If you are trying to prevent the pipe from breaking there is some safety in the difference between freeze point and break point of the AF. We usually speak in terms of freeze point but the breaking point is much lower. Between the two points my limited kitchen research shows a milkshake consistency. If you use the ASHRAE data you are probably fine with no SD. Our friend Scott F. believes we should be using the coldest ever recorded for that area. ASHRAE, coldest ever or some SD plus or not a further safety (8) all have merit but I don't think there is any specific guidance. I thought I read ASHRAE once but have been unable to find a reference. There is also some safety potentially in the location of the piping, in how long it is exposed to a specific cold temp and the time it takes to cool the pipe to ambient. Think in an residential attic, the outside ambient a few degrees below the temp it's rated for and a couple hours vs. an exterior canopy on the north side, exposed piping, a windy day and 20 degrees below the rated point for 8 hours.
The 40 IMHO may be related to the fact to keep something at 40 the HVAC units will be putting out something less than 40 and could cause a local problem. Yeah it doesn't explain an outside reasoning. If you are interested in the ability of cold AF to fight a fire I think there is a gaping hole in the information available. I know 13 went all DW on us for bigger systems but that was a knee-jerk reaction not unlike IMHO the current TIA. And DW doesn't tell us anything about the character of the spray of AF at cold temps or how long it takes the AF to clear. Something needs to be done but we don't really know what yet. In theory we might want to walk a closer line on the rated temp vs. potential ambient to preserve some more firefighting ability or maybe not depending on the flow characteristics, size of the flow path and increased fire contribution of the AF. Pocket refractometers - I have my doubts especially when used in the field after bouncing around a truck for years. I doubt many use pre-mix. At best a few do for the original installation but not on annuals if it needs a little touching up. Chris Cahill -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of David de Vries Sent: Tuesday, November 16, 2010 1:35 PM To: AFSA SprinklerForum Subject: Anti-Freeze Solution Freeze Point Is there any guidance on how much of a safety factor an anti-freeze solution should have? I cannot find any such in 13, but of course 13 requires an 8 degree F cushion for wet systems (maintain at or above 40 F). Looking at the ASHRAE Handbook there is weather data which shows the mean coldest temp and a standard deviation for locations throughout the USA and Canada. Using that data, what should be the design basis, i.e. how many standard deviations below the mean coldest temp? Does it make sense for a locale with a reported mean coldest temp of -10 and 5.8 standard deviation to design for 2 standard deviations below and a safety factor? So, freeze point of anti-freeze solution = -10 - 2(5.8) -8 = -30 F or lower? How accurate are the pocket refractometers used in the field? Do most contractors use pre-mixed anti-freeze solutions? As always, the Forum's insights are welcome. Dave David A. de Vries, P.E., CSP Firetech Engineering Incorporated _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
