IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C Report, Date: 13.01.2009 η ………… water cooling gradation …………………… - ϑ wb ……..wet bulb temperature ……………….………°C Following the information in Recknagel Sprenger (1997/98) the water cooling gradation (η) can be calculated with the aid of the cooling tower operational data (M, m), the cooling tower constant (C K ) and the state of the ambient air at the location of the cooling tower. The important result is the return temperature of the cooling tower, which can be determined with the cooling ratio η. In a first step the relative minimum quantity of air (l min ) is determined with the aid of the diagram in Figure 3-3 and the state of the ambient air at the site. A typical state of the ambient air is assumed with ϑ w 1= 33 °C, and φ = 54% at noon on a sunny summer day. Out of the h,x-diagram the wet bulb temperature can be determined with 16,5 °C. With the aid of the wet bulb temperature and Figure 3-3 now the relative minimum quantity of air can be found. 1,6 air water ) kg kg ( relative minimum air quantity, l min 1,4 1,2 1,0 0,8 0,6 θ w1 = 20 °C 30 °C 40 °C 50 °C cooling water temperature no water cooling in cooling tower θ wb > θ w1 0,4 6 10 15 16,5 20 25 30 wet bulb temperature, ,°C θ wb Figure 3-3: Relative minimum quantity of air (Recknagel Sprenger, 1997/98) The relative minimum air quantity is determined with l min = 1,0 For the further calculations the equations below are used: M l = min min m (3.3) page 21
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C Report, Date: 13.01.2009 M l 0 = (3.4) m l = l 0 λ (3.5) min l min ……………relative minimum air quantity……… ………………….…..- M min …………..minimum air quantity, corresponding to (h2 – h1) ………kg/s ( M min is the minimum air quantity for an ideal cooling tower to cool down the water from ϑ w1 to ϑ wb l 0 …………….. relative real air quantity ………..…………………………..- M ……………..real air quantity ……………………………………………kg/s λ .……………. air ration of a wet cooling tower ………… ……………. – The next step is the calculation of the cooling tower constant. This can be managed by a relation between the water cooling gradation and the air ratio. Equation 3.6 shows this. −λ η = C k ∗ (1 − e ) ………………………………………………………………………………..3.6 C k ……………...cooling tower constant ……………………………..………- C k can be determined by a diagram which is provided by the cooling tower producers and is shown in Figure 3-4 The water cooling gradation (η) can now be read out of the diagram in Figure 3-5 page 22
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- Page 614 and 615: Grundprinzip Solare Wärme thermisc
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<strong>IEA</strong> SHC Task 38 <strong>Solar</strong> Air Conditioning <strong>and</strong> Refriger<strong>at</strong>ion Subtask C Report, D<strong>at</strong>e: 13.01.2009<br />
M<br />
l<br />
0<br />
=<br />
(3.4)<br />
m<br />
l<br />
=<br />
l<br />
0<br />
λ (3.5)<br />
min<br />
l<br />
min<br />
……………rel<strong>at</strong>ive minimum air quantity……… ………………….…..-<br />
M<br />
min<br />
…………..minimum air quantity, corresponding to (h2 – h1) ………kg/s<br />
( M<br />
min<br />
is the minimum air quantity for an ideal cooling tower<br />
to cool down the w<strong>at</strong>er from ϑ<br />
w1<br />
to ϑ<br />
wb<br />
l<br />
0<br />
…………….. rel<strong>at</strong>ive real air quantity ………..…………………………..-<br />
M ……………..real air quantity ……………………………………………kg/s<br />
λ .……………. air r<strong>at</strong>ion of a wet cooling tower ………… ……………. –<br />
The next step is the calcul<strong>at</strong>ion of the cooling tower constant. This can be managed by a<br />
rel<strong>at</strong>ion between the w<strong>at</strong>er cooling grad<strong>at</strong>ion <strong>and</strong> the air r<strong>at</strong>io. Equ<strong>at</strong>ion 3.6 shows this.<br />
−λ<br />
η = C k<br />
∗ (1 − e ) ………………………………………………………………………………..3.6<br />
C<br />
k<br />
……………...cooling tower constant ……………………………..………-<br />
C k can be determined by a diagram which is provided by the cooling tower producers <strong>and</strong> is<br />
shown in Figure 3-4<br />
The w<strong>at</strong>er cooling grad<strong>at</strong>ion (η) can now be read out of the diagram in Figure 3-5<br />
page 22
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