ventilation system on top - up and top - down
A few words about the temperature of the exhaust air feeding fresh air into the upper band, ie, at patterns of ventilation "top - up and top-down ---".
Ventilation on a "top - up", although rare, is used in industry, especially when cooled fresh air in the warm season. The principle of "top - down" is used very rarely, unless, of course, do not talk about conditioning.
When injection of air into the upper zone of concentration or absent and removed from the upper zone is not necessary to be considered as the temperature increases with height. For this case the gradient of a hit zero. However, exceptions are possible. With substantial value At can happen that the temperature of outgoing air temperature drops below the working area. But maybe the opposite phenomenon, so the "top - up" the most reliably take Aq = RZ This is true for the "top - down."
When you remove excess heat from the "top-up" is disadvantageous compared to the normal scheme of "bottom - up". This is most striking for the summer, when the supply air temperature is outside.
We present a numerical example of calculating the difference between m and tn, which depends on the magnitude of air. Suppose we are given the room casting conveyor height of 10 m. For the transition period adopted by the temperature of the working area / 1. A = + 22 В° C, supply air temperature q = + 16 В° C. Heat-stressed in the premises of 70 kcal / m "- and.
In accordance with the Table. 14 for this case the coefficient r is equal to an average of 0.5. Consequently, the temperature of outgoing air
22 - (1 -0.5) -16 on "
ie, the difference between the beats - Ai - 28-16 = 12 В° C.
When a diffuse flow of the working zone of the conveyor casting and extraction from the upper zone of the temperature gradient can be accepted A = 0.7 (Table 16).
In many cases, where permitted by regulations, for heating fresh air mixed with him inside the indoor air in such proportions that the mixture has acquired the required supply air temperature tn.
In calculating the mixing of recirculation units (or air handling units) use the following formulas of mixing.
At high heat is desirable and in the winter feeding is not heated by natural flows, such as through the transom trench. If the room is sufficiently high and low transoms located at a height of 5-b m from the floor (not lower than 4 m), flow is not heated flow usually causes no objections. In the low-rooms - 4 m and below - in the form of exclusion is not allowed to feed the heated flow at a level no lower than 3 m from the floor. However, there is need to take measures to prevent the direct effects of cold air at work, such as device visors have transoms, directing the air upwards.