Selection of micro-cogeneration for net zero energy buildings (NZEB) using weighted energy matching index

Abstract

Recently, the extended matching indices for electrical and thermal energy were defined for different types of energy use and conversion based on two basic matching indices: on-site energy fraction (OEF), which is the load proportion covered by the on-site generated energy, and on-site energy matching (OEM), which is the on-site generated energy proportion utilized by the load rather than being dumped or exported. Additionally, the overall weighted matching index (WMI) was proposed, combining the extended indices by multiplying them by certain weighting factors expressing the preferences of each. This study presents a new model calculating the weighting factors of the WMI based on the non-renewable primary energy factors of different energy carriers involving the imported fuel, for micro-cogeneration (μ-CHP) under thermal and electrical tracking strategies, with electrical and thermal heat grid feed-in schemes reflecting two opposite extreme matching situations in the net zero energy building: load-matching priority and energy export priority strategies. The model is generic and can be used for hybrid micro-generation options. As a case, a single family house served by a μ-CHP is analyzed under a wide range of electrical outputs and power-to-heat ratios. The μ-CHPs’ characteristics are selected according to the highest WMI.