Energy efficiency of hydronic space-heating distribution systems in super-insulated residential buildings
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In space-heating (SH) dominated climates, superinsulated building envelopes, such as passive houses (PH), are often promoted to drastically reduce SH needs. Using hydronic SH distribution in PH, thermal losses from pipes become a relatively large source of internal gains. Nevertheless, buildings with super-insulated envelopes have high utilization factors of heat gains so that the resulting SH distribution efficiency is currently unknown. The article investigates this energy efficiency with dynamic simulations (here using IDA-ICE) and a detailed modelling of the SH distribution system. Such detailed studies are rarely found in the scientific literature where generally the physics is modelled in an oversimplified way. The performance of standard and simplified SH distribution loops are compared and discussed. It is confirmed that the fraction of uncontrolled thermal losses from the SH distribution system is large (up to 50% of the heat delivered to the system can be emitted by pipes), but that the distribution efficiency is nonetheless kept high (above 90%). Compared to other forms of energy losses in superinsulated buildings, the present work suggests that the increase of energy use caused by thermal losses from the hydronic SH distribution remains a secondary problem.