Ventilative cooling in buildings – standardisation perspective and corresponding workshop at AIVC 2024 conference in Dublin, Ireland

Keywords: Ventilative Cooling, standards, natural ventilation, system design, free cooling, overheating, resilience, cooling ladder, design process

Introduction

This article is about Ventilative cooling in buildings seen from a Standardisation perspective, which was presented during a topical session called “Ventilative cooling – latest and greatest. Importance of early design in the world of overheating mitigation using ventilative cooling” at the 44thAir Infiltration and Ventilation Centre (AIVC) & 10th Venticool conference “Retrofitting the building stock: challenges and opportunities for indoor environmental quality” in Dublin, Ireland on October 9, 2024.

Existing and future elevated outdoor temperatures can contribute to increased energy use for cooling in buildings and pose risks to health and wellbeing of occupants, due to both higher peak temperatures in the cooling period and increased number of days per year with space cooling requirements to keep acceptable thermal comfort conditions.

The increasing energy demand (for cooling) in buildings is putting a big strain on the electricity grid, which in many countries could cause grid congestion and intermittent power outages. When designing buildings for future resilience there should be a cooling strategy in place on how to reduce the potential for internal overheating with no or a minimal use of active cooling.

The main drivers for this soaring need for space cooling in the period 2025-2050 are both increasing overheating in buildings due to climate change and rising expectations on thermal comfort during cooling periods by building users. As it is essential to use the full potential of technologies to mitigate or reverse rising electricity needs from space cooling, the use of “free cooling” such as ventilative cooling is considered a very important solution. There are already excellent approaches in this direction, for example, the cooling hierarchy defined into London’s response to climate change, which seeks to reduce any potential overheating and also to reduce as much as possible the need to cool a building through active cooling measures [1].

To diminish the impact of (cooling) energy use in buildings on the climate change, appropriate guidelines and standards of cooling design from free cooling solutions such as ventilative cooling, to supplementary cooling and interventions shall be made in Europe, and one of these projects are highlighted in the coming text.

The workshop

On October 9-10, 2024 we had the utmost pleasure to attend the 44th AIVC & 10th Venticool conference in Dublin, Ireland. It was 2 days packed with valuable insights and good company.

During the conference the parallel tracks were; Indoor air quality, Air tightness and Resilience/Ventilative cooling so very relevant in the “well-being” agenda. We held a 90 min. topical session and as chairpersons on the topic of “Ventilative cooling – latest and greatest. Importance of early design in the world of overheating mitigation using ventilative cooling”. We had lively discussions with roughly 30 participants in the room and thanks to presenters Paul D O'Sullivan (Munster Technological University, Ireland) and Beat Frei (FREI WÜEST EXPERT, Switzerland) for putting their views on a Ventilative cooling design process and how to tackle resilience and the cooling ladder ethos.

The drafting of a new European Technical Specification (CEN/TS) called “Ventilative cooling systems – Design” is underway and sets the design framework for how to design ventilative cooling systems, from the early feasibility phase to the actual design phase for residential and non-residential buildings [3]. Further this CEN/TS is a “system design” document.

This CEN/TS will refer to EN 16798-1, where the “thermal comfort part” is currently under revision). The CEN/TS is about how to design buildings without mechanical cooling that meet the chosen IEQ requirements and explains how to design ventilative cooling systems in Europe. With a better early-stage design prediction method, such as the ventilative cooling potential method, will increase the probability of more resilient cooling solutions and may replace mechanical cooling solutions, when outdoor conditions are favourable – both saving valuable cooling energy and related CO₂ emissions. The integrated “cooling ladder ethos” (as seen below and in [3]), offers a design strategy for resilient buildings by firstly mitigating the solar and internal gains and later if overheating has taken place, to first provide cooling with use of passive means (e.g. ventilative cooling) prior to moving to active means (e.g mechanical cooling).

Figure 1. Cooling ladder ethos. [3]

At the topical session we presented the latest content of the upcoming European Technical Specification (CEN/TS) called “Ventilative cooling systems – Design” which includes [3]:

✔️8 design steps - to follow for a path on how to design Free cooling systems (see Figure 2 which includes the first 7 steps)

✔️Cooling ladder ethos – that guides how to first design passively before going into active cooling means

✔️Ventilative cooling potential method – that enables to find the cooling potential of outdoor air in the early design phase

✔️Flow diagram – enabling a simplified overview of the design steps and cooling ladder ethos incl. which choices to make

✔️Resiliencechecks – enabling checks to enhance readiness for future extreme weather events and probably first standard to include this

✔️Renewable energy for cooling calculations using ventilative cooling – as found in Renewable Energy Directive (RED II/III)

The CEN/TS describes two design approaches allowing to set a framework for designing ventilative cooling systems, where each of these approaches consists of several elements, among others different ventilation requirements and conditions of use to be chosen on national basis and is shown in the corresponding flow diagram [3].

Figure 2. Design steps of Ventilative cooling. [3]

We further learnt during the conference that:

·         Pre-design stage has the same influence for promoting ventilative cooling strategies as the schematic and detailed design stages for practitioners, yet limited impactful decision making occurs at this stage;

·         In the resilience track it was shown that to tackle overheating and enhance resilience that renewable ventilative cooling, dynamic solar shading and high located windows should be used.

In our discussion part of the session, we were asked good questions on:

·         It all starts with Indoor Environmental Quality (IEQ) requirements and perhaps we are currently setting too strict requirements. e.g. that the temperature bands are too narrow, which might not be beneficial in all cases as we might end up oversizing the cooling systems;

·         If the 8 design steps can be used for all types of buildings;

·         Is it a challenge that all non-residential buildings are handled together in this CEN/TS? And that residential and non-residential are “put together” in the same design approach?;

·         Decisions of the micro-climate is an important parameter to take into account in the various design stages;

·         Availability of climate data is key when assessing the “Ventilative Cooling Potential” properly.

We were thankful for the good input that was received during the topical session and it gave us valuable information to go ahead with preparing the CEN/TS on “Ventilative cooling systems - Design”, which is expected to be published Q3:2026. It was a great pleasure to meet familiar faces and talk on important aspects in how to achieve good well-being in buildings, and how standards and legislation can help to support this.

The CEN/TS a good opportunity to define design aspects and processes of ventilative cooling and natural and hybrid ventilation systems on the European and International scene e.g. by applying findings from the Venticool platform and the IEA EBC Annex 62 reports on ventilative cooling [2]. If anybody wants to discuss further on this topic please don’t hesitate to contact us directly.

Related work

Other related documents are “CEN - European Technical specifications, CEN/TS” (lower status than CEN European EN-standards) for “Natural and hybrid ventilation systems in non-residential buildings” running in CEN/TC/156 (ventilation in buildings) and “Ventilation systems in residential buildings – Design (prEN 15665:2023)” is to be delivered as a “CEN - European EN Standard”.

The objective of these documents is to give designers guidance on what to be aware of when designing these ventilation systems, while assisting to set relevant criteria as well.

Appendix

[1]     Energy assessment guidance. Mayor of London. London plan chapter five (GLA); Policy 5.9: Overheating and cooling, UK: https://www.london.gov.uk/programmes-strategies/planning/london-plan/past-versions-and-alterations-london-plan/london-plan-2016/london-plan-chapter-five-londons-response/poli-8.

[2]     IEA EBC Annex 62 Ventilative cooling, Deliverables (2014-2018), https://venticool.eu/information-on-annex-62/annex-62-publications/deliverables/.

[3]     “Ventilative cooling systems – design”, draft CEN/TS (2025), CEN/TC 156/WG21.