The Energy Code is beginning to redefine how we look at multifamily buildings with this upcoming 2019 code cycle and it starts with changes to dwelling unit ventilation requirements. The code has long required outside air to be mechanically provided to the units at a minimum rate. Now code is indicating which ventilation designs are more efficient than others. Balanced ventilation is one of two compliance pathways allowed for multifamily projects under the 2019 Energy Code.
Pathway 1: Balanced Ventilation
- Requires outside air be supplied to a space at a rate where the supply fan airflow and exhaust fan airflow are within 20% of each other
- The average airflow (cfm) between supply and exhaust is the ventilation rate and that rate must meet or exceed code minimums
Pathway 2: Unbalanced Ventilation + HERS envelope leakage testing
- Requires outside air be provided by either a supply only or exhaust only system that meets the minimum required ventilation rate
- Envelope leakage testing must be performed by a HERS rater to prove each unit leaks less than 0.3 cfm/ft3 to other spaces
These new requirements align with ASHRAE 62.2 and are the same across all sizes of multifamily projects whether low-rise or high-rise.
The basic concept of balanced ventilation boils down to a ventilation system that has both supply and exhaust fans running continuously. The airflow rates (cfm) of these two fans must be within 20% of each other to be considered balanced. There are a number of ventilation designs that will meet these requirements including:
- Dedicated outside air supply fan and exhaust fan at each individual unit
Graphic from 2019 Residential Energy Compliance Manual Figure 4-32
Check out CABEC’s Brown Bag webinar about multifamily ventilation strategies to get an in-depth look at some of the many ventilation designs in practice.
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Balanced Ventilation System Pros and Cons |
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Pros |
Cons |
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Improve indoor air quality to the unit |
Extra piece(s) of equipment to install based on type of balanced system |
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Neutral pressurization of the unit |
Potentially more penetrations onto building façade depending on type of balanced system |
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HERS dwelling unit leakage test not required |
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Testing airflows for test out procedures is easy to do |
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| A well designed system can be used an as” energy credit” in a performance calculation to trade away other less desirable features. |
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Watch out! Not all supply and exhaust systems are balanced. Just because both pieces of equipment exist, doesn’t mean the rates fall within 20% of each other.
Balanced ventilation is the way to go for multifamily projects. With little additional cost of equipment, a project is saving time and money on other features of the building while adding to the overall health of the building for the occupants. Stay ahead of the curve and look into the balanced ventilation scheme that will work best for your projects before January 1st 2020. Talk to your mechanical engineers about moving to a balanced system now if they haven’t already!
Article written by Marina Chavez Blanco, Manager, Nonresidential/Senior Energy Analyst
First published in the Gabel Energy Summer/Fall 2019 Newsletter