A typical electric water heater has an efficiency of 95 percent and costs $350 a year to operate at a unit cost of electricity of $0.11/kWh. A typical heat pump-powered water heater has a COP of 3.3 but costs about $800 more to install. Determine how many years it will take for the heat pump water heater to pay for its cost differential from the energy it saves.

A heat engine has a total heat input of 1.3 kJ and a thermal efficiency of 35 percent. How much work will it produce?

A heat engine operates between two reservoirs at 8000 C and 200 C. One-half of the work output of the engine is used to drive a Carnot heat pump that removes heat from the cold surroundings at 20 C and transfers heat to a house maintained at 220 C. If the house is losing heat at a rate of 62,000 kJ/h, determine the minimum rate of heat supply to the heat engine required to keep the house at 220 C.

A nonpolluting power plant can be constructed using the temperature difference in the ocean. At the surface of the ocean in tropical climates, the average water temperature year-round is 30°C. At a depth of 305 m, the temperature is 5.4°C. Determine the maximum thermal efficiency of such a power plant.

A device collects energy from the sun's rays and produces a high temperature of 95 °C. A small heat engine then uses this as a high temperature reservoir and operates at an ambient temperature of 15 °C. What is the maximum possible thermal efficiency of this heat engine? After some improvements are made to the solar energy collector, the high temperature it produces is now Tnew. If it is given that the new maximum possible thermal efficiency of the heat engine is double the previous one, what is Tnew? (Assume that the ambient temperature stays the same)

The coefficient of performance of a residential heat pump is 1.6. Calculate the heating effect in kJ/s this heat pump will produce when it consumes 2 kW of electrical power.

Consider a building whose annual air-conditioning load is estimated to be 40,000 kWh in an area where the unit cost of electricity is RM0.10/kWh. Two air conditioners (Figure 2) are considered for the building. Air conditioner A has a seasonal average COP of 2.3 and costs RM5500 to purchase and install. Air conditioner B has a seasonal average COP of 3.6 and costs RM7000 to purchase and install. All else being equal, determine which air conditioner is a better buy. A Air cond. COP = 2.3 D Win House 40,000 kWh Figure 2 40,000 kWh B Air cond. COP = 3.6 Win

A refrigeration system uses a water-cooled condenser for rejecting the waste heat. The system absorbs heat from a space at 25°F at a rate of 21,000 Btu/h. Water enters the condenser at 65°F at a rate of 1.45 lbm/s. The COP of the system is estimated to be 1.9. Determine the power input to the system in kW.

A heat pump keeps the house at 20°C while the ambient (outside) temperature is 0°C. from the roof and The heat loss from the walls is 3000 kJ/h per degree temperature difference between the indoor and outdoor environment. Determine the minimum theoretical power in kW required to operate the heat pump.

THERMODYNAMICS