2.4 The steam needs of a company are served by a steam boiler, which receives energy as heat from a combustion process. 6 GJ/h is available as heat output in the combustion process. 70% of this heating effect contributes to steam production. The efficiency of the steam boiler can be defined as (utilized heat effect in the form of mass flow of steam) (available heat output) steam in After adjustments to the system, the combustion efficiency goes up to 80%. a) How large is the utilized heating effect before the adjustments and what power requirement steam does the system have after the adjustments when the boiler is to deliver the same steam? inn,new b) During the year, the steam boiler is used for 4200 hours. How much energy is saved per year due to the adjustments? is: c) How much money is saved during a year due to the adjustments when the energy price is $0.0375/MJ? 2.1 A university campus has 30 classrooms and 300 offices. In each classroom, there are 16 fluorescent tubes that use 110 W of electrical power per fluorescent tube. The offices have two fluorescent tubes each, 110 W per fluorescent tube. The university is open 280 days a year. The classrooms and offices are not used for 6 hours per day, but the light is on all day. Assume that the electricity price is NOK 1.5/kWh. How much does the university save each year if all the lights are tumed off for the 6 hours, not even the classrooms or the offices are used? 2.2 Water is pumped from a lake to a large storage tank which is open to the atmosphere at the top. The water surface in the storage tank is 20 m above the water surface of the lake. The volume flow is 40 litres/s and 11.5 kW of electrical power is used to pump the water from the lake to the storage tank. Disregard losses in flow energy due to friction and from changes in the kinetic energy of the water. Use y=998 kg/m3 as the mass density for liquid water. a) Calculate the total efficiency of the pump-motor- the device. b) Calculate the pressure difference between inlet out outlet of the pump that is needed to pump the water up to the tank. 20 m Pump Storage tank 2.3 An electric motor with a maximum output of 75 hp (horse power, English: hp, horse power) on the axle has an efficiency of 91%. It will be replaced with a new motor, which has the same maximum shaft power, but an efficiency of 93.5%. The old engine is operating for 5200 hours per year at 80% of its maximum power (ie '80% load' or '80% load factor). The new engine must run with the same load and the same number of hours. a) How much electrical energy is saved per year by replacing the old one with the new motor? b) How much expenditure on electricity is saved by replacing the old with the new motor when the electricity price is NOK 1.5/kWh?

2.4 The steam needs of a company are served by a steam boiler, which receives energy as heat from a combustion process. 6 GJ/h is available as heat output in the combustion process. 70% of this heating effect contributes to steam production. The efficiency of the steam boiler can be defined as (utilized heat effect in the form of mass flow of steam) (available heat output) steam in After adjustments to the system, the combustion efficiency goes up to 80%. a) How large is the utilized heating effect before the adjustments and what power requirement steam does the system have after the adjustments when the boiler is to deliver the same steam? inn,new b) During the year, the steam boiler is used for 4200 hours. How much energy is saved per year due to the adjustments? is: c) How much money is saved during a year due to the adjustments when the energy price is $0.0375/MJ? 2.1 A university campus has 30 classrooms and 300 offices. In each classroom, there are 16 fluorescent tubes that use 110 W of electrical power per fluorescent tube. The offices have two fluorescent tubes each, 110 W per fluorescent tube. The university is open 280 days a year. The classrooms and offices are not used for 6 hours per day, but the light is on all day. Assume that the electricity price is NOK 1.5/kWh. How much does the university save each year if all the lights are tumed off for the 6 hours, not even the classrooms or the offices are used? 2.2 Water is pumped from a lake to a large storage tank which is open to the atmosphere at the top. The water surface in the storage tank is 20 m above the water surface of the lake. The volume flow is 40 litres/s and 11.5 kW of electrical power is used to pump the water from the lake to the storage tank. Disregard losses in flow energy due to friction and from changes in the kinetic energy of the water. Use y=998 kg/m3 as the mass density for liquid water. a) Calculate the total efficiency of the pump-motor- the device. b) Calculate the pressure difference between inlet out outlet of the pump that is needed to pump the water up to the tank. 20 m Pump Storage tank 2.3 An electric motor with a maximum output of 75 hp (horse power, English: hp, horse power) on the axle has an efficiency of 91%. It will be replaced with a new motor, which has the same maximum shaft power, but an efficiency of 93.5%. The old engine is operating for 5200 hours per year at 80% of its maximum power (ie '80% load' or '80% load factor). The new engine must run with the same load and the same number of hours. a) How much electrical energy is saved per year by replacing the old one with the new motor? b) How much expenditure on electricity is saved by replacing the old with the new motor when the electricity price is NOK 1.5/kWh?

Refrigeration and Air Conditioning Technology (MindTap Course List)

8th Edition

ISBN:9781305578296

Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Chapter42: Heat Gains And Heat Losses In Structures

Section: Chapter Questions

Problem 12RQ

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