1. HOT WATER Understand and apply domestic hot water system installation and maintenance techniques

2. Domestic hot water system installation and maintenance techniques Learning outcome 1 After this session you should know the uses of hot water systems in dwellings

3. We will cover in this unit: Open vented (to Atmosphere) Unvented (sealed systems) Combination boilers Thermal store systems We will also cover the basic design and installation of these different types of systems.

4. British Standards 6700 (BS 8558) As with cold water the design of hot water systems is covered in the Water Regulations and BS6700 (note: the requirements of BS6700 were incorporated in the new British Standard 8558 which, as of August 2012, covers the supply of water at domestic properties) The type of hot water system to be installed will usually be influenced by the type of building and the number of occupants and their requirements. The domestic property today may have a number of different systems installed.

5. The current trend for hot water in new domestic buildings is to install a sealed system (unvented) with a higher proportion towards combination boilers. However there are a great number of hot water systems still working today classed as an open vented (to atmosphere) system. These open vented systems are being replaced with the unvented systems and /or Combi boilers

6. In an atmospheric vented domestic hot water system the water in the storage vessel should be stored at a temperature of not less than 60°C. This temperature allows a distribution of 55°C and restricts the growth of bacteria (Legionnaires’ Disease). We will cover the heat source requirements later in this unit.

7. Which ever heat source is used the temperature of the stored water should not exceed 65°C. Scalding and lime scale can become a serious problem if the water exceeds this temperature. The water stored in the storage vessel (cylinder) is controlled by a cylinder thermostat installed approximately 2/3 from the top of the cylinder. 7

8. A number of factors will influence the design and type of hot water systems; Fuel costs Demand (Users) Storage (capacity) Installation (cost) Safety (Temperature) Waste (length of draw off from heat source)

9. The hot water system can range from a single point outlet to a more complex centralised system supplying several outlets. These systems fall into two basic categories ; Localised Centralised Lets look at these in more detail -

10. Centralised System The hot water is stored centrally within the building. Stored means water held in a vessel (Cylinder) with the temperature controlled by a thermostat. From this central source various distribution pipework is used to deliver to all draw-off points. A problem can develop with this type of pipework distribution -

11. Because the hot water is centrally stored the draw- off points can be some distance away. This can lead to a problem commonly known as dead-legs which is simply excessively long pipework. What other problems do you think this system may have? Lets look at the main issues -

12. Long draw of cold water before the hot Large amounts of waste water Temperature loss through distribution pipework Installation materials (pipework) Risk of bacterial contamination Energy (reheat)

13. Localised Systems As the title suggests the supply of hot water is at the point of draw-off. An example could be a single point water heater positioned above a sink. This appliance would give almost instant hot water. Another type of appliance could be installed under the sink. This would store a small amount of hot water (under 15 litres) giving instant delivery at the tap.

14. Instantaneous Supply Its important to note that only the required amount of hot water is used and heated. This would save fuel bills (energy) and would also save wastage of water. We can now look at hot water systems in more detail.

15. HOT WATER SYSTEMS These can be categorised as being; Direct Indirect Sealed/unvented Mains thermal store Combination

16. Because of the properties of water – when we heat this water it will: Expand in volume (4%) Become less dense Because of this change in density if we were able to look inside of a hot water cylinder we would see the hotter water (less dense) above the colder water This effect is known as Stratification

17. Stratification All stored hot water form layers of differing temperatures. Stratification is required as it would give maximum efficiency. The hot draw-off is at the top of the cylinder.

18. DIRECT SYSTEM This system is not used or installed today. It may still be found in existing older properties. The system works on the principle of convection. Water is heated within the boiler (any heat source) and as the water increases in temperature it becomes less dense and therefore will rise within the Primary flow pipe to the storage vessel.

19. It is possible to heat the water in the storage vessel (cylinder) by using only an immersion heater This immersion heater is normally inserted vertically into the top of the cylinder therefore heating the water Directly:

20. In some cases two small immersion heaters can be used by inserting them horizontally in the top and bottom of the cylinder. All immersion heaters are controlled by an integral thermostat.

21. The direct system can also utilise a heat source direct from a boiler Its important to remember the boilers own heat source can be fuelled by any type of fuel: Natural Gas LPG Solid Fuel Oil

22. Direct Hot Water System This system, using gravity primaries is now not allowed under the Building Regulations (Part L1A/B )

23. INDIRECT SYSTEMS Today we would find the INDIRECT SYSTEM more common if a hot water storage system was Installed. Just as the Direct System the boiler can be of any fuel source. The difference is within the cylinder.

24. The Indirect Cylinder Is the only type of design installed today. The Building Regulation Part L1 makes this a mandatory requirement. All vented cylinders Installed should be to BS 1566. 24

25. INDIRECT SYSTEM

26. The boiler on this type of system would be adequately sized to allow for the heating system. You will notice that a coil or annulus is fitted to this design of cylinder. As the water from the primary flow passes through the coil it transfers its heat energy indirectly to the stored water. The water in the coil is not mixed with the stored water.

27. This indirect storage vessel would be categorised as double feed indirect - manufactured to BS 1566.

28. Can you identify the various pipes?

29. TAP STAT This was one of the first designs which was introduced to control the temperature of the water contained in the cylinder. It is no longer installed as a new installation. It would not achieve “boiler interlock” as required by Part L1.

30. A gate valve would be fitted between the CWSC and the hot storage vessel. The technical name for a gate valve would be referred to as a full-way or full-bore there is little or no resistance through the body of this valve. This valve may require re packing (packing gland) to rectify any leaks. Lets have a look how this system is installed in a domestic property.

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33. Secondary circulation In simple terms this system consists of a pumped hot water ring or loop. You can see that the hot water is constantly pumped to the appliances. 33

34. The pictures below show an indirect cylinder confirming to BS 1566. Lets now look at the high performance cylinder:

35. The coil found in a conventional indirect cylinder utilise a single internal 28mm coil heat exchanger The high performance cylinder utilise a much larger coil ratio: nu learn

36. Sub- standard cylinder coil Current BS 1566 coil Rapid recovery coil

37. High Performance (fast recovery) This type of cylinder offers better energy efficiency and lower fuel running costs They give ultrafast recovery time - under 10 minutes. These can only be used on fully pumped systems

38. Which ever cylinder is installed it should comply to Building Regulations Part L Thermal insulation - minimum thickness All pipework should be insulated up to a metre from the cylinder or to the point of where it becomes concealed.

39. Combined storage unit As can be seen from the following picture the CWSC is Incorporated within the unit This type of cylinder must be positioned so that it will give adequate pressure at the hot taps.

40. Instantaneous Hot Water Appliances These appliances fall into two categories Single point Multipoint Single point can be found fitted above a kitchen sink Multipoint could be found in a one-person flat supplying a number of appliances

41. Instantaneous Water systems The heat source for this type of system is gas or electric. The flow rate from these appliances is limited but they provide unlimited amounts of hot water The only exception is the gas single point water heater which has a maximum usage of 5 minutes

44. Its important to remember that to maintain a constant temperature at the outlet the water flow rate and pressure must also be constant. Other types of instantaneous appliances delivering hot water on demand would include: Combination Boilers Electric Showers

45. Thermal Stores These type of systems can be found in new build properties or as upgraded systems. Like most systems there are some advantages and disadvantages. Lets look at the design of this system -

46. Thermal Store

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48. Thermostatic showers This type of shower installation requires both the hot and cold supply to be of the same pressure. This balanced system will ensure that the thermostatic operates correctly with a good overall temperature range.

49. The vent automatically traps and releases air, preventing back feed of aerated hot water.

50. Its important that the connection to the shower from the CWSC is correct.

51. Unvented Systems The storage vessel on an unvented (sealed) hot water system does not require an open vent pipe. This stored hot water is supplied directly from the mains pressure (reduced)– a CWSC is not required.