Natural Ventilation Strategy for Energy Conservation
Natural ventilation is defined as using passive strategies to supply outdoor air to a building’s interior for ventilation and cooling. It has become a key component of green building today and is a part of the requirements of LEED and the Living Building Challenge (LBC) certifications. During the design, planning and preconstruction phases of the project, natural ventilation was a key focus for the construction of the Brock Environmental Center at Pleasure House Point in Virginia Beach, VA.
Benefits of natural ventilation
The primary purpose of natural ventilation is to allow the outside ambient weather to provide adequate, low humidity, moderate temperature wind currents as an alternate cooling source and provide air circulation into the building. This allows the H.V.A.C. system to either reduce its cooling output or temporarily stop operating—thereby saving the energy required to power the air conditioning equipment.
Similar to natural daylighting, natural ventilation can save both energy and keep occupants comfortable and healthy. It also improves indoor air quality and relies on natural driving forces such as wind and temperature to drive the flow of fresh air through the building. Natural ventilation can replace all or part of a mechanical system—reducing construction, energy and operating costs for the owner.
LEED and LBC requirements
The Brock Environmental Center is targeting both LEED Platinum and Living Building Challenge certifications. According to LEED, the intent of natural ventilation is to “provide mechanical or natural ventilation systems that result in improved occupant comfort over conventional designs, increasing occupants’ well-being and productivity while reducing energy consumption of ventilation systems.” Naturally ventilated spaces must follow the terms defined by ASHRAE 62.1, paragraph 5.1.
The LBC includes natural ventilation in two of its seven petals, or requirements: Equity and Health. The Equity Petal is focused on supporting a just and equitable world. Therefore, the project must not “block access to, nor diminish the quality of fresh air, sunlight and natural waterways.” It must also protect adjacent properties from any harmful emissions that would compromise its ability to use natural ventilation.
The Health Petal of LBC focuses on maximizing physical and psychological health and well being of its occupants, so it requires projects to promote good indoor air quality. Like LEED, ventilation rates must comply with ASHRAE 62 and equipment must be installed to monitor levels of carbon dioxide, temperature and humidity. In addition, it mandates that all kitchens, bathrooms, copy rooms, janitorial closets and chemical storage spaces have separate ventilation systems that exhaust directly to outside air.
Positioning the facility
A natural ventilation study was performed to identify how the Brock Environmental Center needed to be positioned on the site in order to take advantage of prevailing coastal winds during each of the seasons. The final positioning of the building allows an adequate amount of ventilation from the prevailing Northeast to Southwest winds into and out of the building, while minimizing the amount of unwanted outside elements into the interior spaces through the use of screens on all operable windows.
Strategic design elements
The interior design anticipated the need to provide free air access for natural ventilation from the upper clerestory windows to the workspaces below. Therefore, “dropped acoustical ceilings” were not incorporated into the design, which allows the outside heavier cool air to permeate into the interior spaces below and provide natural cooling to the occupants.
The H.V.A.C. system was designed to allow the windows to be opened on days that the appropriate temperature and humidity would not cause an adverse effect on the interior finishes, furnishings, equipment and occupants in the building. The range of ambient weather variables was established as 65-75 degrees Fahrenheit with humidity less than 50% and winds not exceeding 10 to 15 miles per hour.
The use of natural ventilation is calculated to allow the reduction in use of the building H.V.A.C. by approximately 7-8 % of the total number of days in a year, averaging about 2 days per month. To further conserve energy, approximately 75% of all windows in the Brock Environmental Center were designed to be manually operable.
Natural ventilation is one of many green initiatives working toward making the Brock Environmental Center a net-zero energy facility. These tactics will not only conserve energy, but also make the interior air quality better for occupants.