Energy Performance Indicators for Ventilative Cooling

The lack of indicators assessing ventilative cooling effectiveness in a way to compare it with active cooling technics, makes its acceptance more difficult. Practitioners, norms, standards and guidelines are used to design and evaluate cooling systems in terms of Cooling Power (CP) or Seasonal Energy Efficiency Ratio (SEER). What could be the CP of a passive technique based on a day to night offset of the cooling process? What could be the SEER of mechanical night ventilation for summer cooling?
IEA Annex 62 research collaboration for ventilative cooling developed energy performance indicators to characterise natural and mechanical ventilative cooling. The Cooling Requirement Reduction (CRR) expresses the cooling effectiveness of a ventilation strategy. It indicates to which extend an alternative strategy, like natural or mechanical night ventilation, meets the cooling needs, compared to those of a standard scenario without ventilative cooling. The ventilative cooling SEER (SEERvc) relates the additional electrical energy to run ventilation, with the Cooling Requirement Reduction. It can be compared to the SEER of conventional cooling systems.
In this paper we define in details these indicators and use them to assess different ventilative cooling systems, applied to a standard ventilative cooling test building, defined in IEA Annex 62 research works. We use them also to compare the effectiveness of ventilative cooling in specific climatic zones, with different thermal masses and different solar protection boundary conditions.
The results show that mechanical ventilative cooling with Specific Power Input >0.4 W/(m3/h), running more than 800 hours per year for night cooling, might be even less efficient than conventional air conditioning systems of SEER > 3. They also show that the only real "free cooling" is natural ventilative cooling. A parametric analysis illustrates how with the use of these indicators we may quantify the risk of high-energy consumption due to bad design choices, such as very low thermal mass, bad ventilation control, bad solar control or a combination of them.