The energy consumption of hvac equipment can often account for more than 40% of a commercial building’s energy consumption. Simple improvements to the efficiency of installed systems can offer considerable energy and CO2 savings.
According to Ebm-Papst, one aspect that is often overlooked does not require a complete retrofit or replacement of the existing system. The German-owned fans and motors manufacturer insists that just adding variable-speed EC fans to the chillers, AHUs and fan coil units can save between 30 and 60% on annual electricity costs.
While many new facilities already incorporate EC fans into their hvac equipment, there are still thousands of less-efficient AC fans installed in AHUs.
Ebm-Papst UK recently surveyed 12 AHUs in central London and calculated that to upgrade the AC fans to EC fans meant that minimum savings of 28% were almost guaranteed prior to replacement. This estimation proved to be somewhat modest. The measurements taken after a trial installation were said to show overall savings were in the region of 70%, with a payback of just under two and a half years. This payback was calculated by running the AHU ten hours per day, six days per week – savings that would have been even greater had the unit been running for a longer period.
The original AC fans consumed 6.3KW compared to the new EC fan at just 1.9KW providing annual savings of 13,727kW/hr, two tonnes of CO2 and £1,650 for each AHU. The total annual saving for all twelve AHUs was estimated at £19,768.
In addition to the direct savings from converting from AC to EC technology, the retrofit uncovered other inefficiencies in the system which accounted for the enhanced savings achieved. The original fan design incorporated two AC belt driven fans, one running and one for redundancy (in case of belt failure). This meant that the running fan motor not only drove the fan but also pulled the standby motor along with it. The new EC fan is directly driven and as such is maintenance free, which means there is no requirement for a standby motor.
AC fans up to 12KW can normally be upgraded and, in most cases, EC fans are directly interchangeable with the AC predecessors, allowing for simple replacements with minimal disruption. Any voltage combination can be accommodated i.e. DC or AC single or three phase, as the electronics are fully integrated into the motor.
EC fans can be supplied in different configurations including backward curved centrifugal fans (mainly found in AHUs and data centre cooling units), forward curved blowers (found in fan coil units), and axial fans (normally fitted to chillers and condensers).