Practice Exercise: Building Envelope Systems

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1. Analyzing the initial building model

Benchmark scenario:

Operating Schedule
Roof Construction
Predicted Mean EUI
60.9 kBtu/ft^2/yr

This base model has just reached the ASHRAE 90.1 standard.

2. Building envelope-related design decisions impact

  1. Thermal Properties of Wall Surface (Wall Construction) for all orientations
  2. Glazing % (Window-to-Wall Ratio) for each orientation (North, South, East, West)
  3. Thermal Properties of Glazing Surfaces for each orientation
  4. Window Shading amount for each orientation

I have changed the criteria above from the benchmark scenario one by one. Below is a table for the EUI results under different assumptions. Blue cells indicate relatively significant factors, grayed-out cells bring negligent impacts to the model’s energy performance.

Wall Construction
12.25-inch SIP
WWR Western
WWR Eastern
WWR Northern
WWR Southern
Glazing East
Trp LoE
Glazing West
Trp LoE
Glazing North
Trp LoE
Glazing South
Dbl LoE, Sgl Clr, Dbl Clr, Trp LoE, BIM
Shades East
2/3 Win Height
Shades West
2/3 Win Height to no shading
Shades North
2/3 Win Height to no shading
Shades South
2/3 Win Height to no shading
Predicted Mean EUI

We have reached the target — under 54 kBtu per sqft per year.


3. Power and lighting impacts

The following criteria are used for the factor tiles related to power and lighting impacts:

  1. Plug Load Efficiency (the equipment and appliances that draw power)
  2. Lighting Efficiency (based on the efficiency of the lighting fixtures)
  3. Daylighting & Occupancy Controls
Plug load efficiency
1 W/sf
Lighting Efficiency
0.3 - 1 W/sf
Daylighting & occupancy controls
Daylighting & occupancy controls
Predicted EUI (based on Benchmark)
Predicted EUI (based on Building Envelop changes)

We drove the predicted mean EUI down to an even lower value. The range has also been lowered from changing the building envelope only.


4. Photovoltaic panel impacts

In this section, I changed the following criteria to explore the benefits from PV on top of the previous improvements.

  1. Surface Coverage
  2. Panel Efficiency
  3. Payback Limit (how many years you will allow for the panels to pay for themselves
Surface Coverage
Panel Efficiency
Payback Limit
20-30 years
Predicted EUI (along with all other improvements)

Surface coverage and payback limit significantly improved the energy performance. Then mean predicted EUI achieved the Architecture 2030 goal, and the range is a lot lower than without PV too.


Here is a screenshot of the final energy model imposed on the building (facing south). Through this exercise, I am convinced that wall insulation, window-to-wall ratio and glazing on large faces are very important when building the envelope. I have also realized that PV panel qualities are critical for building sustainability.

My final results are not energy-negative, but with more parameter-tweaking, net negative can be achieved. I have chosen my current my factor options based on a more balanced and common setting, for example, I made the roof covered with 75% of PV panels rather than 90%, since there might be other uses for the empty parcel.