Pressure Hot And Cold Domestic Water Systems

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 pressurised system b.jpg (22138 bytes)
click to enlarge.
Simple layout of a pressurised  hot & cold domestic water supply via cold storage tank.

Note: This is only for information purpose and cannot replace a proper designed hot and cold water supply. Wrongly installed pressurised system can cause injuries 

This simple guide will help you understand how pressure hot & cold water systems work.

You may be considering installing new, or changing an existing system to provide pressure hot & cold water at your taps. This may be an ideal choice for you, but before you make your decision understand how these systems work and consider all the facts.
Any system providing pressure hot & cold water supply is only as good as the supply entering the property and the storage of cold water. A product may boast for example - 35 litres per minute flow rate at 3 bar pressure - but if the supply to your property is inadequate and can only muster say 15 litres at 1 bar, you have to increase the size of your cold water storage tank. Figures quoted against products are indicative of their potential based on an adequate supply of cold water.
How does it work? (Hot Water)
In general, a pressure domestic hot water system works by the mains supply is connected to the cold storage tank's) a supply pipe going from the storage tank to a booster pump, the pump pressurise the water and supplies the hot storage tank with water, by means of heating water in the hot water storage the hot water  taken directly to be delivered to your taps. There are several ways to do this and many find different manufacturers interpretations on product design.
(Cold Water)
The cold water is taken before the hot water storage tank and piped directly to your taps.
The Choices
There are two main types of domestic  Pressure Hot & Cold Water Systems.
Unvented Domestic Hot & Cold Pressure Systems
Vented  Domestic Hot & Cold Pressure Systems

The term vented refers to whether the system is partially vented to atmosphere or completely pressurised and therefore unvented.

Unvented Pressure Systems
In an unvented system, incoming pressurised cod  water typically enters a hot water tank suitable for pressurised water up to 10 -13 bar (for example: a Solar storage tanks made by Huch and are available from us, where it is heated either directly by means of electrical heater/s immersion or external type, or indirectly by means of heat exchanger's) within the vessel being supplied by your solar thermal system or central heating boiler. The hot water stored within the vessel  is forced out by the incoming cold water pressure when you open a tap hence - Pressure Hot Water.
Vented Mains Pressure Systems
In a vented system, heat is imparted to the incoming pressurised water by means of a secondary heat exchanger within the "hot water storage tank". Water in the vessel is used rather like a battery for heat - a thermal store. The incoming  water passes through it's heat exchanger within the vessel drawing heat from the store. The Thermal Store temperature is maintained in the usual way - either directly with electrical heaters, or Indirectly by your boiler or solar system.

Because the water within the Thermal Store does not need to be under pressure (as with an unvented system) it is vented to atmosphere. The body of water within the thermal store is used purely as a medium for storing and imparting heat to the secondary exchanger.

Unvented and vented systems both provide hot water at  pressure. They achieve this by slightly different methods. There are however certain considerations when choosing the system that suits you best.
Unvented Pressurised Systems
In an unvented system you will be storing a large volume of hot water under pressure. For reasons of safety such systems must be installed by qualified technicians with relevant experience, CITB training and G3 certification.
As a precaution, pressure-relief pipe work and valves must be installed to protect against unsafe pressure build-up within the vessel which could result in explosion.
Your Local Authority (Building Control Dept) will need to be advised of your intention to install an unvented system.
For reasons of safety, your system will require annual maintenance to ensure safety equipment is functioning correctly (BS2870).
An unvented system must be commissioned and certified by the installer. 
Vented Pressurised Systems
A vented system does not store a large volume of hot water under pressure. The Thermal Store, whilst containing hot water, remains at atmospheric pressure.
There are no hazardous issues with a vented system. Pressure relief valves and pipe work are not therefore required.
Vented systems do not require Building Control approval.
Because of the simplicity and safety of such systems, installers do not need certification or specialist training.
Vented systems do not need certification.
There are no special annual maintenance requirements.


Drawbacks of a pressurised hot water system
Under water bye-laws you may not add a pump directly to your mains to increase the flow rate to your storage tanks. If the mains supply to your house is poor there will be no simple way to improve it. Additional performance usually entails bringing in a new, larger supply pipe to the property. Even then, you should ensure the new improved supply will be adequate, as some areas suffer from frustratingly low pressure.

Always remember - your system can never be better than the supply to it you can add storage tanks to increase the amount of water stored.

Pressurised systems are at the mercy of fluctuations in supply pressure and storage. This may not be an issue in the majority of cases.

Pressurised systems can give 'power shower' performance, providing mains supply  is good. If you like a vigorous showering experience and your mains supply is poor and your storage inadequate remember  some booster pumps will pump 35 -95litres of water per minute.

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