A balancing act: achieving more efficient domestic heating through system balancing

7th Sep 2017


By Steve Sutton, Technical Manager, HHIC

In this day and age, it’s easy to get caught up with new technology relating to the heating industry and forget some of the simple processes which can reduce inefficiency and excessive energy usage in appliances.

With winters getting colder and fuel bills steadily rising, many radiators will need some TLC in order to keep running efficiently. Whilst the practice of bleeding radiators is relatively well known, many consumers are unaware of the merits of balancing heating systems – an intuitive, common sense principle that heating engineers can use to make existing systems more effective. In fact, some consumers unintentionally, unbalance their heating systems. Born out of the mistaken belief it will give their properties more heat, households may open both radiator valves fully, the result being that the radiators nearest the boiler take the bulk of the hot water flow, leaving other radiators with little flow.

As manufacturers continue to pursue their goal of making heating systems more efficient, in order to achieve optimum consumer comfort, we must remember that the heating system itself has to be installed and commissioned correctly to ensure that is works as per the design specification.

Today, condensing boilers, boiler modulation, pump modulation, intelligent energy saving controls and passive flue heat recovery all enable us to achieve the aforementioned goals relating to comfort and energy efficiency. Irrespective of these technologies, installation of the heating system is still a key part of the process.

A relatively simple part of this process is balancing the heating system.

Hydronic balancing (or hydraulic balancing) is the process of optimising the flow of water in a building’s hydronic heating or cooling system by balancing the system pressure so as to provide the desired indoor climate at optimum energy efficiency and minimal operating cost.

Often, the result of an unbalanced system is one or more radiators not heating up properly, causing cold and hot spots to emerge in a house. Sometimes, unbalanced systems can cause the property to not heat at all. Ultimately, if a system is not adequately balanced, its efficiency is significantly reduced.

Understanding pressure drop in the heating system

If we look at how water behaves when flowing through any pipe-work system and the potential for pressure drop, then we can start to understand why a heating system needs to be balanced. Pressure drop in the case of a central heating system occurs when frictional forces, caused by the resistance to flow, act on a fluid as it moves through a pipe.

This resistance is increased by bends and will be higher in a smaller diameter pipe than it will be in a larger one. The water pump has to generate enough pressure to overcome the total pressure drop (pressure loss) in the system. This is made all the more complex by the fact that each radiator in a system will have a different total pressure drop.

 If we combine this with the fact that the pipes connected to and from each radiator will be of different lengths, with some taking straight and others circular routes, we begin to realise how hard the water will have to work to flow around all radiators in the system.

A common solution to this is the water taking the path of least resistance – if radiator A and its associated pipe work has a lower pressure drop than radiator B, then, naturally, more of the water will flow to radiator A. If the pressure drop through radiator B and its pipes is higher than that of radiator A then water may not flow through to radiator B without increasing the boiler temperature significantly or adjusting the pump speed to increase the flow of water to cold radiators. Whilst these actions may temporarily counter the pitfalls of an unbalanced system, these solutions consume more energy than necessary and aren’t efficient.

When the system is balanced by adjusting the lock shield valve on the return side of each radiator, each radiator in the system has a roughly equal pressure drop.

The two valves on the radiator serve to make this balance achievable, allowing consumers or heat engineers to restrict hot water flow to certain radiators in order to divert it to others, balancing the system.

Once the hydraulic balancing is complete, the radiators heat up at an even rate and, in most cases, the boiler can run at a lower temperature, increasing efficiency. Given its clear benefits, this simple process shouldn’t be neglected.