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http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html' rel="external nofollow">3. CONSTRUCTION
Investigation of concrete block floors with respect to material and labor costs proved disheartening. Industrial metal roof decking provided the answer. In simplest form the system is built as follows. For a simple east/west rectangular plan with south glazing (a common enough plan form) the grade is first prepared for a concrete slab in the usual fashion. Rigid foam insulation is carefully laid down over the final layer of screeded sand. I most often use two-inch thick bead-board but polyisocyanurate foam board is recommended for those concerned with toxic combustion products. Most sources advise against placing any insulation under a direct gain slab, but because the delta-T is now substantially increased in this system, insulation is required in order to prevent large heat losses from occurring.
Fig. 1: Alternate manifold layout.
Running east/west along the inside of the north frost wall install a vertical foam board and, as you approach this edge, excavate and turn down the horizontal foam boards at approximately 45 degrees to make a "vee" trench. This manifold runs continuously along the north frost wall and is proportioned like any proper supply duct tree. Along the south frost wall install the insulation in a like manner except the "vee" trench mixing duct need only be eight inches across the top. The steel decking is merely a form and thus is the cheapest grade I II inch type "B'. roof deck, 22 gage, painted finish. It is laid in two lengths lap-spliced in the middle allowing them to be spread tightly against and slightly into the vertical perimeter foam insulation and then locked with either tack welds, pop-rivets, or self-tapping duct screws. The concrete is poured over the decking to a thickness of about six inches to the bottom of the rib. The slab is reinforced with 6'.x 6"/10-10 temperature welded wire mesh and the necessary re-bars to span the manifolds. 1 1/2 inch flats on the bottom of the decking six inches on center bearing on 25 p.s.i. foam provides 900 pounds per square foot safe total loading. Sinuous decking would probably sink into the foam.
4. FINISH AND OPERATION
The slab can be finished with masonry (tile, stone, brick, terrazzo), or treated a la Wright with scored pattern, color, sealer with a wax finish. I have seen one of Wright's floors almost forty years later, and it looked brand new, like burnished leather. One would easily mistake it for some synthetic resilient flooring. My own efforts in this direction have been acceptable but less stunning than Wright's.
Another option is carpeting or wood flooring. This insulation will reduce the radiant delivery fraction and increase reliance on the convective component.
During the solar gain periods, as with any hybrid system, the auxiliary heat blower fan should remain OR. This switching can be performed manually or by automatic thermostatic sensors and solenoids. It is not necessary to operate the fan in order to recover the heat when needed because radiant delivery is usually sufficient. The auxiliary heating system can also be operated manually or by the customary thermostat.
5. VARIATIONS
Because the plenum floor is a distribution system, it can be coupled with any back-up system desired as long as that equipment produces hot air rather than hot water (although a fin-coil may be used here as a boiler adapter). I currently have in operation systems that are coupled to oil-fired furnaces, bottled gas units, "street" gas furnaces, wood/coal furnaces, air-source and water-source heat pumps, and even straight electric resistance furnaces. The system works well with either low temperature "trickle" feed sources or rapidly charging high temperature sources as with a Russian fireplace.
Fig. 2: Most common construction of plenum floor slab. (Larger image)
On more than one system I have tapped a vertical supply duct into the supply manifold to service a second floor space. In two cases both "L" shaped and "V" shaped buildings have been constructed with the slab located off the grade at the second floor level. In these cases an insulated dropped ceiling was installed and supply registers were located to feed both up and down.