1. Lecture 7: Building Modeling Questions Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved

2. 2 Importance of this Lecture to the Simulation of Buildings  Every building is different in many ways: Location/exterior environment Construction/building envelope HVAC system  Building envelope/construction determines how a building will respond to the exterior environment  Thermal simulation requires information about the physical make-up of the building, where various constructions are located and how they are oriented, how the building is subdivided into zones, etc.  Thermal simulation requires information on the building envelope to properly analyze the building from an energy perspective

3. 3 Purpose of this Lecture  Gain an understanding of how to specify the building construction Groups of Surfaces (Zones) and Overall Building Characteristics Walls, Roofs, Ceilings, Floors, Partitions, etc. Materials and Groups of Materials (Constructions)

4. 4 Potential Questions You Might Have  Is every room a zone? How many zones?  How detailed should the building model be?  How accurate will my results be?  Do I need to do a design day run or an annual run?

5. 5 Defining a Building  Getting Started Manual A methodology for using EnergyPlus  Four Step Process Gather information Zone the building Create building model Create input file

6. 6 Step 1 - Gather Information  Location and design climate  Building description Wall constructions Wall sizes Window, door, overhang details Wall locations (shading)  Building use information Equipment and occupancy information Schedule information

7. 7 Step 1 - Gather Information (cont’d)  Building thermostatic controls  HVAC equipment information Equipment types Operating schedules Control information

8. 8 Step 2 – “Zone” the Building  Thermal, not geometric, zones  Heat storage and heat transfer surfaces  Heat transfer  only when expected to separate spaces of significantly diff temps Exterior Walls, Roofs, Floors  Heat storage surfaces  surfaces separating spaces of same temperature

9. 9 Simplifying EnergyPlus Input  Simplify -- Think before typing  Layout simple floor plan  As few zones as necessary  As few surfaces as necessary  Surfaces, NOT volumes  Is shading important?

10. 10 As Few Zones As Necessary  Combine similar zones  Use zone multipliers wisely  Combine vertically and horizontally 10 ZONES OR 6 OR 4 OR 2?

11. 11 Rules of Thumb Reminder  One zone per major exposure minimum  Separate zones for different uses  Separate zones for different setpoints  Separate zones for different fan systems (and radiant systems)  Do not use “rooms” to determine zones

12. 12 Step 3 - Create Building Model  Heat transfer and heat storage surfaces  Define equivalent surfaces  Specify construction elements  Compile surface and subsurface info  Compile internal space gain data

13. 13 As Few Surfaces As Necessary  Combine similar surfaces  Combine small surfaces with larger surfaces  Ignore minor details  Use internal mass 7 WINDOWS OR 3?

14. 14 Step 4 – Create Input File  Materials and Constructions  Building Geometry  Internal Loads  Special Features

15. 15 Case Study  US Army Fort Monmouth education center  Temperate coastal climate, Near New York City  Floor area of over 13,000 sq.Ft.  Building height of 10 ft.  Total window area in excess of 1,400 sq.Ft.  May serve as many as 200 people

16. 16 Ft. Monmouth Floor Plan How many zones should there be?

17. 17 Option 1: One-Zone Model How accurate is this model? 50 ft 16 ft 113 ft 43.3 ft 34 ft 65 ft 39 ft 65 ft 20 ft 10 ft 20 ft 75.3 ft 50 ft 124.6 ft (61 ft2) (42 ft2) (363 ft2) 101 ft2) (82 ft2) (113 ft2) (62 ft2) (190 ft2) (26 ft2) (40 ft2) (209 ft2) (84 ft2) (334 ft2)

18. 18 Option 2: Six-Zone Model  Five fan systems or zoning thermally  Expect higher solar on south and west Zone 1 Zone 5 Zone 4Zone 2 Zone 6 Zone 3

19. 19 Modeling Fort Monmouth with EnergyPlus  With appropriate detail: EnergyPlus can convert a simple model into a powerful energy analysis Complex interactions modeled for an entire year  Designers can then: Size systems and plants Examine performance of various system and plant configurations Determine more efficient operational schemes Calculate annual energy consumption

20. 20 Six-Zone Model Loads How does this compare to 1-zone model?

21. 21 Comparison Between One and Six-Zone Models Difference in Total Cooling Load < 10% Difference in Total Heating Load < 1%

22. 22 Simple EnergyPlus Model Produces Incredible Results  Why? EnergyPlus captured the physics... Building exterior remains the same Solar load equivalent Internal loads unchanged Internal mass accurately approximated Identical weather conditions  Difference: unconditioned spaces

23. 23 Detailed Model Benefits  Improved accuracy  Better resolution of loads for system sizing  Incredible analytical power

24. 24 Another Aspect to Consider...  How much of an effect does the thermal mass of zone surfaces have on zone loads?  Comparison using Ft. Monmouth six zone model Standard EnergyPlus run EnergyPlus run using no thermal mass (R values)  Use output reports from previous run to change the surface definitions to R values only

25. 25 Key Physical Properties  Exterior Walls 4” Dense Face Brick 8” Heavyweight Concrete Block 6” Mineral Fiber Insulation 5/8” Gypsum  Slab on Grade Floor 4” Concrete Tile Flooring  Roof 3/4” Roofing 2” Expanded Polystyrene Insulation Airspace 3/4” Acoustic Tile

26. 26 Case 1: Thermal Mass Effects  Cooling loads higher with no mass Total load off by 14% Peak off by 15%  Larger differences show up in zones 1, 2, and 3 Could result in oversizing of systems and plants  Only thermal mass changed Other EnergyPlus details a factor Cooling Loads No-Mass vs. Mass ZoneTotalPeak 112%32% 216%31% 316%40% 514%16% 615%14% All14%15%

27. 27 Design Day Calculations  Convenient short time period  Established design day conditions easy to obtain  Fairly good estimate for system and plant sizing  Will design day results be an accurate indication of long term trends?

28. 28 Case 2: Adding Roof Insulation  What will the effect of doubling the amount of roof insulation be?  Roof 3/4” Roofing 2” Expanded Polystyrene Insulation Airspace 3/4” Acoustic Tile  Will a design day tell the whole story?

29. 29 Design Day Heating Load Results Daily Decrease for Heating Loads = 8%

30. 30 Design Day Cooling Load Results Daily Decrease for Cooling Loads = 3%

31. 31 Annual Run Building Loads  Why are the cooling loads higher with more insulation? Mild summer + High MRT = High summer heat retention  Overall reduction in loads, but not as expected from design day results Heating Load Cooling Load Peak Heating Peak Cooling Total Loads Cheap Roof468000147500588289615500 Better Roof417700150700561282568400 Annual Diff's10.75%-2.17%4.66%2.42%7.65%

32. 32 Let's Change the Weather...  Champaign, Illinois  Temperate inland climate, south of Chicago  Compare increased roof insulation  Design day heating and cooling loads both decreased  Annual building loads also decreased  EnergyPlus "changed" the weather for every hour of the year  EnergyPlus never forgets the physics!

33. 33 Summary  Simple models can produce good results  Thermal mass can have a significant effect on loads  Design day calculations can be misleading  Annual runs pick up mild weather effects