Outdoor air leaks into a building through cracks in the walls at the rate of 700

Question

Outdoor air leaks into a building through cracks in the walls at the rate of 700 m3/h (this is infiltratation). The outside air is at a temperature of -16.1?C and a humidity ratio of 0.001 kgv/kga. Outside air  density is 1.4 kg/m3. The indoor conditions are: temperature of 20?C and humidity ratio of 0.009 kgv/kga. Evaluate

a) The sensible heat load (in kW) due to the infiltating air.

b) The latent heat load due (in kW) due to the infiltating air.

The specific heat of air at these temperatures is about 1.005 kJ/(kg

Explanation / Answer

humidity of outside air is 0.001 that means 1kg air has 0.001 kg vapour....density of vapour=1000kg/m3

density=1.4kg/m3

mass rate=700*1.4/60 =16.33 kg/sec

mass rate of dry air in outside air=16.33*(1-0.001)=16.317 kg/sec

mass rate of vapour in outside air= 16.33*0.001=0.01633 kg/sec

mass rate of dry air indoor air=16.33*(1-0.009)=16.183 kg/sec

mass rate of vapour in outside air= 16.33*0.009=0.147 kg/sec

a)sensible heat load is due to temperature change =m*s*(T2-T1)

for vapour s=4.18 KJ/Kg .c

temp changes from -16.1 to 0 c and then latent heat load comes into play and temp increases to 0 t0 20 c

sensible heat load = 16.317*1.005*(0-(-16)) + 0.01633*4.18*(0-(-16.1)) +16.183*1.005*(20-0) +0.147*4.18*(20-0)

= 602.6837 KW

b)latent heat load = 2453*(0.147-0.01633)=320.5335 KW

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