Chhaya for Laboratories—Using a Dynamic Balance Point Calculator to Evaluate Strategies for Addressing Internal Heat Gain
Vikram Sami, Perkins and Will
Energy modeling has become commonplace, with designers seeking to obtain high-performance design solutions for their projects. Although designers interact closely with engineers, the process is mainly a linear one, with very little iterative simulation. Chhaya 2.0© is an Excel-based design tool, which can be downloaded for free at www.chhayaonline.org, that helps designers optimize glazing size and orientation, shading to extend the period that the building can run passively. It uses TMY3 weather data and a series of interactive matrices to help the user come up with optimal design solutions. The use of slider bars to allow the user to increase window sizes as well as shades in each direction and allows the architect to get interactive feedback to building shell decisions.
Chhaya for Laboratories is intended to help in the decision-making process at the early planning stages of laboratories' design. Design teams wondering about the applicability of chilled beams often wonder whether a certain laboratory is a good candidate for the technology. If the question is shelved until further analysis and simulations are done, this often means it is too late to integrate it into the process.
The program creates a graph with equipment power density on the X-axis and air changes on the Y-axis. For a given set of conditions, the user can create a gradient that represents a threshold for those conditions. The gradient line becomes a useful benchmark of laboratory characteristics. The user can input multiple laboratories on the same chart in terms of equipment loads and ventilation air changes and compare performance characteristics and the potential issues that arise. For example, anything below the gradient will have an equipment bias (e.g., heat gain exceeds cooling capacity of ventilation air) and is likely to be moving more air than is necessary purely for ventilation. This might make it a good candidate for chilled beams. Similarly, anything above it will have a ventilation bias (e.g., cooling capacity of air exceeds heat gain in the laboratory). In some cases this might indicate that the laboratory will have high reheat loads and might be a candidate for supply air temperature reset or reduced ventilation rates. The slope and Y-intercept of the gradient line depends on a number of input factors such as supply air temperature, room height, lighting power density, occupant density, and solar heat gain, which is taken from the main Chhaya matrix. The user can dynamically manipulate all of these factors—including switching orientations to see the difference in performance.
Chhaya is a schematic design tool and is not intended to replace whole building simulation using more robust tools. Chhaya for Laboratories is currently a beta version that will be made freely available to designers who want to use it.
Biography:
Vikram Sami has spent the last seven years integrating expertise in the field of sustainable building design, daylighting, and energy analysis with building design, using computer simulation as part of the design process to produce integrated design solutions that are high-performance while maintaining their architectural aesthetic.
Mr. Sami has experience with a wide range of project types including residential, commercial, and institutional. His research interests include thermal comfort and ventilation, building simulation techniques, and global carbon reduction techniques. He currently serves as chair of the Solar Buildings Division of the American Solar Energy Society and is a past chair of the Georgia Solar Energy Association. He also currently serves on the Atlanta Branch Leadership Group of the U.S. Green Buildings Council’s Georgia Chapter, and is the chair of the Energy and Atmosphere committee of the Atlanta American Institute of Architects Committe on the Environment (COTE) chapter. He is a visiting lecturer at the Georgia Institute of Technology. He holds a master's degree in building science from Arizona State University and is a frequently published author and researcher.