The root of problematic HVAC systems

By Marcel Ley, Victaulic regional manager
Often an unbalanced system is the root of erratic HVAC systems. An effective and efficient HVAC system must provide energy output when and where required; and proper hydronic balancing is key to ensuring that the system performs efficiently and as intended.

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The typical HVAC system incorporates balancing valves for each terminal unit coil and air handling units. Pictured: the Victualic Oventrop double regulating and commissioning valve. Image credit: Victualic

Flow in an HVAC system is dynamic, with its performance dependent on various changes such as building occupancy rates, and the demand for heating or cooling.

There are however instances where symptoms of HVAC problems result in temperature variations throughout various sections of a building and are seemingly only brought to surface once tenants complain.

In response to this, occupants often compensate by using space heaters, opening windows and adjusting thermostat settings. Further, additional adjustments to the HVAC system may include larger pumps, resizing components, changing night setback and morning start-up times, and flow adjustments in mains, branch lines and circuits independent of the impacts on the entire HVAC system. Most often, these types of ‘fixes’ to alleviate cold and hot zones in a building are typically ineffective and costly, and usually do not correct the situation.

With persistent changes to the system settings, building owners are often subjected to higher energy and operating costs as the HVAC systems tend to operate longer than intended, with the system not making use of the energy savings that night setbacks were designed to achieve. Additionally, the operational costs involve additional wear on pumps and HVAC components.

With these problems comes the fact that the finger will be pointed at system engineers from the get-go, and they will be challenged to defend their design and implementations when in fact the problem lies in the unbalanced nature of the HVAC system.

Indoor temperature and climate problems are not typically caused by control malfunctions or sizing errors. Often, they are traceable to incorrect flow rates in the HVAC system due to improper terminal unit balancing.

Generally, engineers design HVAC systems with excess capacity for the buildings in which they operate, and thus, have the ability to provide adequate heating or cooling when necessary. However, many have identified that getting this energy to the terminal and air handling units is the real problem. We can therefore determine that in most cases, the key to HVAC system effectiveness and efficiency is properly controlling flows throughout the entire system from production and delivery units to terminal units for the comfort of all building occupants.

Proper circuit balancing is essential to ensure that the heating and cooling water systems deliver correct flows to all terminal units in the HVAC system, and most notably, as specified by the system’s design flow. A tell-tale sign of an unbalanced system will be that sectors of a building will have underflow and overflow conditions that impact control valve authority. This is evident where areas closest to the energy production and delivery source may receive excess flows which result in excessive heat or cooling. Likewise, areas that are further away may experience inadequate heating or cooling levels due to insufficient flow rates.

The typical HVAC system incorporates balancing valves for each terminal unit coil and air handling unit. In order to balance a coil that makes use of a manual balancing valve, the technician is required to connect a differential pressure gauge or handheld circuit balancing instrument to the valve’s two test ports.

Depending on the valve size, hand wheel position and the measured differential pressure, the system flow rate through a balancing valve is readily determined with a balancing instrument, balancing flow rate or determining the valves characteristics. The valve hand wheel is then able to be adjusted to obtain the required system flow rate.

Applying this technique to each balancing valve throughout the system will result in proper balance being achieved. When pumps, chillers, and other components operate at the lowest possible load, the benefits obtained from lower wear and tear costs, longer equipment service life, savings in maintenance and energy costs, and happy tenants, would bear testament as to how preventative maintenance and correct procedures are essential in HVAC operations.

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