What are the different types of pipework installations used in central heating systems?

Tue 2nd Dec 2014 - 5:44am Energy and Heating What are the different types of pipework installations used in central heating systems?

Benjamin Clarke

The main ‘ingredients’ of a conventional hot water system are the boiler, the radiators and the pipes through which the water flows from one to the other.

The usual process is that the boiler will heat the water, and then a pump will send the hot water through the pipes, into the radiators and then back into the boiler.

In the vast majority of cases, there are 3 main arrangements that the pipework can have when connecting the boiler to the radiators, each of which has it’s own advantages and disadvantages.

- Feed and Return Pipes
- Single Pipe Loop
- Microbore Pipework

1. Feed and Return Pipes
In this system, the hot water from the boiler is fed to one side of every radiator. This is known as the ‘feed pipe’. The opposite end of the radiator has a ‘return pipe’ which works by taking the cold water away. Each radiator should receive water at approximately the same temperature and therefore heat the room (or area) by a similar amount.

There is a pressure relief valve connected between the feed and return pipes which enables the pump to circulate the water from the boiler in the event that all radiators are switched off.

A disadvantage of the feed and return system is that the number of radiators that can function is limited by the size of the pump that circulates the water. A ‘standard’ pump can feed water to a maximum of 12 radiators, which may not be enough if you have a particularly large house. However, this method is generally considered more efficient that the single pipe loop method, described below.

2. Single Pipe Loop
This system operates a single loop of pipes that flows from and returns to the boiler. Rather than having one pipe to bring in the water and another to take it away, this installation has all radiators sitting on the pipework with both ends of the rad connecting to the same pipe. The hot water is pumped from the boiler along the pipe, where it rises into the radiator and pushes the cold water back into the pipe.

One of the major problems with this system is there is often a huge disparity between the temperature of the radiator closest to the boiler and the temperature of the radiator at the extremity of the system. This is due to the fact that the water will arrive hot in the first radiator, but by the time it reaches the furthest radiator, most of the heat will have dissipated, causing the radiator temperatures to be uneven around the house.

In theory, unlike the feed and return system, it is possible to fit as many radiators as you like to this installation, however there will always be the issue of the last radiator being colder than the first.

In general, although this system can be found in old buildings and industrial premises, the single pipe loop is considered inefficient and antiquated, and is no longer used on new builds.

3. Microbore Pipework
This system utilises regular pipework to feed the water from the boiler to manifolds and then from the manifolds to the boiler on the return side. 8mm pipework connects each manifold to a number of rads, with the length of the pipework usually being kept to below 5 metres.

It’s possible for the radiators to be installed so that the feed and return microbore pipes are connected to the same end of the radiator, but it’s also often the case that the feed and return pipes are connected to each end of the rad.

As with the feed and return system, there is a pressure relief valve between the boiler and the return pipes in the event the rads are all shut off. This helps to protect the boiler, extending it’s longevity.

The main benefit of the microbore system is that because the pipes are smaller. less water is carried through them, which in turn means less heat is lost as the water flows, leading to greater efficiency. The smaller pipes are also easy to bend and reshape whilst they are being installed making the more versatile and decreasing the amount of joints needed. (Joints can be prone to leaks and additional heat loss.)

However, the small pipes can also be a major disadvantage of this system, particularly in hard water areas. The smaller pipes are more susceptible to becoming blocked which can cause a pump to wear out more quickly due to the fact it is working harder to try and pump water through the blocked pipes.

Article by Benjamin Clarke

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