Mp4d0209101

MP4D02

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NANYANG TECHNOLOGICAL UNIVERSITY

SEMESTER 1 EXAMINATION 2009-2010

MP4D02 – BUILDING SERVICES ENGINEERING

November/December 2009 Time Allowed: 2 12 hours

INSTRUCTIONS 1. This paper contains SIX (6) questions in THREE (3) sections and comprises FIVE (5)

pages. 2. Answer ANY FOUR (4) questions, choosing at least ONE (1) question from each of

the THREE (3) Sections A, B and C. 3. All questions carry equal marks. 4. A design manual is provided separately. 5. This is a CLOSED BOOK examination. ___________________________________________________________________________

SECTION A

1 (a) A pool of methanol 1.0 m in diameter burns with a combustion efficiency of χ = 0.8. During combustion, heat is transferred to the surface of the pool at the rate of 33 kW/m2 while 10 kW/m2 is lost from the surface.

(i) Estimate the flame height above the pool surface. (6 marks)

(ii) Estimate the maximum plume temperature at a height of 4 m above the pool. (6 marks)

The ambient air properties are assumed to be as follows: temperature is 300 K, specific heat Cp is 1.0 kJ/kgK, and density is 1.2 kg/m3. Acceleration due to gravity: 9.81 m/s2.

State any other assumptions you have made.

(b) A pilot flame with a heat release rate of 25 kW/m of wall width initiates upward flame propagation on a thermally thick wood-panelled wall in a compartment of 3.5 m height.

(i) Use the Saito-Quintiere-Williams equation to estimate the time taken for the flame to reach the ceiling of the compartment. The following parameters may be assumed in the calculations: n = 1; K = 0.01m2/kW; E” = 250 kW/m2; τ = 170 s The symbols have the usual meanings.

(8 marks)

(ii) Explain the criteria to be considered in the selection of material for use in building interiors.

(5 marks)

ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library

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2 (a) A total flooding system is installed to protect a computer room with a volume of 300 m3. It is decided that Halon is used as the medium, which has a specific volume of 0.15 m3/kg at room temperate and pressure. The design volumetric concentration under the above conditions is 5%.

(i) Calculate the discharged volume of Halon under the above room conditions and

its weight. (6 marks)

(ii) Elaborate on the advantages of using Halon compared with CO2 for total

flooding systems. (6 marks)

(b) There is a fire in a compartment with a door of 3m in height. It is assumed that

clearance at the top is 0.9 times of that at the bottom of the door. Assume that the temperature of the hot gases from the fire is 650 °C, the ambient air temperature is 28 °C and the pressure is 100 kPa.

(i) Estimate the location of the neutral pressure plane in the room.

(6 marks)

(ii) Calculate the density of the hot gases from the fire and the pressure difference across the door clearance at the bottom of the door.

(7 marks) The following equation and Figure 1 can be used as references in the calculations.

o

i

2

2

1

1

2

TT

AA

hh

⎟⎟⎠

⎞⎜⎜⎝

⎛= ,

where is the temperature in the enclosure in Kelvin and is the ambient temperature. NPP is the Neutral Pressure Plane.

iT oT

2A

000 p,T,

Figure 1

1A

N.P.P ρ

1h

2h

00 T,ρ

1ii p,T,ρ

0ii p,T,ρ

2ii p,T,ρ


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SECTION B 3. A mechanical smoke extraction system is designed for a single-storey building. The

design clear headroom is 3 m. It is estimated that the fire will generate 6 MW in heat output and its perimeter is 12 m.

(i) Determine the smoke mass extraction rates (kg/s) required and state the

assumptions made in your calculations; (5 marks)

(ii) Estimate the smoke layer temperature under the ceiling. (7 marks)

(iii) Calculate the smoke volumetric extraction rate and state the assumptions made

in your calculations. (8 marks)

(iv) Elaborate on the objectives of the three smoke control methods and give one

example of application for each method. (5 marks)

You may assume the followings:

Ambient air temperature is 30 °C, and ambient air density is 1.2 kg/m3. The constant pressure specific heat of air is 1.01 kJ/kgK. There is no heat loss from the fire to its surroundings. Air gas constant is R = 0.287 kJ/kg K. 0 °C = 273.15 K. The following equation for mass entrainment rate of air into a fire plume can be used:

2

3188.0 PyM s =&

where sM& = mass entrainment rate of air (kg/s),

P = perimeter of the fire (m), and y = height of clear headroom (m).


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4. Figure 2 shows a schematic diagram of a wet riser installed in a building as a down-feed system. The riser and horizontal pipes both have a nominal diameter of 100 mm, while the length of the horizontal pipe is 20 m.

(i) Calculate the required minimum pump flow rate and output pressure using the

design criteria given below. (10 marks)

(ii) Through hydraulic calculations, determine the location of those valves that

should be fitted with relief valves so that the maximum static pressure will not exceed 800 kPa at shut-off condition. It is assumed that the pump shut-off pressure is 120 % of its operating output pressure.

(10 marks)

(iii) Explain why the running pressure in the risers always increases from the bottom to the top for both down-feed and up-feed systems.

(5 marks)

The following information can be used in your design and hydraulic calculations: (i) the minimum operating pressure in the system is 350 kPa when any three

landing valves are operating simultaneously, and the flow rate should not be less than 38 l/s;

(ii) each landing valve is assumed to have a K factor of 0.6 where PKQ = and Q is discharge rate in l/s and P is operating pressure in kPa; (iii) frictional losses through the pipes and the fitting losses can be ignored in this

particular case. Water tank Pump

Figure 2: Schematic diagram of a Wet riser installation

0m

20m 150 mm

dia.

4m

40m

44m

48m

52m


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SECTION C 5. A prestigious 25-storey building in a downtown location has shops from the 1st to the

5th storey. The office passenger lifts serve the main lobby on the 1st storey and the offices from the 6th to 25th stories. The gross area per floor is 1200 m2. The floor-to-floor height of the 1st storey is 5.5 m, and 3.6 m for the rest of the floors in the building. The average passenger loading time is estimated to be 0.8 s per person.

(a) Select an appropriate lift interval and handling capacity for the lift installation.

(5 marks) (b) Determine the number of lift cars, car capacity, and contract speed for the installation

that will best meet the expected performance for this class of building. Show your calculations and state all your assumptions.

(15 marks)

(c) Suggest a vertical transportation system for the floors occupied by the shops. (5 marks)

6. A 20-storey building in a downtown location has shops and restaurants from the 1st to

the 5th storey. The bulk of the mechanical and electrical machinery space is located on the 6th storey and offices occupy the rest of the floors. The floor-to-floor height of the 1st storey is 5.5 m, and 3.6 m for the rest of the floors in the building. The estimated population in the shops and restaurants is 250 and the offices have 1200 occupants.

(a) Sketch the schematic diagram for the water supply system from the mains onwards.

Include the service tanks, storage tanks, pumps, booster system and distribution piping to each floor. It can be assumed that mains pressure is sufficient to supply water up to the 6th storey level.

(8 marks)

(b) Estimate the service and storage tank capacities to cater to the sanitation requirements for 24 hours interruption of supply. You may assume that the storage requirement for the population on the shop and restaurant floors is 45 l/person per day. The water required to operate the cooling plant on the 6th storey is 3.4 m3 /hour for 12 hours operation.

(7 marks)

(c) If a booster pump system is needed to provide a pressure of 10 m head to serve the top two floors of the office tower at a rate of 5 l/s, determine the flow and pressure rating of the booster pump system and the pressure tank capacity for the booster system where the pump is to operate not more than 15 cycles per hour.

(10 marks) State any assumptions made in the calculations.

End of Paper


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