AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 1. Psychrometrics a) Moist air has a dry bulb temperature of 80°F and a wet bulb temperature of 67°F? What is the enthalpy at sea level? What is the enthalpy at 5000 ft above sea level? b) A building zone is maintained at 76°F dry bulb and 50% RH. The zone has a sensible cooling load of 40,000 Btu/hr and total cooling load of 50,000 Btu/hr. The supply air temperature delivered to the zone is 55°F. Assuming that the return air from the zone is at the same conditions as the zone air, what airflow rate (cfm) is required? c) In winter, 10,000 cfm of ventilation air for a building at sea level is heated and humidified. The air enters at 30°F and 30% RH and is conditioned to 70°F and 30% RH. How much energy is required to heat and humidify the air? d) What if the dew point of air at 70°F and 30% RH at sea level? FINAL EXAM REVIEW PAGE 1 11 DECEMBER 2005AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 2. Comfort a) How much heat is generated by a 6 ft. tall, 180 lb man, performing basic office work? b) A company executive sits in a corner office on a hot summer day, wearing a clothing ensemble with a thermal resistance of 0.5 clo. Due to radiation and heat transfer through the exterior walls, the mean radiant temperature in the office is 80°F. What is an appropriate air temperature to ensure comfort? c) ? FINAL EXAM REVIEW PAGE 2 11 DECEMBER 2005AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 3. Heating Loads a) What is the design heating load associated with infiltration for a 2000 ft2 house in Bou if the infiltration rate is 0.35 ACH? b) What is an approximate R-value of a 0.75-in. airspace between a brick façade and an insulated wall struction for heating load calculations? c) What is rate of heat transfer through a typical 3-ft. by 5-ft. wood framed window having double glazing with a 1/2-in. air gap if the indoor temperature is 70°F and outdoor temperature is 20°F? d) What is the R-value of an 8-in. thich, perlite-filled, normal weight concrete block? FINAL EXAM REVIEW PAGE 3 11 DECEMBER 2005AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 4. Cooling Loads a) What is the CLTD for a dark-colored roof in Detroit? b) Consider the attic of a residential building. The ceiling has an area of 2000 ft2 and the roof has a 22° pitch. The ceiling has an overall R-value, including surface resistances, of R-30. The dark shingled roof and its associated gable endwalls have an overall R-value of R-2. For cooling load calculations in Detroit, what is the cooling load contribution of heat transfer through the ceiling? c) What is the cooling load contribution due to a typical west-facing 3-ft. by 5-ft. wood framed window having double glazing with a 1/2-in. air gap? How much would it decrease if curtains were added on the inside? d) When calculating cooling loads, what is an appropriate heat gain due to equipment in the kitchen area of a residence? FINAL EXAM REVIEW PAGE 4 11 DECEMBER 2005AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 5. Solar Position and Shading a) If the mountains in Boulder (40°N latitude, 105°W longitude) are 10° above the horizon, what time (MST) will the sun disappear behind the mountains on Christmas day? b) How many degrees south of due west will the sun be when the sun dips behind the mountains in a) above? FINAL EXAM REVIEW PAGE 5 11 DECEMBER 2005AREN 3050 ENVIRONMENTAL SYSTEMS FOR BUILDINGS I FALL 2005 6. Ducts and Diffusers a) What is the pressure drop through a 6-in. round duct, 50 ft. long, that terminates with a boot diffuser type G shown in Fig. 7.13, with an airflow of 200 cfm? b) A single-person office measures 12 ft. by 12 ft. with 8 ft. ceilings. The loads in the room require an airflor of 150 cfm. Select a high sidewall diffuser from the performance data in the text that would be appropriate for this room. FINAL EXAM REVIEW PAGE 6 11 DECEMBER