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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
Signature:
I find your lack of faith.... disturbing.
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January 29th 2006 6:53 PM
