Technology selection essential for DCV savings0 pages

/ APPLICATION NOTE
NOVEMBER 2009
Technology selection essential for DCV savings
Optimizing demand controlled ventilation (DCV) will
contribute to an enhanced indoor environment at lower
operating costs. The system can only be optimized by accurate
carbon dioxide (CO2) sensing.
CO2 Highlights Related to DCV
Good indoor air quality can be
achieved based on occupancy
CO2 measurement is the most
economical method to monitor
both air quality and human
presence with one sensor
Energy is saved by minimizing
use of unconditioned outside
air
Inadequate ventilation results
in an elevated CO2 level,
causing drowsiness and
decreased productivity
CO2 Information
CO2 is measured in parts per
million (ppm)
Typical outdoor ambient
CO2 concentrations:
350 – 450 ppm
Acceptable IAQ CO2
concentrations:
600 – 800 ppm
Tolerable IAQ CO2
concentrations:
1000 ppm
Humans spend 90 % of their time
indoors. Studies indicate that indoor
air quality (IAQ) is directly linked to
human well-being and productivity.
The CO2 level can be used as an
indicator for indoor human presense.
A high CO2 level is a sign of poor
ventilation and often an indication of
other unpleasant odors in the air.
As many as 30 % of buildings have
poor IAQ.
The most economical way to
determine the ventilation demand is
to measure carbon dioxide, which
increases in relation to number of
humans present. By controlling
ventilation according to the CO2 level
rather than the assumed amount
of people occupying the space, the
indoor air can be kept fresh without
over-ventilating and wasting energy.
Industry drivers
Limits for CO2 levels in indoor air
differ slightly from one country to
another. For example, interpretation
of ASHRAE (www.ashrae.org)Standard
62.1 “Ventilation for Acceptable Indoor
Air Quality” implies CO2 levels should
not exceed 700 ppm above outdoor
ambient levels of 400 ppm. The EU
Commission has issued an Energy
Performance in Buildings Directive
(2002/91/EC) which specifies that
energy savings should not have a
negative impact on indoor air quality.
Energy savings as stated by the
ETIAQ (Energy Technologies
and Indoor Air Quality) project
coordinated by Rehva, the Federation
of European HVAC Associations,
reports 20-50 % energy savings in
public buildings using DCV, and even
greater savings potential in buildings
with varying occupancy.