Temperature take-back effect in the context of energy efficient ventilation strategies

The European market for residential ventilation is highly driven by energy performance regulations. In new buildings, the share of energy efficient ventilation systems, such as demand controlled mechanical exhaust ventilation or balanced ventilation with heat recovery, is increasing as a result of more stringent energy performance requirements (NZEB).

The methods used to assess the influence of energy efficient ventilation on the energy performance of buildings are typically based on single zone energy balance equations. Multi-zoning is often not considered although heating behaviour and set-points differ between rooms within a dwelling. There are indications that, by neglecting this reality, the energy savings of energy efficient ventilation strategies may be lower than theoretically predicted by rating methods, and that a correction is needed. Part of the savings may be lost because the introduction of energy efficient ventilation strategies can also lead to increased indoor temperatures in some rooms at certain times of the year (‘temperature take-back’). The impact of these strategies on indoor temperatures is not always the same, and therefore the correction factor to be applied may differ depending on the ventilation strategy. The purpose of this study is, specifically for NZEBs, first to provide an indication of the magnitude of the correction and second to evaluate the extent to which substantial differences exist between the various technologies.

The proposed project includes various aspects:

• Definition of a methodology for assessing the temperature take-back effect of energy efficient ventilation strategies in dwellings, including the definition of indoor climate requirements, occupancy patterns and reference buildings
• Application of the methodology to estimate the magnitude of the effect for different energy efficient ventilation strategies, and express the effect in suitable metrics
• Reflection on the findings to propose improvements to energy efficient ventilation strategies and energy performance calculation methods