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 severe 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 in different rooms of a dwelling. There are indications that by neglecting this reality, the energy savings of energy efficient ventilation strategies might be less than theoretically predicted in rating methods, and that a correction is needed. Part of the savings may be lost because the introduction of energy efficient ventilation strategies also lead to increased indoor temperatures in some rooms at some moments of the year (‘temperature take-back’). The impact of these strategies on the indoor temperatures is not always the same and therefore the correction factor which should be applied can be different depending on the ventilation strategy. It is the purpose of this study to have, specifically for NZEB buildings, first an indication of the magnitude of the correction and secondly to evaluate to which extent there is a substantial difference between the various technologies.

The proposed project includes various aspects:

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