Abstract
The purpose of this study is to determine the effects of evaporation and condensation on the underfloor space of Japanese detached houses. In this underfloor space, natural ventilation is applied. A typical Japanese wooden detached house is raised 0.3–0.5 m over an underfloor space made of concrete. The bottom of the underfloor space is usually paved with concrete, and the ceiling which is directly underneath the indoor occupant zone is made of wood. Computational fluid dynamics (CFD) analysis is applied to calculate the rates of the evaporation and condensation generated inside the underfloor under two conditions, namely, a constant (fixed) outdoor environmental condition and a fluctuating environmental condition. In the constant condition, we verified the effects of the outdoor humidity, ventilation rate, and ratio of wetted surface (RWS, ω) on the evaporation and condensation inside the underfloor space. In this condition, the rate of evaporation and condensation was quantified considering the varying outdoor humidity between 0 to 100%, and the RWS (ω = 1 or 0). In addition, the influence of the different ventilation rates at 1.0 m/s for normal and 0.05 m/s for stagnant wind velocities were confirmed. Under fluctuating environmental conditions, the outdoor conditions change for 24 h, so the RWS varies. Therefore, the rate of evaporation and condensation, the amount of the condensed water, and the area of condensation were confirmed. The results were as follows: with a high airflow rate on the underfloor space, the evaporation and condensation phenomenon occurs continuously and is easily affected by outdoor humidity, while under low airflow rate conditions, only the condensation appeared steadily. If the wind velocity is strong, the convective mass transfer on a surface becomes large. In a condition of the outdoor humidity and the airflow rate on underfloor are high, condensation mainly occurs in a corner of the underfloor space due to high evaporation by convection in the mainstream of the airflow. By contrast, when the airflow rate is low, condensation occurs along the air stream. Accordingly, this information could be employed as design considerations for the underfloor space at the architectural design stage.
Highlights
The aim of ventilation of the underfloor space is to prevent moisture generated in the ground from entering the living area and to improve the heating and cooling efficiency of the building, given the large heat capacity of the ground
In a condition of the outdoor humidity and the airflow rate on underfloor are high, condensation mainly occurs in a corner of the underfloor space due to high evaporation by convection in the mainstream of the airflow
The results wind speed conditions, namely, 1.0 m/s and m/s, 0.05 are m/s, as follows: The results forfor thethe twotwo wind speed conditions, namely, 1.0 m/s and 0.05 as are follows: the the wind direction is from the south, with the wind flowing into the underfloor space through two wind direction is from the south, with the wind flowing into the underfloor space through two openings wall southern side, from where dispersed into each internal zone and openings in in thethe wall onon thethe southern side, from where it it is is dispersed into each internal zone and exhausted through the other five openings
Summary
The aim of ventilation of the underfloor space is to prevent moisture generated in the ground from entering the living area and to improve the heating and cooling efficiency of the building, given the large heat capacity of the ground. The underfloor space is generally ignored by generally the residents, as it is only inconspicuous, to clean. Moisturetooriginates ignored bynot the residents, as it is but notalso onlydifficult inconspicuous, and difficult clean. From the ground (soil), originates which absorbs after rain, or from and enters. Moisture from water the ground (soil), whichgroundwater, absorbs water after rain,theorbuilding from through the ventilation openings. It is important to block the source of the moisture in order groundwater, and enters the building through the ventilation openings. It is important to block the to control theofhumidity level in and to prevent the generation of condensation inside the source the moisture order to control the humidity level and to prevent theunderfloor generationspace
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