement and cooling tower water leakage temperature relations statistical table
The date movement number movement number of days moves =24h/d to move =24h/d simultaneously to satisfy (1) tau hotly enters <= tau hotly enters max (2) tau to be cold <= tau is cold max the timely breeze machine running time /h most high fever water temperature mean value tau hotly to enter the max/ �?nbsp;高冷 water temperature mean value tau to be coldest max/ �?br>    A number accumulation time /h number equally moves /h/b accumulation time /h   
On March 27 ~5 month on 17th 1 34 0 0 1 16.7 56.956569 million 517 37.6 27.6
On May 18 ~6 month on 16th 2 45 1 1,080 1 15 673 561 35.3 28
On June 17 ~8 month on 26th 3 69 2 3,312 1 21.45 1,480 1,028 38 28.8
On August 27 ~10 month on 13th 2 30 1 720 1 10.8 324 157 34.5 28.4
On October 14 ~11 month on 15th 1 44 0 0 1 15.8 693 442 34.5 28.4

Table 32,002 year different month of air blower energy conservation potential and income predicted value
The project content date cooling tower enters the water temperature/�?nbsp;temperature difference Zeta 1 �?nbsp;wet-bulb temperature/�?nbsp;correspondence different power ratio cold water temperature/�?nbsp;running time /h air blower power air blower energy conservation potential income rate/ten thousand Yuan
    Z2 Z1     
3.27-5.17 3.6 10 20.5 7.45 7.87 29.73 517 0.46P 0.54P 1.883
5.18-6.16 35.3 7.3 22.5 6.50 5.31 29.69 561 0.46P 0.54P 2.044
6.17~8.26 38 9.2 22.5 7.00 7.70 30.30 1,028 0.46P 0.40P 2.774
8.27~10.13 34.5 6.1 24 5.80 4.05 30.45 157 0.46P 0.54P 0.572
10.14~11.15 34.5 6.1 24 5.80 4.05 30.45 442 0.46P 0.54P 1,610
Note: The income rate = may running time * air blower energy conservation potential ×0.56 Yuan /kW• H×100%; In table P = 120.5kW;

Total income value =8.883 Yuan.

May know various cooling towers air blower energy conservation potential by table 3 is 40% ~ 54%.

4.2.3 air blowers frequency conversion velocity modulation implementation plan discussion

4.2.3.1 systems structures

By P �?n3 knowledge: The air blower conserves energy the preferred plan controls the air blower rotational speed, the passable change electrical machinery control system has adjusted the electrical machinery movement rotational speed, thus achieves the control air blower rotational speed the goal.

Because 3 typhoons machine actuations electrical machinery power is 160kW, may select 1 frequency conversion controller circulation method to move this system to be composed by 2 parts: Frequency conversion return route: 1 frequency changer, air switch Q1, exchanges contact device C1, C2, C3 and the automatic operating control return route and the signal reports to the police the return route composition frequency conversion shuttle service return route; Labor frequency return route: Air switch Q2, exchange contact device C4, C5, C6 and thermal relay T1, T2, T3 as well as constitution labor frequency and so on manual operating control return route (50Hz) moves the return route.

4.2.3.2 movements ways

The normal state, change-over switch QK cuts to the automatic movement return route, determines the cooling tower water leakage temperature by the temperature sensor, transforms the standard the electric current signal, delivers to the frequency changer temperature detector, uses in to control the cooling tower air blower rotational speed, changes the air blower the amount of wind, thus changes the cooling tower water leakage temperature; When 1 typhoon machine revolution frequency approaches the labor frequency movement still could not answer the purpose, this frequency conversion movement air blower changes the labor frequency movement, again the frequency conversion started another 1 typhoon machine, until satisfied the circulating water temperature which each production installment needed <= 32 �? The entire control system is a closed loop governing system.

According to the technological requirement, automatically determined the electrical machinery is the frequency conversion movement perhaps the labor frequency movement, and achieves the air blower which first moves first to excise, various electrical machinery shuttle service, thus lengthens the useful life of equipment. When the frequency changer crashes, the change-over switch QK cut to the manual condition, 3 Taiwan Telegraphic Transmission machine movement still might satisfy the movement request in the labor frequency condition.

Uses the frequency changer velocity modulation the method, changed the former electrical machinery to open, to stop is only the hand control sole labor frequency movement way, thus avoided for satisfying the cooling tower water leakage water temperature <= 32 �? had to cause 1 or several typhoons machine occupies under the labor frequency condition to move, but created the water temperature excessively to be low, forms the nonessential energy waste. Selects the frequency conversion velocity modulation movement method, enhanced the water temperature control accuracy, and may realize smoothly starts the electrical machinery, causes 3 Taiwan Telegraphic Transmission machine shuttle service, thus enhances the electrical machinery the service life.

4.2.4 air blowers energy conservation economic analysis

(1) the cooling tower movement parameter which shows by table 1 may know: 1 # tower handling ability only is 2# or the 3# tower 66%, but it processes the 1m3/h hot water air blower electric power only to consume really is the 2# tower and the 3# tower air blower electric power only consumes mean value 1.783 times (namely its big 0.0313kW/m3/h), its reason was this tower padding still for the old-style low effect padding, if changed to the 1# tower padding with the 2# tower same performance new highly effective padding, then each hour handling ability might enhance 1000m3. If according to the 1# tower process load is the 2000m3/h computation, each hour electricity saving 2000×0.0313 = 62.6kW, the energy conservation effect is quite considerable. The 1# tower every year the running time is 3000h, the replacement padding must invest approximately 450,000 Yuan.

Income rate = 3000×62.6×0.56/45×104×100% = 23.37%.

(2) uses the frequency conversion velocity modulation plan, may result in every year total income value according to table 3 is 88,830 Yuan, the implementation frequency conversion control needs to invest approximately 150,000 Yuan, the income rate =8.883/15×100% = 59.2%, approximately 1.7 years can take back the investment cost, moreover the equipment depreciation rate greatly reduces, obviously conserves energy the effect to be remarkable.

5. always states
The intelligent building and the function workshop high speed development, causes the present building and the workshop energy consumption is more and more big, the energy conservation method use is a question which each superintendent and the operators all must consider. But conserves energy is the present whole world attention idea subject, but speaks the frequency changer energy conservation on at present is the best investment least energy conservation way and the control mode. Then, as cooling tower user if after understood the frequency changer conserves energy advantage. Regarding the such few investments naturally is extremely being glad.

Said regarding the cooling tower production factory that, one kind of new product investment production first looked the market the demand and can produce the benefit, through the above economic analysis, we may obtain the use only then so long as after understood the frequency changer application merit, based on the movement cost and the maintenance of equipment consideration, inevitably could have the strong interest to such investment. But in fact at present in market regarding cooling tower frequency changer application already extremely maturity, moreover also is facing this direction fast development. The frequency changer application is the present entire cooling tower market and even the entire central air conditioning market tendency, looked according to the present market conditions, more early invests the economic efficiency which the frequency changer the application merchant receives inevitably is quicker. Certainly this need cooling tower merchant sales personnel carries on the frequency changer technology explanation to the customer which exhaustive arrives. But the cooling tower producer after has grasped the frequency changer technology, the control section hardware income and the technical service income, all might become a new profit growth spot. In the long-range view, the cooling tower frequency changer application superiority can more and more obvious, the frequency changer use also can be more and more common, the merchant after used the cooling tower frequency conversion technology not only to be allowed to obtain the income moreover also to be possible to cause own cooling tower to be in the initiative position for a long time in the intense market competition.

Although can have the personnel in the earlier period investment to provide and so on the investment, but looked from the long term standpoint that, this investment to the cooling tower merchant said will certainly to receive the rich profit repayment.