Thursday, April 19, 2012

Ventilation Reduction in Multifamily

Spent yesterday, an overcast Wednesday in April, testing ventilation rates on the roof of a 25 story multifamily building in NJ.  HOW DID I GET A WICKED SUN BURN?  It was overcast, slight rain, and its APRIL!  I look like a hot-house tomato today.  Unbelievable.

The goal of our work was to get a thorough understanding of baseline exhaust ventilation loads.  We will be looking to dial-back and "right size" the ventilation loads, and also to balance the system for optimized indoor air quality.

We tested 26 fans on the roofs of two attached buildings in the same complex.  Eighteen of the fans were up-blast, mushroom-style fans, which exhausted the bathrooms within the apartments.  We tested these using an innovative technique my firm has developed with a blower door.  The remaining 8 fans were side-blast utility exhaust fans, which are ventilating kitchens within the building.  These were tested with a similarly innovative technique that involves fitting a calibrated flow hood over the fan and measuring laminar discharge velocities with a hot-wire anemometer traverse.  Good stuff all around.

The results of the field-testing shows that the building is about 40% over-ventilated while being significantly out of balance.  We will recommend cleaning the sheet metal ventilation riser shafts, sealing them with a spray applied duct mastic, installing constant airflow regulator (CAR) dampers at every exhaust inlet to balance flows up-and-down the building, and installing new direct-drive exhaust fans with ECM motors.  We anticipate the building will realize substantial energy reductions related to the reduction in total ventilation.  For the layperson, every CFM of exhaust we can reduce is a CFM of air that already been conditioned and thus contains concentrated embodied energy.  Most buildings are significantly over-ventilated; right-sizing ventilation loads saves energy and money.

Also involved with this project is the installation of an HRV, which will allow the energy contained within the remaining exhaust to be partially recovered and re-introduced to the building.  More good stuff.

This project will receive funding from a public utility program and will provide an excellent case-study in the effectiveness of ventilation retrofits on existing multifamily buildings.


UPDATE: 4/24/2012
Calculations have shown that the building is actually 56% over-ventilated, rather than the 40% initially assumed, making this measure considerably more cost-effective than suspected.  Kitchens are exhausting around 100 CFM, and bathrooms around 50-75 CFM.  We will right-size the load on all of them to 30 CFM, which will allow for ASHRAE 60.2 compliant residential air change rates.  Yeah!

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