An energy efficiency optimization control method for evaporative condensing chillers

Abstract

The present invention discloses an energy efficiency optimization control method for an evaporative condensing chiller, which couples and calculates the operating powers of the fan, water pump and compressor of an evaporative condenser, selects the optimal point of total power in real time according to the current load based on a calculation model embedded in a controller of the unit, sets the operating frequency of a frequency conversion device according to the optimal point parameters, and can achieve the highest energy efficiency point under each load, thereby reducing the operating energy consumption and operating cost of the chiller; at the same time, by controlling the operating frequency and guide vane opening of the compressor, low-load and full-load protection of the fan and water pump of the chiller is achieved, thereby ensuring the stable operation of the unit under extreme working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of chiller operation control, and in particular to an energy efficiency optimization control method for an evaporative condensing chiller. Background Art

[0002] During the operation of the evaporative condensing chiller, the refrigerant on the condensing side does not enter the cooling tower for heat exchange through cooling water, but is directly condensed in the evaporative condenser. The system does not require cooling water circuits and cooling towers. The system has a simple structure, good operating stability, and high heat exchange efficiency, and has been widely used in the industrial field.

[0003] The existing conventional evaporative condenser energy adjustment method is to determine the load increase and decrease of the fan and water pump according to the high and low pressure difference of the system, so as to adjust the fan and water pump frequency. In this way, the evaporative condenser is adjusted independently, and the load increase and decrease of the fan and water pump are not comprehensively considered with the energy consumption of other equipment in the unit. The frequency of each frequency conversion device cannot be adjusted in real time according to the overall energy efficiency optimal point of the unit, and the optimal operating efficiency of the whole unit cannot be achieved. In addition, when the unit is in extreme operating conditions, because the condensing temperature reaches the set value boundary, the fan and water pump will run at full load for a long time or start and stop frequently, which will affect the operating life of the unit. Summary of the invention

[0004] Technical purpose: In view of the shortcomings of the existing energy regulation methods of chillers, the present invention discloses an energy efficiency optimization control method for evaporative condensing chillers.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0006] A method for optimizing energy efficiency of an evaporative condensing chiller, wherein the chiller comprises an evaporative condenser, a compressor, an evaporator and a liquid storage tank, and is characterized in that the method comprises the following steps:

[0007] S01. Calculate the heat release of the evaporative condenser according to the user-side refrigeration load and the compressor operating power;

[0008] S02. Determine the state parameters of the air and water in the chiller according to the dry-bulb and wet-bulb temperatures of the air, wherein the state parameters include the enthalpy and moisture content of the inlet and outlet air, the enthalpy and moisture content of the air at the water film, and the average enthalpy and moisture content of the air;

[0009] S03, calculating the condensing pressure according to the current evaporative condenser heat release, wet bulb temperature, evaporative condenser fan frequency, and evaporative condenser water pump frequency, and using the condensing pressure as the exhaust pressure of the compressor;

[0010] S04. Establish a total power and user-side load model for the chiller, take the operating point with the minimum total power as the optimal operating point, and adjust the operation of the chiller.

[0011] Preferably, in step S01 of the present invention, the cooling capacity and operating power of the compressor are calculated based on the compressor suction pressure, exhaust pressure, isentropic efficiency, guide vane opening and bearing speed of the chiller, and the heat release of the evaporative condenser is the sum of the user-side refrigeration load and the operating power of the compressor.

[0012] Preferably, in step S02 of the present invention, the inlet air enthalpy value h i and the humidity content of the incoming air d in The dry-bulb and wet-bulb temperatures of the air are determined in the psychrometric diagram, and the outlet enthalpy is Where Q is the heat released by the evaporative condenser, m a is the inlet air mass flow rate, outlet air humidity content d out It is calculated and determined by the isothermal and humid ratio lines of the psychrometric diagram; the air enthalpy value at the water film h w and moisture content d w Determine the spray water temperature by looking up the enthalpy-humidity diagram; the average enthalpy of the air Average moisture content m It is determined by calculation using the isothermal and humid ratio lines on the psychrometric diagram.

[0013] Preferably, in step S03 of the present invention, the process of calculating the condensing pressure of the chiller includes:

[0014] S031. Calculate the air volume and spray water flow rate under the current working condition according to the frequency and flow rate of the evaporative condenser fan and water pump under the design working condition;

[0015] S032. Calculate the heat transfer coefficient inside the tube, the heat transfer coefficient between the water film and the tube wall, and the equivalent heat transfer coefficient between the water film and the air of the evaporative condenser; and then determine the total heat transfer coefficient of the evaporative condenser;

[0016] S033. Calculate the condensation temperature based on the total heat transfer coefficient, and determine the final condensation pressure based on the condensation temperature.

[0017] Preferably, the process of determining the operating power of the compressor of the present invention includes:

[0018] S011. Obtain the current guide vane opening, frequency, suction pressure and exhaust pressure of the compressor from the chiller, and calculate the mass flow rate and isentropic efficiency of the compressor;

[0019] S012. Calculate the compressor inlet and outlet enthalpy difference, and calculate the compressor operating power based on the mass flow rate and the inlet and outlet enthalpy difference.

[0020] Preferably, in step S04 of the present invention, the process of determining the optimal operating point includes:

[0021] S041. According to the upper and lower limits of the equipment frequency adjustment of the chiller under the current user-side cooling load, the chiller is divided into scales, the total power of the chiller corresponding to each scale point is calculated, and the scale point with the minimum total power of the chiller under the current scale is determined as the primary minimum scale point;

[0022] S042, performing secondary division on the division range adjacent to the primary minimum division point, calculating the total power of the chiller again, and determining the secondary minimum division point;

[0023] S03. Referring to the division method of the primary minimum division point, divide the division range adjacent to the secondary minimum division point again, and iterate in sequence. After reaching the set number of iterations, take the division point with the minimum total power of the chiller determined by the last calculation as the optimal operating point, and adjust the operation of the chiller.

[0024] Preferably, in the process of determining the optimal operating point of the chiller, the present invention sets low-load protection and full-load protection for the evaporative condenser fan and water pump, and makes the load of the fan and water pump stay away from the full-load operating point and the shutdown operating point by changing the operating frequency or guide vane opening of the chiller compressor.

[0025] Beneficial effects: The energy efficiency optimization control method of an evaporative condensing chiller disclosed in the present invention has the following beneficial effects:

[0026] 1. The present invention couples and calculates the operating power of the evaporative condenser fan, water pump and compressor, selects the optimal operating point with the minimum total power according to the current load in real time, and sets the operating frequency of the frequency conversion equipment according to the parameters of the optimal operating point, so as to achieve the highest energy efficiency point under each load, thereby achieving the purpose of energy saving.

[0027] 2. The present invention sets full load and low load protection at the full load operating point and shutdown operating point of the fan and water pump. By adjusting the operating frequency or guide vane opening of the compressor, the operation of the condenser is protected to avoid overload or frequent start and stop, thereby extending the service life of the equipment.

[0028] 3. The control method of the present invention can embed the overall control model into the controller of the chiller, thereby automatically acquiring the operating parameters of the chiller for automatic control. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are set forth herein below. Each embodiment and example is provided by way of explanation of the apparatus, composition and materials of the present disclosure, rather than limitation. On the contrary, the following description provides a convenient illustration of an exemplary embodiment for implementing the present disclosure. In fact, it will be clear to those skilled in the art that various modifications and variations may be made in the teachings of the present disclosure without departing from the scope or spirit of the present disclosure.

[0030] The present invention discloses an energy efficiency optimization control method for an evaporative condensing chiller, wherein the chiller comprises an evaporative condenser, a compressor, an evaporator and a liquid storage tank, wherein the evaporative condenser and the compressor in the chiller may be one or more units, and in this embodiment, one unit is used as an example for description; wherein the compressor is a variable frequency centrifugal compressor with adjustable frequency and guide vane opening, and the fan and the water pump in the evaporative condenser are both variable frequency with adjustable frequency; the control method comprises the steps of:

[0031] S01. Calculate the heat release of the evaporative condenser according to the user-side refrigeration load and the compressor operating power;

[0032] The cooling load at the user end can be obtained through the gateway device, which is recorded as Q1; the process of determining the compressor operating power Ps includes:

[0033] S011. Obtain the current guide vane opening, frequency, suction pressure and exhaust pressure of the compressor from the chiller, and calculate the mass flow rate and isentropic efficiency of the compressor;

[0034] By using CFD simulation analysis, the relationship between the compressor pressure ratio, frequency, guide vane opening, flow rate, and isentropic efficiency is established, and different performance relationship equations are fitted to realize the calculation of the isentropic efficiency and refrigerant mass flow rate at any operating point of the compressor.

[0035] S012. Calculate the compressor inlet and outlet enthalpy difference, and calculate the compressor operating power based on the mass flow rate and the inlet and outlet enthalpy difference.

[0036] The superheated steam enthalpy value h1 at the compressor suction port is determined in the pressure-enthalpy diagram according to the evaporation pressure and superheat; the isentropic compression outlet enthalpy value h2 is determined in the pressure-enthalpy diagram according to the isentropic line of the compressor suction state point and the condensation pressure; the actual compressor outlet enthalpy value h3 is determined according to the isentropic efficiency: η represents the isentropic efficiency.

[0037] The compressor operating power Ps = M (h3-h1), where M is the refrigerant mass flow rate.

[0038] The heat release of the evaporative condenser is Q=Q1+Ps.

[0039] S02. Determine the state parameters of the air and water in the chiller according to the dry-bulb and wet-bulb temperatures of the air, wherein the state parameters include the enthalpy and moisture content of the inlet and outlet air, the enthalpy and moisture content of the air at the water film, and the average enthalpy and moisture content of the air;

[0040] Inlet air enthalpy h i and the humidity content of the incoming air d in The dry-bulb and wet-bulb temperatures of the air are determined in the psychrometric diagram, and the outlet enthalpy is Where Q is the heat released by the evaporative condenser, m a is the inlet air mass flow rate, outlet air humidity content d out It is calculated and determined by the isothermal and humid ratio lines of the psychrometric diagram; the air enthalpy value at the water film h w and moisture content d w Determine the spray water temperature by looking up the enthalpy-humidity diagram; the average enthalpy of the air Average moisture content m It is determined by calculation using the isothermal and humid ratio lines on the psychrometric diagram.

[0041] S03. Calculate the condensing pressure according to the current heat release of the evaporative condenser, the wet bulb temperature, the fan frequency of the evaporative condenser, and the water pump frequency of the evaporative condenser, and use the condensing pressure as the exhaust pressure of the compressor.

[0042] The process of calculating the chiller condensing pressure includes:

[0043] S031. Calculate the air volume and spray water flow rate under the current working condition according to the frequency and flow rate of the evaporative condenser fan and water pump under the design working condition;

[0044] Use similarity theory to calculate air volume and spray water flow:

[0045] where f f0 、f p0 is the fan and water pump frequency under design conditions, V0 and G0 are the fan and water pump flow rates of the evaporative condenser under design conditions, f f1 、f p1 It is the fan and water pump frequency under the current working condition.

[0046] S032. Calculate the heat transfer coefficient in the tube of the evaporative condenser Where q is the heat flux, d i is the inner diameter of the heat exchange tube, β is the material coefficient, Where λ is the thermal conductivity of the refrigerant, ρ is the density of the refrigerant, g is the acceleration of gravity, γ is the latent heat of vaporization of the refrigerant in this state, and μ is the dynamic viscosity of the refrigerant in this state;

[0047] Calculate the heat transfer coefficient between water film and tube wall: Where G is the spray water flow rate, L is the pipe length, n is the number of pipes directly sprayed by the spray water, and d o is the outer diameter of the heat exchange tube;

[0048] Calculate the equivalent heat transfer coefficient between water film and air: Where Z is the water film temperature correction coefficient, βw 是 The correction coefficient of the contact area between the water film and the air is 1.3 to 1.5, hw is the saturated air enthalpy on the water film surface, h m is the average enthalpy of air, t w is the water film temperature, t m is the average air temperature, a wc is the convective heat transfer coefficient between water film and air: where λ m is the average thermal conductivity of air, υ m is the average kinematic viscosity of air, v max is the air velocity at the narrowest surface, Where s is the distance between heat exchange tubes, v is the headwind speed, Where L1 is the length of the air inlet, and W is the width of the air inlet;

[0049] Finally, determine the total heat transfer coefficient of the evaporative condenser: where r i is the thermal resistance of dirt in the pipe, r o It is the thermal resistance of dirt outside the tube.

[0050] S033. Calculate the condensation temperature based on the total heat transfer coefficient, and determine the final condensation pressure based on the condensation temperature.

[0051] Evaporative condenser heat transfer Q = kA (t k -t m ), where A is the total heat exchange area of ​​the evaporative condenser, t k is: condensation temperature; t m is: the average temperature outside the tube; from this condensation temperature, the condensation pressure pc = f(t k ).

[0052] S04. Establish a total power and user-side load model for the chiller, take the operating point with the minimum total power as the optimal operating point, and adjust the operation of the chiller.

[0053] The total operating power of the refrigeration unit = compressor power + fan power + water pump power. Change the compressor frequency, guide vane opening, fan frequency and water pump frequency within the set range to obtain the corresponding total power. Adjust the compressor frequency, guide vane, fan and water pump frequency based on the minimum total power value among all the data.

[0054] Fan power: Pump power: Where N f0 、N p0 is the power of the fan and water pump under design conditions.

[0055] The process of determining the optimal operating point includes:

[0056] S041. According to the upper and lower limits of the equipment frequency adjustment of the chiller under the current user-side cooling load, the chiller is divided into scales, the total power of the chiller corresponding to each scale point is calculated, and the scale point with the minimum total power of the chiller under the current scale is determined as the primary minimum scale point;

[0057] S042, performing secondary division on the division range adjacent to the primary minimum division point, calculating the total power of the chiller again, and determining the secondary minimum division point;

[0058] S03. Referring to the division method of the primary minimum division point, divide the division range adjacent to the secondary minimum division point again, and iterate in sequence. After reaching the set number of iterations, take the division point with the minimum total power of the chiller determined by the last calculation as the optimal operating point, and adjust the operation of the chiller.

[0059] In addition, in the process of determining the optimal operating point of the chiller, the present invention sets low-load protection and full-load protection for the evaporative condenser fan and water pump, and by changing the operating frequency or guide vane opening of the chiller compressor, the load of the fan and water pump is kept away from the full-load operating point and the shutdown operating point. In extreme summer conditions, it is ensured that when a certain range is reached before the full-load operating point of the fan or water pump, the compressor operating frequency or guide vane opening is increased to reduce the load of the fan and water pump, thereby ensuring that the fan and water pump will not run at full load for too long; in extreme winter conditions, when a certain range is reached before the shutdown operating point of the fan or water pump, the compressor operating frequency or guide vane opening is reduced to increase the load of the fan and water pump, thereby ensuring that the fan and water pump will not start and stop frequently. By using the control method of the present invention, it is possible to automatically control according to the operating conditions during the operation of the chiller, reduce operating energy consumption, and ensure long-term stable operation of the unit under extreme conditions.

Claims

1. A method for optimizing energy efficiency of an evaporative condensing chiller, wherein the chiller comprises an evaporative condenser, a compressor, an evaporator and a liquid receiver, wherein: Includes steps: S01. Calculate the heat release of the evaporative condenser according to the user-side refrigeration load and the compressor operating power; S02. Determine the state parameters of the air and water in the chiller according to the dry-bulb and wet-bulb temperatures of the air, wherein the state parameters include the enthalpy and moisture content of the inlet and outlet air, the enthalpy and moisture content of the air at the water film, and the average enthalpy and moisture content of the air; S03, calculating the condensing pressure according to the current evaporative condenser heat release, wet bulb temperature, evaporative condenser fan frequency, and evaporative condenser water pump frequency, and using the condensing pressure as the exhaust pressure of the compressor; S04, establish the total power of the chiller and the user-end load model, take the operating point with the minimum total power of the chiller as the optimal operating point, and adjust the operation of the chiller; In step S01, the compressor cooling capacity and compressor operating power are calculated according to the compressor suction pressure, exhaust pressure, isentropic efficiency, guide vane opening and bearing speed of the chiller. The heat release of the evaporative condenser is the sum of the user-side refrigeration load and the compressor operating power. In step S03, the process of calculating the condensing pressure of the chiller includes: S031. Calculate the air volume and spray water flow rate under the current working condition according to the frequency and flow rate of the evaporative condenser fan and water pump under the design working condition; S032. Calculate the heat transfer coefficient inside the tube, the heat transfer coefficient between the water film and the tube wall, and the equivalent heat transfer coefficient between the water film and the air of the evaporative condenser; and then determine the total heat transfer coefficient of the evaporative condenser; S033. Calculate the condensation temperature according to the total heat transfer coefficient of the evaporative condenser, and determine the final condensation pressure according to the condensation temperature; Evaporative condenser heat transfer , where A is the total heat exchange area of ​​the evaporative condenser, is: condensation temperature; is: the average temperature outside the tube, k is the total heat transfer coefficient of the evaporative condenser.

2. The method for optimizing energy efficiency of an evaporative condensing chiller according to claim 1, characterized in that: In step S02, the air inlet enthalpy and humidity content of incoming air The dry-bulb and wet-bulb temperatures of the air are determined in the psychrometric diagram, and the outlet enthalpy is , where Q is the heat released by the evaporative condenser, is the inlet air mass flow rate, outlet air humidity Calculated and determined by the isothermal and humid ratio lines of the psychrometric diagram; the air enthalpy at the water film and moisture content Determine the spray water temperature by looking up the enthalpy-humidity diagram; the average enthalpy of the air , average moisture content It is determined by calculation using the isothermal and humid ratio lines on the psychrometric diagram.

3. The method for optimizing energy efficiency of an evaporative condensing chiller according to claim 1, characterized in that: The process of determining the compressor operating power includes: S011. Obtain the current guide vane opening, frequency, suction pressure and exhaust pressure of the compressor from the chiller, and calculate the mass flow rate and isentropic efficiency of the compressor; S012. Calculate the compressor inlet and outlet enthalpy difference, and calculate the compressor operating power based on the compressor mass flow rate and the compressor inlet and outlet enthalpy difference.

4. The method for optimizing energy efficiency of an evaporative condensing chiller according to claim 1, characterized in that: In step S04, the process of determining the optimal operating point includes: S041. According to the upper and lower limits of the equipment frequency adjustment of the chiller under the current user-side cooling load, the chiller is divided into scales, the total power of the chiller corresponding to each scale point is calculated, and the scale point with the minimum total power of the chiller under the current scale is determined as the primary minimum scale point; S042, performing secondary division on the division range adjacent to the primary minimum division point, calculating the total power of the chiller again, and determining the secondary minimum division point; S03. Referring to the division method of the primary minimum division point, divide the division range adjacent to the secondary minimum division point again, and iterate in sequence. After reaching the set number of iterations, take the division point with the minimum total power of the chiller determined by the last calculation as the optimal operating point, and adjust the operation of the chiller.

5. The method for optimizing energy efficiency of an evaporative condensing chiller according to claim 4, characterized in that: In the process of determining the optimal operating point of the chiller, low-load protection and full-load protection are set for the evaporative condenser fan and water pump. By changing the operating frequency or guide vane opening of the chiller compressor, the load of the fan and water pump is kept away from the full-load operating point and the shutdown operating point.

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