Lecture 1: An Overview of Simulation and EnergyPlus Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2 Purpose of this Lecture  Gain an understanding of Simulation as a Concept EnergyPlus as a Simulation Tool  Briefly review topics important to your understanding of building thermal simulations

3 What is Simulation?  Definition: “the imitative representation of the functioning of one system or process by means of the functioning of another ” (Merriam-Webster Dictionary On-Line)

4 What is Building Thermal Simulation?  Approximate definition: a computer model of the energy processes within a building that are intended to provide a thermally comfortable environment for the occupants (or contents) of a building  Examples of building thermal simulation programs: EnergyPlus, Energy-10, BLAST, DOE-2, esp-R, TRNSYS, etc.

5 Goals of Building Thermal Simulation  Load Calculations Generally used for determining sizing of equipment such as fans, chillers, boilers, etc.  Energy Analysis Helps evaluate the energy cost of the building over longer periods of time

6 Why is Simulation Important?  Buildings consume roughly one-third of all the energy consumed nationally every year Much of this energy is consumed maintaining the thermal conditions inside the building and lighting  Simulation can and has played a significant role in reducing the energy consumption of buildings

7 How does Simulation save Energy?  Building thermal simulation allows one to model a building before it is built or before renovations are started  Simulation allows various energy alternatives to be investigated and options compared to one another  Simulation can lead to an energy-optimized building or inform the design process  Simulation is much less expensive and less time consuming than experimentation (every building is different)

8 Quick Review of Important Background Concepts  Control Volumes and the Conservation of: Mass Energy (First Law of Thermodynamics)  Heat Transfer Mechanisms: Conduction—transfer of thermal energy through a solid Convection—exchange of thermal energy between a solid and a fluid that are in contact Radiation—exchange of thermal energy via electro-magnetic waves between bodies or surfaces

9 What is EnergyPlus?  Fully integrated building & HVAC simulation program  Based on best features of BLAST and DOE-2 plus new capabilities  Windows 95/98/NT/2000/XP & Linux  Simulation engine only  Interfaces available from private software developers

10 EnergyPlus Concepts  Time dependent conduction Conduction through building surfaces calculated with conduction transfer functions Heat storage and time lags  Migration between zones Approximates air exchange using a nodal model  Only models what is explicitly described Missing wall does not let air in Missing roof does not let sun in

11 EnergyPlus Concepts (cont’d)  Heat balance loads calculation (one of two load calculation methods recommended by ASHRAE)  Moisture balance calculation  Simultaneous building/systems solution  Sub-hourly time steps  Modular HVAC system simulation  WINDOW 5 methodology

12 EnergyPlus Concepts (cont’d)  Simple input/output file structures  No surface, zone or system limits Defaults to 50 coils per HVAC loop Can be increased  Links to other software COMIS, wind-induced airflow TRNYSYS, Photovoltaics

13 EnergyPlus Structure

14 Integrated Simulation Manager  Fully integrated simulation of loads, systems and plant Integrated simulation allows capacity limits to be modeled more realistically Provides tighter coupling between the air- and water-side of the system and plant

15 Integrated Simulation Manager (cont’d)

16 Input/Output Data  EnergyPlus input and output data files designed for easy maintenance and expansion  Will accept simulation input data from other sources such as CADD programs (AutoCAD, ArchiCAD, Visio), and preprocessors similar to those written for BLAST and DOE­2  An EnergyPlus input file is not intended to be the main interface for typical end-users

17 Input/Output Data (cont’d)  Most users will use EnergyPlus through an interface from a third-party developer  Utilities convert portions of BLAST and DOE­2 input to EnergyPlus input Materials and constructions Schedules Building envelope surfaces

18 Summary  EnergyPlus builds on the strengths of BLAST and DOE-2 and includes many new simulation capabilities: Integrated loads, system and plant calculations in same time step. User-configurable HVAC system description. Modular structure to facilitate the addition of new simulation modules. Simple input and output data formats to facilitate graphical front-end development.

19 Basic Input and Output Issues General Philosophy Input/Output Files Overall File Structures Input Object Structure Input Data Dictionary (IDD) Weather Files

20 General Philosophy of Input/Output/Weather  Simple, free-format text files  SI units only  Comma-separated  Object-based  Somewhat self-documenting  Two parts—dictionary and data or simulation results  Not user-friendly » Interfaces will help  Can become large

21 Input–Output Files Input Data Dictionary This file is created by EnergyPlus developers. Input Data File This file will be created by User Object,data,data,…,data; Input Data Dictionary (IDD) EnergyPlus Program Main Program Module File Types: Standard Reports Standard Reports (Detail) Optional Reports Optional Reports (Detail) Initialization Reports Overview of File Format: Header Data Dictionary Data Note: These files will be created by EnergyPlus. Output Files Output Processor Input Data Files (IDF)

22 Input Object Structure  Begin with object type followed by comma  A (alpha) and N (numeric) fields in exact order  Fields separated by commas  Last field followed by semi-colon  Commas are necessary placeholders BASEBOARD HEATER:Water:Convective, Zone1Baseboard, !- Baseboard Name FanAndCoilAvailSched, !- Available Schedule Zone 1 Reheat Water Inlet Node, !- Inlet_Node Zone 1 Reheat Water Outlet Node, !- Outlet_Node 500., !- UA {W/delK} , !- Max Water Flow Rate {m3/s} 0.001; !- Convergence Tolerance

23 Input Object Structure (cont’d)  Alpha fields 60 characters maximum  “!” exclamation point begins comments  IDF objects can be in any order IDF Editor may rearrange the order “!-” IDF Editor automated comments IDF Editor cannot be used with HVAC Templates BASEBOARD HEATER:Water:Convective, Zone1Baseboard, !- Baseboard Name FanAndCoilAvailSched, !- Available Schedule Zone 1 Reheat Water Inlet Node, !- Inlet_Node Zone 1 Reheat Water Outlet Node, !- Outlet_Node 500., !- UA {W/delK} , !- Max Water Flow Rate {m3/s} 0.001; !- Convergence Tolerance

24 Input Object Structure (cont’d)  Not case-sensitive  Input processor checks basic rules, A vs. N, number of fields, valid object type, max/min, etc.  IDF objects are generally retrieved by each component simulation module BASEBOARD HEATER:Water:Convective, Zone1Baseboard, !- Baseboard Name FanAndCoilAvailSched, !- Available Schedule Zone 1 Reheat Water Inlet Node, !- Inlet_Node Zone 1 Reheat Water Outlet Node, !- Outlet_Node 500., !- UA {W/delK} , !- Max Water Flow Rate {m3/s} 0.001; !- Convergence Tolerance

25 Input Data Dictionary (IDD File)  Energy+.idd  Located in EnergyPlus folder  Conceptually simple A (alpha) or N (Numeric) BASEBOARD HEATER:Water:Convective, A1, \field Baseboard Name \required-field A2, \field Available Schedule \required-field \type object-list \object-list ScheduleNames... N1, \field UA \required-field \autosizable \units W/delK... N3 ; \field Convergence Tolerance \type real \Minimum> 0.0 \Default 0.001

26 IDD File (cont’d)  Lists every available input object If it isn’t in the IDD, then it’s not available IDD version must be consistent with exe version IDD is the final word (even if other documentation does not agree)

27 IDD File (cont’d)  “\”code Specifications Field descriptions Units Value ranges (minimum, maximum) Defaults Autosizing

28 IDD File (cont’d)  Get to know the IDD file  Easy way to quickly check object syntax  Refer to Input Output Reference for detailed explanations of inputs

29 Allowable Ranges and Defaults  Allowable ranges Some max/min declared in IDD  Fatal error if outside of range Some max/min hidden in source code  May reset value and issue warning, may be fatal  Defaults Some defaults declared in IDD Some defaults hidden in source code Some values have no defaults  Alphas become blank  Numerics become zero

30 Weather Data (epw file)  Weather year for energy use comparisons, similar to other programs  Hourly, can be subhourly  Hourly data is linearly interpolated  Data include temperature, humidity, solar, wind, etc.  Several included in standard install

31 Output Data Format  Same philosophy as for input; somewhat human readable output files  EnergyPlus can perform some output processing to help limit output size  User definable variable level reporting

32 Output Reporting Flexibility  User can select any variables available for output  User can specify output at time step, hourly, daily, monthly, or environment intervals  User can schedule each output variable  User can select various meters by resource and end-use

33 Questions  How long will my simulation take? Depends on size of input file, length of simulation period (day vs. year), and speed of computer Might range from a few seconds to several minutes (some detailed simulation modules may require even longer) EnergyPlus will display progress in a window on the desktop so that the user knows where it is at

34 Questions (cont’d)  How do I know whether the program read my input correctly? Take a look at the.EIO file (EnergyPlus initialization output)—this may indicate that you have misinterpreted an input parameter Check results output files and see if they are reasonable  How will I know whether my simulation results are reasonable or outrageous? See previous question Consider “Load Check Figures” available from sources such as ASHRAE Compare to other simulations or consult your instructor Do some simple hand calculations (such as UA  T) and see if the numbers are “in the ballpark”