HEATING SYSTEM CALCULATION

1. HEATING SYSTEM CALCULATION Peculiarity of heating system calculation

2. Circulation pressure • Calculation of heating systems must take into account particular conditions of operation of the system.A heating system accumulates certain circulation pressure which depends on the amount of the flow passing through the system.Upon verification of the flow,the network needs to be recalculated,taking into account the pressure change. • Calculating pressure in the ringed network is find: Dpsk = Dps + B(Dppr + Dpv), where: - pump pressure; - pressure after water cooling in heating apparatus; - pressure after water cooling in pipes; B – coefficient.

3. In naturally circulating heating systems pressure is variable and • dependent from the heating conditions.According that B is select. • For vertical 1 pipe systems with compulsory circulation B=1 • psk=ps + ppr + pv . • For vertical 2 line pipe systems B=0.5: • psk=ps + 0,5(ppr+ pv). • For dependant scheme without water mixing : • (p1 = ps); • Where : - pressure difference in between supply and return • lines of building; • For dependent system scheme with elevator mixing: Where: -mix coefficient ; tg and tt –water temperature in return and supply lines

4. Natural circulating pressure in heating system Natural circulating pressure in circular loop is equal to pressure difference in inflow and outflow end of radiator: ppr = (g – t)gh = Drgh,

5. Amount of heat transfer from apparatus to room is named Heat Capacity : F = cQm(tįt – tiš) = cQmt, Where : Qm – flow mass rate; Δt – temperature difference; c= 4187J/kg K – specific heat of water; Φ – heat capacity (in watt W); Heat load of stand is: Fst=  Fpr = cQm st t , Where :Фst – sum of heat capacity of all stand heating apparatus; Qm st – stand flow rate; After simple readjustment: Qm = t=

6. Scheme of calculation pc = ppr + pv. pv = (i+1 – i)ghi, ppr = (g – t)gh = Drgh, p = 0,5(1 + 2)gh = 0,51gh + 0,52gh. VSP – comparative table of water heating; AC – water cool center

7. Water temperature ti in the point of stand is find according formula: Water density change ρ is depending from the change of temperature: Dr = b (t1 – t2) = b Dt ,

8. t, oC tt – tg 40–50 t = tt – tg , 0C 60–70 90–100 b, kg/m3K Slėgis bt106, 1/ oC 422 556 719 p = 0,1 MPa 85 – 65 95 – 70 105 – 70 115 – 70 135 – 70 20 25 35 45 60 0,60 0,64 0,66 0,68 0,72 bt106, 1/ oC 422 548 714 p = 1,0 MPa

9. After some readjustment find magnitude of circulating pressure of radiator: In the one pipeline system: ,

10. In the one pipeline heat supply bottom distrbution system:

11. In the two-pipeline parallel heat supply system: ppr = (g – t)gh,

12. Circulation pressure in the minor loop , ppr = (įt – iš)g 0,5hpr = 0,5bgtprhpr,

13. ppr =0,5btprghpr = 0,5 . Coefficient  and schemes of connection: = 0,5.

14. , . Main peculiarity of heat system hydraulic calculation 4000 < Re < 106 . , Z = 485v2 .

15. Water heating system is composite loop network with complicated discharge distribution; • Heat transfer directly depend from the flow rate and temperature deference t. • When performing hydraulic system calculations the temperature gradient t must be designed the same in all heating apparatus. • Calculation is performing by trial and error method. • The laminar flow regimes exist in natural circulating systems and cast iron radiators.In central systems with compulsory circulation flow regimes are turbulent. • An empirical coefficient of hydraulic resistance  is used according flow regimes and corresponding formulas(see “formulas”). • Two calculation methods is used:comparative pressure loss and characteristic of hydraulic resistance. • Due the circulating pressure in systems and less kinematics viscosity coefficient  pressure loss and hydraulic resistance in heating systems is less.That must be estimated when calculate.

16. Formulas , 4000 < Re < 106 . G.A Murin D Darsi-Veisbach , When =970 kg/m3; Z = 485v2 .