1. Hot Water Systems
Cylinders and Systems

2. Recap Which regulation covers hot and cold supplies?
Heat is a form of energy created by:
At what temperature should water be stored?
What material are secondary pumps made from and why?
By what means does heat travel by in gravity systems?
What are the two main categories of hot water systems?
What is a ‘Centralised’ hot water system
What factors should be taken into consideration when designing hot water systems?
Barry Spick

3. Cylinder / Cistern
Cylinder / Cistern systems are the traditional ‘OPEN VENTED’ type of hot water system.
The system comprises:
A Hot water storage cylinder
to store the hot water
A feed cistern
to supply water to the cylinder
A power source
Boiler or Immersion Heater – to heat the water in the cylinder to a temperature of approx C.
Pipework
to connect the components and supply hot water to the terminal fittings (Taps, showers etc)
Barry Spick

4. Cylinder / Cistern There are three main types of system: Direct
Indirect Single Feed
Indirect Double Feed
On larger installations a secondary return may be used.
This will be discussed later
Barry Spick

5. Cisterns
What is the minimum size of a cistern only supplying a cylinder?
cistern used only to feed the hot water supply system shall conform to all the requirements for a cold water storage cistern. It shall have a capacity at least equal to that of the hot water cylinder
If cistern supplies Cold distribution also then capacity is min 230 litres
Cistern must comply with BS 6700 and water regulations for installation of a cistern for cisterns
Barry Spick

6. 28mm cold feed with full-way valve
Direct
Water heated directly from boiler or immersion heater
Gravity circulation from boiler to cylinder
Primary and secondary water not separated
Not suitable to be used with central heating
Greater risk of scale formation (Furring) of pipes in hard water areas
Slow heat-up / recovery period
22mm Open Vent
22mm Distribution Pipe
28mm cold feed with full-way valve
Secondary Water
28mm Flow & Return
Primary Water
Barry Spick

7. Indirect single feed Water heated indirectly from boiler.
Gravity or pumped circulation from boiler to cylinder
Primary and secondary water separated by air lock.
Less risk of scale formation (Furring) of pipes in hard water areas
Heating can be easily incorporated onto system.
Cannot use inhibitor on primary side of system
22mm Open Vent
28mm cold feed with full-way valve
22mm Distribution Pipe
28mm Primary Flow & Return
Barry Spick

8. Single Feed Cylinder (Primatic) how it works……
Barry Spick

9. Single feed Cylinder (Primatic)
Water enters the cylinder through a number of holes
The system is self venting via the vent
Primary circuit fills, then the secondary circuit
Two air seals are formed and a permanent seal is maintained
The water is heated and expands into the upper dome
Barry Spick

10. Key points to remember
The primary circulation must not be too large, excessive water once expanded could displace the seal
Care must be taken when using circulating pumps on the primary circuit, this could result in seal loss
The loss of air seal would convert the system into a ‘direct system’ water from the central heating system would mix with the secondary water
Corrosion inhibitors or other additives must not be added to primary circuits
The disadvantages tend to outweigh the advantages of single-feed vented cylinders so they are not widely used
Barry Spick

11. Indirect double feed
Primary and secondary water separated (Separate feeds)
Less risk of scale formation (Furring) of pipes in hard water areas
Gravity or pumped circulation from boiler to cylinder
Water heated indirectly from boiler
Heating can be easily incorporated onto system.
Can use inhibitor on primary side of system
Most popular cylinder/Cistern system
22mm open vent (HW)
Feed Cistern
22mm open vent (HTG)
15mm cold feed
HTG F & E cistern
28 / 22mm cold feed with full-way valve
22mm HW distribution pipe
28mm primary flow & return
Barry Spick

12. Vent pipes
Vent pipe should terminate not less than twice the internal diameter of the vent pipe above the level of the top of the float valve
Barry Spick

13. Vent Pipes
Minimum height of top of vent pipe above top of overflow pipe to be determined by V = 0.04H where V and H are in metres
The above minimum height refers to gravity circulation systems. If a secondary circulation pump is installed allowance should be made. V H
Barry Spick

14. Connection from cylinder
Minimum 450mm for hot water distribution pipe from top of cylinder to vent.
This is to avoid heat loss through one pipe circulation.
What is one pipe circulation?
450mm min.
Barry Spick

15. One pipe circulation Vent pipe taken vertically Up from cylinder
Circulation begins in pipe
Water cools in cylinder
Barry Spick

16. Cylinders

17. Cylinder Grades
Grades indicate fitness for installation in open vented conditions and relate to working head, i.e.
the distance from the base of the cylinder to the top of the water level in the feed cistern.
Grade 1: 25 metres maximum
Grade 2: 15 metres maximum
Grade 3: 10 metres maximum

18. Indirect Cylinder Types
Coil type of heat exchanger by far the most popular in domestic cylinders
Annulus type uses a copper jacket within the cylinder, was often used on larger cylinders

19. Cylinders Copper cylinders are manufactured to the following standards
BS 1566: 2002 Direct Copper Cylinders
BS1566: 2002 Double Feed Indirect Copper Cylinders
BS 1566:2002 Single Feed Indirect Copper Cylinders
BS 3198: 1981 Combination Units
Cylinders are normally insulated with CFC free polyurethane foam

20. Immersion heaters Must comply with BS EN 60335-2-73
Main way to heat the water in a direct cylinder.
New or replacement heaters now include 2 thermostats
So that if the normal operating thermostat fails, a secondary overheat thermostat will ensure that the cylinder does not overheat
Useful as a back-up in case of boiler failure.
Can have twin elements, these are top-entry cylinders

21. Cylinder Heated by Immersion Heater (Direct)
One Immersion heats all of the water in cylinder
Two immersion (twin)
Can work on timer
At times of least use.
Only one immersion timed to be used
At times of most usage.
Both immersions are in use HW CH

22. Combination Storage Heaters
Cold water cistern incorporated into the unit
Base of the cistern must not be lower than the highest connected water outlet
Should be high enough to give adequate water flow
Clearance should be allowed to maintain the valve in the cistern

23. Instantaneous Hot Water Systems
The Water-jacketed heater
Must be sized according to demand
It is a bit like an indirect system in reverse
Can be fed Direct or Indirect
With the advent of the Combi-boiler these heaters became redundant
Heat store

24. Thermal Storage Unit Mains fed hot water throughout the home.
No cisterns in the loft.
Flow rate more than double most combination boilers.
Hot water temperature set at 55°c
Mains pressure showering without a pump.
Fills a bath in 3 minutes

25. End of Lesson