Primary energy and economic implications of ventilation heat recovery for a multi-family building in a Nordic climate

Abstract In this study the primary energy and economic implications of exhaust ventilation air heat recovery are analysed for an existing multi-family building, considering alternative air handling units (AHUs) encompassing centralised and semi-centralised units with counter-flow plate or rotary heat exchangers. The performance of the heat recovery AHUs are analysed considering different economic scenarios, frost conditions, building energy efficiency levels, energy tariffs and heat supply options including electric heat pump and district heating based on cogeneration or heat-only boiler production. Focus has been on understanding the impacts of key economic and technical parameters on the financial viability of the heat recovery AHUs, which seem lacking in current literature. The primary energy is modelled based on hourly energy balance calculations and analysis of entire natural resource chains. The economic performance is analysed considering investment costs as well as net present values of energy cost savings of the AHUs. The results show that the heat recovery AHUs are less cost-effective when using electric heat pump compared to when using district heating in the studied context. The semi-centralised AHUs with rotary heat exchanger seem slightly more cost-effective among the analysed alternatives. Frosting and defrosting need significantly influence the peak heating load and have noticeable impact on the energy and economic performance of the heat recovery AHUs. This study highlights the need for careful design and analysis of AHUs for ventilation heat recovery in buildings, for improved primary energy and cost efficiency.