Document veY1q0d5gMvrJQqa8ynrr4z9

Heating Ventilating Air Conditioning Guide 1939 PROBLEMS IN PRACTICE j 1 What is the relation between the sensible heat loss from a building and the heat required for humidification? A house with a volume of 14,000 cu ft has a heat loss 120 Mbh for standard uninsulated frame construction and a 70 F temperature difference. Assuming a leakage rate of air changes per hour it would require about 10 Mbh to maintain a relative humidity of 45 per cent when the outside air is 0 F and 50 per cent relative humidity. By using an insulation such as rock wool, the sensible heat loss of this house may be reduced to ' approximately 77 Mbh. The insulation does not affect the humidification load, which ! now assumes greater importance. 2 What Inside dry-bulb temperatures are usually assumed for: (a) homes. ' (b) schools, (c) public buildings? Referring to Table 1: a. 70 to 72 F. ; b. Temperature varies from 55 to 75 F, depending on the room. Classrooms, for instance, ' are usually specified as 70 to 72 F. ^i c. 68 to 72 F. ! 3 How is the outside temperature selected for use in computing heat losses? The outside temperature used in computing heat losses is generally taken from 10 to 15 F higher than the lowest recorded temperature as reported by the Weather Bureau during i the preceding 10 years for the locality in which the heating system is to be installed. ` In some cases where the lowest recorded temperature is extremely unusual, the design ! temperature is taken even higher than 15 F above the lowest recorded temperature. 4 # What are the effects of wind movement on the heating load? a. Wind movement increases the heat transmission of walls, glass, and roof; it affects poor walls to a much greater extent than good walls. * b. Wind movement materially increases the infiltration (inleakage) of cold air through ] the cracks around doors and windows, and even through the building materials them- \ selves if such materials are at all porous. 5 Calculate the heat given off by eighteen 200-watt lamps. 200 X 18 X 3.415 = 12,294 Btu per hour.. \ 6 A two-story, six-room, frame house, 28-ft by 30-ft foundation, has the ,V following proportions: Area of outside walls, 1992 sq ft. Area of glass, 333 sq ft. Area of outside doors, 54 sq ft. Cracks around windows, 440 ft. Cracks around doors, 54 ft. Area of second floor ceiling, 783 sq ft. Volume, first and second floors, 13,010 cu ft. Ceilings, 9 ft high. ' | 1 i J \ j The minimum temperature for the heating season is --34 F, and the required | inside temperature at the 30-in. level is 70 F. The average number of degree | days for a heating season is 7851, and the average wind velocity is 10 mph, | northwest. The walls are constructed of 2-in. by 4-in. studs with wood sheathing, building | paper, and wood siding on the outside, and wood lath and plaster on the inside..) Windows are single glass, double-hung, wood, without weatherstrips. The | second floor ceiling is metal lath and plaster, without an attic floor. The roof | is of wood shingles on wood strips with rafters exposed. The area of the rftof b 20 per cent greater than the area of the ceiling. Select values for the following: i (a) U for walls; (b) U for glass; (c) U for second floor ceiling; (d) U for roof; | Chapter 7. Heating Load ... ,, ,,,,a roof combined; (f) air leakage, cubic feet per hour per foot (e) U for ceiling a jeakage, cubic feet per hour per foot of door crack. window cracK, vb; "" * o 0.25 (Table 5, Chapter 5). b 1.13 (Table 13, Chapter 5). c 0.69 (Table 8, Chapter 5). d 0.46 (Table 12, Chapter 5). e o 31 (Equation 6, Chapter 5): f. 21.4 (Table 2, Chapter 6). ^ n 1_ f _1~ t_ iJm.kla 4lin urtn/4nnr laoWrrn j Us.ing t.h.e.^ datao<nf Oues^tion 6, calc^ulatepethrceemntaagxeimoufmtheBttuotlaosl shpeeart hwohuicrhfour Though each construction described. o. Outside walls b. Glass c. Doors d. Second floor ceiling e. Air leakage, windows /. Air leakage, doors 46,200 Btu loss 34,950 Btu loss 5,670 Btu loss 24,050 Btu loss 15,750 Btu loss 3,865 Btu loss 35.4 per cent of total 26.7 per cent of total 4.4 per cent of total 18.4 per cent of total 12.1 per cent of total 3.0 per cent of total Total 130,485 Btu loss 100.0 per cent of total D For the house in Question 6, place 1-in. insulation in the outside walls aud nd floor ceiling; k for insulation = 0.34. Use weatherstrip on doors and windows and double glass on the windows; C = 0.55.. Calculate or select the following values: (a) U for walls; (b) U for glass; (c) V for second floor ceiling; (d) U for combination of ceiling and roof; (e) air leakage, cubic feet per hour Lj foot of door crack; (f) air leakage, cubic feet per hour per foot of window a. 0.144 b. 0.55 c. 0.23 d. 0.16 e. 15.5 /. 31.0 9 Calculate the maximum Btu loss per hour and show the percentage loss by each channel for the house as insulated in Question 8. a. Outside walls b. Glass c. Doors d. Ceiling c. Air leakage, windows / Air leakage, doors 26,650 Btu loss 17,000 Btu loss 5,670 Btu loss 12,420 Btu loss 11,400 Btu loss 2,795 Btu loss 35.1 per cent of total 22.4 per cent of total 7.4 per cent of total 16.4 per cent ol total 15.1 per cent of total 3.6 per cent of total Total 75,935 Btu loss. 100.0 per cent of total TO From the results of Questions 7 and 9, calculate the Btu saved and the percentage saved by each change in construction. Uninsulated 0. Outside walls b. Class c. Doors .... d. Ceiline' ........ e. Air leakage, windows________ J/. Air leakage. doors -- 46,200 34,950 5,670 24,050 15,750 3,865 Insulated 26,650 17,000 5,670 12,420 11,400 2,795 Btu Saved Pqa Cent Saved 19,550 17,950 0 11,630 4,350 1,070 42.3 51.4 0 48.3 27.6 27.7