Design HVAC systems to reduce disease transmission while aiming for Carbon Zero
August 30, 2021 By Anthony Broatch
We are moving into an age where all buildings will be designed to reduce the spread of pathogens and at the same time become carbon zero for a healthier planet and population.
“Although many cases of disease transmission can be reduced by social distancing or wearing the recommended PPE, the air surrounding us indoors requires much better management to safely remove air borne pathogens.” – Quote from Tomasz Lipinski.
The 2021 CIBSE Technical Symposium was centered around the impact of Covid-19 on the design of the built environment.
Of particular interest was a paper by Tomasz Lipinski, voted as making the most significant contribution to the art and science of building services engineering, on the Impact of various ventilation strategies on indoor airflow dynamics and the spread of pathogens such as Covid-19.
According to Tomasz Lipinski the best method for reducing the spread of air pathogens such as Covid-19 is achieved by the following two factors; displacement ventilation and introducing outdoor air at a rate greater than required by the New Zealand building code. The findings are covered in this article however, if you’re interested in diving into the details, his article can be found here.
A displacement ventilation system is one in which air is introduced at a low level in the space and is exhausted at high level in the space above the occupied zone. This differs from a traditional ventilation system where air is supplied at ceiling level and blown down into the occupied zone to mix with the room air. The below figures show the difference between the two systems and how they relate to reducing spread of air pathogens such as Covid-19.
Figure 1: Traditional ventilation system
Figure 2: Displacement ventilation system
With introducing outdoor air at a rate greater than what the New Zealand building code requires, heat recovery is essential to ensure an energy efficient system operation.
Heat recovery, in HVAC, is a process where energy is transferred from the exhaust air leaving a space to the outdoor air being introduced to the space via a heat exchanger. The image below shows a situation where the building is in heating mode and it’s cold outside. Heat recovery systems should also incorporate a heat exchanger bypass so cold air outside can be utilized when the building requires cooling.
Figure 3: Heat recovery ventilation system when heating is required
The article also explored natural ventilation and naturally assisted displacement ventilation strategies that further reduce energy consumption getting buildings closer to carbon zero. These natural ventilation strategies are ideally suited to applications where larger variations in temperature are acceptable.
Natural ventilation is a method of ventilation that does not rely on fans to supply outdoor air into a space or exhaust air from a space. With natural ventilation air is usually introduced and exhausted by well paced openings in the building façade. Natural ventilation systems also exist with integrated heat recovery that work on the same principles described above.
Conclusion
The majority of current HVAC systems rely on traditional ventilation strategies that heavily mix the air in a space. These traditional systems provide ideal conditions for the spread of pathogens. Displacement ventilation is an alternative system type that reduces the spread of pathogens in a space compared to traditional systems. In addition to the use of displacement ventilation systems, introducing outdoor air at a rate greater than required by the New Zealand building code also helps remove contaminates from the space providing a healthier environment for the occupants.
The displacement ventilation systems can be enhanced by the use of heat recovery or naturally assisted displacement ventilation strategies. These reduce energy consumption getting your building closer to being carbon zero for a healthier planet. Reshape engineering consultants can design your new HVAC system, or review an existing system, to incorporate displacement ventilation strategies as well natural ventilation strategies.
About the Author
Anthony Broatch - Chartered Senior Mechanical & Hydraulic Engineer
I have had been involved in a large number of healthcare projects across New Zealand, the largest being the mead clinical centre in Waikato, a five-storey 32,000m2 clinical centre completed in 2014. My healthcare knowledge combined with my enthusiasm for my work keeps me up to date with the latest industry practices and provides me with a solid understanding of HVAC system design to control the spread of pathogens.
Further Reading
If you’re also interesting in learning more about going carbon zero check out our article below.
September 2, 2020