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How to size a pressurized expansion tank?

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366 views asked Mar 1, 2015 by Devan Talebi

1 Answer

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Pressurized Tank Sizing (Bladder & Diaphragm): 

The tank is charged to a pre-determined pressure resulting in Pa = Pf, thus:

                     Vt = EVs / (1-(Pf/Po))

  Vt = Compression Tank Size (gal) 
  Vs = Total System Water Volume (gal) (in pipes, coils, etc.) 
  Pf = Minimum System Pressure (Fill Pressure, psia) 
            This is building static pressure over the tank +14.7 psia, atmospheric pressure + 5 psig for venting). 
  Po = Maximum System Pressure (relief Valve Pressure, psia) 

  E = Net Water Expansion Factor (Refer to Table 1 for water and Table 2 for glycol-water) 
    To use Table 1 and 2 the mean temperature is required (160-200℉ for hot water,100℉ for chilled water) 

*The term of EVs is called Acceptance Volume. Vt is the Tank Volume. 

Thank size must satisfy two conditions:

 The volume of the tank must be large enough so that the system operates within the range of the fill pressure and the relief valve setting.

 The tank’s Acceptance Volume must be at least as large as the system’s Expansion Volume.                    

Table 1

Temperature ℉

Factor

Temperature ℉

Factor

Temperature ℉

Factor

100

0.0057

155

0.0198

210

0.0391

105

0.0068

160

0.0208

215

0.0415

110

0.0080

165

0.0225

220

0.0433

115

0.0092

170

0.0243

225

0.0457

120

0.0097

175

0.0261

230

0.0475

125

0.0115

180

0.0279

235

0.0505

130

0.126

185

0.0296

240

0.0523

135

0.0138

190

0.0314

245

0.0547

140

0.0149

195

0.0332

250

0.0571

145

0.0167

200

0.0350

255

0.0595

150

0.0178

205

0.0374

 

 

 

Table 2                                 Temperature ℉

Type

% By volume

Approx. Freeze Temp.℉

100

110

120

130

140

150

160

180

200

220

240

250

Ethylene Glycol

10

20

30

40

50

25

16

4

-13

-35

1.70

1.75

1.96

2.06

2.24

1.47

1.54

1.68

1.77

1.91

1.46

1.51

1.66

1.75

1.88

1.31

1.38

1.49

1.56

1.67

1.28

1.29

1.38

1.45

1.55

1.24

1.29

1.38

1.45

1.55

1.20

1.25

1.35

1.41

1.49

1.13

1.18

1.25

1.31

1.38

1

1.15

1.22

1.27

1.34

1.08

1.12

1.18

1.23

1.29

1.06

1.10

1.15

1.20

1.25

1.05

1.09

1.14

1.19

1.24

Propylene Glycol

10

20

30

40

50

26

18

8

-7

-28

1.76

2.07

2.42

2.61

2.87

1.53

1.70

2.08

2.25

2.47

1.52

1.76

2.05

2.19

2.42

1.37

1.58

1.83

1.96

2.15

1.34

1.55

1.77

1.90

2.07

1.29

1.47

1.68

1.81

1.97

1.26

1.43

1.63

1.75

1.90

1.18

1.34

1.50

1.62

1.75

1.16

1.30

1.46

1.56

1.68

1.12

1.28

1.40

1.50

1.61

1.11

1.24

1.37

1.46

1.57

1.10

1.23

1.35

1.45

1.55

answered Mar 1, 2015 by Devan Talebi

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