1 Domestic Hot Water Systems: Regulations and Types

• Domestic hot water systems have various regulations and system types that need to be understood

Regulations and Systems

• Regulations for hot water systems, water, and building include the WRAS Guide and British Standards
• Instructions are provided by the manufacturer
• System types include centralized, localized, gravity, pumped, direct, indirect, and primatic systems

Regulations and Guidelines

• The Water Regulations were established in 1999
• The Water Regulations Guide is provided by WRAS (Water Regulation Advisory Scheme)
• Building Regulations includes Part G (Sanitation, hot water safety and water efficiency)
• A directory of fittings approved by WRAS is available

British Standards

• BS EN 806 covers design, installation, testing, and maintenance.
• BS8000 pt15 gives guidance on workmanship on building sites for hot and cold water services

Centralized Systems

• Supply hot water from a central location within a building to multiple outlets.
• They use stored or instantaneous hot water

Localized (Single-Point) Systems

• Supply hot water directly at the point of use, often instantaneous

Open Vented Systems

• These are low-pressure systems that require a CWSC (Cold Water Storage Cylinder) for system pressure and a vent pipe for atmospheric pressure
• The vent pipe allows air to exit when filling and enter when draining
• The vent pipe is for safety relief from expansion, contraction, overheating, or control failure

Vent Pipe Requirements

• A vent pipe should be a minimum size of 22mm
• Valves on vent pipes are prohibited to ensure safety
• A minimum distance of 450mm is needed from the cylinder exit to the vent pipe connection

Cold Water Storage Cylinder (CWSC) Capacity

• BS EN 806 recommends that the CWSC capacity be at least that of the hot water cylinder
• For systems feeding both hot and cold water, the minimum CWSC size is 230 liters
• For systems only feeding the hot system, the minimum size of CWSC is 115 liters

Direct Hot Water Cylinders

• Do not utilize a heat exchanger coil
• Boilers or electric immersion heaters directly heat the water that comes out of the draw-off points.

Indirect Hot Water Cylinders

• Have an internal coil that acts as a heat exchanger
• The cylinders use a back-up immersion heater.

Cylinder Installation

• Cylinders should be installed on two pieces of wood or a purpose-built vented stand

Double Feed Systems

• Have two cisterns in the loft area
• The CWSC feeds water to the hot water cylinder as hot water is used
• The F&E cistern feeds water to the primaries

Key Components of Centralized Open Vented Indirect Gravity Systems

• Boiler
• Primary flow and return pipes
• Heat exchanger coil
• Hot water cylinder
• Cold water storage cylinder
• Feed and expansion cistern
• Open vent pipe
• Cold feed pipe
• Hot distribution pipe

Cylinder Primary Flow and Return

• Is usually 22mm, but 28mm is required if the source is a solid fuel boiler
• The thermostat is positioned about one-third of the way up the cylinder.
• Heat up time Under Part L is 25 minutes, whereas high recovery cylinders can heat water in only 10 minutes

Types of Hot Water Systems

• Hot water: Water heated to a specific temperature for domestic use
• Centralized: Water heated and/or stored centrally, then distributed to all outlets
• Localized: Water heated/stored locally for a single draw-off point
• Stored: Water heated in a cylinder before distribution
• Instantaneous: Water heated on demand when outlets are opened

Centralized system types

• Stored hot water: Uses a hot water cylinder in an airing cupboard, which is heated by a boiler or immersion heater. which distributes water through pipework
• Instantaneous hot water: Uses a combi boiler for on-demand heating which distributes water through pipework

Direct vs. indirect systems

• Direct System - the cold water from the mains enters the tank and is heated directly via an element within the tank
• Indirect system - the cold water from the mains enters the tank and passes through a coil that heats the water up.

Study Questions

• What is the BS EN number for Hot Water system design, installation testing and maintenance?
• What do the manufacturer's instructions outline?
• What are the 3 different types of hot water cylinder?
• Name the 3 types of hot water systems
• What are the two types of centralized systems?
• What does the F&E feed?
• What does the CWSC feed?
• Are open vented systems high or low pressure?
• What is the minimum size of the open vent pipe?
• What is the main purpose of an open vent