There are many places around the globe where designers, builders and building owners are faced with environmental conditions that can contribute to poorly performing buildings. Areas that experience high heat and humidity much of the year face the challenge of unmet cooling loads, and likewise, locations in colder climates must deal with heating loads. My firm recently had the opportunity to work with a team delivering green buildings in the Gulf Region. This geographical location faces long periods of high humidity and extreme temperatures, along with very dry conditions, high winds and sandstorms. All of these elements provide key challenges for the design of a high-performance building.
In this area, creating the design concept for an efficient cooling system for a building is of highest importance. The design of a building and its systems requires a balance of equipment size and total load (or the amount of required cooling). During my team’s experience, we found that before the typical equipment sizing exercise could occur, we had to focus on strategies to improve the building envelope to keep the heat and humidity out of the building. Reducing adverse environmental conditions that are allowed to enter into a building decreases the need to mechanically condition or reverse those adverse conditions. To improve the building envelope to meet the climate conditions in the Gulf, our project team had to examine the walls, roof and windows before the mechanical systems were addressed.
Walls
A project team should be encouraged to evaluate multiple assembly methods for the walls during the early design phases of a project. The evaluation process for each of the proposed assemblies looks at aspects of cost, constructability, structural integrity, maintainability, aesthetics and energy efficiency. Each of these aspects are weighed and measured to create a final product that hits a balance of each of these elements. In the Gulf, building envelopes typically look like some type of an insulated structural wall system with a stone façade cladding. The combination of materials and insulation used in the project my team worked on resulted in a minimum insulation value of R-27.
Roof
The color and insulation value of a roofing system can contribute to the overall energy efficiency of a building. In cold climates, high insulation values with a dark roof color can aid in lowering the energy demand needed for heating the building. In hot harsh conditions, a light-colored roof with good insulation values lowers energy used to cool a building. During the project in the Gulf, the team specified a combination of concrete, insulation, membrane and paver system for the roof, resulting in an insulating value of R-41.
Windows
The placement of the glazing in a building is key in determining how affected the occupant’s experience will be while in a building. Windows also can either be a key point of energy efficiency or waste in a building. The designers for the building in the Gulf moved the glazing to the inboard, allowing a portion of the solid wall structure to serve as an external shading device, thereby reducing the amount of solar heat gain on the windows. The Solar Heat Gain Coefficient (SHGC) is the window property used to rate the amount of energy allowed through windows. The SHGC is the fraction of incident of solar radiation that passes through a window and becomes heat inside the building. The color and thermal properties of glass provide the thermal properties needed for the enhanced performance of the building’s energy use. Combining a high-performance criterion for the glass selection with the fixed shading elements enhanced indoor environment and energy performance for the project.
Once a team has tackled the challenge of designing a high-performance building envelope, the designers can turn their sites on the mechanical systems within the building. A starting point for our team was to develop an understanding of heat transfer and the temperature distribution through building materials and assemblies, thermal comfort, thermal movements, durability, and the potential for moisture problems. The project team took the same approach they had used for the wall assemblies, so several concepts for the mechanical systems were evaluated before the final selection was made.
A Variable Air Volume (VAV) system was coupled with a chilled water system. The system is capable of delivering 100 percent outside air. The majority of the cooling comes from recirculating constant volume air handling units that deliver variable temperature air to spaces, giving occupant(s) temperature control. Carbon dioxide sensors are located within the primary return air from each room, allowing the outside Air Handling Unit (AHU) to reduce airflow when occupancy levels reduce. An energy recovery system was incorporated to recover energy from the building extract ducts, pre-cooling the outside air going throughout the building.
Result
Achieving the delicate balance of aesthetics, cost, durability and energy performance is a challenge. A team that takes this challenge seriously can achieve respectable results. In the case of the Gulf project, the team achieved the performance goal, resulting in a final design that indicated that the building will consume approximately 32 percent less energy than if the same building was designed and constructed in a traditional manner. Results will always vary, and it is important to remember that these results were evidenced by an energy model. The energy model is only as good as the information that it is based upon. When a team wants to improve the performance of a building, they’ll need to look at more than one system; they’ll need to look at the entire building as a system.
Thomas Taylor, a 30-year veteran of the construction industry and noted expert on sustainability, is the general manager of St. Louis-based Vertegy. His recent book, “Guide to LEED 2009: Estimating and Preconstruction Strategies,” provides step-by-step information about the LEED 2009 for New Construction process. To learn more about Vertegy or Taylor’s new book, visit www.vertegyconsultants.com for more information.