Print this page HVAC Ventilation for Indoor Air Quality
Fred W. Dougherty, P.E.,B.A.E, M.M.E
Course Outline
The term “ventilation” is defined and the principles and rules governing building ventilation are established. Building air balance and air motion within the conditioned space are described. Ventilation must always exceed exhaust by a sufficient margin to inhibit infiltration. Ways to maintain pressure differentials between building zones and between the building and outdoors are outlined. The methods of calculating minimum ventilation based on required building exhaust and using ASHRAE Standard 62.1-2010 to determine ventilation for acceptable indoor air quality are introduced. The special requirements of buildings with large exhaust volumes, such as restaurants, are discussed. Means of efficiently inducing ventilation air in to a building are described with advantages and special capabilities of each. The methods and objectives of ventilation controls are discussed.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
At the conclusion of this course, the student will:
- Understand building ventilation air balance and the motion of air within a conditioned space;
- Be able to set minimum outdoor air ventilation and exhaust air flow rates that will control indoor air quality and meet required standards and codes while using the least possible amount of energy;
- Understand and apply the requirements of ASHRAE Standard 62.1-2010;
- Understand the principles of and be able to set pressure gradients within air handler zones;
- Be familiar with methods and equipment to bring ventilation air into a conditioned space; and
- Be familiar with controlling ventilation rates to provide the required minimum under varying conditions.
Intended Audience
This course is intended for design professionals that plan, design, and implement HVAC systems for non-residential buildings.
Benefit to Attendees
Attendee of this course will be able to avoid inadequate or excessive outdoor air ventilation rates for air conditioned non-residential buildings.
Course Introduction
Prior to performing heat loss and heat gain calculations, the minimum required outdoor air to be delivered to the air handling systems must be determined. There are two ways to determine the minimum ventilation air that must be mechanically supplied to the air handler zone. One is by adding the required exhausts and multiplying by 1.25. The other is by determining the minimum “Ventilation for Acceptable Indoor Air Quality” as calculated based on use and occupant load using ASHRAE Standard 62.1. The designer must evaluate both to determine which will be applicable to his project. After a minimum rate is determined, the designer must deal with the heat and moisture loads added to the system, and specify controls that will maintain the rate under varying conditions.
Course Content
This course content is in the following PDF document:
HVAC Ventilation for Indoor Air Quality
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Course Summary
Prior to performing final cooling and heating load calculations, the minimum required ventilation air must be determined. Local and national codes and standards set minimum exhaust requirements for categories such as restrooms, showers, medical isolation rooms, and restaurant food service. Other codes and standards such as ASHRAE Standard 62 set minimum requirements for outdoor air needed to ensure acceptable indoor air quality. Finally, even if there were no codes regulating exhaust or intake, it would be necessary to induce enough outdoor air through the air handlers to pressurize a building and inhibit infiltration.
In general, outdoor air must exceed exhaust by a factor of about 1.25 in order to pressurize the building and mitigate infiltration. In some cases, particularly if the building has a commercial kitchen, required exhausts will be large enough that the required offset outdoor air will exceed the outdoor air required to maintain air quality standards. If required ventilation air is larger than the required exhaust offset, then supplemental exhaust may be required to prevent over-pressurization of the building.
To make these determinations, the designer should perform an air balance showing all required exhausts, required outdoor air for air quality, and supplemental exhaust or outdoor air as needed to provide pressurization. If the building has a commercial kitchen, then air balances should be performed for all expected operational configurations of kitchen exhaust fans. Special controls may be needed to prevent over pressurization or negative pressure. The pressure in the dining areas of a restaurant must always exceed the pressure in the kitchen, and the kitchen pressure must always exceed outside ambient pressure.
Once the required amount of ventilation air is determined, the designer must decide on a method to induce the required air, and must set up compatible controls to ensure that ventilation air is neither excessive nor insufficient regardless of the zone operating conditions. Controls must also be specified that will prevent unscheduled entry of outdoor air into the conditioned space, especially during unoccupied periods.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
