The installation of a hydronically balanced variable flow system can have a positive effect on both energy consumption and costs, according to Peter Rees.
The Carbon Trust says that hvac systems can increase a building's energy consumption and associated carbon emissions by up to 100 per cent. With this in mind, it is important that steps are taken to ensure such systems use as little energy as possible.

A balanced variable flow system offers a good way to deliver energy savings of up to 50 per cent due to the reduction in pump speed and power required when the two-port control valves are closing. However, this energy saving is only achievable if the variable flow system itself has been correctly designed and commissioned and continues to operate at the set design flow after installation.

That is why, once commissioned, a hvac system must be regularly checked and maintained to ensure that it works at its optimum level. Without a maintenance schedule of this nature, the energy efficiency of a system will deteriorate over time.

In older office buildings where there is a need to refurbish a hvac system rather than install a completely new one, it is important to consider the building's layout and how each area is used in order to employ the best possible solution.

Taking refurbishment and system upgrades into account, it is vital to ensure that terminal units consistently operate at the desired flow, delivering a steady level of performance throughout the building. If the system is not commissioned and regularly checked for flow accuracy the temperature in different areas of the building is likely to vary. This will cause discomfort for staff and building users.

Through the constant altering of a thermostat, rather than addressing the underlying balancing issues, the components within a variable flow system can soon degrade over time. In an unbalanced system, water will work its way throughout the pipework via the quickest route back to the pump, finding shortcuts throughout the system. The result is an unregulated flow, which can cause severe fluctuations in temperature as well as affecting the integrity of the materials used within the system itself.

As a result, rooms not favoured by balanced water flow will not receive the set temperature until far later in the day, or in some cases, not at all. When the demand is increased, by way of the thermostat being altered, added pressure is placed upon the boiler/chiller and the pumps to work overtime to meet the requirement. System efficiency is reduced while energy costs are hiked up.

To avoid such issues, hydronic balancing methodologies must be implemented. A differential pressure control valve (DPCV) or a pressure independent control valve (PICV) must be installed to help stabilise the system pressure and flows.

Following commissioning, the DPCV prevents the flow and balance in the sub-circuit being affected by pressure changes caused by other subcircuits opening and closing or pump speed changes. DPCV's are designed to alter their position in response to changes in pressure, to maintain pressure equilibrium on branches. Alternatively, PICV can be used to reduce flow on terminals where there is excess pressure, or open to increase flow where there is insufficient pressure to maintain the design flow. Using a PICV requires only one valve to be fitted instead of three. A PICV incorporates three functions - differential pressure control alongside flow limitation and two-port control functionality.

For consultants and energy managers, the integration of such measures can significantly help to achieve notable levels of energy reduction. As such, there is a need for the balancing of variable flow systems to take place to ensure that energy consumption and associated financial costs do not reach excessive levels leading to a need to employ the services of a specialist hydronic balancing expert.

• Peter Rees is technical director of TA Hydronics