UCCS PES/ENSC 1500 Energy Science I
Chapter 5 Problems HW
name: __________________________
I
1.
How many Btu per hour per square foot will be lost through the wall when the outside temperature is:
50 degrees F colder than the inside? (Disregard the inside temperature)
a.
List the following Rvalues for the following wall construction materials:
material
Rvalue
0.5 inch wood siding lapped
0.5 inch plywood sheathing
3.5 inch fiberglass
0.5 inch sheet rock
b.
Total Σ Rvalue:
_____________________________
c.
Solve for: 1 / Rvalue:
_____________________________
d.
( value from part “c” ) ( 50 degrees F ) =
_____________________________ Btu/hr/ft2
2.
A house with the following dimensions: (28 ft) (40 ft) (10 ft) has an outside temperature of 40 degrees F
and is constructed with the following:
Walls outside & inside materials:
2-in. hardwood planks
R-Value: ________________ (ft2-h-°F/Btu)
0.5 lapped wood siding
R-Value: ________________ (ft2-h-°F/Btu)
0.5 sheetrock
R-Value: ________________ (ft2-h-°F/Btu)
Σ of R-Value
________________ (ft2-h-°F/Btu)
Roof is flat with the following materials:
1-in. plywood
R-Value: ________________ (ft2-h-°F/Btu)
Asbestos shingles
R-Value: ________________ (ft2-h-°F/Btu)
3.5-in. fiberglass insulation
R-Value: ________________ (ft2-h-°F/Btu)
Σ of R-Value
________________ (ft2-h-°F/Btu)
The floor is built with:
25/32 in. wood subfloor
R-Value: ________________ (ft2-h-°F/Btu)
0.75 hardwood floor over an unheated crawl space
R-Value: ________________ (ft2-h-°F/Btu)
Σ of R-Value
________________ (ft2-h-°F/Btu)
Windows are 25% of the wall areas:
single-pane windows
R-Value: ________________ (ft2-h-°F/Btu)
Σ of R-Value
________________ (ft2-h-°F/Btu)
II.
Calculate the heating needs in Btu/h
1. Qwalls
[ ( area of wall1 ) ( 2 ) ] + [ ( area of wall2 ) ( 2 ) ] ( % of walls to windows ) ( temp. / Σ R-Value )
2. Qroof
( area of roof ) ( temp. / Σ R-Value )
3. Qfloor
( area of floor ) ( temp. / Σ R-Value )
4. Qwindow
[ ( area of wall1 ) ( 2 ) ] + [ ( area of wall2 ) ( 2 ) ] ( % of windows to walls ) ( temp. / Σ R-Value )
5. Sum of items: 1 – 4:
__________________________ Btu/h
6. What is the new: Qroof & Qtotal if house is insulated with a total of: 6 inch fiberglass in the attic?
a. Qroof
=
_____________________ Btu/h
b. Qtotal
=
_____________________ Btu/h
c. Savings of:
_____________________ %
7. What is the new: Qwalls & Qtotal if house is insulated with a total of: 3.5 inch fiberglass in the walls?
(Ceiling remains the same 3.5-in.)
a. Qwalls
=
_____________________ Btu/h
b. Qtotal
=
_____________________ Btu/h
c. Savings of:
_____________________ %
8. What is the new: Qwindow & Qtotal if the house has its current single-pane windows replaced with:
double-pane windows (0.5 in air space)?
a. Q window =
_____________________ Btu/h
b. Q total
_____________________ Btu/h
=
c. Savings of:
_____________________ %
19. Using the equation for rate of heat loss for infiltration in the gray box on pg. 134, & using the same
dimensions for the house in the previous problem: (28 ft) x (40 ft) x (10 ft), calculate the infiltration
heat losses in Btu/hr when the change in temperature is: 40 degrees F.
K=2
Qinfil / t
=
( constant ) ( volume ft3 ) ( K ) ( Δ T )
________________________________ Btu/hr