Question

It is found that 40 kJ.s- of heat energy is lost from a building when the internal air temperature is maintained at 22°C and the outside air temperature is 6°C. (a) What is the overall rate of entropy generation? (b) To match this heat loss a heat pump is to be employed which extracts heat from an outside, under-ground heat source. Sketch the heat-pump system diagrammatically and show the heat pump cycle on a sketch of the pressure-enthalpy diagram relating the respective processes on the diagrams. (c) If the coefficient of performance of the heat-pump system is 2.3, calculate the electrical power consumption of the compressor required to drive the heat pump. (d) Estimate the rate of heat absorption from the external under-ground heat source. (e) R134a is to be used as the working fluid in the heat pump. The compressor output pressure and temperature is 7.5 bar and 39°C and the condenser outlet temperature is 30°C. Estimate the mass flow rate of the refrigerant to achieve the required heat output. (f) In 500 words or fewer, discuss the advantages and disadvantages of heat pumps compared to gas fired central heating for buildings.

Answer 1

Please refer to the attached images where i have shown the entropy generation calculation and other answers asked in the question. Do comment in case of any query and please up-vote this answer if you find it to be usefuk.

P.s We are provided a stipulated time period for solving a question, as per HOMEWORKLIB POLICY it is mandatory to attempt atleast first four sub questions. I have answered the first five. Sorry, for the inconvinience caused.

Ik Data provided: Temperature of outside air Ta= 66 =2494 Temperature of inade aur To = 22°c= 295k Heat energy lost ☺ - 40kh Sgen f so 40x (la To, ca :. nox (1/279 1293) 7.776X163 Itaget or 1.7761 Overall rate of entropy generation Sketch or heat pump. Qoot E Yalve Expanuon LLLLLLLL Evaporator 19 around source Cheat input) Din

* Ph diagram of heat pomp. P Qout 1 N Qin 3-2 2-1 (compresion procen) (Heat out) (4-3) (expansion Valve) (9-4) (Heat Inpot) Coeffichent of performance (cophap 2.3 COPHR- QH QH-QL OH HOHL Contuned 40 KI S Hork consumed by compresso ΟΥ 2:3 12.39 kw (d) Rate of heat absorption in QH - QL= 17-39 = work consumed 40 -14.39 22.61 kW

the red Rigua is going to be used worlling eisid Compresor prewore and temperature Coutlet) P2- 7.5bar T2 = 39°c. Condenser P2c7-Shar T3 = 30°C He are asked to find Plow rate. Now At the inlet of condenser, B2 7.Sbar & T2 = 39°C. from Bigya thermodynamie property table, by 277.51 kg kg. CA-13 table) At expt of condenser, P2= 7.5 bar. & Tz 306 At 7.5bar, T = 29 c. Since I3 7T The expt state is superheated. from A-13 table; he 267.27 جرملم Qus mi (hahz) 40= moo (277:51 – 267.27) 3.90625 kgle