Numerical analysis of a ground-source heat-pump system in traditional Japanese “Kyo-machiya” dwellings

Kyo-machiya, which is a traditional wooden dwelling in Kyoto, is generally equipped with a shallow well. The well water can be potentially utilized as a heat source with a geothermal heatpump system without incurring a high drilling cost. Hereby, more energy saving in the traditional dwelling can be realized with the heat-pump system. However, an appropriate technique to utilize geothermal heat from a shallow well has not been established yet in Japan. To promote the geothermal use, we have continued an experiment to evaluate the practicability of a simple geothermal heat-pump system installed in a shallow well since the winter of 2013. In this study, the condition of the water flow in the well was examined using the computational fluid dynamics (CFD) technique, and the velocity of flow of the groundwater into the well was also estimated. We show that constant buoyancy was generated because of the temperature difference due to the heat-pump operation. Based on the results, a three-dimensional heattransfer numerical analysis model, proposed in the previous study, was developed so that moisture transfer in the ground could be considered. Using the estimated buoyancy of the well water and the groundwater velocity, the calculated results seemed to reproduce the characteristic of the measured value. Furthermore, we show that the groundwater velocity has a large influence on the well water temperature

Effect of Air Pressure on Moisture Transfer inside Porous Building Materials Three-dimensional Behavior of Moisture and Air

The effect of air pressure on moisture transfer inside porous building materials cannot be ignored in cases in which air cannot escape through the surfaces of the materials; in such cases, the air is compressed by the movement of the moisture. Therefore, in a situation in which most surfaces of a specimen are sealed or treated with surface-protecting materials (a situation that is often encountered in typical water-absorption tests), the experimental results may differ from those without sealed or treated surfaces. In the present study, the influence of air pressure on moisture transfer was investigated quantitatively. First, the following water-absorption test was conducted. Water infiltrated into a brick through its top surface, whereas the side surfaces were sealed to prevent the transfer of moisture and air. The bottom surface was exposed to the ambient air. The water content was measured twodimensionally during the experiment using gamma-ray attenuation. Next, to investigate how air pressure affects water infiltration, another experiment was conducted after sealing the bottom surface. The air inside the brick was expected to be compressed by the infiltrating water when the bottom surface was sealed. A water-absorption test was then performed after a small hole was made in a side surface of the bottom-sealed brick to reduce the interior air pressure. Finally, we analyzed the experiments numerically using a three-dimensional calculation model for simultaneous air and moisture transfer, assessing the validity of the model by comparing the calculated and measured water contents. The experimental and numerical results show that water infiltration is slowed by higher air pressure inside the specimen when it is difficult for air to escape. It is also shown that the hole in the side surface helped limit the rise in air pressure to some extent

Natural ventilation around open round floors with pilotis in high-rise residential buildings in tropical areas: harmonization of modern and traditional housing in tropical areas

In this paper, we propose using pilotis in tropical urban areas to harmonize the benefits of modern and traditional housing. The thermal and airflow conditions of a building that has pilotis are compared with those of a building that does not have pilotis, and we examine how the thermal and airflow conditions near the ground floor of the high-rise building can be improved by constructing the pilotis. Furthermore, the notion that natural ventilation on the upper floors is not seriously worsened by constructing pilotis is also examined by computational fluid dynamics CFD)analysis

Evaluating the Energy Consumption and Heat Loss in the Hot Water Supply and Heating Systems of a Nursing Home

The demand for nursing homes has increased recently due to an increase in the aging population in Japan. Nursing homes are generally equipped with hot water supply and heating systems for bathing, preparing meals, and heating rooms. This equipment utilizes a considerable amount of energy. Few studies have measured heat loss from the hot water supply and heating systems in such facilities. This study evaluated the hot water supply and heating systems of a nursing home located in a cold climate area in Japan. The temperature and flow rate of the hot water were continuously measured, and the energy consumption and heat loss for each subsystem were calculated. These results clarified that the energy consumption in the hot water supply subsystem was slightly larger than that in heating subsystem. Inefficiencies of the system were also continuously evaluated throughout the study. Heat losses in piping attributed to 38% of the total energy consumed by the hot water supply subsystem. Subsequently, a thermal analysis of the hot water subsystem was performed. The calculated return temperature agreed with the measured return temperatures when the resistance of thermal insulation was decreased by an average of 45%; this result was possibly due to the deterioration of thermal insulation materials or the presence of thermal bridges

Predicting Hygrothermal Behavior of an Underground Stone Chamber with 3-D Modeling to Restrain Water-Related Damage to Mural Paintings

Cultural properties are variously influenced by their surrounding environmental conditions. One of the reasons for the deterioration of mural paintings in the Takamatsuzuka Tumulus was the humid microclimate on their surface. In order to control the deterioration of mural paintings caused by such problems, it is important to investigate the environmental factors from various aspects, such as the temperature, humidity, water content of cultural properties, wetting and drying cycles and so on. As for the research concerning hygrothermal behavior on mural paintings, these variables may not be thoroughly predicted by 1-D or 2-D for determination of the location and degree of the deterioration of mural paintings. This paper shows how a 3-D hygrothermal model developed with a view to analyzing the preservation measures that allow quantifying of the degree of drying and condensing processes occurred on the surfaces of the underground chamber. The findings show that for the purpose of preserving mural paintings within the underground chamber, the temperature difference between the surrounding mound and the protected object should be kept as constant as can be practically achieved. This method is applicable for estimating the effects of preservation measures for the conservation of other mural paintings

Airborne Algal Growth on the Roofs of Membrane-Structured Residences in a Cold Areas of Japan

Discoloration of building facades due to airborne algae is observed in our surroundings. The growth conditions of these algae are not fully clear yet, and efficient preventive measures have not yet been determined. This study was aimed at investigating the influence of ambient environment and building structure on algal growth. A residential building in the cold region of Japan was surveyed. The roof was a multilayered structure consisting of a semi-transparent film, an air layer, an outside insulation layer, and was supported by rafters. The soiled state was visually observed and recorded through pictures, and seemed to be particularly increased in autumn. Several black stripes appeared on the northeast (NE) roof four months after its cleaning. The soiling first appeared on the film backed by the rafter, and then extended to the film backed by the air layer. It rarely appeared on the southeast roof. The roof-surface temperature was measured and a stripe-shaped distribution was observed. The temperature of the film with rafter was higher and lesser than that of the film with the air layer during the night and in the early morning, respectively. Although condensation occurred nightly, its frequency showed no orientational difference. Algae can die when exposed to a temperature higher than 40 °C. The southwest roof had the longest period of a surface temperature over 40 °C, while the northwest (NW) roof had the shortest period of this surface temperature. These measurements corresponded well to the survey results according to which soiling mainly occurred on the NE and NW sides of roofs. The time for algal growth was estimated assuming that algae can grow at surface temperatures between 0 and 40 °C

Relationship between Environmental Conditions and Algal Growth on the Exterior Walls of the Ninna-ji Temple, Kyoto

6th International Building Physics Conference, IBPC 2015We can find that many building facades are discoloured black and/or green. Some previous studies showed that the soiling of building facades is caused by the growth of airborne algae. The algal growth is strongly influenced by the water supply, including the rain, the condensation, and high humidity. However, the influence of the other environmental factors, such as the solar radiation, the temperature, and the wind on the algal growth, has not been investigated yet. The relationship between the algal growth and the environmental factors on the building facades which the algae grow for long term has not been investigated. Therefore, we quantified the relationship between the algal growth and the environmental factors based on the field survey on the algal growth in Kyoto City and the measurement on the building facades at Kusyo Myojin Shrine, Ninnna-ji Temple in Kyoto, Japan. Kusyo Myojin Shrine was constructed from 1641 to 1647. Some parts of the roof, walls and the painting were repaired from 2004 to 2006. However, the building facades have already been colored black by the algal growth. To investigate the cause of the soiling by the algal growth, the ambient conditions, and surface temperature and humidity of walls were has measured since 2011. The soiling state of the walls was investigated by the L* values and the photographs of the walls. As a result, the order of the L* values of the wall surfaces agreed well with the darkness of the photographs. We concluded that the algal growth and death on the wall surface were affected by the surface temperature of the wall

The Effect of Air leakage through the Air Cavities of Building Walls on Mold Growth Risks

Mold growth poses a high risk to a large number of existing buildings and their users. Air leakage through the air cavities of the building walls, herein gaps between walls and air conditioner pipes penetrating the walls, may increase the risks of interstitial condensation, mold growth and other moisture-related problems. In order to quantify the mold growth risks due to air leakage through air cavity, an office room in a historical masonry building in Nanjing, China, was selected, and its indoor environment has been studied. Fungi colonization can be seen on the surface of air conditioner pipes in the interior side near air cavity of the wall. Hygrothermometers and thermocouples logged interior and exterior temperature and relative humidity from June 2018 to January 2020. The measured data show that in summer the outdoor humidity remained much higher than that of the room, while the temperature near the air cavity stays lower than those of the other parts in the room. Hot and humid outdoor air may condense on the cold wall surface near an air cavity. A two-dimensional hygrothermal simulation was made. Air leakage through the air cavities of walls proved to be a crucial factor for mold growth

Hygrothermal Regulation of Brick Masonry of Nanjing City Wall by Plants

Nanjing City Wall, one of the most important cultural heritages in China, has been damaged in a natural environment for centuries. Plants can be a candidate to regulate the micro-environment and mitigate the influence of local climates, which cannot be easily controlled by human efforts. Therefore, we examined the potential of the roadside trees along the City Wall to buffer the hygrothermal cycles that can deteriorate the City Wall. We surveyed the deteriorated state and measured the temperature and moisture content of the City Wall. Measured results showed smaller temperature fluctuation at shaded surface than the unshaded with a maximum temperature difference of 10.9 ℃ in summer. The measured water content decreased with height. A coupled two–dimensional hygrothermal ‘City Wall–plant’ model was proposed to clarify the influence of the roadside trees on the hygrothermal distribution of the City Wall. The proposed city wall-plant hygrothermal model could predict the surface temperature and water content well