Socio-Environmental Engineering

Katsunori Nagano

Towards the Implementation of Net Zero Energy Buildings

Katsunori Nagano , Professor

Faculty of Engineering, Graduate School of Engineering (Environmental Engineering Course, Department of Socio-Environmental Engineering, School of Engineering)

High school : Hokkaido Tomakomai Higashi High School

Academic background : Masters from Hokkaido University

Research areas
Urban energy system, building equipment, air conditioning, energy conservation
Research keywords
ZEB, heat pump, ground thermal energy, heat storage, dehumidification, heat island

What is your goal?

I am carrying out research on the elemental technologies required for net zero energy buildings that are suited to cold regions such as Hokkaido. Research on net zero energy buildings, known as ZEB for short, is being pursued around the world. As a building that supplies the energy it needs on its own on an annual balance basis, ZEB represents technologies indispensable for creating a sustainable society. Because the amount of energy consumed for cooling and heating, hot water supply, lighting, and other purposes in homes and office buildings accounts for 23% of the total in Japan, it is very important to reduce energy consumption in this area. ZEB may seem difficult, but the concepts thereof are simple (Fig. 1) and can be summarized in the following three points:

Fig. 1 Image of a Low-energy Building

1) Reduce the load of cooling and heating as much as possible;
2) Implement high-efficiency equipment; and
3) Use renewable energies.

The idea is to decrease the amount of energy consumed by the building in the form of heat and electricity as much as possible (turning a building into a low-energy building), making up for any shortage in energy by natural energies such as solar water heaters and solar cells. We are studying heat pump, ground thermal energy, heat storage, and dehumidification technologies, which we consider to be realistic and provide the biggest implementation benefits as we turn a building into a low-energy building.

A heat pump, also known as a “thermal pump,” pumps up low-temperature heat sources and causes their temperature to rise before dissipating the heat. While “low-temperature heat sources” include natural energies, such as ground water, seawater, river water, and solar heat, and exhaust heat, for example, only the heat of the earth beneath your feet or ground thermal energy, can be used anytime and anywhere. Sapporo has an underground temperature of about 10°C, which is not sufficient to carry out heating. Accordingly, a small amount of electric energy is applied to this machine known as a heat pump to pump up underground heat and warm it to a temperature necessary to carry out heating. This is much more efficient than heating by electric heaters and kerosene oil stoves because thermal energy several fold greater than the applied energy becomes available for heating purposes.


What equipment do you use and what experiments do you carry out?

We are developing a dehumidifying rotor that uses siliceous shale from the Wakkanai formation as raw material, carrying out research and development of a heat pump unit that uses the rotor as the core component thereof, that incorporates heating and cooling, hot water supply, ventilation, and dehumidification functions in a single unit, and that is compatible with ground thermal energy, as illustrated in Fig. 2. Compared with conventional approaches, this unit reduces annual primary energy consumption by 35% because it not only carries out heating and hot water supply with high efficiency but also produces hot water utilizing the dehumidification by moisture absorption and the exhaust heat from cooling in summer. Siliceous shale from the Wakkanai formation is porous sedimentary rock abundantly available in the northern part of Hokkaido. This rock has many pores of 4-20 nm, which are effective for autonomous moisture absorption and desorption (Photo 1). As shown in the electron microscope image of Photo 2, they have a slightly more advanced crystalline structure, with a specific surface area and volume of the pores five to seven times greater than common Diatomaceous earth. Paper comprising approximately 50% of this fine powder was made and processed into a pleat shape to develop a honeycomb dehumidifying rotor, on which we tested the dehumidification performance (Photos 3 and 4, and Fig. 3).


What is your next goal?

We have found that the following technologies are indispensable for ZEB in cold regions: 1. a ground thermal energy heat pump; 2. solar cells; 3. heat recovery by ventilation; and 4. dehumidifying air conditioning. As a next step, we are going to take on the issue of net zero energy cities, in which the interchange of energies is the key.



Division of Ground Thermal Energy System, Hokkaido University, Chichunetsu Heat Pump System (Ground Thermal Energy Heat Pump System), Ohmsha (2007) ISBN: 9784274204487