Electrical Demand Uplift and Coil Performance Constraints in Air-Source Heat Pump Retrofits for Commercial Office Buildings

Decarbonising existing commercial buildings requires replacing combustion-based heating systems with electrically driven alternatives such as air-source heat pumps (ASHPs). Although the energy and emissions benefits of heat pumps are well established, less attention has been given to the plant-level electrical demand uplift and hydronic constraints that can limit retrofit feasibility in existing buildings. This study quantifies the electrical demand uplift and air-handling unit (AHU) coil performance limitations associated with ASHP retrofitting in an existing Australian commercial office building. A peak design-load assessment was undertaken to compare the baseline gas-fired heating system with an electrified ASHP configuration under equivalent thermal load conditions. The principal electrical outcomes are derived from a specified 1900 kW Stage 3 plant-screening heating boundary. This boundary reflects the prevailing installed plant-screening condition, rather than the aggregate of scheduled AHU heating duties. First-principles energy balances and hydronic relationships were used to translate thermal demand into plant electrical demand under winter design conditions, while existing AHU heating coils were re-rated under low-temperature hydronic operation. The results show that baseline winter heating is associated with only a small auxiliary electrical load, whereas the governing baseline plant peak occurs during cooling at 399 kW. When referenced to the adopted 1900 kW Stage 3 installed-capacity screening boundary, the peak winter ASHP plant electrical demand increased to 956.66 kW, corresponding to an upper-bound electrical uplift of 557.7 kW relative to the governing baseline plant electrical demand. In parallel, low-temperature hydronic operation (55/45 °C) reduced AHU heating-coil capacity, requiring increased flow rates and, in many cases, coil modification to maintain scheduled duty. These findings indicate that, in the assessed case-study building, the principal barriers to ASHP retrofitting are not annual energy performance alone, but peak electrical infrastructure implications and hydronic system compatibility. The study therefore provides a transparent, building-scale screening methodology for assessing electrification feasibility in existing commercial buildings, while recognising that the reported numerical results are specific to the case-study building and stated design assumptions.