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Selecting pressure stabilizers

Relations:

 

  1. Initial pressure in the expansion vessel:
p = pst+0,2
  1. Increase in heating charge volume due to change in temperature from T1 = 10ºC to TZ (minimum vessel storage capacity):
Vu = V * ρ1 * ∆V
  1. Minimum total expansion vessel capacity:
          pmax+1
 Vn = Vu ————————
          pmax-1
  1. Minimum total expansion vessel capacity for TERMAT set:
        Vu
 Vn = ——————
       0,85
  1. Minimum total expansion vessel capacity for TERMAX set:
        Vu
 Vn = ——————
       0,75

CAUTION: If the total expansion vessel capacity is higher than recommended or room dimensions does not allow use of high vessels, use more than one small vessels instead.

Quantities and units:

 

V       m3            – total water heating system capacity

 

Vu      dm3         – minimum storage expansion vessel capacity

 

Vn      dm3         – minimum total expansion vessel capacity:

 

ΔV     dm3/kg    – increase in water volume due to increase in temperature from T1 = 10ºC to TZ

 

TZ      ºC            – design supply water temperature

 

pst     bar           – static water heating system pressure at T1 = 10ºC

 

pmax  bar           – maximum design water heating system pressure (safety valve opening pressure)

 

p       bar           – initial pressure in the expansion vessel:

 

ρ1      kg/m3      – water density at initial temperature T1 = 10ºC (ρ1 = 999.7)

 

Increase in volume ΔV vs. supply water temperature TZ.
Tabela wartości liczbowych przyrostu objętości DV, w zależności od temperatury wody na zasilaniu instalacji T

EXAMPLE 1.

 

Select the expansion vessel for the central heating system based on the following data:

 

Data:

V = 17.5 m3             total water heating system capacity

pst = 3.2 bar            static system pressure (building height 32 m)

pmax = 6 bar            safety valve opening pressure

TZ = 90ºC                supply temperature

Procedure:

select-stabilizers

  1. Expansion vessel designation:

2 x TerNWP 900              – expansion vessel (6 bar)
Dobrać naczynie przeponowe dla instalacji centralnego ogrzewania dla

Comments:

 

  1. Add additional 2 m column of water (0.2 bar) to the calculated static pressure to ensure heating medium supply to the highest heating system point. It also guarantees a minimum water reserve in the system.

 

  1. The key factor when selecting the expansion vessel is to determine the increase in heating charge volume Vu due to heating from T1 = 10ºC to TZ (max. medium temperature).

 

  1. Determine the expansion vessel size using a known increase in heating charge volume Vu,, initial pressure p and maximum system pressure pmax,. Determine the vessel designation after calculating the total vessel capacity Vn for required operating conditions. Select total capacity corresponding to the nearest higher calculated capacity from TerNWP data sheet, Specifications (6 bar expansion vessel) / Total capacity table.

 

  1. Specify vessel type and total capacity, see Expansion vessel designation. Include pressure value in the symbol for 10 bar expansion vessels.

 


EXAMPLE 2.

 

Select the pressure stabilizing system and top-up system based the following data:

  1. Minimum total expansion vessel capacity:

Dobrać naczynie przeponowe dla instalacji centralnego ogrzewania dla

For TERMAX system from TerNWP data sheet

Specifications (expansion vessel 6 bar) / Total capacity

– expansion vessel with total capacity: 900 dm3

 

  1. Set designation:

TERMAX; 1 x TerNWP 900; pst = 3.2 bar; water loss 0.1 m3/h

 

Comments:

  1. Determine total expansion vessel capacity for the TERMAX system using the increase in heating charge volume Vu, calculated in example 1. Select total capacity corresponding to the nearest higher calculated capacity from TerNWP data sheet, Specifications (6 bar expansion vessel) / Total capacity table.
  1. Specify equipment type, expansion vessel type (gravity vessel by default), static pressure and water loss, see Set designation.

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