Fact Section

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


References

[1]European Committee for Standardization, “Ventilative cooling systems”, CEN/European Technical specification (draft document), May, 2021

How to design a ventilative cooling system?

There is a wide range of ventilative cooling principles, and their application depends on climate and microclimate, building type, ventilation approach and user expectations. Depending on possibilities and limitations in the actual case, the ventilative cooling (VC) system may come out as mechanical, hybrid or natural ventilation and may also be supplemented by other natural cooling technologies like ground cooling, earth-to-air heat exchangers or evaporative cooling.

In design and optimization of ventilative cooling the challenge is to sequentially minimize the cooling load, maximize the VC capacity to remove the load and, as a last step, minimize the electricity consumption of the supplementary cooling systems (if needed).

A design procedure adapted to ventilative cooling design is shown in the Figure 1. A ventilation design procedure consists of different phases: conceptual design phase, basic design phase, detailed design phase and design evaluation consisting of:

  • The conceptual design phase for ventilative cooling sets off by setting targets for indoor environment, energy use and cost and by performing an analysis of the ventilative cooling potential of the site taking into account both the climate, the surroundings, as well as overall building characteristics.
  • The basic design phase, the internal heat, solar and contaminant loads are estimated on room level and the ventilative cooling system layout is designed.
  • The detailed design phase, thermal loads are re-evaluated, and source control options are considered and/or optimized.
  • The design evaluation phase, detailed predictions of thermal comfort can be performed to ensure that the design fulfils the targets of the project.

Figure 1: Design procedure for ventilation and ventilative cooling [1]


References

[1] Heiselberg, P., Ventilative Cooling Design Guide, IEA EBC Annex 62, Aalborg University: Aalborg, Denmark, 2018

Is ventilative cooling a good cooling strategy in all weather conditions?

IEA ECB Annex 62 Ventilative Cooling has summarized the appropriate ventilative cooling principles for different outdoor climatic conditions (Table 1). For differences between indoor comfort and average outdoor temperature between -10°C and 2°C, ventilative cooling is an attractive strategy. Supplementary natural or mechanical cooling strategies are listed. Their findings also show that it is not recommended to use ventilative cooling strategies under humid and hot conditions because of the effect of relative humidity.

Table 1: Overview of typical ventilative cooling strategies applied depending on outdoor climatic conditions and type of ventilation system [1]

References

[1] Heiselberg, P., Ventilative Cooling Design Guide, IEA EBC Annex 62, Aalborg University: Aalborg, Denmark, 2018

Are there barriers/limitations for using ventilative cooling?

The following critical limitations are mentioned in the work performed by IEA ECB Annex 62 Ventilative Cooling [1]:

Impact of climate change on the cooling potential

In the next few decades, in Europe (from South to North), extended periods with negligible to very low night cooling potential are expected to become more frequent. However cooling by night-time ventilation is likely to remain an attractive option in the transition seasons (considering that the cooling season will tend to start earlier in spring and end later in autumn).

Impact of urban environment (heat island and reduced natural driving forces)

The urban environment has a negative impact on the ventilative cooling potential and also imposes constraints for the use of natural driving forces. Urban environments have typically lower wind speeds, higher temperatures at night and higher noise and pollution levels (see below).

  • Outdoor Noise levels

Outdoor noise levels in the urban environment can be a major barrier for application of ventilative cooling by natural driving forces and methods for estimating noise levels in urban canyons is needed to assess the potential as well as to assess the risk that occupants will close windows to keep out noise but also compromise the ventilative cooling strategy.

  • Outdoor air pollution

Key outdoor pollutions like NO2, SO2, CO2, O3 and suspended particulate matter PM are usually measured continuously in larger urban environments and are often considered as a major barrier for application of natural ventilative cooling. Along the same line, ventilative cooling by natural driving forces might not be suitable to use during pollen season considering occupants with allergies.

Other barriers

Ventilative cooling by natural driving forces (i.e. night ventilation) might not be suitable to use because of safety concerns as well as during extreme weather (i.e. wind & rain).


References

[1] Kolokotroni, M., Heiselberg, P., Ventilative Cooling. STATE-OF-THE-ART REVIEW, IEA EBC Annex 62, Aalborg University: Aalborg, Denmark, 2015

 

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.


Links

Does the Energy performance of buildings directive (EPBD) support the use of ventilative cooling?

The Energy performance of buildings directive (EPBD) stimulates the use of passive techniques such as ventilative cooling, aiming to reduce the energy needs for heating or cooling, the energy use for lighting and for ventilation and hence improve thermal and visual comfort. Although inclusion of ventilative cooling in the energy calculation is not obligatory, more and more countries enter ventilative cooling in their Energy Performance (EP) regulation (e.g. Austria, Denmark, Switzerland, Belgium , France and Germany [1]). As the energy calculation is mostly monthly, the effect of ventilative cooling is usually assessed in a rather simplified way.


References

[1] Plesner C., Status and recommendations for better implementation of ventilative cooling in standards, legislation and compliance tools, 2018, venticool/IEA EBC Annex 62 

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.


References:

[1] Chiesa G., Kolokotroni M., Heiselberg P.,  Ventilative cooling and control systems, Innovations in Ventilative Cooling, 2021, ISBN: 978-3-030-72384-2

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.

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.