13 - Pipe Sizing Example 10

Pipe Sizing Example 10
Size the pipes and the pump in the system shown below. The heating system is for Factory Radiant Panel Heaters and the design inside temperature is 15oC Use welded mild steel pipe and fittings at average water temperature 75oC.
Section 1 2 3 4 5 6 7
Length (F&R) (Metres) 25 30 18 15 40 18 15
Pressure Drops from Equipment

3-Port Diverting Valve
Pressure drop 3 port valves Radiant Panels
= = =
r x g x H 1000 x 9.81 x 3.6 m 35,316 Pa
Powermatic Radiant Panels, type Aquamatic ARP (see http://www.powrmatic.co.uk/) Total emissions from catalogue , 75 MWT, 15oC ambient, 4 tubes horizontal - 734 W per m run. (from Table 5) Pipe length of each panel is; 40,000 Watts output / 734 W/m = 56 metres. Mass flow rate for each panel is 40 kW / 42 = 0.95 kg/s. For each tube mass flow rate is 0.95/4 = 0.25 kg/s + 15% heat loss = 0.28 kg/s From hydraulic resistance graph (on website), resistance for each panel = 38 Pa/m run Total resistance for each panel 38 x 56 m = 2128 Pa.
Pipe Sizing Table

Section Ref. 1 Heat Output in section (kW) 40 2 Pipe Heat loss. 15% of 1. (kW) 6 3 Total Heat Col. 1+2 (kW) 46 4 Water Flow Rate (kg/s) 5 Pipe Size (mm dia.) 6 Length of pipe (m) 7 Total Equivalent length of Fittings (m) 8 Total Pipe Length Col. 6+7 (m) 18 + 3.15 = 21.15 9 Pressure drop per metre (Pa/m) 10 TOTAL PRESSURE DROP Col. 8 x 9 (Pa)
6,3
1.1
40
18
40
46
1.1
40
15
40
46
1.1
40
15
2elbow weld @ 0.4 = 0.8 1 st. thro tee = 0.2 3 gate valve @ 0.25 = 0.75 Total z = 1.75 T.E.L. = Total z x le = 1.75 x 1.8 = 3.15m 4elbow weld @ 0.4 = 1.6 1 st. thro tee = 0.2 3 gate valve @ 0.25 = 0.75 Total z = 2.55 T.E.L. = Total z x le = 2.55 x 1.8 = 4.59m 2elbow weld @ 0.4 = 0.8 1 st. thro tee = 0.2 3 gate valve @ 0.25 = 0.75 Total z = 1.75 T.E.L. = Total z x le = 1.75 x 1.8 = 3.15m
180
21.15 x 180 = 3807 + panel 2128 + 3 port valve = 35,316
= 41,251
15 + 4.59 =19.59 180 19.59x 180 = 3526 + panel 2128 + 3 port valve = 35,316
= 40,970
15 + 3.15 = 18.15 180 18.15 x 180 = 3267 + panel 2128 + 3 port valve = 35,316
= 40,711
Pipe Sizing Table

Section Ref. 1 Heat Output in section (kW) 80 2 Pipe Heat loss. 15% of 1. (kW) 12 3 Total Heat Col 1+2 (kW) 92 4 Water Flow Rate (kg/s) 5 Pipe Size (mm dia.) 6 Length of pipe (m) 7 Total Equivalent length of Fittings (m) 8 Total Pipe Length Col. 6+7 (m) 9 Pressure drop per metre (Pa/m) 10 TOTAL PRESSURE DROP Col. 8 x 9 (Pa) 55 x 52.77
2.19
65
30
le = 3.3 1 DRV 2.0 2 Tees @ 0.5 + 0.3 + red. Reduction p 652 / p 802 = Ratio = 0.59 z = 0.25 2 Tees @ 1.25 = 2.50 2 Tees @ 0.5 + 0.3 + red. Reduction p 402 / p 652 = Ratio = 0.38 z = 0.40 2 Tees @ 1.20 = 2.40 Total z = 6.90 T.E.L.= 6.90x 3.3 = 22.77m 60o oblique =
30+ 22.77 = 52.77
55
= 2,902
80
12
92
2.19
65
40
le = 3.3 1 DRV 60o oblique = 2.0 4 elbows@ 0.3 = 1.20 2 Tees @ 0.5 + 0.3 + red. Reduction p 652 / p 802 = Ratio = 0.59 z = 0.25 2 Tees @ 1.25 = 2.50 2 Tees @ 0.5 + 0.3 + red. Reduction p 402 / p 652 = Ratio = 0.38 z = 0.40 2 Tees @ 1.20 = 2.40 Total z = 8.10 T.E.L.= 8.1 x 3.3 = 26.73m
40 + 26.73 = 66.73
55
55 x 66.73 =
3,670
Pipe Sizing Table

Section Ref. 1 Heat Output in section (kW) 160 2 Pipe Heat loss. 15% of 1. (kW) 24 3 Total Heat Col. 1+2 (kW) 184 4 Water Flow Rate (kg/s) 5 Pipe Size (mm dia.) 6 Length of pipe (m) 7 Total Equivalent length of Fittings (m) 8 Total Pipe Length Col. 6+7 (m) 9 Pressure drop per metre (Pa/m) 10 TOTAL PRESSURE DROP Col. 8 x 9 (Pa)
4.38
80
25
le = 4.2 3 Gate valves @ 0.10 = 0.30 1 NRV = 2.0 1 Boiler = 2.5 2 Elbows @ 0.3 = 0.6 Total = 5.4 T.E.L. = 4.2 x 5.4 = 22.68 m
25 + 22.68 = 47.68
92.5
= 4,410
Index Circuit
Sections 1,2,3 1,2,4 1,5,6 1,5,7 Pressure Drop (Pa) 4410 + 2902 + 41,251 4410 + 2902 + 40,711 4410 + 3670 + 41,251 4410 + 3670 + 40,970 Total P.D. (Pa) 48,563 48,023 49,331 49,050
The circuit containing sections No. 1,5 & 6 have the highest resistance and are therefore the index run with a 49,331 Pa pressure drop. The pump should be capable of a minimum 4.38 kg/s (l/s) flow rate against a minimum head of 4.93 metres or ( 49.3 kPa or 49.3 kN/m2.) Allowance to pump size may be made for margin or inefficiencies.
Regulating Valves
A commissioning engineer would balance the system using double regulating valves (D.R.V.s) or metering stations. This process is briefly outlined in BSE Notes Pipe Sizing section, page 9 entitled Balancing Circuits. The drawing of the system for this example shows two D.R.V.s; one in section 2 and one in section 5. Before these can be adjusted the sub-circuits No.3 and No.4 must be balanced as well as sub-circuits No.6 and No.7. When these sub-circuits are balanced then the D.R.V.s can be regulated. The amount of extra resistance needed in the D.R.V. in section 2 is; Resistance in section 5 = 3670 Pa Resistance in section 2 = 2902 Pa Difference between these resistances = 3670 - 2902 = 768 Pa. Therefore the D.R.V. in section 2 is to be turned down to give a resistance to flow of 768 Pa. This means that the circuits are balanced.
Diverting Valves By-Pass Pipe
The by-pass pipe for the 3-port Diverting valves should also be regulated with a D.R.V so that when the valve is fully closed to the panel and fully open to the by-pass port, the resistance of the by-pass section of pipework is equal to that of the radiant panel. This means that the D.R.V in the by-pass pipework should be turned down to give a resistance of 2128 Pa. from the panel (see Radiant panel section) plus the resistance of two gate valves. See pipe sizing table pipe section 3. 2 No. 40mm gate valve @ z = 0.4 therefore total z = 0.8. Equivalent length is 0.8 x le 1.8 = 1.44 metres. 1.44 x 180 Pa/m pressure drop = 259 Pa pressure drop for 2 gate valves. The total resistance applied by the D.R.V. is therefore 2128 Pa + 259 Pa = 2387 Pa

13 - Pipe Sizing Example 10

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Pipe Sizing Example 10

Length (F&R) (Metres) 25 30 18 15 40 18 15

Pressure Drops from Equipment

Pressure drop 3 port valves Radiant Panels

r x g x H 1000 x 9.81 x 3.6 m 35,316 Pa

Pipe Sizing Table

21.15 x 180 = 3807 + panel 2128 + 3 port valve = 35,316

Pipe Sizing Table

30+ 22.77 = 52.77

Pipe Sizing Table

Diverting Valves By-Pass Pipe

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