Click here for the actual article - Use of Demand Control Ventilation Article.pdf
There is a lot of talk in the HVAC industry about use of
Demand Control Ventilation (DCV) and how important it has
become in saving energy in buildings. With the recent
legislation in the U.S. Congress and the state of California,
many more people are becoming aware of the energy crisis.
What is DCV? DCV is a method of controlling the ventilation
in a space based on the actual occupancy using CO2
sensors. Building HVAC ventilation systems are designed to
provide fresh air to the maximum design occupancy of the
space. But not all spaces are at the maximum occupancy all
of the time. DCV control allows the building
owner/occupants to save energy by lowering the ventilation
rate to the actual occupancy of the space.
When you lower the ventilation rate to allow for the exhaust
of the building effluents, you need a reliable method of
determining when to provide additional fresh air. But you
don’t want to over-ventilate and waste energy.
Some people in the industry use a CO2 sensor with a 0-
10Vdc output to a damper actuator to achieve DCV. In a
system using a CO2 sensor for DCV, the outside damper
modulates open based on the call for ventilation from the
CO2 sensor. The damper is allowed to drive full open.
What if it is -30° F outside or 99°F plus 90% RH? Do you
want the damper wide open? The obvious answer is no.
You want a control that will allow the installer to set the
minimum position to the level of ventilation required for
building effluents and a small number of people.
When the occupant level increases and the CO2 level goes
up, you need to open the outdoor dampers above the
minimum building effluent level for the increased number of
occupants. But you do not want to open the outdoor
dampers to let in air that needs to be conditioned. To solve
this issue, you need a DCV maximum control on the
damper that allows only the amount of air required by the
building code or design code for the building. Then when
the CO2 sensor opens the outdoor damper to allow fresh air
into the building, you are meeting the ventilation code for
the number of occupants (based on CO2) but aren’t
exceeding the ventilation required by code.
W7212 Economizer Logics With DCV
Honeywell has a solution: the W7212 economizer logics
with DCV. The operator sets the minimum position
Use of Demand Control Ventilation in Your HVAC System
By Adrienne Thomle, Product Manager
potentiometer to ventilate for
the building effluents and low occupancy.
A DVC setpoint on the logic module allows
the operator to determine the CO2 ppm threshold (e.g., 800
ppm) where additional ventilation is required for the number
of people in the space. When the CO2 level in the space
reaches the threshold, the outdoor dampers will modulate
open to ventilate for the higher occupancy. But not too
much ventilation. There is a DCV maximum potentiometer
setting that the operator sets to the design ventilation rate,
the ventilation rate for the maximum occupancy. The space
will not be over-ventilated, and the building code will be met.
And, most importantly, the building owner will be saving
energy—not over-ventilating with cold air or hot and humid
air that would need to be conditioned.
Combining the DCV with the economizer function of using
fresh air to cool your building improves your energy usage
and insures the right amount of ventilation for good indoor
air quality. No more closed dampers to prevent higher
energy bills—no complaints from occupants from lack of
fresh air.
Saves Money, and Easy to Use
Honeywell provides a product simulator for your PC that is
simple to set up and use. The tool allows you to make
changes on the economizer logic and observe the operation
of the damper’s LEDs, etc. You can see when the outdoor
air is bad for economizing and what happens if you have an
input from the DCV CO2 sensor.
Show your customer how he can save energy in his area
with the Honeywell savings estimator. Not every area needs
to use enthalpy for control. You may only need temperature
input in your area. The savings estimator is a quick and
simple tool to determine the right control for a specific area.
Take advantage of those energy rebates. Be prepared
when tax time comes around. Save energy today.