(61) Distinguish between a dry return and a wet return on a steam-heating system.

(65) Clearly explain the use of an expansion tank in a hot-water heating system. How should it be connected up?

(66) Explain the equalized system of hot-water heating and state its advantages.

(67) What are the chief points to be considered regarding the arrangement of the heating surfaces in a hot-air furnace?

(68) Clearly explain how humid air can be dried, and state the objections to cold-water coils for this purpose.

(69) Briefly describe the plenum system of warming and ventilating a building.

(70) (a) State the use of cowls in ventilation work, and distinguish between eduction cowls and induction cowls. (b) Draw a section through an automatic induction Cowl and describe the mechanism.

(71) Describe the process of direct-indirect heating.

(72) Show, by sketch, how an indirect radiator can be arranged so that hot and cold air may be mixed to regulate the temperature of a room without cutting off the ventilation.

(73) Mention a few of the most important details to be considered in writing specifications for boiler settings.

(74) What diameter of low-pressure steam main is required to supply direct radiators having a total heating surface of 4,900 square feet? Ans. 8-inch pipe, nearly.

(75) Is it necessary for the several sections of a hot-water radiator to be connected together at the top? Give your reasons.

(76) A certain hot-water pipe will conveniently supply 84 square feet of direct radiation on the first floor; how many square feet will it supply on the third floor with equally good results? Ans. 142.8 sq. ft

(77) What is a combination hot-air heater? Under what circumstances is it advisable to use a combination heater?

(78) Explain how dust, soot, etc. can be filtered from an air-current.

(79) What should be considered regarding the ventilation of cloak rooms in school buildings?

(80) What is the relative humidity when the temperature of the atmosphere is 75° and the dew point is found to be 35°?

Ans. 24.07%.

(81) Two rooms, A and B, each require precisely the same amount of heat (30,525 B. T. U. per hour) to maintain them at a temperature of 70°. It is proposed to heat the room A with a direct radiator composed of a single row of vertical tubes, each 40 inches high. The room B is to be heated with a direct radiator composed of a single row of vertical tubes, each 12 inches high. The temperature of the steam in both cases shall be 220°. (a) How many square feet of heating surface are required for A? (b) How many square feet of heating surface are required for B?

(82) What is a thermostat? Explain its use, and, in a general way, describe its operation.

(83) Mention three safety devices for boilers, and state the use of each.

(84) How should steam pipes be tested before being concealed?

(85) Are standard steam-pipe fittings suitable for use in a hot-water heating system? Give reasons.

(86) A 4-inch main, forming a circuit of 300 feet, supplies hot water to four 100-square foot direct radiators situated at a level of 10 feet above the boiler bottom. It is proposed to remove three of these radiators to the third floor and supply them from the same main, along with the radiator that remains on the first floor. How many square feet of additional surface on the third floor will the main conveniently supply? Neglect resistance due to the new risers, and allow for a fall in temperature of 20° F.

Ans. 193 sq. ft.

(87) What should be considered regarding the location of a heater? Give reasons.

(88) Mention a few of the most important points to be considered indesigning a system for distributing air for ventilation purposes, as regards the proper mixing and diffusion of the air.

(89) What are the principal objections to the dry-closet system of warming and ventilating school buildings?

(90) What are the principal factors upon which the efficiency of an evaporating and drying apparatus chiefly depend? Give reasons.

(91) If the velocity of the air which flows through between the pipes of the heater, shown in Fig. 34, Heating and Ventilation of Buildings, is 20 feet per second, and the amount of heating- surface in the heater is 3,000 square feet, how much heat would the heater give off to the air, supposing that the original temperature of the air is 60°, and the average temperature of the heater is 210°?

Ans. 4,050,000 B. T. U. per hour.

(92) (a) Describe a centrifugal fan. (b) Distinguish between exhaust fans and pressure fans.

(93) What is a steam trap? Explain its use.

(94) (a) What precautions must be taken when a steam-heating system is being installed, to prevent a future fire? (b) Describe good floor and ceiling flanges.

(95) What kind of valves should be used in a hot-water heating system? Give reasons.

(96) Suppose that in Fig. 80, Heating and Ventilation of Buildings, the radiators were of the following sizes:

The radiator e has a surface of GO square feet. Draw to a scale double the size of the figure, the several lines of pipe shown, and mark the diameters of the different pipes.

(97) What is a cold-air duct in a hot-air heating system? Explain its use and state where it should be run and of what material it should be made.

(98) What is the acoustic effect of a large hot-air current rising in an auditorium? Explain the cause.

(99) About what should be the velocity of the air-currents in the several conduits of a forced-blast ventilating system?

(100) Describe combustion of fuel and state the products of complete combustion and incomplete combustion.