CO2 & Overnight Flushing (cont)

[Guest guest]

What resource(s) do you use for acceptable levels of CO2? I have seen less than 700 ppm above outside air levels with 300-500 ppm being acceptable outside air, 400-1000 ppm as acceptable indoors, 400 ppm acceptable indoors etc. The more searching I did, the more variations I came up with. Your input would be greatly appreciated.

Thanks,

Greg Hatfield, CIE

iaqman2@...

From: iequality [mailto:iequality ] On Behalf Of AirwaysEnv@...Sent: Monday, February 06, 2006 10:53 AMTo: iequality Subject: Re: CO2 & Overnight Flushing (cont)

I once did CO2 testing in an office area adjacent to an unventilated warehouse/service area heated by gas-fired radiant heaters suspended from the ceiling. The levels were over 1500 ppm before anyone came in to work.Steve Temes

In one building investigation I performed years ago where the CO2 levels were higher than logically expected, I discovered an inadequately vented gas-fired hot water heater that was "spilling" into an occupied area of the building. Therefore, in addition to people being generous sources of CO2, combustion devices cannot be excluded.

[Guest guest]

Bob---

You mentioned that one HVAC unit serves two rooms in school 2 and one for each room in school one. Do you have more than one monitor? Are they any variations between the classroooms?***First, if you mean between the 2 classrooms serviced by same HVAC unit: In most cases, the two rooms are nearly equal in area/volume. Since they are located side by side they are usually occupied by same number of students studying similar subjects simultaneously (like the tongue-twister?). In other words, each classroom has 24 students sitting quietly bored to death by English teachers. If ductwork to and from HVAC unit and OA damper settings were configured identically, both classrooms would likely register the same CO2 readings unless room 2 has more hotties, then the guys would be breathing harder and register higher CO2 readings. Sorry, couldn't resist.

In reality, the HVAC unit tends to set closer to one room than the other (because contractor didn't care one way or the other or for structural reasons, who knows?) and teacher in room 1 (furthest from HVAC) has control of the thermostat and experiences constant shivers so the thermostat is cranked to the hilt, thus roasting out students and teacher in room 2 and causing higher CO2 elevations in 2 than 1.

Okay, Bob, I'm through being a wise guy. Yes, I have measured differences between two classrooms on same system simultaneously with separate monitors but in most cases CO2 differences were minor (maybe 100ppm). Of course, the first time I did this I had one room at 850ppm and the adjacent room at 1600ppm. I called maintenance to report the problem. Later found out, the room with the high CO2 had cheer leaders practicing for the afternoon football game. Even when there are differences in amount of CO2 being generated between rooms connected to same unit, both returns mix with OA at the unit and both rooms tend to receive similar supply air which of course, in time, equilibrates the two rooms.

***Second, if you are referring to efficiency and environmetal control variations between unit serving two classrooms versus unit serving one classroom: In every case I have monitored, the unit serving one classroom is superior to the unit serving two classrooms. Often, $$$ dictate an HVAC serving 2 rooms senario (retrofit/remodel) and it usually is undersized to handle both rooms.

Any difference in CO2 levels between the heating season and the cooling season?

***I have not attempted to compare these seasonal differences. This would likely require some serious thought about controls (which some may think I am incapable of) to ensure that we are comparing apples to apples, instead of cucumbers to squash. Very good question, Bob. Maybe or Steve or others have done this. Help us listers!

Miles