Holdfast Training Services Trial Blog

As I wind down in the design office, I will give a quick recap of the Fort Drum UAV underfloor radiant heating design I have (mostly) completed.  Having calculated the likely heating needs of the building using modeling software I set about designing the radiant system. From the total heating load required it is necessary to work out how much this load is per hour per square foot.  In my case this was 96 BTU/h/ft2 which is double the recommended capacity of radiant floor heating which is limited to 50 BTU/h/ft2.  In real terms this means the floor can provide half the heating needed and an alternate source, gas powered radiant heaters in the roof in this case, is needed.  From this the floor temperature and supply water temperatures fall out from the manufacturers design parameters based on flow rate.  If the full heating demand is used the concrete would have a surface temperature of 117F (48C) and would need a supply water temp of 180F (81C).  In the International Building Code this is too hot for concrete which could undergo thermal shock if these temperatures are used.  Instead the optimum is 90F(31C) floor temperature with 120F (48C) supply water with a ΔT of 20F (6C).  The next stage is placing the pipework on the design.  Without knowing the lengths of pipe you need in each run, you cannot see how the runs will fit, what lengths of the individual loops are (700ft is a rough maximum but it depends on several factors) or how many manifolds are needed.  With 4 zones to heat I thought I would get by using one manifold for 10x 700ft loops per zone but the total flow of 50gpm in the system was too much for one manifold which could only take 45gpm. Having split each zone in 2, I was able to size the pipes for the system, from the under floor to the supply pipes, in Crosslinked Polyethylene (Pex) which prevents oxygen from dissolving in to the system and causing rust in boilers.  With all the pipes sized and laid I calculated the pump size based on the static pressure (with a dual pump, lead/lag system to allow for failures and maintenance and the use of 40% glycol (for the extremely cold winter should the heating system fail)), the size of the expansion vessel needed and the heat loss from the distribution pipe work to ensure that the boilers are correctly sized.   And that is it really.  For interest, here is my finished design (ignore the duct work):

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There are still some issues to resolve.  Sometime this week the orientation of the trench drains in the centre of each zone was rotated by 90 degrees which has meant a last minute redesign.  Originally my pipes were perpendicular and able to go under the drains.  Now they are parallel they have to go round.   The main hot water system is still not complete so I have not integrated that yet but that should just be a case of connecting to the header when it is designed.  I am also completing the controls which are very simple.  Essential the thermostats in each zone dictate the temperature that heating is necessary at whilst there are alarms to indicate pump failure, low flow rate and low temperature.  The original brief called for a door switch so that the system would stop if the hangar doors opened but this only really applies to forced air heating systems where the energy could be blown out of the building.  As radiant heating heats the object not the air, this is unnecessary.

A little bit more of a technical post but not a bad place to finish. 

And in other news:

The gun debate continues after yet more school shootings, the East Coast is currently under several flood watches because of the unseasonable rain (8 inches due today) but at least it is warm and a soldier has been freed from teh Taliban but did he desert in the first place?  I now have a week to sell the cars and electrical goods, reduce my possesions down to 11.5m3 (sorry kids the toys are going) and make the furniture look like new before the Embassy takes possession of it again.  See y’all in Phase 4 if not before!