Simulation Evaluation of the Humidification Effect in a Residential Ducted Central Air Conditioning System Equipped with a Humidification Device
Nao Yamaguchi1, Daisuke Umemoto2, Keiko Sekiya2, Hiroshi Nakagawa2, Keizo Yokoyama3, Takashi Akimoto4
1graduate student at Shibaura Institute of Technology, Tokyo, Japan; 2researcher at Panasonic Homes Co., Ltd, Osaka, Japan; 3visiting Professor at Shibaura Institute of Technology, Tokyo, Japan; 4Prof., at Shibaura Institute of Technology, Tokyo, Japan
In recent years, the promotion of high thermal insulation in residential buildings in Japan has led to an increased adoption of ducted central air conditioning systems that heat and cool the entire house. These systems typically maintain high indoor temperatures during winter, but they also tend to reduce indoor relative humidity. To address this issue, water-fed humidifiers are commonly used. However, these devices pose a risk of microbial growth if they are not properly maintained, prompting growing interest in humidification methods that do not rely on water.
To address this issue, the authors developed a humidification device that utilizes desiccant materials, driven by the difference in relative humidity between the supply air of a ducted central air conditioning system and outdoor air. Furthermore, a computational model was developed to reproduce measured values and evaluate system performance. This paper presents an analysis using the developed model to evaluate the humidification effects under varying conditions, including region, indoor set temperature, and the overall heat transfer coefficient of the building envelope.
The results confirmed that higher indoor set temperatures and greater overall heat transfer coefficients enhance humidification. For example, at an indoor set temperature of 20 °C (68.0 °F), the daily humidification amount reached 6.9 L (1.82 gal), resulting in a 12.6%RH increase in indoor relative humidity. Conversely, at 24 °C (75.2 °F), humidification increased to 8.1 L (2.14 gal), with a 10.8%RH increase. Furthermore, regional comparisons showed that colder climates exhibited higher humidification. This is due to higher relative humidity retention in cold outdoor air, creating favorable conditions for moisture absorption. Moreover, in colder regions, increased heating loads lead to higher airflow and air temperatures, which enhance moisture release. This in turn increases system humidification.
Novel Method to Estimate Radiative Heat Transfer on Human Body Using Spherical Thermography
Shohei Yasuda1,2, Takashi Asawa2, Tsuyoshi Ueno1
1Central Research Institute of Electric Power Industry; 2School of Environment and Society, Department of Architecture and Building Engineering, Institute of Science Tokyo
To achieve both energy conservation and thermal comfort in housing, evaluating thermal comfort by considering the nonuniformity of the thermal environment is important. Thermal comfort is mainly realized through the heat balance between the ambient environment and the human body. Even if the ambient thermal environment is neutral, local convection and radiation affect thermal comfort. Therefore, it is important to evaluate the convective and radiative heat transfer on human body parts. However, previous study requires complex heat transfer analysis to obtain the distribution of radiative heat transfer on human body. Therefore, this study proposes a novel and simple method for estimating the distribution of radiative heat transfer on human body using a spherical thermography system. This system has the capability to acquire the radiant temperature distribution of the entire surfaces from the measurement point. Furthermore, the spherical thermography can define the radiant temperature distribution of the plane normally to each part of the human body; it is possible to determine the radiative irradiance on the body part, including the effect of wall reflection. The proposed method is expected to enable a simple and highly accurate evaluation of radiant heat transfer. In this report, the proposed method was validated by comparing it with a method based on previous heat transfer analysis. The results showed that, although there were some differences depending on the view factor, the proposed method was able to appropriately evaluate the radiative heat transfer on each part body part, confirming its validity.
Hygrothermal Performance of Cool Exterior Wall Materials for Urban Heat Island Mitigation in Toronto, Montreal, and Vancouver
David Lefebvre1, Cynthia A. Cruickshank1, Zahra Jandaghian2
1Carleton University, Canada; 2National Research Council
The Urban Heat Island (UHI) is a prevalent effect where dense urban settings experience higher local temperatures than their rural counterpart, primarily due to the extensive use of low-albedo materials, anthropogenic heat emissions, and compact urban design. A potential mitigation strategy involves applying so-called cool materials to a building’s exterior envelope. Cool materials are characterized with high solar reflectivity and thermal emissivity, reducing heat absorption. This study investigates the hygrothermal performance of cool materials applied to the exterior wall of commercial buildings in an urban environment, focusing on the moisture engagement properties. The analysis was conducted using WUFI Pro 6.7 to assess moisture transfer, condensation risks, and mold growth potential. The model was compared and verified with existing models of identical parameters before it was employed for this study. The analysis compared the hygrothermal performance of a typical commercial wall assembly with and without cool materials for three different Canadian cities, Vancouver, Montreal, and Toronto. Results indicated the application of cool materials introduces negligible risks of moisture accumulation or mold growth for each city. The findings demonstrated the benefits of using cool materials as the exterior wall of an urban building to reduce overheating risks and urban heat island effects without compromising hygrothermal performance.
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