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Market viability assessment of a net-zero energy house
Author:
Riccardo Dalla Francesca
Supervisor:
Christian Langhoff Thuesen
DTU Management Engineering
Department of Management Engineering
Technical University of Denmark
Produktionstorvet
Bygning 424
DK-2800 Kgs. Lyngby
Denmark
Tel: +45 45 25 48 00
Fax: +45 45 93 34 35
www.man.dtu.dk
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INTRODUCTION
Buildings account for over 40% of global energy consumption and 24% of greenhouse
gas emissions (IEA, 2009). In the specific case of residential housing, more than 70% of
the energy is used for space and domestic hot water heating, while appliances represent
a smaller yet fast growing portion of demand (IEA, 2007).
Due to their relatively long lifetime, the energy efficiency of new buildings has a great
impact on the energy consumption of the whole sector in the long-term. From a home-
owner perspective, implementing measures to improve efficiency during the planning
phase requires limited efforts and costs than making improvements later on in the fu-
ture. In this way, not only is the household provided with a better indoor climate and
lower energy expenses, but the society as a whole can benefit from lower emissions,
both locally and globally (Laustsen, 2008).
During the last years there has been increasing attention in the development of so-called
zero energy buildings (ZEBs), which have become part of the energy policy in several
countries (Marszal A. J., et al., 2011).
This study aims to assess the market viability of a ZEB developed by students at the
Technical University of Denmark for Solar Decathlon Europe, an international competi-
tion among universities directed at promoting research in the design of energy efficient
houses.
1.1 Background
1.1.1 Zero energy buildings
The idea behind ZEBs is to use renewable sources to produce enough energy to equal or
exceed the annual energy use (Torcellini, Pless, & Deru, 2006). In practice, this means
that energy is sold back to the utility grid when the amount of energy generated on-site
exceeds the current building load, and that energy is purchased from the grid when the
current generation is not able to satisfy the demand (Leckner & Zmeureanu, 2011).
Despite the increasing number of demonstration projects and research in the field, there
is no clear definition and international agreement on what a ZEB is (Marszal &
Heiselberg, 2009). This lack of common understanding appears to be an obstacle to the
Introduction
2
comparison and further development of ZEBs: different definitions imply different
goals in terms of energy performance and thereby lead to substantially different design
strategies (Sartori, Napolitano, Marszal, Pless, Torcellini, & Voss, 2010). In order to
cover this gap, the International Energy Agency (IEA) has launched a joint activity of
the Solar Heating and Cooling and the Energy Conservation in Buildings and Commu-
nity Systems Programmes, which objectives are to understand the current development
of ZEBs and develop a commonly agreed framework for definition and calculation
methodology (IEA, 2009). However, for the purpose of this paper, the following defini-
tions are sufficient for the understanding of the product under assessment:
“A net zero energy building is a residential or commercial building with
greatly reduced needs for energy through efficiency gains, with the bal-
ance of energy needs supplied by renewable technologies. A zero energy
home combines state-of-the-art, highly energy-efficient designs and
equipment with on-site renewable energy generation (which typically in-
cludes a solar hot water production system and a rooftop photovoltaic, or
PV, system) to return as much energy to the utility as it takes on an annual
basis.” (NAHB Research Center, 2006)
“Zero net energy buildings are buildings that over a year are neutral,
meaning that they deliver as much energy to the supply grids as they use
from the grids. Seen in these terms they do not need any fossil fuel for
heating, cooling, lighting or other energy uses although they sometimes
draw energy from the grid.” (Laustsen, 2008)
Note that both definitions use the term ‘net’ to underline that a ZEB is connected to the
energy infrastructure and that there is a balance between the energy taken from and sup-
plied back to the utility grid.
Although common guidelines for the construction of ZEBs have not been developed
yet, a common two-step approach consists in:
1. Reducing the energy demand making use of low-energy building technologies
(e.g. implementing passive solar building design, high efficient HVAC systems,
natural ventilation, etc.);
2. Using renewable sources to supply the building with energy (Sartori,
Napolitano, & Voss, 2012).
Figure 1-1 highlights how this approach significantly reduces the amount of energy that
has to be generated to reach the ZEB balance.
Introduction
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Energy efficiency (1
st
step)
Energy generation
(2
nd
step)
Energy
supply
Energy
demand
Net ZEB
Net zero balance line
Building without
low-energy technologies
Figure 1-1: Pathway to a Net ZEB (adapted from Sartori, Napolitano, and Voss (2012))
1.1.2 The competition
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Solar Decathlon Europe (SDE) is organised by the Spanish Ministry of Housing in col-
laboration with the US Department of Energy. The competition originated in the US in
2002 and comprises now two editions: the American (held in odd years) and the Euro-
pean (held in even years). In addition, the National Energy Administration of China will
host the first edition of Solar Decathlon China in 2013.
The main purpose of the competition is to demonstrate to the public that it is both tech-
nically feasible and financially viable to build houses that produce more energy than
what they consume. Most importantly, this can be done by implementing already exist-
ing technologies and exploiting renewable energy sources more efficiently. Student par-
ticipants, on the other hand, have the unique opportunity of working in multi-
disciplinary teams to develop innovative solutions that face the major sustainability
challenges of the future. In doing so, a new integrated approach to construction is inher-
ently required, since interaction of all building components and systems need to be con-
sidered to obtain a more comfortable, energy-wise and environmentally friendly solu-
tion.
Behind these educative goals, the competition allows professionals to access to tech-
niques and processes that they can study and implement in their working life. In the
same way, universities, companies, and public institutions have the opportunity to estab-
lish new collaborations, ranging from feasibility studies of scientific projects to the de-
velopment of final products for the commercial market.
The Solar Decathlon Europe competition consists of ten contents that jointly guide the
teams in the holistic development of a house that relies only on solar energy for heating
and cooling, displays an appealing design, and provides its occupants with a comforta-
ble indoor environment. These contests are summarised in Figure 1-2.
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Information provided in this chapter is based on SDE (2012a) and NREL (2012).
Introduction
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SDE contests
Architecture
Design coherence, space flexibility, integration of
technologies, and implementation of bioclimatic
strategies.
Architecture
Energy
Comfort
Social
-
Economic
Strategic
Engineering and Construction
House structure; design and construction of plumbing
system, electrical system, PV system, and solar thermal
system.
Energy Efficiency
Efficiency of the house envelope, passive and active
systems, and appliances; energy analysis; annual
consumption estimation.
Industrialization and Market Viability
Market viability of the product, economic feasibility
study and affordability, degree of industrialization,
possibilities for grouping.
Electrical Energy Balance
Electricity autonomy, temporary generation-
consumption correlation, load consumption per
measurable area.
Comfort Conditions
Temperature, humidity, lighting, acoustic, quality of the
interior air.
Communication and Social Awareness
Communicate to the public information regarding
sustainability, innovation, and energy efficiency in a
effective, efficient, and creative way.
House Functioning
Functionality and efficiency of the selected appliances
(i.e. washing machine, dryer, dishwasher, oven,
refrigerator, home electronics, etc.).
Innovation
Innovation degree of the project with regard to the
previous contests.
Sustainability
Environmental sensibility of the team in terms of house
design, techniques, systems, and components.
Figure 1-2: Solar Decathlon Europe contests (adapted from SDE (2012b))
Introduction
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1.2 Product description
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Students at the Technical University of Denmark are participating in the final round of
the 2012 competition with a house named FOLD. This name reflects the architectural
idea underlying the design of the house, i.e. a shell wrapped around itself as a folded
rectangular paper. A high-insulated building envelope (made of plywood) eliminates the
thermal bridges around the joints, while a non-linear design guarantees an optimal ar-
rangement of the house towards the sun. In fact, while a correct orientation of the build-
ing ensures an optimal lighting and a reduced solar heat gain, the specific inclination of
the roof provides solar panels with high levels of insolation. In other words, the struc-
ture of the house can be tailored to the specific geographical location of the building
site, in order to maximise its energy performance.
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Figure 1-3: Exterior rendering – Front (DTU, 2012b)
Figure 1-4: Exterior rendering – Back (DTU, 2012b)
Moving inside FOLD, one big room comprises kitchen, living room, workstation, and
bedroom as an open living space. The bathroom, together with other appliances (e.g.
washing machine, dryer, etc.) and technical installations (e.g. plumbing, central control
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Information provided in this chapter is based on DTU (2012a).
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Choosing an optimal form and orientation of the building for a given site is the first major requirement
for a solar-optimized house (Charron, 2006).
Introduction
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unit, etc.) are embedded in a module denominated technical core, which is placed
against the wall. The total net floor area is 68 m
2
.
Figure 1-5: Floor plan with appliances (DTU, 2012b)
In designing the house and its components a systems thinking approach was followed,
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with the aim of achieving exceptional levels of energy efficiency and living comfort,
while limiting the environmental impact of the building throughout its entire life cycle
(which means, in practice, to take into consideration issues such as water utilisation,
materials quality and footprint, building transportation, and waste disposal).
To provide an example, some of the links between architecture, energy requirements,
and indoor environment are now explored. As shown in Figure 1-3 and Figure 1-4, the
house is equipped with windows on four surfaces, i.e. the roof and the façades facing
north and south. Opening these windows allows an upward flow of air that produces
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Systems thinking is “a framework that is based on the belief that the component parts of a system can
best be understood in the context of relationships with each other and with other systems, rather than in
isolation. The only way to fully understand why a problem or element occurs and persists is to understand
the part in relation to the whole.” (Capra, 1997)