Q.9 The following data refers to an air conditioning plant used for retail shop
ID: 2088777 • Letter: Q
Question
Q.9 The following data refers to an air conditioning plant used for retail shop located in a city: [14 pts RSH gain 310 kW RLH gain 100 kW Room DBT-25 °C Room RH 50% Outdoor Air DBT-38°C Outdoor air RH-50 % ADP-9 °? The amount of returned air is 90% of the total air supplied to the room. The air supplied to the space is at temperature 18 °C. The plant layout is shown in figure below. air space coil 1. Calculate RSHF 2, Determine hand vs if DBT;-26.3°C 3. Calculate the mass flow rate of air supplied to space in kg/s 4. Calculate the BPF Page |4 of 20 O Faculty of Engineering Technology and ScienceExplanation / Answer
Q9:
(a) RSHF = RSH / (RSH + RLH) = 310 / (310 + 100 ) = 0.756
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(b)
let m = mass flow rate , h specific enthalpy, v = specific humidity
DBT1 = 38oC , RH1 = 50 % ,
therefore , specific enthalpy = h1 = 92.32 kJ/kg , v1 = 0.0211 kg/kg
DBT2 = 25oC, RH2= 50 % ,
therefore Specific enthalpy = h2 = 50.31 , v3 = 0.0099 kg /kg
according to question : m2 = 0.9 * m3 ; m1 = 0.1 * m3
according to energy conservation : h3 = 0.9 * h2+ 0.1 * h1
h1 = 0.9 * 50.31 + 0.1 * 92. 32 = 54.11 kJ /kg
similarly by conservation of mass : v3 = 0.9 * v2 + 0.1 * v1
v3 = 0.9 * 0. 0099 + 0.1* 0. 0211 = 0. 01102 kg /kg
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(c)
mass flow rate of air supplied = m4 = RSH / [(1.005 + 1.88 *v4 ) * ( DBT2 - DBT4)]
m4 = 310 / [(1.005 + 1.88 *v4 ) * ( 25 - 18)] ..................(1)
specific humidity = v4 = v2 - [ RLH / ( m4 * latent heat of vapourisation )
v4 = 0.0099 - [ 100 / ( m4 * 2500 ) ....................................................(2)
putting the value of v4 in equation 1 from the equation 2 and solving it.
mass flow rate of air supplied = m4 = 43.33 kg/sec
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(d)
Bypass factor = (DBT4 - ADP) / (DBT2 - ADP) = (18 - 9 ) / (25 - 9 ) = 0.5625
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