ASHRAE Journal - June 2013 - 54

building sciences
midifiers (Figures 3 and 4 and Photo
6) in houses if they are small and, for
Exhaust Air
sure, we need them in apartments and
condominiums.#
Heat Exchange
Bedroom
Bedroom
Ventilator
This is the part where I am going to try
Outside Air
Bath
Bath
to be constructive and make some sugExhaust Air
gestions on fixing Standard 62.2. Lower
the rates for ventilation systems that have
Radiant Heat
good ventilation effectiveness. This will
encourage good systems and discourage
bad systems. Heresy, I know.
Here is my take on exhaust-only ventilation. Extracting air out of one location with Figure 2: Fully Ducted HRV or ERV. The “Porsche” of ventilation systems. Only slightly
an exhaust fan does not help other rooms less expense than a Porsche….and certainly not as much fun. Kitchen exhaust is vented
and does not address the quality or location separately—not through the HRV or ERV. I prefer not to run the bathroom exhaust
of the air being drawn into the building. through them either, but I am in the minority.
What is the “effectiveness” of the ventilation in a secondary bedroom with an exhaust fan in the master
get exhaust-only ventilation to work minimally well you need
bedroom? With a single point exhaust you need about three times
to provide mixing and distribution with the house central air
the flow rate compared to supply air ducted to a central air handler
handler, and even then you don’t get to filter the air before you
that distributes the air and provides mixing to get similar ventilabring it in, you don’t get to pick where the air comes from, and
tion “effectiveness.” Yet Standard 62.2 treats them the same. To
you certainly don’t get to precondition it.
Supply
Air

Pressure
Relief Grille to
“Bleed”
Pressure Field
from Floor
Cavity

Air
Handler

Supply
Return

Motorized
Damper

Outside
Air Duct
Return
Air
Short Return
Plenum
(“Sleeve”)

Motorized
Damper
Outside
Air Filter

Air Handler
Filter
Full Height Louvered
Closet Door for Access
And to Supply Return
Air to Air Handler and
for Dehumidifier

Dehumidifier

Air
Handler

Pressure
Relief Grille to
“Bleed”
Pressure Field
from Floor
Cavity

Flexible Connection for
Vibration and Sound
Control
Expandable
Filler Slot
Full Height Louvered
Closet Door
For Access and to Supply Air
For Dehumidification

Dehumidifier

Condensate
Overflow Pan

Figure 3 (left): Dehumidifier in Return Closet. Standard off-the-shelf dehumidifier inside a return closet. Works great. Folks hate
this because the return is not ducted. Not a rational objection in my view, but what do I know? Figure 4 (right): Dehumidifier with
Ducted Return. Standard off-the-shelf dehumidifier in a closet with a hard ducted return.
#Did the folks on the committee that voted for these rates know they were also voting for dehumidification? Interesting question. The comment I got from one
luminary is that it is the job of the engineer to figure this out, not the job of the committee. I mentioned the energy penalty as well. The response from another
luminary is that Standard 62.2 is not supposed to consider energy, and it does not consider it. The Standard 62.2 committee has managed in the last set of
changes to waste all of the energy the model building codes have saved in the past two decades of encouraging the construction of energy-efficient buildings
due to the energy penalty from excessively high ventilation rates.

ASHRAE Journal

ashrae.org

June 2013

ASHRAE Journal - June 2013

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