February 28, 2018 - by Susan MacDougall
Back in the day, the word “model” typically referred to a physical representation of a building built by the architects out of balsam and plastic that we would all “ooh” and “aah” over. These days, computer models are used to simulate lots of different aspects of the building. The energy model is used to evaluate the energy profile of a building, that is, how the building uses energy, how much it uses, when it is used, etc.
An energy model is typically as simple or complex as the building it is representing.
What's the purpose of an energy model?
Energy models can be used for multiple purposes, which will have a big impact on its inputs, complexity and cost. Most often, models are requested for one of the following reasons:
Green Building Certification, or
How is a model built?
An energy model is a software representation of a building operating over the course of a "typical" year. There are lots of modelling tools available, however the most important component is the modeller her/himself!
An energy model will be based on the designs of several consultants, which together represent all aspects of the building that impact its energy consumption. Typically, this includes drawings and specifications from the architect, mechanical engineer, electrical engineer and building envelope consultant.
The energy model also includes all major weather, operational, controls, and schedule information representing a typical year. Depending on the end-use of the model, operational profiles can be based on actual anticipated operational parameters (for example, a bank’s operating hours are likely known at the time of design). Otherwise, codes and standards will often provide operating parameters that must be used to demonstrate compliance.
What codes are models based on?
Code compliance requirements will vary between jurisdictions and the differences can be significant. In British Columbia, there are two set of rules to follow, outlined in the:
Vancouver Building Bylaw (VBBL), and
British Columbia Building Code (BCBC).
Some building codes refer to other published standards. The most common in Canada are:
ASHRAE 90.1-2010 (the date can vary), and
National Energy Code for Buildings (NECB) 2011.
Both are currently referenced by the VBBL and the BCBC.
What does the energy modelling process look like?
The process of analyzing a building with a model can vary based on the type of project being undertaken, and the purpose of the model (discussed earlier).
A typical process for a new construction model is shown below.
Block loads models are often used to help optimize passive design features such as orientation, massing, shading and glazing percentage.
EARLY STAGE ANALYSIS
Models created around the rezoning/ schematic design stage are typically used to check if the initial design is on track to meet the project targets, or come up with design criteria to meet an energy requirement.
The modeller will ask questions of the design team to understand the design intent which is then represented in the model. Assumptions are often included to cover items that are still unknown on the project.
This is the “what if…?” stage and helps inform the design. With a preliminary model complete, the team can run iterations to examine the impact of design options on the building. Typical examples include:
Iterating design options (ex. Looking at different wall details & associated R-values)
Examining the impact of product selection (ex. Condensing boiler vs. natural draft)
Looking for targets (ex. What glazing SHC will maintain comfortable summer temperatures?)
Sensitivity analysis (ex. If the desired airtightness isn’t achieved, how does that impact my certification?)
You guessed it… there are tons more scenarios that a modeller can run… so if you have a question, ask!
This model is used to represent the final building design/as-built conditions. All of the energy-impacting systems (envelope, mechanical, lighting, etc.) need to be represented per the team’s drawings and specifications.
Depending on the model’s purpose, the final building’s energy consumption, cost, or other metric will be compared with a baseline model or set criteria from a code/ standard, to demonstrate performance.
How long do models take? How much do they cost?
The time and cost associated with a model depend on the complexity of the building that it’s representing. A house will be faster and less expensive than a tower, and the tower will take longer the more complex and unique the systems are. (Think of the detail in the final arch/ mech/ elec sets that have to be read, interpreted and represented in the model!)
The best way to get a cost for your project is to reach out to a modeller (or several) and ask. If you’re requesting a quote, the most helpful information you can provide:
Project information (drawings/ descriptions/ as much info as you have based on the stage of design)
An idea of the iterations needed
Any unique features of your project
Original Article: Susan MacDougall -February 28, 2018 - energy-modelling-101-back-to-basics
The TLJ Team