You need a rented apartment and you can see that the 3rd floors of each of the 2, 3 and 4 blocks of the buildings built in adjacent order as shown in the figure (front side) are for rent. You also learn that Block 2 is heated by a coal boiler operating at 75% efficiency, Block 3 is heated by a natural gas boiler operating at 92% efficiency, while Block 4 is heated by a heat pump with a COP of 4.5. All three blocks, as you know that the heating process takes place uninterruptedly for 150 days, the inside of the apartment is constantly constant at 22 ℃ for 150 days, the outside temperature is average ?∞ = 0 ℃ and the wind speed is average ∞ = 5 ? / ? Find the total heating cost for. Take the average heat transfer coefficient in the circle as ℎ?ç = 10 ? / ?2?, and the thermal resistance of the wall as ? wall = 1 ?2? / ?. Assume that heat is lost only from the front and back of the blocks. Also take the unit price of electricity as 0.71 TL / kWh, the unit price of natural gas as 0.14 TL / kWh, and the unit price of coal as 0.1 TL / kWh. (L1=15meter,L2=30 meter,L3=45 meter,L4=60 meter , 3.floor, H=4 meter
Firstly, we shall calculate the average heat transfer coefficient of outside air.
It is given that only 3 blocks add heat to the outside air, therefore, the total length of blocks through which heat is added to the outside air is 15 + 15 + 15 = 45 m
This can be considered as the vertical plate subjected to forced convection.
So, first, we will calculate the Reynold's number of the flow.
where
The FLOW IS TURBULENT.
From the heat transfer data book, the appropriate Nusselt's Number relation is as follows:
where
Now, we know,
where
Now, for all the heat producing blocks, the following thermal resistances occur in series:
-----
Internal convection (R1)
Thermal resistance =
where
Thermal resistance =
-----
Conduction through wall (R2)
Thermal resistance =
where
Thermal resistance =
-----
External convection (R3)
Thermal resistance =
where
Thermal resistance =
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So, heat required from one wall =
where
Now, the building has 3 front facing walls and 3 rear facing walls.
Therefore, net heat lost from ONE floor of ONE block is 1105.534 x 2 = 2211.067 W
Now, the following table applies:
Block 2 | Block 3 | Block 4 | |
Net heat loss rate | 2211.067 W | 2211.067 W | 2211.067 W |
Heating medium | Coal Boiler | Natural gas | Heat pump |
Efficiency/COP | 0.75 | 0.92 | 4.5 |
Actual energy input | 2211.067 / 0.75 = 2948.089 W | 2211.067 / 0.92 = 2403.333 W | 2211.067 / 4.5 = 491.348 W |
No. of days working | 150 | 150 | 150 |
Total energy consumption | 3.8207e10 J | 3.1147e10 J | 6367872960 J |
No of kWh | 10613.055 | 8651.944 | 1768.854 |
Unit cost | 0.1$ / kWh | 0.14 $ / kWh | 0.71 $ / kWh |
Net cost | 1061.306 $ | 1211.273 $ | 1255.89 $ |
TOTAL COST | $ 3528.465 / 150 DAYS |
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You need a rented apartment and you can see that the 3rd floors of each of...