Closed Expansion Tanks are designed to meet the volumetric change of the heated water in heating systems, to keep the static pressure created by the pump at the usage level in sanitary applications, and to compensate for the changes in the water flow. A correctly selected expansion tank in the system prevents sudden pressure changes and prolongs the life of the installation elements and the pump.
CHART: 1
CHART: 2
CHART: 3
CALCULATION OF THE AMOUNT OF CIRCULATING WATER IN THE SYSTEM
Vs : Q x f (litres)
Vs: The total volume of water in the system (lt)
Q: Heating capacity of the boiler (kCal/h)
f: Heat dissipation power of the heater (CHART: 1)
Vg: Vs x n (liters)
Vg: The volume of water that the system will expand (lt)
n: The expansion coefficient of the water according to the temperature difference (CHART: 2)
Vn: Vg ÷ K (liter)
Vn: Normal expansion tank volume (liter)
K: The coefficient according to the pressure setting of the safety valve with the pre-pressure (CHART: 3)
CONSTANT PRESSURE AND SAFETY VALVE CALCULATE
Static Pressure: Building Floor Number x 2.8 m/floor + Boiler Room Level Difference = Total Level Difference ÷ 10 = Bar
Pre-Gas Pressure: Static Pressure + (0.2 ~ 0.5 bar is added.)
Safety Valve Pressure Value: Pvalve = Psafety – Ptolerance
Pem: OPERATING PRESSURE
Ptolerance: Pem ≤ 5 bar is accepted as 0.5.
If; Ptolerance: If Pem > 5 bar, Pem x 0.1 is taken.
SAMPLE CALCULATING-1
A panel radiator was used as a heating element in an apartment with 10 floors and 22 flats. 70/50 °C water circulates in the system. There is a boiler in the building with a heating power of 200,000 kCal/h. What is the pressure and volume of the expansion tank to be used in the system?
1) PRESSURE CLASS
Static Pressure: 10 x 2.8 + 3 ==> 31 ÷ 10 ≅ 3.1 bar
Front Gas Pressure: 3.1 + 0.4 = 3.5 bar
Pem: 5.5 bar (operating pressure)
Safety Pressure Value: 5.5 – 0.5 = 5 bar
2) NORMAL VOLUME OF WATER
Total Water Volume in the System:
Vs: Q x f, f: (from TABLE: 1)
Vs: 200,000 x 10 ÷ 1000 = 2000 liters
Expanded Water Volume in the System:
Vg: Vs x n, n: (from TABLE: 2)
n: 900 - 100 = 0.0359 – 0.00027 = 0.0356
Vg: 2000 x 0.0356 = 71.2 Liters
3) NORMAL VOLUME OF EXPANSION TANK
Vn: Vg ÷ K
K: (Assuming the pre-gas pressure is 3.5 bar, safety valve pressure is also 5 bar (CHART: 3), from K: 0.25 )
Vn: 71.2 ÷ 0.25 = 284.8 liters
Vn : 300 liters ==> STANDARD: LR 300/6 is SELECTED.
SAMPLE CALCULATE-2
Calculation of the expansion tank to be selected for a boiler with a heating power of 180,000 kCal/h operating at 70/50 °C in the steel panel radiator system of a 4-storey and 16-flat apartment; boiler operating pressure is 5 bar. According to this;
Static Pressure: 4 x 2.8 + 3 ==> 14.2 ÷ 10 = 1.42 bar.
Front Gas Pressure: 1.42 + 0.1 = 1.52 ==> 1.5 bar. (22lbs)
Normal Volume;
Total water volume in the system:
Vs= Q x f = 180.000 x 12 ÷ 1000 = 2160 Liters
Expanded water volume in the system:
Vg= Vs x n = 2160 x 0.0356 = 76.89 Liters
Normal Volume of Expansion Tank;
Vn = Vg ÷ K (Pre-gas pressure 1.5 bar Safety valve (3-0.5)= 2.5 bar)
K: K = 0.28 from Table 3
Vn= 76.89 ÷ 0.28 = 274.6 Liters
Vn= 300 lt STANDARD: LR 300/6 is selected.