Page 54 - Green Builder July-August 2020 Issue
P. 54
IAQ: Breathe Easier
Products, Research and Advice for Improving Indoor Air Quality
Comfort Level
A lot goes into ensuring that a multi-story residential building is energy efficient,
as this case study demonstrates.
BY ARNAUD GIRIN
HEN PEOPLE ARE DISSATISFIED with the
thermal environment, their productivity, capacity
of concentration, well-being and health can be
negatively aected. Thus, ensuring thermal comfort
W for any new building design project through its
HVAC system, as well as positioning of windows, doors, stairs and occupant metabolic rate, clothing insulation, temperature, airspeed,
other components, is paramount. mean radiant temperature and relative humidity.
When it comes to green buildings, the challenge is even bigger, Once the PMV is determined, the PPD—“an index that establishes
as other factors—such as energy consumption or noise and air a quantitative prediction of the percentage of thermally dissatised
pollution—need to be kept to a minimum simultaneously. Several occupants determined from PMV” (i.e., people that may feel too
factors that determine if a building is “green,” including having warm or too cold)—can be dened.
heating, ventilation and air conditioning systems with low energy The PPD indicates the percentage of people that could experience
consumption, employing renewable energy, efficiently using a condition called local discomfort. There are a few factors causing
resources, proper indoor air quality, measures against pollution, and local discomfort, including draft or lack of airow, but the resulting
recycling, to name a few. consequence is the undesired cooling or heating of an occupant’s
Both in the case of green and standard buildings, energy eciency body. In the presented case, these factors will be taken into account
is essential, and nding a middle ground between this and thermal to assess the level of thermal comfort but only the PMV value will
comfort is one of the most commonplace tasks for engineers and be used as a measure.
architects.
The main tool for accurately testing these two elements for a CAD MODEL
building’s design is numerical simulation with computational uid The model presented includes three apartments of about square
dynamics (CFD). This method allows users to investigate elements meters on top of one another, separated by millimeter slabs. At
such as airow, temperature distribution, pressure eld, wind speed the ground oor level, there is also a . square meter oce space
and air exchange rate more quickly and eciently. that has its own independent access. In each apartment, there are
FIRST STEPS
In this project, a residential building design was virtually tested
with the goal of nding the right capacity settings for its HVAC
system in order to ensure thermal comfort in winter. To that end,
a computational uid dynamics (CFD) simulation was performed
online to determine a suitable heating capacity of the three-story
building in order to guarantee the occupants’ thermal comfort while
maintaining recommended indoor air quality.
To quantify the thermal comfort of the occupants, two quantities
can be calculated through the results of the CFD simulation. These
values are predicted mean vote (PMV) and predicted percentage
of dissatised (PPD), and they determine the probability that an
occupant feels cold or warm. The ASHRAE standard denes the
PMV as “an index that determines the mean value of votes of a group
of occupants on a seven-point thermal sensation scale.” The thermal
sensation scale is depicted in the picture below.
The PMV takes into consideration dierent factors—the predicted
52 GREEN BUILDER July/August 2020 www.greenbuildermedia.com
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