A heating system must maintain the interior of a building at 20°C during a period when the outside air temperature is 5°C and the heat transfer from the building through its roof and walls is 3 × 106 kJ. For this duty heat pumps are under consideration that would operate between the dwelling and
a. the ground at 15°C.
b. a pond at 10°C.
c. the outside air at 5°C.

Respuesta :

Answer:

a. W = 51,194.54 kJ

b. W = 102,390 kJ

c. W = 153,585 kJ

Explanation:

[tex](COP)_{HP} =\frac{Desired-effectx}{Work-done}= \frac{Q_{1} }{W} \\\\(COP)_{HP} =(COP)_{Ideal}\\\\\frac{Q1}{W} =\frac{T_{1} }{T_{1} -T_{2} }[/tex]

[tex]W=Q_{1} \frac{T_{1}-T_{2}  }{T_{1} }[/tex]

a. the ground at 15°C.

[tex]T_{1}[/tex]=20°C = 273 K + 20 = 293 K

[tex]T_{2}[/tex]=15°C = 273 K + 15 = 288 K

[tex]Q_{1}=3x10^{6} kJ[/tex]

[tex]W=3x10^{6} kJ \frac{293 K-288 K}{293 K}=3x10^{6} kJ \frac{5 K}{293 K}=3x10^{6} kJ x 0.017065}[/tex]

[tex]W = 0.051195x10^{6} kJ[/tex]

W = 51,194.54 kJ

b. a pond at 10°C.

[tex]T_{2}[/tex]=10°C = 273 K + 10 = 283 K

[tex]W=3x10^{6} kJ \frac{293 K-283 K}{293 K}=3x10^{6} kJ \frac{10 K}{293 K}=3x10^{6} kJ x 0.034130}[/tex]

[tex]W = 0.102390x10^{6} kJ[/tex]

W = 102,390 kJ

c. the outside air at 5°C.

[tex]T_{2}[/tex]=5°C = 273 K + 5 = 278 K

[tex]W=3x10^{6} kJ \frac{293 K-278 K}{293 K}=3x10^{6} kJ \frac{15 K}{293 K}=3x10^{6} kJ x 0.051195}[/tex]

[tex]W = 0.153585x10^{6} kJ[/tex]

W = 153,585 kJ

Hope this helps!

(a) For ground at 15°C, the input be "51194 kJ".

(b) For a pond at 10°C, the input be "1.06 × 10⁵ kJ".

(c) For outside air at 5°C, the input be "1.54 × 10⁵ kJ".

Heat and temperature

According to the question,

Temperature, T₁ = 293 K

                       T₂ = 288 K

Heat transfer, Q₁ = 3 × 10⁶ kJ

(a) Ground at 15°C

We know that,

→ [tex](COP)_{HP} = (COP)_{Ideal}[/tex]

              [tex]\frac{Q_1}{W} = \frac{T_1}{T_1-T_2}[/tex]

or,

The minimum theoretical net work input will be:

→ W = Q₁ × [tex]\frac{T_1-T_2}{T_1}[/tex]

By substituting the values,

      = 3 × 10⁶ × [tex]\frac{293-288}{293}[/tex]

      = 51194 kJ

(b) A pond at 10°C

Now,

→ W = Q₁ × [tex]\frac{T_1-T_2}{T_1}[/tex]

       = 3 × 10⁶ × [tex]\frac{293-283}{293}[/tex]

       = 1.06 × 10⁵ kJ

(c) The outside air at 5°C

→ W = Q₁ × [tex]\frac{T_1-T_2}{T_1}[/tex]

       = 3 × 10⁶ × [tex]\frac{293-278}{293}[/tex]

       = 1.54 × 10⁵ kJ

Thus the responses above are correct.

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https://brainly.com/question/19666326