Hiromi Habara

Estimation of Cooling Energy Reduction by Utilizing Cross-Ventilation in Detached Houses, within the Japanese newly introduced Energy Regulation - Evaluating Energy Consumption for Different Uses

Abstract The reduction of carbon dioxide emission due to energy consumption in the household sector is an urgent task, worldwide. As a measure to respond to the task, a new regulation has just been enforced since April 2009, in Japan. This regulation evaluates the energy performance of detached houses by estimating the primary energy consumption for different uses, namely, heating, cooling, ventilation, domestic hot water and lighting. Especially in mild or hot climates, it has been frequently claimed by practitioners that the regulation, which is heavily focused on insulation performance, is not enough and broader aspects should be equally evaluated. The effectiveness of cross ventilation in reducing cooling energy is one of these aspects. However, there have been difficulties to overcome in predicting the effectiveness of cross ventilation on cooling energy reduction. Among such difficulties are the decrease of the discharge coefficient of openings with inclined airflow, variation of the wind pressure coefficient depending on surrounding conditions, etc., occupants’ window opening behaviour and actual energy efficiency of air conditioners depending on their output and outdoor conditions. By referring to the results from experiments and observations on cross ventilation and air conditioners, the authors have proposed a solution for the Japanese new energy regulation on how to predict cooling energy consumption, taking the above factors into consideration. Even though there are still problems to be solved, the solution by the authors, shown in this paper, can be a guidepost to a more reasonable evaluation of the energy performance for cooling in buildings, as well as to a more reasonable design practice for windows and openings on the partition walls.

Meso-Level Research towards Low Carbon Society

To achieve the Low Carbon Society, not only the technological progress but also change of the society is required. It includes land use planning, life style, institutional design, consumer’s behavior, and so on. For example, consumer’s choice of energy efficient technology is not always agreed with economical optimum in household economy. In Japan, preference to photovoltaic is very high and there is large amount of willingness to pay for photovoltaic technology. On the other hand, preference to solar water heater is low and total number of installation has been decreasing. The authors propose several types of “eco-design of low carbon society” in residential and commercial sector. Examples are as follows: 1) Design of energy efficient land use. 2) Industrial and institutional design of building integrated solar energy systems.

Measurement of Natural Ventilation Rate in a Japanese Residential Building

Abstract It is difficult to design a naturally ventilated indoor environment because there is insufficient knowledge to evaluate the effect of the natural ventilation space quantitatively. Especially, natural ventilation rate is not yet fully understood. In this paper, the properties of natural ventilation with large openings are examined mainly from the results of measuring ventilation rate. This measurement analysis shows that the resistance of the interior doors is large and the ventilation rate is almost caused by air exchange through a single opening when the interior doors are closed (single-sided ventilation). By contrast a high ventilation rate is observed when the interior doors are opened (giving cross ventilation). This paper also identifies which factors influence the ventilation rate through the large openings.

Verification of the Effect of Cross-Ventilation on Energy Conservation by Simulating Occupant Behaviour

Abstract Recently, natural ventilation, which is a traditional cooling method in Japan, has become considered as the key method for cooling energy conservation. The results of experiments are presented to measure the indoor thermal environment and cooling power consumption in an experimental dwelling by simulating occupants’ life-style including thermal control with natural ventilation and air conditioning. Based on the experimental results the cooling power consumption from July to September has been estimated. The results show that natural ventilation is an effective technique for saving cooling energy consumption. They also suggest that temperature parameters (the upper limit of room temperature, without using an air conditioner, and the preset temperature of an air conditioner) are very important to estimate the cooling energy saving effect with or without using natural ventilation.