CVEN 5020 BUILDING ENERGY AUDITS FALL 2007
University of Colorado at Boulder 1
Homework No. 4
Due October 9, 2007
Problem No. 1:
A blower door test on a 30 ft × 50 ft × 9 ft house located in Denver, CO, revealed that under 4 Pa
pressure differential between indoors and outdoors, the leakage area is about 200 in2.
(a) Determine in air changes per hour, the annual average infiltration rate for the house.
(b) It was decided to weather-strip the house so that the infiltration is reduced to just 0.25
ACH (for 4 Pa pressure differential). Determine the payback period of weather-
stripping the house given the following parameters:
Heating Degree-Days: 6,000
Cooling Degrees-hours: 5,000
Fuel Cost: $5/MMBtu
Boiler Efficiency: 0.70
Electric Rate: $0.10/kWh
Refrigeration requirement: 0.75kW/ton
Cost of weather-stripping: $150
Problem No. 2:
(i) Estimate the annual energy loss/gain from 100 ft by 50-ft slab-on-grade floor of a
building located in Denver, CO. The floor is made up of 4-in concrete floor.
(ii) Estimate the annual heating energy use savings if the slab is insulated uniformly with R-
10 rigid insulation. Assume a furnce efficiency of 80%.
(iii) (ii) Implement the calculation procedure for slab-on-grade floor heat loss in a
spreadsheet and determine if there is an optimal cost-effective insulation level (i.e., R-
value) for the foundation. Assume that the fuel cost is $10.0/MMBtu, the efficiency of
the heating system is 0.80, the cost of adding insulation is 0.5 per ft2 of R-5 rigid
insulation, and the discount rate is 5%.
Problem No. 3:
(a) Estimate the annual fuel energy use and cost savings due to retrofitting all the walls of a
house to dynamic walls. The house is located in Denver (CO) and has R-11 walls (1,650
ft2), R-19 ceiling (2,000 ft2), and R-2 windows (200 ft2). Assume that the
infiltration/ventilation rate is 0.75 ACH.
(b) If we include the effect of heat losses through the foundation (assume U-effective of Ueff=
0.07 Btu/ft2.hr.oF and an area of 2,000 ft2 for the foundation, do your estimations change
significantly.
(c) Determine the impact of dynamic walls if the infiltration/ventilation rate is reduced to 0.35
ACH.
