The ground temperature a few meters below the surface is fairly constant throughout the year and is near the average value of the air temperature. In areas in which the air temperature drops very low in the winter, the exterior unit of a heat pump designed for heating is sometimes buried underground in order to use the earth as a thermal reservoir. Why is it worthwhile to bury the heat exchanger, even if the underground unit costs more to purchaseand install than one above ground?

Solar energy is used for air conditioning a house. To maintain a pressurized water tank at 443 K solar radiation is allowed. At a particular time interval, 301kJ of heat is extracted from the house to maintain its temperature at 301K when the surroundings temperature is 310K. Consider the tank of water, the house and the surroundings as heat reservoirs, what is the minimum heat (in kJ ,2 decimal places) that must be extracted from the tank of water by any device built to accomplish the required cooling of the house. No other sources of energy are available.

A heat pump is used to maintain a house at a constant temperature of 23°C. The house is losing heat to the outside air through the walls and the windows at a rate of 85,000 kJ/h while the energy generated within the house from people, lights, and appliances amounts to 4000 kJ/h. For a COP of 3.2, determine the required power input to the heat pump.

A 68 kg cyclist is pedaling down the road at 15 km/h, using a total metabolic power of 480 W. A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy. As he cycles at a constant speed on level ground, at what rate is chemical energy being converted to thermal energy in his body, assuming a typical efficiency of 25% for the conversion of chemical energy to the mechanical energy of motion?A. 480 W             B. 360 W             C. 240 W            D. 120 W

You have just bought a Carnot refrigerator to keep your frozen vegetables frozen. If you intend to run your refrigerator between the cold temperature reservoir at -5°C (the inside of the box) and the high temperature reservoir at 26°C (your kitchen temperature) how much work will be needed to draw 15 J of heat from the cold reservoir?

A Carnot heat engine uses a hot reservoir consisting of a large amount of boiling water and a cold reservoir consisting of a large tub of ice and water. In 5 minutes of operation of the engine, the heat rejected by the engine melts a mass of ice equal to 3.25×10−2 kg. Throughout this problem use Lf=3.34×105J/kg for the heat of fusion for water. During this time, how much work W is performed by the engine?

The rate at which a resting person converts food energy is called one’s basal metabolic rate (BMR). Assume that the resulting internal energy leaves a person’s body by radiation and convection of dry air. When you jog, most of the food energy you burn above your BMR becomes internalenergy that would raise your body temperature if it were not eliminated. Assume that evaporation of perspiration is the mechanism for eliminating this energy. Suppose a person is jogging for “maximum fat burning,” converting food energy at the rate 400 kcal/h above his BMR, and putting out energy by work at the rate 60.0 W. Assume that the heat of evaporation of water at body temperature is equal to its heat of vaporization at 100°C. (a) Determine the hourly rate at which water must evaporate from his skin. (b) When you metabolize fat, the hydrogen atoms in the fat molecule are transferred to oxygen to form water. Assume that metabolism of 1.00 g of fat generates 9.00 kcal of energy and produces 1.00 g of…

A rigid tank contains a hot fluid that is cooled while being stirred by a paddle wheel. Initially, the internal energy of the fluid is 800 kJ. During the cooling process, the fluid loses 500 kJ of heat, and the paddle wheel does 100 kJ of work on the fluid. Determine the final internal energy of the fluid. Neglect the energy stored in the paddle wheel.

In a Styrofoam cup containing 60.0 grams of water at 87.6°C, a 13.9 gram sample of an unknown metal is put at 27.5°C.The water cools down and the metal warms up until thermal equilibrium is achieved at 64.3°C. Determine the specific heat potential of the unknown metal by assuming that all of the heat lost by the water is gained by the metal and that the cup is completely insulated. The specific heat capacity of water is 4.18 J/g/°C.