The ongoing transition towards sustainable heat energy production is being propelled by the deployment of large-scale air source heat pumps (ASHPs) in the form of urban-based energy centres. These innovative systems are at the forefront of the drive towards net zero emissions and the decarbonisation of energy production. While the integration of these energy centres in dense urban areas aligns well with high energy demand locales, it also introduces specific challenges that need careful consideration and strategic solutions.
Image: CFD thermal results presented as a particle trace. The flow path of rejected air can be reviewed to assess risks of pedestrian cold comfort and indicate re-circulation.
Challenges in Urban Implementation of ASHPs
Implementing ASHPs in urban environments is not without its hurdles. The very architecture of cities can interfere with the effectiveness of these systems. For instance, buildings can shelter and limit the dispersion of cold air rejected by the heat pumps, hindering air from mixing with the ambient environment.
Another concern is the impact on pedestrian comfort. The cold air rejected by these systems can create discomfort for people in the vicinity, a critical factor to consider in designing urban energy solutions. Moreover, visible cold plumage from these systems could be subjectively considered aesthetically displeasing, an important consideration during planning phases.
The largest risk to system performance is the recirculation of rejected air from the heat exchangers. When the exchanger fans jet the discharged cold air and it does not effectively mix into the warmer ambient environment, the colder dense air can sink downwards and be pulled back into the system, leading to recirculation. The same air can then repeatedly cycle through the system, undermining the efficiency and effectiveness of the heat pump. In densely built-up areas, where buildings and other structures can obstruct natural airflow, this risk is heightened. Recirculation not only diminishes the operational efficiency of ASHPs, leading to increased energy consumption and reduced performance, but it also impacts the overall sustainability of the system. Addressing this challenge is crucial to ensure the deployment of air-source heat pumps in urban settings.
Image: CFD Velocity plot showing rejected air recirculating back into the system.
The Role of CFD Simulations in Addressing Challenges
This is where Computational Fluid Dynamics (CFD) simulations become invaluable. CFD, with its advanced computational capabilities, offers an insight into how proposed designs for energy centres will perform in real urban settings. Through these simulations, the common risks can be entirely omitted, or at least the outcome of reduced performance can be understood and managed by the energy centre operator.
By predicting how cold air will disperse, and identifying potential re-circulation, these simulations help in optimising the system’s efficiency while mitigating any impact on the urban environment and its inhabitants.
The use of CFD in designing urban energy centres is not just about enhancing efficiency; it's also about integrating these systems harmoniously with the urban environment and the people that inhabit it. The insights gained from these simulations are instrumental in ensuring that the deployment of energy systems is effective, sustainable, and contributing to the overall energy resilience of urban areas.
Image: CFD results plotting the pressure range of rejected air. Pressure differentials outside of the exchanger operating range can result in unacceptable noise as the fans work harder to maintain air exchange through the system.
CFD simulations
Element, in collaboration with Joel Gustafsson Consulting (JGC), has been enhancing the clarity and effectiveness of our client's energy centre proposals. We achieve this using cloud-based Computational Fluid Dynamics (CFD), a technology that surpasses the capabilities of local computing in terms of speed and efficiency. This advanced approach enables us to conduct concurrent studies, each encompassing various environmental and geometric variations. This method not only accelerates the delivery of results but also provides a more comprehensive analysis by examining a range of scenarios, thus ensuring a more thorough and reliable understanding of each energy centre proposal.
Image: CFD plot of velocity magnitudes showing variations as an effect of the scale of the array and the surrounding built environment.
CFD simulations play a pivotal role in achieving a balance between the demands of efficient, sustainable energy production and the complexities of the built environment. These simulations facilitate early-stage clarity which is vital for meeting net zero targets and delivering the best-case efficiencies of proposed centres.