annular duct with shields
Fig. 47. Annular duct with flaps
/ - Circular duct, 2 - upper panel, and 3 - lower panel, 4 - suction holes 5 - insulation ceiling, 6 - groove for draining
In comparison with the veil of circular ducts have many drawbacks. They clutter and obscure the premises, they are difficult to clean both inside and outside, they are ugly and most importantly, ineffective. Without the cladding sheet metal space between the upper bound of the annular duct and the ceiling air duct does not ring serves as a local aspiration.
Such a duct, especially if it is located at a considerable distance from the ceiling, is, in essence, a device for drawing general exchange, not even from the upper zone, and from the middle. The main part of the upstream bearing gases is Uncaptured, plank on the ceiling and spreads around the room.
Annular duct must have top flaps, reaching to the ceiling. Only then it will work as a local suction. But the duct with the upper flaps becomes essentially the same veil that only complicated and opaque. This decision, of course, irrational.
Fig. 47 shows a circular duct with upper and lower plates.
In accordance with the recommendations of CH 87-60 in the calculation of the air, remove the veils and the annular duct at a cooker, take that veil removed 75% of the heat generated by the cooker, and an annular duct - 60%, respectively. The temperature of outgoing air in both cases assumed to be 45 В° C. These figures were obtained and almost no objection is called.
The value of Q3 = 0,75 Q for the hanging and Q3 = 0,6 Q - for the annular duct, where Q - the total heat from the stove.
Some designers, hoping the veil for the summer, rather than the temperature of the zone into the formula (78) The estimated outside temperature, which is wrong.
If Q - total heat stove, in the light of this, the amount of heat is not collected on the veil and enters the room, will be equal
Qn = 0,25 Q [kcal / h].
This amount of heat end up in other heat-release, removable general ventilation.
With a significant number of digesters and their compact arrangement sometimes over them establish a veil. Here, in addition to heat trapped water vapor, periodically escaping from the digesters.
The amount of air removed through the veil of digesters, to be determined by the speed in its horizontal section. Speed can be taken in the range of 0,08 to 0,1 m / sec.
Calculate the amount of exhaust air and its temperature at the device of the veil over the three digesters at 250 hp at the working area for the summer +25 В° C, the veil in terms of size 1,5 x5 m, F = 7,5 m2:
at a speed in the horizontal section of 0.1 m / s volume exhaust air
L = 3600-7,5-0,1 2700 m3 / h, heat from the three boilers
Q = 2300-3 = 6900 kcal / h, under the veil comes 75% of heat, ie
<2s = 0,75-69005200 kcal / h air temperature, removed from under the veil,
t = 25 + - 5200 USG. 0,3-2700
When calculating the general ventilation in the hot shops have to ask the temperature of outgoing air. The temperature of the working area for the summer, usually taken at 5 В° C above the estimated outdoor temperature on the parameters A for both rooms with large excess of the sensible heat.