are 25°C DBT, 50% RH and 40°C DBT and 27°C WBT respectively. The RSHF is 0.8. 50% of the room air is rejected to atmosphere and an equal quantity of fresh air added before the air conditioning apparatus. If the fresh air added is 100 m3/min determine (i) Room sensible and latent heat loads (ii) Fresh air sensible and latent heat loads (iii) ADP (iv) Humidity ratio and DBT of entering air at air conditioning room.

Assume bypass factor =$0; ρ_air=1.2kg/m^3$ at total pressure of 1.01325 bar

Subject:- Refrigeration and Air Conditioning

Topic:- Design of air conditioning systems

Difficulty:- Low

$t_d1=40℃,t_w1=27℃, t_d2=25℃, RH_2=50%,BPF=0$

Locate points 1 and 2 on psychrometric chart and join them. Mark RSHF point and draw RSHF line passing through point 2. Wherever the RSHF line intersects the saturation curve is point 4 since BPF =0.

To locate point 3, we know it lies on line 1-2

$\frac{m ̇_1}{m ̇_3} =\frac{length(23)}{length(12)} $

$\frac{m ̇_1}{m ̇_3}$ =0.5 (given)

length(23)=2.95 cm

Now mark point 3 and join 3 and 4. Draw vertical from 1 and horizontal from 2 to obtain point A.

Let $Q ̇_sf$ be sensible heat load added by fresh air=$ m ̇_1 ×(hA-h2)$

$V ̇_a1=100\frac{m3}{min}=1.667 m3/s $

$m ̇_1=\frac{V ̇_a1}{v_1} =\frac{1.667}{0.915}=1.82 kg/s$

∴$Q ̇_sf=1.82×(67-51)=29.14 \frac{kJ}{s}$

Let $Q ̇_lf$ be latent heat load added by fresh air= $m ̇_1 ×(h1-hA)$

∴$Q ̇_lf=1.82×(85-67)=32.76 \frac{kJ}{s}$

ADP=$t_d4=11.4℃ $

Since $\frac{m ̇_1}{m ̇_3} =0.5 ∴m ̇_3=m ̇_4=m ̇_2=3.64 kg/s$

By energy balance of room

$m ̇_4×h4+RSH+RLH=m ̇_2×h2$

RSH+RLH=65.52…(1)

Also,

RSHF=$\frac{RSH}{(RSH+RLH)}$=0.8…(2)

From (1) and (2),

RSH= 52.416 kW

RLH=13.104 kW

Humidity ratioof entering air at air conditioning room=$ω_4$=$\frac{0.0086 (kg \ of \ moisture)}{(kg \ of \ dry \ air)}$

DBT of entering air at air conditioning room =$t_d4=11.4℃$