ENGY 670 – Assignment 1 Section 1: Due Feb 25th, 2019 Section 2: Due Feb 27th, 2019 Total Marks: 50 1/ A Water Cooling Coil (fan coil unit) has air and water flowing in and out of it. Heat is transferred from the air to the water flowing through the fan coil unit. The unit provides 2 Ton of cooling to the air. (Air: 1.2 kg/m3, 1 kJ/kgK, Water: 1000 kg/m3, 4.2 kJ/kgK) The operating information is: i/ water flow rate through the unit = 15 litres/minute. ii/ input water temperature = 6ºC iii/ inlet air temperature = 30ºC iv/ air flow rate is 800 CFM a/ Write a heat balance equation for the energy flowing in and out. Then calculate the water temperature exiting the unit. (5 marks) b/ What is the air exit temperature? (5 marks) Air Out Water Out Fan Coil Unit Water In Air In 2/ Central Canada has experience extremely cold temperatures this winter. For the person in the picture below, explain how she is losing heat through the following modes of heat transfer: (5 marks) 1. 2. 3. 4. 5. Forced Convection Natural Convection Conduction Radiation Mass Transfer 3/ A building has a fan that provides fresh air from 7am to 5pm, which is turned off at night. The fan is driven by a 2 HP motor. How much energy would this fan consume in a year (in MJ), and what would the daily energy cost to run the fan if electricity costs $0.15/kWh? (4 marks) 4/ A wall is made up of 2” x 6” studs (18” OC) with R-19 batt insulation. There is ½” of plywood on the outside, and 12 mm of gypsum on the inside. a/ The studs act as a thermal bridge allowing more heat loss than if there was simply insulation in the walls. Determine how thick a layer of mineral wool board (MWB) insulation would need to be placed on the outside of the wall such that the resulting total wall Rvalue was R-30. (5 marks) MWB: ? Plywood: ½ inches Batt Insulation: R-19 Gypsum: 12 mm Other data for kstud = kply MWB: kgypsum Toutside, avg. Vwind Troom Wall area hin ho the wall is: 0.12 W/m.K R-4/inch 0.16 W/m.K 8ºC 4.5 m/s 22ºC 6 m2 7 W/m2.K 22 W/m2.K 4b/ If the average annual outdoor temperature is 2ºC, and the room temperature is maintained at 20ºC, how much energy will be lost through the wall in a year? (4 marks) 4c/ What is the room-side surface temperature of the wall on a cold night when it is -20 ºC outside? (4 marks) 5/ Five pounds per minute of Refrigerant 12 is compressed from 170 psig to 225 psig at a constant temperature of 450ºF in a steady flow device. a/ Determine the amount of work required to compress the gas. (4 marks) Atmospheric pressure = 14.6 psia. R freon = 12.8 ft ⋅ lbf lbm ⋅ ° R 5 b/ If the compressor is 98% efficient, what would it cost to run the compressor around the clock for 365 days if electricity costs $0.15/kWh? (3 marks) 6. A 2,500 ft2 house was built to the Passive House standard, and achieved a modelled heating load of 14 kWh/m2. a) How much energy would be consumed by the following heating systems to provide the 14 kWh/m2 of heat (3 marks): • • • 85% efficient gas furnace 95% high efficiency condensing furnace 100% efficient electric baseboard heaters b) If a ground-source heat pump was used to heat the Passive House that had a seasonal coefficient of performance of 2.7 how much energy would be consumed? (3 marks) 7/ You are asked to do an energy audit of an arena. For the following peak power conditions: • Rink Ceiling Area = 25 m x 65 m • Normal ceiling emissivity = 0.9 (ice emissivity of 0.97) • Maximum Ceiling Temperature = 28ºC How many tons of cooling capacity can be reduced by installing a radiative cover on the ceiling with an emissivity of 0.05? (5 marks) 8/ You place 5 L of water in a closed pot of water on a 1.5 kW heating element. Only 90% of heat heating element’s heat goes into the pot, and of that 85% goes into the water, with the rest of the heat going to the pot, and to heat loss to the room. The water temperature starts at 10ºC. You want to poach some eggs, which the recipe calls for a water temperature of 75ºC. How long will it take for your water to get to the right temperature, and how much energy will the heating element have consumed? (5 marks)
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