Hiroshi Ishibashi
President
Nagasaka Corporation, Tokyo

Ken Miyoshi
Engineering Director - Engineering Department
Nikken Sekkei Ltd, Tokyo

Optimizing High-Rise Energy Performance With a Hybrid Ventilation System

The project team for this high-rise office tower in the center of Tokyo focused on achieving high-performance energy use, comfort, and resiliency. Its hybrid natural ventilation system uses uses wind and stack pressure in a complementary fashion. The system can either double the air volume by exploiting both effects simultaneously, or enable natural ventilation during a period when there is no external wind pressure, expanding the effective period. A micro-dedicated outdoor air system (Micro-DOAS) was developed and integrated with the façade to minimize the thermal conveyance of energy while improving the controllability of outdoor air intake. The Micro-DOAS, located between the columns along the north and south perimeter, uses a high-efficiency electronically commutated (EC) fan. Underfloor air distribution (UFAD) was introduced to distribute the outdoor air effectively to the 4.2-meter-high ceiling space, while minimizing zoning. A water-cooled variable-refrigerant-flow (VRF) system was adopted for heating and cooling, which minimizes thermal conveyance energy and allows optimal control according to usage conditions.

This building challenged the perception that it is impractical to attempt to harness naturally occurring wind effects to ventilate high-rises. Its hybrid ventilation system is expected to reduce energy for cooling, especially during the seasons when the outdoor temperature is between 15 and 26 degrees Celsius. Using standard meteorological data, it is estimated that out of 4,745 hours of annual HVAC system operation time, 30 percent are available for wind ventilation, and an additional 3 percent can be used for stack ventilation during hours with low winds. The project is expected to yield energy savings of 30% or more over standard design.

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