27$^{°}C$ dry bulb temperature and 60 R.H. The ambient condition is 40°C dry bulb temperature and 30°C wet bulb temperature. The total sensible heat load is 100000 kj/hr and the total latent heat load is 40000 kj/hr. 60% of the return air is recirculated and mixed with 40% of make-up air after the cooling coil. The condition of air leaving the cooling coil is at 18°C. Determine i. RSHF

ii. Condition of air entering the auditorium

iii. Amount of make-up air

iv. ADP

v. BPF of cooling coil.

Show the process on the Psychrometric char

Subject:- Refrigeration and Air Conditioning

Topic:- Design of air conditioning systems

Difficulty:- Low

RSH=27.77 kJ/s RLH=11.11 kJ/s

$t_d3=18℃ $

$RSHF=\frac{RSH}{(RSH+RLH)}=0.714$

Locate points 1 and 2 on psychrometric chart. Now mark the RSHF value on SHF scale and join with alignment circle. Draw a line parallel to this from point 2. This is RSHF line. We know point 4 will lie on RSHF line and also between 2 and 3. Also points 2, 3 and 4 should be in straight line. Hence if points 2 and 4 lie on RSHF line then 3 also lies on it. So intersection of RSHF and 18°C DBT line is point 3.

Mark point 4.

Condition of air entering the auditorium

$t_d4=23.4℃,t_w4=19.8℃,〖RH〗_4=71% $

Amount of make-up air

By energy balance of room

$m ̇_4×h4+RSH+RLH=m ̇_2×h2$

But from the layout, $m ̇_4=m ̇_2$

$m ̇_4=7.07$ kg of dry air/sec

$\frac{m ̇_1}{m ̇_4}$ =0.4 (given)

$m ̇_1=2.827 kg/sec$

Also,$v_1=0.92 \frac{m3}{kg}$

∴ $m ̇_1=\frac{V ̇_a1}{v_1}$

$V ̇_a1=2.6 \frac{m3}{sec}=9365.13 \frac{ m3}{hr}$

ADP

Coil ADP=14°C

BPF of cooling coil

BPF = $\frac{length(C3)}{length(C1)} =\frac{1.5}{10.2}=0.147$