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Carbon Dioxide (CO2) demand controlled ventilation - HVAC-Talk: Heating, Air & Refrigeration Discussion
Do you guys have any thoughts about Carbon Dioxide (CO2) demand controlled ventilation?
Are you seeing it commonly used?
They seem to be the trend in movie theaters and schools, but what about offices?
Does CO2 mean good indoor air quality?
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Something that is mainly empty then heavily occupied by a group of people like a theatre is a good application for demand ventialtion.
OSHA will say 8 hours exposure to 5000 PPM is a CO2 limit, fresh air in an area away from urban traffic gridlock would be about 400 PPM.
They mainly use CO2 as an indicator of how much ventialtion you are getting rather than high CO2 being bad for you.
If the CO2 is kept under a certain level the hygeinists feel that VOCs, allergens etc are also likely being purged, but to those types even a low level of CO2 is not good enough.
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In wisconsin we see it used very little due to the fact local code requires constant ventilation according to the air exchange rule and cfm per person rule.
The CO2 can be used to increase past that but we only see it in areas like you mentioned.
I Illinois however you can use it to determine your ventilation and fresh air rate based on demand.
I have noticed though that C02 is only half of the problems, you have VOC'S that need to be vented when areas are being used like conference rooms with dry erase markers, new buildings which still are off gassing.
My 2 Cents
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CO2 sensors are often put in spaces with inconsistent occupancies like movie theaters and classrooms (which were mentioned) and also in conference rooms and other assembly areas.
The theory behind demand control ventilation is that a space will require a certain amount of minimum ventilation based on occupancy (from ASHRAE/ local code), and CO2 is a way to ventilate based on people in the room.
This saves energy from having to supply a constant minimum ventilation to a space that is unoccupied a lot of the time.
This would not be a good system for an office space, since offices generally have a constant occupancy.
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One of the last controls jobs I did for my previous employer before I retired was at a well known music school.
The job consisted of installation of two new Air Handler units that supplied two concert theaters and three orchestra/band practice studios.
The theaters were also used as classrooms/lecture halls.
These rooms could have anywhere from hundreds of people in them to just a few people.
Or no people at all.
Part of the specifications for all of the rooms required CO2 sensors for outside air control.
Due to concerns about stagnant air on the part of the schoolÂ’s building and event managers I added standard enthalpy control for low usage hours.
If the CO2 in the rooms climbed above a certain value then the system would switch to CO2 Mode.
If it was below that value then it would switch to Enthalpy Mode.
Enthalpy Control by itself is an excellent energy conserver and CO2 Control works very well in rooms that are occupied by large amounts of people.
For an office environment I would be more concerned about Indoor Air Quality and opt for Enthalpy Control with minimum outside air.
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What is your take on CO2 and IAQ control then?
I've used the combination of the two and I believe it is a great application.
Someone burns popcorn in the microwave and the IAQ sensor(s) pick it up and begin ventilation.
I've been really happy with what I've seen of the usage and from the techs that work in the area they are happy with it as well, but it is a remote site that I cannot monitor.
On thing that sold me on the IAQ combo it is that they were painting a small room and the IAQ picked up the fumes and was ventilating the place.
I could not smell the paint at all until I came into the doorway of the room that was being painted.
I initially thought something went wrong with my IAQ sensor, but after walking around found the guys painting.
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Some Of The Citys In My Area Require Dcv.we Did A Job Recently That Had A Plan Check Requirement That Required Us To Add Dcv Controls.the Funny Thing About It Was The Menchinal Inspector Never Asked Us To Test It.i Asked Our Engineer Why It Came Up In Plan Check And She Told Me It Was A New Code .she Told Me That Each Person Needed Forty Squire Feet Of Space If Their Wasn't The Area Would Need To Be Controled By Dcv.we Installed Two Sensors One In The Lunch Room And One In The Confrence Room.so I Would Say That You Will See Alot More Of Dcv.
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We have added Co2 sensors to most of our systems to provide ventilation minimum levels.
One of our customers was getting complaints of stuffiness in a building so we calculated and controlled the actual outside air volume on the system through the DDC system.
With Co2 and outside air calculatios we dialed in the dampers to optimise energy usage while ensuring a healthy environment for the tenants.
We had an article published in Plant Engineering Magazine in 1999 on the subject.
http://www.plantengineering.com/article/CA123729.html
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I've started using the CO2 calc on a reset block in my controllers at my job site.
I'm also going to incorporate Enthalpy from my national weather service temp and humidity data to calculate the control econimizer switchover based on the difference from the return air temp and humidity, in the AHU's.
As the energy prices go up I can see this combo to be very valuable to my customers.
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Quote: : I've started using the CO2 calc on a reset block in my controllers at my job site.
I'm also going to incorporate Enthalpy from my national weather service temp and humidity data to calculate the control econimizer switchover based on the difference from the return air temp and humidity, in the AHU's.
As the energy prices go up I can see this combo to be very valuable to my customers.
I'd be careful using data from the weather service into your logic.
I'm assuming here you're using AX.
We always install our own outside air and humidity sensors on site.
I's ok to use the data, as long as you have a fail over method in case the data goes stale.
What happens when the weather service fails to update the weather report, let's say due to lost Internet connectivity?
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They have been using the National Weather service for over a year now without failure on a univeristy network.
Not using AX, the customer had David Hagemann's NWS import utility installed to use.
I haven't seen netowrk failure since I've been here, yet....
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Like the others I have used them in schools and performing art theaters.
I have also had to use them in a project for a court house.
The buses for the prisoners parked right next to the AHU air intake so the court rooms would fill with the exhaust odor.
Also I used them in a parking structure to turn on exhaust fans when for after hour use.
Matt
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