Hi.. I'm kinda confused with this one... i hope someone helps me here !A dryer operates for 60 hours/week, 50 weeks/year. It exhausts 200 kW/hr of heat and the value of energy is 6p/kWh. A heat exchanger with a 50% efficiency is put into the exhaust stream to recover a proportion of this heat. The installed cost of the heat exchanger is ?22,500. The heat exchanger pressure drop needs a 2 kW fan to overcome it, and the cost of electricity is 10p/kWh. (I have the final answer - but no luck getting it !! - 10 points to the one who gets it right with good enough explanation for me to understand :)Thanks !
You don't actually ask a question! But I can guess where the problem is going. Always carry the units along to help keep things straight. BTW, dryer is 200kW hr / hr or 200kW. Dryer operates = 50 wk/yr * 60 hr/wk = 3000 hr/yr Dryer cost = 3000 hr/yr * 200 kW * ?0.06/kWhr = ?36,000/yr Cost to operate heat exchanger: = 3000 hr/yr * 2 kW * ?0.10 /kWhr = ?600/yr The heat exchanger recovers: ?36,000/yr * 50% efficiency - ?600/yr = ?17,400/yr Now, if the question is payback period, it is: = ?22,500 / ?17,400/yr = 1.293 yr
