This document proposes a hybrid PID-cascade control system for HVAC systems to improve control performance. It models the heat exchanger and air conditioning space components of an HVAC system. It then designs a hybrid PID-cascade controller that combines traditional PID control with an internal cascade loop. Simulations show the hybrid controller has faster response, better setpoint tracking and disturbance rejection compared to traditional PID, compensator and Ziegler-Nichols tuned PID controllers. The cascade control inner loop improves response speed and precision, while the outer PID loop enhances stability and disturbance rejection for the HVAC system.
Solar air heater (SAH), which is the most essential component of solar drying systems, receive solar energy and convert it into thermal energy. This review presents descriptions and previous works conducted on performances analysis of SAHs. Exergoenviroeconomic, exergoenvironmental, environmental, and exergy analyses are also presented. In addition, results on the performances of SAHs are summarized. The exergy and energy efficiencies of SAHs at laboratorium testing range from 8% to 61% and from 30% to 79%, respectively.
Solar air heater (SAH), which is the most essential component of solar drying systems, receive solar energy and convert it into thermal energy. This review presents descriptions and previous works conducted on performances analysis of SAHs. Exergoenviroeconomic, exergoenvironmental, environmental, and exergy analyses are also presented. In addition, results on the performances of SAHs are summarized. The exergy and energy efficiencies of SAHs at laboratorium testing range from 8% to 61% and from 30% to 79%, respectively.
Comparative Study of ECONOMISER Using the CFD Analysis IJMER
This paper presents a simulation of the economizer zone, which allowsstudying the flow
patterns developed in the fluid, while it flows along the length of the economizer. The past failure
details revelsthat erosion is more in U-bend areas of Economizer Unit because of increase in flue gas
velocity near these bends. But it isobserved that the velocity of flue gases surprisingly increases near
the lower bends as compared to upper ones. The model issolved using conventional CFD techniques by
FLUENT software. In which the individual tubes are treated as sub-gridfeatures. A geometrical model
is used to describe the multiplicity of heat-exchanging structures and the interconnectionsamong them.
The Computational Fluid Dynamics (CFD) approach is utilised for the creation of a three-dimensional
modelof the economizer coil of single column tube. With equilibrium assumption applied for
description of the system chemistry. The flue gastemperature, pressure and velocity field of fluid flow
within an economizer tube using the actual bounda
The use of a new control method for grid-connected inverters for reducing the output current harmonic distortion in a wide range of grid-connected distributed generation (DG) applications, including wind turbine (WT) and fuel cell (FC) inverters is proposed in this paper. The control method designed to eliminate main harmonics in a microgrid (MG) and between MG and point of common coupling (PCC) and responsible for the correction of the system unbalance. Another advantage of the proposed control method is that it can be easily adopted into the DG control system without the installation of extra hardware. The proposed control method is comprised of the synchronous reference frame method (SRF). Results from the proposed control method are provided to show the feasibility of the proposed approach.
IRJET-Detailed Energy Audit in a Captive Cogeneration PlantIRJET Journal
D.Rajani Kant , B.Sudheer Prem Kumar, N.Ravi Kumar, R.Virendra,J.Suresh Babu " Detailed Energy Audit in a Captive Cogeneration Plant ", International Research Journal of Engineering and Technology (IRJET), Volume2,issue-01 April 2015.e-ISSN:2395-0056, p-ISSN:2395-0072. www.irjet.net
Abstract
The rate of exploitation of the energy resources has been expanding over time and resulted in reduction of fossil fuel reserves. Efficiency of all resources is crucial both in environmental and economic sense. Using energy inefficiently creates waste in all the world’s economies. It has environmental impacts with regional, local and global implications.The key object is to adopt energy management in every field in order to reduce the wastage of energy sources and cost effectiveness without affecting productivity and growth.
Exergy analysis of inlet water temperature of condenserIJERA Editor
The most of the power plant designed by energetic performance criteria based on first law of thermodynamics. According to First law of thermodynamics energy analysis cannot be justified the losses of energy.The method of exergy analysis is well suited to describe true magnitude of waste and loss to be determined. Such information can be used in the design of new energy efficient system and increasing the efficiency of existing systems.In the present study exergy analysis of the shell and tube condenser is carried out. As the condenser is one of the major components of the power plant, so it is necessary to operate the condenser efficiently under the various operating condition to increase the overall efficiency of the power plant. In the present study inlet temperature of the condenser is optimized using the exergy method. The main aim of paper is to be find out causes of energy destruction that can be helpful to redesign the system and to increase the efficiency
Cfd and conjugate heat transfer analysis of heat sinks with different fin geo...eSAT Journals
Abstract Heat sinks are commonly used for cooling of electronic devices. Heat sinks, an array of heat fins, remove the heat from the surfaces of the chips by enhancing the heat Transfer rate through heat conduction process. Heat can also be removed from the chip surfaces through forced convection heat transfer. In this project work, CFD and conjugate heat transfer analysis is carried out for various fin geometries with Zigzag, Fluted, Slanted mirror, Custom pin fin and staggered array configurations for low thermal resistance and minimum pressure drop. Numerical simulations are carried out for each of the above mentioned fin geometries with common base plate thickness of 2 mm, fin height of 28 mm and fin thickness of 1 mm for three different heat loads namely 50 W, 75 W and 100 W with air flow of 3.933 m/s (15 ft3/min or 15 CFM) and air inlet temperature of 25oC. The results are compared for thermal performance of a heat sink for each of above geometries and it is observe that the fin with Slanted Mirror geometry gives the best performance among all the other geometries for minimum Pressure drop. The average heat transfer coefficients for fins with slanted mirror geometry, zig zag configuration, fluted type, custom pin fin and staggered array are found to be 215 W/m2K, 164 W/m2K, 164 W/m2K, 157 W/m2K and 145 W/m2K respectively Keywords: Fin geometries of Heat sinks, Computational Fluid Dynamics, Conjugate heat transfer.
ESTIMATION AND ANALYSIS OF CYCLE EFFICIENCY FOR SHELL AND TUBE HEAT EXCHANGER...IAEME Publication
Shell and tube Heat exchanger (STHE) is one of the most common and widely used energy transporter suited for domestic usages as well as industrial applications. In this paper, we consider shell and tube heat exchanger as a device with known input and output parameters. This work utilizes imperative design constraints like tube configuration, fluids, surface and temperature (constant magnitude) as input parameters and energetic cycle efficiency considered as desired output parameter depicting performance of the device. The model was trained and tested by proposed Genetic algorithm (GA) technique. This entire computational procedure is implemented in MATLAB platform.
Comparative Study of ECONOMISER Using the CFD Analysis IJMER
This paper presents a simulation of the economizer zone, which allowsstudying the flow
patterns developed in the fluid, while it flows along the length of the economizer. The past failure
details revelsthat erosion is more in U-bend areas of Economizer Unit because of increase in flue gas
velocity near these bends. But it isobserved that the velocity of flue gases surprisingly increases near
the lower bends as compared to upper ones. The model issolved using conventional CFD techniques by
FLUENT software. In which the individual tubes are treated as sub-gridfeatures. A geometrical model
is used to describe the multiplicity of heat-exchanging structures and the interconnectionsamong them.
The Computational Fluid Dynamics (CFD) approach is utilised for the creation of a three-dimensional
modelof the economizer coil of single column tube. With equilibrium assumption applied for
description of the system chemistry. The flue gastemperature, pressure and velocity field of fluid flow
within an economizer tube using the actual bounda
The use of a new control method for grid-connected inverters for reducing the output current harmonic distortion in a wide range of grid-connected distributed generation (DG) applications, including wind turbine (WT) and fuel cell (FC) inverters is proposed in this paper. The control method designed to eliminate main harmonics in a microgrid (MG) and between MG and point of common coupling (PCC) and responsible for the correction of the system unbalance. Another advantage of the proposed control method is that it can be easily adopted into the DG control system without the installation of extra hardware. The proposed control method is comprised of the synchronous reference frame method (SRF). Results from the proposed control method are provided to show the feasibility of the proposed approach.
IRJET-Detailed Energy Audit in a Captive Cogeneration PlantIRJET Journal
D.Rajani Kant , B.Sudheer Prem Kumar, N.Ravi Kumar, R.Virendra,J.Suresh Babu " Detailed Energy Audit in a Captive Cogeneration Plant ", International Research Journal of Engineering and Technology (IRJET), Volume2,issue-01 April 2015.e-ISSN:2395-0056, p-ISSN:2395-0072. www.irjet.net
Abstract
The rate of exploitation of the energy resources has been expanding over time and resulted in reduction of fossil fuel reserves. Efficiency of all resources is crucial both in environmental and economic sense. Using energy inefficiently creates waste in all the world’s economies. It has environmental impacts with regional, local and global implications.The key object is to adopt energy management in every field in order to reduce the wastage of energy sources and cost effectiveness without affecting productivity and growth.
Exergy analysis of inlet water temperature of condenserIJERA Editor
The most of the power plant designed by energetic performance criteria based on first law of thermodynamics. According to First law of thermodynamics energy analysis cannot be justified the losses of energy.The method of exergy analysis is well suited to describe true magnitude of waste and loss to be determined. Such information can be used in the design of new energy efficient system and increasing the efficiency of existing systems.In the present study exergy analysis of the shell and tube condenser is carried out. As the condenser is one of the major components of the power plant, so it is necessary to operate the condenser efficiently under the various operating condition to increase the overall efficiency of the power plant. In the present study inlet temperature of the condenser is optimized using the exergy method. The main aim of paper is to be find out causes of energy destruction that can be helpful to redesign the system and to increase the efficiency
Cfd and conjugate heat transfer analysis of heat sinks with different fin geo...eSAT Journals
Abstract Heat sinks are commonly used for cooling of electronic devices. Heat sinks, an array of heat fins, remove the heat from the surfaces of the chips by enhancing the heat Transfer rate through heat conduction process. Heat can also be removed from the chip surfaces through forced convection heat transfer. In this project work, CFD and conjugate heat transfer analysis is carried out for various fin geometries with Zigzag, Fluted, Slanted mirror, Custom pin fin and staggered array configurations for low thermal resistance and minimum pressure drop. Numerical simulations are carried out for each of the above mentioned fin geometries with common base plate thickness of 2 mm, fin height of 28 mm and fin thickness of 1 mm for three different heat loads namely 50 W, 75 W and 100 W with air flow of 3.933 m/s (15 ft3/min or 15 CFM) and air inlet temperature of 25oC. The results are compared for thermal performance of a heat sink for each of above geometries and it is observe that the fin with Slanted Mirror geometry gives the best performance among all the other geometries for minimum Pressure drop. The average heat transfer coefficients for fins with slanted mirror geometry, zig zag configuration, fluted type, custom pin fin and staggered array are found to be 215 W/m2K, 164 W/m2K, 164 W/m2K, 157 W/m2K and 145 W/m2K respectively Keywords: Fin geometries of Heat sinks, Computational Fluid Dynamics, Conjugate heat transfer.
ESTIMATION AND ANALYSIS OF CYCLE EFFICIENCY FOR SHELL AND TUBE HEAT EXCHANGER...IAEME Publication
Shell and tube Heat exchanger (STHE) is one of the most common and widely used energy transporter suited for domestic usages as well as industrial applications. In this paper, we consider shell and tube heat exchanger as a device with known input and output parameters. This work utilizes imperative design constraints like tube configuration, fluids, surface and temperature (constant magnitude) as input parameters and energetic cycle efficiency considered as desired output parameter depicting performance of the device. The model was trained and tested by proposed Genetic algorithm (GA) technique. This entire computational procedure is implemented in MATLAB platform.
Research, Development Intelligent HVAC Control System Using Fuzzy Logic Contr...theijes
The paper describes an automatic climate in offices, describes the principles of the automation equipment climate, considered air parameters described control algorithms were compared automation system PIDcontroller and using fuzzy logic controller is designed microclimate model in Mathlab program with a fuzzy logic controller.
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
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# Students can catch up on notes they missed because of an absence.
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Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
Like Us - https://www.facebook.com/FellowBuddycom
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
Benefits:-
# Students can catch up on notes they missed because of an absence.
# Underachievers can find peer developed notes that break down lecture and study material in a way that they can understand
# Students can earn better grades, save time and study effectively
Our Vision & Mission – Simplifying Students Life
Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
Like Us - https://www.facebook.com/FellowBuddycom
Functions of fuzzy logic based controllers used in smart buildingIJECEIAES
The main aim of this study is to support design and development processes of advanced fuzzy-logic-based controller for smart buildings e.g., heating, ventilation and air conditioning, heating, ventilation and air conditioning (HVAC) and indoor lighting control systems. Moreover, the proposed methodology can be used to assess systems energy and environmental performances, also compare energy usages of fuzzy control systems with the performances of conventional on/off and proportional integral derivative controller (PID). The main objective and purpose of using fuzzy-logic-based model and control is to precisely control indoor thermal comfort e.g., temperature, humidity, air quality, air velocity, thermal comfort, and energy balance. Moreover, this article present and highlight mathematical models of indoor temperature and humidity transfer matrix, uncertainties of users’ comfort preference set-points and a fuzzy algorithm.
an experiment on a co2 air conditioning system with copper heat exchangersINFOGAIN PUBLICATION
This paper presented an experiment on a CO2 air conditioning system with copper heat exchangers. In this study, the compressor and cooler were tested with hydraulic method to determine the deformed and torn temperatures. The results show that conventional compressor is not suitable for using high pressure, due to the COP of cycle is very low (0.5 only). With CO2 compressor, the cycle can be achieved COP of 3.07 at the evaporative temperature of 10C. This value equals with COP of commercial air conditioning system presently.
A novel hybrid modelling structure fabricated by using Takagi-Sugeno fuzzy to forecast HVAC systems energy demand in real-time for Basra city
Raad Z. Homod
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
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Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
2. 1. INTRODUCTION
m
Heating, Ventilation and Air-Conditioning (HVAC) systems
are widely used in different environments. HVAC systems
are composed of a large number of subsystems, each of
which may exhibit time-varying and/or nonlinear
characteristics as in Jiangjiang et al. (2006). Furthermore,
increase in capacitance of building structure raises thermal
inertia (Szymon (2010)). It would be very difficult to
dedicate control system to a specific building due to great
variety of building technologies and its dynamical properties.
Such these complexities indicated that the use of some simple
control schemes (like on-off control that many HVAC
systems are using) may not be appropriate for some of the
new load-management technologies and systems. Traditional
PID controller sometimes doesn’t satisfy the control purpose
for the object, which has large inertia, delay and nonlinear
characteristic and uncertain disturbance factor, like the tall
and big space, because of the dissatisfaction of tuning
parameters, the effect of dissatisfying performance and the
adaptability to different running medium (Wang et al. (2008)
and Servet et al. (2009)). To overcoming the failing of
traditional PID control, we will add cascade (Cheng (2006)).
Cascade control is especially useful in reducing the effect of
a load disturbance that moves through the control system
slowly (Riccardo (2009)). The inner loop has the effect of
reducing the lag in the outer loop, resulting in the cascade
system responds more quickly with a higher frequency of
oscillation. Simulations have illustrated this effect of cascade
control (Donald (1991) and Antonio (2006)).
In this study, the heat exchanger and air-conditioning space
in the HVAC system are modeled. Then the hybrid PID-
cascade control system is presented, which combines the
traditional PID control and cascade. The cascade internal
loop control is designed in terms of the robust control H2
optimal performance specification as in Vojtech et al. (2009).
Through the simulation in the HVAC system, it is found that
the PID controller enhances the stability and rejects the
disturbance and the cascade control increases the response
speed and control precision in the HVAC system.
2. MATHEMATICAL MODEL FOR HVAC SYSTEM
Figure (1) Room-air conditioning system
There are basically two ways of determining a mathematical
model of a system: by implementing known laws of nature or
through experimentation on the process (Xiaosh (2001) and
(2002)).
The first one will take to obtain the mathematical model for
HVAC which contain from the first part is the air-processing
unit (heating/cooling system) and the second part is the air-
conditioning room. These two parts are illustrated in Figure
1.
2.1 Heat Exchanger model
Based on the law conservation of energy, the thermal balance
equation (Wang et al. (2007a)) is shown as follows:
(1)
The transfer function of handled air temperature can be
derived from (1) :
(2)
where K1 is the coefficient of amplify, (Co
.s /kg); T1 is time
constant, (s); τ1 is the pure time delay of the controlled object,
(s); Gr is the disturbance of heat exchanger, (kg/s) where:
, ,
2.2 Conditioning space model
The supposition for the temperature control model of air-
conditioning space is described as follows: firstly the space is
airtight and there is not the direct heat exchange between
indoors and outdoors; secondly the temperature in the space
is almost equal; thirdly the heat capacity of the door,
windows and the goods in the space is ignored. The thermal
balance equation is similar to the heat exchanger by Wang et
al. (2007a).
(3)
Here, the supply air temperature to room is the handling air
temperature after AHU and Ts= Tl. Assumption is that the
specific heat capacity of air in air-conditioning room is equal
to specific heat capacity of supply air and Cr = Ca. The
transfer function of conditioning space temperature can be
derived from (3).
International Journal of Systems Control (Vol.1-2010/Iss.4)
Raad et Al. / Hybrid PID-Cascade Control for HVAC System / pp. 170-175
171
3. (4)
where K2 is the amplify coefficient of room, (Co
. s /kg); T2 is
time constant, (s); τ2 is the pure time delay of the controlled
object, Tf (s) is the disturbance to room, which include the
disturbances from outdoor and indoor, (Co
). Here,
, ,
The following transfer function of heat exchanger and
conditioning space can be derived from (2) and (4).
(5)
3. CONTROL SYSTEM DESIGN
An air-handling unit for a commercial building consists of a
fan, heating-coil and discharge air duct to deliver
heated/cooled air into the space. In a conditioned space, a
throttling-type thermostat (not the on/off type common in
residential applications) senses the temperature and controls a
steam (or chilled water) valve on the heating coil. Return air
from the space is mixed with outdoor air at the inlet to the
fan. The fixed ratio of outdoor air to return air is used to meet
the requirements for ventilation as shown in Figure 2.
In normal operation, the thermostat does an adequate job of
maintaining a stable space temperature. However, in the
particular climate of this application, the outside air
temperature sometimes drops very rapidly. When it does the
mixed air temperature drops, as does the discharge air
temperature. This eventually causes a drop in the space
temperature. The thermostat senses and corrects for this, but
because of the large volume of space, it takes an excessively
long time to recover to the desired temperature.
We can improve the control system to alleviate this problem,
by adding an intermediate measurement which is used in an
inner feedback loop that will encompass the disturbance
(Riccardo (2009)).
Therefore the possible solution is to measure the steam flow
and cascade the output of the thermostat to a steam-flow
controller. But the flaw in the inner loop (steam flow) does
not encompass the disturbance (change in outdoor air
temperature).
Figure (2) A Cascade Control Application in the HVAC
The possible solution is to measure the discharge temperature
and let that control the steam valve, as shown in Figure 2.
When the outside air temperature drops, and consequently the
mixed air temperature, the discharge temperature controller
will sense this. The discharge temperature control loop will
be rapid, in comparison with the space temperature control
loop. Hence, the discharge temperature will be maintained
approximately constant at its set point (Harold (2004), Jairo
et al. (2005) and Riccardo (2009)).
3.1 Architecture of the hybrid PID-cascade
There are researches who studied simple controller design
and tuning rule of traditional cascade control system such as
Wang et al. (2007a).
Here we designed the cascade control system for the air-
conditioning system, which is shown in Figure (3). G1 and G2
are respectively the controlled process of heat exchanger and
air-conditioning room; G1m and G2m are respectively
identification models; PID is the setpoint response controller
and F (s) is the internal loop controller; Qroom is the internal
load disturbance; and Ta is the outside load disturbance.
3.2 PID tuning
There are a large number of methods of tuning a PID
controller.
Figure (3) Block diagram of proposed model based on Cascade
control
The most popular ones amongst them are the reaction curve
method and instability method. Both are referred to as the
Ziegler–Nichols tuning method.
International Journal of Systems Control (Vol.1-2010/Iss.4)
Raad et Al. / Hybrid PID-Cascade Control for HVAC System / pp. 170-175
172
4. From the Ziegler-Nichols rules the parameters of the
traditional single PID control are tuned as follows: Kp=0.199,
Ki= 0.0006 and Kd= 7.063 (Graham (2000)).
3.2 Internal loop controller
As Figure 3 shows, the disturbance transfer function of
middle process is shown as follows:
(6)
where Ts is the output of G1(s).
Then the closed-loop complementary sensitivity function is
obtained as follows:
(7)
where f is the inner feedback.
In the ideal condition, Td(s) should be in the form:
, which means that when the Ta disturbance
inputs to the middle process, the internal loop controller F
should detect the error of Ts after τ1 time delay. Then the
controller F outputs a reverse isoperimetric signal to reject
the disturbance. Actually it is considered that the output of
controller is limited and the error is gradually offset. Here
based on the robust control H2 optimal performance
objective, the actual desired closed-loop complementary
sensitivity function is designed as the follows:
(8)
where λf is a control parameter.
λf is needed to tune in the control system. In practical
application, λf can be initialized to τ1 and then be tuned
monotonically on-line to obtain better control performance.
The F(s) can be solved from (7) and is shown in (9).
(9)
To carry out conveniently, (9) is transferred and F(s) can be
shown as follows:
(10)
where F1(s) can be expressed as follows:
(11)
The configuration of observer F is shown in Figure 4.
Figure (4) Configuration of observer F Wang et al. (2007a)
When λf is relatively large, the robust of control system is
relatively strong, but in the meantime the disturbance
rejection will be weak. When λf is small, robustness of
control system is relatively weak and the disturbance
rejection will be relatively strong. So the robustness and
disturbance rejection should be both considered during the
tuning of λf. In practical application, λf can be initialized near
the time delay of P1, τ1. If the process P1 has no pure time
delay, λf can also be initialized near to the time constant of P1.
Then λf is tuned automatically online to obtain better control
performance.
4. SIMULATION
To evaluate the advantages of the proposed techniques
implemented on the HVAC system, the following simulation
has been conducted.
The PID parameters are tuned in using the robust PID tuning
method (Li et al. (2005)) while PID industrial tuning used
Ziegler-Nichols method (Jairo et al. (2005)).
Bode plot and root-locus are used to design the compensator
(Donald (1991) and Brian et al. (2006)). The bode plot is a
plotting of the frequency transfer function that can be
systematized and simplified by using logarithmic plots.
The parameters of the HVAC system are as follows: the
volume of air conditioning room is 10m length, 8m width
and 4.5m height; the air specific heat capacity is Ca=1.0
kJ/kg.Co
; and the air density is 1.2 kg/m3
. Based on the
criterion in the heating, ventilation and air-conditioning field,
and the number of taking a breath in air-conditioned room,
the calculation of the supply air is Ga=1.08kg/s, the heat
resistance of wall is 1/R=0.2kw/Co
and the temperature error
of supply cold-water and back-water to the heat exchanger in
summer is Twin-Twout= - 5Co
. Lastly, the parameters of the
middle process, heat exchanger, are calculated as following:
K1= -19.35Co
. s /kg, T1=30s.
The parameters of air-conditioned room are calculated as
follows: K2=0.4Co
s /kg, T2=338s. So the controlled object
G1(s) and G2(s) can be expressed as: (Wang et al. (2007b))
(12)
International Journal of Systems Control (Vol.1-2010/Iss.4)
Raad et Al. / Hybrid PID-Cascade Control for HVAC System / pp. 170-175
173
5. (13)
(14)
and the disturbances from outdoor and indoor can be
expressed as:
Simulation (1): The comparison curves of four controllers are
shown in Figure 5. It can be seen that the setpoint response of
the hybrid PID-cascade control system has accurate response
while the others all have offset and the hybrid PID-cascade
control responses quicker.
Figure (5) Simulation results of four controllers
Simulation (2): To validate the rejection to the
disturbances of hybrid PID-cascade control in the HVAC
system, the input of disturbance is increased from 0 to 50 in
step of 4000th
per second while the controllers’ parameters
are kept the same as in Simulation (1).
The simulation results of traditional PID, compensator,
Ziegler-Nichols PID tune and hybrid PID-cascade controllers
are shown in Figure 6. The overshoot of hybrid PID-cascade
control is lesser that other controllers while its governing
time is near to the traditional PID control. The rejection to the
disturbances of traditional PID and hybrid PID-cascade
controllers is similar. Moreover, the hybrid PID-cascade
controller’s response was quicker.
Figure (6) Response for four controllers when the disturbance is
inserted at 4000 seconds
Simulation (3): To certify the robustness of hybrid PID-
Cascade control in the HVAC system, the controlled process
parameters are changed during simulation while the
controllers are kept unchanged. The gains of the controlled
process, K1=-19.35 CO
s/Kg, K2=0.8 CO
s/Kg are increased by
10% to K1= -21.3 CO
s/Kg, K2=0.924 CO
s/Kg respectively.
The simulation results are shown in Figure 7. It can be seen
that the setpoint response is similar to the Simulation (1).
However, the overshoot of traditional PID control is greater
than the Simulation (1). Based on this simulation, the
robustness of the hybrid PID-Cascade control system has
been proven.
Figure (7) Step response for four controllers when the parameters of
process are changed
5. CONCLUSION
The hybrid PID-cascade controller, which is a method for
adaptively adjusting the PID gains using cascade feed
forward, is adopted the constant temperature central air-
conditioning system. It has shown better performance than
traditional PID control system. Through simulation, hybrid
PID-cascade control has shown better robustness and
adaptability for nonlinear object. The central air-conditioning
system, which is controlled by the proposed hybrid PID-
cascade controller, has faster response and better
performance even with the seasonal outdoor heat disturbance
and uncertain indoor heat disturbance compared to the
conventional system. The hybrid PID-cascade control can
also be applied to objects with large inertia, pure lag,
nonlinear characteristic and uncertain disturbance factor.
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AUTHORS PROFILE
Mr. Raad Z. Homod graduated with a B.Eng. in
Mechanical Engineering from the University of
Basrah, Iraq in 1991. He worked as engineer for five
years in General Establishment of Steel & Iron (Iraq)
and ten years as HVAC engineer in Al-Tomoh Al-
Kabir Company (Libya). He received his Master in
Mechanical Engineering from the University of
Malaya, Malaysia in 2009. Currently, he is pursuing
his PhD in HVAC Systems and Control at the Department of Mechanical
Engineering in Universiti Tenaga Nasional, Malaysia.
Dr. Khairul Salleh Mohamed Sahari is a senior lecturer
in the Department of Mechanical Engineering,
Universiti Tenaga Nasional where he has been
working since 2007. He obtained his Bachelor in
Mechanical Engineering from Waseda University,
Japan in 2000. He then obtained his Masters (2002)
and PhD (2006) in Engineering from Kanazawa
University, Japan in the field of robotics. He later
continued to work as a postdoctoral research fellow in Kanazawa University
from 2006 to 2007. He is currently a research fellow in Kanazawa University
under sponsorship by Ministry of Science, Technology and Industry,
Malaysia. His current interests are in control system, image processing,
mobile robotics, robotics for power industry, deformable object manipulation
by robot and home service robot.
Dr. Haider A. F. Mohamed received his PhD in
Electrical Engineering from the University of Malaya,
Malaysia in 2006. He worked as a computer engineer
for two years and as a researcher for four years before
he became a lecturer in the Department of Electrical
Engineering in University of Malaya, in 2000. He is
currently an associate professor in the University of
Nottingham Malaysia Campus. His main research
fields are identification and nonlinear intelligent control of various systems
such as robot arms, automated guided vehicles, and electric drives.
Dr. Farrukh Nagi is an associate professor in
Universiti Tenaga Nasional in the area of
Mechatronics. After his graduation in 1982 he joined
Pakistan International Airline for seven years as a
project engineer on development of guidance and
control systems. He completed his MS from university
of Miami USA (1989) and PhD (1993). During this
period he has gained practical experience of working
with distributed control system ‘MODCOMP’ used by
NASA for space shuttle program and IBM robots.
From 1993-2000, he worked in Pakistan Navy engineering college –NUST
and had undertaken research projects pertaining to submarine acoustic signal
detection. He is currently working in UNITEN since 2001. He is one of the
most senior users of MATLAB when he started using it back in 1990 for his
PhD work in array signal processing. He is actively involved in MATLAB
activities in the country and has supervised numerous undergraduate, masters
and PhD thesis related to MATLAB/SIMULINK. Currently, his interests are
in real time signal processing, artificial intelligence and optimization of
control systems.
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Raad et Al. / Hybrid PID-Cascade Control for HVAC System / pp. 170-175
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