Environmental-Friendly Ventilations; A Life Cycle Assessment of VAV and Active chilled beams system

Abstract

Based on the European commission, climate change has become a serious threat for all aspects of our lives, urgent action needs to be taken. All the industries need to monitor their contributions, among them the building industry has the highest emission (European Commission)
This study aims to compare energy efficiency and global warming potential (GWP fossil) emission in two ventilation systems including Variable air volume (VAV) and active chilled beams (ACB) in their entire life cycles. The system boundary of this study covers Construction (A), use (B) and end of life (C) stages, however for use stage, maintenance (B2), replacement (B4) and operational energy use(B6) are calculated. The reference study lifetime of the project is 25 years.
Although A stage of two systems was calculated through a reference project, in this study thanks to newly published EPD the A stage is updated, and an uncertainty of data is calculated to assess the validity of A1-A5 results compared to reference study. An energy simulation is done by IDA-ICE version 4.8 for B6 module calculation. This energy simulation only focuses on energy use of fan, cooling, and heating of building. Finally, three scenarios are assessed for B6 module’s results, including fossil-free energy target, and different geographical locations. Moreover, in order to assess the certainty of this module’s results, two types of databases for B6 were compared including, average values provided by Boverket and location specific values provider by district heating network and electricity grid providers. For maintenance (B2), cleaning of HVAC systems is taken into account and for B4, the replacement of those products that have a lower service life span than 25 years are calculated.
Results indicate that ACB is more energy efficient than VAV, while the ACB system consumes more energy for cooling, it ultimately proves to be more energy efficient. Regarding GWP fossil emissions, ACB in an entire life cycle perspective has a lower contribution compared to VAV. In both systems, B stage contributes to a higher share compared to A stage and C stage, due to the combination of operational GWP fossil from B6 and GWP fossil from replacement and maintenance.
Considering the impact of geographical scenarios on energy consumption and GWP fossil emissions, ACB system consistently shows lower impacts across different locations. Additionally, the transition to future fossil-free energy sources significantly reduces operational GWP fossil emissions for both systems, highlighting the importance of focusing on the manufacturing process to lower embodied emissions. In summary, ACB shows superiority over VAV based on the gained results in this study.
Finally, by changing the fan operation schedules the results can be completely different compared to base scenario. Which means that the final decision will be affected by several aspects that needed to be taken into account.

Popular Abstract

Based on the European Commission, climate change poses a serious threat to all aspects of our lives, it needs urgent actions. The construction industry, with a high emission, plays a critical role in this effort. This study compares the energy efficiency and global warming potential (GWP) of two ventilation systems, Variable Air Volume (VAV) and Active Chilled Beams (ACB), across their entire life cycles.


The Variable Air Volume (VAV) system provides conditioned air through an air handling unit (AHU) via fans and ducts. The airflow rate changes during operation, based on the number of occupants and temperature in the rooms, this changing airflow is controlled by device name VAV box in each zone, to adjust airflow based on cooling demand.

Active Chilled Beams (ACB) are air-water convection units integrated with a constant air volume (CAV) air handing unit. They provide cooling through chilled water pipes and maintain air quality with fresh air. Since a part of cooling demand of rooms provides by chilled water, therefore, the need for airflow rate is minimum, and accordingly the air volume is less than air volume in VAV system. So, by having a lower airflow the size of duct and air handling units can be smaller compared to VAV system.

Each product has different life cycle stages from when it is produced till it will be deconstructed. These life cycle stages include construction (A), use (B), and end-of-life (C) stages. You might don’t know what these stages include, so let see what are they?
A stage includes the steps from producing, transporting it to the user site and finally installing it for usage proposes. In B stage, there are stages about using a product, and all the aspects that will occur during usage time, like replacement, maintenance, any energy use, etc. In C stage, the lifespan of the product is over, and it needed to be removed and throw away or even reuse or recycled. So, in all these stages, some harmful impacts might be occurred to our environment. Therefore, the amount of these harmful emissions is calculated in each stage and sum up together to see if the product is a environmental friendly option or not. In this study only global warming potential impact is calculated through all these stages. This means that two system were compared in their entire life cycle stages to see which one resulted in a lower global warming potential.

This is important to know that in B stage, there is a module named operational energy use, which shows the amount of global warming potential while using any kinds of energy sources for operating the product in its use stage. This module can be sensitive and might be results in different outcomes by changing the geographical location of the usage, changing the time from now to the fossil free future, or even changing the operation time of the product. Therefore, this operational energy use which is also called B6 is studied during different scenarios to see if the results can be reliable.


ACB systems show lower total GWP fossil emissions across their entire life cycle. The reduced primary supply air results in less weight and material use in AHU and duct systems, leading to lower embodied emissions. Additionally, lower operational energy use further reduces GWP emissions for ACB compared to VAV.

In Sweden's different climates, operational GWP fossil emissions increase in colder regions due to the higher need for heating. However, ACB systems consistently show lower emissions than VAV systems across all locations.

Transitioning to fossil-free energy sources significantly reduces operational GWP emissions for both systems. By 2049, both systems achieve low emissions, with ACB maintaining a slight advantage.

Different fan operation schedules show that ACB systems' efficiency can vary. Continuous fan operation without off times diminishes ACB's advantages, highlighting the need for optimized operational strategies to maximize efficiency. But what if we consider entire life cycle for this scenario? In this case, VAV presents lower global warming potential when both systems always operate without any turning off.

ACB systems demonstrate superior energy efficiency and lower GWP fossil emissions compared to VAV systems, making them a preferable choice for environmentally friendly ventilation. However, operational strategies and geographical factors must be carefully considered to fully realize these benefits.

• author: Mohebi Nouraldin Vand, Mitra
• supervisor: Karin Farsäter; Kerstin Bergström
• organization: Department of Building and Environmental Technology; Division of Energy and Building Design
• course: AEBM01 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Global warming potential fossil, Variable air volume, Active chilled beam, Life cycle assessment, Ventilation system
• language: English
• id: 9157650
• date added to LUP: 2024-06-04 11:23:46
• date last changed: 2024-06-04 11:23:46