#6 and #7 1. Moist air at standard conditions is at a dry bulb temperature of 50F and a relative humidity of 70%. It is sensibly heated (constant moisture) to 72F. Use the psychrometric chart to determine the following properties of the air after it is heated: Relative humidity, Dew point temperature, Specific volume, Humidity ratio, Enthalpy 2. A building owner is considering replacing single-gazed windows with double glazed windows to eliminate condensation moisture problems during cold weather. Moist air at standard conditions in the indoor building space reaches a maximum dry bulb temperature of 72F and relative humidity of 40%. 3. At what dry bulb temperature will condensation begin to occur on the window surfaces? Will the double glazed windows prevent condensation under these indoor space conditions if it the interior surface temperature of the glass drops to 50F in cold weather? A residence has a 2000 ft2 floor area and 8 ft high ceilings. Inside air temperature is 70F and outside ambient temperature is 10F. Assume the heat capacity of air is 0.018 Btu/ft 3F. Calculate the heat removed if the entire air volume of the house is replaced by outdoor air in one hour. 4. Find the total thermal resistance (Rt) and overall coefficient of heat transmission (U) of the following windows and doors in U.S. units: a. Double insulating glass ( in air space) b. Triple insulating glass (low-e) c. Solid wood swing door with metal storm door (1 in thick) 5. A solid load-bearing masonry wall is constructed of 4 in face brick, 8 in standard weight concrete block, 2 in expanded polystyrene insulation board (unfaced), and 5/8 in gypsum wallboard. Determine the temperatures at the surfaces of each material in the construction assembly based on an outside air temperature of 10F and an inside air temperature of 72F (winter conditions). 6. For single-family dwellings in Denver, Colorado, the International Energy Conservation Code (IECC) offers the following minimum R-value ranges for the construction assemblies shown (depending on option). Convert these Rvalues to the metric equivalent thermal resistance (RSI). a. Ceiling: 38 to 49 hrFft2/Btu b. Wall cavity: 17 to 19 hrFft2/Btu c. Basement wall: 9 to 13 hrFft2/Btu d. Floor (above crawl space): 21 to 30 hrFft2/Btu e. Slab-on grade: 5 to 13 hrFft2/Btu 7. A building has indoor air conditions of 70F dry bulb temperature and 50% relative humidity. Determine the direction of water vapor flow under the following outdoor air conditions that represent a cooling climate that is warm and humid: 60F dry bulb temperature and 60% relative humidity (winter conditions) 90F dry bulb temperature and 70% relative humidity (summer conditions) 8. Calculate the annual heat loss (in U.S. units) through the following wall assemblies using U-factors and the annual heating degree days over a typical heating season at the geographical location where you reside. Base your analysis on 1000 ft2 of wall area. 2x6 wood framed wall with R-19 insulation 8 in solid brick uninsulated wall 8 in concrete masonry unit CMU wall, with perlite insulated cores 14 in thick uninsulated abobe wall 16 in solid log wall 23 in straw bale (R-1.45/inch) wall 3 in structural insulated panel (SIP) with EPS core wall 9. A building has a 9 ft deep basement (foundation) wall that is 160 ft long. The wall has no windows. On average, 8 ft of the wall is below grade (underground). Assume an outside air temperature of 10F, an inside temperature of 70F, and an average ground temperature of 45F. Determine the rate of heat loss through the wall below grade if it is uninsulated. Determine the rate of heat loss through the wall below grade if it is insulated with an R-value of about 12 hrFft2/Btu. 10. Calculate the rate of infiltration heat loss of a room with a 380 ft 2 floor area and 10 ft high ceilings. Use an inside temperature of 72F, an outside ambient temperature of 5F. Assume the heat capacity of air is 0.018 Btu/ft 3F. Base the analysis on the following hourly air exchange rates: tight, energy efficient construction (ACH = 0.5) loose construction (ACH = 1.5) 11. A college lecture auditorium is designed for occupancy of 300 persons. The ASHRAE Standard calls for a minimum outside airflow rate for classrooms of 2 L/s per person. The target inside design temperature is 22C and the outside design temperature is 15C. Determine the sensible heating load from ventilation. 12. A building has a heat loss of 100 MBtu/hr at design conditions at the geographical location where you reside. Calculate fuel consumed over the heating season at the geographical location where you reside. Base your analysis on the following fuels and efficiencies: Natural gas (92% efficiency) Liquid petroleum gas/propane (80% efficiency) Fuel oil number 2 (78% efficiency) Electricity, resistance heating (100% efficiency) Wood (pine) (50% efficiency) Coal (60% efficiency) 13. Determine the CLTD for a wood-framed single-family detached residence at the geographical location where you reside, for exterior walls with the following orientations: Facing South Facing North Facing East Facing West 14. A single-family detached residence of moderate construction has a total sensible load of 53 300 Btu/hr. The design humidity ratio is 0.021 lb of vapor/lb of dry air. Determine the latent load. Determine the total cooling load. 15. Approximate the annual energy consumption and annual cost of operation of an air conditioner with an SEER of 13 that is serving a cooling load of 36 000 Btu/hr. Use an energy cost of $0.10/kWh. o For a home in San Francisco, California o For a home in Miami, Florida o For a home in Columbia, Missouri o For a home in Raleigh, North Carolina 16. A church sanctuary is designed for occupancy of 300 persons. The outside airflow rate of 15 cfm per person. The inside design temperature is 74 F and the outside air design temperature is 89 F. Approximate internal heat gains per occupant are 215 Btu/hr for sensible heat and 135 Btu/hr for latent heat. Determine the sensible cooling load component from ventilation. Determine the latent cooling load component from occupants. Determine the total cooling load from occupants. 17. In a commercial building, the heating load at winter design conditions is 211 400 Btu/hr (with pick-up allowance) and the cooling load at summer design conditions is 232 800 Btu/hr. From the performance specifications for commercial, gas-electric, heating and cooling, packaged rooftop units provided in Table 6.9, select an RTU that can efficiently meet these loads. Information for question #18: Selecting the best-suited HVAC system depends on factors such as cost and availability of the energy source; appliance or system efficiency; cost to purchase, install, and maintain the appliance or system; and environmental impacts associated with the fuel. Energy prices tend to vary somewhat by geographic location because of availability of fuel type and supply, market pressures, production capacity, weather, season, and politics. A common way to compare heating energy costs is by determining the delivered heating cost, expressed in consistent units (i.e., $/MMBtu or $/GJ), based on the cost of the fuel ($/unit), heating value of the fuel (HV), and seasonal efficiency of the system or appliance (hs) expressed in decimal form (i.e., 80% = 0.80): Delivered Heating Cost ($/MMBtu) = ($/unit 1 000 000 Btu/MMBtu)/( hs HV) Delivered Heating Cost ($/GJ) = ($/unit 1 000 000 kJ/GJ)/( hs HV) 18. Compute the delivered heating cost ($/MMBtu) for a natural gas fired heating unit (i.e., furnace, boiler) based on a heating value of 103 000 Btu/CCF and a cost of $1.50/CCF. For an older, low-efficiency unit with a seasonal efficiency of 65%. For a modern, middle-efficiency unit with a seasonal efficiency of 80%. For a modern, high-efficiency unit with a seasonal efficiency of 96%. 19. A school district is considering heating systems for a high school anticipated to have an annual heating load of 6200 MMBtu/year. Compute the annual cost of heating the building with these systems: An electric-resistance boiler with a seasonal efficiency of 100% that is electrically powered with a heating value of 3413 Btu/kWh and a cost of $0.15/kWh. An air source heat pump system with a seasonal efficiency* of 150% that is electrically powered with a heating value of 3413 Btu/kWh and a cost of $0.15/kWh. A geothermal heat pump system with a seasonal efficiency* of 350% that is electrically powered with a heating value of 3413 Btu/kWh and a cost of $0.15/kWh. 20. A fan in a residential furnace is needed to move 1700 standard cfm (ft 3/min) of warm air at a temperature of 120F. The fan will be installed in a building at an elevation of 6000 ft above sea level. Approximate the required fan rating in standard cfm at this elevation and temperature. 21. At a mountain ski resort, a fan in an AHU is needed to move 15 000 standard cfm (ft 3/min) of warm air at a temperature of 120F. The fan will be installed in a building at an elevation of 5000 ft above sea level. Approximate the required fan rating in standard cfm at this elevation and temperature. 22. A large boiler is rated at 8000 MMBH heating output and will be installed at 5000 ft above sea level. Approximate its actual Btu/hr output at this elevation. 23. An air-cooled condenser is rated at 40 tons will be installed at an elevation of 5000 ft (1640 m) above sea level. The manufacturer advises a correction factor of 0.89 at an altitude of 5000 ft (1640 m). Determine the condenser rating at this elevation. 24. The minimum required equivalent diameter of a duct is 16 in but is too deep for the ceiling clearance allowed by the architect's design. The vertical clearance available for ductwork is 12 in. Identify a cost-effective rectangular duct section that meets these clearance and equivalent diameter requirements. Assume the duct is not lined. 25. A 12 in diameter galvanized steel (smooth) straight duct section conveys air at 1000 ft 3/min. It is 100 ft long. Determine the pressure loss, in inches of w.c. Determine the average velocity of air flowing through the duct. Identify a cost-effective rectangular duct section with an equivalent pressure loss that has a side depth of 8 in. 26. A branch duct will convey air at a volumetric flow rate of 500 ft 3/min. The pressure loss available for this duct is 0.1 in w.c./100 ft. The duct is not lined. Identify the minimum diameter of a round duct. Identify a cost-effective rectangular duct section with an equivalent pressure loss that has a side depth of 8 in. 27. A 2 in 5 in 24 gauge-1-in steel tube convector (from Table 9.1) has an output of 860 Btu/hr per foot of tube at a fluid temperature of 200F. A classroom in an elementary school has a heating load of 17 850 Btu/hr. Determine the length of convector tube (in feet) needed to meet the load. At a flow rate of 1 gal/min (8.3 lb/min), determine the temperature of the water leaving the convector, if the water enters the convector at a temperature of 200F. 28. Electric baseboard heaters will be used to heat a room with a design heating load of 5050 Btu/hr. Identify the length of each of the following units (in feet) required to meet the load. Standard electric resistance baseboard convectors Series A high-output, electric resistance baseboard convectors Series B high-output, electric resistance baseboard convectors 29. For year-round heating applications (i.e., generating domestic and process hot water), solar collectors should be tilted at an angle relative to the horizontal plane that is approximately equal to the latitude angle. Determine the closest architectural roof slope (i.e., 4/12, 6/12, and so forth) related for the optimum collector tilt for year-round heating at the following locations: Fargo, North Dakota (47 north latitude) Columbus, Ohio (40 north latitude) Savannah, Georgia (32 north latitude) Miami, Florida (26 north latitude) Lihue, Hawaii (22 north latitude) 30. A small residence has a domestic hot water load of 90 gal/day at an 80F temperature rise. A solar system at the location of the residence can collect, store, and deliver about 1350 Btu/day per square foot of collector area. Approximate the collector area needed to fully meet this hot water load. Approximate the required storage tank capacity based on 1.5 gal of water for each ft 2 of collector area. 31. Approximate the passive solar glazing area requirements and solar savings fraction for a 2000 ft 2 residence in New York City, New York. Find the minimum and maximum solar collector (aperture) area. Estimate the solar savings fraction without night insulation for these the minimum and maximum solar collector (aperture) areas. Estimate the solar savings fraction with night insulation for these the minimum and maximum solar collector (aperture) areas. 32. A 4.5 m by 6.75 m master bedroom will be heated with a sun-tempered system. Determine the following: The maximum percentage of south-facing glass area that can be used to prevent overheating. The maximum area (m2) of south-facing glass area that can be used to prevent overheating. 33. A 6 m by 10 m room will be heated with a direct-gain system having a solar savings fraction of 40%. The collector (glass) area will be about 6.5 m 2. Determine the mass requirements for this system. For a 100 mm thick concrete floor For water storage 34. A 4.5 m by 6.25 m master bedroom will be heated with a thermal storage wall. It should have approximately 0.2 to 0.3 m2 of thermal mass wall surface per m2 of floor area being heated. Determine the following: The maximum percentage of south-facing glass area. The maximum area (m2) of south-facing glass area