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LBNL-48371
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GenOpt -- A Generic Optimization Program
Michael Wetter, Proc. IBPSA "Building Simulation 2001" Conference, August 13-15, 2001, Rio de Janeiro. |
GenOpt Design Optimization with GenOpt
Abstract:
Despite the fact that thermal building simulation is increasingly being
used for system design, the possibilities that a simulation model
offers are not used by the designer: To achieve better system
performance, designers merely guess different settings of system
parameters that may lead to better performance. This practice is
inefficient and labor intensive. Also, if the number of parameters
being varied exceeds two or three, the designer is overwhelmed by
trying to understand the nonlinear interactions of the different
parameters being varied. However, mathematical programming is a
technique that allows multidimensional optimization of a computer
simulation model. It assists the analyst in designing better systems in
a more cost-effective way. This paper describes how such
optimization can be done using GenOpt, a generic optimization program,
which has been developed to allow optimization for building and HVAC
design. The article shows how to use GenOpt for designing an office
building such that source energy consumption for heating, cooling, and
lighting is minimal with respect to the design parameters. In the test
case being presented, the optimization yields 14 percent
energy savings. The
additional time required to set up the optimization is about an hour.
The measures found by using optimization not only decrease operating
costs, but also lead to better daylighting usage which results in
higher comfort for the building occupants.
LBNL-46302
JOINT US-CHINA DEMONSTRATION ENERGY EFFICIENT OFFICE BUILDING
Abstract:
In July 1998, USDOE and China's Ministry of Science and Technology
(MOST) signed a Statement of Work to develop a demonstration
energy-efficient office building and demonstration center in Beijing
that will eventually house the Administrative Center for China's Agenda
21 (ACCA21). The statement calls for the Chinese side to be responsible
for the basic construction of the 13,000 m 2 9-story building, the US
side for technical assistance and the incremental costs of the energy
efficiency improvements, and the joint establishment of a Demonstration
Center to provide outreach and exhibit energy-efficient building
technologies. The US technical team made several trips to China to
meet with ACCA21 and the design team, and used the DOE-2.1E simulation
program to analyze the energy performance of a preliminary building
design and study alternative designs and energy-efficient strategies.
A feasibility study completed in September found the largest and most
cost-effective savings potentials in reducing cooling and lighting
energy use, and identified eight generic measures in lighting, windows,
daylighting, and HVAC systems and controls. Following these and other
recommendations from the US team, the design team produced a schematic
cross-shaped building design that, based on the DOE-2 analysis, lowered
total energy use by 40% compared to standard practice. While the
design and analysis were underway, a task force called ACCORD21
(American-Chinese Council Organized for Responsible Development in the
21 st Century) was formed in April 1999 under the leadership of NRDC to
solicit support and contributions from U.S. industry, A/E firms, and
universities. Two
design workshops were held, first in Pittsburgh and then in Beijing,
that brought together the Chinese and US project participants and
produced further refinements and energy-efficiency improvements to the
building design. As of June 2000, the authors are completing the final
energy analysis and selection of of energy-efficiency measures.
Construction is expected to begin in the early part of 2001.
LBNL-46304
IMPROVING DOE-2'S RESYS ROUTINE: USER-DEFINED FUNCTIONS TO PROVIDE MORE
ACCURATE PART LOAD ENERGY USE AND HUMIDITY PREDICTIONS
Abstract:
In hourly energy simulations, it is important to properly predict the
performance of air conditioning systems over a range of full and part
load operating conditions. An important component of these calculations
is to properly consider the performance of the cycling air conditioner
and how it interacts with the building. This paper presents improved
approaches to properly account for the part load performance of
residential and light commercial air conditioning systems in DOE-2.
First, more accurate correlations are given to predict the degradation
of system efficiency at part load conditions. In addition, a
user-defined function for RESYS is developed that provides improved
predictions of air conditioner sensible and latent capacity at part
load conditions. The user function also provides more accurate
predictions of space humidity by adding lumped moisture capacitance
into the calculations. The improved cooling coil model and the
addition of moisture capacitance predicts humidity swings that are more
representative of the performance observed in real buildings.In hourly
energy simulations, it is important to properly predict the performance
of air
LBNL-46303
BOTTOM-UP ENGINEERING ESTIMATE OF THE AGGREGATE HEATING AND COOLING
LOADS OF THE ENTIRE US BUILDING STOCK
Abstract:
A recently completed project for the U.S. Department of Energy's
(DOE) Office of Building Equipment combined DOE-2 results for a
large set of prototypical commercial and residential buildings
with data from the Energy Information Administration (EIA) residential
and commercial energy consumption surveys (RECS, CBECS) to
estimate the total heating and cooling loads in U.S. buildings
attributable to different shell components such as windows, roofs,
walls, etc., internal processes, and space-conditioning systems.
This information is useful for estimating the national conservation
potentials for DOE's research and market transformation activities
in building energy efficiency. The prototypical building
descriptions and DOE-2 input files were developed from 1986 to 1992
to provide benchmark hourly building loads for the Gas Research
Institute (GRI) and include 112 single-family, 66 multi-family, and 481
commercial building prototypes. The DOE study consisted of two
distinct tasks: 1) perform DOE-2 simulations for the prototypical
buildings and develop methods to extract the heating and cooling loads
attributable to the different building components; and 2) estimate
the number of buildings or floor area represented by each
prototypical building based on EIA survey information. These building
stock data were then multiplied by the simulated component loads to
derive aggregated totals by region, vintage, and building type. The
heating and cooling energy
consumption of the national building stock estimated by this
bottom-up engineering approach
was found to agree reasonably well with estimates from other
sources, although significant
differences were found for certain end-uses. The main added
value from this study, however,
is the insight it provides about the contributing factors behind
this energy consumption, and
what energy savings can be expected from efficiency improvements
for different building
components by region, vintage, and building type.
LBNL-46005
LINKING THE COMIS MULTI-ZONE AIRFLOW MODEL WITH ENERGYPLUS
Abstract:
This paper describes an effort to link the COMIS 3.0 multizone
airflow model with the EnergyPlus building energy simulation
program. COMIS 3.0 is a network based multizone airflow model
developed by a multinational team in the frame work of the
International Energy Agency's Annexe 23 for simulating airflows
through the building fabric due to infiltration or natural
ventilation and from zone to zone, as well as the interactions
of the HVAC system, ducts, and exhaust hoods and fans.
EnergyPlus is a new whole building energy simulation program
being developed for the US Department of Energy that combines
the best features of the DOE-2 and IBLAST programs. The
EnergyPlus program is modular in structure and uses the heat
balance technique to simulate builidng thermal loads. The
EnergyPlus program calls COMIS from the air heat balance manager
module and passes to COMIS the ambient weather conditions and
zone air temperatures from the previous time step. COMIS uses
these as boundary conditions to calculate the airflows, which
are used by EnergyPlus in the subsequent heat balance
simulation. This paper describes how this linkate was
implemented and discusses issues such as convergence, time
steps, program run time, and alternate solution methods.
LBNL-46004
A MODULAR LOOP-BASED APPROACH TO HVAC ENERGY
Abstract:
This paper presents the new EnergyPlus HVAC simulation
environment, which differs from existing energy analysis
programs in three key respects.
(1) the EnergyPlus HVAC simulation
is based on a "manager-interface" protocol that
supports multiple solution techniques within the overall context
of the simulation;
(2) the EnergyPlus HVAC simulation
is based on high level component connectivity; and
(3) the EnergyPlus HVAC simulation and component modules enforce
a high degree of data encapsulation. These three features,
together with input and output processing services provided by
the environment, result in a simulation tool that is ideally
suited for collaborative development of component models,
evaluation of solution techniques and design of HVAC
sub-systems. The paper describes the features of the simulation
environment, discusses currently implemented algorithms, and
includes an example of the type of results that can be
expected.
LBNL-46003
ENHANCING AND EXTENDING THE CAPABILITIES OF THE BUILDING HEAT BALANCE
SIMULATION TECHNIQUE FOR USE IN ENERGYPLUS
Abstract:
With the advent of the computing age, heat balance based techniques
for simulating thermal loads in buildings became a reality for
architects and engineers. However, since the 1970s, the capabilities
of most of the well-known heat balance based simulation programs
have remained fairly stagnant. Much of the reason behind this
trend lies with the complexity of the programming required to deal with
the fundamental physics encountered in a building and the relative
simplicity of the programming languages that were available. With the
ever-increasing capabilities of the desktop personal computers and
the improved features of the modern
programming languages, it is now possible and
prudent to revisit the basic heat balance formulation
and investigate how its capabilities can be expanded.
This paper discusses some of the technical details
behind recent advances in heat balance based
simulation capabilities achieved by the team of
researchers developing the EnergyPlus program for
the United States Department of Energy. The
EnergyPlus project seeks to combine the best features
of the DOE-2 program and the IBLAST program
(research version of BLAST). This paper focuses on
the marriage of the basic heat balance engine of
BLAST with advanced simulation ideas from the
IBLAST and DOE-2 programs. This complex task
requires careful attention to algorithmic integrity as
well as overall program construction and data
management. This paper provides the theoretical
background for several of the enhancements to the
heat balance based simulation technique used in
EnergyPlus.
LBNL-46002
ENERGYPLUS: ENERGY SIMULATION PROGRAM
Abstract:
Various building energy simulation programs developed around the
world are reaching maturity.
Many use simulation methods (and even code) that originated in
the 1960s. Without substantial
redesign and restructuring of the programs, continuing to expand
their capabilities has become
difficult, time-consuming, and prohibitively expensive. However,
phenomenal advances in analysis
methods and computational power have increased the opportunity
for significant improvements in
the flexibility and comprehensiveness of these tools.
The U.S. Department of Energy (DOE) began planning for a new
generation of simulation tools in
1995 using a three-step process:
(1) Create an inventory of existing DOE-sponsored tools
(2) Sponsor workshops to get recommendations from users and
developers about needs in
energy simulation, and
(3) Define new generation tools based on the recommendations from
the workshops and
experience in developing BLAST and DOE-2.
Three organizations formed the initial development team:
Lawrence Berkeley National Laboratory
(developers of DOE's DOE-2 program), the U.S. Army
Construction Engineering Laboratory, and the University of
Illinois (developers of DOD's BLAST program).
This paper focuses on the structure, features, and capabilities of
EnergyPlus.
LBL-45936
EFFICIENT SOLUTION STRATEGIES FOR BUILDING ENERGY SIMULATION
Abstract:
The efficiencies of methods employed in solution of building
simulation models are considered and
compared by means of benchmark testing. Direct comparisons
between the Simulation Problem Analysis
and Research Kernel (SPARK) and the HVACSIM+ programs are
presented, as are results for SPARK
versus conventional and sparse matrix methods. An indirect
comparison between SPARK and the IDA
program is carried out by solving one of the benchmark test
suite problems using the sparse methods
employed in that program. The test suite consisted of two
problems chosen to span the range of
expected performance advantage. SPARK execution times versus
problem size are compared to those
obtained with conventional and sparse matrix implementations of
these problems. Then, to see if the
results of these limiting cases extend to actual problems in
building simulation, a detailed control system
for a heating, ventilating and air conditioning (HVAC) system is
simulated with and without the use of
SPARK cut set reduction. Execution times for the reduced and
non-reduced SPARK models are
compared with those for an HVACSIM+ model of the same system.
Results show that the graph-theoretic
techniques employed in SPARK offer significant speed advantages
over the other methods for
significantly reducible problems, and that by using sparse
methods in combination with graph theoretic
methods even problem portions with little reduction potential
can be solved efficiently.