The "extended building energy hub": a new method for the simultaneous
optimization of energy demand and energy supply in buildings.
Among the energy consumer groups, it is known that buildings
account for almost one-third of the global energy use in a country, and
consequently contribute, to a great extent, to greenhouse gas greenhouse gas
Any of the atmospheric gases that contribute to the greenhouse effect.
greenhouse gas emissions.
Therefore, the energy performance of buildings has become a subject that
is frequently investigated and discussed by designers, researchers,
policy makers, and appliers.
The energy consumption of buildings depends on several factors,
such as indoor and outdoor climate, building fabric, HVAC (Heating Ventilation Air Conditioning) In
the home or small office with a handful of computers, HVAC is more for human comfort than the
machines. In large datacenters, a humidity-free room with a steady, cool temperature is essential
for the trouble-free systems, the
behavior of the occupants, etc., and it is one of the major costs during
the life cycle of a building. Designers are, therefore, expected to
choose the best alternative, in terms of energy efficiency and economy,
from among many technologies and options that exist. However, as a
result of the inter-dependent interactions between these variables, and
the large number of parameters that have an impact on building energy
performance, it can be rather difficult to find the overall optimum
alternative by only adopting best practice codes or traditional design
methods. The introduction of optimization optimization
Field of applied mathematics whose principles and methods are used to solve quantitative
problems in disciplines including physics, biology, engineering, and economics. methods into the
process of buildings and systems allows the problem to be approached
rationally and rigorously. The "optimization" process can be
described as an attempt to find the best possible values for a set of
variables (decision variables) of a system, while satisfying various
Lately, there have been several research advances in the fields of
both building energy efficiency and energy systems design and
optimization (Fong et al. 2006; Parameshwaran et al. 2010), but most of
these studies have treated energy demand and supply separately and
In the first area, the energy saving potential achievable by means
of intensive thermal insulation The term thermal insulation can refer to materials used to reduce
the rate of heat transfer, or the methods and processes used to reduce heat transfer.
Heat is transferred from one material to another by conduction, convection and/or radiation., a
dynamic and adaptive envelope, heat
recovery units, passive heating and cooling, and free cooling has been
investigated in great depth and the result is a series of measures that
can significantly reduce the energy consumption of a building.
In the second field, besides an increase in the energy efficiency
of traditional converters and the adoption of low exergy equipment,
there has been an increasing trend towards a greater use of renewable
energy Renewable energy utilizes natural resources such as sunlight, wind, tides and geothermal
heat, which are naturally replenished. Renewable energy technologies range from solar power,
wind power, and hydroelectricity to biomass and biofuels for transportation. sources and the
integration of various primary and secondary
energy sources in a single system. This latter research topic has also
exploited the know-how that has been developed since the 1990s in the
field of hybrid energy systems, a concept that, in its early development
phase, was only used in stand-alone applications (Manwell 2004).
However, despite some remarkable advances in research, these two
subjects (i.e., energy demand and energy supply optimization) were, and
still are, investigated separately in the framework of the typical
building design process. The usual approach consists of a 2-step
procedure in which the analysis and identification of the best
technologies for energy demand reduction is first performed and then the
most suitable solution for the primary energy conversion and supply is
explored (Fong et al. 2006; Parameshwaran et al. 2010). With such a
procedure, the relationship between demand and supply may not be clearly
understood, and not all the possible scenarios that can be derived from
the permutation One possible combination of items out of a larger set of items. For example, with
the set of numbers 1, 2 and 3, there are six possible permutations: 12, 21, 13, 31, 23 and 32.
(mathematics) permutation - 1. of the variables that influence the energy demand and
the energy supply can be considered and evaluated.
Therefore, at present, it is of the utmost importance to bridge the
gap between these approaches, which result in being inadequate for the
design of the latest energy technologies (where traditional building
installations interact with solar and renewable systems and, possibly,
with the building envelope A building envelope is the separation between the interior and the
exterior environments of a building. It serves as the outer shell to protect the indoor environment
as well as to facilitate its climate control. and structure--see, e.g., IEA-ECBCS Annex an*nex
tr.v. an*nexed, an*nex*ing, an*nex*es
1. To append or attach, especially to a larger or more significant thing.
2. 44), and for the requirements posed by the use of integrated energy
systems fed by multiple sources and carriers.
Starting from the most recent advances in both fields, the aim of
the present work is to propose and develop a procedure that could
jointly and simultaneously optimize the energy demand and the energy
supply of a building. This will be pursued by introducing the extended
building energy hub (EBEH) concept.
EBEH is an analysis method that can be used to evaluate the
potential of an integrated building energy demand-supply optimization.
It is relatively easy to use and, at this development stage, it can be
adopted as a pre-design tool to identify the best strategy for energy
efficiency and to assess the potential for simultaneous optimization of
building energy demand and supply.
In the following sections, the EBEH concept will be introduced as
an evolution of the original concept of the building energy hub (BEH BEH Bulletin Epidemiologique
BEH Behind Enemy Lines (movie)
BEH Bureau of Environmental Health (Ohio)
BEH Bureau of Education for the Handicapped ).
The approach philosophy and its structure will be discussed and the
methods adopted to implement this idea will be presented.
Finally, a case study is used to demonstrate the potentialities of
the EBEH and to illustrate its relevant differences from a traditional
Concepts and methods
The hybrid energy hub (HEH) modeling framework
The HEH concept was first introduced in 2004 by a research team at
the Power System and High Voltage The term high voltage characterizes electrical circuits, in
which the voltage used is the cause of particular safety concerns and insulation requirements.
High voltage is used in electrical power distribution, in cathode ray tubes, to generate X-rays and
particle beams, to Laboratories of the Zurich ETH eth
Variant of edh. led by
Goran Andersson and Klaus Frolich in a series of papers (Geidl and
Andersson 2005a, 2005b; Klockl et al. 2005; Geidl et al. 2006; Koeppel
and Andersson 2009; Geidl 2007; Koeppel 2007). This team developed an
integrated modeling framework to simulate simulate - simulation and optimize highly
interlinked energy systems for a future multi-carrier and multi-product
network. The energy hub concept was developed within a European project
named "Vision of future energy networks," concerning the study
and the optimization of a series of centralized cen*tral*ize
v. cen*tral*ized, cen*tral*iz*ing, cen*tral*iz*es
1. To draw into or toward a center; consolidate.
2. units that transform,
convert, store, and supply various forms of energy (that is hybrid (1)
energy hubs) linked by a combined electrical, chemical, and thermal
energy thermal energy
Internal energy of a system in thermodynamic equilibrium (see thermodynamics) by virtue of its
temperature. A hot body has more thermal energy than a similar cold body, but a large tub of cold
water may have more thermal energy than a cup of boiling interconnector.
A series of algebraic 1. (language) ALGEBRAIC - An early system on MIT's Whirlwind.
[CACM 2(5):16 (May 1959)].
2. (theory) algebraic - In domain theory, a complete partial order is algebraic if every element is
the least upper bound of some chain of compact elements. relations was developed by Geidl
order to couple system inputs and outputs. In the HEH approach, the
energy inputs vector, namely the energy supply fluxes, is related to the
energy outputs vector that is the energy demands, by a coupling matrix.
The coefficients of this matrix are functions of the efficiency of the
various energy conversion systems and of the distribution of energy
fluxes in the energy converters. As a result, this model provides the
best combination of the energy supply fluxes for a fixed, given
configuration of the energy system (use of the model in the operational
phase) and/or the optimal configuration of the energy system (use of the
model during the design phase).
The main advantage of the energy hub theory, which is also the
reason for its success, is that it can handle complex and interlinked
systems in a simple and rational way. In other words Adv. 1. in other words - otherwise stated; "in
other words, we are broke"
put differently, this framework
generalizes the problem of modeling and, under a certain set of
assumptions, optimizes any energy system fed by various energy sources.
The hybrid energy hub concept was mainly applied by its authors to
perform structural optimizations of network energy systems and to study
the reliability of supply systems, even in the presence of energy
The usefulness of the hybrid energy hub concept can be measured by
the number of applications carried out by several researchers from The
Netherlands, Spain, Iran, and Italy in various fields.
A typical application that can be found in the existing literature
is the one by del Real et al. (2009), who performed a sizing
optimization of a wind-fuel cell-battery storage-hydrogen storage power
system. Nazar and Haghifam (2009) developed a three-stage optimization
technique for the optimal planning of the extension of an electric
The HEH approach, as can be deduced from the available examples,
was originally focused more on the problem of studying and optimizing
the electric energy networks (at a local or mid-size scale).
The BEH modeling framework
In order to extend the applicability of the concept to the building
sector, a further development was proposed by Fabrizio (2008).
Fabrizio et al. (2009a, 2010) used the energy hub concept to model
a framework--hereafter called BEH--to size a multi-energy system that
served a building.
This methodology is able to take into account the quality/value of
the energy, the variability of the conversion efficiency as a function
of the boundary conditions and of the part loads, and, finally, the
variability of the operating conditions. The BEH method can be seen as a
parameter (1) Any value passed to a program by the user or by another program in order to
customize the program for a particular purpose. A parameter may be anything; for example, a file
name, a coordinate, a range of values, a money amount or a code of some kind. estimation
In mathematics, use of a function or formula to derive a solution or make a prediction. Unlike
approximation, it has precise connotations. In statistics, for example, it connotes the careful
selection and testing of a function called an estimator. technique.
When using the BEH, the energy demand of a building is a known
(pre-assessed) variable and is entered into the hub as an output vector,
[P.sub.out] ("output ports" of the hub [Figure 1]). The
energy-wares that feed the energy converters are then derived in
function of the conversion efficiency and of the [epsilon] factors,
which represent the fraction of a certain building load (e.g., energy
for space heating Space heating is the heating of a space, usually enclosed, such as a house or
room. A space heater keeps the air and surroundings at a comfortable temperature for people or
animals, or even plants in a greenhouse., space cooling, electric energy, etc.) that is covered
by a specific converter (1) A device that changes one set of codes, modes, sequences or
frequencies to a different set. See A/D converter.
(2) A device that changes current from 60Hz to 50Hz and vice versa. (k). The set of possible
therefore, a vector of dependent variables, [P.sub.in], which is
supplied at the "inlet inlet /in*let/ (-let) a means or route of entrance.
pelvic inlet the upper limit of the pelvic cavity.
thoracic inlet the elliptical opening at the summit of the thorax. ports" of the hub.
The best distribution of the primary energy sources required to
meet the demand is determined on the basis of the selected objective
functions, the output vector (energy demand), the input vector
(energy-wares), and the eventual constraints, through identification of
the hub parameters (that is, the fractions [[epsilon].sub.i] of the
building demands, [P.sub.out], covered by each possible
Figure 1 schematically sche*mat*ic
Of, relating to, or in the form of a scheme or diagram.
A structural or procedural diagram, especially of an electrical or mechanical system. shows the
use of the BEH. It should be noted
that the input/output vectors of the hub (the energy-wares vector,
[P.sub.in], and the energy demands vector, [P.sub.out], respectively)
are not the input/output of the calculation process; they just represent
the energy fluxes entering/exiting from the hub.
[FIGURE 1 OMITTED]
The results of the calculation process, as highlighted in Figure 1,
are the model parameters (i.e., the hub parameters, represented by
factors [[epsilon].sub.i]) that satisfy the constraints and optimize the
energy exploitation on the basis of suitable objective functions.
Two methods have been developed from the original energy hub: a
seasonal method (Fabrizio et al. 2010) and an hourly method (Fabrizio et
al. 2009a). The first one is more suitable for use at an early design
stage, while the second one is more appropriate for a final design
The BEH surely represents a relevant improvement and it is an
effective tool in the optimization of the energy efficiency of
buildings, but it was only aimed at the analysis of the energy supply.
In other words, the method starts to be used from a point where all the
technologies and actions necessary for an energy demand reduction have
already been chosen and implemented, as outlined in Figure 2.
This feature could, in some cases, be a significant drawback DRAWBACK, com. law. An
allowance made by the government to merchants on the reexportation of certain imported goods
liable to duties, which, in some cases, consists of the whole; in others, of a part of the duties which
had been paid upon the importation.. It is
well known that many HVAC systems, installations, and technologies used
for the exploitation of renewable energy sources can be coupled
effectively with certain building categories and envelope component
types, but are unsuitable or less effective with others. Moreover, it
has been extensively demonstrated (IEA-ECBCS Annex 44, 2010) that future
development towards zero energy buildings (ZEB ZEB Zero Energy Building
ZEB Zero Emission Bus ) will need to adopt
integrated building concepts and responsive building elements. As a
consequence, traditional building construction elements (like floors,
walls, facades, roofs, foundation, etc.) will, in the near future, be
functionally and rationally combined and integrated with building
service functions, such as heating, cooling, ventilation, and lighting,
and used to actively transfer and store energy and mass. Therefore, the
design process can no longer consider the building elements and the
In order to overcome the above-mentioned flaws, and to effectively
face the challenges posed by ZEB requirements, a new approach is needed,
whereby both the energy demand side and the energy supply side could be
considered together and simultaneously.
For these reasons, the authors propose the so-called EBEH concept
(Bayraktar et al. 2010) in the present article.
EBEH adopts the optimization approach that is characteristic of the
BEH application, but extends the set of decision variables of the
optimization problem In computer science, an optimization problem is the problem of finding the
best solution from all feasible solutions. More formally, an optimization problem is a quadruple to
the relevant aspects of the thermal design of a
building (on which the energy demand depends).
In this way, for example, the opportunities of increasing the
thermal resistance of the walls of a building is contrasted with the
opportunity of using solar energy for electricity production, where the
decision criterion is either the primary energy savings or the financial
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
The EBEH concept scheme presented in Figure 3 summarizes the main
entries (input data and boundary conditions), results (output data), and
The idea behind this concept is that the results of a
"one-sweep" optimization, performed in a domain that spans
from the building features to the systems features and energy source
opportunities, can give results that are significantly different from
those that may be reached using two successive optimizations (or
selections, in the case of a finite set In mathematics, a set is called finite if there is a bijection
between the set and some set of the form where n is a natural number. (The value n = 0 is
allowed; that is, the empty set is finite.) An infinite set is a set which is not finite. of design
alternatives) in a
cascading procedure, where the building characteristics are first
considered and then the system configuration is taken into account
In other words, both the demand side options (regarding the heating
energy, cooling energy, and electricity demands) and the supply side
options are simultaneously treated together and contrasted one against
the other in an overall optimization approach (Figure 3).
With the proposed concept, the energy flow that is saved by
adopting an energy saving measure (insulation, heat recovery, solar
shading See Phong shading, Gouraud shading, flat shading and programmable shading., glazing
The application of finely ground glass, or glass-forming materials, or a mixture of both, to a
ceramic body and heating (firing) to a temperature where the material or materials melt, forming a
coating of glass on the surface of the ware., etc.) is considered and treated in the same way as an
energy flow that is produced by means of a renewable source. This allows
the energy saving measures to be taken into account in a framework that
is similar to that of the BEH.