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Saved by Brian Matthews
on November 9, 2008 at 3:38:44 am
 

Energy Modeling of Buildings

 

Description:

     Energy modeling of buildings is a practice of evaluating the energy use of a building.             

 

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 real life identical buildings, one energy efficient, the other not, and compare their utility bills to find differences that energy efficient practices make.   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.  

     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.   Though helpful in instigating change these incentives often make the energy savings calculations more complex and the efforts of savings energy bogged down with Red Tape.

     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 Guides -with a brief review of 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. 
    • What it lacks:
      • Clear indication on which modeling technique should be applied to 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. 
      •  
    • What it lacks:  (Technically, it covers all modeling assumptions with sweeping 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.
      •  
    • What it lacks
      • General modeling practices applicable to other regions in the country.
      •  

Software:

 

Modeling Resources

 

The place of Energy Modeling in the Construction Process and when/where information is available.

    * Information Time-of-Availability chart.'

Fundamental building characteristics, physics, and principals

  • Making Sense of Utility Bills
    • Special NYC utility Bill Section:
      • Con Ed, commercial, industrial, residential
  • Outside Air
    • Air Changes Per Hour
    • HVAC exhaust-supply offsets
    • Wind 
    • 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
      •  

 

Baseline Building Information -Special notes on Baseline construction to the following codes and standards

  • ASHRAE 90.1 2004 APPENDIX G
  • MPP
  • LEED analysis methodology (per Credit)

 

Improved Building Information - Special notes and approaches on modeling complex Energy Conservation Measures

  • SOLAR PV
  • CONDENSING BOILERS
  • ENVELOPE IMPROVEMENTS
  • REFRIGERATED STORAGE FACILITY
  • ENVELOPE
  • LIGHTING
  • PROCESS IMPROVEMENT
  • BUILDING MANAGEMENT SYSTEMS
  • ENERGY & HEAT RECOVERY
  • COMBINED HEAT AND POWER (CHP)
  • NATURAL GAS RECIPROCATING ENGINE GENERATOR, CHILLER
  • BIODIESEL RECIPROCATING ENGINE GENERATOR/ CHILLER
  • ABSORPTION CHILLER
  • HVAC IMPROVEMENT
  • ELEVATOR AND PEOPLE MOVING APPARATUS
  • COMPUTERS, OFFICE EQUIPMENT
  • DAY LIGHTING
  • WIND
  • GROUND-SOURCE GEOTHERMAL
  • RADIANT FLOOR
  • OCCUPANCY SENSING LIGHTING, HVAC
  • EXHAUST AIR DAMPERS
  • EXHAUST CONTROLS

 

 

 

 

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