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Multifamily Passive House Ventilation Design Part 1: Unitized or Centralized HRV/ERV?

 

Project teams pursuing Passive House frequently ask, “Where do we locate the HRV/ERV?” The answer is complex when the Passive House concept is scaled to a multifamily program.  While there are two primary arrangements for HRV/ERV systems, the trade-off is dynamic and needs to be carefully considered as multifamily Passive House projects begin to scale. A low volume HRV/ERV unit ventilating an individual apartment is a unitized HRV/ERV. High volume HRV/ERV units ventilating multiple apartments and often servicing several floors, is referred to as centralized HRV/ERV.

As Passive House consultants we can attempt to address the system arrangement question with building science; however, in New York City rentable floor space is very valuable, so considering the floor area trade-off is of particular interest to project teams. When a unitized HRV/ERV system cannot be located in a drop-ceiling due to low floor-to-floor height, it is placed in a dedicated mechanical closet. This closet is typically no smaller than 10 ft2 and includes the necessary ductwork connections to the HRV/ERV unit. The alternative solution is to increase the floor-to-floor height to accommodate the HRV/ERV unit and horizontal duct runs in the ceiling. Centralized HRV/ERV systems, however, allow short horizontal duct runs but require floor space to accommodate vertical shafts. With supply and exhaust ducts coupled together the required floor area is about 8-12 ft2. As a result, centralized HRV/ERV systems may actually require more floor area than a unitized system.

Example: In the case of Cornell Tech, vertical supply and exhaust duct work for the centralized HRV/ERV system required 222.5 ft2 per floor, or 13 ft2 per apartment (see image 1 below). Unitized HRV/ERV mechanical closets would have required an estimated 170 ft2 per floor, or 10 ft2 per unit (image 2 on right).

Comparison images HRV/ERV

Image 1 & 2:  These images compare the amount of floor area required for centralized and unitized HRV/ERV systems. Image 1 on the left, shows the 12ft2 floor area required for vertical shafts servicing the centralized ERV at Cornell Tech. Image 2 on the right is hypothetical, showing the typical location and 10ft2 floor area required for a unitized HRV/ERV mechanical closet.

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It Can Take Years – A Market Adoption Story

Earlier this year, at the AHR Expo in Orlando, the biggest trade show for HVAC professionals, Aeroseal’s duct sealing technology was declared the Product of the Year, the top honor of the Innovation Awards. Aeroseal was recognized as “a groundbreaking solution to an industry-wide problem.”

The unique appeal of the Aeroseal technology is that it seals ducts from the inside. Walls and ceilings do not need to be removed or damaged to gain access for traditional mastic sealing. Aerosolized vinyl polymer particles from 2 to 20 micrometers are injected into a pressurized duct system. The particles stay suspended in the air stream until they reach the leaks, where they are deposited and built up at the leak edges until the leaks are sealed.

The Aeroseal technology has been around for more than two decades. It was developed at Lawrence Berkeley National Laboratory in the early nineties and patented in 1997. It has received many awards over the years including the Best of What’s New award from Popular Science magazine in 1996 and the Energy 100 award from the U.S. Department of Energy.

So what’s the big deal?

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