Water Heating

Storage Water Heating

Storage recovery time

Approximate time in minutes to heat 10oC to 65oC
Ltrs. Loading in Kw
  2 3 4 5 6 7 12 18
5 10 6 5 4 3 3 2 1
10 19 13 10 8 6 5 3 2
15 29 19 14 12 10 8 5 3
50 96 64 48 38 32 27 16 11
100 192 128 96 77 64 55 32 21
200 384 256 192 154 128 110 64 43
300 577 384 288 231 192 165 96 64
400 769 513 385 308 256 220 128 85
600 1153 769 577 461 385 330 192 128
1000 1923 1282 962 769 641 549 320 214
 

Time in minutes

Guidelines for usage of hot water

Average Hot Water Requirements
Application Demand in litres Temperature oC
 Hand wash 1 37
 Basin fill 5 37
 Sink fill 10 50
 Shower 20 - 50 37
 Bath 80 - 120 40
 Comm. sink 25 50
 Cup: tea/coffee 0.2 100

Schematic SHW,SB

Tech
1. Isolating valve
2. Combined control valve
    (SHW only)
3. Line strainer
4. Pressure limiting valve
5. Balanced pressure cold draw
    off
6. Check valve
7. Expansion valve
8. Expansion valve		 9. Tundish
10. Electrical earthing bond
11. Drain valve
12. Temperature & pressure relief
      valve
13. BGC element & thermostat
14. Blank plate (for additional
      element, SB only)
15. Element & thermostat assembly

 

Useful design formulae - Storage
 Storage
 Time in minutes
 to heat water
=

Litres x Temp. rise oC
_________________

Kw loading x 14.3
 Kw loading
 required to heat
 water
=

Litres x Temp. rise oC
_________________

Time in minutes x 14.3
 Hot water
 required
=

Mixed water required
x
Temp.diff. mixed oC
________________

Temp. difference: hot/cold oC

 
Pictures & Information supplied by Stiebel Eltron (www.stiebel-eltron.co.uk)

Guidelines for instantaneous water heater sizing
     

Application

Load per outlet Kw

Performance*
 Spray tap 3.0 1.6L/m at 37oC
 Bib tap 6.0 3.2L/m at 37oC
 Shower 8.0 4.2L/m at 37oC
 Hairdresser 8.0 4.2L/m at 37oC
 Sink 12.0 4.3L/m at 37oC
 Commercial sink 24.0 8.6L/m at 37oC
 Bath 24.0 11.4L/m at 37oC

 

Instantaneous flow chart *
                     
oC Loading in Kw
  4 6 8 12 18 21 24 45 60 90
40 1.9 2.9 3.8 5.7 8.6 10.0 11.4 21.4 28.6 42.9
45 1.6 2.5 3.3 4.9 7.4 8.6 9.8 18.4 24.5 36.8
50 1.4 2.1 2.9 4.3 6.4 7.5 8.6 16.1 21.5 32.2
55 1.3 1.9 2.5 3.8 5.7 6.7 7.6 14.3 19.1 28.6
60 1.1 1.7 2.3 3.4 5.1 6.0 6.9 12.9 17.2 25.7
 

Flow rate L/m

 

Useful design formulae - Instantaneous
 Instantaneous
 Temp. rise oC              =
Kw loading x 14.3
________________

Flow in Litres / min
 
Flow in Litres / min      =
Kw loading x 14.3
________________

Temp. rise oC
Pictures & Information supplied by Stiebel Eltron (www.stiebel-eltron.co.uk)