HUMIDITY CONTROL
provided by an air handling unit (AHU) connected to ducting that runs through the building. AHUs remove air from contaminated indoor spaces, or air that is simply too hot or too cold, and replace it with clean, fresh air at the right temperature and humidity. In the past, indoor air quality regulations were mainly focused on providing a minimum level of thermal comfort. Over the years, increased attention to
sustainability and new eco-design regulations have helped resolve the difficult dilemma between reducing energy consumption and creating a comfortable indoor environment. Nonetheless, the new safety guidelines that need to be applied have a negative impact on energy consumption. An intelligent ventilation control and
monitoring system can therefore be the key to successfully combining the objectives of health and efficiency. An intelligent system is one that reacts and adapts the set points and operating modes to the specific requirements of the user and the controlled environment. For example, when occupancy is lower, ventilation can be reduced to an acceptable minimum level, guaranteeing adequate indoor air quality while reducing energy consumption. Furthermore, by adapting to user habits, the system will be able to predict critical conditions, and take action in advance to adapt to periods in which occupancy is highest. Let’s take a practical case: in general, the more people there are in an indoor space, the greater the need for ventilation with fresh outside air to ensure occupant comfort.
Traditionally, the concentration of CO2 has
been used as the sole reference parameter for adjusting the level of indoor ventilation. This is in fact a commonly-adopted solution for combining comfort and energy saving. However, this parameter is insufficient on its own to ensure a healthy environment. Indeed, it has been found that other chemical contaminants, for example relating to massive use of sanitising agents above all in this period, reach peaks in concentration that are on a time scale are not perfectly aligned with the level of occupation. What technological solution can help solve this problem then? First of all, an indoor air quality monitoring system. The starting point is the assumption that “if you can’t measure it, you can’t improve it”. Using multiple sensors to read information on indoor and outdoor air conditions provides a real-time understanding of how the building is used and how this changes over time. The second step involves controlling the AHU with advanced operating logic. Multiple parameters can be used to together understand the level of contamination, and these have different trends in terms of both space and time. As mentioned, controlling ventilation based on the CO2
concentration alone is
generally insufficient. DCV (demand-controlled ventilation) therefore needs to be based on multiple parameters - CO2
, VOC, PM 2.5-
10 - so as to control different indicators of contamination at the same time and thus adapt the ventilation system so that each of these is kept inside the pre-defined limits at all times.
Pre- and post-ventilation and purging
functions based on the building’s occupancy profiles can ensure that indoor spaces are always safe before use. Moreover, adjusting indoor pressurisation and monitoring absolute filters for clogging can help maintain a high level of hygiene. Finally, advanced humidification control, in particular using adiabatic systems, is a key factor in ensuring optimal conditions with minimum energy consumption.
The third step is a data collection and analysis system. IoT technologies make it possible to continuously know both the quality of the air supplied by the system and the operation of the units, so as to verify whether there are any deviations between ideal and actual conditions. This allows service to be planned in the event of declines in performance or malfunctions. The power of data can be exploited to develop new reference indices and KPIs to provide new types of feedback and create new benchmarks. In conclusion, as we have seen there is a wide range of factors that can influence indoor air quality and potentially increase the health risk. However, there are ways to manage HVAC systems safely, without jeopardising sustainability and zero-emission targets. Awareness, control and optimisation are key concepts to achieving these goals. There is clearly no one single answer, but rather an intelligent set of different design steps and technologies that can help make buildings healthier, safer and more sustainable.
www.acr-news.com
March 2021
21
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