Letter Re: Introduction to UV Air Treatment

Dear Editor:
Can Michael M. provide a bit more detail in his process of developing a UV air treatment solution?  The part about” “Slack tube manometer and did a static test with the air handler running and the house closed up tight. I had a negative pressure of .45″ water column vacuum. I concluded that I needed a fresh air return duct if I was going to use my air handler to try and pressurize the house” is difficult for me to visualize.  Is the manometer on the upstream side of the Air Handler fan or the down stream?  Also I don’t understand the math used. I do understand the 4940ft^3 / 1170ft^3/min =  4.2 minutes, but how did he calculate or measure the 1170ft^3/min of airflow?  How did he come up with “a needed 60 to 75 sq in fresh air duct to compensate for the tight construction to bring my static pressure to 0?”   This appears to be very important information but is difficult to understand.   Thanks for the good work and words. – Mark X.

I Forwarded This to Michael M. and He Replied:

Daer Jim & SurvivalBlog Readers:
Let me first explain what the Slack Tube Manometer can be used for:
Mainly it is an instrument that can be used to measure static pressure, pressure differential, or total pressure. In my case I used a Dwyer Model 1212  to measure pressure differential from the outside ambient air pressure to the inside air pressure. One could call it a static pressure. I did this by putting one side of the tube on the outside through a window and blocked the remaining area of the open window and the other side of the meter on the outside of the door of the heat exchange closet. It could be placed anywhere as long as one side of the meter is outside and the other inside. I used this area as it was easy to change the fan speeds and see the result. When the air handler was on a negative pressure was seen on the tube.  

Next would be the issue of the 1,170 cfm air rate. This number was supplied to me through the Manufacturer’s manual as to the cfm at the various fan speeds available. i.e.: fan speeds available Low–820 cfm Med low–1,003 cfm Med high–1,170 cfm High–1,532 cfm.  

How I came up with the  fresh air return needed and wanted:

First I obtained a copy of the Rules and Rules of Thumb for Duct Systems on the Internet. This gave the necessary numbers for a filtered grille area to compensate  for the negative pressure. At this point with the fan on the med high speed I open a window away from the air handler till the pressures equalized in the manometer. I measured the calculated the square inches of the opening and had my filter size to equalize pressure per the rules. I added the other 2 filters and with the air return from the house blocked achieved a positive pressure of .35″ of pressure.

It should also be noted that not all homes can use this type of system as many are not sealed tight enough to maintain the slight pressures.

Another interesting side note is that we are also able with this configuration to use one small bedroom as a negative pressure room simply by opening the window in the room making a perfect place for a quarantine room for the sick.   I hope this helps, – Michael M.