Innovations in Comfort, Efficiency, and Safety Solutions.
& Angela Lewis
January Issue - BAS Column
One of the challenges
we have with commercial buildings is the fine
line between providing a safe and healthy indoor environment and
maximizing energy efficiency. This challenge is exasperated when it
comes to the topic of the “V” in HVAC or ventilation. Ventilation
air (or minimum outside air) is essential for balancing building
pressurization and for removing, or diluting, the impact of indoor
pollutants including various chemicals such as VOC’s as well as
CO2. Of course during part of the year, we can also use
ventilation air for free cooling or economizer. Bringing in too
little outdoor air can result in building pressure issues and can
jeopardize the health of the building occupants. On the other
hand bringing in too much ventilation air can have a significant impact
on the amount of energy required to heat, or cool and dry the makeup
Ideally we want to bring in just enough outdoor air to keep the building at a net positive pressure and to maintain healthy indoor environmental quality. Of course this is not as easy as it sounds since the distribution of contaminants is not uniform. Fortunately there has been extensive research and discussion conducted by industry over the last several decades, much of which is reflected in ASHRAE Standard 62 and eventually adopted into state and local mechanical codes. While you should consult your local code for more details, the general trend for ventilation management is as follows:
The codes and standards for ventilation design have changed significantly over the last 20 years. We often find existing buildings that may still be operating as originally designed (back when indoor smoking was common) or those that over the years have gone too far in reducing ventilation levels. For any new or existing building, the first step in evaluating ventilation is to look closely at the building pressurization, occupancy, code when constructed, and the current code requirements. Often we find that just re-balancing to the current code can have a significant impact on energy efficiency.
Demand Controlled Ventilation:
Many state codes now allow for the use of demand controlled ventilation or DCV. The concept of DCV is to measure and control the amount of ventilation air based on indicators of occupancy. ASHRAE Standard 62 has a series of tables that outline the required levels of building area and occupant ventilation for various building types. The area rates are intended to deal with the impact of chemicals and odors and must be provided at all times when the building is occupied. The people portion of ventilation can be varied based on occupancy using counts or an indicator such as CO2. In order to properly apply DCV you need a method of measuring and controlling ventilation air as well as a way of measuring occupancy. The use of DCV is a natural for buildings, or areas of buildings, that have highly variable occupancy. For example a church or an auditorium is a perfect application. Properly applying DCV in facilities with VAV systems is more complicated to do properly.
Proper management of ventilation is an essential task for any BAS, and when properly applied it can result in a building that is both healthy and efficient.
About the Authors
Paul and Ira first worked together on a series of ASHRAE projects including the BACnet committee and Guideline 13 – Specifying DDC Controls. The formation of Building Intelligence Group provided them the ability to work together professionally providing assistance to owners with the planning, design and development of Intelligent Building Systems. Building Intelligence Group provides services for clients worldwide including leading Universities, Corporations, and Developers. More information can be found at www.buildingintelligencegroup.com We also invite you to contact us directly at Paul@buildingintelligencegroup.com or firstname.lastname@example.org
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