1. 5508BESG Services and Utilities Lecture 2
HOT WATER SUPPLY
John Gammon
Private Practice

2. Domestic Hot Water
Hot water for domestic purposes may be generated either:
Locally (at point of use) or
Centrally (in a plant room)
Each of these may be either an instantaneous or a storage system.

4. Central: hot water is generated at a convenient point within the building and distributed via pipework to the draw off points.
Local: hot water is generated at or close to the point of consumption.

6. Storage v Instantaneous
Storage : hot water is generated before it is required and stored in an insulated vessel until required.
Instantaneous: hot water is generated on demand as and when required, there is no hot water storage.
Note: The hybrid, semi-storage systems is a instantaneous system with a small amount of storage

15. Combination Boiler Boiler Typical combination boiler arrangement
Temporary filling loop
22mm heating flow pipe
22mm heating return pipe
DHW supply
CW service pipe
Gas supply

16. Commercial Centralised Non-storage or Semi-Storage Water Heaters
Fuel: Gas
Heat Input: 50 to 500kW
Flow rate: 500 to 9000 litres/hour with 50oC temp rise.
Can be installed as multiple units to increase flow rates

17. Direct Centralised, Storage Systems
Boiler
Service pipe
Cistern
Hot storage cylinder
Cold feed to cylinder
Open vent pipe
Distribution to appliances
Circulation pipes

18. Direct Cylinder Drain cock Cold feed pipe Lower immersion heater
Upper immersion heater
Open vent pipe
Hot water distribution pipe
Return pipe to boiler
Flow pipe from boiler

19. Direct System - Problems
Domestic hot water passes through boiler
Corrosion – dissimilar metals (copper cylinder and steel section boiler)
Furring – temporary hard water leaves deposits when water heated above 60oC
Cannot connect radiators to same system

20. Indirect Centralised Storage Hot Water System
Feed & expansion cistern
Indirect Centralised Storage Hot Water System
Open vent pipe
Open vent pipe
Distribution to appliances
Cold feed to boiler
Storage cistern
Heating system
Cold feed to cylinder
Service pipe
Zone valve
Indirect hot storage cylinder
Boiler

21. Indirect Cylinder Drain cock Cold feed pipe Return pipe to boiler
Flow pipe from boiler
Heat exchanger coil
Immersion heater
Hot water distribution pipe
Open vent pipe

25. Installation Using Solar Collector

29. Renewable Heat Incentive
A financial incentive scheme designed to reduce the pay-back period by providing an income to help meet the additional capital costs of renewable technologies.
Currently available for Non-Domestic Applications
Current tariff for solar hot water is 8.9p/kWh
RHI is currently available for both domestic and non-domestic solar installations.

30. Prevention and Control of Legionellosis (aka Legionnaires’ Disease)
Refer to:
HSE ACoP L8: Legionnaires’ disease — The control of Legionella bacteria in water systems.
CIBSE TM13: Minimising the risk of Legionnaires’ disease.
IoP: Plumbing Design Guide

31. Legionnaires Disease Key Points for Domestic Hot Water Installations
Legionnaires Disease is caused by a group of bacteria that occur naturally in water.
Inhaling droplets of water that contain large concentrations of Legionnella bacteria can cause severe pneumonia type repertory illnesses known as Legionnaires Disease which can be fatal.
In domestic water systems the main risks are via showers, spa baths, spray taps.
Legionella bacteria can multiply rapidly in warm warm water (20 to 35oC) providing a source of nutrients are available (scale, slimes, organic compounds).

32. Legionnaires Disease (continued)
The bacteria is dormant below 20oC and instantly killed at about 60oC. So keep cold water cold (less than 20oC) and hot water hot, (heated and stored at or above 60oC. )
Disinfect new installations.
Keep systems clean
Make sure all hot water has been heated to at least 60oC on a regular basis.

33. Safe Operating Temperatures
Keeping hot water at 60oC or above keeps prevents Legionnaires Disease but it is too hot to be used safely in many circumstances To prevent risk of scolding particularly for people “at rick” (the elderly, infants and infirm), the following maximum temperatures available at the draw off points are recommended.