Microgrid techno-economic optimisation for benchmarking operational net-zero metrics in a hotel typology

Abstract

Hotels account for about 1.5% of global energy-related emissions and an estimated 0.6% of UK energy demand in the operational phase. Hence, they have significant potential to contribute to sustainability and Net Zero through reduction in energy and carbon intensity. In the UK, the ongoing reform of the Energy Certificate System to include headline metrics suitable for monitoring energy efficiency, and the introduction of the UK Net Zero Carbon Buildings Standard (UKNZCBS) are beneficial initiatives for the achievement of net zero in hotels. This work applied a quantitative case study research design framed on a three-pronged methodology to evaluate feasibility of operational net zero for a mid-range (3-star) non-resort hotel located in London, UK over a 28-year lifetime. A baseline dynamic simulation model of the hotel (with 2022 as base year) was developed in IESVE™ and calibrated against the measured power consumption, using ASHRAE-14 Guidelines. The calibration confirmed the model within the verification acceptance range (NMBE= 4.75%, CvRMSE = 12.6%). Additional models were developed from the calibrated model by application of 30 energy efficiency measures and future weather files under SSP2-4.5 scenarios. Evaluation of the energy and carbon performance of the models between the baseline year and 2050 showed that climate change resulted in a 15% and 230% reduction in EUI and emissions, respectively. The highest reduction in EUI (40%) over the corresponding period occurred from reduction of envelope U-values to conform with the “2025 UK Future Buildings Standard” (UKFBS), lighting retrofit from fluorescent to LED, and application of Adaptive Ventilation (AV) strategy, translated to 236% emissions reduction. The second part of the methodology entailed creation of a solar- PV generation model in HelioScope™ and in the third part, electrical and thermal loads from IESVE™ and the solar-PV generation HelioScope™ were coupled to a microgrid model in HOMER Pro™, with random day-to-day and timestep variability of 10% and 20%, respectively. The variabilities accounted for the sensitivities of the energy profile to uncertainties in weather, occupancy and operational schedule, service levels, and occupant energy behaviour. The microgrid model was simulated under existing and projected macroeconomic (medium GDP growth) conditions, reference energy and emissions forecasts, and sensitivity variables (expected inflation rate, grid carbon intensity and minimum renewable fraction). The least cost microgrid yielded an IRR (6.2%), ROI (4.1%), discounted payback (12 years) and energy cost savings of £109,698. The benchmark values of operational net zero metrics calculated from the least-cost microgrid model were: EUI of 256 kWh/m2 (EUIel = 105 kWh/m2, EUIth = 406 kWh/ m2), CEI (87 CO2/m2), ECI (29.48 £/m2). The solar-PV generation model for the case study gave: (40.1 kW capacity, 43.8 MWh annual production, 75.5% Performance Ratio, and 906 kWh/kWp specific yield). Comparison of the results to the limits and targets of operational net zero metrics in the UK Green Building Council (UKGBC) Paris Proof Methodology (PPM), UKNZCBS and Cornell Hotel Sustainability Benchmark Index (CHSBI) for fifty 3-star non-resort hotels located in London, UK. The computed EUI, CEI and ECI values were significantly-above the CHSBI benchmarks due to disproportionate thermal and electrical energy demand. The retrofit pathway with the highest EUI reduction did not lead to operational net zero in 2050 under the UKGBC-PPM, nor the UKNZCBS frameworks. In addition, the target 40 kWh/m2 of Gross Internal Area (GIA) for onsite renewable energy generation specified in the UKNZCBS was not met. Unlike the hotelspecific room-night normalised energy, carbon, and cost metrics such as kWh/roomnight, kgCO2e/room-night and RevPAR (Revenue per Available Room, the metrics in this study were floor-area normalised to align with the UK Building Regulations thereby easing regulatory oversight of hotel energy efficiency and decarbonisation. The methodology of this work is a novel contribution to the planning of energy efficiency and net zero projects, applicable to any building typology and the benchmark values of EUI, CEI and ECI are a useful addition to the body of evidence for operationalisation of the UKNZCBS. Regardless, the generalisability of the results is limited by the purposive sampling technique adopted to select the case study, and the application of deterministic safety margins to electrical and thermal loads in the microgrid model to account for uncertainties in weather, occupancy, and operational schedules. Hence, statistical sampling and detailed sensitivity and uncertainty analysis should be incorporated in future research to enhance the application of the results to energy efficiency and decarbonisation policy and project planning.