Jump to content
Sign in to follow this  
Ops

SURVIVAL HOW-TO: VENTILATION AND FILTRATION OF AIR

Recommended Posts

User Info IM User Email User Reply Quote Edit

--------------------------------------------------------------------------------

 

I am very comfortable with this topic, I was a commercial HVAC mechanic for mot of my adult life.

 

the basic requirements of a safe room or shelter ventialtion system is to remove contaminants from the air, and provide enough fresh incoming air to replace the oxygen absorbed by the occupants. A high density occupancy will need ventilation air to help control temperature and reduce humidity build up.

 

We in the trade use the term 'air changes per hour' or AC/HR to determine ventialtion requirements. One AC/HR is the amount of air needed to replace the air volume in the space. For comfort purposes in normal times, we try to have about 3 to 6 AC/HR in a home, with 10% of that being fresh air. To break it donw further, let's use a shelter space 10ft by 20 ft by 8 ft high, or 1600 cubic feet. 3 AC/HR would be 4800 cf/hr, or 800 cubic feet per minute. 10% of this would be 80 cfm. A person at rest uses 10 to 20 cfm to breathe, so this space would support up to 8 people at rest with ann outside air intake of 80 cfm. Ventilating humidity or heat build up would taek up to 10 times that, or once again, back to 800 cfm.

 

The next project is determining how to move 800 cfm in and out of the space. a '2 ton' (24000 btu) cental AC system runs about 800 cfm, so we will use the above design. Most folks would think of an 800 cfm exhaust fan. this is a bad idea, as uncontrolled air would leak in everywhere. The solution is to use an 800 cfm fan unit, drawing outside air thru filters and dumping the filtered air into the space. this will maintain a positive air pressure inside the space, so that any air leakage will leak filtered air out, rather than contaiminated air in.

 

This air must be filtered. Chemical contaminants can be filtered out with charcoal filters. These tend to clog up quickly, and are rahter costly. My research led me to believe that the best course of action wold be to shut down the ventilation system and let nature take its course, and letting the chem contaminants settle out. Chemical agents are aerosols, and settle quickly. Biologicals hitch a ride on dust particles, and we can easily filter dust. Radiological fallout is simply dust, and any hi efficiency filter will remove even fine dust.

 

I have devised a two stage filter system that will work for even fine particles. Allergies are a common problem, and most allergens are fine dust in the form of pollen. You will need a duct fabricatiiong outfit you make up a filter frame for two 20 by 20 filters, to give an area 20 by 40 inches. this willneck down to a single 20 by 20 filter, then an adapter (called a 'transition') to the intake side of the fan unit. Have the air intake of the fan unit attach to a louver with a bird screen on an outside wall. Use two 20 by 20 fiberglass furnace filters for the first stage filters, and duct tape all edges to prevent dust from leaking by. Next, use a high efficiency pollen removing filter, available at any home store, for the final filter. Duct tape the edges of this filter also. Hopefully the air unit and filters can be located indoors away from the shelter, so you can change the filters as they become contaminated. Remember to d-contaminate yourself if you do handle dirty filters.

 

Power requirements are about 400 to 500 watts for the fan motor. A battery/inverter with a solar panel should be adequate, but that is subject for another post.

 

The fan unit will be the most costly part of the setup, running about $400 or so. Duct work for the filter racks and transition should go for about $200.

 

IM or Email if you are in the process of setting up a shelter, I'd be glad to customize this.

 

Ops

Share this post


Link to post
Share on other sites

Nice article OPS thanks.

Share this post


Link to post
Share on other sites
The solution is to use an 800 cfm fan unit, drawing outside air thru filters and dumping the filtered air into the space. this will maintain a positive air pressure inside the space, so that any air leakage will leak filtered air out, rather than contaiminated air in.

 

Great post! Out of curiosity, how would you envision the complete environmental system being set up for a shelter? How would the exhaust system be set up to ensure a pressurized space inside?

 

My research led me to believe that the best course of action wold be to shut down the ventilation system and let nature take its course, and letting the chem contaminants settle out.

 

If you shut down the intake and don't have a sealed exhaust then you would leak air in. I assume that you are going to need filters on both intake and exhaust so if you have to shut down then both sides will keep out bad air.

 

Regards,

Share this post


Link to post
Share on other sites

Great information!! Now you have me thinking.

Share this post


Link to post
Share on other sites

3 questions

 

1 where are the filters located? inside the shelter or outside the shelter? if inside you risk the chance of contamination every time you replace them... if out side you risk being contamenated when you go outside

 

2 if you go outside are you willing to risk bringing in contamenants to the rest of your family?

 

3 how will you run the fan? by a generator? you can't keep the generator inside and someone has to keep it gased up

 

the only safe way would be a no intake exhaust only system which can only be accomplished with bottled air/oxogen and how can you calculated the amount needed to sustain X amount of people for Y amount of time when the disaster is still undetermined... a minor miscalculation and all you have is temporary life sustaining burial vault... and would you really want your childrens last memories to be of being imprisoned in a tomb that you built?

Edited by AllRighty15

Share this post


Link to post
Share on other sites

Good info. Thx OPS!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.

×