Efficient Water Supply in HVAC Systems

PhD: Mohammad Komareji

 Casestory

Project Partners:	CISS, Aalborg University
	Grundfos, Exhausto, DTI

Project Partner Contact Information

CISS, Aalborg University
Professor Kim G. Larsen
Fr. Bajers Vej 7B
9220 Aalborg Ø, Denmark
Phone: +45 96 35 72 20
E-mail: kgl@cs.aau.dk

Exhausto
Project Manager Finn Nielsen
Exhausto A/S
Odensevej 76
5550 Langeskov, Denmark
Phone: +45 65 66 11 36
E-mail: fni@exhausto.dk

Danish Technological Institute
Project Manager Peter Svendsen
Technologisk Institut, Energi
Gregersensvej, Postbox 141
2630 Taastrup, Denmark
Phone: +45 77 20 25 56
E-mail: Peter.Svendsen@teknologisk.dk

Grundfos
Project Manager Niels Bidstrup
Grundfos
Poul Due Jesnes vej 7-9
8850 Bjerringbro, Denmark
Phone: +45 87 50 45 17
E-mail: nbidstrup@grundfos.dk

1. Purpose of the Project
An air conditioning automatic control system or simply a control system, primarily modulates the capacity of the air conditioning equipment to maintain predetermined parameter(s) within an enclosure of the fluid entering or leaving the equipment to meet the load and climate changes at optimum energy consumption and safe operation. As it is known, the HVAC system is a nonlinear system and its strongly coupled parameters change. Thus, classical HVAC control techniques can not be optimal solutions. HAVC systems can be categorized in three main configurations:

1. primary only systems
2. primary-secondary systems
3. primary-secondary-tertiary systems

In this project we deal with primary-secondary systems. A typical mixing loop for a heating surface in a primary-secondary HVAC system is outlined in the following figure.

As can be seen in the figure, quite simply, return water from the surface is mixed with either cold or hot water. Therefore, the inlet water temperature varies by changing the mentioned mixing ratio. The regulation valves (SVn) are used to make the desired water flow. The motorized valve (MV) regulates the amount of water that should be supplied to the secondary loop to have the desired temperature of water.

The porpose of this project is to eliminate all the valves and to use a variable flow pump instead. By using this pump, the HVAC system can be supplied by (hot or cold) water in an efficient way regarding the set points. As was described, the palnt is multi-variable, nonlinear, and time-varying. Inputs of the palnt are either hot or cold water flow and air flow that will be controlled by variable flow pump and variable speed fans respectively. The output of the plant is desired room temperature. The cost function is energy consumption. As a result, the controller of the plant will be an advanced (likely nonlinear) robust model-based controller. Finally, we expect the resulting system to be cheaper and more energy efficient.

2. Background
Classical HVAC control techniques such as the ON/OFF controllers (thermostats) and the proportional-integral-derivative (PID) controllers are still very popular because of their low cost. However, in the long run, these controllers are expensive because they operate at a very low-energy efficiency. So, there is a high potential to apply advanced controllers to save large amount of energy (For example, just by efficient water supply of HVAC system almost 100 GWh energy can be saved yearly in Denmark).

3. Perspective
The consumption of energy by heating, ventilating, and air conditioning (HVAC) equipment in industrial and commercial buildings constitutes 50 percent of the world energy consumption. In spite of the advancements made in microprocessor technology and its impact on the development of new control methodologies for HVAC systems aiming at improving their energy efficiency, the process of operating HVAC equipment in commercial and industrial buildings is still an inefficient and high-energy consumption process.

4. Industrial Application
HAVC systems are necessary part of every place such as plants, buildings, and shops. It means that in every place that heating, ventilating, and air conditioning are needed an HVAC system exists. As was mentioned, current HVAC controllers are not optimal ones. So, there is a potential for substituting new controllers for old ones.

5. Timetable for the project
The project is split up into the following five parts:

1. System analysis

Period: 1 September 2005 - 19 January 2006.

2. Modelling

Period: 19 January 2006 - 20 April 2006.

3. Control Analysis

Period: 20 April 2006 - 17 August 2006.

4. Control Synthesis

Period: 17 August 2006 - 1 January 2007

 1 April 2007 - 1 January 2008

5. Verification

Period: 1 January 2007 - 1 April 2007

 1 January 2008 – 1 April 2008

 

References

• A.J. Chapman, Heat Transfer, 4th edition, Macmillan Publishing Company , 1984.
• P. Brath, Towards Autonomous Control of HVAC Systems, PhD thesis, Aalborg University,1999.
• K. Ogata, Modern Control Engineering, Prentice Hall, 1987.
• P. Svendsen and H. Anderson, Energy Efficient Pump Coupling in HVAC Systems, technical report, Danish Technological Institute (Industry and Energy), 2005.
• M.S. Imbabi, Computer Validation of Scale Model Tests for Buildings Energy Simulation, Int.J. Energy Res., vol 14, 1990.
• R. Shoureshi, Intelligent Control Systems: Are They for Real, J. Dynamic Syst., Measurment,Contr., vol 115, 1993.
• B.A. Serrano and M.V. Reyes, Nonlinear Control of a Heating, Ventilating, and Air Conditioning System with Thermal Load Estimation, IEEE Trans. on Control Systems Technology, 1999.
• I. Ionel, Pumps and Pumping, Elsevier, 1986.
• ASHRAE/IESNA Energy Standard for Building Except Low-Rise Residential Buildings, ASHRAE Inc., Atlanta, GA, 1999.
• L. Tillack and J.B. Rishel, Proper Control of HVAC Variable Speed Pumps, ASHRAE Journal, 1998.
• J.B. Rishel, Simplifying Contemporary HVAC Piping, ASHRAE Journal, 2005.
• J. Schwartzenbach and K.F. Gill, System Modeling and Control, 2nd edition, Edward Arnold, 1984.
• A. Alleyne, S. Brennan, R. Rasmussen, R. Zhang, and Y. Zhang Controls and Experiments: Lessons Learned, IEEE Control Syst. Mag., 2003.
• B.D.O. Anderson, Controller Design: Moving from Theory to Practice, IEEE Control Syst. Mag., vol 13, 1993.