Striking a balance

The drive to make heating systems more efficient and cost-effective remains a pressing priority

The drive to make heating systems more efficient and cost-effective remains a pressing priority. Christian Engelke, Technical Director at Viessmann, explores the path of least resistance for implementing hydraulic balancing.
Gas central heating systems are still widely prevalent in present day homes, contributing to a significant proportion of domestic energy consumption.
A straightforward solution to reduce energy usage, thus cutting carbon emissions and fuel bills, is to ensure a central heating system is delivering warmth to a property in the most efficient way possible. Fitting a condensing boiler is the fastest and most cost-effective solution to cut gas bills by up to 30%, but after that is becomes increasingly difficult to find energy saving modifications and adjustments.
Advanced control systems such as weather compensated controllers, low temperature radiators, and thorough home insulation do offer some alternative energy saving measures. Hydraulic (radiator) balancing is one such method that has fallen by the wayside.
In simple terms, hydraulic balancing is a method to ensure that all the radiators in a property heat up at the same rate. This prevents an uneven distribution of heat, wasted energy, and can boost heating efficiency while reducing fuel consumption by 15%.
Managing circuit flow
In a property with multiple radiators over several floors, it is not uncommon to find that some will heat up much faster and to higher temperatures than others. In some systems, the furthest radiator in the circuit may not heat up at all. The crux of this issue lies with flow of the hot water entering the radiators – some radiators receive too much hot water becoming overly warm, while colder units receive too little.
The flow of water around a system is both governed and constrained by resistance; even in a fully pumped system water will naturally flow along the path of least resistance. In an unbalanced heating system, the radiators closest to the pump offer the least resistance and will typically receive the highest flow of hot water and, therefore, the most heat. The further along the circuit the water has to travel, the more frictional resistance it encounters. This means that radiators at the zenith of the circuit will receive less hot water than those at the beginning and consequently take longer to heat up, or in some cases not heat up at all.
Often, a common solution to this problem is to increase the boiler temperature or install a larger pump to increase the flow of hot water to cold radiators. While this may overcome the shortcomings of an unbalanced system, such solutions consume more energy than necessary and are inefficient.
Even resistance
Hydraulic balancing requires the adjustment of lock shield valves so that every radiator in the circuit has the same frictional resistance. This allows the hot water to flow into the radiators’ heat exchangers at the same time, enabling even heating to be achieved.
Once all the radiators on a circuit are correctly balanced they will not require any additional balancing unless significantly different equipment, such as a new radiator, is added to the heating system. Even if the temperatures of individual radiators are adjusted, no additional balancing is needed as the flow resistance in the circuit remains the same.
Out of practice
Once the hydraulic balancing is complete, not only will the radiators heat up at an even rate, but it is likely that the boiler can be run at a lower temperature. For example, it may be possible to reduce the weather compensator slope because it will no longer need to compensate for radiators receiving an inadequate flow of hot water.
Yet, in spite of the clear advantages of hydraulic balancing, this once common practice amongst installers and plumbers has fallen out of favour. The advent of the mandatory fitting of thermostatic radiator valves (TRVs), which allow the adjustment of individual radiator temperatures, has resulted in balancing being overlooked.
While sounding simple in theory, radiator balancing requires an understanding of a system’s specific details such as its heat load, design and flow rate; this can often require specialist knowledge and equipment.
Moreover, radiator balancing is an arduous sequence of ‘rinse and repeat’ processes, potentially taking a whole day to carry out correctly. Subsequently, for busy contractors with a long list of tasks, radiator balancing tends not to be a priority.
Equally, a lack of awareness among homeowners means that radiator balancing is not considered as a method to improve heating output. In many cases, homeowners will assume uneven radiator heating is a fault or inefficiency with the boiler. Therefore, in many ways hydraulic balancing remains in limbo – offering plenty of efficiency benefits yet troublesome to implement and rarely requested.
Exploiting an opportunity
There could be a gap in the UK market for the adoption of hydraulic balancing as an easy-to-implement ‘added value’ service that installers and plumbers can offer their customers. By reducing the time, effort, and training needed to correctly balance radiators, the initial cost of the equipment could be passed on to the customer as part of an additional service.
Balancing the system is normally part of the job when fitting a heating system, like flushing an old system. However, while balancing tools and guides are available, they require expensive temperature measurement equipment. Unless it is written as a ‘must do’ job in the building regulations some contractors are reluctant to invest in such tools. It is worth remembering that no amount of commission or adjustment will compensate for poorly designed or installed systems.
In Germany, hydraulic balancing has become part of its heating regulations in a bid to increase the energy efficiency of domestic heating across the nation. To facilitate its implementation, the German Government provides subsidies to cover the cost of balancing. Unfortunately, no such subsidies currently exist in the UK.
Regardless, imagine the efficiency benefits that hydraulic balancing could deliver if incorporated into energy
saving schemes, such as the Green Deal, which already subsidises home insulation and the use of renewable energy.
The continued focus of efficiency throughout many industries will hopefully see the progression of once respected techniques become mainstream processes, as the drive to reduce costs, energy consumption and carbon emissions remains at the forefront of policy and best practice.