HVAC is commonly known as the heating and air conditioning trade. Those who call it a profession refer to themselves as comfort specialists. They sell HVAC systems with slogans such as, “Comfort, that is what we do best,” or “You’re always comfortable with us.” Unfortunately, one thing both of these slogans omit is an integral element to a complete understanding of a proper HVAC system: ventilation. We focus all our efforts on delivering on the comfort guarantee and completely forget good IAQ is part of our job. This lack of representation is also found in most HVAC technician education and residential state licensing exams. Gone are the days of just providing heating and cooling. In order to stay in the comfort business, we must learn ever-changing building materials, code changes, and code program standards that include the installation of ventilation in homes that used to breathe on their own.
What do we do now? With ventilation being a key component to comfort and safety in all HVAC systems, we need to promote ventilation to a level pillar as we do the other letters in our professional titles.
The Valuable ‘V’
A vast majority of technical institutions focus on teaching the fundamentals of electrical systems, gas characteristics, and air properties as well as troubleshooting system components. For example, if a six-year-old comfort system is not operating, the problem will most likely be unrelated to the ventilation system, and the diagnostic focus will be on what’s changed since yesterday. Therefore, very little or no time is spent on ventilation calculation or design because it will most likely not be needed to repair the heating and cooling system. While attending an HVAC technician school, I brought up the topic of ventilation, which was covered by simply saying: Sometimes you need it. They were right.
Residential state licensing exams also have reasons for not testing on the subject. Their focus tends to center on areas such as proper gas line sizing, system sizing manuals, or legal matters such as how much time we have to renew an expired license. The main goal is to cover topics dealing with safety and administration questions. If any focus is placed on ventilation calculations, systems, or components, it is brief. Also, some states do not require HVAC contractors to attend continuing education classes to maintain mechanical licenses. This can quickly lead to a situation where the adoption of new building codes requires us to design and install ventilation systems, and, in most cases, we are completely unprepared to do so.
Today’s HVAC contractor is responsible for far more regarding ventilation than previous generations. Buildings are tighter, and IAQ technologies are far more advanced. With new building materials, techniques, and above-code programs, buildings are becoming tighter and tighter, with no end in sight.
As these new homes are no longer able to breathe on their own, smells, excess moisture and contaminants — in the forms of volatile organic compounds (VOCs), particulates, and other ingredients — may build up inside the home. If not addressed, this may lead to comfort complaints such as sick home syndrome. Because of this, national above-code programs such as Energy Star® and Environments for Living® have not only made the installation of ventilation mandatory, but contractors are required to submit ventilation documentation, including the type, location, rate, frequency, and duration of the ventilation to be installed.
Considerations such as climate zone should also be included in the design, since different ventilation strategies — positive pressure, negative pressure, balanced, etc. — work better in different climate zones. For instance, exhaust-only ventilation is not recommended for hot-humid climate zones because raw-humid outdoor air may contribute to indoor moisture problems due to the house being under a negative pressure. Supply only ventilation is not recommended in cold climate zones because humidity in the indoor air may contribute to moisture problems inside exterior walls due to the house being under a positive pressure. Balanced ventilation may be skipped in any climate because it may be more expensive to install than the other two. If you are unfamiliar with the requirements, just the calculations, considerations, and paperwork for a design can be exhausting and time consuming.
ASHRAE created the calculations for determining the minimum ventilation rate needed in a home. Currently, there are two standards to follow: ASHRAE 62.2-2009 or ASHRAE 62.2-2012. These calculations are not only different, but the 2012 ASHRAE calculation provides optional ventilation credits for having certain items in a room such as an operable window. While this is great for flexibility in the requirement, it can quickly become a mathematical nightmare in the field.
After the strategy is chosen and the correct ventilation cfm is determined, most of the paperwork is completed. Unfortunately, our job is not over as we now must begin the design phase. We must install a one-of-a-kind ventilation system to deliver the needed rate consistently and reliably while keeping in mind access to filters, ventilation inlet locations, and construction access. With the huge number of different products and controls available, it may be very difficult to decide which one would be best for a project.
Free tools do exist. Websites such as www.advancedenergy.org/ritevent, www.residentialenergydynamics.com, and www.heyokasolutions.com/category_s/64.htm
help us strengthen the ‘V’ in HVAC. Also, not only can you pick the ASHRAE standard you wish to follow and get the needed cfm, but these standards can assist in selecting equipment and compatible controls to meet ventilation requirements. Finally, with additional features like duct sizing and report generation compliance available with all efficiency programs, these tools may quickly become part of your daily practice.
Publication date: 1/12/2015