Q&A

What is ventilative cooling?

Ventilative Cooling is an airborne system to utilize air from outside at its actual temperature and humidity. Air transfer may be by natural, mechanical or hybrid means.

Natural ventilative cooling is an aspect of ventilative cooling whose operation is based solely on the effect of wind and the stack effect

Mechanical ventilative cooling is an aspect of ventilative cooling whose operation is based solely on the operation of fans

Hybrid ventilative cooling is an aspect of ventilative cooling whose operation is based on the combination or alternation of natural ventilation and mechanical ventilation

Source: “Ventilative cooling systems” [CEN/European Technical specification (draft document), May, 2021]

Does ventilative cooling make sense in a building with active cooling?

Yes, ventilative cooling can reduce the cooling capacity of active cooling if both cooling strategies are used alternately and not running simultaneously, for a given room of space. The switch point between ventilative and active cooling can vary between parts of the building, depending on the solar or internal gains for instance. A smart reliable control system has to assure that both cooling principles support each other instead of counteracting.

Does a simplified tool exist to predict the potential of ventilative cooling in early-design phase?

Yes. A ventilative cooling potential tool (VC Tool) was developed within IEA EBC Annex 62 to assess its potential by taking into account climate conditions, building envelope thermal properties, occupancy patterns, internal gains and ventilation needs. This tool calculates the ventilative cooling potential by the number of hours when ventilative cooling is useful and estimates the airflow rates needed to prevent building overheating.

Link to VC tool:  http://venticool.eu/wp-content/uploads/2017/05/V1.0_Ventilative-cooling-potential-analysis-tool.xlsm

Links to user guide: https://venticool.eu/wp-content/uploads/2016/11/Ventilative-cooling-potential-tool_User-guide.pdf and example:  http://venticool.eu/wp-content/uploads/2016/11/Example1_Copenhagen.xlsm

Is ventilative cooling taken into account in national EPBD related regulations?

Yes, for example: Austria, Denmark, Switzerland, Belgium , France and Germany.

The way ventilative cooling is  taken into account in legislation varies among the countries and also between the type of buildings (residential vs. non-residential).

Source : “Status and recommendations for better implementation of ventilative cooling in standards, legislation and compliance tools”, 2018, Venticool/IEA EBC Annex 62 (http://venticool.eu/wp-content/uploads/2018/09/venticool_ebc62__background_report.pdf)

What type of benefits can be obtained through ventilative cooling?

Benefits obtained through ventilative cooling include:

  • Reduction of the need of cooling capacity (kW)
  • Reduction of the cooling energy consumption (kWh)
  • Reduction of the CO2 emission
  • Comfortable or lower indoor air temperatures in case of a cooling demand

Is automatic control of ventilative cooling devices better than manual control?

The answer is two-fold. On the one hand, automatic control is preferred to manual control of ventilative cooling because of guaranteed the cooling effect and reduced overheating risk. The effectiveness of occupant manually operated windows or louvres to control ventilative cooling reduces over time. Occupants take less responsibility for maintaining the indoor thermal comfort. On the other hand, case studies show that it is really important that the user can overrule the automatic control of ventilative cooling. Users are satisfied that they are able to control the ventilative cooling system.

It can be concluded that an automated control with the possibility to ignore or overrule this control is the best option for a reliable system with a maximum cooling efficiency as well as a maximum user satisfaction.

Source: Chapter 15: Ventilative cooling and control systems, Innovations in Ventilative Cooling (2021), ISBN: 978-3-030-72384-2, https://www.springer.com/gp/book/9783030723842

What is natural ventilation?

Ventilation provided by thermal, wind, or diffusion effects through doors, windows, or other intentional openings in the building.

Natural ventilation systems may be either manually or automatically controlled. The latter is normally needed in non-residential buildings in order to realize the thermal and indoor air quality criteria.

What is night cooling?

Cooling of the exposed thermal mass of a building by the use of nighttime outdoor air and thus providing a heat sink during the following day. The airflow is induced by pressure differentials, while the cooling mechanism is based on convective heat transfer.

What is hybrid (mixed mode) ventilation?

Hybrid ventilation is a two mode system which is controlled to minimise the energy consumption while maintaining acceptable indoor air quality and thermal comfort. The two modes refer to natural and mechanical driving forces.

How does thermal comfort relate to ventilative cooling?

Ventilative cooling can both remove excess heat gains and increase air velocities – thereby increasing the thermal comfort range.

Is ventilative cooling more than openable devices?

Yes. Ventilative cooling should be conceived as an integral part of an overall design strategy including adequate solar protections, intelligent use of thermal mass and sometimes support of active cooling which can help improve thermal comfort.

Is ventilative cooling always achieved through natural ventilation?

No. Ventilative cooling may be achieved either through natural or mechanical ventilation or a combination of both.

Does ventilative cooling exclude active cooling?

No. However, ventilative cooling may reduce the need for active cooling.

What is the importance of legislation to ventilative cooling?

In order to be correctly accounted for, ventilative cooling strategies require rather mature assessment methods for thermal comfort and ventilation effects. These assessment methods should include thermal comfort criteria as well as ideally, indoor air quality, visual comfort, and noise. They should also reflect the large variation of the effective cooling potential within a single day, thus calling for rather sophisticated calculations, currently seldom used in regulations.

Are there demonstrated energy savings from ventilative cooling techniques?

Several studies have demonstrated the energy savings potential of ventilative cooling techniques. Consult the list of articles below with details on the energy saving potential.

  • Milbank, Neil O., Energy savings and peak power reduction through the utilization of natural ventilation Energy and Buildings, 1977. 1(1): p. 85-88.
  • Fletcher, J., Martin, A.J., 1996. Night cooling control strategies, ISBN:0860224376.
  • Blondeau, P., Sperandio, M., Allard, F., 1997. Night ventilation for building cooling in summer. Solar Energy 61 (5), 327–335.
  • Givoni, B., 1998. Effectiveness of mass and night ventilation in lowering the indoor daytime temperatures. Part I: 1993 experimental periods. Energy and Buildings 28 (1), 25–32.
  • Kolokotroni, M., Webb, B.C., Hayes, S.D., 1998. Summer cooling with night ventilation for office buildings in moderate climates. Energy and Buildings 27 (3), 231–237.
  • Geros, V., Santamouris, M., Tsangrasoulis, A., Guarracino, G., 1999. Experimental evaluation of night ventilation phenomena. Energy and Buildings 29 (2), 141–154.
  • Kolokotroni, M., Aronis, A., 1999. Cooling-energy reduction in air-conditioned offices by using night ventilation. Applied Energy 63 (4), 241–253.
  • Shaviv, E., Yezioro, A., Capeluto, I.G., 2001. Thermal mass and night ventilation as passive cooling design strategy. Renewable Energy 24 (3–4), 445–452.
  • Pfafferott, J., Herkel, S., Jaschke, M., 2003. Design of passive cooling by night ventilation: evaluation of a parametric model and building simulation with measurements. Energy and Buildings 35 (11), 1129– 1143.
  • Pfafferott, J., Herkel, S., Wambsgans, M., 2004. Design, monitoring and evaluation of a low energy office building with passive cooling by night ventilation. Energy and Buildings 36 (5), 455–465.
  • Gratia, E., Bruyere, I., De Herde, A., 2004. How to use natural ventilation to cool narrow office buildings. Building and Environment 39 (10), 1157–1170.
  • Breesch, H., Brossaer, A., Janssens, A., 2005. Passive cooling in a low energy office building. Solar Energy 79 (6), 682–696.
  • VeeTech Ltd. 2006. VENT Dis.Course. Distant learning vocational training material for the promotion of best practice ventilation energy performance in buildings. Module 1: Natural and Hybrid Ventilation. 
  • IEA, 2006.Technical Synthesis Report. Annex 35.Control Strategies for Hybrid Ventilation in New and Retrofitted Office and Education Buildings (HYBVENT).International Energy Agency.
  • Finn, D., Connolly, D., Kenny, P., 2007. Sensitivity analysis of a maritime located night ventilated library building. Solar Energy 81 (6), 697–710.
  • Awbi, Hazim B., Ventilation Systems. Design and Performance, 2008: Taylor & Francis.
  • Wang ,Z., Yi,L., Gao,F., 2009. Night ventilation control strategies in office buildings. Solar Energy. 83: p. 1902–1913.