COLD WATER SYSTEMS

Many people take for granted the seemingly endless supply of wholesome water to their homes. As a plumber, it’s your responsibility to make sure the cold water that reaches people’s taps is clean and ready for human consumption, in order to prevent severe illnesses. To do this, you will need a good understanding of the water regulations, water treatment and the supply and distribution of cold water.

WHAT DO I NEED TO KNOW?

In this article, we will look at the two different types of cold water systems: direct and indirect.

Direct cold systems - The most commonly installed system, where appliances are fed ‘directly’ from the mains water supply.

Indirect cold systems - This is where all the appliances are fed ‘indirectly’, via a cistern. The incoming main feeds a cistern at high level and then the appliances are fed, indirectly, from that cistern.

The Pros And Cons

Direct System

Pros

■ Mains pressure across both hot and cold supplies

■ Cheaper to install as there is less pipework needed, and reduced risk of frost damage

■ Drinking water is available from all draw-off points

Cons

■ If the mains is off, everything is off

■ More wear and tear on taps and valves due to high pressure

■ Water pressure noise can be a problem

Indirect System

Pros

■ If the mains goes off, you still have a supply as long as there is water in the cistern

■ Can be pumped to improve it further

■ Reduced amount of system noise, due to low pressure

Cons

■ More pipework, so greater cost and higher risk of frost damage

■ If installed poorly, the cistern can be the source of contamination

■ Without a pump, pressure will still be low, but at least it works!

TEST YOUR KNOWLEDGE:

1

2

3

4

5

Which is the most commonly installed type of cold water system? Direct or indirect.

Name two advantages of an ‘indirect’ system.

Name two advantages of a ‘direct’ system.

If the water pressure in a property is below 1 bar which type of system would be most suitable?

What is the difference between a pressure gauge and a weir cup?

Go to hip-magazine.co.uk to download exercise answers for free

HOW DO I DECIDE WHICH TYPE OF SYSTEM TO INSTALL IN A PROPERTY?

The first thing you need to do is measure the water pressure at the property. To do this, attach a pressure gauge to a mains fed point like the kitchen cold tap, washing machine valve or garden tap. It’s a good idea to do this when demand on the mains is higher (in the morning, for example) so you get a reading that reflects the lowest pressure the system will receive. If you have to take a reading during the day, try and make an allowance for high demand. You need to measure static pressure (when all outlets are closed) and working pressure (when at least one outlet is open).

Read the manufacturer’s instructions for the appliances you are planning to install. Most combi boilers and showers will require at least 1 bar of pressure to operate. If you have less than this you may want to consider an ‘indirect’ supply. Water supply pressure has improved in most areas but some areas still suffer from low pressure, especially in rural locations. If you have good mains pressure, you will probably want to install a ‘direct’ system.

I’M NOT JUST INSTALLING COLD WATER, I’M INSTALLING HOT WATER AND HEATING TOO!

For hot water and heating on a direct cold supply, you may want to think about a combi boiler or a system boiler with unvented hot water. This will also depend on the size of the property. If you have poor water pressure and are installing an ‘indirect’ cold supply then you may want to think about a heat only boiler with an open vented heating system and open vented hot water. You may want to consider adding a pump to boost the cold supply from the cistern and hot supply from the open vented hot water cylinder.

WHAT PRESSURE WILL AN ‘INDIRECT’ SUPPLY GENERATE?

For every metre of head height, the system will generate 0.1 bar of pressure. 10 metres of head height will give you 1 bar. Head height is measured vertically in a straight line between the point of use to the cistern. If you measure the height between the floor and ceiling on each storey in the building, you can accurately estimate the head height.