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UNIVERSITY OF WAH

HEATING, VENTILATION & AIR-CONDITIONING TECHNOLOGY (MT-362) Cooling Load Calculations- Numericals LECTURE NO. 27, 28 Prep By: Engr. Shahid Iqbal

Components

Cooling Load Calculations Internal Loads: a. Occupancy Load b. Lighting Load c. Appliances Load d. Product Load e. Process Load

Heat Transfer through Wall Q = U  A  T Where; U = Overall heat transfer coefficient of wall A = Area of wall  T = Effective temperature difference for wall

Heat Transfer through Roof Q = U  A  T Where; U = Overall heat transfer coefficient of roof A = Area of roof  T = Effective temperature difference for roof

Heat Transfer through Glass Q = [ U  A  T ] + U [ sensible heat gain through glass x Shading coefficient of glass ] Where; U = Overall heat transfer coefficient of glass A = Area of glass either shaded or un-shaded  T = Dry bulb temperature difference of outside and inside design conditions

Shading Coefficient (SC) It is an expression used to define how much of the radiant solar energy, that strikes the outer surface of the window, is actually transmitted through the window and into the space.

Mass flow rate of Infiltrated Air Mass flow rate of Infiltrated Air = m = Where; = density of air (kg/m³)

Heat Gain from People QS = Number of people x Sensible heat gain per person QL = Number of people Latent heat gain per person

Ton of Refrigeration TR TR = x FOS Where; = Total sensible heat + Total Latent Heat FOS = Factor of Safety

Problem

An air conditioned room that stands on a well-ventilated basement having 3m Height and 6m length. One of 3m wall its faces west and contains a double glazed wall window and having dimensions 1.5m x 1.5m. 2D view of Wall 3 m 1.5 m 3 m 1.5 m WINDOW

With following data;

Inside design conditions = 25 C o DBT with φ = 50% Outdoor design conditions = 43 C o DBT 24 C o WBT Overall Heat Transfer Coefficients: U for wall = 1.78 W/ m 2 C o U for roof = 1.316 W/ m 2 C o U for floor = 1.2 W/ m 2 C o U for glass = 3.12 W/ m 2 C o

Problem

Effective temperature difference for wall = 25 C o Effective temperature difference for roof = 30 C o Solar heat gain factor for glass = SHGF = 300 W/ m Internal shading coefficient for glass = SC= 0. Occupancy of Room= 12 persons; [90W Qs and 40W QL] per person Lighting load = 37 W/ m2 of floor area Appliances load = Qs + QL = 400 W + 100 W Infiltration = 0.45 air charges/hr Barometric pressure=101KPa

Problem