Improving operation and control
Many building managers would agree that the symptoms of indoor climate problems most often surface as complaints from tenants, as living or working spaces are too cold in winter, too hot in summer or a combination of both extremes.
All too frequently, ‘fixes’ to HVAC systems prove both costly and ineffective. Costs may include the installation of larger pumps, the resizing of components, the changing of night-setback and morning start-up times, and flow adjustments in mains, branch lines and circuits. For example, the resetting of a workplace HVAC system start-up time from 7:30am to 5:30am leads to a plant operating at capacity two additional hours per day. This equates to a 25% increase in energy consumption, cancelling any energy savings that night setbacks are designed to achieve. Additional consequences include increased wear on pumps and HVAC components and reduced control-valve authority.
Indoor temperature and climate problems are not typically caused by control malfunctions or sizing errors. Often, they can be traced to incorrect flow rates attributable to improper terminal-unit balancing. Engineers normally design HVAC systems with excess capacity in mind, so that the ability to provide necessary heating or cooling energy is present. Transferring that energy to terminal units and air-handling units (AHUs) is the challenge. Therefore, the key to HVAC-system effectiveness and efficiency is properly controlled flows from production and delivery units to terminals.
Balancing valves maintain flow conditions so that control valves may function properly, providing correct flows to the heat transfer coils, which results in the correct output of energy to a space.
HVAC-system flows are dynamic, changing throughout a typical 24 hour period. Because of heat gain from the sun and changes in building occupancy, the demand for heating and cooling varies, not only throughout the day and night, but also by building sector. An effective and efficient HVAC system must provide correct energy output when and where required, and proper hydronic balancing is the key to correct performance in the most cost-effective way.
Circuit balancing is essential to ensuring that heating and chilled-water systems deliver correct flows to all terminal units in a HVAC circuit. In an unbalanced system, sectors of a building have underflow or overflow conditions that impact control-valve authority and therefore indoor climate. For instance, areas closest to an energy-production and delivery source could receive excess flow, resulting in excessive heating or cooling. On the other hand, areas furthest from an energy-production and delivery source could receive insufficient flow, resulting in inadequate heating or cooling.
For every single degree that the temperature is increased above 20°C there is an 8% increase in heating costs, whilst each and every degree of cooling below 23°C adds on 15% to costs.
By properly applying circuit balancing techniques to each balancing valve it is possible to achieve proper balance throughout a system so that all circuits receive specified design flows for optimal performance. When pumps, chillers and other components operate at the lowest possible load, owners benefit from less wear and tear, longer equipment life, and lower energy and maintenance costs.
An improperly adjusted balancing valve, clogged strainer/coil or other system issue that changes the specified flow rate through a coil or AHU typically causes insufficient or excessive heating or cooling. Diagnostic analysis can be performed readily by checking the rate of flow through a balancing valve. Moreover, issues can be identified during building commissioning and before the tenant moves in.
In addition to providing a comprehensive record of specified and actual flows, circuit balancing helps simplify the setup and monitoring of control equipment which reduces capital costs, as well as the time needed for commissioning.
Far too many buildings are plagued by temperature variations that can lead to tenant complaints, high energy consumption and increased operating expenses. In most cases, these faults can be easily resolved through proper balancing of the heating or cooling system in conformance with original design performance specifications.
Effective circuit balancing can help determine the causes of improper heating and cooling. Therefore a comprehensive circuit balancing programme should be integrated into any commissioning to save time and energy and to improve the long-term value of the building.