ASHRAE Journal - March 2022 - 35

2022 ASHRAE AWARD OF ENGINEERING EXCELLENCE
FIGURE 5 Operation mode patterns of the TWU.
Exhaust Operation
AC + Ventilation
Power Consumption:
1.3 kW/Unit
Exhaust by Outdoor
Unit Fan (Ventilation)
Indoor Fan: ON
EAEA
EAEA
AC
ON/OFF
SASA
RARA
Ventilation
Power Consumption:
0.1 kW/Unit
Room Air Circulation by Indoor
Unit Fan (Air Conditioning)
Outdoor Fan: ON
RARA
Return Air from Baseboard Slit
Compressor: ON
Automatic
Switching
Circulation Operation
3. affected areas identifi cation;
and 4. Report compilation.
AC Mode
Power Consumption:
1.7 kW/Unit
Outdoor Air Circulation
By Outdoor Unit Fan OAOA
SASA
Indoor Fan: ON
EAEA
EAEA
3. This enables natural ventilation without using
electrical power for the AHUs and TWUs when the power
supply is interrupted.
The new TWU is easy to install as it only needs to be
installed inside a perimeter enclosure. It is versatile for
other projects as air-conditioning and ventilation operations
are available by connecting a single-phase power
source. This can be generally applied to most high-rise
buildings.
Operation and Maintenance
There is no difference in the maintenance method
between the new TWU and the conventional TWU. It can
be maintained and updated even if there are partitions
at the windows within the 3.6 m (11.8 ft) installation
width. Installing a peripheral balcony for safe maintenance
above the railway reduces maintenance cost and
improves effi ciency.
This building incorporated life-cycle design commissioning
using building information modeling (BIM).
It has been widely recognized that recent high-rise
buildings with complex systems are facing serious
problems with a shortage of skilled facility managers.
Furthermore, the need for remote management
is increasing in the new coronavirus era. The effi cient
building operation was achieved by using digital twin
technology, such as BIM and simulations. Facility management
by digital twin was accomplished by developing
a facility management support tool that links virtual
building location information stored in BIM, which is
displayed on tablets, to the as-built drawings and documents
in Excel and PDF forms.
A specialized tool was developed that leverages BIM for
the four basic functions of building management operations:
1. Equipment search; 2. Systems identifi cation;
RARA
AC
ON/OFF
Stop
Room Air Circulation by Indoor
Unit Fan (Air Conditioning)
Outdoor Fan: ON
Compressor: ON
Return Air from Baseboard Slit
Cost Effectiveness
The new TWU requires a 25%
increase in initial investment
compared to the standard type
of TWU. On the other hand, this
device eliminates the need for
indoor drain pipe work by connecting
the drain pipe of the
sash at the installation point,
and drain pipe has been signifi cantly reduced. The
increase in initial (2015) investment, which includes
not only TWU, but also the sash chamber and automatic
control was $28/m2 ($2.60/ft2). The current annual cost
reduction is $26,000, with a simple payback of about 4.9
years to recover the additional investment, under the
assumption that utilities' price rates remain unchanged.
As for the entire building, compared to the unit construction
cost of steel reinforced concrete construction in the
Tokyo area ($4,500/m2 [$418/ft2), the highly constrained
construction spanning across the railway was realized at the
unit construction cost of $6,000/m2 ($557/ft2). The rentable
ratio of a standard offi ce fl oor is 84.3%, which is 10% higher
than the usual 65% to 75%. Besides, the 30-year life-cycle
cost reduction is expected to be reduced by 36% ($145 million
compared to $227 million for a standard building).
Environmental Impact
The CO2 emissions of this building have been signifi
cantly reduced through the successful integration
of TWUs, high effi ciency heat source systems, thermal
storage, and improved operation. The actual reduction
in CO2 emissions was 50.3 kg CO2/m2·yr for this building,
compared to the average value for offi ce buildings
in Tokyo (2017) of 88.9 kg CO2/m2·yr, a reduction
of about 43% from the average value. This building is
ranked in the top 3% of the 462 samples of Tokyo offi ce
buildings in 2017 and is a very low carbon building. As a
result, LCCO2 was reduced by 24% (113.21 kg CO2/m2·yr
compared to 152.90 kg CO2/m2·yr for a standard building).
Further, ultra-water-saving toilets (3.8 L/fl ush)
and rainwater fi ltration for reuse were installed to save
resources. The percentage of rainwater and condensate
water to the amount of graywater use is 75%. Overall
water savings is nearly 35% above the local baseline.
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