Case Study 1: House Builders / Construction Companies / Architectural Design Studios
Project Brief: Development of Real ZEH (Net Zero Energy Housing)
We are developing ‘Real ZEH (Net Zero Energy Housing)’, a concept designed to minimise energy consumption in homes and ultimately achieve a net-zero energy balance over the course of a year.
Firstly, we reduce the energy required for heating and cooling by enhancing the performance of the building itself. For example, by improving insulation and airtightness, or by designing to either utilise or block solar radiation, we make it easier to maintain a comfortable indoor thermal environment naturally. Secondly, we generate energy ourselves using technologies that actively utilise renewable energy sources, such as solar power generation and double-skin facades. Furthermore, we ensure energy is used efficiently by employing high-efficiency, top-of-the-range equipment for systems such as air conditioning and lighting.
In this way, by combining multiple technologies—namely ‘(1) reduction of energy demand’, ‘(2) utilisation of renewable energy’, and ‘(3) efficient use of energy’—we are developing and demonstrating homes that achieve net-zero energy consumption whilst maintaining a comfortable living environment.
Case Study 2: House Builders / Construction Companies / Architectural Design Studios
Request: Bioclimatic design suited to climates across Japan (from Hokkaido to Okinawa)
Bioclimatic design is an approach that optimises building design to suit the climatic characteristics of different regions across Japan, aiming to achieve comfort and energy efficiency without over-reliance on mechanical systems.
Japan stretches from north to south, and climatic conditions vary significantly from Hokkaido to Okinawa. Consequently, rather than a one-size-fits-all design, designs that take into account regional differences in temperature, humidity, solar radiation and wind are required. For example, in the cold climate of Hokkaido, where outdoor temperatures are low, it is essential to design buildings with high thermal insulation and airtightness to prevent heat loss. Conversely, in hot and humid regions such as Okinawa, it is crucial to prevent heat and humidity from accumulating indoors through measures to block solar radiation and designs that promote good ventilation. Furthermore, in the temperate regions of Honshu, seasonal adjustments are necessary; for instance, by appropriately designing the placement of eaves and windows to capture winter sunlight whilst blocking it in summer.
In short, bioclimatic design is a design methodology that actively utilises regional climatic conditions and the natural environment to achieve a balance between ‘energy efficiency’ and ‘comfort’, and it plays a vital role in the realisation of Real ZEH. We undertake thermal environment design for BD homes across the country in accordance with client requirements.
Case Study 3: House Builders / Construction Companies / Architectural Design Studios
Request: A nature-friendly home with constant temperature and humidity performance that remains comfortable without air conditioning
A nature-friendly home is a residence that aims to stabilise the indoor environment by utilising natural energy and the building’s own performance, whilst minimising reliance on air conditioning systems.
Firstly, to stabilise the indoor temperature, the thermal mass of the interior building envelope materials is appropriately adjusted; by storing and releasing heat, temperature fluctuations are moderated, ensuring a constant temperature. Furthermore, by using building materials with moisture-absorbing and -releasing properties for the interior finishes, humidity is naturally regulated, maintaining a constant humidity level. Furthermore, in winter, the interior is heated using solar heat (such as direct gain). In summer, however, the rise in daytime indoor temperatures is suppressed through the building’s thermal mass, utilising atmospheric radiative cooling and night purging (ventilating cool night-time air into the interior). Combined with ventilation design and solar shading, this allows for the comprehensive utilisation of natural heat, light and wind to create a comfortable environment.
Underlying such homes that utilise natural energy is a ‘nature-friendly mindset’ on the part of the occupants: rather than artificially maintaining a completely constant temperature and humidity, they accept conditions that may occasionally fall outside the comfort zone. Depending on the client’s requirements, we design nature-friendly homes that strike a balance between energy efficiency and comfort, based on the premise that people live by adapting to the natural environment.
Case Study 4: House Builders / Construction Companies / Architectural Design Studios
Client Request: A PDSC (Passive Dehumidification and Solar Collection) home that utilises renewable energy to naturally cool and dehumidify in summer, and collect heat and humidify in winter.
We are developing and demonstrating PDSC homes as a type of housing that makes advanced use of renewable energy.
This is a passive system home that actively utilises solar heat and atmospheric radiative cooling to perform different functions depending on the season. During the summer daytime, solar heat is used to remove water vapour from the interior, whilst at night, the interior is cooled by atmospheric radiation (a natural cooling and dehumidification system achieved through structural design and air circulation control). Conversely, in winter, the same system is used for solar heat collection to heat and humidify the interior.
The PDSC house is a passive house with variable thermal performance and air circulation that utilises renewable energy to perform ‘cooling and dehumidification’ in summer and ‘heat collection (heating) and humidification’ in winter. It is characterised by its ability to regulate the indoor environment whilst reducing dependence on air-conditioning equipment. This concept aligns with the philosophy of nature-friendly housing, aiming to achieve comfort with minimal energy consumption by effectively utilising naturally occurring sources of cooling and heating.
PDSC homes represent a concrete form of energy-efficient housing adapted to Japan’s climatic conditions, centred on renewable energy, and constitute a key technology for achieving Real ZEH.
Case Study 5: House Builders / Construction Companies / Atelier-style Design Firms
Request: Whole-house air-conditioning homes using an air circulation system (air handling unit method)
We are working to advance whole-house air-conditioning systems to achieve an energy-efficient and comfortable living environment.
One example of this is the system known as the ‘MaHAt System’. This is an air-circulation type whole-house air-conditioning system, which circulates temperature- and humidity-controlled air throughout the entire building via air-handling units installed within the structure. Rather than installing individual air-conditioning units in each room as in conventional systems, a single air-conditioning system can comprehensively manage the thermal environment and ventilation of the entire home.
This system is characterised by its ability to create a uniform indoor environment with minimal temperature and humidity variations throughout the building. It achieves energy savings by efficiently coordinating air conditioning and ventilation, and maximises performance when combined with well-insulated, airtight housing. Furthermore, by circulating air whilst ensuring appropriate ventilation, it contributes to maintaining good indoor air quality. Additionally, by combining it with renewable energy technologies, it is possible to reduce dependence on mechanical equipment.
In this way, the MaHAt System is an advanced residential system that achieves both comfort and energy efficiency in high-performance homes through the integrated control of air conditioning and ventilation.
Case Study 6: Architectural Design Firm / General Contractor
Project: Namiki Square
Namiki Square is a civic centre and hall featuring a large entrance hall; its mechanical and electrical design is characterised by a focus on achieving both comfort and energy efficiency.
In particular, radiant panel air conditioning has been adopted for the HVAC system to reduce energy consumption. Radiant panel air conditioning is a system that regulates the indoor thermal environment through radiation and convection from panels installed on walls and ceilings, rather than directly heating or cooling the air. This method enables a uniform and gentle thermal environment even in large spaces, whilst minimising excessive air circulation and allowing for efficient energy use. Furthermore, in spaces with high ceilings, such as large entrance halls, conventional air-based air conditioning systems tend to result in significant energy loss. Radiant air conditioning, however, can effectively supply and remove heat within the targeted spatial area, thereby contributing to energy savings.
By introducing a radiant air conditioning system tailored to the characteristics of the architectural space, Namiki Square has achieved a balance between energy efficiency and comfort, reducing energy consumption by approximately 25% compared to conventional air conditioning systems.
Case Study 7: Architectural Design Firm / General Contractor
Project: Itoshima City Hall
Itoshima City Hall is an advanced, environmentally conscious building (ZEB) that integrates architectural planning with building services engineering, and features systems designed to balance energy efficiency with comfort.
The air conditioning system employs an advanced method combining radiant panel air conditioning with underfloor air supply. Radiant panels are installed within the floor slab, gently regulating the indoor thermal environment through radiant heat from the floor. Furthermore, air supplied from the outdoor air handling unit passes through the ventilation layer beneath the radiant panels; it is cooled or heated through heat exchange with the panels and then distributed into the room via underfloor air supply. The radiant panels and the outdoor air handling unit operate in tandem; by appropriately treating fresh air and supplying it from the floor surface, the system achieves integrated, efficient ventilation and air conditioning. The combination of radiant heating from the floor and underfloor air supply ensures that air conditioning is centred on the occupied zone, thereby maintaining a comfortable and efficient environment in the living areas and enabling operation with minimal energy wastage, even in large spaces.
This system achieves: (1) the creation of a comfortable thermal environment centred on the occupied zone; (2) efficient management of air quality, temperature and humidity through the coordination of the outdoor air handling unit and floor-supply air conditioning; and (3) improved energy efficiency through the cooling and heating of incoming outdoor air via the outdoor air handling unit.
In this way, the Itoshima City Hall is an architectural example that successfully balances high levels of energy efficiency and comfort through a hybrid system featuring advanced coordination between radiant heating and cooling and underfloor air distribution.
Case Study 8: Architectural Design Firm / General Contractor
Project: JR Kumamoto Station Building / Amu Plaza
The JR Kumamoto Station Building / Amu Plaza adopts Biophilic Design (BPD), which actively incorporates natural elements into the building’s interior.
BPD is a design approach based on the innate human instinct (biophilia) to connect with nature, incorporating natural light, wind, water and plants into architectural spaces. In this building, natural elements have been introduced into the large atrium entrance space extending from the first to the seventh floor, including: ① the use of daylight (sunlight) through large openings and skylights; ② the utilisation of natural breezes through airflow control; ③ evaporative cooling and prevention of excessive dryness via waterfalls and water features (water); and ④ environmental regulation through indoor plants and vertical greening (plants). A particularly distinctive feature is the use of a 10-metre-wide, 10-metre-high waterfall (flowing from the third floor to a water basin on the ground floor) to regulate temperature and humidity solely through the adjustment of water temperature and volume, exhaust ventilation from the side of the water basin (dehumidification), and air circulation within the atrium (convective heat diffusion).
This enables a comfortable environment to be achieved in this vast space without the use of air-conditioning equipment, making it a highly advanced and rare example. Furthermore, analysis and testing have demonstrated that this passive environmental control system can reduce the energy consumption of the air conditioning systems in the adjacent commercial facilities by approximately 25%.
In this way, the JR Kumamoto Station Building and Amu Plaza is a pioneering architectural example that integrates natural energy with architectural design to achieve environmental control in a large space without relying on mechanical systems.
Case Study 9: Manufacturer of Building Materials, Construction Products, and HVAC Equipment
Request: Development of moisture-regulating building materials and assessment of their effectiveness
We theoretically elucidated the moisture absorption and desorption properties of moisture-regulating building materials and established an efficient material development methodology based on these findings.
The performance of moisture-regulating building materials is determined by the attractive force of the pores (capillaries) present within the material; this force is defined as a thermodynamic potential (referred to as the water potential). Furthermore, as this water potential depends on pore size, the relationship between moisture content and water potential can be uniquely determined by measuring the pore size distribution of the material. In the Ozaki Laboratory, we define water potential by applying non-equilibrium thermodynamics and theoretically derive the relationship between water potential and moisture content (equilibrium moisture content). Furthermore, we have formulated a coupled heat and moisture transport equation using water potential and are conducting high-precision numerical analyses.
Based on these theories, we have designed and developed humidity-regulating building materials through pore size distribution measurements and numerical analyses based on the coupled heat and moisture transport equation. Whereas the conventional approach involved empirically fabricating materials and verifying their performance through experimentation, this method enables material design with specific pore size distributions as targets, thereby significantly reducing the time and cost required for the development of humidity-regulating building materials.
Furthermore, as the architectural environment analysis tool ‘ThermalOne’ incorporates the aforementioned theory, we used this tool to verify the effects of applying the developed materials to buildings, evaluating their effectiveness in improving indoor humidity conditions and reducing air conditioning loads. As a result, we derived practical design guidelines and demonstrated the feasibility of their application in buildings.
Case Study 10: Manufacturers of Building Materials, Building Products, and HVAC Equipment
Request: The impact of differences in window glazing and window frames on a building’s thermal environment and energy-saving performance
We quantitatively assessed the impact of differences in the performance of window glazing and window frames on a building’s thermal environment and HVAC energy consumption, and clarified the method for selecting optimal window specifications.
Firstly, regarding window glazing, we examined a diverse range of products, including double-glazed units, Low-E double-glazed units, vacuum double-glazed units and triple-glazed units, and conducted a detailed analysis of the differences in indoor thermal environment and HVAC energy consumption when each was used. The results revealed that whilst high-performance glazing improves thermal insulation and heat shielding, thereby contributing to energy savings, it is important to consider the balance with cost (affordability).
Furthermore, regarding window frames (sashes), we empirically evaluated the impact of performance differences between aluminium sashes, aluminium-plastic composite sashes and plastic sashes on the building’s overall heat loss and air-conditioning load. In particular, we confirmed that, compared to aluminium sashes with high thermal conductivity, plastic sashes offer superior thermal insulation performance and deliver significant energy-saving benefits.
Based on these results, we demonstrated that window performance varies significantly depending on the combination of glass and sash. We proposed a design method that allows for the rational selection of optimal window specifications by comprehensively considering regional climatic conditions, building specifications (such as insulation and solar shading), and window orientation.
We have provided guidelines for significantly improving a building’s energy performance through the design of openings, offering important insights for the realisation of energy-efficient buildings aiming for Real ZEH / ZEB.
Case Study 11: Manufacturers of Building Materials, Building Products, and HVAC Equipment
Request: Prevention of thermal bridges and internal condensation using insulated window frames
Window frames conduct heat more easily than external walls; not only do they act as thermal bridges (heat bridges), thereby increasing heat loss, but they are also areas where condensation is likely to form due to a drop in surface temperature. Furthermore, if condensation forms inside the joints between structural members and window frames, there is a risk of serious moisture damage, such as mould growth and timber rot.
To address this issue, this case study conducted a two-dimensional analysis of the combined heat and moisture transport at the interface between the external wall and the window, enabling a detailed understanding of the temperature and humidity distribution around the window frame, as well as long-term moisture behaviour. Based on these results, we are designing and developing insulated window frames that are less prone to thermal bridging. Furthermore, by simulating long-term heat and moisture transport under various climatic and indoor environmental conditions across Japan, we evaluated temperature and humidity changes within walls and at joints. The results confirmed that the proposed sash structure suppresses the formation of internal condensation and prevents moisture damage.
This has enabled the quantitative assessment of condensation risks in the unseen areas around window frames, the design of window frames that minimise thermal bridges, and the design of safe, high-performance building envelopes tailored to regional climates. Consequently, it has made a significant contribution to achieving both improved building durability and energy efficiency.
Case Study 12: Manufacturer of Building Materials, Construction Products, and HVAC Equipment
Request: Indoor thermal environment control and energy-saving effects using automatic opening and closing windows
Automatic opening and closing windows installed in the building were used to control the indoor thermal environment through natural ventilation (air exchange) whilst aiming to reduce energy consumption for air conditioning.
By controlling the opening and closing of the automatic windows in response to factors such as the temperature difference between indoors and outdoors, wind direction and speed, and solar radiation conditions, natural ventilation can be ensured at the optimal time. This suppresses the rise in room temperature by efficiently expelling trapped heat from the room and introducing cool outside air. In particular, this enables operations such as thermal storage through natural ventilation (e.g. night purging) during the night and in the transitional seasons, as well as the use of outdoor air conditions to replace or supplement mechanical air conditioning, thereby contributing significantly to the reduction of air conditioning loads. Furthermore, as the system is automatically controlled, appropriate ventilation is always ensured regardless of occupant intervention, thus achieving a balance between comfort and energy efficiency. Furthermore, combining this with other passive technologies further enhances its effectiveness.
This enables: (1) the advancement of indoor environmental control methods utilising natural energy; (2) the provision of design guidelines adapted to local climatic conditions; and (3) the reduction of air-conditioning energy consumption. We have demonstrated that this is a key technology contributing to the realisation of Real ZEH and bioclimatic design.
Case Study 13: Manufacturer of building materials, building products, and air-conditioning and ventilation equipment
Project Brief: Passive housing utilising the thermal storage effects of PCM (Phase Change Material)
By utilising the cooling and heating storage properties of PCM (Phase Change Material), we have realised passive housing that does not rely on mechanical air conditioning. PCM is a material that undergoes a phase change between liquid and solid within a specific temperature range, absorbing and releasing heat in the process; utilising this property enables the efficient storage of thermal energy. In this method, chambers incorporating PCM (PCM units) were installed within the building, and heat was stored and released through air circulation.
In summer, indoor air is blown into the roof ventilation layer at night; the air, cooled by atmospheric radiative cooling on the roof surface, is then sent to the PCM units to store cold, before being returned to the interior. During the day, indoor air is blown directly into the PCM units; the stored cooling energy is recovered and supplied to the interior to provide a cooling effect. In winter, the method of air circulation during the day and night is reversed compared to summer: heat is stored in the PCM via solar collection during the day, and this thermal energy is recovered at night for use in heating. It was demonstrated that, under favourable weather conditions, a comfortable indoor environment can be maintained throughout the day in both summer and winter without the use of mechanical air conditioning.
This case study is characterised by the integration of: (1) highly efficient thermal energy storage utilising the phase-change properties of PCM; (2) practical system design combined with air circulation; and (3) passive environmental control driven by renewable energy. It represents an advanced technology aimed at realising high-performance, energy-efficient housing.
Case Study 14: Manufacturer of Building Materials, Construction Products, and HVAC Equipment
Request: Energy-saving effects of total heat exchangers and humidity-controlled outdoor air handling units
To reduce energy losses incurred during building ventilation, we demonstrated the effectiveness of energy-saving technologies utilising total heat exchangers and humidity-controlled outdoor air handling units (heat pump-type desiccant ventilation).
Firstly, a total heat exchanger is a device that exchanges both sensible heat (temperature) and latent heat (humidity) between the exhaust indoor air and the incoming outdoor air. This allows the energy from the conditioned indoor air to be reused, compared to simply drawing in outdoor air as it is, thereby enabling a significant reduction in the air-conditioning load associated with ventilation.
On the other hand, a humidity-controlled outdoor air handling unit is a system that combines heat pump and desiccant technologies, actively controlling not only the temperature but also the humidity of the outdoor air as it is drawn in. Particularly in climates such as Japan’s, which are hot and humid, humidity control has a significant impact on the air-conditioning load; consequently, this unit enables highly efficient dehumidification and humidification, as well as the separation of sensible heat loads from the air-conditioning system.
The introduction of these systems has achieved: (1) a reduction in heat and moisture loss during ventilation; (2) a reduction in the load on air-conditioning equipment and more efficient operation; and (3) improved comfort through the stabilisation of indoor temperature and humidity. Furthermore, by integrating with the building’s central air-conditioning system, we have optimally divided the processing of outdoor air and indoor air conditioning (sensible and latent heat separation air conditioning), thereby minimising energy consumption. Heat exchange ventilation is a key enabling technology in high-performance buildings (such as Real ZEH and energy-efficient homes and buildings), serving as a means to make the unavoidable process of ventilation more energy-efficient.
Case Study 15: Other
Scope of Work: Assessment of thermal environment improvements and measures to prevent condensation in a thermally upgraded home
We investigated the effects of thermal upgrading on the indoor thermal environment and energy efficiency in an existing home, as well as measures to mitigate the associated risk of condensation.
Thermal upgrading reduces the influence of outside air and stabilises indoor temperatures, thereby mitigating the cold in winter and the heat in summer, and improving comfort. Furthermore, as the energy required for heating and cooling is reduced, energy savings are achieved through a lower air-conditioning load.
However, problems may arise if only partial insulation retrofitting (e.g. limited to living areas) is carried out. Unrenovated rooms remain at a lower temperature, and when air flows from heated rooms into unheated ones, condensation is likely to form on surfaces where the temperature has dropped. Consequently, it has been noted that this increases the risk of moisture-related damage, such as mould and rot. To prevent such problems, it is important to consider either (1) comprehensive insulation renovation covering the entire building, or (2) the installation and operation of a 24-hour ventilation system that appropriately removes indoor moisture.
This case study demonstrated that, in order to maximise the benefits of insulation renovation whilst preventing side effects such as condensation, it is necessary to plan insulation, ventilation and the indoor environment as an integrated whole. It provided practical guidelines for simultaneously improving the safety, comfort and energy efficiency of existing homes.
Case Study 16: Other
Request: Building envelope configurations suitable for various regions of Japan to prevent winter and summer internal condensation
The aim is to identify building envelope configurations suitable for the climatic conditions of various regions across Japan in order to prevent winter and summer internal condensation occurring within the building walls.
Internal condensation occurs due to temperature and water vapour movement within walls, and has a significant impact on the durability of buildings, including reduced thermal insulation performance, mould growth and structural decay. In Japan, it is necessary to address both winter-type condensation, which occurs when water vapour moves from the interior into the wall cavity during winter, and summer-type condensation, which occurs when hot, humid outside air penetrates the wall cavity during summer.
In this case study, we conducted a detailed analysis of the combined movement of heat and moisture and evaluated the temperature and humidity behaviour within the wall cavity, taking into account regional outdoor conditions and indoor environments. Based on these results, we propose a building structure that prevents internal condensation by appropriately combining the following elements: a) the arrangement of vapour barriers and vapour-permeable layers on the indoor and outdoor sides; b) the type and position of insulation (internal, external or supplementary insulation); c) moisture removal through the installation of a ventilation layer; and d) the use of buffer materials with high moisture capacity. Furthermore, as Japan’s climate varies significantly by region, we have compiled design guidelines tailored to regional characteristics, such as prioritising measures against winter condensation in cold regions and considering measures against summer condensation in warm and humid regions.
This enables: (1) structural design capable of addressing condensation risks in both winter and summer; (2) the realisation of buildings that are safe and highly durable in the long term; and (3) the simultaneous achievement of thermal insulation and airtightness whilst preventing moisture damage. Consequently, it serves as a fundamental technology for the widespread adoption of high-performance, energy-efficient buildings.
Case Study 17: Other
Request: Measures to prevent moisture damage in non-residential spaces such as underfloor and loft spaces
We have elucidated the mechanisms behind moisture damage in non-residential spaces such as underfloor and loft areas, and identified design methods to prevent condensation.
Firstly, caution is required in underfloor spaces even when ventilation is provided. From spring to summer, the temperature and humidity of the outside air rise rapidly, but the temperature in the underfloor space rises more slowly due to the influence of the ground. This phase difference in temperature means that when warm, humid outside air flows into the relatively cooler underfloor space, the air cools and there is a risk of condensation forming. In other words, ventilation is not necessarily safe, and design and control that take weather conditions into account are essential.
Conversely, in loft spaces (where the ceiling is insulated), if the moisture barrier in the ceiling is inadequate, indoor humidity may flow into the loft during winter. Consequently, condensation may form on the roof surface (roof sheathing), which has cooled due to the influence of the outside air.
To address these issues, this case study conducted an analysis from the perspective of combined heat and moisture transfer. It demonstrates that it is important to combine measures such as careful consideration of outdoor air intake methods, ventilation control and insulation layout in the subfloor space, and the reliable installation of a moisture barrier on the ceiling surface and ensuring airtightness in the loft space.
This case study provided a quantitative analysis of the mechanisms of condensation formation in non-residential spaces and proposed appropriate design methods to address each risk, offering important insights for preventing moisture damage that contribute to improving the durability and healthiness of the entire building.
Case Study 18: Other
Scope of Work: Thermal Environment Analysis and Energy-Saving Measures for a Data Centre
Taking into account the heat generation characteristics of server equipment in the data centre, we conducted a detailed analysis of the indoor thermal environment and examined air-conditioning and operational methods to achieve energy savings.
In data centres, the large amount of heat generated by servers tends to create significant temperature variations (hot spots) within the room, requiring a substantial amount of air conditioning energy to control these effectively. In this case study, we conducted a detailed analysis of airflow and temperature distributions and examined ways to optimise equipment layout and airflow (separation of cold air supply and exhaust). Specifically, we quantitatively evaluated the effectiveness of measures from an energy-saving perspective, including: a) airflow control to enhance cooling efficiency (such as the separation of hot aisles and cold aisles); b) mitigation of hot spots; c) homogenisation of temperature distribution to prevent localised overcooling; and d) high-efficiency air-conditioning operations that provide the necessary cooling where required. Furthermore, we analysed methods for reducing air-conditioning energy consumption whilst ensuring the safe operation of servers through operational improvements based on thermal environment analysis, including the use of outside air cooling and high-efficiency air-handling units.
Through this, we provided: (1) visualisation and optimal design of thermal and airflow behaviour within the data centre; (2) reduction of excessive air-conditioning energy consumption; and (3) sustainable operational guidelines for high-heat-generating equipment, thereby presenting important technical insights that contribute to energy conservation in information infrastructure.