Thermal Component Design Heat pump water heaters are serious

Thermal Component Design

Heat pump water heaters are seriously considered to replace the electrical resistance water heaters typically employed in many buildings including residential buildings. For buildings such as hospitals, restaurants, campuses, military barracks, and many industries, there exists a large amounts of waste water leaving at high temperatures. By using a heat pump water heater, one can recover energy from the waste water streams and pick up heat energy at high temperatures from the condenser of the heat pump. Compare the cost of producing the hot water by use of heat pump water heaters compared to that from gas water heaters, and resistance water heaters. Write a report with an executive summary. The guidelines for writing the executive summary is as shown on the other side of the page. Check pay-back period of H.P water heater compared to others. Assume the following data: Gas is available at $ 0.75/therm with a gas heater efficiency of 85%. (cost: $ 6,000) Electrical resistance water heater (cost: $ 8,000) has efficiency of 100% and electricity costs $ 0.10/kWh Hot water requirements: 5000 gallons/day at temperatures of 150 degree F with city water supplied at 70 degree F. Cost of Heat Pump water heater: $ 18000 including the storage tank, with heat loss from storage tank 5% hot water heat supply. You might assume heat pump operating between the pressures of 70 and 300 psia and waste water is available at 85 degree with an isentropic efficiency of 85 percent and T_2 = 90 degree F

Solution

COP(Heat Pump)= (Tmax)/((Tmax) - (Tmin)) = 338.706 / (338.706 - 294.261) = 7.62078974

T3 = T2 = 302.594 K

T1\'= T2 * (p1/p2)^((y-1)/y)

y=1.4

p1=70psi

p2=300psi

T1\' = 199.6669471 K

T1 = T2 - (T2 -T1)* (Nisentropic efficiency)

T1= 215.096655 K

Note: Farenheit to Kelvin

Conversion factor = 8.5359375

COP = Heating effect / Work done

m= 5000 gallons / day

gallon to cubic metre

m = 0.000219063 cubic metre/ second

Work done = 0.000219063 * (Tmax - T1)= 0.027078257 W

Heating effect = COP * Work done = 0.206357703 W

Cost = USD 0.7428877308/ KWh

There is 5% heat loss

Cost (New)=USD 0.705743344/ KWh

Therefore, Heating effect (New) HP Water heater = 25505.02269KWh

Heating effect of Gas heater = 234400.9 KWh

Heating effect of electric resistance water heater = 80000 KWh

With the same Cost HP Water heater give highest heating effect.

The order is as follow:

Heating effect with same cost.

HP Water heater < Electric resistance water heater < Gas Water heater