Correct balancing is widely recognised as one of the keys to ensuring a heating system works as per the design specification. As every heating professional knows hydronic balancing is the process of optimising the flow of water in a hydronic heating (or cooling) system by balancing the system pressure. Pressure drop in a central heating system occurs because of the way water behaves when flowing through any pipework system. Balancing ensures that water flows equally to individual radiators and so prevents cold or hot spots occurring, or the property not heating at all.
As well as the discomfort factor, the efficiency of an unbalanced system is significantly reduced, increasing energy consumption and fuel bills for consumers. Furthermore, TRVs with too much flow may not operate properly and can become noisy as water streams through the valves, particularly as they start to close when the room temperature increases.
When faced with a customer complaint of cold radiators some installers may consider putting the system pump onto a higher speed or put the boiler thermostat onto a higher temperature setting. Although this might seem like a quick fix compared with hydronic balancing it may not solve the problem and will increase the system’s energy consumption. It could also result in noisy radiator valves, leaving an even more dissatisfied customer.
Although not currently mandatory, hydronic balancing is considered best practice. However, industry reports suggest that uptake of this process amongst installers is sometimes neglected during the installation and commissioning of domestic hydronic heating systems. This could be down to a lack of expertise or confidence to balance a system – or simply because of the time it can take using traditional methods. Whatever the reason, let’s begin this guide by reflecting on the basic principles of hydronic balancing and the method of adjusting lockshield valves that most installers will be familiar with.
Adjusting the lockshield valves on the return side of each radiator ensures that each radiator circuit in the system has an equal pressure drop and receives the correct flow of hot water to heat the space in which it is fitted. As any installer who has performed this process knows this can be very time-consuming. Firstly, air must be removed from the system by bleeding the radiators. Then the heating is turned off and radiators left to cool down before the heating is turned back on. Flow valves or TRVs (if fitted) are then set to the fully open position and the lockshield valves by turning them anti-clockwise. The installer then checks by touch and makes a note of which radiators heat up first. If they are not heating evenly the radiators that get hottest quickest should have the flow restricted by closing the lockshield valve – allowing a couple of minutes after each adjustment for the temperature to stabilise before moving on to other radiators. Return valves on the hottest radiators will probably need to be restricted by 50% or 60% to start with, however, to balance a poorly designed system it may be necessary to close a valve more than 80%. The lockshield valve is adjusted until the required temperature drop between the flow and return pipe is achieved. This is typically 20°C for condensing gas boilers but always check the appliance manufacturer’s guidance.
Using lockshield valves to limit flow is a static form of balancing and probably the most common method but it’s not very accurate and takes time.
An accurate flow limiter with a presetting function is an alternative static solution whereby the installer calculates the flow required for each radiator and adjusts to ensure the required amount of water is delivered. Although more accurate than a lockshield valve this form of balancing is only optimised for the coldest days (winter) when the heating system is operating at full (design) load. This means flow could be unnecessarily high on milder days (spring/autumn). If TRVs are fitted the room temperature can be controlled, but flow through the radiators will be the same, resulting in over-delivery and wasted energy.
A dynamic solution such as the new Danfoss RAS-B2 functions as both a flow limiter and dynamic pressure valve. It limits flow through the TRV but does this independently of pressure fluctuations, so it is optimised for all days. The valve’s built-in differential pressure controller ensures that pressure drops over the valve remain at a constant level, which means flow through the valve is maintained at both full and partial loads. As well as improved consumer comfort, a dynamic solution can enhance system efficiency as the return temperature is lower (condensing boiler efficiency is best at below a return temperature of 55o C) and the pump can run at a lower speed and so consumes less electricity.
Tests suggest that potential savings using the RAS-B2 Dynamic valve could be 13–16% kWh/m2 compared with 5-9% kWh/m2 for a static accurate flow limiter with presetting. Furthermore, because presetting of the desired flow is done on the Danfoss RAS-B2 valve, rather than on the lockshield, installers could save up to two hours of valuable working time and correctly balance a system in a fraction of the time it would normally take.
Developments utilising new technology are now making system balancing even easier for domestic installers. The Danfoss Installer App, for example, provides an interactive guide to the process of calculating, recording and documenting the correct flow and subsequent setting for each radiator on a smartphone or tablet. Using the App’s radiator presetting tool, installers can perform quick and easy calculations based on the selected valve, sensor and key system parameters. Having defined flow, return temperature and differential pressure (the difference between static and dynamic pressure in the heating system) the App displays the calculated flow in litres/hour and emission in watts for each radiator. Based on these calculations it will recommend the setting for the TRV. Using the App’s project function also makes it possible to calculate the correct setting for each radiator prior to installation, allowing for much quicker commissioning on site. Once complete, a report of the settings is generated for future reference and will also document that the system has been adequately balanced and can be e-mailed to the customer if required.
Given the clear comfort and efficiency benefits, and the expectation that forthcoming updates to Part L will include an increased legal requirement to prove that domestic heating systems are well balanced, we advise all installers to embrace balancing as best practice on every installation. And now, thanks to innovations like the RAS-B2 Danfoss Dynamic Valve and Installer App, hydronic balancing doesn’t have to be a daunting or time-consuming task.
2-in-1 temperature control and automatic balancing valve