Research ActivitiesWaseda University


Waseda Frontline Research Vol.12-1: Heat pumps converting ambient heat into energy

Part 1: Using heat as renewable energy

Heating systems control researcher
Professor Kiyoshi Saito, Department of Applied Mechanics and Aerospace Engineering, School of Fundamental Science and Engineering, Faculty of Science and Engineering

1改In the 5th Science and Technology Basic Plan, which was approved by the Cabinet Office in January 2016, “Ensuring stable energy and improving energy efficiency” was listed as one of the most important policy issues. Professor Kiyoshi Saito explains the technology for improving energy efficiency and simulations for technology development. (Interview date: October 24, 2016)

Discovering the possibilities of heat

My research interests include designing optimum systems and regulating the heating systems control to efficiently utilize thermal energy. For example, I study next-generation heat pumps, which converts low quality environmental heat, such as ambient heat, and industrial waste heat (which has been discarded at half-way temperature) into high quality, high temperature for thermal energy. I am also conducting research on devising and controlling air conditioning systems using heat pumps, as well as carrying out thermal fluid simulations which will serve as the basis of system construction.

Initially as a graduate student, I wanted to engage in research for controlling vibrations of cars, and I had hoped to join the laboratory of Dr. Sunao Kawai, a specialist in control engineering. Luckily, I was assigned there, but my assigned research topic was on heat exchangers. I was not interested at first, but when I observed the strong motion of a solution flowing through tubes due to the Marangoni convection (convection caused by surface tension due to the differences in temperature of liquids) the moment a small amount of alcohol was dropped and the performance of heat exchange improve at once, I became very much drawn to the phenomena caused by heat. From my graduate research to the end of the doctorate course, I became dedicated to understanding why the Marangoni convection occurs. Even now, after about 20 years have passed since I received my Ph.D., I still continue to study heat.


Figure 1. Marangoni convection after adding alcohol

Understanding phenomena through simulations and utilizing them in control

The reason why Professor Kawai, who specializes in machine control, dealt with thermal related themes was because of Professor Toshiei Takahashi, who was Professor Kawai’s mentor. Professor Takahashi proposed “the theory of physical quantity,” emphasizing that physical phenomena can be expressed with duality by treating them as energy amounts. For instance, in an electric system, the amount of current flowing = the current flow rate, and since voltage is the potential difference, the amount of change representing the difference = the potential difference. Hence, current (flow rate) × voltage (potential difference) = power consumption (energy) [W]. On the other hand, in a dynamic system, force is treated as a circulation volume, and velocity becomes the potential difference amount. Power (circulation volume) × velocity (potential difference amount) = work per unit of time (energy) [W]. As illustrated, this theory handles the world’s phenomena from the perspective of energy.

In this physical quantity theory, Professor Kawai was trying to summarize heat in a systematic manner. Eventually, I fully took over the systematization, and built a simulator that reflects the theory, after numerical calculation methods and non-thermal areas such as machinery and electricity became finalized to some extent. Now, we are seeing the light of day at last. The principle of a heat pump operation is also difficult to work out by theorizing it straightforwardly because it continues to list abstract mathematical formulas. However, by using the physical quantity theory, the simulation becomes easier.

In addition, we aim to handle micro to macro phenomena consistently in the simulation. For example, from the macro perspective, it can be used for analyzing the efficiency performance of regional heating and cooling in places such as Shinjuku Ward. On the micro side, it can analyze fluid boiling in capillaries of 1mm or less. The phenomenon of capillaries actually occurs in air conditioners. In the future, it will become important to clarify the reason for this phenomenon and then redesign the system for reducing refrigerant and conserving energy in the heat exchangers inside air conditioners. Although there is a solid formula that uses nano-order silica gel as a dehumidifying agent in a dehumidifier, research into the principle of how water molecules enter holes called pores, which are abundant in silica gel and only slightly larger than a water molecule, is also a research topic in the next 10 years. Because we only specialize in control, we must study the kinds of phenomena and how to control them after fully understanding the principle of each element. I believe our research is characterized by connecting analysis of micro phenomena to macro control.


Figure 2. General energy system analysis simulator developed in the laboratory

Collaborating with researchers to cover broader topics

In recent years, there are many researchers who study unprecedented research topics that differ from their professors. Fortunately for me, I have expanded on research which has been passed down from my professor. Systematization of the physical quantity theory was not possible in one generation. Under the steady accumulation of theories, it has finally reached a form as a simulator and the level in which it can be utilized for cutting-edge research. Energy is a topic that should be studied for a long period of time, and Waseda University is generous for allowing us to do so.

Also, because the campus is located in a metropolitan area, we have been able to find partners who are willing to collaborate for basic and applied research, as well as social implementation on diverse and large-scale topics. My experience as a visiting researcher at the University of Illinois, when I was an associate professor at Waseda, influenced me to take interest in a broad range of research topics. The research laboratory which accepted me was one of the top groups in the United States for its size and research capacities, and they studied a broad range of related topics, from basic research in air conditioning to product development. Having the chance to see all this was a great learning experience. After resuming research at Waseda University, I began to pursue my research in a well-balanced manner from micro to macro scales, and in the past decade, I have made my best efforts in working as an educator, researcher, and sales personnel. Currently, the laboratory is a group of 25 students and 25 research fellows.


Figure 3. At the University of Illinois at Urbana-Champaign, a great year devoted to research

One of the achievements thus far is the outcome of the NEDO project completed in FY 2015. Previously, heat-driven pumps could only raise the temperature up to 120°C, but we were able to improve its quality and commercialize a large-scale heat pump for industrial use. It can now raise the temperature up to 180°C, and because many factories have a steam piping network of 180-190°C, our heat pump can use that heat. It is possible to reuse and utilize waste heat of 80-90°C by raising it to the level of efficiency. Currently, we are also advancing projects towards raising the temperature even higher at 200°C with electrically driven pumps.


Figure 4. Absorption-type heat pump, capable of generating 180°C steam from exhaust heat of about 90°C

The next section will be about the latest research and development trends.

☞Part 2


プロフィール改Kiyoshi Saito
Professor Kiyoshi Saito graduated from the Mechanical Engineering Department, Faculty of Science and Engineering, Waseda University in 1992. He received his Master’s degree in 1994 and a doctorate in 1997 from the Graduate School of Science and Engineering. He is a Ph.D. professor of Engineering at the School of Fundamental Science and Engineering’s Department of Applied Mechanics and Aerospace Engineering in the Faculty of Science and Engineering. Professor Saito served as a research associate at Waseda University, research fellow at National Institute for Resources and Environment, Agency of Industrial Science and Technology (now the National Institute of Advanced Industrial Science and Technology), and full-time lecturer and associate professor at Waseda University before becoming professor in 2008. He was a visiting researcher at the University of Illinois from 2005 – 2006, visiting professor at the University of the Philippines in 2011, and adjunct professor at the University of Indonesia in 2014.

Professional Achievements

Selected Publications

  • N.Giannetti, A.Rocchetti, A.Lubis, K.Saito and S.Yamaguchi, “Entropy parameters for falling film absorber optimization”, Applied Thermal Engineering, 93, pp.750-762 (2016).
  • A.Lubis, J.Jeong, K.Saito, N.Giannetti, H.Yabase, M.Idrus Alhamid, and N.V.Nasruddin, “Solar-assisted single-double-effect absorption chiller for use in Asian tropical climates”, Renewable Energy, 99, pp.825-835 (2016).
  • N.Giannetti, S.Yamaguchi and K.Saito, “Wetting behavior of a liquid film on an internally-cooled desiccant contactor”, International Journal of Heat and Mass Transfer, 101, pp.958-969 (2016).
  • K.Saito, N.Inoue, Y.Nakagawa, Y.Fukusumi, H.Yamada and T.Irie, “Experimental and numerical performance evaluation of double-lift absorption heat transformer”, Science and Technology for the Built Environment, 21(3), pp.312-322 (2015).
  • S.Yamaguchi and K.Saito, “Numerical and experimental performance analysis of rotary desiccant wheels”, International Journal of Heat and Mass Transfer, 60(1), pp.51-60 (2013).

Awards and Honors

  • Award from Japan Society of Mechanical Engineers (2013)
  • Awards from Japan Society for Refrigerating and Air Conditioning Engineers Science (2010, 2012)
  • SAREK Best Paper Award(2010)
  • ERDT Best Paper Award(2010)
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