Winter Issue 2022 - 79

(Zero emissions is defined as a building
that generates and/or purchases a sufficient
level of renewable energy to offset
carbon emissions generated through its
annual operations. This analysis excludes
embodied carbon costs.)
This case study is based on a project
submitted by a team of students from
the Harvard Graduate School of Design to
the 2021 U.S. Department of Energy Solar
Decathlon. The objective was to design a
sustainable office building that balances
occupancy and neighborhood needs while
earning a financial return commensurate
with the risk/return profile of unsubsidized
private capital.
To achieve the 90 percent reduction in
energy demand, the design focuses on four
key strategies:
reducing peak heating and cooling
loads;
reducing energy consumption for artificial
lighting and plug loads;
maximizing on-site renewable energy
generation; and
using building materials with low
embodied-energy costs.
The property's return on investment
(ROI) was calculated for each of six main
design decisions:
using efficient lighting systems and plug
loads;
maximizing the building's geometry to
increase solar photovoltaics potential;
adding an atrium and skylights to
reduce the need for artificial lighting, and
adding PV panels;
installing a solar chimney to support
buoyancy-driven air flow, reducing cooling
loads;
installing a ground-source heat pump
to increase the energy yield of the heating,
Solar Chimney
The tapered shape of the solar chimney is a
result of the added air flow toward the top of the
building.
ventilation, and air-conditioning (HVAC)
system; and
applying an ethylene tetrafluoroethylene
(ETFE) pillow facade system. This conceptual
system, composed of gold-coated
silicone film, stretches and contracts
throughout the day to adjust the amount
of solar heat coming through the building's
windows.
An estimate of the contribution to
energy reduction and cost for each of these
six strategies is below.
This case study uses DesignBuilder
EnergyPlus software to adjust how ResilientHub
would perform using a range of
building systems under environmental
development scenarios for 2025 through
2080. Site energy data calculated from
DesignBuilder's simulation summary was
used to calculate ROI for each of the building's
core design decisions.
The analysis was divided into design
scenarios to demonstrate how changes to
the property's design and building systems
would affect energy demand in kilowatthours
(kWh) per square foot. The first step
of this analysis involved designing a tradiThe
height and size of the chimney are varied to
ensure that enough fresh air can be ventilated into
each zone.
tional 16-story, rectangular office building
as a benchmark that maximized the site's
floor/area ratio (FAR) but used traditional
HVAC systems, inefficient plug loads, and
traditional building envelope systems.
(Some aspects of this benchmark fall short
of the current Massachusetts energy code.)
From that baseline, 45 kBtu per square foot
(540 kBtu per sq m), six additional simulations
were run to calculate total site energy
for each major design choice.
To calculate the ROI for each phase,
total site energy use was simulated in
DesignBuilder and converted into annual
operating expense according to local
energy pricing. It was then assumed that
for every dollar decrease in operating
expenses, rents could be increased by 95
cents. The return on capital investment
is directly related to the incremental rent
that developers can charge for each dollar
of reduction in operating expenses, which
are normally passed through to the tenant.
(The 95-cent ratio is consistent with a 2013
study, " The Economics of Green Building "
in The Review of Economics and Statistics,
conducted by Piet Eichholtz, Nils Kok, and
WINTER 2022
URBAN LAND
77
L.TOMHOLT, K. KHARBANDA, S. CHEN, K. CHEN, AND A.GIBBS
Winter Issue 2022

Table of Contents for the Digital Edition of Winter Issue 2022
