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Saved by Brian Matthews
on November 11, 2008 at 10:58:49 pm
 

Energy Modeling of Buildings

 

Description:

     Energy modeling of buildings is a practice of evaluating the energy use of a building through simulating the many energy related components.             

 

Purpose:

     The goal of energy modeling of buildings is to accurately predict the energy use of a particular building to either test the energy performance of the building with regards to an established standard, or to compare and contrast two buildings in order to find the resulting energy savings from energy conservation efforts.   In abstract logic, it would be most desirable to have two, identical buildings in real life, one energy efficient, the other not.   Comparison between the two buildings energy bills are the savings.   It is seldom that such a situation exists so energy modeling is used to simulate and estimate a building's energy use.   

 

Industries served:

     All buildings that have significant utility or energy use would benefit from energy modeling.    This is due to energy modeling's ability to predict the useful savings that result from the installation of mechanical equipment with greater energy efficiency, or the implementation of new practices that reduce peak or yearly energy use.  The cost of doing energy analysis is strongly dependent on the energy savings potential of the project. 

     Not all energy efficient equipment or practices fit all situations.   Analysis is necessary to find the most worthwhile savings created in exchange for the typically higher up-front cost and effort.   At the end of the day what must be known is, "Will this energy efficient activity save money in the long run?"  

 

Role of Federal, State, or Governing Authority

     Often, the design process is encouraged to implement energy efficient measures by federal, state, or other governing body by providing diverse incentives.   Incentives help to offset the usual higher initial cost of equipment and to reduce the number of years that energy saving equipment will take to break even where their initial cost equals the money earned through energy savings year after year.     

     Incentive websites:

 

Methods:

     Classification of the different methods are diverse in their practice but generally subscribe to the goal of predicting energy use.   The choice between the different methods is primarily based on level of accuracy desired and what methods, codes, or standards a governing body requires the modeler to adhere to.   

 

  • Computational Fluid Dynamic (CFD) simulations
  • Hourly/Sub-Hourly simulations (Equest)  -A detailed summary of each hour of the year and the hour-by-hour energy operation of the building.
  • Comparative Summary Tools -Use a database to rate the building's energy efficiency in regard to other buildings.
  • Custom Measure tools.  -Non-Interactive method of looking at one measure at a time.
  •  

 

Existing Guidelines -with a brief review of useful content

  • MPP Guidebook
    • What it has:
      • Nearly all Residential modeling information: Dhw, Room temps, Ach, plug loads, Dorm vs. Apartment building adjustments, schedules, etc. 
    • What it lacks:
      • It is not ASHRAE 90.1 2004 APPENDIX G
      • Anything commercial or industrial in nature.
  • LEED NC 2.2
    • What it has:
      • Different methods of calculating energy use in buildings
      • Charts of typical building energy use, along with some occasionally useful assumptions.
      • Charts of shower flow rates
      • References to ASHRAE 90.1 2004 Appendix G. 
      • Many great references to energy efficiency efforts, rules, and standards around the country and the world.  
      •  
    • What it lacks:
      • Estimation techniques are often very LEED specific and thereby not adaptable to other situations. 
      •  
  • ASHRAE 90.1 2004 Appendix G.
    • What it has:
      • Lighting loads, nearly all baseline information, detailed descriptions of modeling techniques with respect to what can and what cannot be in the models. 
      • HVAC efficiencies of baseline (from references to ASHRAE 90.1 2004 main document)
      • Wall construction assembly U values, etc. (from references to ASHRAE 90.1 2004 main document)
      • Zone definitions, what makes up a segmented thermal zone.
      • Heating Degree Day values for most regions, including Design Day temperatures. (from references to ASHRAE 90.1 2004 main document)
      •  
    • What it lacks:  (Technically, it lacks nothing, but covers all undefined modeling assumptions with broad statements that vaguely fill in the blanks when questions arise.)  
      • Schedules, or guidance in scheduling of occupancy, hvac, special equipment.
      • Air change and exhaust specifications
      • Dhw values
      • Clear definitions of accuracy of modeling besides: "Less than 300 hours of load not met for entire building"  -regardless of sf of building.
      • Electric plug values.
      • Easy application to situations where measure complexity exceeds the modeling capability of the software modeling program. 
      • A clear explanation for the reason behind wrap around windows in the baseline model.
      • Easy application to Commercial, Residential hybrid buildings. 
      • Any general guidance on facilities where the magnitude of energy use is extreme, such as with Data Centers, IT rooms, etc.  
      •  
  • NREL 2005 California Nonresidential ACM Approval Manual
    • What it has
      • Receptacle loads for typical spaces
      • General modeling information to conform to California's modeling practices
      • Schedules and thermostat settings.
      • Thermostat setback control schedules  
      • Schedules for Equipment, occupancy for residential and non-residential
    • What it lacks
      • Overlaps other Modeling Standards such as ASHRAE 90.1 2004 APPENDIX G
      • Before using the people/sf values read the fine print about double occupancy factor within the data.

Software:

 

Modeling Resources

 

BASELINE BUILDING fundamental characteristics 

     The below information is to either fill in the blanks when Modeling Guidelines are incomplete or provide guidance on understanding      fundimental building thermal and energy principals

 

  • ASHRAE 90.1 2004 APPENDIX G Application notes: 
    • Translating units used in ASHRAE 90.1 2004 to units acceptable for a modeling program
    • Unique attributes to an ASHRAE baseline building.
    • ASHRAE 90.1 2004 compliant baseline checklist
    • Easy implementation of the wrap-around windows in modeling software
      • Equest function code for auto- window generation
    • Fan energy adjustments
    • Over sizing adjustments
    • Lighting and thermostat Controls of an ASHRAE 90.1 2004 compliant building
    • ASHRAE ZONE MAP.
    • Interpreting the hvac chart in APPENDIX G with simulation program names vs. ASHRAE names vs. industry typical names for different systems.

 

  • Fundimental Building Principals, Phyics, and Attributes.
    • Outside Air
      • Air leakage
      • HVAC exhaust-supply offsets
      • Wind effect on Air Infiltration
      • Cracks in building envelopes
      • Stack effect through all Elevator, mechanical shafts, and stairwells.
      • Air buoyancy effect through all elevator, mechanical shafts, and stairwells.
    • Exhaust
      • Affect exhaust fans have on building infiltration
      • Typical rooms under exhaust
      • Specialty Exhaust rooms
        • Parking Garages
        • Bathrooms
        • Chemical work stations and Laboratories
        • Repair Garages
    • Fresh Air Supply (Mechanical Ventilation)
      •   Code required Outside Air per Space use
      •   Common Outside Air assigned to spaces for additional comfort.
    • HVAC
      • CVCT systems
      • VAV systems
      • PTAC systems
      • Typical residential systems (urban)
      • Typical industrial systems
      • ASHRAE SYSTEM TYPES VS EQUEST PROGRAM INPUTS
      •  
    • ENVELOPE
      • Thermal bridging
      • Exposed floor slab, balconies
      • Roof dynamics
      • Cavity wall physics
      • Moisture barrier
      • Wall construction type dependencies on local climate.
      •  
    • Occupancy
      • Occupancy Schedules: 
        • Residential
        • Health Care facilities
        • Commercial
        • Office
        •  
      • Thermostat Schedules
        • Residential
        • Health Care facilities
        • Commercial
        • Office
        •  
      • Lighting Schedules
        • Residential
        • Health Care facilities
        • Commercial
        •  

 

IMPROVED BUILDING Information - Special notes and approaches to implement a measure on a building model

 


 

Online Resources and References

 

 

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