![]() Where feasible, use central HVAC air handling units (AHUs) that serve multiple rooms in lieu of unit ventilators or individual heat pumps. The selection of equipment for heating, cooling and ventilating the school building is a complex design decision that must balance a great many factors, including: In most parts of the country, climatic conditions require that outdoor air must be heated and cooled to provide acceptable thermal comfort for building occupants, requiring the addition of HVAC systems. Windows are placed to take maximum advantage of wind direction, with openings on opposite sides of the building to maximize cross-ventilation.Windows are adjustable and can close tightly and securely and.Openings for outdoor air are located between 3-6 feet from the floor (head height).If operable windows will be used to supplement the HVAC system, ensure that:.Consider outdoor sources of pollutants (including building exhausts and vehicle traffic) and noise when determining if and where to provide operable windows. Designers should consider the use of natural ventilation and operable windows to supplement mechanical ventilation.The proper sizing and placement of openings is critical and the flow of air from entry to exit must not be obstructed (e.g., by closed perimeter rooms). Both types of natural ventilation require careful engineering to ensure convective flows. Strategies using natural ventilation include wind driven cross-ventilation and stack ventilation that employs the difference in air densities to provide air movement across a space. Uncontrolled ventilation with outdoor air can allow outdoor air contaminants to bypass filters, potentially disrupt the balance of the mechanical ventilation equipment and permit the introduction of excess moisture if access is not controlled. However, sealed buildings with appropriately designed and operated HVAC systems can often provide better IAQ than a building with operable windows. They can also provide supplemental exhaust ventilation during renovation activities that may introduce pollutants into the space. Windows that open and close can enhance occupants' sense of well-being and feeling of control over their environment. In some parts of the country, where temperature and humidity levels permit, natural ventilation through operable windows can be an effective and energy-efficient way to supplement HVAC systems to provide outside air ventilation, cooling and thermal comfort when conditions permit (e.g., temperature, humidity, outdoor air pollution levels, precipitation). Potential for Natural Ventilation and Operable Windows Ensure familiarity with and adherence to, all state and local building codes and standards.Design in accordance with ASHRAE standards Design systems to provide outdoor air ventilation in accord with ASHRAE Standard 62.1-2007 and thermal comfort in accord with ASHRAE Standard 55–1992 (with 1995 Addenda) Thermal Environmental Conditions for Human Occupancy.In addition, some states and localities have established ventilation and/or other IAQ related requirements that must also be followed. Many state codes also specify minimum energy efficiency requirements, ventilation controls, pipe and duct insulation and sealing and system sizing, among other factors. This standard is often incorporated into state and local building codes and specifies the amounts of outside air that must be provided by natural or mechanical ventilation systems to various areas of the school, including classrooms, gymnasiums, kitchens and other special use areas. The national consensus standard for outside air ventilation is ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality and its published Addenda. Designing for Efficient Operations and Maintenance. ![]() Location of Outdoor Air Intakes and Exhaust.Potential for Natural Ventilation and Operable Windows.The following actions detail how engineers can design a quality system that is cost-competitive with traditional ventilation designs, while successfully providing an appropriate quantity and quality of outdoor air, lower energy costs and easier maintenance. The choice and design of the HVAC system can also affect many other high performance goals, including water consumption (water cooled air conditioning equipment) and acoustics. HVAC systems are among the largest energy consumers in schools. The main purposes of a Heating, Ventilation and Air-Conditioning (HVAC) system are to help maintain good indoor air quality (IAQ) through adequate ventilation with filtration and provide thermal comfort.
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