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

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.

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.

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

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

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

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

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

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

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

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

Installation Using Solar Collector

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.

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

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).

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.

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.