Air conditioning

Question 1

What is meant by the comfort zone in engineering?

Answer 1

• ‘Comfort’ is a function of temperature, humidity and local air velocity of flow.
• Human comfort is subjective, so comfort for most people can be found from statistical surveys
• 90% of people are comfortable when air temperature is between 18-22°C and percentage saturation is 40-65%.
• This can be shown on psychometric chart ‘comfort zone’

Question 2

Straight through design air conditioning (summer + winter)

Answer 2

In order to bring conditions to within the comfort zone, we need to

• cool it/dehumidify it and reheat in the summer
• heat it/humidify it , and reheat in winter

Question 3

Mass flow rate

Answer 3

ṁ = V̇/v
mass flow rate=
Volume flow rate/
specific volume

Question 4

Cooling and heating load

Answer 4

Q̇c=ṁ(h1-h2)

Q̇h=ṁ(h3-h2)

Question 5

Drainage

Answer 5

ṁ(w)=ṁ(a)(w1-w2)

Question 6

Determine power-saving if system recirculates return air (%) using the COP given.
(for cooling)

Answer 6

h5 found on chart
find Qc2 (hf-h2)

electric power demand=
Q̇cooling/cop
Energy saving (kW)
= Q̇c1-Q̇c2/COP

Energy saving (%)
=Q̇c1-Qc2/Q̇