BCIT 5th class boiler engineer quiz 4 Flashcards
Two methods of calculating air infiltration into a building are
a) the crack method and the air change method.
b) the door-count method and the recirculation method.
c) the crack and the solar method.
d) the air change and the minimum air method.
e) the per person and the minimum air method.
a) the crack method and the air change method.
B02 CH01 Q010
In order to estimate the infiltration or ventilation load, the amount of air involved must be determined. There are two methods of estimating the quantity of air entering by means of infiltration:
1. The crack method
2. The air change method.
The thermal transmission through unit areas of a particular body or assembly where the difference between the fluid temperatures on either side of the body or assembly is unity is defined as
a) thermal resistance.
b) standard thermal transmission.
c) thermal conductivity.
d) thermal conductance.
e) thermal transmittance.
e) thermal transmittance.
B02 CH01 Q004
Thermal transmittance or U-factor (U): the thermal transmission through unit areas of a particular body or assembly (including its boundary films) where the difference between the fluid temperatures on either side of the body or assembly is unity (W/m2K or W/m2°C).
In determining the heat conducted through a surface, the U-factor is the
a) inverse heat exchange factor.
b) overall coefficient of heat transmission.
c) thermal conductance.
d) thermal conductivity.
e) overall coefficient of thermal resistance.
b) overall coefficient of heat transmission.
B02 CH01 Q006
The resistance to heat flow is known as the “Overall Coefficient of Heat Transmission”, and is commonly called the “U” Factor.
A radiator valve is used to control the amount of
a) steam entering the radiator.
b) steam leaving the radiator.
c) air leaving the radiator.
d) air flowing over the radiator.
e) condensate leaving the radiator
a) steam entering the radiator.
B02 CH02 Q008 Manually operated radiator valves, used to control the flow of steam to the radiators, are a special design of globe valve. They are made in either a straight-through or an angle design. Some types are packless in order to avoid the trouble of leakage around the valve stem and the necessity of repacking.
To increase heat transfer, unit heaters differ from convectors because they incorporate
a) metal fins.
b) blowers.
c) auxiliary heat exchangers.
d) dampers.
e) radiant elements.
b) blowers.
B02 CH02 Q004
A unit heater is a convector type heater which employs a blower or fan to force the air through the heating coil instead of using natural circulation. This results in a large heat output for a fairly small unit.
Unit ventilators use
a) only inside air for heating.
b) a mixture of inside and outside air.
c) only outside air for heating.
d) natural draft.
e) an auxiliary fin-coil heater.
b) a mixture of inside and outside air.
B02 CH02 Q006
Unit ventilators, also called univents, are basically cabinet type unit heaters which, in addition to the standard heating coil and blower or fan, are also equipped with an air filter, several dampers and an outside air inlet to admit fresh air for ventilation.
In radiant heating system changes are
a) as easy to make as in any other heating system.
b) easy to make.
c) dependent on availability of materials.
d) dependent on location
e) difficult to make.
e) difficult to make.
B02 CH04 Q012
There are also some disadvantages of radiant systems which make the system unsuitable for use in certain types of buildings. These disadvantages are:
Due to their large heat storing capacity, the panels are fairly slow in heating up and cooling down. This causes problems maintaining a steady room temperature when outside temperatures change quickly.
Any leakage in the panels is costly to repair.
Changes in the heating system are difficult to make.
A forced hot water circulating system can be classified as
a) All of the above.
b) loop system.
c) two pipe direct return system.
d) two pipe reverse return system.
e) one pipe system.
a) All of the above.
B02 CH04 Q010
Forced circulation hot water systems are classified according to the methods of piping. Systems may be considered to be of two general types, upfeed and downfeed. These systems may be further classified into the following types:
1. Loop system
2. One-pipe system
3. Two-pipe direct return system
4. Two-pipe reverse return system
Advantages of hot water heating systems compared to steam heating include:
- Ability to modulate the temperature of the medium to match the demand.
- Small and compact size.
- Lower operating pressure in high-rise buildings.
- Lower pump power requirement.
- Lower maintenance costs.
a) 1, 4 and 5 only.
b) 1, 2, 3 and 5 only.
c) 3, 4 and 5 only.
d) 1, 2, 3, 4 and 5.
e) 1, 2 and 5 only.
e) 1, 2 and 5 only.
B02 CH04 Q020
Advantages of hot water heating systems:
- The temperature of the supply water can be varied in relation to the changing outdoor temperature much more readily than steam temperature can be varied. This allows for variations in load without shutting off and opening up the supply to the radiators.
- A hot water boiler is smaller and more compact than a steam boiler of the same output, since no boiler steam space is required. In addition, pipe sizes are generally smaller in a hot water system than in a steam system, and fewer and less expensive fittings are required.
- The piping pitch or slope is not as critical in a forced circulation hot water system as in a steam system where proper drainage of condensate is important.
- Maintenance costs are usually less in a hot water system, due to the fact that traps are not required and also because there is less corrosion in the piping.
The disadvantages of hot water gravity circulation systems include:
- Large pipe sizes are required:
- Circulation is difficult to maintain to radiators on the same level as the boiler.
- Slow responses to changes in heat demand.
- Maintenance costs are usually high.
- Maximum water temperature is limited to 77 degrees Celsius.
a) 1, 2, 4 and 5 only.
b) 2, 3, 4 and 5 only.
c) 1, 2, 3 and 5 only.
d) 1, 3, 4 and 5 only.
e) 1, 2, 3, 4 and 5.
c) 1, 2, 3 and 5 only.
B02 CH04 Q022
Although the gravity hot water system has the advantages of simple operation and low maintenance, its use has sharply declined because of the following disadvantages:
- Large pipe sizes are necessary in order to keep flow resistance to a minimum since flow depends only upon gravity.
- Circulation is difficult to maintain to radiators on the same level as the boiler.
- There is a slow response to changes in heat demand.
- The maximum water temperature is limited to approximately 77°C (170°F).
To ensure the water supply line does not open, the minimum pressure to be maintained at the boiler pressure gauge on a small building hot water system is
a) 101 kPa.
b) 60 kPa.
c) 83 kPa.
d) 51 kPa.
e) 25 kPa.
c) 83 kPa.
B02 CH05 Q014
A minimum pressure of 83 kPa (12 psi) indicated on the boiler pressure gage (8.5 m or 28 feet of water on the altitude gage) should be maintained on all hot water heating systems of smaller buildings, such as residences and single-story commercial buildings where the boiler and circulator are usually located on the lowest level. Any drop in pressure below this value will cause the pressure reducing valve in the water supply line to open and to feed water into the system until pressure has returned to normal.
In a hot water heating system incorporating a converter, the type of boiler you would expect to find is a
a) single pass boiler.
b) steam boiler.
c) two pass boiler.
d) hot water boiler.
e) forced circulation boiler.
b) steam boiler.
B02 CH05 Q012
Under some circumstances, it may be preferable to heat the water for a hot water heating system by means of steam from a steam boiler. This is done in a converter which is usually a shell and tube heat exchanger in which the water to be heated flows through tubes and the steam admitted to the shell surrounds the outside of the tubes.
In a hot water heating system, air removed by the separator is vented to the
a) air space at the top of the boiler.
b) relief valve.
c) expansion tank.
d) supply header.
e) dip tube.
c) expansion tank.
B02 CH05 Q006
The separator contains a baffle which causes the air bubbles to rise and accumulate in the upper part of the housing. The bubbles then pass upwards to the expansion tank, which is directly connected to the separator, where they help to maintain the air cushion, or they are vented to atmosphere via an air vent.
An air separator should always be installed in a/an
a) expansion tank.
b) cross tee.
c) horizontal pipe.
d) vertical pipe.
e) converter.
c) horizontal pipe.
B02 CH05 Q020
An air separator is installed in the first horizontal stretch of the supply piping after the water leaves the boiler.
Shown in the illustration is a/an
a) condensate pump system.
b) Hartford loop.
c) variable vacuum system.
d) vacuum return system.
e) two pipe gravity return system.
e) two pipe gravity return system.
B02 CH03 Q012
Figure shows a diagram of a return trap system. It is an example of a two pipe, gravity return system.
Shown in the illustration is a/an
a) vacuum return system.
b) one pipe gravity return system.
c) return trap system.
d) two pipe gravity return system.
e) condensate pump system.
e) condensate pump system.
B02 CH03 Q014
Two Pipe, Condensate Pump System: all the condensate flows by gravity to a condensate tank which may be located well below the boiler water level. A condensate pump then returns the water from the tank through a Hartford loop into the boiler.
A Hartford loop is installed in a low pressure steam heating boiler to
a) relieve the steam pressure in the system.
b) make the boiler more efficient.
c) improve boiler level control.
d) equalize the steam and water pressure.
e) prevent boiler water from being forced back into the return line.
e) prevent boiler water from being forced back into the return line.
B02 CH03 Q004
The condensate is fed into the boiler through a return or Hartford loop. If the condensate return line would be directly connected to the feed connection in the lower part of the boiler, the possibility then exists that the steam pressure could force the boiler water back into the return line should the check valve fail to close, and the water level in the boiler could drop below the safe minimum level. The Hartford loop prevents this. The return line is connected to the loop at the height of the lowest safe water level. At that level the steam pressure in the boiler and in the loop will be equal and so will be the height of the water. No water can be forced out of the boiler and sufficient water will cover the heating surface to prevent overheating.
The major disadvantage of an electric resistance coil furnace for warm air heating is the
a) danger from electric shock.
b) larger size of the furnace.
c) higher operating costs.
d) higher cost of maintenance.
e) lower thermal efficiency.
c) higher operating costs.
B02 CH06 Q010
Notwithstanding all the advantages of an electric furnace, however, its use is restricted by the high cost of electric power.
In the pulse combustion condensing warm air furnace, the heat recovered from the secondary exchanger
a) is both flue gas sensible and latent heat.
b) is both water vapour latent heat and flue gas sensible heat.
c) is only the latent heat from the water vapour in the flue gas.
d) is only the sensible heat from the flue gases.
e) is only the latent heat from the flue gases.
b) is both water vapour latent heat and flue gas sensible heat.
B02 CH06 Q018
In the secondary heat exchanger the gases give up more heat and cool down to 38°C (100°F). Since this temperature is well below the dewpoint of the gases, water condenses out of the gases so that latent heat is given up as well. The remaining gases are now vented through a 50 mm (2 in.) PVC pipe either through a side wall or the roof. The pipe can also be run up an existing chimney. The condensate drained from the secondary exchanger flows via a plastic pipe to a sewer drain.
On a high efficiency furnace with secondary heat exchanger, if the flue gas temperature drops below 65°C
a) the furnace vent will close.
b) the furnace burner will shut down and will not restart until reset by the operator.
c) the furnace burner will shut down.
d) the flue gas will condense.
e) water vapour in the flue gas will condense.
e) water vapour in the flue gas will condense.
B02 CH06 Q016
As in a conventional furnace, the flue gases leave the primary heat exchanger at a temperature of about 230 - 250°C (446 - 482°F), but by passing them through the secondary exchanger more heat is transferred to the air so that the temperature of the gases drops to about 65°C (149°F) and the efficiency is raised to 85-87% AFUE. Since the temperature of the flue gases drops below the dewpoint in the secondary exchanger, condensation of the water vapor takes place.
A warm air furnace using electric elements as its heat source is usually controlled with a
a) two stage thermostat.
b) heat exchanger temperature sensor.
c) single stage thermostat.
d) low temperature limit switch.
e) high temperature limit switch.
a) two stage thermostat.
B02 CH06 Q008
The power to the elements is usually supplied at 240 volts. Each element or bank of elements is protected against overheating in case of low air flow by a high temperature limit control. The power supply to the elements is usually controlled by a two-stage thermostat which actuates the elements in stages. This method matches the heat supply more closely with the building heat loss so that more even room temperatures can be maintained. Larger furnaces are often equipped with control systems that actuate the elements in three or four stages.
Electronic filters will remove
a) fumes from the air.
b) fine particles from the air.
c) All of the above.
d) smoke from the air.
e) odour producing gases from the air.
c) All of the above.
B02 CH07 Q020
The electrostatic filter is the best filter available for the removal of fine dust, smoke and fumes and, therefore, is extensively used in buildings where the air supply has to be as clean as possible, as in hospitals.
The heat exchanger on a warm air furnace should be checked for corrosion because
a) air leaks could blow out the flame, causing an explosion.
b) carbon monoxide could leak into the building.
c) the holes reduce the furnace efficiency.
d) the air may become too dry.
e) too much air may enter into the furnace.
b) carbon monoxide could leak into the building.
B02 CH07 Q016
After long service, some heat exchangers develop corrosion holes or cracks in the welded joints. Careful examination should reveal any deterioration. If the heat exchanger has failed, carbon monoxide from the flame could enter the warm air stream, putting the building occupants in danger.
The perimeter loop warm air distribution system is ideal
a) for use with a lowboy furnace installed in a crawl space.
b) for use with a lowboy furnace installed in the basement.
c) for a multi-story building.
d) for buildings with a concrete slab floor and no basement
e) for use with a hiboy furnace installed in a basement.
d) for buildings with a concrete slab floor and no basement
B02 CH07 Q008
A
Perimeter loop system is ideal for buildings with a concrete slab floor and no basement. The supply ducts are cast into the slab and so help prevent a cold floor condition.
