2
SPACE HEATING AND DOMESTIC WATER HEATING LOADS
ANSWERS TO TEXTBOOK QUESTIONS AND EXERCISES
1. The temperature difference across the material is 68-5=63 degrees F.
2. The total effective R-value of the wall in Figure 2-34 is obtained by adding the individual
R-values of the materials that make up the wall. Values chosen are from Figure 2.6 and
3. In this problem, the area and R-value are unknown but are constant. 500 Btu/hr / 60F =
4. The basement wall is divided into three vertical zones, each with a different effective R-
value. The uppermost zone is from the top of the basement wall above grade extending to
5. The slab-on-grade floor shown in Figure 2-35 is both heated and insulated. Equation 2.7b
6. The design heat loss of the room shown in Figure 2-36 is given by the summation of the
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remaining part of the wall (15.85*8/18.33)(80)=553 Btu/hr. Total heat loss from the west
wall is 1065 Btu/hr.
The south wall contains both a window and door. The window area is 24 sq. ft. The door
area is 20 sq. ft. Heat loss from the door is 320 Btu/hr. Heat loss from the window is 768
Btu/hr. Heat loss from the remaining wall area is 142.8/18.33*80=623.4 Btu/hr. The total
heat loss from the south wall is 1711.4 Btu/hr. Heat loss from the ceiling is
370.16/30*80=987.1 Btu/hr. Heat loss from the floor is 370.16/20*80=1480.6 Btu/hr.
Total conduction heat loss from the room is 5244 Btu/hr.
The infiltration heat loss is given by 0.018(0.75)(2961)(80)=3198 Btu/hr.
Total design heat loss is 8442 Btu/hr.
7. The total building heating load is obtained by summing the heating loads of each room.
8. Use Equation 2.11. Assume 15 gallons of water per day per person. 5*15(8.33)(120-45)=
9. There is no difference in cost because the amount of energy required to raise the
10. The peak hourly usage is 16 percent of daily hot water usage. 0.16*80= 12.8 gallons.