Numerous tools and techniques for building energy analysis have been developed since the 1960s. These tools and techniques include databases, spreadsheets and simulation programs (US DOE 2006). Certain programs specialize in limited applications such as analysis of specific
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building component and system, ventilation/air flow, daylighting and solar/climate analysis. On the other hand, certain other programs have the capabilities to perform whole-building energy analysis. An up-to-date comparison of the various whole-building energy simulation programs is provided in Crawley et al. (2008). Five programs for whole-building analysis were reviewed for this study. The programs include: DOE-2.1e (Winklemann et al. 1993), eQUEST (LBNL &
Hirsch Associates 2004), TRNSYS (Klein et al. 2004), and EnergyPlus (Crawley et al. 2004). A brief description is provided in the section that follows. In addition, several simulation programs have been reviewed for assessing the performance and feasibility of co-generation systems.
2.7.1 Whole Building Energy Analysis Programs
DOE-2.1e is a fixed-schematic, whole-building energy simulation program that predicts hourly energy use and energy cost of the building using hourly weather data inputs. The program uses one subprogram for translation of inputs (BDL Processor) and four simulation subprograms (LOADS, SYSTEMS, PLANT and ECONOMICS) executed in sequence to perform the
simulation and economic analysis. The program performs the calculation of thermal loads by using the weighting factor method93,94. The weighting factor either implements custom weighting factors or uses pre-determined ASHRAE weighting factors (Winklemann et al. 1993). DOE-2.1e has the capability of simulating a wide range of design features and has been widely used to evaluate the energy performance of buildings. The accuracy and consistency of DOE-2.1e has been extensively validated by tests such as those the ASHRAE Standard Method of Test for Evaluation of Building Energy Analysis Computer Program (BESTEST) (Judkoff et al. 1995). A refrigeration module is provided in DOE-2.1e that allows for the simulation of refrigerated case-work. However, several limitations to this module restrict the use of this software program to model buildings such as the grocery store, which have complex refrigeration systems.
The Quick Energy Simulation Tool (eQUEST) is software that uses the DOE-2.2 simulation program, combined with a Graphical User Interface (GUI) that includes a building creation wizard, an energy efficiency measures wizard, industry standard input defaults, and a graphical results display module (LBNL & Hirsch 2004), that can be used to perform detailed analysis of building energy performance. The DOE-2.2 program is based on the earlier versions
93 Weighting factors are a set of parameters that quantify how much energy that enters the room should be stored and how fast this energy should be released (Winkelmann et al. 1993).
94 Weighting factor method, which is one of the several methods that have been used in building energy analysis, represents a compromise between the simpler methods such as the steady-state methods and more complex methods such as complete energy-balance calculations (Winkelmann et al. 1993).
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of DOE-2 (Hirsch 2008). A number of other commercial versions of DOE-2 are also available including EZDOE, DOE-PlusTM, and VisualDOE3.1. These programs also use the DOE-2.1 simulation program with specially developed user interfaces to simplify data input procedures.
Similar to DOE-2.1e, a basic refrigeration module is provided in this simulation program too, which cannot be used in the analysis of complex refrigeration systems.
eQUEST-Refrigeration (ver. 3.61) is a version of eQUEST that has been exclusively developed for refrigeration in commercial facilities (grocery stores and food services) and industrial facilities (warehouses, food processing). The program was developed as part of the Energy Design Resources program, which is funded by the California utility customers. The program is useful in assessing the impact of refrigeration systems in whole-building simulations by providing the ability to model refrigeration systems in detail. Capabilities of the refrigeration version include modeling of components such as display fixtures, compressors, condensers, subcoolers, refrigerants etc. (Hirsch 2008). Unlike the parent eQUEST program, the algorithms in the refrigeration version are component based, allowing the users to build an entire system out of individual components. Each major device in the refrigeration system such as the refrigeration circuit, display fixture, compressor, condenser etc. can be is specified separately and
subsequently connected to each other. A library of refrigeration components is included to help the user select appropriate components in order to build an entire system.
Developed by the Solar Energy Laboratory at the University of Wisconsin TRNSYS (TRaNsient SYstem Simulation Program) was originally used as a program for simulating solar thermal systems (Klein 1973). In subsequent versions, the program incorporated general HVAC and refrigeration system simulation routines. The modular structure of TRNSYS configures and assembles a series of smaller components to facilitate the simulation of complex energy systems (Klein et al. 2004). The subroutines representing the physical components are combined and solved simultaneously with a building envelope thermal balance and an air network model at each time step (Crawley et al. 2004). The TRNSYS library includes components for multi-zone building models, low energy buildings, HVAC systems, renewable energy systems, including passive solar, active solar thermal and photovoltaic systems, wind energy, fuel cells, CHP and refrigeration etc. The modular nature of TRNSYS also facilitates the creation and use of new mathematical models to the program (Klein et al. 2004), a task that cannot be easily
accomplished with DOE-2.
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EnergyPlus is a modular, structured code that combines selected features of BLAST and DOE-2.1e. Similar to BLAST and DOE-2.1e, EnergyPlus also uses the response factor method for transient heat transfer through multilayered opaque building envelope components. The simulation uses a heat balance method based zonal simulation. In contrast to BLAST and DOE-2.1e, EnergyPlus allows user-specified time steps of less than an hour. The program then performs the load calculation and the simulation of the response of the systems and plant for each time step95. This integrated solution provides more accurate space temperature predictions crucial for more accurate system and plant sizing as well as other features such as designing for occupant comfort and occupant health calculations. The program also allows users to evaluate realistic system controls, moisture absorption in the building envelope and desorption in building elements, radiant heating and cooling systems, and inter-zonal air flow, photovoltaic systems and fuel cells (Crawley et al. 2009). The EnergyPlus (ver. 7.2.0) has been updated to include simple and detailed models of refrigeration system components and refrigerants. Capabilities of the refrigeration model include calculating the electric consumption of refrigerated cases, impact of the refrigerated cases on zone cooling and humidity conditions, calculating the electric
consumption of the compressor rack including auxiliary energy consumptions, and determine the total amount of heat rejected by the compressor racks condenser which potentially can be used in heat reclaim models (EnergyPlus 2012). The models account for nearly all performance aspects of typical refrigerated case equipment.
All of the programs mentioned above have different levels of capability for the analysis of refrigeration, absorption systems and co-generation systems. Being modular in structure, eQUEST-Refrigeration, EnergyPlus and TRNSYS are probably the best suited to simulate refrigeration components of whole building energy simulationDOE-2.1e and eQUEST can handle limited options of refrigerated display-cases and refrigeration systems and hence can only approximately model a complex refrigeration entity such as a grocery store.
2.7.2 Analysis of CHP Systems
CHP systems require careful evaluation in order to be deemed thermodynamically and economically feasible for a given site. For this purpose a number of computer programs and simulation models have been developed. This study summarizes the software that is used to
95 In contrast to EnergyPlus, DOE-2 has four simulation sub-programs (i.e. LOADS. SYSTEMS, PLANT and ECONOMICS) that are executed in sequence, with the output of one becoming the input for the next (Winkelmann et al.,1993).
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evaluate CHP applications for buildings, campuses, industries and district systems. CHP assessment programs can be categorized into detailed engineering analysis models, combined thermodynamic and economic analysis models, financial analysis models and forecasting models (Baxter 1997). CHP programs can also be categorized by intended use, type of calculations, analysis duration and time step, CHP technologies, data libraries, type of CHP processes and cost and availability (Hudson 2003). This study categorizes the available CHP software considering the time step provided by the software for analysis.
To perform a feasibility analysis using only monthly thermal and electricity data, several software are available, which provide both energy as well as economic analysis of the installed CHP systems. The list of software includes (but is not limited to) CHP Ready Reckoner,
RECIPRO, BCHP screening tool, Building Energy Analyzer (BEA), D-Gen Pro and RETScreen.
o CHP Ready Reckoner was developed for the Australian Department of Industry, Science and Resources by Sinclair Knight Merz (2002). The software is used primarily in the screening on industrial applications and is free of cost. In addition, the software provides a baseline comparison and has access to equipment data library for gas turbine and IC engines.
o RECIPRO is a program developed by Thermoflow, Inc. (2010) and is primarily used in the screening of small commercial and industrial CHP applications. The program is designed as an add-in module to Microsoft Excel 2000 spreadsheet. The program is used to primarily assess the performance of IC engines ranging from 70 kW to 11MW. The program can also analyze the impact of using absorption chillers instead of electric chillers.
o BCHP is a screening tool that has been at the ORNL (MacDonald 2007). The tool is primarily used in screening CHP applications that use DOE-2 simulation engine. The
software provides a grid-based baseline comparison for the assessment of CHP options. Data libraries provided by this software include generation equipment, HVAC equipment, utility rates, weather, and certain specific building types.
o Building Energy Analyzer (BEA) was developed by the InterEnergy Software and Gas Technology Institute (InterEnergy 2004) and is primarily used in screening of CHP
applications in commercial buildings using DOE-2 simulation engine. The program includes capabilities of quick economic analysis of cooling, heating, thermal storage in addition to the analysis of components such as on-site power generation capabilities and life cycle cost analysis.
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o D-Gen Pro has been developed by the Architectural Energy Corporation and the Gas Technology Institute and is primarily used in the preliminary screening of CHP heating applications in commercial buildings. The program provides a baseline comparison of grid electricity and separate steam boiler. D-Gen Pro consists of improved on-site generation modeling capabilities (weekend operation, part load efficiency, thermal recovery, automatic generator deployment) and enhanced rate-handling capability.
o GT Pro is a program developed by Thermoflow, Inc.(2010) and is primarily used in the detailed design of industrial gas turbine applications with/without HRSG and / or combined cycles.
o The CHP model of RETScreen (NRC 2012) developed by the Natural Resources Canada (NRC) evaluates energy production and savings, costs, emission reductions, financial viability and risk for central-grid, isolated-grid and off-grid CHP (CHP) projects on a monthly basis. The software tool is Excel-based and can model a wide variety of projects ranging in size from large scale coal-fired steam turbine central plants or natural gas-fired gas turbine - combined cycle central plants connected to district energy networks, to biomass-fired distributed energy systems providing cooling, heating and power to institutional and commercial buildings and industrial facilities, to stand-alone energy supplies for commercial and institutional buildings, to small-scale remote IC engine CHP systems. The software can also be used to incorporate a variety of power, heating and cooling equipment operating under design as well as part-load conditions. The program can also analyze a wide range of renewable and conventional fuels.
When considering hourly simulation tools, several programs have been identified to do the job. These include HeatMap CHP, CHP Capacity Optimizer and HOMER.
o HeatMap was developed by the Washington State University Cooperative Extension Energy Program to assess the use of CHP systems in conjunction with district heating and cooling (DHC) and thermal storage (Bloomquist and O’Brien 2000). The program provides a detailed 3-D design simulation of both proposed and existing CHP systems using DOE-2 simulation engine. The program provides a baseline comparison with the existing grid-operated system. The program provides various data libraries, which include libraries for weather, building loads, production equipment, fuels and piping.
o CHP Capacity Optimizer (Hudson 2005) is an automated standalone spreadsheet program that assesses the cost of the CHP system provided the electrical and thermal load behavior of
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the facility, the tariff structure, the price of primary fuel the operating strategy and characteristics of the CHP system, the installed capacity of the prime mover and the absorption chillers are known. Using an hour-by-hour operation simulation the program is designed to compute the optimal capacities of prime movers and chillers that will maximize the life cycle, net present value savings from the CHP system. The program has been designed to provide guidance on proper installation of properly sized prime movers and absorption chillers in commercial applications.
o HOMER (Lambert et al. 2005) a program developed by the NREL evaluates alternative off-grid and off-grid connected system options for a variety of applications using hourly
simulations. The program allows results to be compared on economic as well as technical merits. In addition to modeling IC engine generators and microturbines, HOMER can also model other micropower systems such as wind turbines, fuel cells and hydrogen storage.
o Finally, CHP models have also been incorporated in whole building simulation programs such as DOE-2.1e and eQUEST and more recently in TRNSYS, ESP-r and EnergyPlus (Beausoleil-Morrison 2008).
From the above discussion it can be concluded that no single simulation program has the potential of providing a complete assessment of this interaction between a grocery store, a co-generation system and the surrounding community. Therefore, in this study several existing simulation programs will be used in conjunction with each other to provide a complete
assessment of the following: 1) Whole building energy reduction strategies in grocery stores; and 2) Whole building energy reduction in grocery store on implementing CHP systems.
It is also necessary to determine whether the inputs provided for the simulation model are correct and whether the model is performing the way it should. Hence, it is required to calibrate the simulation models to better represent the facility. Over the years several calibration methods have evolved to validate the simulation process. Several of these methods are
elaborated in the next section.