Convection Coeficient In An Attic Through Ceilling

Good reasons to insulate ceilings in order to avoid damage to the roof deck you should insulate ceilings to create an air barrier between the living space and an unfinished attic or airspace underneath.

Convection coeficient in an attic through ceilling.

Low speed flow of air over a surface. The moisture condenses as water droplets or frost. The measurements show that th e. Wg which is 1270 acfm.

Natural convection occurs in low density materials only leading to an increase in h eat flow through the insulation and thus to a de crease in the thermal resistance of the in sulation. In attics natural convection is a cold weather phenomenon only. Into an attic is by air moving through openings cut into a vapor barrier. Forced convection in an attic ceiling system typically results from wind pressure and hvac equipment.

The blower door air flow of 5200 cfm was converted to air flow at normal building differential pressure of 3 pascals 0 012 in. This disperses warmth evenly throughout the room from floor to ceiling. If all of this air flow travels through the tongue and groove ceiling into the attic the water vapor it carries will be 23 70 lb per hr if the home is maintained at 68 f 35 percent rh. According to the natural laws of convection heated air entering through floor ducts rises.

The problems start when moist air hits cooler rafters trusses and roof sheathing. Natural convection results from thermal buoyancy effects. The attic was ventilated by a blower with air entering through soffit vents and exiting through a ridge vent. If it is possible to ventilate the air gap between the roof and the ceiling then we could expect a reduction of heat transfer especially by convection.

Convective heat transfer coefficients table chart the following table charts of typical convective convection heat transfer coefficients for fluids and specific applications. Eventually the condensation drips on the insulation below. The ceiling we are referring to in this case is the dividing line between your living space and the attic or airspace beneath the roof deck. If the ventilation is effective then the air in the void will remain close to the ambient temperature thus reducing the convective heat transfer to zero.

Through the attic floor due to convection. Wind washing and air infiltration are primarily the result of forced air movement. Low cfm similar to a bathroom vent 300cfm and only in the hot spots basically by adding an inline ducting fan to the return ducts for the hotspot rooms. Flow type w m 2 k forced convection.

The ceiling consisted of o 5 inch thick gypsum board and the gables of 0 5 inch thick plywood. Heat entering through ceiling ducts however naturally tends to accumulate at the ceiling warming the room from top to bottom more slowly than floor ducts. Such openings are commonly found for example at recessed ceiling boxes and attic entries.