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paulward (Mechanical)
20 Dec 04 10:57
Workers leave overhead doors open even in the coldest weather. How can I estimate the heat loss from the building assuming constant temperature inside and 20 degrees, 30 degrees and 40 degrees outside?
I need this estimate for a cost justification for quick-opening automatic doors (or perhaps air curtains)
redtrees (Mechanical)
21 Dec 04 7:59
By assuming a velocity of air over the door you could use :-
Q=M.C.delta_T
Where
Q = the heat loss in kw
M = the mass flow rate of air in kg/s
delta T = the temp difference.
If you assumed that the internal building temp is 20 deg.C and it is 10 deg.C outside, and at worst case cold air is entering the building at say 0.5m/s velocity over a door 2m x 1m, then........
Q = [((2 x 1)x 0.5)x1.2] x 1.01 x (20-10) = 12.1 kW 字串3
If the door were left open for an hour then then 12kWh of heat is potentially wasted and a cost to provide this amount of heat could be worked out.
sterl (Mechanical)
23 Dec 04 14:18
Steady State and short term air movements for doors at least similar to Rolling Overhead were measured and a mathematical model created for Cold Storage Warehouse doors some years ago, with the basic justification being: How fast should a door move? and the Life Cycle Costing of automatic closing systems...
Experience has indicated pretty reasonable accuracy for air exchange through the large opening, but of course both sides of the door are exposed to enclosures and the pressure difference generating flow was a result of both the reduced pressure inside the cold storage as opposed to the warmer, more humid space of the truck dock.
Particpants inlcuded a J. Moreno; Pham, Oliver, Barat, Aime, Longdill and others. Much of the research was done in Europe and was sponsored by the International Congress on Refrigeration. 字串6
Hope this helpful.
MintJulep (Mechanical)
23 Dec 04 14:26
I suspect that both automatic door operator and air curtain manufacturers would have some nice canned presentations to this end, as it helps sell the product.
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