CN118066678A - Variable differential pressure set value optimization control method for air conditioner water system for improving thermodynamic stability - Google Patents

Variable differential pressure set value optimization control method for air conditioner water system for improving thermodynamic stability Download PDF

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CN118066678A
CN118066678A CN202410204922.8A CN202410204922A CN118066678A CN 118066678 A CN118066678 A CN 118066678A CN 202410204922 A CN202410204922 A CN 202410204922A CN 118066678 A CN118066678 A CN 118066678A
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valve position
branch
set value
air
temperature
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赵天怡
王翌婷
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Dalian University of Technology
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Dalian University of Technology
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

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Abstract

The invention relates to the technical field of building environment control, in particular to an air conditioner water system variable pressure difference set value optimization control method for improving thermal stability. The method comprises the following steps: s1, identifying an active branch and a passive branch. S2, controlling a water pump differential pressure set value control strategy based on thermal stability: s2.1, defining an optimal valve position domain; s2.2, evaluating an index Ts of overall thermodynamic stability; s2.3, controlling a strategy based on a water pump differential pressure set value of the thermal stability Ts. The method defines a parameter reflecting the coupling characteristic between branches and the influence degree of external disturbance on the branch energy supply capacity, namely thermodynamic stability, and introduces the concept of thermodynamic stability into actual variable flow control. The method can improve and balance the thermodynamic stability of each branch in the air conditioner water system, enhance the adjustability of the cooling capacity of the active branch unit, and can better realize the energy-saving effect.

Description

Variable differential pressure set value optimization control method for air conditioner water system for improving thermodynamic stability
Technical Field
The invention relates to the technical field of building environment control, in particular to an air conditioner water system variable pressure difference set value optimization control method for improving thermal stability.
Background
Building energy conservation is an important measure for realizing carbon-to-peak carbon neutralization. With the increase of labor cost and energy cost, the operation and maintenance of automatic and energy-saving building equipment systems are increasingly important to building owners, particularly managers of large public buildings. The heating ventilation air conditioner is an energy-saving large household in a building, is also an electromechanical system with the most complex control, and the building automation is a key for realizing the automatic and energy-saving operation of building equipment. Among them, the problems presented by the central air-conditioning water system are more common and prominent, and the variable flow technology is one of the most representative optimizing control means for the air-conditioning water system.
In the pressure difference control process of the building central air-conditioning water system, the strong coupling relation of hydraulic and thermal characteristics of each branch and the change of pressure difference set values can influence the energy supply of a non-adverse thermal loop, and the energy supply is reflected as the valve position of a branch regulating valve: the branch with the smaller valve position consumes more water pump energy, and the branch with the larger valve position is likely to become the most unfavorable thermodynamic loop in the next period, and the pressure difference set value is required to continue to be optimally set. The reciprocating circulation is performed in such a way, along with the random change of the user load, the global branch is more likely to have 'bipolar differentiation' of energy supply capacity, valve positions of some branches are larger and larger, and the adjustability is deteriorated to cause that the branches are more sensitive to fluctuation of system pressure and poorer in external disturbance resistance; the valve positions of other branches are smaller and smaller, so that more water pump energy consumption is consumed, the system impedance is increased, and the energy-saving effect of pressure difference optimization setting is weakened. However, some existing differential pressure control strategies for obtaining good energy-saving effects cannot obtain ideal thermal stability, frequent movements of each branch valve position are unfavorable for service life of an executing mechanism, and from the consideration of a longer evaluation period, poor thermal stability leads to poor overall energy conservation of the water pump, and poor robustness of a control system.
Disclosure of Invention
Aiming at the problem that the overall stability of the system is reduced due to the fact that part of branches actively regulate flow and then influence the cooling effect of users in other branches due to the load change in the operation process of the building air-conditioning water system, the invention defines a parameter reflecting the influence degree of coupling characteristics and external disturbance between branches on the energy supply capacity of the branches, namely thermodynamic stability, and introduces the concept of thermodynamic stability into actual variable flow control, thereby providing an air-conditioning water system variable pressure difference set value optimization control method for improving the thermodynamic stability. The method can improve the thermal stability of the pipe network, improve and balance the thermal stability of each branch, enhance the adjustability of the cooling capacity of the active branch unit and better realize the energy-saving effect.
The technical scheme of the invention is as follows:
An air conditioner water system variable differential pressure set value optimization control method for improving thermodynamic stability comprises the following steps:
S1, identification of active branch and passive branch
In the regulation process of the variable flow air conditioner water system, due to random change of load, a group of active branches and passive branches exist in the system in any period, and the branches actively regulated due to load change of a user in the system are defined as active branches C; the remaining branches in the system are passive loops E. The active branch is subject to flow regulation because the user load demand on the active branch changes, which can cause the flow of the passive branch to change, thereby affecting the cooling or heating capacity. When the amount of cooling or heating of the passive branch changes to a certain extent, the regulating valve of the passive branch starts to regulate, which is caused by the influence of the regulation of the active branch on the flow of the passive branch.
S2, controlling strategy of pressure difference set value of water pump based on thermodynamic stability
S2.1 optimal valve position Domain definition
As the equal-percentage regulating valve commonly adopted by the terminal equipment has the characteristics that the valve position is close to the full opening, the impedance change rate of the regulating valve is smaller, the influence of the valve position change on the impedance change is very small when the valve position is close to the full opening, and the valve position area has a wider valve position change range. The valve position range [ delta MIN, 100% ] with very little influence of valve position change on impedance at near full open is defined as the optimally set valve position range for the differential pressure set value; for regulating valves with other characteristics, the selection method of the optimally set valve position domain of the differential pressure set value is consistent with that of the equal-percentage regulating valve.
The loop in which the branch with the maximum regulating valve position delta MAX in a certain period is positioned is defined as the maximum valve position loop of the air-conditioning water system in the period. Defining a range of δ MAX [ δ RSTMIN,δRSTMAX ] as the optimal valve position range, wherein the upper limit of the range, δ RSTMAX, is some level close to 100%; while at the same time ensuring that the variation range of delta MAX is within the pressure differential set point optimum set valve position, the lower limit of this range delta RSTMIN is at a level slightly greater than delta MIN. The pressure difference set point is optimally set to maximize delta MAX in the optimal valve position range.
The optimal valve position domain may be expressed as [ delta RST-δD,δRST+δD ] with the center of the optimal valve position domain defined as delta RST and the width defined as delta D.
S2.2 evaluation index Ts of overall thermodynamic stability
S2.2.1 end control algorithm
Let t AOSPTi be the air supply temperature set value of the air conditioning unit surface cooler on branch i, DEG C; t AODi is the robust area of the air supply temperature set value of the surface cooler of the air conditioning unit on the branch i, and is at the temperature; t AOi is the air supply temperature of the surface cooler of the air conditioning unit on the branch i, and the temperature is lower than the air supply temperature.
For continuously adjustable air conditioning terminals, the control algorithm for the supply air temperature of the variable air handling unit AHU may be expressed as follows: when the air supply temperature changes in the area [ t AOSPTi-tAODi,tAOSPTi+tAODi ], the regulating valve does not act; when the air supply temperature is greater than t AOSPTi+tAODi or less than t AOSPTi-tAODi, the valve position change delta i of the regulating valve is proportionally regulated according to the deviation between the air supply temperature and the set value, as shown in the following formula.
Wherein K TD is a proportional adjustment constant corresponding to valve position adjustment; k TI is a proportional adjustment constant corresponding to the valve position increase.
For the AHU and the fan coil FCU of the constant-air-volume air processing unit, the opening degree of the valve is adjusted according to the return air temperature, and the air supply temperature can be changed into the return air temperature.
S2.2.2 integral thermodynamic stability evaluation index Ts
The total amplitude of the changes of the cooling capacity or the heating capacity corresponding to each passive branch in the current period is defined as the overall thermodynamic stability, and the index can reflect the overall thermodynamic stability of each passive branch in the current period and can be simply obtained through monitoring parameters. And selecting the maximum value of the absolute deviation between the air supply temperature of each passive branch and the set value of the air supply temperature in the investigation period as an evaluation index of the overall thermal stability of each passive branch, and setting the maximum value as T S. T S has different expressions depending on the control form of the terminal.
For a variable air handling unit AHU,
Wherein T Sj is the j passive branch thermodynamic stability evaluation index, and the temperature is lower than the temperature; m is the total number of sampling points in the investigation period; i is the serial number of the sampling point in the investigation period; t SAj (i) is the ith sampling point of the air supply temperature on the passive branch j, and is at the temperature; t SASPTj is the air supply temperature set point on the passive branch j, DEG C.
For the constant air volume air handling unit AHU and the fan coil FCU, the air supply temperature is changed into the return air temperature.
The smaller the T S value is, the smaller the fluctuation of the cold supply or the heat supply of the passive branch is, and the smaller the influence of the active branch on the passive branch is, namely, the good thermodynamic stability is provided. The larger the value of T S, the larger the fluctuation of the cooling/heating power of the passive branch is, and the larger the influence of the active branch on the passive branch is, which means that the thermal stability is poor.
The reference value T S used to evaluate the thermodynamic stability depends on the control accuracy of the system and the fluctuation of the user load. On the one hand, if the reference value of T S is too high, the air conditioning effect of the user or the indoor environment control precision will be affected, on the other hand, for the user with frequent load fluctuation, the heat exchange working condition of the air conditioning equipment has larger variation amplitude in a specific period, at this time, the reference value of T S should not be too low, and the thermal stability can be classified into very good, better, general, worse and very poor according to the setting of the reference value.
Ts < a, very good thermal stability; a is less than or equal to Ts < b, preferably; b is less than or equal to Ts < c, and is general; c is less than or equal to Ts < d, and is worse; ts is more than or equal to d, very bad; wherein a, b, c, d is a constant, defined as the very good, better, general, worse threshold of thermal stability, respectively.
S2.3 control strategy for pressure difference set value of water pump based on thermal stability Ts
Comprehensively considering the adjustability of the cooling or heating capacity of the unit, the thermodynamic stability and the energy consumption of the water pump, and combining the tail end adjusting mode in S2.2.1, a linear adjusting algorithm of a water pump differential pressure set value DP SPT is provided:
For an AHU of a variable air volume air conditioning unit,
(1) When Ts > b, i.e. thermally unstable, the pressure set point is adjusted in combination with the end valve opening condition, considering that the end device has a certain adjustment capacity:
When the maximum valve opening of the end is large, i.e., δ MAX>(δRST+δD), it indicates that the end device cannot meet the user's demand by adjusting the valve opening, and thus it is necessary to increase the cold or heat supply capacity of the end device by increasing the differential pressure set point.
When the opening of the end maximum valve is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, and the energy consumption of the water pump is further reduced.
In the rest of the cases, no adjustment is required.
(2) When Ts < = b, i.e. thermally stable, the end valve state can be combined to determine whether the energy consumption can be further reduced:
when the end maximum valve opening is large, i.e., δ MAX>(δRST-δD), no adjustment is required.
When the opening of the tail end valve is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, and then the energy consumption of the water pump is reduced.
In the rest of the cases, no adjustment is required.
The mathematical expression of the differential pressure set point DP SPT is as follows:
Where δ MAX is the maximum valve position loop valve position (%); t AOMAX is the maximum valve position loop corresponding to the air supply temperature of the unit, if a plurality of maximum valve position loops exist in the system, the maximum value (DEG C) of the air supply temperature of the unit on the loops is taken; δ RST is the center (%) of the optimal valve position domain; δ D is the width (%) of the optimal valve position domain; k DPD is the corresponding linear adjustment constant for the pressure difference set value reduction; k DPI is the corresponding linear adjustment constant of the pressure difference set value increase.
For the AHU of the constant-air-volume air conditioning unit, the air supply temperature in the algorithm is replaced by the return air temperature.
For the on-off regulation type air conditioner water system with the tail end of the fan coil FCU, the system form can be simplified into n air conditioner water systems with continuous regulating valve risers, and the valve opening can reflect the working condition of a considerable number of fan coils. Therefore, for on-off regulated water systems, the above end valve opening is replaced with a riser valve opening.
The invention has the beneficial effects that:
The invention firstly defines an evaluation index for the thermodynamic stability of the variable flow air conditioner water system, and based on the evaluation index, provides a thermodynamic stability-based optimal control strategy for the variable pressure difference set value of the air conditioner water system, which can improve and balance the thermodynamic stability of each branch in the water system, can better realize the energy-saving effect, and solves the optimal control problem of the variable pressure difference of the continuous adjustment type air conditioner water system aiming at improving the conveying energy efficiency to a certain extent.
Drawings
Fig. 1 is a flowchart of an optimal control method for a variable differential pressure set value of an air-conditioning water system for improving thermal stability.
Fig. 2 is a schematic diagram of an active branch and passive branch adjustment process.
Detailed Description
Specific embodiments of the present invention will be described in detail below with reference to the summary and drawings.
As shown in fig. 1, an air-conditioning water system variable pressure difference set value optimization control method for improving thermal stability comprises the following steps:
S1, identification of active branch and passive branch
In the regulation process of the variable flow air conditioner water system, due to random change of load, a group of active branches and passive branches exist in the system in any period, and the branches actively regulated due to load change of a user in the system are defined as active branches C; the remaining branches in the system are passive loops E. The active branch is subject to flow regulation because the user load demand on the active branch changes, which can cause the flow of the passive branch to change, thereby affecting the cooling or heating capacity. When the amount of cooling or heating of the passive branch changes to a certain extent, the regulating valve of the passive branch starts to regulate, which is caused by the influence of the regulation of the active branch on the flow of the passive branch.
S2, controlling strategy of pressure difference set value of water pump based on thermodynamic stability
S2.1 optimal valve position Domain definition
As the equal-percentage regulating valve commonly adopted by the terminal equipment has the characteristics that the valve position is close to the full opening, the impedance change rate of the regulating valve is smaller, the influence of the valve position change on the impedance change is very small when the valve position is close to the full opening, and the valve position area has a wider valve position change range. The valve position range [ delta MIN, 100% ] with very little influence of valve position change on impedance at near full open is defined as the optimally set valve position range for the differential pressure set value; for regulating valves with other characteristics, the selection method of the optimally set valve position domain of the differential pressure set value is consistent with that of the equal-percentage regulating valve.
The loop in which the branch with the maximum regulating valve position delta MAX in a certain period is positioned is defined as the maximum valve position loop of the air-conditioning water system in the period. Defining a range of δ MAX [ δ RSTMIN,δRSTMAX ] as the optimal valve position range, wherein the upper limit of the range, δ RSTMAX, is some level close to 100%; while at the same time ensuring that the variation range of delta MAX is within the pressure differential set point optimum set valve position, the lower limit of this range delta RSTMIN is at a level slightly greater than delta MIN. The pressure difference set point is optimally set to maximize delta MAX in the optimal valve position range.
The optimal valve position domain may be expressed as [ delta RST-δD,δRST+δD ] with the center of the optimal valve position domain defined as delta RST and the width defined as delta D.
S2.2 evaluation index Ts of overall thermodynamic stability
S2.2.1 end control algorithm
Let t AOSPTi be the air supply temperature set value of the air conditioning unit surface cooler on branch i, DEG C; t AODi is the robust area of the air supply temperature set value of the surface cooler of the air conditioning unit on the branch i, and is at the temperature; t AOi is the air supply temperature of the surface cooler of the air conditioning unit on the branch i, and the temperature is lower than the air supply temperature.
For continuously adjustable air conditioning terminals, for variable air handling unit AHU, the control algorithm for supply air temperature can be expressed as follows: when the air supply temperature changes in the area [ t AOSPTi-tAODi,tAOSPTi+tAODi ], the regulating valve does not act; when the air supply temperature is greater than t AOSPTi+tAODi or less than t AOSPTi-tAODi, the valve position change delta i of the regulating valve is proportionally regulated according to the deviation between the air supply temperature and the set value, as shown in the following formula.
Wherein K TD is a proportional adjustment constant corresponding to valve position adjustment; k TI is a proportional adjustment constant corresponding to the valve position increase.
For the AHU and the fan coil FCU of the constant-air-volume air processing unit, the opening degree of the valve is adjusted according to the return air temperature, and the air supply temperature can be changed into the return air temperature.
S2.2.2 integral thermodynamic stability evaluation index Ts
The total amplitude of the changes of the cooling capacity or the heating capacity corresponding to each passive branch in the current period is defined as the overall thermodynamic stability, and the index can reflect the overall thermodynamic stability of each passive branch in the current period and can be simply obtained through monitoring parameters. And selecting the maximum value of the absolute deviation between the air supply temperature of each passive branch and the set value of the air supply temperature in the investigation period as an evaluation index of the overall thermal stability of each passive branch, and setting the maximum value as T S. T S has different expressions depending on the control form of the terminal.
For a variable air handling unit AHU,
Wherein T Sj is the j passive branch thermodynamic stability evaluation index, and the temperature is lower than the temperature; m is the total number of sampling points in the investigation period; i is the serial number of the sampling point in the investigation period; t sAj (i) is the ith sampling point of the air supply temperature on the passive branch j, and is at the temperature; t SASPTj is the air supply temperature set point on the passive branch j, DEG C.
For the constant air volume air handling unit AHU and the fan coil FCU, the air supply temperature is changed into the return air temperature.
The smaller the T S value is, the smaller the fluctuation of the cold supply or the heat supply of the passive branch is, and the smaller the influence of the active branch on the passive branch is, namely, the good thermodynamic stability is provided. The larger the value of T S, the larger the fluctuation of the cooling/heating power of the passive branch is, and the larger the influence of the active branch on the passive branch is, which means that the thermal stability is poor.
The reference value T S used to evaluate the thermodynamic stability depends on the control accuracy of the system and the fluctuation of the user load. On the one hand, if the reference value of T S is too high, the air conditioning effect of the user or the indoor environment control precision will be affected, on the other hand, for the user with frequent load fluctuation, the heat exchange working condition of the air conditioning equipment has larger variation amplitude in a specific period, at this time, the reference value of T S should not be too low, and the thermal stability can be classified into very good, better, general, worse and very poor according to the setting of the reference value.
Ts < a, very good thermal stability; a is less than or equal to Ts < b, preferably; b is less than or equal to Ts < c, and is general; c is less than or equal to Ts < d, and is worse; ts is not less than d, very bad.
Wherein a, b, c, d is a constant, defined as the very good, better, general, worse threshold of thermal stability, respectively. The recommended value of a, b, c, d is 0.1,0.3,0.5,1 in consideration of the thermal comfort of the user.
S2.3 control strategy for pressure difference set value of water pump based on thermal stability Ts
Comprehensively considering the adjustability of the cooling or heating capacity of the unit, the thermodynamic stability and the energy consumption of the water pump, and combining the tail end adjusting mode in S2.2.1, a linear adjusting algorithm of a water pump differential pressure set value DP SPT is provided:
For an AHU of a variable air volume air conditioning unit,
(1) When Ts > b, i.e. thermally unstable, the pressure set point is adjusted in combination with the end valve opening condition, considering that the end device has a certain adjustment capacity:
When the maximum valve opening of the end is large, i.e., δ MAX>(δRST+δD), it indicates that the end device cannot meet the user's demand by adjusting the valve opening, and thus it is necessary to increase the cold or heat supply capacity of the end device by increasing the differential pressure set point.
When the opening of the end maximum valve is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, and the energy consumption of the water pump is further reduced.
In the rest of the cases, no adjustment is required.
(2) When Ts < = b, i.e. thermally stable, the end valve state can be combined to determine whether the energy consumption can be further reduced:
when the end maximum valve opening is large, i.e., δ MAX>(δRST-δD), no adjustment is required.
When the opening of the tail end valve is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, and then the energy consumption of the water pump is reduced.
In the rest of the cases, no adjustment is required.
In summary, the adjustment logic is summarized as follows:
The mathematical expression of the differential pressure set point DP SPT is as follows:
Where δ MAX is the maximum valve position loop valve position (%); t AOMAX is the maximum valve position loop corresponding to the air supply temperature of the unit, if a plurality of maximum valve position loops exist in the system, the maximum value (DEG C) of the air supply temperature of the unit on the loops is taken; δ RST is the center (%) of the optimal valve position domain; δ D is the width (%) of the optimal valve position domain; k DPD is the corresponding linear adjustment constant for the pressure difference set value reduction; k DPI is the corresponding linear adjustment constant of the pressure difference set value increase.
For the AHU of the constant-air-volume air conditioning unit, the air supply temperature in the algorithm is replaced by the return air temperature.
For the on-off regulation type air conditioner water system with the tail end of the fan coil FCU, the system form can be simplified into n air conditioner water systems with continuous regulating valve risers, and the valve opening can reflect the working condition of a considerable number of fan coils. Therefore, for on-off regulated water systems, the above end valve opening is replaced with a riser valve opening.
S2.3.2 default parameter set
The parameters in the algorithm of the embodiment should be selected by comprehensively considering the adjustability of the cooling/heating capacity of the unit, the thermodynamic stability of the system and the energy consumption of the water pump. From the perspective of the thermodynamic stability of the system, the change condition of the air supply temperature can represent the thermodynamic stability condition, and the thermodynamic stability of the system can be judged according to the reference value Ts for evaluating the thermodynamic stability. From the angle of adjustability, the larger the step length of the pressure difference set value change is, the better the adjustability is, and the unit can reach the cooling capacity required by a user in a shorter adjustment time. The following are default values for each parameter in the present algorithm:

Claims (1)

1. An air conditioner water system variable pressure difference set value optimization control method for improving thermal stability is characterized by comprising the following steps:
S1, identification of active branch and passive branch
In the regulation process of the variable flow air conditioner water system, due to random change of load, a group of active branches and passive branches exist in the system in any period, and the branches actively regulated due to load change of a user in the system are defined as active branches C; the rest branch circuits in the system are passive loops E;
S2, controlling strategy of pressure difference set value of water pump based on thermodynamic stability
S2.1 optimal valve position Domain definition
As the constant percentage regulating valve commonly adopted by the terminal equipment has the characteristics that the valve position is close to the full opening, the impedance change rate of the regulating valve is smaller, when the valve position is close to the full opening, the influence of the valve position change on the impedance change is very small, and the valve position domain has a wider valve position change range; the valve position range [ delta MIN, 100% ] with very little influence of valve position change on impedance at near full open is defined as the optimally set valve position range for the differential pressure set value; for regulating valves with other characteristics, the selection method of optimally setting valve position domain by the pressure difference set value is consistent with that of the equal-percentage regulating valve;
Defining a loop where a branch with a maximum regulating valve position delta MAX in a certain period is located as a maximum valve position loop of an air-conditioning water system in the period; defining a range of δ MAX [ δ RSTMIN,δRSTMAX ] as the optimal valve position range, wherein the upper limit of the range, δ RSTMAX, is some level close to 100%; at the same time, in order to ensure that the variation range of delta MAX is within the pressure difference set point optimization setting valve position, the lower limit value delta RSTMIN of the range is a certain level which is slightly larger than delta MIN; the aim of optimally setting the differential pressure set value is to ensure that delta MAX is in the optimal valve position range as far as possible;
Defining the center of the optimal valve position domain as delta RST and the width as delta D, the optimal valve position domain is denoted as [ delta RST-δD,δRSTMAX+δD ];
S2.2 evaluation index Ts of overall thermodynamic stability
Let t AOSPTi be the air supply temperature set value of the air conditioning unit surface cooler on branch i, DEG C; t AODi is the robust area of the air supply temperature set value of the surface cooler of the air conditioning unit on the branch i, and is at the temperature; t AOi is the air supply temperature of the surface cooler of the air conditioning unit on the branch i, and the temperature is lower than the air supply temperature;
(1) For continuously adjustable air conditioning terminals, the control algorithm for the supply air temperature of the variable air volume air handling unit AHU is expressed as follows: when the air supply temperature changes in the area [ t AOSPTi-tAODi,tAOSPTi+tAODi ], the regulating valve does not act; when the air supply temperature is greater than t AOSPTi+tAODi or less than t AOSPTi-tAODi, the valve position change delta i of the regulating valve is proportionally regulated according to the deviation between the air supply temperature and a set value, as shown in the following formula;
wherein K TD is a proportional adjustment constant corresponding to valve position adjustment; k TI is a proportional adjustment constant corresponding to valve position increase;
for the AHU and the fan coil FCU of the fixed-air-volume air processing unit, the opening of a valve is adjusted according to the return air temperature, and the supply air temperature can be changed into the return air temperature;
(2) The total amplitude of the change of the cooling capacity or the heating capacity corresponding to each passive branch in the current period is defined as the overall thermodynamic stability, and the index reflects the overall thermodynamic stability of each passive branch in the current period and can be simply obtained through monitoring parameters; selecting the maximum value of the absolute deviation between the air supply temperature of each passive branch and the set value of the air supply temperature in the investigation period as an evaluation index of the overall thermal stability of each passive branch, and setting the maximum value as T S; t S has different expressions according to the control forms of the terminals;
for a variable air volume AHU,
Wherein T Sj is the j passive branch thermodynamic stability evaluation index, and the temperature is lower than the temperature; m is the total number of sampling points in the investigation period; i is the serial number of the sampling point in the investigation period; t Sj (i) is the ith sampling point of the air supply temperature on the passive branch j, and is at the temperature; t AOSPTj is the air supply temperature set value on the passive branch j, and DEG C;
for the constant air volume AHU and FCU, changing the air supply temperature into the return air temperature;
The smaller the T S value is, the smaller the fluctuation of the cold supply or the heat supply of the passive branch is, and the smaller the influence of the active branch on the passive branch is, namely the good thermodynamic stability is achieved; the larger the T S value is, the larger the fluctuation of the cold supply/heat supply quantity of the passive branch is, and the larger the influence of the active branch on the passive branch is, namely the poor thermal stability is;
The reference value T S used to evaluate the thermodynamic stability depends on the control accuracy of the system and on the fluctuation of the user load; thermal stability can be classified as very good, better, general, worse, and very poor according to the setting of the reference value;
Ts < a, very good thermal stability; a is less than or equal to Ts < b, preferably; b is less than or equal to Ts < c, and is general; c is less than or equal to Ts < d, and is worse; ts is more than or equal to d, very bad; wherein a, b, c, d is a constant, defined as very good, better, general, worse thresholds of thermal stability, respectively;
S2.3 control strategy for pressure difference set value of water pump based on thermal stability Ts
Comprehensively considering the adjustability of the cooling or heating capacity of the unit, the thermodynamic stability and the energy consumption of the water pump, and combining the tail end adjusting mode in S2.2.1, a linear adjusting algorithm of a water pump differential pressure set value DP SPT is provided:
(1) When Ts > b, i.e. thermally unstable, the pressure set point is adjusted in combination with the end valve opening condition, considering that the end device has a certain adjustment capacity:
When the maximum valve opening of the tail end is larger, namely delta MAX>(δRST+δD, the tail end equipment cannot meet the user requirement by adjusting the valve opening, so that the cold and heat supply capacity or the heat supply capacity of the tail end equipment needs to be improved by improving the pressure difference set value;
when the opening of the maximum valve at the tail end is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, and then the energy consumption of the water pump is reduced;
(2) When Ts < = b, i.e. thermally stable, the end valve state can be combined to determine whether the energy consumption can be further reduced:
when the opening of the end maximum valve is larger, delta MAX>(δRST-δD is not needed to be adjusted;
when the opening of the tail end valve is smaller, namely delta MAX<(δRST-δD, the pressure difference set value can be reduced, so that the energy consumption of the water pump is reduced;
The rest conditions are not required to be regulated;
The mathematical expression of the differential pressure set point DP SPT is as follows:
Wherein, delta MAX is the maximum valve position loop valve position value,%; t AOMAX is the maximum valve position loop corresponding to the air supply temperature of the unit, if a plurality of maximum valve position loops exist in the system, the maximum value of the air supply temperature of the unit on the loops is taken, and the temperature is DEG C; delta RST is the center,%; delta D is the width of the optimal valve position domain,%; k DPD is the corresponding linear adjustment constant for the pressure difference set value reduction; k DPI is the corresponding linear adjustment constant of the pressure difference set value increase.
CN202410204922.8A 2024-02-23 2024-02-23 Variable differential pressure set value optimization control method for air conditioner water system for improving thermodynamic stability Pending CN118066678A (en)

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