CO2 Sensors/ Demand Controlled Ventilation 2

[hvacnerd]

Has anyone had experience with Demand Controlled Ventilation (DCV) specifically using CO2 sensors? Does this type of system work well? How sensitive are the sensors (if one person walks into a room, will it notice and increase the airflow)? We are looking to use this to control the flow through a Terminal unit (as more people come in, the unit opens more).

The Carrier literature tells how much money can be saved with a system like this, but the client is cautious about using a new type of system.

Any input about DCV systems would be appreciated.

Thanks,

keith

 

[walkes]

We use similar DCV methods, we either have a local CO2 sensor in the space that controls the flow of ventilation air from the dedicated outside air system via a VAV box. Another method is to take an average by putting the sensor in the return air stream near the unit. The latter may not necessarily guarantee precise ventilation rates in a particular space but overall the building will be ventilated properly.

Savings can be generated when the occupancy is less than design and the outside air can be reduced below what most systems would be set for their minimum position. Beware though it may not work for all scenarios, for instance if you have an economizer on the system that provides a 55°F mixed condition, if on your coldest day your mixed condition is providing suitable ventilation for the space you will be ventilating or over-ventilating until the point at which your mechanical cooling is engaged. Where the DCV wouldn't do anything for you.

If you have a situation where you can reduce the air flow in heating with the DCV you would save some money. (This is all dependant on your operating and outside air conditions in your locale)

 

[lcleveland]

dcv will save the client money in a very short time. for most units the design fresh air frequently unneeded due to the max occupancy not being maintained. depending on the accuracy of the co2 monitor used yes yo can almost count the people in the room, though you will only see increases in co2 when the occupants remain in the space. i have designed/installed these systems in school gyms and found the occupants very satisfied and unaware of the oad position.

 

[wayne29446]

Here in SW Florida, we seek a target rate of about 1100 ppm CO2 plus of minus 50 ppm. Our hardware and electronics will achieve that quite well, both in zone operation and in whole building operation.
One piece of hardware we have had especially good success with is for temporary or relocatable classrooms and small zones. It will deliver correct ASHRAE Standard air with very good precision for 0-33 students. It can also deliver correct pressurization to very greatly or totally eliminate mold growth in exterior wall cavities and moldy odors in a breathing zone. Along with implementation of a few "esoteric" building science principles and concepts, we have totally eliminated long duration moldy odors in as little as two hours. We have seen energy consumption decreases of about $2.00 per day per classroom in SW Florida.
Correct and dynamic balancing of exhaust and fresh air flow rates is very simple with the hardware we have developed. It is also very effective at improving indoor air quality.
None of this require BACNet, as the systems can stand alone and work fully automatically according to the conditions in the zone receiving attention. Lower costs, simple installation, very easy troubleshooting and effectiveness evaluation.
We have measured ventilation rates in very expensive hotels that average over 700 cfm per occupant. Humidity, mold and odor problems are rampant, but the hotel says: "we have an expert who takes care of this and he is doing a good job." We try to talk to them about significant energy cost reductions as well as improvements in indoor air quality, but no one seems to care.
Curiously, the greatest barrier to implementing these systems, which have proven very effective in portable classrooms is typically the PE who is the head of the department. They are generally not well informed regarding building science, and they are often resistant to learning anything new. But of course, politics and "my brother in law is in the business" are constant inhibitors of improvements in students' and teachers' health and safety as well as school districts' reductions in energy use.
We suspect that Demand Controlled Ventilation DCV can reduce energy costs as much as 60% in many cases, But Nooooooo.
Overventilation is costly in terms of energy use, high indoor relative humidity and associated comfort problems and serious mold and other microbiological consequences.
We have designed and built broad rate delivery ventilation systems operating on electronically commutated motors that can deliver 0-650 cfm and a large capacity unit that will deliver 30-8700 cfm for large buildngs of greatly varying occupancy capacity. We are not aware of anyone else who has developed similar hardware. We would be most pleased to learn otherwise.
The systems we build work very well.

The CO2 control ventilation guru is Michael Schell, who is a bit hard to find. He has remarkable resources including an excellent program that can predict energy savings based upon a number of data that are easy to collect.
We suspect that to utilize such CO2 or Demand-controlled ventilation requires a person who is willing and able to "think outside the box."
In our experience, it is rare for us to find a school district PE who can do it. If the answers are not written in a book, they seem unable or unwilling to even consider the concepts. Perhaps a little of the "not invented here" syndrome. Surprising, but true.
We have come to share Mark Twain's cynicism about many of our fellow human beings.

Wayne

http://www.radonman.net

 

[HVAC68]

Check these links :

http://www.xpedio.carrier.com/idc/groups/public/documents/marketing/wp001.pdf

http://www.xpedio.carrier.com/idc/groups/public/documents/marketing/wp003.pdf

HVAC68

 

[hvacnerd]

Thanks for your inputs. After discussions with the client, they decided to stick with the normal innefficient methods. Oh well, we tried. I agree with wayne29446, people don't like to try new things or think outside the box.

Thanks again for the advise.