Why you need to pay attention to Ventilation Effectiveness (EZ)!
Written by Nathan Martin, P.Eng. President of O’Dell Associates
In our quest for ever-increasing energy efficiency, ventilation effectiveness can deliver exceptional results. I might suggest more valuable than the most efficient ERV! Sure, new tech is delivering efficiencies greater than 90%, but with thoughtful application of ventilation effectiveness we can significantly reduce the amount of outdoor air required to produce acceptable IAQ.
Ventilation effectiveness (Ez) can either penalize or benefit your design, depending on what air distribution criteria you apply. The formula for determining occupied zone ventilation rate (Voz) is as follows:
The breathing zone ventilation rate (Vbz) is determined using the Ventilation Rate Procedure (VRP) or Indoor Air Quality Procedure (IAQp). From my experience, the majority of designs apply an Ez of 0.8, basically adding 25% more ventilation air to the space to account for design or equipment deficiencies. Consider that Ez can range from 0.5 to 1.5 (See Table Below), effectively we can reduce ventilation by up to 66% with thoughtful and deliberate design decisions.
The obvious advantage to reduced ventilation is energy efficiency. There is no greater load in a building than the ventilation air! But we can also find some other valuable benefits.
- Reduced capital costs for energy recovery equipment
- Eliminate need to apply more expensive technologies
- Mitigate humidity issues associated with ventilation.
- Reduce filtration load on air handling equipment
- Reduced building loads result in smaller heat/cool plants resulting in significant mechanical costs savings
- Smaller heat/cool plants use less space, which can be repurposed for amenities
I think it’s important to consider the fundamentals of our designs before chasing more tech! Look at the table below and consider some of the simple strategies to implement in your next design. Simple changes, like relocating return air openings or adjusting supply air temperature can have a significant positive impact (20% improvement). Displacement ventilation (warehouses, schools, atriums, etc.) strategies offer a 33% improvement over typical designs.
I love innovation, but it should augment our designs, not save them!