US Customary:
Vt = (0.00041T - 0.0466)Vs
(Pa/Pf) - (Pa/Po)
where,
Vt = minimum volume of tanks, gallons
Vs = volume of system, not including tanks, gallons
T = average operating temperature, °F
t1 = lower temperature
t2 = higher temperature
Pa = atmospheric pressure, psia
Pf = fill pressure, psia
Po = maximum operating pressure, psia Metric:
Vt = (0.000738T - 0.3348)Vs
(Pa/Pf) - (Pa/Po)
where,
Vt = minimum volume of tanks, liters
Vs = volume of system, not including tanks, liters
T = average operating temperature, °C
Pa = atmospheric pressure, kPa
Pf = fill pressure, kPa
Po = maximum operating pressure, kPa; and
TABLE 3.7.9.1-a
EXPANSION TANK CAPACITIES FOR GRAVITY HOT-WATER SYSTEMS
Based on a two-pipe system with average operating water temperature 170°F(77°C), using cast-iron column radiation with heat emission rate 150 Btu/hr/ft2 (473 W/m2) equivalent direct radiation) | ||
Installed Equivalent Direct Radiation, ft2 (m2) (Note) | No. | Tank Capacity, gallon (l) |
up to 350 (33) | 1 | 18 (68) |
up to 450 (42) | 1 | 21 (79) |
up to 650 (60) | 1 | 24 (91) |
up to 900 (84) | 1 | 30 (114) |
up to 1,100 (102) | 1 | 35 (132) |
up to 1,400 (130) | 1 | 40 (151) |
up to 1,600 (149) | 2 | 60 (227) |
up to 1,800 (167) | 2 | 60 (227) |
up to 2,000 (186) | 2 | 70 (265) |
up to 2,400 (223) | 2 | 80 (303) |
Note:
For systems with more than 2,400 ft2 (223 m2) of installed equivalent direct water radiation, the required capacity of the cushion tank shall be increase on the basis of 1 gallon (3.79 l) tank capacity/33 ft2 (3.1 m2) of additional equivalent direct radiation.
TABLE 3.7.9.1-b
EXPANSION TANK CAPACITIES FOR FORCED HOT-WATER SYSTEMS
Based on average operating water temperature 195°F [91°C], fill pressure 12 psig [83 kPa], and maximum operating pressure 30 psig [200 kPa] | ||
Tank Capacities, gallon (l) | ||
System Volume | Pressurized Diaphragm Type | Nonpressurized Type |
100 (379) | 9 (34) | 15 (57) |
200 (757) | 17 (64) | 30 (114) |
300 (1136) | 25 (95) | 45 (170) |
400 (1514) | 33 (125) | 60 (227) |
500 (1893) | 42 (159) | 75 (284) |
1,000 (3785) | 83 (314) | 150 (568) |
2,000 (7571) | 165 (625) | 300 (1136) |
Note: System volume includes volume of water in boiler, radiation, and piping, not including the expansion tank. Expansion tank capacities are based on an acceptance factor of 0.4027 for pre-pressurized types and 0.222 for non-pressurized types. For other cases or metric calculations see Chapter 12 of the 1996 HVAC Systems and Equipment Volume of the ASHRAE Handbook.
Haw. Code R. § 12-223.1-13