Question

6-104 A Camot heat pump is to be used to bcat a house and nutintain it at 25% in winter. On a day which the average outdoor temperature remains at about 2'C, the house is esti- mated to lose heat at a rate of 55,000 Jh. Iſ the heat pump consumes 4.8 kW of power while operating, determine (a) how long the heat pump ran on that day: (b) the toul heating costs, assuming an average price of 11e/kWh for clectricity: and (c) the heating cost for the same day if resistance bcat- ing is used instead of a heat pump. Answers (a) 5.90 h. tb $3.11 a $40.9 SAMO Jh 250 NAM E 20 FIGURE P.104

Answer 1

carnot heat pump! PH TH 25+273 248 cop - Z TH-TC 25-2 QH 298 23 W QH = 298 x 4.8= 62.19130435 kW 23 * Energy balance: 62.19130435 X 3660xt- 55000x24 t=5-89578 h a) t=5.9hr need to run the * The total input work is heat pump: pamp. system by W = 4.8x s. 983650 kJ = 4.885.9x3600 KI/3XS = 4.8*59*3600 kW.S 1 kw.h. = 4.8*5.9 *3600 x 3600 W = 4.885.9 knih Total hast, =4.8 xs-9)x0.11 = ($3:1152

2 The total input work is needed to run the system by resistance heating heating method: 55000 X24 KJ Wc KJ/xS - 24X55000 kW.h. - 24 * 55000 3600 Total cost, 24ననం 3600 * 0.11 $40.3