Reversing Airflow Direction

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Old 11-24-20, 06:53 AM
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Reversing Airflow Direction

I am interested in reversing the direction of the airflow in our HVAC system. I contacted the company that installed the units and they told me no, but the coronavirus urges me to keep investigating. The units are mounted on the side of the buildings and ducted from above. I am trying to remove as much CO2 out of the room as possible, as fast as possible and from above. If I can use the current system to do this, it would be a game changer in decreasing the viral load in our classrooms. We are a small farm school in Washington state and are looking for ways to make our classrooms safer. The name on the HVAC units says Bard.
 
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Old 11-24-20, 07:17 AM
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You've got a bunch of issues all rolled together, so working simple to hard-

First: Photos. Those look like modular plywood classrooms, is that correct?

Second: CO2. Unless you're heating the classrooms with individual kerosene space heaters, you're NOT going to have a significant C02 issue. Air infiltration into most structures results in total turnover in a matter of hours for a small building (volume scales as the cube, area available for air leakage scales as the square, smaller buildings leak MUCH more than larger ones.

Third: Reversing Air Circulation
Modern HVAC systems often utilize soft flexi-pipe for heating/cooling ducts that blow air under positive pressure, while steel "returns ducts" are used for negative pressure that sucks air back. You CAN'T realistically reverse these

Fourth: viral load. Unless you're dealing with actual Covid-19 positive students, you shouldn't HAVE a viral load. There ARE easier ways to ensure that the school's surfaces are kept clean
Students in Japan clean their own classrooms and school toilets and the reason is incredible - Education Today News (indiatoday.in)



 
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Old 11-24-20, 07:21 AM
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I don't think it's possible.
You'd be better off to buy a room air purifier.
But you should contact a professional to properly size it.
If it's strictly for the sake of CORVID, you may be over thinking it.
Whole window fans may be just as good in terms of evacuating or making an air exchange.
In my opinion as well as many experts, the school setting is perhaps one of the safer places in terms of limiting CORVID. And that is because of discipline, distancing and limited close social closeness. Besides it has been determined that children are less susceptible and can recover quicker if infected. Teachers are at higher risk.
 
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Old 11-24-20, 10:43 AM
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We're using CO2 as a substitute for virus particles as we conduct experiments with airflow and ventilation.
They are modular buildings with no shared air space between rooms.
Thanks for the info so far!
 
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Old 11-25-20, 05:39 AM
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Thumbs up Welcome to our forums!

It is an accepted practice to measure CO2 as an indication of air exchange in an occupied room.
The theory being that with a normal outdoor background CO2 level of about 400 ppm any higher level within an occupied space shows that people's breath is causing the CO2 level to rise.
It is generally accepted that CO2 levels in an occupied space can be as high as 1000 ppm.

Presumably you are trying to lower the CO2 levels in the rooms to potentially reduce the amount of virus in the airspace.
This is a good idea for sure but reversing airflow in an air handler is not a workable solution.
The supply/return ducts and fan are designed for one airflow direction only.

What you will have to address however you increase air exchange is to condition the outdoor air that you bring into the space.
Unfortunately you have not filled in your approximate location in your profile so have no idea what sort of climate you are in.
Regardless, you will have to heat or cool that air.
If you have a budget for this an air/air heat exchanger of a type that is installed in modern homes would be a big help.
The existing heat/cool unit might be able to deal with the air from an exchanger.
A more simple solution would be to install two windows, one on each side of the room to get a cross draft.

As an afterthought these modular units must have a building department approval to be occupied.
Air change within a public space is legislated and I would expect it to be in the range of 2 - 6 air changes /hr.
What is the design and approved air change/hr for these buildings?
 
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Old 11-25-20, 12:10 PM
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The OP might need to go with some UV sterilization setup, can you install a UV-C light fixture in an air-return duct?

Originally Posted by GregH
have no idea what sort of climate you are in.
Originally Posted by BryanMcGriff
We are a small farm school in Washington state
Wet and rainy.
 
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Old 11-25-20, 12:34 PM
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I don’t understand how reversing the flow would accomplish anything. That big coil your looking at in the photo isn’t bringing in air to the inside of the building.
Bard units typically have a manual outdoor damper inside of them. But like I said, it’s manually controlled.
 
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Old 11-26-20, 06:56 AM
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I checked and Washington Sate has specific ventilation requirements for schools.:

Ventilation. Operate the ventilation system continually when the school is in use, including during custodial work. Supply at least 15 cubic feet per minute per person of fresh outside air whenever the school is in use. See WSU Energy Program's Good Ventilation is Essential for a Healthy and Efficient Building (PDF).
 
 

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