# How to size a pressurized expansion tank?

367 views asked Mar 1, 2015

+1 vote

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