ASHRAE Journal - April 2020 - 12

TECHNICAL FEATURE

Another HVAC Design Parameter to Consider

Stack Pressure-Created
Airflows in Insulation
Envelopes, Part 1:
Buildings
BY DOUGLAS S. WALKINSHAW, PH.D., P.ENG., FELLOW/LIFE MEMBER ASHRAE; RAYMOND H. HORSTMAN, P.E., FELLOW ASHRAE

Building design codes with one exception* generally do not recognize the impact
stack pressures play in finished basement energy use and the moisture and air quality concerns and problems they are responsible for creating. Neither do they provide
measures to resolve these concerns and problems, and this is the focus of this paper.
The authors' stack pressure and basement batt insulation envelope flow measurement
experience and related calculations to quantify and solve these problems indicate that
when countermeasures are not taken, a substantial portion of thermally conditioned
air circulates behind the basement insulation in winter due to these stack pressures;
in summer lower stack pressures create stagnant air pockets behind the insulation air
barrier, which trap ground-sourced humidity and moisture.
Stack pressures arise across insulated boundaries
such as insulated perimeter basement walls due to
the air density differences on either side, which in
turn arise from their temperature differences. The
higher the wall, the greater the temperature difference; and the denser the air, the higher the equal and
opposite stack pressures at the top and bottom of the

wall. In winter the air behind the insulation is coldest
at the top basement wall at the aboveground portion
of the envelope. This cold air, being denser than the
*The Ontario Building Code (BMEC approval 97-05-214) allows
the interior finished basement insulated envelope ventilation system described in this paper as an alternative to foundation exterior
water sealing and drainage measures. It also solves basement soil
gas and odor air quality concerns.

Douglas S. Walkinshaw, Ph.D., P.Eng., is president, Indoor Air Technologies, Inc., VEFT Aerospace Inc., and ECHO Air Inc, Canada and USA. Raymond H. Horstman, P.E., is an Indoor Air
Technologies Affiliate.
12

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ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020

Contents
ASHRAE Journal - April 2020 - Intro
ASHRAE Journal - April 2020 - Cover1
ASHRAE Journal - April 2020 - Cover2
ASHRAE Journal - April 2020 - 1
ASHRAE Journal - April 2020 - Contents
ASHRAE Journal - April 2020 - 3
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ASHRAE Journal - April 2020 - Cover3
ASHRAE Journal - April 2020 - Cover4
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