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Energy Modeling Inputs & Engineering Assumptions for Energy Efficiency Analysis & Building Design

Posted by: Bhushan Avastthi | Posted on: October 29th, 2014

An energy model is used to simulate the energy operation in both new built and retrofit buildings. In both these cases, there might be situation where the energy modeler has to counter unknown or missing information. In such cases, the requirement of the missing information has to be fulfilled via accurate engineering assumptions and estimations. Let us elaborate on what are the inputs, that an engineer/energy modeler needs to completely design and simulate a building for energy efficiency.


Location Data:

  • Weather conditions
  • Local vegetation
  • Interior conditions and set points
  • Other pertinent site features

The energy modeler should be supplied with location data; this includes the details about the site location, the climatic conditions, natural vegetation in the area, the building topography, existing structures or data pertaining to the scope of new structures.

Building Envelope:

  • Air infiltration goals
  • Area orientation
  • U value and glazing component shading
  • Building component mass
  • Solar absorbance and visible light transmittance

Building envelop details is an important input for energy modeling. Special consideration to high performance glazing, shading devices, building mass or any massive construction, etc, helps model better and hence derive accurate simulations.

Internal Gains:

  • Lighting in watts per square foot
  • Plug Loads in watts per square foot
  • Sensible and latent loads from occupants

Internal gains, such as the estimation of lighting wattage, for varied occupancy types, plug loads and the apt mechanical system types are also important.


  • Occupancy schedules
  • Lighting schedules
  • Plug load schedules

How the building is utilized and what are the schedules of occupants is an important input. This also gives an idea of the lighting schedules and the plug loads in the building. This is an essential input to estimate the average energy usage by occupants.

Energy Systems:

  • Types of HVAC systems
  • Fan and pump types and inputs
  • Economizers and heat recovery systems
  • Water heating systems
  • Specialty systems
  • Renewable energy systems

Last but a vital input required for energy modeling, is the details regarding the types of HVAC systems, use of renewable resources if any and the installation and usage of other specialty systems.

With all these inputs on hand, developing a model and simulating it for energy consumption becomes easy and accurate. However these inputs should be collected by experts with great dexterity, as any errors in inputs can result in a flawed energy model. The principle of ‘Garbage in Garbage out’ completely holds true for the purpose.

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About Author:

Bhushan Avsatthi

Bhushan Avsatthi is a senior manager, consultant, BIM expert and a green building advisor with more than 15 years of industry experience. Bhushan imbibes the prophecy of efficient and prudent use of energy in his day to day life and advices his team to do so as well. He is also involved in green initiatives like nonprofit tree plantation project and promotes using cycles for commuting small distances. Bhushan, handles a team of architects, Structural and MEP engineers, LEED consultants and Energy modeling experts.