Renovating primary school buildings in Malta to achieve cost-optimal energy performance and comfort levels

Abstract

The Energy Efficiency Directive (EED) (2012/27/EU) [1] requires that 3% of the total floor area owned and occupied by public buildings be renovated each year to meet the Minimum Energy Performance Requirements (MEPRS) based on the Cost Optimal Methodology (COMet) as defined by the EPBD recast [2]. The MEPRS for the retrofitting of educational buildings in Malta still have not been defined. In this study, an innovative and energy efficient COMet approach for the retrofitting of Public Primary School Buildings (PPSBs) in Malta has been applied. All current PPSBs are naturally ventilated and have diverse footprints and envelope constructions. This prompted us to move away from the commonly adopted COMet approach, which assumes that one or two Reference Buildings (RBs) is sufficient for defining the MEPRS for all school buildings and that the building is assumed to be mechanically ventilated with active heating/cooling sources to reach comfort defined by pre-determined temperature set-points. In contrast, this study aims to achieve comfort using the EN 15251 [3] adaptive thermal comfort approach for naturally ventilated buildings and provides an Excel tool that calculates the MEPRS based on the actual building construction and orientation. Results have shown that for the summer season, the PPSB can attain adaptive comfort if its glazing is externally shaded and night purging is applied. The space cooling demand should therefore not be required in the MEPRS calculations. In contrast, for the winter period, mechanical ventilation plus an active heat source is required to achieve comfort. For all ten RBs considered having the same total occupied area but different construction and orientation, the MEPRS is circa 0 kWh/m2/annum with the same retrofitting measures required for all RBs to achieve this EP. However, despite this similarity in MEPRS for all RBs, there is a large difference in the Global Cost required and the resulting Net Present Value (NPV) to achieve this EP for the different RBs. This difference is very important from an investor's perspective and cannot be shown by defining one or two RBs but by the Excel tool that was developed in this work. In addition, despite the large difference in NPV, the retrofitting measures to achieve MEPRS resulted in a positive NPV for all RBs and therefore the Energy Performance Contracting financing model (EnPC) for retrofitting PPSBs should be considered. One notes that the highest NPV鈥榮 occur when PV systems occupy a large percentage of the roof area (60%), even if this does not coincide with the cost optimal life cycle costing which requires PVs to occupy only 20% of the roof area. Therefore, it makes more sense not only to achieve the MEPRS by introducing the cost optimal measures, but by achieving the highest NPV through additional PV installations, thus positively contributing towards the RES target for Malta, besides achieving better PR for the building. Measures such as insulation that provide a low/negative NPV when based on site energy may still have an investment potential from a national perspective as they generally result in a positive NPV when primary energy is considered, and therefore incentives can be given to attract the private investor to apply such measures, given that it would be difficult for them to justify capital expenditure without having a reasonable financial return.