Key Takeaways

Learn how to use performance analysis to:

  • Avoid the pitfalls of unproven design assumptions;
  • Identify the right design and performance questions;
  • Respond efficiently to late design stage changes.

Project Stats

  • Project type: High rise residential
  • Location: Mumbai, India
  • Floor area / stories / occupancy: 106,000SqM gross / 80 Floors / 333 Units
  • Project stage & completiondate: Construction / Early 2018
  • Performance Baseline: Local Code and Best Practice

Designed by Pei Cobb Freed and Partners, World View is one of three towers that make up Mumbai’s tallest residential development. During the project’s design development stage, the local government enacted changes to the zoning code requirements. This meant that the design team needed to change the building enclosure and assess the impact of these changes on the building’s energy performance while maintaining aesthetic coherence with the other towers.

Read on to learn how they responded to unexpected later stage zoning changes, identified the right problem to solve and how they solved it.

The Challenge

PCF’s original facade design featured glazing units that were set back from the finished envelope, creating a loggia(1) for each apartment. Changes to Mumbai’s local zoning codes meant that these loggias counted against the development’s approved Floor Area Ratio (FAR) (2).

Image 2: Left – SketchUp Rendering of the original design showing inset glazing and loggias. Right – Render showing the updated design without loggias.

To rectify the FAR discrepancy, the design team was left with no choice but to push out the glazing to the finished facade, inevitably removing the original design’s self-shading attributes. The team, led by senior associate and architect Francis Cooke, set out to study the increased solar exposure and mitigate any resultant increase in energy consumption.

The team started by testing different shading strategies to reduce solar exposure and the corresponding facade heat gains. Next, it analysed the shaded and unshaded options, with an expectation that the right shading strategy would produce a marked improvement on Energy Use Intensity (EUI).

According to Cooke, the primary challenge for the team was their perception of the problem they needed to solve. Cooke said, “Having a visceral appreciation of the heat of the Indian sun, our attention was immediately drawn to providing shade for the glass… but we were trying to solve a problem that did not exist to a large degree.”

Task 1: Tackling solar loads
To tackle their first goal, the PCF-P design team analysed the solar gain loads per exposure (Image 3) for the unshaded building (option A); the design with 700mm horizontal shading above all glazed openings (option B); and the design with varied shading fins added per exposure (option C).

Image 3: From top to bottom- SketchUp renders of design option A, B & C. Table showing the total solar load and percentage reduction from unshaded option.

For option C, it is worth noting that the team used an evolutionary solver in a different software to pinpoint the ideal shading per exposure and tier that reduced solar loads while using the minimal amount of shading material. To round off the first study, they compared the solar load of options B and C (shaded options) against option A (the unshaded design).

Task 2: Tackling EUI
Option C reduced solar heat gain loads by 25.4% when compared to the unshaded design option. This reduction however proved to be less impactful than it would first appear. Energy analysis in Sefaira showed that these shading values improved Energy Use Intensity by only 0.3%! Although Option C led to a 25% reduction in solar loads, it did not translate into an equal reduction in EUI. The proposed shading would only impact the building during the day (peak load time (3)) when the building’s air conditioning system would not be engaged, as most occupants would be out of their homes. Realizing the direct solar loads were less pressing, the team sought other measures to reduce energy use.

Click to enlarge

Image 4: Further analysis in Sefaira shows the building factors that impact energy use. Space cooling contributes greatly to monthly consumption. Heat gains through the glazing and walls via conduction appear to be the major cause of the high cooling loads.

They discovered that reducing the thermal conductive loads by improving the wall U-Value (4) of the unshaded design from 0.86 to 0.17 decreased the building EUI by 6.88%.

Image 5: Parametric analysis in Sefaira showing that better wall u-values reduce annual energy consumption (yellow) and lower EUI (red).

Results

To summarise, the shading fins did a remarkable job of reducing incident solar radiation on the glazing, a reduction of 25.4%. This however did not translate into a linear reduction of energy consumption when analysed in Sefaira.

“Using performance analysis, we realized that conduction heat gains (through the walls) were an issue during peak occupancy hours (early mornings and evenings). Sefaira helped us identify the substantial energy savings we could make by enhancing the wall insulation instead. We finally concluded that the solution to our problem was not the addition of a new design component but simply a modification of specifications and details.

By carrying out performance analysis, the team was able to overcome the pitfalls of assumptions and avoid following ineffective rules of thumb to pinpoint the most effective strategy. For future projects, Cooke hopes to implement performance analysis early and often to identify effective and ineffective strategies specifically with respect to program type.

About Pei Cobb Freed and Partners

With projects in more than 100 cities around the world, Pei Cobb Freed & Partners is one of the world’s leading architecture and planning practices. Working from a single studio in New York, the firm is consistently recognized for excellence in design and sustainability, with 200 major design awards.

Footnotes

  1. A loggia differs from a balcony in that it is not bolted onto the overall form but is carved out of the floor plate. The loggia is accessed only from inside and intended as a place for leisure.
  2. Floor Area Ratio (FAR) refers to the ratio between the total floor space of a building (including all floors) and the area of land it is built on.
  3. The peak load time would be when the sun is at its hottest and spaces need to be cooled. This also happens to be the period during the day when most people are out of their homes, and most spaces aren’t occupied or in use. As such, contrary to expectation, the air conditioning system will not be switched on.
  4. U-Value of a material is the measurement of how well it insulates. The lower the number the better the material’s insulating property.