To ensure the effective running of a waterborne heating and cooling system, a set of simple yet effective balancing procedures must be put into place to make sure that the system runs at an optimum level of performance without using excessive energy. A well balanced system can help to eradicate temperature fluctuations and increased energy use, while saving time and cost for more efficient balancing and commissioning.
During the initial commissioning stages, it is important to consider how a balanced waterborne system can help to improve its efficiency in the long term. As such, it is necessary to employ measuring and balancing methodologies to help improve flow rates to ensure the design flow prevails.
When the flow of a waterborne system is altered with the introduction of a balancing valve, the pressure loss changes in the valve and pipe. Following this, the differential pressure across other balancing valves also changes. Balancing is a process of methodically measuring and adjusting flow to fit design conditions and accomplishing the right prerequisites for the system to work properly at optimum efficiency.
In short, to measure is to know; hydronic balancing ensures the system performs both during and after commissioning as it was designed to do. In a hydronically balanced system problems with efficiency derived from fluctuations in flow, pressure and temperature can be removed, preventing the need for extra demands on the pump and boiler, therefore ensuring it runs with both cost and carbon efficiency for the end user.
In practice the perception is that regular analysis and adjustments to plant with the system can be time-consuming and expensive — two elements the building-services or energy manager will want to avoid.
Even the best-designed systems must be balanced and then maintained utilising manual measuring to ensure the cost of staff discomfort (which prompts manual alterations to thermostat settings) does not overload the system and create energy waste. The cost of discomfort can be very high, with increased fluctuations in room temperature caused by excessive use of room thermostats and windows and doors being opened. Stable fluctuations in output will help preserve energy waste.
When adjusting the flow of a system with a balancing valve, the pressure loss in the valve and pipe is altered. Because the circuits in a system are interactive, these adjustments change the differential pressure across other balancing valves in the system. The main difference between different balancing methods is how they compensate for the interaction and its knock-on effects between circuits within a system.
Some balancing methodologies do not compensate at all, so the engineer will need to set the same valve several times until the flow finally converges towards the desired flow rate. This is a time-consuming and, therefore, costly process that can also cause disruption within the building where access to different valves is required.
Other methods compensate directly or indirectly — examples being the proportional method, the compensated method and the TA Balance method.
The fundamental principle of the proportional method is that variations in the differential pressure across the circuit will change the flow at the terminals in the same proportion throughout the whole system.
The compensated method is a further development of the proportional method, over which it has three main advantages. The compensated method makes possible staged commissioning. Plant can be balanced as construction proceeds, and there is no need to rebalance the entire system when it has been completed. Clearly the time and cost advantage here is a major benefit over the proportional method.
The compensated method saves significant amounts of time because it is not necessary to measure the flows in all balancing valves and calculate all flow ratios and just one flow adjustment is required at each balancing valve. In turn pumping costs are minimised. When balancing is finished the system engineer can read off the pump oversizing directly on the main balancing valve. The pump head may be reduced correspondingly. In these instances large energy savings can be made, particularly in cooling plants.
The TA Balance method embodies multiple benefits over both the systems described above. TA Balance is a computer program that is built into the TA Scope measuring instrument interfacing with the TA Select software. It offers all the advantages of the compensated method, as well as providing very significant time and cost savings by enabling one person to measure and balance an entire system single handedly.
Staged commissioning enables the system to be commissioned in phases as construction goes on, saving time because there is no need to rebalance the whole system once the building has been completed. Commissioning is even quicker because there is no need to measure the flows in all balancing valves and calculate all flow ratios. The method requires only one flow adjustment at each balancing valve.
When balancing using the TA Balance method is finished the engineer can again read off the oversizing on the main balancing valve. After having carried out pressure and flow measurements the program calculates the correct settings of the valves in order to achieve the desired flows.
Designing a system that is properly balanced will result in stable and accurate control for the best possible indoor climate, with minimum energy expenditure and reduced carbon emissions. Good hydronic balancing can actually cut the energy use of a system by up to 40%, equating to a considerable section of a building’s overall energy cost.
Employing an effective balancing technique during commissioning significantly reduces the risk of future problems. Likewise, the use of measuring devices such as the TA Scope will also ensure effective measuring and balancing in the longer term.
A hydronic balancing specialist can offer a raft of specialist techniques and recommend the most efficient methodology for the design and long term maintenance stages of any system, helping to eradicate energy efficiency issues brought about by an unbalanced system.
Peter Rees is technical director with Tour & Andersson.