OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
with hemispherical sensible heat gain coefficient.
6.) Multiply the direct radiation transmitted by sunlit area and scattered radiation transmitted by total area of
the window. Adding these two values will give instantaneous heat gain through window. But this value does
not contribute any thing to the cooling load immediately as we already assume air to be completely transparent
for radiation. So the heat gain through window should be first absorbed by components like furniture, floor etc
and should be reradiated back to the room for it to be considered as a cooling load. To take this in to account we
have a storage factor to multiply the instantaneous heat gain.
7.) Determine the heat gain due to conduction through glass.
8.) Add the convective heat gain with the scattered portion and split the summation in to radiative and
convective component. The normal trend is to take 37% as convective and the rest as radiative.
9.) Multiply the direct radiation by RTF for solar radiations and obtain the cooling load using equation.
10.) Multiply the radiative component of by RTF given for non-solar radiation according to equation.
11.) Summation of the results of number 9, 10, and convective component of number 8 will give hourly cooling
load due to window heat gain.
11. Heat Gain Through Infilitration & Ventilation
Air exchange of outdoor air with the air already in a building can be divided into two broad classifications:
infiltration and ventilation
Infiltration
Infiltration is uncontrolled flow of air through unintentional openings such as cracks in the walls and ceilings
and through perimeter gaps of windows and doors driven by wind, temperature difference and internally
induced pressures. It is caused by a greater air pressure on the outside of the building than the inside. The amount
of infiltered air depends on the pressure difference, the number, size and the shape of cracks involved; the
number, the length and width of the perimeter gaps of the windows and doors; and the nature of the flow in the
crack or gap (laminar or turbulent). The relation connecting these quantities are given by
where Vi - flow rate of leaking air
∆p- pressure difference, if outside is greater than inside it is positive.
n - flow exponent if flow in the crack is laminar, n=1 if turbulent, n=0.5
Usually flow will be transitional thus n will be between 0.5 and 1
C- flow coefficient, determined experimentally and includes the crack or opening size
where∆pst-pressure difference caused by stack effect
∆pw-pressure difference caused by wind effect
∆pp-pressure difference caused by pressurizing the building
Crack Wall Infiltration Per Floor or Room
Where
k- leakage coefficient (C=KA)
A- wall area in m 2
Crack Infiltration for Doors And Movable Windows
where P – perimeter of the windows or door,in ‘m’
k- Perimeter leakage coefficient (C=kxP).
n-0.65
Ventilation
Ventilation is the intentional introduction of air from the outside into a building; it is further subdivided into
natural ventilation and forced ventilation. Natural ventilation is the intentional flow of air through open
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