Question

a. the sensible heat ratio (SHR) for the cooling and dehumidifying process; (2 Marks) b. the supply air volume flow rate to the office in m3 /s; (5 Marks) c. the air dry bulb temperature and specific enthalpy of the mixture of outdoor and recirculating air; (4 Marks) d. the cooling coil’s load in kW. (5 Marks) e. the apparatus dew point during the cooling and dehumidifying process; and (4 Marks) f. Discuss, with reasons, the possible effects on the CAV system if people are bringing in a large number of hot lunch boxes into the office due to the policy of Novel Coronavirus. (5 Marks)

3. A single zone constant air volume (CAV) air-conditioning system for an office, which is designed to accommodate 20 people, is operated with the following conditions: 23°C Outdoor air dry bulb temperature: Outdoor air web bulb temperature: Indoor air dry bulb temperature: Indoor air wet bulb temperature: Supply air temperature: Total space sensible load: Total space latent load: The required fresh air flowrate: Supply and return system heat gains: 17 °C 12 °C 55 kW 20 kW 8 litres per second per person neglected Given: Specific heat capacity of air: 1.02 kJ/kg K Specific heat capacity of water: 4.18 kJ/kg K Specific latent heat of fusion of water vapour: 2,501 kJ/kg Determine: a. the sensible heat ratio (SHR) for the cooling and dehumidifying process; (2 Marks) the supply air volume flow rate to the office in m/s; (5 Marks) the air dry bulb temperature and specific enthalpy of the mixture of outdoor and recirculating air; (4 Marks) d the cooling coil's load in kW. (5 Marks) the apparatus dew point during the cooling and dehumidifying process; and (4 Marks) Discuss, with reasons, the possible effects on the CAV system if people are bringing in a large number of hot lunch boxes into the office due to the policy of Novel Coronavirus. (5 Marks)

Answer 1

;-) 0 - Indoor Condition (23°c abt 17°C wbt) Outdoor Condition (33c abt 28c obt) 1 - 2 > 2.A - A-1 = AdP -> Point After Mixing Supply Air temperature (Assuming Sensible heat gain in room Latent heat gain in toom. Apparatus dew point. 2-B - Brl - Sensible heat on Latent heal on Coil Coil.

(kJ/kg Sensible heat factor Son. SHE Enthalpy 05 03- og specific humidity Adp 2 TARP 12°C 23°C 334 Day Bulb temperature Fixing the point i (23°c dot, ite wbt hi = 48 kilkg sto (33 c abt, 28 C obt) no 90 kilky Now for finding the Supply Condition (2) only available it's temperative = 12°c. so that we have Room S.H å ram L.H. (2-A & A :) ) Calculating sensible . heat factor of room - tal head - 55+20 I from chort refering si HF = 0.733 Parallel to SHF = 0.733 from Cut the line of t = 12°C is = 0.733 draw a line point i which may Point 2.

Point @ - t = 12°C h = 31.3 kJ/kg tale Maso flow Inonday to find mixing Porpet should be determine. Given 20 Persons design, 0.897 = 8 Lt/s/ren - 8x20 4s for 20 persons = 160 l/s = 0.16 m3/s. ve from chart: 0.897 miling m en 0:16 - 0.1784 kals we have sensible heat factor (room) = 0 . 733 S.HF = hA-ha (s.lt hot ( Total heat hinha =) 0.733= h - 31.3 48 - 31.3 : h = 43.54 King

(4 sensible heat - 58 kW = m(hAh m[43.54-31-37 in = 4.493 kg/s (for 20 persons) It represent to toul Mass flow rate to the room supply hence A Portion will be removed for out side Air Circulation. in tim = in no 0.1784 + im 4.493 m = 4.314 kg/s Now for finding mixing Gadition, Energy balace we have mih = mihi & in hopard 4.493 (hr) (4.314x48) + ( 1784 x 90 ho= 49.67 kJ/kg Cooling & de hum, dification a) sensible head ratio of o S.H ho-hy - S.HR: T.H h - ha Proces = la For finding ho extend like horizontaly from 2 a verticaly from the meeting point is ª ho: 43.4 kolky

0.658 S.HR 434 - 31.3 49.67 -31.3 ly At Floo to office 6 from choot, 2 = 0.811 = 4.493 x 0.818 = (3.675 m/s Mixture and a 1 h = 49.67 ks/ kg / from chart. Tong = 23.4°C al det & I Cooling (o) load ) in [h, hz] . 4-493 x [ 49.67-31.8] = 182.54 kW) Appolatas dew Point & Extent 1-2 to sat line is Adp = Tadp = 8.5°c) Everithing is from psy chornedric chart Available can have some measured Variations. Thank you.