We have a condition at where the contractor has asked to use blue duct for underground locations in lieu of Armaflex insulation and concrete encasement. We specified a perlite type product as backfill around the blue duct with an R value of 0.6 per inch.
The contractor is saying that perlite will not work structurally and wants to use sand. A field rep has said they typically do not insulate because the duct is equivalent to R10.
Since ASHRAE 90.1 requires insulation around the duct and meeting 90.1 is also a requirement for LEED, what type of options does the contractor have? Would armaflex without concrete encasement as the insulating material be acceptable? We have discussed with the project mechanical engineer who says insulation is really not necessary in this condition but is required to meet 90.1.
Scott Bowman
LEED FellowIntegrated Design + Energy Advisors, LLC
LEEDuser Expert
519 thumbs up
January 22, 2016 - 11:33 am
Ralph...interesting place to ask! I do not have access to the standard, but that never stops me from giving my opinion, and maybe an idea to ask the engineer. First, insulated backfill is a unique application. What I have used in the past, but admittedly for chilled water and steam piping, is Gilsulate. This is a structural insulating fill that has a R value of 1.8 per inch at lower temperatures. It is structural so might solve your structural issue, however the ductwork itself may not allow the pressure and requires concrete.
Also, my memory is not that 90.1 requires "insulation", it requires an R value. Ductwork can be made of insulation and something other than galvanized metal, so I would say that if you can show performance that meets the required R value of insulation, that should be compliance with the standard. So parse the language carefully to see if it requires "insulation" or performance.