For starters the ratio between R attic over R inside (the resistance ratio) must be greater than the ratio between 40F - min. outside temp over min. indoor temp - 40 F (the driving force ratio). R attic is the R value between the pipe and the attic. R inside is the R value between the pipe and the heated space. For example if it is -10 F outside and 50 F inside then the temp ratio (the driving force ratio) is 60/10. Therefore the R attic must be at least 6 times the R inside.
This direction assumes there is no outside air leakage that introduces outside air into the space under the insulation where the pipe is. The 40 F number is the minimum temperature for the pipe. The 50 F number is a judgement you make for how cold the indoor temperature will be when the going gets tough. So make a reasonable judgement. Obviously it might be a bad judgement to assume normal indoor heating conditions. A building where there is staff on hand to maintain some heat most of the time or be able to drain down is different from a vacant building where the residents are out of town for a season. The R inside is the R value between the pipe and the heated space. You must make a reasonable estimate for that value without omitting any factors because omissions sway your final result in the wrong direction. Insulating materials between the pipe and the heated space slow down the heat transfer to the pipe. You want to make sure the heat transfer into the pipe is faster than the heat transfer out of the pipe. That is what this ratio comparison build down to. This simplistic direction assumes the attic temperature is the same as the outside temperature. You might think that may not be the case but in a very well ventilated attic that might actually be the case right near the attic vents. So again you need to make a judgement call. Also keep in mind how easily the insulation installation could get screwed up during installation and afterwards. There also must be a vapor barrier between the heated space and the R attic insulation. Get your minimum outdoor design temperature from a published source intended for heating system design referenced by the building code. The minimum temperature is probably lower than you think it might be. Allan Seidel St. Louis, MO > On Jul 6, 2015, at 1:01 PM, Brian Harris <[email protected]> wrote: > > Can someone point me in the right direction to determine what the minimum R > value is required to protect steel pipe in an attic in SC ? > > Brian Harris, CET > BVS Systems Inc. > Sprinkler Division > bvssystemsinc.com<http://bvssystemsinc.com/> > Phone: 704.896.9989 > Fax: 704.896.1935 > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
