Energy-Efficient Heating, Ventilating and Air Conditioning

Homework

FOR ALL RELEVANT PROBLEMS USE TMY3 DATA NOT TMY2 DATA

TMY3 DATA IS EASIER TO DOWNLOAD BECAUSE IT DOES NOT NEED TO BE UNZIPPED. JUST READ IT DIRECTLY INTO WEATRAN.

Problem 1

Calculate hourly fuel use for a facility (Btu/hr) using the explicit and balance temperature methods, if the facility has the following characteristics:

Length =300 feet, width = 250 feet, ceiling height = 40 feet

Average thermal resistance of walls and ceilings = 12 ft2-F-hr/Btu

Average ventilation rate = 12,000 cfm

Outdoor air temperature = 35 F

Indoor air temperature = 70 F

Average electrical power = 120 kW

Efficiency of heating system = 80%

Problem 2

Calculate annual fuel use (mmBtu/yr) using HDDs for a facility in Boulder, Colorado with the following characteristics:

Length = 250 feet, width = 250 feet, ceiling height = 35 feet

Average thermal resistance of walls and ceilings = 8 ft2-F-hr/Btu

Average ventilation rate = 8,000 cfm

Average indoor air temperature during heating season = 70 F

Average internal electrical power = 80 kW

Efficiency of heating system = 80%

Problem 3

A 3PH model of facility natural gas use versus outdoor air temperature yields the following coefficients:

Heating slope = 0.600 mmBtu/day-F

Change-point temperature = 60 F

Independent fuel use = 0

Calculate fuel use for the facility (Btu/hr) when:

Indoor air temperature = 70 F

Outdoor air temperature = 20 F

Efficiency of heating system = 80%

Problem 4

Model coefficients of 3PH model of natural gas use for a facility in Chicago, IL are:

HS = 100 (mmBtu/mo-F)

Tb = 60 (F)

Independent NG use = 0.00 (mmBtu/mo)

The indoor air temperature is 70 F. The facility is heated by a mix of 100% efficient make-up air units and 80% efficient indoor air heaters; with an average heating efficiency of 90%. Calculate the annual fuel savings (mmBtu/yr) if the R value of the 250,000 ft2 roof is increased from R = 5 hr-ft2-F/Btu to R = 15 hr-ft2-F/Btu during a required resurfacing of the roof.

Problem 5

Consider a facility in Indianapolis, IN whose length is 400 ft, width is 300 ft and ceiling height is 25 ft. The walls have 8 ft-high single-pane windows with thermal resistance 1 hr-ft2-F/Btu on all sides. The thermal resistance of the roof is 5 hr-ft2-F/Btu, the thermal resistance of the walls is 12 hr-ft2-F/Btu. The ventilation rate is 20,000 cfm and the average electrical power requirement of equipment in the facility is 150 kW. The indoor air temperature is 70 F. The facility is heated by a mix of 100% efficient make-up air units and 80% efficient indoor air heaters; with an average heating efficiency of 90%. Calculate the annual fuel savings (mmBtu/yr) if the R value of the 120,000 ft2 roof is increased from R = 5 hr-ft2-F/Btu to R = 20 hr-ft2-F/Btu during a required resurfacing of the roof, and polycarbonate covers increase the R-value of the windows from 1 to 2 hr-ft2-F/Btu.

Problem 6

Model coefficients of 3PH model of natural gas use for a facility in Dayton, OH are:

HS = 80 (mmBtu/mo-F)

Tb = 60 (F)

Independent NG use = 0.00 (mmBtu/mo)

The indoor air temperature is 65 F. The facility is heated by a mix of 100% efficient make-up air units and 80% efficient indoor air heaters; with an average heating efficiency of 90%. Calculate the annual fuel savings (mmBtu/yr) if the average indoor air temperature were reduced to 55 F by reducing thermostat set point temperature during unoccupied hours. Assume the actual savings would be about 60% of the savings estimated using a steady state analysis.

Problem 7:

Calculate hourly cooling electricity use (kWh/hr) for a facility with the following characteristics:

Length = 200 feet, width = 300 feet, ceiling height = 25 feet

Average thermal resistance of walls and ceilings = 10 ft2-F-hr/Btu

Average ventilation rate = 10,000 cfm

Indoor air temperature = 70 F

Outdoor air temperature = 83 F

Outdoor air temperature specific humidity = 0.012 lbw/lba

Average facility electricity use = 90 kW

Air conditioner SEER = 10 Btu/Wh