Derivative Control; Demand Controlled Ventilation; Theory And Operation Demand Controlled Ventilation; Dcv Operation - Honeywell LCBS Applications Manual

Derivative Control

Proportional-integral-derivative (PID) control adds the derivative function to PI control. The derivative function opposes
any change and is proportional to the rate of change. The more quickly the control point (actual sensed temperature)
changes, the more corrective action the PID system provides. The higher the derivative setting, the greater the effect. In
LCBS Connect controllers, the derivative default value is factory set to zero resulting in no control. It is strongly
recommended that the derivative remain at zero (0) unless you have a very good reason to adjust it.
control is not needed in the vast majority of HVAC applications.

DEMAND CONTROLLED VENTILATION

Theory and Operation Demand Controlled Ventilation (DCV).
As energy costs increased in the last half of the 20th century, coupled with the cost of providing ventilation to building
spaces during height and depth of winter and summer, ventilation codes have been altered. It is acceptable to supply
ventilation at a rate equivalent to the number of building occupants as opposed to a fixed minimum ventilation rate of
outdoor air actuator and dampers.

DCV Operation

As energy consumption continues to be a driving part the economics to operate HVAC systems, we continue to support
HVAC strategies that will allow systems to dynamically "decrease" fresh air ventilation rates if there are a few occupants in
a building space. Unfortunately, many building owners and operators have figured this out and have purposefully
restricted fresh air ventilation flow to building occupants. Incorrectly executed, this can result in sluggish behavior and
illness directly caused by stale, recirculated air.
Without writing an HVAC physics paper, scientists have determined that the presence of carbon dioxide gas is
proportional to oxygen content in air due to human respiration. Fact is that the "primary function (of human respiration)
is to obtain oxygen for use by body's cells and eliminate carbon dioxide that cells produce." The less content of carbon
dioxide in the air, the less presence of human respiration (and humans) exists. This makes people drowsy, ill, and worse.
Find levels and associated human impact of CO2 in confined building spaces provided by "Engineering Tool Box:"
NORMAL OUTDOOR AIR PPM LEVEL
ACCEPTABLE PPM LEVEL
COMPLAINTS OF DISCOMFORT, ODORS BY BUILDING OCCUPANTS
ASHRAE AND OSHA STANDARD, EXPECTATION
GENERAL DROWSINESS
ADVERSE HEALTH EFFECTS EXPECTED
MAXIMUM ALLOWED CONCENTRATION WITHIN AN EIGHT (8) HOUR WORKING
PERIOD
Source: http://www.engineeringtoolbox.com/
The Honeywell LCBS Connect control can reduce ventilation in a building space with feedback from a CO2 sensor. As you
can see from the table above, it is desirable to keep interior building space CO2 levels at 1,000 PPM or below during
building occupancy periods. If sensed CO2 level falls, it is acceptable to reduce outdoor air damper minimum position
and still conform to building code. The LCBS Connect controller will reduce outdoor air damper position until sensed CO2
begins to rise. Again, if it is very cold or very warm outdoors, reducing outdoor air position can save substantial negative
energy consumption and associated cost outlay.
First "law" of ventilation
The bigger the rate is, the more my energy bills will be. The more extreme the climate, the more damaging high rates of
ventilation are. So, what if I only have five (5) people in my building, instead of 20? I only need to provide 50 CFM of fresh
air to the building. As a building owner I could do two things. First, if I could control to this lower level and I could 1]
provide appropriate fresh air to my building guests and 2] save a bunch of energy dollars by backing off ventilation rate.
Demand Controlled Ventilation (DCV) unlocks the promise of dynamically provide lower ventilation rates automatically
and delivering benefits described above.
SITUATION
17
LCBS CONNECT SOLUTION
Derivative
CO2 PPM LEVELS
350-450 PPM
<600 PPM
600-1,000 PPM
1,000 PPM
1,000-2,500 PPM
2,500-5,000 PPM
5,000 PPM
31-00118EFS—01