Are you feeling the pressure?

Published:  03 July, 2008

Storing water at mains pressure provides a neat way of delivering higher flow rates by enhancing the mains.

Low pressure and poor flow rates can cause serious water problems at existing and new-build properties. Darren Cooper explores the issue and suggests various solutions.

Larger living spaces with multiple bathrooms and modern fittings are increasingly popular. However properties with high water demand and multiple outlets need good flow and pressure rates to meet customer expectations.

Flow rate is the amount of water carried in the mains supply to the property and in the internal pipe-work, measured in litres or gallons per minute. Pressure is the force driving the water in the pipe, measured in bars or pound per square inch. Poor flow rates and pressure fluctuations are common and can compromise showers, mains-fed fittings and cold supplies to unvented cylinders and combination boilers.

GAH believes it is essential to carry out pressure and flow tests before the specification of mains-fed systems to ensure that water supplies are adequate for the property and customer demand. The water-board minimum supply requirements are one bar and 9 l/min at the boundary, although these figures are rarely found. However, without the appropriate tests, how can you be sure how good the supply is?

When testing a mains supply, the average UK pressure will be around two to three bars. However, it is not unusual to find premises with pressures lower than two bars and flow rates of below 15 l/min. It is recognised by most manufacturers of unvented systems that the minimum requirement to operate an unvented cylinder is 1.5 bar and around 20 l/min. It some cases flow rates will fall below this requirement, leading to fluctuating pressures, poor performance and — ultimately — unhappy customers. Even good mains supplies can have issues, if the demand outweighs supply.

What people don not realise is that pressure is nothing without good flow rate behind it. For example, if a property with one main bathroom has a shower running at 22 l/min and a tap in the kitchen is running at 10 l/min, it would be practically impossible to supply both outlets if the property had a standing pressure of 4 bar and only 22 l/min from the mains supply. High pressures will not provide a substitute for poor flow rates.

A pressure and flow test is fast and easy and can quickly indicate any potential problems at the beginning of a project, so installers can look at ways of overcoming them.

In systems with a cold-water storage tank, increasing this tank size and installing a suitable booster pump set will help to improve pressure and flow rates. However, siting may be impractical, and the booster pump set must meet with water bylaws. Cost might be a concern and noise levels may not please property owners.

A pressure and flow test of the water supply to a building is quick and easy to carry out.

An alternative would be to upgrade the mains supply with a larger pipe. Again, this could be costly. Unfortunately renewing the main does not guarantee better performance because the legal requirement supplied by the water authority remains the same.

A solution for properties with mains-pressure systems like an unvented cylinder or combi boiler is accumulator technology. This will boost flow rate and help to maintain pressure. Accumulator technology does not require a power supply and is virtually silent when running. It uses no energy — achieving increased volume in an efficient, environmentally friendly way.

GAH also have a solution to flow rate problems — the patented Dualstream system, which consists of an indirect or direct unvented stainless-steel cylinder with the added bonus of an accumulator. These link together to provide maximum performance of the hot and cold outlets, even if two or more supplies are being used.

The accumulator vessel stores mains water at incoming pressure in a butyl diaphragm. This becomes the driving force that increases water volume. Water pressure is balanced between the accumulator wall and the diaphragm. When taps are turned on, water in the accumulator vessel enhances the main, which feeds the cylinder to boost hot and cold water flow rates and maintain mains pressure.

Whether you are specifying fittings, designing a property or converting a traditional system to unvented, adequate pressure and volume is essential — otherwise top-notch fittings may be compromised and customers will be left disappointed.

Darren Cooper is sales and technical director for Dualstream with GAH Heating.

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