Hep20 Technical Handbook

Hep 2
O ® Design Considerations
Systems Planning
System Sizing Calculation Examples
Domestic cold water pipe sizing
Question: What is the effect on the tap head when 22mm
Hep 2 O ® is used as the distribution pipe from storage cistern?
System information assumptions
Design flow at tap
Frictional loss at tap
Proposed Hep 2 O ® size
0.3 l/s
0.8m head
22mm
Calculation (read with Figure 14 and Table 12)
Measured pipe length (ML): 0.5 + 3 + 5 + 0.5 = 9.0m
Equivalent pipe length (EL): 3 elbows x 0.8 = 2.4m
Total equivalent pipe length (TEL) 11.4m
Head available at tap: 3 – (0.5 + 0.8) = 1.7m head
Available head loss per 100m: 100 x 1.7 = 14.9m
11.4
Using Nomogram 1 (page 61), plot a line from 14.9m on head loss scale
through 0.3 l/s on flow scale and extend over to pipe size scale (shown
by dash line on nomogram).This indicates that proposed 22mm pipe size
would be suitable.To check what the actual head loss is for this size, plot
a line from 22mm on pipe size scale through 0.3 l/s on flow scale, and
extend over to head loss scale (shown by dotted line on nomogram).
This indicates that head loss is 11m per 100m (0.11m per m).
Actual head loss through pipework: 11.4m x 0.11 = 1.254m
Actual flow rate at tap would therefore be slightly higher than design flow.
1m head loss = 9.81 kN/m 2
0.5m
Figure 14
0.5m
Bath tap
Table 12 Equivalent Pipe Lengths for Pipe Sizing
5m
3m
Storage cistern
Gate valve
Domestic hot water pipe sizing
Given sufficient system information for domestic hot water
layouts, pipe sizes may be ascertained with nomogram 2
(page 62) and the calculation method used for domestic cold
water pipe sizing.
Central heating pipe sizing
Question: What is the effect on the pump head when
10mm Hep 2 O ® is used for radiator connections?
System information assumptions
Length of radiator flow pipe
4m
Length of radiator return pipe 5.5m
Flow and return design temperatures 80ºC and 70ºC
Allowance for unusable pipe heat loss 5%
Specific heat capacity of water 4.2
Design output of ‘index’ radiator
1.2 kW
Calculation (read with Figure 15 and Table 12)
Heat load: 1.2 kW + 5% = 1.26 kW
Flow rate: 1.26 = 0.03 l/s
4.2 x (80-70)
Using Nomogram 3 (page 63), plot a line from 10mm diameter on pipe
size scale through 0.03 l/s on flow scale and extend over to head loss
scale, (shown by dash line on nomogram). read head loss value as 14m
per 100m, i.e. 0.14m per m run.
Measured pipe length (ML): 4 + 5.5 = 9.5m
Equivalent pipe length (EL): 4 elbows x 0.2 = 0.8m
2 tees x 0.3 = 0.6m
Total equivalent pipe length (TEL): 10.9m
Pipework head loss: 0.14 x 10.9 = 1.526m head
or 15 kPa
This head must be added to frictional loss of all other circuits on
‘index run’, together with allowances for radiator valves, control valves,
boiler, etc., in order to determine minimum pump head required.
Like copper ‘microbore’ systems, the use of 10mm Hep 2 O ® will require
slightly more pump head than systems using 15mm radiator circuits.
As a general precaution, 10mm Hep 2 O ® should not be used for a
radiator output in excess of 1.5 kW (approximately 5,000Btu) unless
proven by calculation.
Index radiator
Hep 2 O ® diameter Elbow Tee Stopcock
(mm) (m) (m) (m)
10 0.2 0.3 –
15 0.5 0.6 4.0
22 0.8 1.0 7.0
28 1.0 1.5 10.0
Notes:
1. This table is appropriate for pipeline water velocities not exceeding 1.5m/s.
Refer also to Table 15 on page 72.
2. Frictional loss through tees occur on a change of direction only.
3. Frictional loss through fully open gate valves can be ignored.
4. Frictional loss through cold formed bends can be ignored.
Figure 15
60