Unit 316 Session 2a Unvented hot water components

​SPECIALIST COMPONENTS IN HOT WATER SYSTEMS

​In this section, we will look at some of the specialised components that are used in unvented hot water storage

systems.

Open Ended

Can you name any of the specialised

components that are used in unvented hot water storage

systems?

​The controls for unvented hot water storage systems (UHWSS) fall under two categories.

​These are:

1. safety

2. functional.

​The Building Regulations Approved Document G3 states that unvented hot water storage systems must have a three-tier level of safety built into the system.

This takes the form of three components that are fitted to the storage vessel. The aim of these components is to ensure that the water within the system never exceeds 100 °C.

​Safety controls – control thermostat, high limit thermostat and temperature relief valve

​These components are:

A control thermostat (set to 60 to 65 °C) – this can take two forms depending on the type of storage vessel:

• With direct heated vessels this is the immersion heater user thermostat

• With indirectly heated vessels it is the cylinder thermostat wired to the central heating wiring.

  An overheat thermostat (thermal cut-out 90 °C maximum but more usually factory set at between

85 and 89 °C) – again, this can take two forms:

• with direct heated systems, it is incorporated into the immersion heater thermostat

• with indirectly heated systems, it is a separate component factory wired into the vessel and

designed to operate the motorised valve at the primary hot water coil.

A temperature/pressure relief valve (95 °C) designed to discharge water when the temperature

exceeds 95 °C.

​Control thermostat (set to 60 to 65 °C)

​Control thermostat (set to 60 to 65 °C)

​Overheat thermostat
(thermal cut-out 90 °C maximum but more usually factory set at between

85 and 89 °C)

Temperature/pressure relief valve (95 °C)

​a standard component used on most vessels that is designed to discharge water when the temperature exceeds 95 °C.

​In-line strainer

The in-line strainer is basically a filter designed to prevent any solid matter within the water from entering and fouling the pressure reducing valve and any other mechanical components sited downstream.

​Pressure reducing valve

​The pressure reducing valve of an unvented hot water storage system reduces the pressure of the incoming water supply to the operating pressure of the system.
In all cases this will be set by the manufacturer and sealed at the factory. The outlet pressure will remain constant even during periods of fluctuating pressures.

​Single check valve

The single check valve (also known as a non-return valve) is fitted to prevent hot water from backflowing from the hot water storage vessel causing possible fluid category 2 contamination of the cold water supply.

​Single check valves are classified as either:
type EA or EB backflow prevention devices.

Open Ended

Follow the link, research and report on the difference between an EA and an EB single check valve:

Tim Water Regulations Guide.pdf

​Expansion device (vessel or integral to cylinder)

Water expands when heated.
Between 4 and 100 °C it will expand by approximately 4 per cent. Therefore 100 litres of water at 4 °C becomes 104 litres at 100 °C.
It is this expansion of water that must be accommodated in an unvented hot water storage system.
This can be achieved in one of two ways:

By the use of an externally fitted expansion vessel
By the use of a purpose designed internal expansion space or ‘expansion bubble’.

​The bladder (bag) type expansion vessel

​The diaphragm type expansion vessel

​Floating baffle plate

​Pressure relief valve

​Often referred to as the expansion relief valve, the pressure relief valve is designed to automatically discharge water in the event of excessive mains pressure or malfunction of the expansion device (expansion vessel or air bubble).

​The pressure relief valve will not prevent the storage vessel from exploding should a temperature fault occur and, as such, is not regarded as a safety control.

​Tundish

​Tundish arrangements

​The tundish is part of the discharge pipework and is supplied with every unvented hot water storage system.
It is the link between the D1 and D2 pipework arrangements.
It has three main functions:

• to provide a visual indication that either the pressure relief or temperature relief valves are discharging water due to a malfunction

• to provide a physical, type A air gap between the discharge pipework and the pressure relief/ temperature relief valves

• to give a means of releasing water through the

• opening in the tundish in the event of a blockage in the discharge pipework.

​Composite valves

These days, it is very rare to see individual controls fitted on an unvented hot water storage system unless it is an early type manufactured in the 1990s. Most manufacturers now prefer to supply composite valves which incorporate many components into one ‘multivalve’.

A typical composite valve will contain:

• a strainer

• a pressure reducing or pressure limiting valve, followed immediately by

• a balanced cold take off, and finally

• a pressure relief valve.

​The discharge pipework

​The pipe size and positioning methods for safety relief (discharge) pipework connected to unvented hot water cylinder safety valves

Multiple Choice

A customer wishes to have an unvented hot water

storage system installed. You have been asked by the site supervisor to size the discharge pipework.

The temperature and pressure relief valves both have ½“ BSP outlets. Therefore, the D1 pipework can be installed in 15 mm tube.

The discharge pipe run is 9 m long to the final termination and there are five elbows installed in the run of pipe.

What size of discharge pipework should be installed?

• 15mm

• 22mm

• 28mm

• 35mm

​Correct termination of the discharge pipework

Labelling

Label the diagram

Drag labels to their correct position on the image

Pressure reducing valve

P.R.V

Tundish

Iso valve

Line strainer

Single check valve

T&P.R.V

Multiple Choice

What is the purpose of the control thermostat in an unvented hot water storage system?

• To regulate the water pressure

• To control the system temperature

• To filter solid matter in the water

• To prevent backflow contamination

Multiple Choice

In a directly heated vessel, which component serves as the control thermostat?

• Overheat thermostat

• Temperature/pressure relief valve

• Immersion heater user thermostat

• Cylinder thermostat

Multiple Choice

What is the function of the overheat thermostat in an indirectly heated system?

• Control water temperature

• Prevent backflow contamination

• Provide a visual indication of malfunctions

• Operate the motorised valve

Multiple Choice

At what temperature does the temperature/pressure relief valve discharge water?

• 60 °C

• 85 °C

• 95 °C

• 100 °C

Labelling

Label the diagram

Drag labels to their correct position on the image

D1

300mm Max

600mm Min

D2

Multiple Choice

What is the purpose of the in-line strainer in an unvented hot water storage system?

• Regulate water pressure

• Prevent backflow contamination

• Control system temperature

• Filter solid matter in the water

Multiple Choice

What is the role of the single check valve in the system?

• Regulate water pressure

• Prevent backflow contamination

• Control system temperature

• Operate the motorised valve

Multiple Choice

What do modern manufacturers prefer to supply for unvented hot water storage systems?

• Individual controls

• Composite valves

• Overheat thermostats

• Immersion heaters

Labelling

Label the diagram

Drag labels to their correct position on the image

Single check valve

Line strainer

Pressure relief valve

Pressure reducing valve

Multiple Choice

What is one of the tundish's functions in an unvented hot water storage system?

• Filter solid matter in the water

• Regulate water pressure

• Provide a visual indication of malfunctions

• Prevent backflow contamination

Multiple Choice

What does the pressure relief valve do in the system?

• Control water temperature

• Regulate water pressure

• Prevent backflow contamination

• Discharge water in case of excessive pressure