UTILITIES | Mechanical Systems | 12 Questions (EASY-MODERATE)

MECHANICAL SYSTEMS

(12 Questions, Difficulty Level: EASY to MODERATE)

by Raison John J. Bassig

Q#1: In the refrigeration process, identify the characteristic of the fluid passing through the tube within the portion "C" as labelled in the illustration below.

(Image courtesy of Real Refrigeration, Modified)

a. Low Pressure Liquid
b. High Pressure Gas
c. Low Pressure Gas
d. High Pressure Liquid

In the refrigeration cycle, the refrigerant enters the COMPRESSOR as a low-pressure gas. This low-pressure gas is then COMPRESSED, thereby converting the GAS from a low-pressure state to a HIGH-PRESSURE state as it leaves the COMPRESSOR.

The high-pressure gas moves into the CONDENSER where the refrigerant is changed from GAS to LIQUID (condensation) as it GIVES OFF HEAT to the outside air.

The high-pressure liquid then flows into the EXPANSION VALVE. This valve will RESTRICT the flow of the refrigerant, thereby converting the LIQUID from a high-pressure state to a LOW-PRESSURE state as it goes out the EXPANSION VALVE.

The refrigerant now enters the EVAPORATOR as a low-pressure liquid. This low-pressure liquid then ABSORBS heat from the inside air, where the refrigerant is changed from LIQUID to GAS (evaporation).

The low-pressure gas then enters the COMPRESSOR and the whole cycle is repeated.

(Image courtesy of Real Refrigeration, Modified with additional texts)

Therefore, the correct answer is d. High Pressure Liquid.

Q#2: According to the Mechanical Regulations of the National Building Code of the Philippines, pipes carrying Low-Pressure Helium gases should be colored what?
a. Green
b. Red
c. Yellow
d. Orange

(Rule XIII, Sec. 1302.11 of the 2004 IRR of PD1096)

Tip for easier familiarization and/or memorization is to re-arrange the above table by pipe color:

GREEN	YELLOW	ORANGE	RED
Air-Low Pressure	Acid	Acetylene	Carbon Dioxide
Argon-Low Pressure	Air-High Pressure	Blast Furnace Glass	Water (Fire Service)
Helium-Low Pressure	Ammonia	Gasoline
Nitrogen-Low Pressure	Steam-High Pressure	Grease
Water-Cold	Steam-Low Pressure	Hydrogen
Water-Distilled	Water-Boiler Feed	Oxygen
Water-Low Pressure	Water-Hot	Oil
Water-Treated	Water-High Pressure	Tar
Oil and Water*		Producer Gas
		Liquid Petroleum Gas
		Vacuum-High Pressure
		Oil and Water*

Therefore, the correct answer is a. Green.

Q#3: Ton of Refrigeration is the cooling effect obtained when 1 ton of ice at 0°C (32°F) melts to water at the same temperature in _______.
a. 3.5 hours
b. 60 minutes
c. 1 day
d. 12,000 seconds

The Ton of Refrigeration (TR) is a unit of power describing the heat-extraction capacity of refrigeration and air-conditioning equipment. It is defined as the rate of heat transfer that results in the melting of 1 ton (2,000 lb or 907 kg) of pure ice at 0°C (32°F) in 24 hours.

1 TR is also approximately equivalent to 12,000 BTU/h (British Thermal Unit per hour) or 3.5 kW (kilowatts).

Therefore, the correct answer is c. 1 day (or 24 hours).

Q#4: As per the 2004 Implementing Rules and Regulations of the National Building Code of the Philippines, the angle of inclination of an escalator shall not exceed ___ degrees from the horizontal.
a. 28.5
b. 30
c. 35
d. 45

This provision can be found in the 2004 Implementing Rules and Regulations (IRR) of the National Building Code of the Philippines (PD1096), under Mechanical Regulations on Escalators,

"The angle of inclination of an escalator shall not exceed 30° from the horizontal."
(Rule XIII, Sec. 1302.6.a of the 2004 IRR of PD1096)

Note that the OLD 1978-1979 IRR of PD1096 specified this provision at 35°. That old provision has already been repealed by the 2004 IRR.

Therefore, the correct answer is b. 30.

Q#5: A device for controlling the flow of warm or conditioned air from an outlet, composed of a grill with a number of parallel blades that may be adjusted so as to overlap and close the opening.
a. Manifold
b. Register
c. Diffuser
d. Bonnet

Manifold:
"A pipe or duct fitting having several outlets for making multiple connections."

Register:
"A device for controlling the flow of warm or conditioned air from an outlet, composed of a grill with a number of parallel blades that may be adjusted so as to overlap and close the opening."

Diffuser:
"A device having slats at different angles for deflecting warm or conditioned air from an outlet in various directions."

Bonnet:
"A chamber at the top of a hot-air furnace from which the leaders emerge. Also called plenum."

(Page 122, A Visual Dictionary of Architecture by Francis D.K. Ching)

Therefore, the correct answer is b. Register.

Q#6: Which among the following cross-sectional dimensions of an air duct conforms with the provisions of the current building code?
a. 250mm x 1300mm
b. 525mm x 575mm
c. 325mm x 900mm
d. 450mm x 600mm

This provision can be found in the 2004 Implementing Rules and Regulations (IRR) of the National Building Code of the Philippines (PD1096), under Light and Ventilation,

"Air ducts shall open to a street or court by a horizontal duct or intake. Such duct or intake shall have a minimum unobstructed cross-sectional area of not less than 0.30 sq. meter with a minimum dimensions of 300 millimeters. The openings to the duct or intake shall be not less than 300 millimeters above the street surface or level of court."
(Sec. 809.3 of the 2004 IRR of PD1096)

So, in my given choices,

Choice a. 250mm x 1300mm = 0.325 sq.m. but only 250mm dimension --> Does NOT conform to the code.
Choice b. 525mm x 575mm = 0.301875 sq.m. --> CONFORMS to the code.
Choice c. 325mm x 900mm = 0.2925 sq.m. --> Does NOT conform to the code.
Choice d. 450mm x 600mm = 0.27 sq.m. --> Does NOT conform to the code.

Therefore, the correct answer is b. 525mm x 575mm.

Q#7: An index of the efficiency of a refrigerating unit, expressing the BTU removed per watt of electrical energy input.
a. Enthalpy
b. ToR
c. CoP
d. EER

Enthalpy:
"A measure of the total heat contained in a substance, equal to the internal energy of the substance plus the product of its volume and pressure. The enthalpy of air is equal to the sensible heat of the air and the water vapor present in the air plus the latent heat of the water vapor, expressed in Btu per pound (kilojoules per kilogram) of dry air. Also called heat content."
(Page 120, A Visual Dictionary of Architecture by Francis D.K. Ching)

ToR (or TR) means Ton of Refrigeration.
The Ton of Refrigeration (TR) is a unit of power describing the heat-extraction capacity of refrigeration and air-conditioning equipment. It is defined as the rate of heat transfer that results in the melting of 1 ton (2,000 lb or 907 kg) of pure ice at 0°C (32°F) in 24 hours.

CoP means Coefficient of Performance.
It is a ratio of useful heating or cooling (Q) provided to work (W) required (CoP = Q / W).

EER (or Energy Efficieny Rating):
"An index of the efficiency of a refrigerating unit, expressing the Btu removed per watt of electrical energy input."
(Page 124, A Visual Dictionary of Architecture by Francis D.K. Ching)

(Page 124, A Visual Dictionary of Architecture by Francis D.K. Ching)

Therefore, the correct answer is d. EER (Energy Efficiency Rating).

Q#8: The rated speed of escalators, measured along the angle of inclination, shall not be more than _____________, according to the National Building Code.
a. 38 meters per minute
b. 30 meters per minute
c. 35 meters per minute
d. 42 meters per minute

This provision can be found in the 2004 Implementing Rules and Regulations (IRR) of the National Building Code of the Philippines (PD1096), under Mechanical Regulations on Escalators,

"The rated speed of escalators, measured along the angle of inclination, shall not be more than 38 meters per minute."
(Rule XIII, Sec. 1302.6.d of the 2004 IRR of PD1096)

Therefore, the correct answer is a. 38 meters per minute.

Q#9: An air-conditioning assembly containing the fans, filters, and other components necessary to treat and distribute conditioned air to an entire building or to specific zones within the building.
a. Damper
b. AHU
c. HVAC
d. Blower

Damper:
"A movable plate for regulating the draft in an air outlet, air duct, or the throat of a fireplace."

AHU (Air-Handling Unit):
"An air-conditioning assembly containing the fans, filters, and other components necessary to treat and distribute conditioned air to an entire building or to specific zones within the building."

HVAC:
"Abbreviation for heating, ventilating, and air conditioning."

Blower:
"A fan for supplying air at a moderate pressure, as to supply forced drafts in a heating or air-conditioning system."

(Page 125, A Visual Dictionary of Architecture by Francis D.K. Ching)

Therefore, the correct answer is b. AHU (Air-Handling Unit).

Q#10: According to the National Building Code, one (1) passenger elevator must be kept on 24-hour constant service if an apartment building is how many storeys high?
a. 4
b. 5
c. 6
d. No such requirements for apartment buildings as far as the National Building Code is concerned.

This provision can be found in the 2004 Implementing Rules and Regulations (IRR) of the National Building Code of the Philippines (PD1096), under Mechanical Regulations on Elevators,

"In apartments or residential condominiums of five (5) storeys or more, at least one (1) passenger elevator shall be kept on twenty-four (24) hour constant service."
(Rule XIII, Sec. 1302.5.i of the 2004 IRR of PD1096)

Therefore, the correct answer is b. 5.

Q#11: 1 Horsepower (1 hp) is equivalent to:
a. 33,000 ft-lbf/min
b. Approx. 735.5 watts
c. 746 watts
d. All of the above

During the Industrial Revolution, the mechanical engineer James Watt determined that a horse, pulling at a force of 180 lbf, could turn a 24-foot diameter mill wheel 144 times in 1 hour (or 2.4 times per minute). So,

P = W / t = Fd / t = 180lbf [2.4 x 2π x 12ft] / 1 min = 32,572 ft-lbf/min

The value was standardized by Watt by rounding to an even 33,000 ft-lbf/min. (Mechanical Horsepower)

The German national organization for standardization (DIN) set an equivalent metric unit to the above english value. DIN 66036 defined 1 metric hp as the power to raise a mass of 75kg against the Earth's gravitational force over a distance of 1m in 1 second. So,

P = 75kg x 9.80665m/s² x 1m/s = 735.49875 W (Metric Horsepower)

When used in electrical machines, the horsepower is defined as exactly 746 W, derived from,

33,000 ft-lbf/min x [1min/60sec] x [0.3048m/ft] x [0.45359237kg/lb] x [9.80665kg-m²/s³] = 745.69987158227022 W ≈ 746 W (Electrical Horsepower)

So,

Mechanical Horsepower, hp(I) = 33,000 ft-lbf/min

Metric Horsepower, hp(M) = Approx. 735.5 watts

Electrical Horsepower, hp(E) = 746 watts

Therefore, the correct answer is d. All of the above.

Q#12: A cafeteria having a 3-m ceiling height is to be provided with artificial ventilation. What is the minimum requirement for air changes for such space as per the current building code?
a. 1-3/4 air changes per hour
b. 4-1/2 air changes per hour
c. 3-1/2 air changes per hour
d. 6 air changes per hour

This provision can be found in the 2004 Implementing Rules and Regulations (IRR) of the National Building Code of the Philippines (PD1096), under Artificial Ventilation,

(Rule VIII, Table VIII.4 of the 2004 IRR of PD1096)

Therefore, the correct answer is b. 4-1/2 air changes per hour.