A heat pump with a coefficient of performance of 3.5 provides energy at an average rate of 70,000 kJ/h to maintain a building at 20 deg C on a day when the outside temperature is -5 deg C. If electricity costs 8.5 cents per kWh, (a) determine the actual operating cost and the minimum theoretical operating cost, each in $/day. (b) compare the results of part (a) with the cost of electrical-resistance heating.

A heat pump with a coefficient of performance of 3.5 provides energy at an average rate of 70,000 kJ/h to maintain a building at 20 deg C on a day when the outside temperature is -5 deg C. If electricity costs 8.5 cents per kWh, (a) determine the actual operating cost and the minimum theoretical operating cost, each in $/day. (b) compare the results of part (a) with the cost of electrical-resistance heating.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.46P

See similar textbooks

Similar questions

In your own words, define efficiency as it applies to a device designed to perform an energy transformation.
A house is to be maintained at 20°C when the outside air is at -25°C. It is determined that 1800 kJ is required each minute to accomplish this.f an electric heat pump is used to supply this energy, determine the minimum theoretical work input for one day of operation, in kJ/day.Evaluating electricity at 13 cents per kWh, determine the minimum theoretical cost to operate the heat pump, in $/day. ($1 = 100 cents).f a heat pump whose coefficient of performance is 3.0 provides the required heating, determine the operating cost, in $/day
A heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 7 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min.(a) Determine the coefficient of performance.(b) Evaluating electricity at $0.08 per kW · h, determine the cost of electricity in a month when the heat pump operates for 300 hours.
A Carnot refrigerator absorbs heat from a space at 15°C at a rate of 16,000 kJ/h and rejects heat to a reservoir at 36°C. Determine the COP of the refrigerator, the power input, in kW, and the rate of heat rejected to high-temperature reservoir, in kJ/h.
A house is to be maintained at 20°C when the outside air is at -25°C. It is determined that 1800 kJ is required each minute to accomplish this.If an electric heat pump is used to supply this energy, determine the minimum theoretical work input for one day of operation, in kJ/day. Evaluating electricity at 13 cents per kWh, determine the minimum theoretical cost to operate the heat pump, in $/day. ($1 = 100 cents)If a heat pump whose coefficient of performance is 3.0 provides the required heating, determine the operating cost, in $/day
A heat pump cycle delivers energy by heat transfer to a dwelling at a rate of 40,000 Btu/h. The coefficient of performance of the cycle is 2.8. Evaluating electricity at $0.085 per kW•h, determine the cost of electricity during the heating season when the heat pump operates for 2000 hours.
By removing energy by heat transfer from a room, a window air conditioner maintains the room at 20°C on a day when the outside temperature is 28°C.(a) Determine, in kW per kW of cooling, the minimum theoretical power required by the air conditioner.(b) To achieve required rates of heat transfer with practical sized units, air conditioners typically receive energy by heat transfer at a temperature below that of the room being cooled and discharge energy by heat transfer at a temperature above that of the surroundings. Consider the effect of this by determining the minimum theoretical power, in kW per kW of cooling, required when TC = 16°C and TH = 32°C, and determine the ratio of the power for part (b) to the power for part (a).
A heating system must maintain the interior of a building at TH = 20°C when the outside temperature is TC = 2°C. If the rate of heat transfer from the building through its walls and roof is 16.4 kW, determine the electrical power required, in kW, to heat the building using (a) electrical-resistance heating, (b) a heat pump whose coefficient of performance is 3.0, (c) a reversible heat pump operating between hot and cold reservoirs at 20°C and 2°C, respectively.
1. A cooling tower has an efficiency of 65%. Water enters the tower at 55°C. The wet bulb temperature of surrounding air is 27°C. What is the temperature of water leaving the tower? a. 36.8°C b. 44.5°C c. 46.9°C d. 30.4°C 2. The change of temperature entering the cooling tower and wet bulb temperature of surrounding air is 25°C and efficiency is 65%. If mass of water leaving the tower is 10 kg/s, determine the heat carried by air. a. 720 kW b. 540 kW c. 680 kW d. 700 kW 3. The approach and efficiency of cooling tower is 10°C and 60%, respectively. If temperature of water leaving the tower is 37°C, what is the temperature of water entering? a. 46°C b. 52°C c. 68°C d. 48°C 4. A cooling tower is used to cool a jacket water loss from the engine. The heat generated by fuel is 2,500 kW and cooling loss is 30%. If temperature range of the tower is 15°C. Determine the mass flow of water entering the tower. a. 12 kg/s b. 14 kg/s c. 16 kg/s d. 18 kg/s
At steady state, a heat pump provides energy by heat transfer at the rate of 25,000 Btu/h to maintain a dwelling at 70°F on a day when the outside temperature is 30°F. The power input to the heat pump is 4.5 hp.Determine:(a) the coefficient of performance of the heat pump.(b) the coefficient of performance of a reversible heat pump operating between hot and cold reservoirs at 70°F and 30°F, respectively, and the corresponding rate at which energy would be provided by heat transfer to the dwelling for a power input of 4.5 hp.
A 30-kW motor drives a fan and delivers air through a duct 1.0 m x 1.0 m at 11.684 cm WG static pressure and 2.159 cm WG velocity pressure. The density of air is 1.20 kg/m³ and the density of water is 1000 kg/m³. Determine: 2. The capacity of fan, m3/s 3. Fan efficiency, %
The maximum thermal efficiency possible for a power cycle operating between 1096°F and 267°F is _____. Express in four significant figures, not in percentage.