Improving the Efficiency of Air Handlers
Air handlers are designed to provide sufficient airflow when the building is at full occupancy. However, supplying the design airflow when indoor areas are not full is a waste of energy. Consider that not only fan power is wasted, but also part of the cooling or heating output.
Demand-controlled ventilation (DCV) consists on adjusting airflow according to occupancy, with the purpose of saving energy. HVAC engineers can suggest an adequate method to monitor occupancy, and this information is used to ramp down airflow when the full capacity is not required.
When deploying demand-controlled ventilation, the speed of fans can be adjusted with variable frequency drives (VFD). The potential savings are significant, since fan power is reduced in cubic proportion to fan speed. For example, if a VFD reduces fan speed to 80% of its rated RPM, power consumption is reduced by almost 50%.
The performance of air handlers can also be increased with heat recovery systems, which exchange heat between the outdoor air supply and the exhaust of a ventilation system. Consider that building codes establish minimum outdoor airflow rates, which are calculated based on the type of building and its expected occupancy. However, the exhaust air often has cooling or heating potential that is wasted.
- During summer, a heat recovery system uses the exhaust air to remove heat from the outdoor air supply. Since the outdoor air reaches air handlers at a lower temperature, the cooling load is reduced.
- The opposite process applies during winter, where the exhaust air is used to preheat the outdoor air supply. In this case, the heating load is reduced.
Heat recovery systems decrease the load on HVAC system in both heating and cooling mode, thus reducing the energy expenses of a building.
Like with many other building systems, adequate maintenance is important to keep air handlers under optimal operating conditions. Filters cause an increased pressure loss as they accumulate particles, and this represents a waste of fan power. Also, dust accumulation on the surface of heating and cooling elements reduces their effectiveness. Air handlers should be cleaned are regular intervals to prevent these issues.
Troubleshooting Noise and Vibration Issues in Air Handlers
Noise and vibration are common issues when air handlers are not designed properly or when maintenance has been deficient.
- Oversized fans and inadequate air handler supports are two common causes of noise and vibration issues.
- Consider that some mechanical components wear down over time, and rotating elements of motors and fans can start experiencing unbalance and misalignment.
A certain degree of noise and vibration is unavoidable when using air handlers, especially when dealing with a large unit. However, regular inspections from qualified MEP engineers are recommended to detect issues and solve them proactively. In new installations, noise and vibration can be minimized with smart design decisions.
