AIR CONDITIONING
How Ecodesign and smart control have raised the bar
In the realm of air-conditioning and heating solutions, rooftop units have often represented a low-first-cost solution. While easy to install, the relatively lower cost compared to traditional air-handling systems came with the compromise of a lower efficiency – until now. Dominique Silva, product manager at Trane, explains.
R
ooftop units are packaged air-to-air systems that combine heating, air- conditioning, ventilation and controls
within a single frame. They are typically connected directly to ductwork systems and can operate stand-alone or with remote temperature and humidity sensors. Rooftops do not require ancillary systems like pumps or fan coil units to operate and can be relatively easily commissioned thanks to their ‘plug and play’ nature. The Ecodesign directive brought a lot of
change to the HVAC industry and rooftops were no exception. In 2014, a study conducted by Eurovent and EPEE showed that almost 80% of the rooftop units commercialised in Europe were not ready to comply with Ecodesign efficiency thresholds coming into force January 2018. Ecodesign brought on much more than higher
efficiency thresholds. Even the interpretation of efficiency changed, as the industry moved from nominal load energy efficiency ratios (EER) to Seasonal Energy Efficiency Ratios (SEER). An average SEER for a rooftop unit sold in Europe ranged between 2.0 and 2.5 kW/kW, whereas the new Ecodesign directive required a minimum SEER of 2.9 by 2018, and 3.4 from 2021 onwards. That represented a need for efficiency improvement between 30% and 70%. In other words, a leap for the rooftop HVAC industry.
30 February 2020 This meant that oversizing heat exchangers to
increase efficiency would not be sufficient. The challenge for engineers all across the industry was to find innovative ways to improve the performance of the unit, both at full load and at part load. The industry, as usual, lived up to the
challenge. Most rooftops commercialised in Europe today use more sophisticated technologies, such as variable volume scroll compressors, electronic expansion valves and EC motor plug fans. The use of variable speed technology has also allowed design engineers to go back to the core of understanding how the unit should operate in order to adapt itself to indoor and outdoor conditions, in order to achieve the required level of comfort while consuming less electrical energy.
One example of how higher efficiency can be achieved is with variable airflow. Available now as a standard feature on most rooftops, variable airflow drastically increases the efficiency of the unit by adapting the indoor fan speed – and consequentially, the airflow - according to the actual building load. In other words, when the load inside the building decreases, the indoor fan will reduce the corresponding airflow to reduce
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