An unforeseen pandemic is facing the world caused by a corona virus known as SARS-CoV-2. Numerous measures are being put in place to try and reduce the spread of this deadly disease, with the most effective response to the outbreak being mass quarantines, a public health technique borrowed from the Middle Ages. The widely accepted main transmission mechanism is through droplet borne pathways. However, many researchers and studies are considering that this virus can also spread via the airborne route and remain for up to three hours in the air. This is leading to questions as to whether enough is being done regarding ventilation to reduce the risk of the spread of this or other diseases that may be air borne. Ventilation and air conditioning systems are the main focus when it comes to the transmission of such deadly pathogens and should be appropriately designed and operated. This paper reviews and critically evaluates the current ventilation strategies used in buildings to assess the state of the art and elaborates if there is room for further development, especially for high occupancy buildings, to reduce or eradicate the risk of pathogen transmission and adapt ventilation measures to new threats posed by pandemics.

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This paper presents the ventilation performance of a Passive Ventilation System with Heat Recovery (PVHR) based on in-situ monitoring in a primary school in London. The study involves long-term (15month) monitoring of temperature, relative humidity and Carbon dioxide (CO 2 ) concentrations in both the classrooms and the outdoor environment. In addition, short term (1&2 week) observational monitoring was performed in two classrooms at ventilation system level and classroom level, during both the heating and non-heating seasons. Temperatures and air velocities were measured within the PVHR system while instances of window opening and the number of students were noted in daily diaries. Air permeability and infiltration measurements were performed to characterise the spaces.Time-varying ventilation rates were estimated through a form of continuity equation considering CO 2 generation rates by occupants. Preliminary results show that the operation of the ventilation system is more sensitive to changes in wind speed and direction than to buoyancy. When negative pressure was observed on the classrooms" facades the ventilation system was supplying two to three times more air in comparison to instances when positive pressures were observed. The assessment of the ventilation performance of such natural ventilation systems depending solely on wind and buoyancy is complicated as they are dynamic systems that constantly balancing with the surrounding conditions, and the operation is highly correlated to the airtightness of the building"s envelope. Highlights: CO 2 concentrations in classrooms with passive ventilation systems (PVHR) were satisfactory  Airtightness significantly affects the performance of the passive ventilation system  Passive ventilation system appears more sensitive to wind changes than to buoyancy ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T 2  Human behaviour such as window opening can significantly boost the ventilation rate of the PVHR system 1 Introduction According to the Climate Change Act (2008), the UK government is committed to tackling climate change by reducing greenhouse gas emissions for the year 2050 by at least 80% from the 1990 baseline (DECC 2008). Space Heating, Ventilation and Air-Conditioning (HVAC) account about two thirds of the total non-industrial energy use (Deuble and de Dear 2012, Lomabrd et al., 2008, Khan et al., 2008) from which 30-50% is related to ventilation and infiltration and about 40% accounts for heating. A reduction in the energy required to heat and ventilate buildings will contribute to a significant reduction of greenhouse gas emissions. Natural ventilation strategies consume negligible amount of energy by utilizing natural driving forces of wind and buoyancy (temperature differences between the indoor and outdoor environment-stack effect) can provide a viable alternative to energy consumption for mechanical air-conditioning systems and a fundamental method towards energy efficient design of buildings (Calautit and Hughes 2014, Khan et al., 2008). Sev...

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