Room Co2 Concentration

[burly]

Hi all,

I am working on a Masters thesis while working, and would like to use IES-VE as part of the research.

I have been monitoring CO2 concentrations in a cellular office using physical sensors, but I would like to try and simulate the CO2 in the space using IES also.

I know 'Room CO2 Concentration' is one of the many results you get from Vista, but no matter how people I add as internal gains, or how many windows I open, the 'room co2 concentration' value is always 360ppm.

Anyone know if the CO2 concentration changes in IES or is it always fixed at 360ppm. I'd be particularly interested in any information from the forum administrators about how IES treats carbon dioxide CO2 in its the calculation methods.

Thanks in advance.

[Complex Potential]

Hi Burly

I think the CO2 emission rate is linked directly to the latent component of the people gain. The 360ppm value is basically the background level that you would expect the room to drop to overnight while unoccupied.

If you are adding significant people gains into the space and seeing no CO2 increase then it is likely that there is an error in your setup somewhere because you should be seeing noticeable changes. Check that you have latent gains and that the activation profile is not set to off continuously within the occupancy gains.

Before you run the simulation under output options you can set the internal gains to be broken down which should then allow you to look at the occupancy gains specifically to make sure they are activating. Also, ensure you are running an ApacheSim (Dynamic Simulation) and not a CIBSE or ASHRAE loads calc.

Once you have checked all of that, the only other thing I can think of is that you have a huge amount of fresh air entering the space either via windows or through the air exchanges tab that is basically keeping the room at ambient levels regardless of occupancy density.

Good luck.

CP

[burly]

Thanks CP,

I got that sorted.

I am trying to create a model which replicates that is actually going on in the office I am looking at.

I carried out an all day on site survey of people movement and window openings etc, and found that people in the office got up to open windows when the co2 got close to 1000ppm, or when the temperature rose above 23.2C. I have set up macroflo profiles along these lines, and the good news is that the vista results for Room Co2 concentration are following pretty much he same profile as the actual recorded data which I am representing in EXCEL graphs. The simulated data and actual data are close enough.

One question I have which hopefully you can answer. Is that base co2 concentration of 360ppm the standard within IES-VE? Would you know where I could find in the IES manuals the basis for this 360ppm, so I can refer to it in my dissertation paper.

Many thanks CP.

[Complex Potential]

Hi Burly

I'm pretty sure the 360ppm (or something close) is a standard background ppm within IES but you'd have to search through the technical manuals to find it referenced. It's likely to be under the thermal sub catagory but I don't know for sure.

http://www.iesve.com/support/knowledgebase

A quick email to IES support may be the easiest way of finding this particular needle in a haystack.


Good luck.
CP

[burly]

HI CP,

I found this myself by checking the 'ApacheSim Calculation Methods' guide.

I am quoting below from page 16 of the guide;

"Carbon dioxide gain is treated in a similar way, c = m(k1 - k)
where
c is the carbon dioxide gain (kg/s)
k1 is the carbon dioxide concentration of the supply air (kg/kg)
k is the carbon dioxide concentration of the room air (kg/kg)

In the case of an air supply for which the supply temperature is defined by an
absolute profile, the supply humidity ratio is assumed to be that of the outside
air, unless this would imply a percentage saturation of more than 90% when the
supply humidity is adjusted to this limit.
The carbon dioxide concentration of outside air is assumed to take the fixed
value of 360 ppm (volumetric)."

This answer my question, thought you'd like to know for future reference!

Thanks again

burly