141103 GOT Guidebook (with cover & back)_final - page 38

CH 4
As a building involves a large amount of variables and stakeholders, it is essential to normalise
the data collected and to formulate a comparable benchmark. For example, factors that might
affect the benchmark and overall system within the building include:
• Changes in Occupancy
• Area Usage
• Equipment
• Usage Duration
• Size of Area (Net Usable/ Carpetable Floor Area, Net Floor Area, Lettable Floor Area,
Gross Floor Area)
So, why is there a need to carefully consider and normalise indicators
The factors within an
office building mentioned above often vary. Multiple factors may even change coincidentally,
resulting in a cascade of reactions. For example, in a case where air cooled chiller is replaced
with water cooled chiller, water consumption may increase from established baseline while
electricity consumption for cooling (kWh/m
of conditioned space) may decrease. Given that
there are the changes in both electricity and water consumption, calculating the efficiency gains
from the replacement of air cooled chillers is not an easy sum if these two variables are
In addition, there is a need to represent human behaviour with numbers and figures. Hence
indicators should be normalised, for example, by conditioned/unconditioned area, different
usage of space, density of population, outdoor temperature, etc. To factor in these consequences,
the GOT Committee should first collect raw data to aid in the formulation of indicators. The
GOT Committee should then compare or calculate the indicators with regards to aspects such as
nature of usage, units and scope of indicators to determine the most suitable one to use.
HKGBC Green Tenancy Driver for Office Buildings
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