Japan Sustainable Building Database

Air conditioning system combining natural ventilation and ceiling fans

Figure A1: CFD of natural ventilation

natural ventilation

An effective amount of natural ventilation is ensured by minimizing the resistance in the ventilation route. Additionally, since there is a major road in front of the site, outside air is not introduced directly through windows. Instead, it is slowed down by a chamber and then introduced into and passed through an underfloor trench at low velocity to prevent the ingression of noise and dust into rooms. As a result of CFD analyses, the air velocity in the rooms on the typical floor was about 0.2 m/s, and that in the staircase was 0.5 to 0.7 m/s.

Air conditioning system combining natural ventilation and ceiling fans

ceiling fan

Figure B1: Air velocity distribution on plane at a height of 1.1 meters from the floor surface of the typical floor with the ceiling fans in operation

From the results of air velocity distribution measurement on planes at a height of 1.1 meters from the floor surface of the offices on the typical floor with the ceiling fan in operation, an uniform air flow of 0.2 to 0.3 m/s was obtained on the whole, and we confirmed that the inside air of the rooms was circulated with a gentle air flow.
The results of the questionnaire given to residents conducted during air conditioning with the ceiling fans revealed that 86% of residents had a sense of coolness in connection with the thermal environment of their rooms, both visually and in terms of air flow.

Air conditioning system combining natural ventilation and ceiling fans

construction and operation performance of control system

Figure C1: Ratio of operation modes for cooling period from April through November 2004

We studied the performance of diverse air conditioning modes for all air conditioning hours from April through November 2004 in which cooling took place to verify energy-saving operation in these air conditioning modes. "Natural ventilation" using neither a heat source nor an air conditioning system and the air conditioning mode of "natural ventilation + ceiling fans" accounted for 17% of all modes,which increased to 23% when times using floor diffusion air conditioning in addition to natural ventilation were added. Air conditioning hours using ceiling fans comprised as much as 87%. With regard to air conditioning modes in October, which is an in-between season, 56% of the air conditioning hours did not use a heat source or air conditioning system. Natural ventilation was used for 66% of the total time period.
The results of room temperature variation measurement in the intermediate season showed that various air conditioning modes were selected in air conditioning hours, and the room temperature did not remain constant as with standard air conditioning systems but varied within a comfortable range. We confirmed that air conditioning modes were selected according to outside air conditions and while internal load variations were accepted, and the thermal environment inside the office space was controlled using as little energy as possible and within a specific allowance.

Use of exhaust heat for a cascade by micro gas turbine cogeneration

 

Figure D1: CGS Energy saving rate

Exhaust heat is recovered by an exhaust gas input type cold/warm water gas system and then transformed into warm water by an exhaust gas heat exchanger. Exhaust heat recovery is performed by a desiccant air conditioning system during the cooling period, by a warm water heat exchanger for heaters during the heating period, and by a heat exchanger for hot water supply to hot water supply loads throughout the year using exhaust heat for a cascade.The energy saving rate throughout the year was 8.4%.