2 Domestic Hot Water Systems

• Types of domestic hot water systems will be identified
• The difference between each type will be clarified

Types of Hot Water Systems

• Immersion Heaters
• Combination Cylinders
• Primatic Cylinders
• The Pros and Cons of different types of cylinders
• Renewable energy systems
• Unvented Systems
• Instantaneous systems
• Combination Boiler
• Water Jacket Heaters
• Single Point Water Heaters (Inlet and Outlet controlled)
• Multi Point Water heater
• Under sink Water Heater

Immersion Heaters

• All immersion heaters installed today require a reset button and a non-reset cut-out device
• The thermostat is easily replaced
• Domestic immersion heaters are rated at 3kW
• Common sizes are 27" and 14", but 11", 18", 30" and 36" are available

Open Vented Combination Units

• These are pre-plumbed with the cylinder and cold water storage cistern joined together
• These units only need the mains feed to be run and the distribution pipe connected
• They are sometimes found in flats
• Open vented combination units have a disadvantage due to the lack of head pressure
• They are easy and quick to install

Single Feed Systems

• In this system, only one CWSC is in the loft and fills both the primary and secondary waters through the same pipe
• It does not require a feed and expansion cistern
• These systems use a primatic cylinder where the heat exchanger uses an air lock to separate the primary water from the secondary waters
• It is an indirect system

Primatic Cylinders cont.

• If the air bubble is lost, the secondary water mixes with the primary water, and brown water could be discharged from an outlet
• Cold water enters the cylinder and heat exchanger
• An air lock is formed once the cylinder and primaries are full
• Water is heated, and pushes the air bubble into the lower dome

Advantages and Disadvantages of Cylinder Types

• Direct Cylinders Advantages: Quick heat-up time, Cheap to install
• Direct Cylinders Disadvantages: Risk of rusty water, Risk of scale build up, Lack of temperature control
• Indirect Cylinder Advantages: Can be fully pumped, Various size cylinders available, Compliant with part L, Inhibitor can be used
• Indirect Cylinder Disadvantages: Expensive to install, Two cisterns in loft area
• Combination Unit Advantages: Cheap to install, Suited for flats/chalets, Easy to install, Compliant with part L
• Combination Unit Disadvantages: Lack of pressure, Lack of CW storage, Pumped showers cannot be fitted

Stored Water

• With any cylinder, the customer has a secondary heat source
• There is always a backup water supply if the mains are cut off
• Suitable for areas with low water pressure
• Systems with a cylinder and cistern take up more space than a combination boiler
• They are also more expensive to install with fewer design options
• Combination boilers provide instant hot water
• Stored hot water systems have a longer heat-up time

Renewable Energy systems

• Water can be heated via solar panels on the roof or solid fuel units
• It can be incorporated into a domestic hot water system
• By introducing a second or third coil in the hot water cylinder
• The system requires antifreeze
• The lower coil is connected to the solar circuit

Unvented Hot Water Cylinder

• These cylinders and systems do not have an open vent, so the safety relief must be incorporated elsewhere in the system
• They operate under mains pressure
• Known as high-pressure systems
• They do not require a CWSC in the loft
• The cylinder must be fitted with a range of safety (temperature) controls so the hot water never reaches 100°C
• The discharge pipes must be located in a safe place
• The system must be maintained by a competent person
• Installations must be notified to the local authority or self-certified (Competent Persons Scheme)

Instantaneous Hot Water Systems

• These systems can be centralized or localized using single or multi-point heaters
• They heat domestic hot water only when needed
• They transfer heat to the cold water very quickly through the heat exchanger

Combination Boiler

• These boilers are designed to heat up cold mains water instantaneously
• They supply water to a property
• It is done using a plate heat exchanger with a large surface area
• Combination boilers are a high-pressure system

Water Jacket Heater (Thermal Store Unit)

• This system is a form of instantaneous hot water under mains pressure
• Works in a similar way to an indirect cylinder, except in reverse
• The cylinder is filled with primary water, and the coil is filled with the water that needs heating
• When a hot draw-off point is opened, water flows through the coil and is heated
• It then passes through a blending valve, which regulates the temperature

Single Point Water Heater

• Commonly used where an isolated basin/sink is too far away from a DHW storage vessel (dead leg) or where there is no other form of DHW in a building
• They rely on an open spout that is always open to atmosphere
• This type of unit generally needs to be mains fed, but some units can be fitted to a cistern
• Always check the manufacturer's instructions
• These units have a small capacity of stored hot water (5 litres).
• Some require a flow restrictor to be fitted so flow is maintained at 7 litres per minute If the appliance capacity is over 15 litres they come under an unvented appliance
• Single point water heaters can be fitted above or below a sink
• They also can be fitted in loft conversions or extensions
• These units are also known as inlet controlled
• The tap allows mains water to enter the unit and pass down the open spout (open vent)

Multi-Point Water Heater

• These items store a small amount of water and supply water to a number of outlets on one location
• These are often kept at mains pressure and are outlet controlled, unlike single point heaters

Under Sink Water Heater

• This appliance works on the same principle as the over-sink heater
• Instead of the swivel spout, it is piped into a special tap or mixer tap
• The outlet is permanently open to atmosphere and the flow is controlled from the tap/mixer
• It will store 10-15 litres of hot water