What is the impact of operable glazing fraction on thermal comfort and natural ventilation potential?

PROJECT INFORMATION

Graphic Name:  What is the impact of operable glazing fraction on thermal comfort and natural ventilation potential?

Submitted by: Carl Sterner

Firm Name: Sefaira

Other contributors or acknowledgements (optional) 

What tools did you use to create the graphic?

  • Sefaira

  • Adobe Photoshop

  • SketchUp

What kind of graphic is this? Scatter Plot

Primary Inputs: Building geometry (zoned) with glazing; location (weather file); envelope properties, internal conditions, and HVAC parameters.

Primary Outputs: Comfort: % occupied hours within setpoint range (dry bulb temperature). Free area: the ratio of operable window area to floor area for each zone, measured against a target of 5%.

GRAPHIC INFORMATION

What are we looking at?

The graphic is showing two pieces of data relevant for determining the optimal amount of operable glazing for natural ventilation. The first chart (on the left) shows the impact of increasing operable glazing on predicted thermal comfort (the percent of occupied hours with dry bulb temperatures within setpoints). Thermal comfort improves until approximately 75% of glazing is operable, and tops out at 72% of occupied hours being comfortable. The second graphic (on the right) shows the current design’s “free area” -- the ratio of operable window area to floor area for each zone. A free area of 5% is a typical target value for naturally ventilated buildings, and has been codified in standards such as BREEAM in the UK and Title 24 in California. This graphic shows that a number of the building’s zones fail to meet this prescriptive criteria as currently designed. Taken together, the graphics indicate that more operable glazing is needed in many of the zones in order to provide good natural ventilation.

How did you make the graphic?

  1. Modeled building geometry in SketchUp

  2. Uploaded the model to the Sefaira web application

  3. Set up the various simulations (envelope, internal conditions, and HVAC parameters)

  4. Ran a Response Curve for Operable Glazing %, looking at the impact on Thermal Comfort. Exported the resulting graphic.

  5. Ran a Free Area assessment, with a target of 5% free area. Exported the resulting graphic.

  6. Combined the two graphics in Photoshop

What specific investigation questions led to the production of this graphic?

  • Is there enough operable window area in each zone to provide good natural ventilation?

How does this graphic fit into the larger design investigations and what did you learn from producing the graphic?

This graphic was combined with other analyses related to the window area, related to daylighting and solar gain. The purpose of these combined investigations was to evaluate whether the glazing strategy and facade design was effective from energy, daylight, and natural ventilation perspectives. The initial glazing ratios were fairly conservative, and the analyses showed that the design would benefit from more glazing in many of the zones, for both natural ventilation and daylighting.

What was successful and/or unique about the graphic in how it communicates information?

The graphic summarizes and clearly presents fairly complex analysis, making the results actionable. It is easy to see how operable glazing affects comfort, and where the problem areas are in the existing design.

What would you have done differently with the graphic if you had more time/fee?

More clearly connected to two graphs, perhaps by finding a way to put them both in terms of absolute glazing area. The Response Curve is currently terms of % of glazing that is operable, while the Free Area chart is currently based on operable glazing area. This makes it difficult to clearly relate the two.

What is the impact of operable window openings on the distribution of peak air velocities at different levels of a facade?

PROJECT INFORMATION

Graphic Name: What is the impact of operable window openings on the distribution of peak air velocities at different levels of a facade?

Submitted by: Michael Sawford

Firm Name: EDSL USA, Inc.

Other contributors or acknowledgements (optional) EDSL Tas consultancy services

What tools did you use to create the graphic? EDSL Tas 

What kind of graphic is this? Natural Ventilation Vectors / Spatially Integrated

Primary Inputs: building geometry, window operability information

Primary Outputs: Peak air velocities by hour (m/s), mass flow rate (kg/s)

GRAPHIC INFORMATION

What are we looking at?

3D model of part of a building depicting the natural ventilation air flows in and out of modelled spaces taking into account; the wind speed/direction of the location at a given hour (day 74 hour 14, as shown at the top of the image), the altitude, and the stack effect. Light blue arrows at the base of the building section indicate the wind direction for the hour being displayed. Magnitude of each arrow (ligh blue, red, navy blue) represents the speed of the air. Direction of the red/navy blue arrows show the direction of flow. The wind rose is depicted on the ground plane, the metres per second scale for wind speed is found on the right hand side of the image. The mass flow rate in kg/s for the wind speed is found on the left hand side of the image. A key is located in the lower left hand side for the flow arrows.

How did you make the graphic?

EDSL Tas was used to create the 3D model, input natural ventilation openings and their control functions, and simulate the building. The results were then showed visually in the tool for live interaction. Using automated reporting tools in EDSL Tas software the image was produced.

What specific investigation questions led to the production of this graphic?

Validation of a natural ventilation scheme. Understanding the impact of the location of openings and the building form together with the wind data for the location. Understanding the impact of the Chinook winds on the natural ventilation strategy. Understanding the impact of the full building section height atrium space on the concave side of the building and its interaction with open plan office spaces in the greater floor plate of the building.

How does this graphic fit into the larger design investigations and what did you learn from producing the graphic?

This is one snap shot of the visual data used to communicate the natural ventilation strategy to the design team/owner. Videos showing the natural ventilation scheme varying by hour were also produced to communicate the results. Natural ventilation could maintain comfort levels in the office spaces.

What was successful and/or unique about the graphic in how it communicates information?

Being able to show the natural ventilation scheme in action, whether in still images or in videos, allowed for easier communication of the data in context with the building and subdivided spaces. Flexibility in choosing which information to display and how the output is created was a great benefit in visualising the data. (For example, options to create a single image for one hour, or creating a series of images in order to step through each hour of a particular day for a slide deck could be automatically created. It is also possible to create a video to capture the responses of the building to changing wind conditions hour by hour.) The visual data can also be accompanied with tabulated hourly data of aperture air flow rates where peak flow rates can be assessed in a more granular fashion. When viewing the 3D model view uploaded within the EDSL Tas software (prior to export), if you mouse over a particular surface/arrow in the model, information about the surface/space/air flow rate is displayed, this allows you to interrogate the data in real time in an interactive fashion.

What would you have done differently with the graphic if you had more time/fee?

I could have opted to remove the compass (showing the North arrow) from the view as it is not visible in the current view. By orbiting around, zooming out further I could have navigated the 3D model view whereby the North arrow information could have been useful to the graphic output. Accompanying the data with an indication of peak air velocities would have provided context to the feasibility of naturally ventilating the building.