Masaya Okumiya

A ventilated courtyard as a passive cooling strategy in the warm humid tropics

The paper investigates the potential of a courtyard for passive cooling in a single storey high mass building in a warm humid climate. The inclusion of an internal courtyard in building design is attributed to the optimization of natural ventilation in order to minimize indoor overheating conditions. However, the efficiency of this strategy greatly depends on the design details of the building composition in providing appropriate airflow pattern to the courtyard. From the results of thermal measurements, a significant correlation between wall surface temperatures and indoor air temperatures is evident. A reduction of indoor air temperature below the levels of ambient is seen as a function of heat exchange between the indoor air and high thermal mass of the building fabric. However, this behavior is affected by indoor airflow patterns, which are controlled through the composition between envelope openings and the courtyard of the building.

Feasibility study of a district energy system with seasonal water thermal storage

Abstract In this paper, performance of three types of district heating/cooling and hot water supply system with natural and unused energy utilization were examined by using system simulation. An area zoned for both commercial and residential buildings was chosen for this study. The first system is the conventional system in which an electric driven turbo chiller and a gas-fired boiler are installed as the heat source. This is considered as the reference system. Two alternative systems utilize waste heat from space cooling and heating. One is designed based on short-term heat recovery and the other employs the concept of an annual cycle energy system (i.e. seasonal heat recovery). All of the three systems use solar thermal energy for hot water supply to the residential zone. The index for evaluation is the coefficient of performance of the overall system, based on primary energy. As a result, it was found that the seasonal storage system could decrease the energy consumption by about 26% and the short-term heat recovery system could decrease it by about 16% compared with the reference system. In designing the heat recovery system, a balance of cooling/heating demand is an important factor. Therefore a sensitivity analysis of performance of the overall system and the seasonal thermal storage for several load patterns was performed. From these results, it was found that if the amount of heating/cooling demand were well balanced, an improvement of energy performance could be achieved and the utilization factor of the seasonal tank would become higher. Furthermore, the volume of the seasonal storage tank could be reduced.

Indoor Thermal Modification of a Ventilated Courtyard House in the Tropics

Abstract This paper investigates the effects of airflow patterns and airflow rates on thermal behavior of a ventilated courtyard building in a warm humid climate. With some airflow patterns indoor air temperature can be brought to a level below the ambient, while with others the indoor air temperature may be higher than the ambient. The integration of a courtyard in the building design can optimize indoor airflow and is of significant importance with regard to the indoor thermal environment provided the courtyard maintains correct contacts with the outdoor environment. The current paper explores airflow patterns and airflow rates in a modern tropical courtyard house in respect to corresponding indoor thermal modifications. A thermal investigation was carried out on the site by manually changing the composition of airflow inlets (openings) found in the building envelope. From the results it is observed that the different airflow patterns affected different thermal environments and sometimes a cool condition within the courtyard and in the surrounding indoor spaces. Relatively low indoor air temperature was observed with a particular air movement pattern created through the openings found on a longitudinal horizontal axis through the courtyard. The temperature was below the ambient by 1.3 degree C with an airflow range of 1.5 to 2.0 air changes h-1.

Revolution of Urban Energy System

Fragility of energy supply structure in Japan was exposed with Great East Japan Earthquake as a turning point. Then it is required to reduce consumption of fossil fuel and utilize renewable and unused energy for securing the safety of society. Also shift of energy supply from centralized system to decentralized one for improving efficiency of system. There are many kinds of unused energy such as river/sea water and waste heat in city. However, it is difficult to use these energy by individual buildings. Therefore area energy system and energy network play an important role. Also networking of energy system functions as a mutual help system in the city at an emergency. Under this background in this paper energy interchange in urban central district and utilization of waste heat from heating/cooling of building are discussed with the results of studies on these topics.

AN EXAMINATION ON ADEQUATE CAPACITY FOR MULTI-SPLIT TYPE AIR CONDITIONING USING CENTRALIZED CONTROLLER WITH A FUNCTION OF GAS RATE PROPORTIONAL DIVISION

This paper discusses about an examination on adequate capacity for multi-sprit type air conditioner using centralized controller with a function of gas rate proportional division. The objective system is a gas heat pump air-conditioner of an agricultural research building. The effect of energy saving was analyzed by LCEM tool using the estimated actual thermal load under the assumption of retrofit / renewal for airconditioning equipment. The energy savings from the current situation was that the case of proper capacity repair is 5% reduction, and the case of renewal can be reduced 15% of the operation energy consumption.

Experimental and Simulation Studies on Photovoltaic/Thermal Hybrid Collectors

For increasing total efficiency of solar collectors, PV/T hybrid collectors are focused. A number of simulation models for the PV/T hybrid collector have been proposed, but there are few models that checked the relevance by comparison with the actual measurement. Therefore we picked up sheet-tube type hybrid collectors and measured the thermal and electrical outputs in Tsukuba, Japan to compare with calculation results. We focused the Extension Hottel-Whillier model that is proposed by Florschuetz, 1979, as a basic simulation model. Also proposed the Modified Extension Hottel-Whillier model to increase the accuracy of the electrical performance. Both models showed good agreements with the measured thermal collection positively. The Extension Hottel-Whillier model constantly calculated the large electrical output but the Modified model kept it down ideally. Under the low solar radiation, however, there was large error of the electrical output by the limit of the solar cell model.Copyright