Expansion Tank Sizing Calculation Hydronic System

Expansion Tank EasyCalc

Job no.: Date Prep. 5/6/2013

For Closed Tanks with air/water interface: Equation (12) (Sometimes called a plain steel tank)

Open Tanks with air/water interface: (i.e., A tank open to the atmosphere & must be Equation (13)

located above the highest point in the system)

For Diaphragm Tanks: (Flexible membrane between the air & the water. Equation (14)

Another configuration is the bladder tank)

REQUIRED DATA FOR CALCULATIONS Data Entry

Where: Site Altitude-Elevation (m) 0 Closed Open Diaphragm

V t = vol.of expansion tank, gal (Closed, Open, Diaph) 39 Temp T2 Hi 144

V s = volume of water in system, gallons 3000 3000 3000 3000

t 1 = lower temperature, F 40 40 40 40

t 2 = higher temperature, F 220 220 220 220

P a = atm.pres.psia (14.696 psia at sea level) 14.696 14.696 not reqrd. not reqrd.

P 1 = pressure at lower temperature, psia 4.0 4.0 not reqrd. 4.0

P 2 = pressure at higher temperature, psia 39.7 39.7 not reqrd. 39.7

v 1 = specific vol.of water at lower temp., ft3/lb 0.01602 0.01602 0.01602 0.01602

v 2 = specific vol.of water at higher temp. ft3/lb 0.01677 0.01677 0.01677 0.01677

t = (t2t1),F, temperature differential 180 180 180 180

= linear coef.of thermal expansion, in/in-F 6.50E-06 6.50E-06 6.50E-06 6.50E-06( equals to 6.5 10

6 in/in-F for steel or 9.5 10

6 in/in-F for copper)

`

Water Volume in Hydronic System Components (Cooling or Heating)

System Vol. of Water in System

Hydronic Components Capacity Liters Gallons

Piping Distribution System 11356.25 3000.00

0.0057 Liters

Total Lps

1.2 Liters

Total Tons

0.7 Liters

Total Tons

1.9 Liters

Total Kw

2 Liters

Tot. m2

of H.S

Total 11356.25 3000.00

Plus safety factor for other components, fittings etc. (%) 0.0% - -

11356 3000

Liters Gallons

EasyCalc Software Email Address

Grand Total Volume of Water in System

Radiators

Chillers

-Boilers -

-

-

per m2 of Heat Surface

per Kw

per lps of airflowFan Coils

Expansion Tank Calculation

- -

HYDRONIC SYSTEM EXPANSION TANK CALCULATION(c) 2000 ASHRAE Handbook, HVAC Systems & Equipment, Hydronic Heating & Cooling System Design, Chap.12

MODA GDMW, Engineering Design Branch, Developed by: Edgar I. Lim, EasyCalc Software

Equations for Sizing Expansion Tanks:

Air Handling Units

per Ton of Refrigeration

Equipment Data (Sys. Components)

Water Content

-

-

-

per Ton of Refrigeration-

eil software 2008 1 Expansion Tank EasyCalc


aTable 2 Steel Pipe Data (excerpts) (c) 2000 ASHRAE Hndbk, Chap.40 HVAC Sys.& Equipment

Nom. Pipe Size Pipe Length Flow Area.a

Liters per Water Vol. Water Vol.

Inch mm meters mm2 Lineal meter Liters Gallons

1/2" 15 4.25 196 0.196 0.8 0.2

3/4" 20 344 0.344 - -

1" 25 557.6 0.558 - -

1-1/4" 32 965 0.965 - -

1-1/2" 40 19 1313 1.313 24.9 6.6

2" 50 333 2165 2.165 720.9 190.5

2-1/2" 65 3089 3.089 - -

3" 75 4769 4.769 - -

4" 100 8213 8.213 - -

5" 125 822 12907 12.907 10609.5 2802.7

6" 150 18639 18.639 - -

8" 200 32280 32.280 - -

10" 250 50870 50.870 - -

12" 300 72190 72.190 - -

14" 350 87290 87.290 - -

16" 400 114000 114.000 - -

18" 450 144300 144.300 - -

20" 500 179400 179.400 - -

11356.25 3000.00

Liters Gallons

NOTES:

(c) 2000 ASHRAE Handbook, HVAC Systems & Equipment, Hydronic Heating & Cooling System Design, Chap.12

Low-temperature water (LTW) system. Medium-temperature water (MTW) system.

Max. allowable working pres. for low-pres. boilers is Operates at temperatures between 250 & 350F,

160 psig,with a max. temp. limitation of 250F. with pressures not exceeding 160 psi.

Usual max. working pres. for boilers for LTW Usual design supply temperature is approx. 250 to 325F,

systems is 30 psi with a usual pres.rating of 150 psi for boilers & equipment.

High-temperature water (HTW) system. Chilled water (CW) system.

Operates at temp. over 350F & usual pressures Normally operates w/ design supply water temp.of 40 to

of about 300 psi. 55F, usually 44 or 45F, & at a pres. of up to 120 psi.

Max. design supply water temp.is usually about 400F,

w/ a pres.rating for boilers & equipt. of about 300 psi

The connected piping in hydronic systems is subject to expansion & contraction due to changes in system temp. especially during

initial system fill. Expansion tanks (or compression tanks) are required to protect against thermal expansion of the piping system

due to temperature rise. During initial fill the piping system could experience the largest thermal expansion.

In good design practice, in order to reduce the size of the expansion tank, it is preferred to install the tank before the system pump.

The size of the tank can also be reduced when the tank is installed at the highest point of the piping system where the pressure is

the lowest.

As an example, the lower temp. for a heating system is usually normal ambient temp. at fill conditions (e.g., 50F) & the higher

temp. is the operating supply water temp. for the system. For a chilled water system, the lower temp. is the design chilled water

supply temp., & the higher temp. is ambient temp. (e.g., 95F or 115oF for KSA hot areas). For a dual-temp. hot/chilled system,

the lower temp. is the chilled water design supply temp., & the higher temp. is the heating water design supply temperature.

Pressures at the expansion tank are generally set by the following parameters:

1) The lower pressure is usually selected to hold a positive pressure at the highest point in the system (usually about 10 psig

or 24.696 psia).

2) The higher pres. is normally set by the max. pres. allowable at the location of the safety relief valve(s) without opening them.

Other considerations are to ensure that (1) the pres. at no point in the system will ever drop below the saturation pres. at the

operating system temp. and (2) all pumps have sufficient net positive suction head (NPSH) available to prevent cavitations.

Total water volume in distribution pipe works

Water Volume Calculation in System Distribution Pipe Works



Enable/Disable notes on page 2 above yes

Example Calculation of Expansion Tanks From 2000 ASHRAE Handbook, HVAC Systems & Equipment, Chap. 12

Example 1. Size an expansion tank for a heating water system that will be operated at a design temperature range of 180 to 220F.

The minimum pressure at the tank is 10 psig (24.7 psia) & the maximum pressure is 25 psig (39.7 psia). (Atmospheric pressure

is 14.7 psia.) The volume of water is 3000 gal. The piping is steel.

1. Calculate the required size for a closed tank (plain steel tank) with an air/water interface.

Solution: For lower temperature t 1 , use 40F

From Table 3 in Chap. 6 of the ASHRAE HandbookFundamentals, v1 at 40F = 0.01602 ft3/lb v2 at 220F = 0.01677 ft

3/lb

Users Entry

Data Page1

V s = 3000 Solution: Using Equation (12) , t 1 = 40 t 2 = 220 ASHRAE Data in Formula as per Example no.1)

P a = 14.696

P 1 = 4.0

P 2 = 39.7

v 1 = 0.01602

v 2 = 0.01677

t = 180 Answers: Volume of Diaphragm Expansion Tank

= 6.50E-06 V t = 578 Gallons (ASHRAE Data as per Example no.1)

V t = 39 V t = 39 Gallons ( User's Entries calculation at page 1)

Example 2. If a diaphragm tank were to be used in lieu of the plain steel tank, what tank size would be required?

Users Entry

Data Page1 Solution: Using Equation (14) ,V s = 3000

t 1 = 40 ASHRAE Data in Formula as per Example no.2)

t 2 = 220

P 1 = 4.000

P 2 = 39.7

v 1 = 0.01602

v 2 = 0.01677

t = 180 Answers: Volume of Diaphragm Expansion Tank

= 6.50E-06 V t = 344 Gallons (ASHRAE Data as per Example no.2)

V t = 144 V t = 144 Gallons ( User's Entries calculation at page 1)

EXPANSION TANK MINIMUM PRESSURE

The expansion tank must be pressurized to provide at least 4 psi (28 kPa) of positive pressure at the highest point in the

hydronic piping system. This will also ensure no air is drawn into the piping. The amount of charge pressure in pounds per

square inch (psi) that is required in the expansion tank is equal to 4 psi (28 kPa) plus the height (in feet) from the chiller

to the highest point in the hydronic system divided by 2.31.

Example: The expansion tank elev. is 10 feet. The hydronic system is piped to an air handler on the roof with an elevation

of 100 feet. The total pressure required in the expansion tank is:

4 psi + (100 ft 10 ft)/2.31 = 42.96 psi

Thus an expansion tank with a pre-charged pres. at 40 psi from factory will require an additional 3 psi pressure.

0.01677

344

ASHRAE Data

Example 2

ASHRAE Data

Example 2

578

180

6.50E-06

220

24.7

39.7

0.01602

3000

40

40

220

0.01677

180

6.50E-06

Given Data:

0.01602

24.7

39.7

3000

14.7

Given Data:



Boiler System Types: Common Boiler Design Pressures ( psig.)

1. Low Temperature Heating Water Systems: Add 14.696 to get absolute pressure at sea level.

a. 250F. &Less.

b. 160 psig maximum. 1. 15 Psig 6. 200 Psig

2. Medium Temperature Heating Water Systems: 2. 30 Psig 7. 250 Psig

a. 251350F. 3. 60 Psig 8. 300 Psig

b. 160 psig maximum. 4. 125 Psig 9. 350 Psig

3. High Temperature Heating Water Systems: 5. 150 Psig

a. 351450F.

b. 300 psig maximum.

EXPANSION TANKS COMMERCIAL LISTED SIZES (ARMSTRONG)

EXPANSION TANKS LISTED COMMERCIAL SIZES

liters gallons liters gallons liters gallons

29.5 200.6 53 56.8 15.0

41.3 302.8 80 90.8 24.0

82.1 401.3 106 113.6 30.0

127.2 499.7 132 151.4 40.0

168.1 598.1 158 227.1 60.0

210.8 798.7 211 302.8 80.0

257.4 999.3 264 378.5 100.0

291.5 1200.0 317 454.2 120.0

340.7 1400.6 370 511.0 135.0

416.4 1597.4 422 662.4 175.0

499.7 1998.7 528 832.8 220.0

601.9 2498.4 660 908.5 240.0

798.7 2998.0 792 1154.6 305.0

3997.4 1056 1116.7 295.0

1514.2 400.0

1911.6 505.0

1987.3 525.0

A. Class I Boilers. ASME Boiler &Pressure Vessel Code, Section I:

1. Steam Boilers, Greater than 15 Psig

2. Hot Water Boilers:

a. Greater than 160 Psig

b. Greater than 250F.

B. Class IV Boilers. ASME Boiler &Pressure Vessel Code, Section IV:

1. Steam Boilers, 15 psig &less

2. Hot Water Boilers:

a. 160 psi &less

b. 250F. &less

90.0

Diaphragm Tank Bladder Tank Configuration

7.8

10.9

21.7

77.0

Closed Tank

33.6

44.4

55.7

68.0

110.0

132.0

159.0

211.0



Hot Water Boilers Steam Boilers Chillers

A. Boiler Types: A. Boiler Types: A. Chiller Types:

1. Fire Tube Boilers: 1. Fire Tube Boilers: 1. Centrifugal:

a. 15800 BHP. a. 15800 BHP. a. 200 Tons &Larger.

b. 50026,780 MBH. b. 51827,600 Lb./Hr. b. 0.550.85 KW/Ton.

c. 30300 psig. c. 15300 psig. c. 4.146.39 COP.

2. Water Tube Boilers: 2. Water Tube Boilers: d. Turndown Ratio, 100% to 10%.

a. 3502,400 BHP. a. 3502,400 BHP. 2. Reciprocating:

b. 13,00082,800 MBH. b. 12,07582,800 Lb./Hr. a. 200 Tons &Smaller.

c. 30525 psig. c. 15525 psig. b. 0.901.30 KW/Ton.

3. Flexible Water Tube Boilers: 3. Flexible Water Tube Boilers: c. 2.703.90 COP.

a. 30250 BHP. a. 30250 BHP. d. Turndown Ratio, Staged or Stepped

b. 1,0008,370 MBH. b. 10,00082,000 Lb./Hr. based on nos of cyl.& unloadingcontrol.

c. 0150 psig. c. 15525 psig. 3. Rotary Screw:

4. Cast Iron Boilers: 4. Cast Iron Boilers: a. 501100 Tons.

a. 10400 BHP. a. 10400 BHP. b. 1.001.50 KW/Ton.

b. 34513,800 MBH. b. 1,0358,625 Lb./Hr. c. 2.343.50 COP.

c. 040 psig. c. 0150 psig. d. Turndown Ratio, 100% to 25%.

5. Modular Boilers: 5. Electric Boilers: 4. Absorption (Steam or Hot Water):

a. 4115 BHP. a. 155,000 KW. a. 100 Tons &Larger.

b. 1364,000 MBH. b. 5117,065 MBH. b. 18,750 Btuh/Ton; 0.64 COP 1-Stage.

c. 0150 psig. c. 0300 psig. c. 12,250 Btuh/Ton; 0.98 COP 2-Stage.

6. Electric Boilers: d. Turndown Ratio, 100% to 10%.

a. 155,000 KW. 5. Absorption (Gas or Oil):

b. 5117,065 MBH. a. 100 Tons & Larger.

c. 0300 psig. b. 11,720 Btuh/Ton; 1.02 COP Gas.

c. 12,440 Btuh/Ton; 0.96 COP Oil.

d. Turndown Ratio, 100% to 10%.

Low Temperature Heating Water Systems: Chilled Water Systems:

1. Leaving Water Temperature (LWT): 180200F. 1. Leaving Water Temperature (LWT): 4048F.

2. T Range 2040F. (60F.Maximum)

3. Low Temperature Water 250F. & less; 160 psig maximum 2. T Range 1020F.

Medium &High Temperature Heating Water Systems: Low Temperature Chilled Water Systems

1. Leaving Water Temperature (LWT): 350450F. (Glycol or Ice Water Systems)

2. T Range 20100F. 1. Leaving Water Temperature (LWT): 2040F.

3. Medium Temperature Water 251350F.; 160 psig maximum (0F. minimum)

4. High Temperature Water 351450F.; 300 psig maximum 2. T Range 2040F.

Dual Temperature Water System Types: Condenser Water Systems:

1. Leaving Cooling Water Temperature 4048F. 1. Entering Water Temperature (EWT): 85F.

2. Cooling T Range 1020F. 2. T Range 1020F.

3. Leaving Heating Water Temperature: 180200F. 3. Normal T 10F.

4. Heating T Range 2040F. Water Source Heat Pump Loop

1. Range: 6090F.

2. T Range 1015F.



AC Condensate Flow:

1. Range: 0.020.08 GPM/Ton 5. AHU (50% Outdoor Air): 0.065 GPM/1,000 CFM

2. Average: 0.04 GPM/Ton 6. AHU (25% Outdoor Air): 0.048 GPM/1,000 CFM

3. Unitary Packaged AC Equipment: 0.006 GPM/Ton 7. AHU (15% Outdoor Air): 0.041 GPM/1,000 CFM

4. AHU (100% outside Air): 0.100 GPM/1,000 CFM 8. AHU (0% Outdoor Air): 0.030 GPM/1,000 CFM

AC Condensate Pipe Sizing

1. Minimum Pipe Sizes are given in the following table.

AC Tons of Refrigeration 0-20 21-40 41-60 61-100 101-250 251 &Larger

Minimum Drain size (inch) 1" 1-1/4" 1-1/2" 2" 3" 4"

Expansion Tanks &Air Separators

A. Minimum (Fill) Pressure:

1. Height of System + (5 to 10 psi)

or 510 psi, whichever is greater.

B. Maximum (System) Pressure:

1. 150 Lb. Systems: 45125 psi

2. 250 Lb. Systems: 125225 psi

C. System Volume Estimate:

1. 12 Gal./Ton

2. 35 Gal./BHP

The sizing of low-temperature hot water pipes is usually based on a pressure drop of 1 to 3 ft per 100 ft of pipe length. For a small

low-temp. hot water heating system, an open-type expansion tank is often used. An open expansion tank has the disadvantage of

allowing air to enter the system via absorption in the water. A diaphragm tank is often used for a large system. On-line circulating

pumps with low head are often used.

Table 1 Standard Atmospheric Data Atmospheric Data Calculation

for Altitudes to 10 000 m For Different Altitudes

Altitude, Pressure, Altitude, Pressure,

m kPa psia m kPa psia

500 107.478 15.588 555 94.833 13.754

0 101.325 14.696

500 95.461 13.845

1 000 89.875 13.035

1 500 84.556 12.264

2 000 79.495 11.530

2 500 74.682 10.832

3 000 70.108 10.168

4 000 61.64 8.940

5 000 54.02 7.835

6 000 47.181 6.843

7 000 41.061 5.955

8 000 35.6 5.163

9 000 30.742 4.459

10 000 26.436 3.834

(c) 2005 ASHRAE Handbook, Fundamentals, Chapter 6



hydronic piping system. This will also ensure no air is drawn into the piping. The amount of charge pressure in pounds per

Thus an expansion tank with a pre-charged pres. at 40 psi from factory will require an additional 3 psi pressure.



1. Leaving Water Temperature (LWT): 4048F.

1. Leaving Water Temperature (LWT): 2040F.


ASHRAE Fundamentals

Table 3 Thermodynamic Properties of Water at Saturation

Temp., Specific Vol. Temp., Specific Vol. Temp., Specific Vol. Temp., Specific Vol. Temp., Specific Vol.

F ft3/lbw F ft

3/lbw F ft

3/lbw F ft

3/lbw F ft

3/lbw

32 0.01747 60 0.01604 88 0.01609 116 0.01619 144 0.01631

33 0.01602 61 0.01604 89 0.0161 117 0.01619 145 0.01632

34 0.01602 62 0.01604 90 0.0161 118 0.0162 146 0.01632

35 0.01602 63 0.01604 91 0.0161 119 0.0162 147 0.01633

36 0.01602 64 0.01604 92 0.01611 120 0.0162 148 0.01633

37 0.01602 65 0.01604 93 0.01611 121 0.01621 149 0.01634

38 0.01602 66 0.01604 94 0.01611 122 0.01621 150 0.01634

39 0.01602 67 0.01605 95 0.01612 123 0.01622 151 0.01635

40 0.01602 68 0.01605 96 0.01612 124 0.01622 152 0.01635

41 0.01602 69 0.01605 97 0.01612 125 0.01623 153 0.01636

42 0.01602 70 0.01605 98 0.01612 126 0.01623 154 0.01636

43 0.01602 71 0.01605 99 0.01613 127 0.01623 155 0.01637

44 0.01602 72 0.01606 100 0.01613 128 0.01624 156 0.01637

45 0.01602 73 0.01606 101 0.01613 129 0.01624 157 0.01638

46 0.01602 74 0.01606 102 0.01614 130 0.01625 158 0.01638

47 0.01602 75 0.01606 103 0.01614 131 0.01625 159 0.01639

48 0.01602 76 0.01606 104 0.01614 132 0.01626 160 0.01639

49 0.01602 77 0.01607 105 0.01615 133 0.01626 161 0.0164

50 0.01602 78 0.01607 106 0.01615 134 0.01627 162 0.0164

51 0.01602 79 0.01607 107 0.01616 135 0.01627 163 0.01641

52 0.01603 80 0.01607 108 0.01616 136 0.01627 164 0.01642

53 0.01603 81 0.01608 109 0.01616 137 0.01628 165 0.01642

54 0.01603 82 0.01608 110 0.01617 138 0.01628 166 0.01643

55 0.01603 83 0.01608 111 0.01617 139 0.01629 167 0.01643

56 0.01603 84 0.01608 112 0.01617 140 0.01629 168 0.01644

57 0.01603 85 0.01609 113 0.01618 141 0.0163 169 0.01644

58 0.01603 86 0.01609 114 0.01618 142 0.0163 170 0.01645

59 0.01603 87 0.01609 115 0.01619 143 0.01631 171 0.01646

172 0.01646 206 0.01667 270 0.01717 338 0.01785 415 0.01886

173 0.01647 207 0.01668 272 0.01719 340 0.01787 420 0.01894

174 0.01647 208 0.01669 274 0.01721 342 0.01789 425 0.01901

175 0.01648 209 0.01669 276 0.01722 344 0.01792 430 0.01909

176 0.01648 210 0.0167 278 0.01724 346 0.01794 435 0.01918

177 0.01649 212 0.01671 280 0.01726 348 0.01796 440 0.01926

178 0.0165 214 0.01673 282 0.01728 350 0.01799 445 0.01935

179 0.0165 216 0.01674 284 0.01730 352 0.01801 450 0.01943

180 0.01651 218 0.01676 286 0.01731 354 0.01804 455 0.01952

181 0.01651 220 0.01677 288 0.01733 356 0.01806 460 0.01961

182 0.01652 222 0.01679 290 0.01735 358 0.01808 465 0.01971

183 0.01653 224 0.0168 292 0.01737 360 0.01811 470 0.01980

184 0.01653 226 0.01682 294 0.01739 362 0.01813

185 0.01654 228 0.01683 296 0.01741 364 0.01816

186 0.01654 230 0.01684 298 0.01743 366 0.01818

187 0.01655 232 0.01686 300 0.01745 368 0.01821

188 0.01656 234 0.01688 302 0.01747 370 0.01823

189 0.01656 236 0.01689 304 0.01749 372 0.01826

190 0.01657 238 0.01691 306 0.01751 374 0.01828

191 0.01658 240 0.01692 308 0.01753 376 0.01831

192 0.01658 242 0.01694 310 0.01755 378 0.01834

193 0.01659 244 0.01695 312 0.01757 380 0.01836

194 0.01659 246 0.01697 314 0.01759 382 0.01839

195 0.0166 248 0.01698 316 0.01761 384 0.01842

196 0.01661 250 0.01700 318 0.01763 386 0.01844

197 0.01661 252 0.01702 320 0.01765 388 0.01847

198 0.01662 254 0.01703 322 0.01767 390 0.01850

199 0.01663 256 0.01705 324 0.01770 392 0.01853

200 0.01663 258 0.01707 326 0.01772 394 0.01855

201 0.01664 260 0.01708 328 0.01774 396 0.01858

202 0.01665 262 0.01710 330 0.01776 398 0.01861

203 0.01665 264 0.01712 332 0.01778 400 0.01864

204 0.01666 266 0.01714 334 0.01780 405 0.01871

205 0.01667 268 0.01715 336 0.01783 410 0.01878

Expansion Tank Sizing Calculation Hydronic System

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