MECH3005: Building Services
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Self-evaluation Exercises (for Air Conditioning & Refrigeration)
(* Please try to do this without referring to the lecture notes.)
1.
Who is the great person well-known as the “Father of Air Conditioning”? Please name one important
invention he made that has significant impact on the industry.
Dr. Willis Haviland Carrier, his important invention includes rational psychrometric formulae, centrifugal
water chiller, unit air-conditioning systems for the home, high velocity induction systems for offices
2.
3.
The humidity of air can be assessed using various different parameters. Which of the following parameters
for air humidity has a close relationship with the energy content or enthalpy of the moist air?
(a)
Moisture content
(b)
Relative humidity
(c)
Wet-bulb temperature
(d)
Dew-point temperature
At the air-handling unit of an air conditioning system, the outdoor air (at condition A) is mixed with the
return air (at condition B) in a ratio of 1 : 9. Based on the following data, estimate the temperature,
moisture content and enthalpy of the mixed air stream (at condition M).
ta = 33 oC
tb = 25 oC
ha = 89.3 kJ/kg
hb = 50.3 kJ/kg
ga = 0.022 kg/kg
gb = 0.010 kg/kg
Mixed air conditions:
tm = __25.8 oC _______________
gm = __0.0112 kg/kg _______________
hm = __54.2 kJ/kg _______________
4.
5.
Which of the following contains a parameter which is not a criterion for predicting thermal comfort using
the Fanger’s comfort equation?
(a)
Metabolic rate and clothing
(b)
Air temperature and water vapour pressure
(c)
Air velocity and mean radiant temperature
(d)
Mean skin temperature and air humidity
For easy understanding, air-conditioning systems can be divided into five sub-systems or loops. List down
the five sub-systems in the space below.
Air-side, water-side (chilled water), refrigeration, heat rejection and controls
6.
The diagram below shows the basic principles of cooling load calculation. Fill in the blanks below for the
terms represented by (a) to (d) in the diagram.
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(a)
Convection
(c)
(d)
Radiation
(b)
Convection
(with time delay)
± Temperature swing
7.
(a) _____Heat gain____________________
(b) _____Heat storage_______________
(c) _____Cooling load______________
(d) _____Heat extraction_____________
Write down the four basic components of cooling coil load for a typical air conditioning cycle of a central
all-air system running in the summer mode.
Space cooling load, supply system heat gain, return system heat gain, ventilation (fresh air) load
8.
The characteristics of a forward curve centrifugal fan installed in an air duct system is shown in the
following diagram. Determine the system operating point and estimate the values of the following
parameters at the design conditions.
(a) Air flow rate = __7.15 m3/s_
(b) Fan total pressure = _1250 Pa_
(c) Fan power = __14 kW____
9.
A chilled water pump is rated at 20 l/s at 400 kPa of pressure. Assuming no static pressure, estimate the
flow, pressure and power if the impeller size is increased to 125% of its original diameter.
20 x 125%
400 x (125%)2
(20 x 400) x (125%)3
(a) Flow rate = ____25 l/s___ (b) Pressure = ____625 kPa___ (c) Pump power = ____15.6 kW___
10.
What are the four types of alternative refrigerants commonly found in the market? List down also the type
of conventional refrigerants that they are substituting.
R-123 replaces R-11, R-134a replaces R-12, R-404A and R-407C replaces R-22, R507 replaces R-502
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