Night ventilation is a technique in which the indoor air and the building’s thermal mass is cooled down during nighttime to provide a heat sink available during the next day to help mitigating overheating and reducing the daytime space cooling demand. This paper proposes a framework on evaluating the use of mechanical night ventilation today and in the future. It considers analysis of the ventilative cooling system, including mechanical night ventilation, by means of key performance indicators that involve thermal comfort, energy use and resiliency criteria as suggested by IEA Annex 80. It, additionally, introduces an economic parameter in form of diurnal and nocturnal price ratio of electricity as economic trade-off between nighttime fan- and daytime fan and chiller use in terms of electricity. A historic office building in north-central Sweden is presented as a detailed case as to illustrate the use of the framework. The investigation was done using a validated model of the building in IDA-ICE building simulation program at both current climate and future climate in 2050s. It was revealed that an upgraded ventilative cooling system with three times larger capacity is required to fulfill thermal comfort. Even though mechanical night ventilation could result in the annual cooling source electricity saving intensity up to 0.9 kWh/(m²∙a) at extreme current climate (2018), it could just insignificantly reduce the total electricity use for space cooling (up to 2 %) and only at some night ventilation rates at all mentioned climates. Mechanical night ventilation, however, could be applied in an economically beneficial way if the electricity network has different nocturnal and diurnal electricity prices. A unitless index of maximum nighttime over daytime electricity price ratio was proposed representing the maximum tolerable price for nighttime electricity, given a daytime electricity price, based on night- and daytime ventilation electricity demand. For economically justified application of mechanical night ventilation, lower nighttime over daytime electricity price ratios were required for higher night ventilation rates. For the typical future climate with night ventilation rates larger than 2.6 ACH, it will be necessary to have nighttime prices that are lower than daytime if mechanical night ventilation is to be economical. The approach used in the framework can be applied to future research and practice, regardless of the case-specific parameters such as building type, climate zone, location, etc.

The study investigates the impact of improved synthetic amorphous silica, specifically developed aerogel-based insulating coatings, Quartzene (Qz), on energy efficiency in buildings across cold and warm climate zones. Simulations were conducted on various coatings and thicknesses for exterior and interior wall surfaces, as well as roofs. These were evaluated using a prototype residential building under dynamic thermal conditions. Wall coatings were analyzed, including a base plaster and a mixture with 10%Wt aerogel-based Quartzene. Additionally, three roof coating samples were tested: Qz 12.5%Wt, TiO2 3.3%Wt, and a blend of aerogel-based mixtures and TiO2. Mixtures containing Qz exhibited the lowest thermal conductivity (0.05 W/(m·K)) and high short-wave reflectance (up to 0.93 μm), impacting transmission loads, time lag, and decrement factor. Energy savings of up to 11% were observed in warm climates when implementing the coatings (unaged performance). Overall, the coated surfaces increased time lag and reduced decrement factor compared to uncoated surfaces. Aerogel-based coatings showed enhanced effectiveness in lowering transmission loads.

Historical buildings account for a significant portion of the energy use of today’s building stock, and there are usually limited energy saving measures that can be applied due to antiquarian and esthetic restrictions. The purpose of this case study is to evaluate the use of the building structure of a historical stone building as a heating battery, i.e., to periodically store thermal energy in the building’s structures without physically changing them. The stored heat is later utilized at times of, e.g., high heat demand, to reduce peaking as well as overall heat supply. With the help of Artificial Intelligence and Convolutional Neural Network Deep Learning Modelling, heat supply to the building is controlled by weather forecasting and a binary calendarization of occupancy for the optimization of energy use and power demand under sustained comfortable indoor temperatures. The study performed indicates substantial savings in total (by approximately 30%) and in peaking energy (by approximately 20% based on daily peak powers) in the studied building and suggests that the method can be applied to other, similar cases.

This IEA Annex 80 Subtask C report and the associated brochures provide examples of well-documented field studies. These field studies apply resilient cooling technologies to reduce energy demand and carbon emissions for cooling and reduce the overheating risk in different types of buildings, including newly constructed and existing buildings. Examples and details on building information, energy systems, resilient cooling technologies, key performance indicators (KPIs), and performance evaluation amd lessons learned are included in the report and the brochures.

The present report summarizes all 13 field study buildings collected in Subtask C of IEA-EBC Annex 80. This summary presents information on the field studies, the resilient cooling technologies applied in the field studies, the KPIs, and the performance evaluation and lessons learned. The values of KPIs for building similar functions, i.e., residential buildings, under different climate conditions were discussed. In the field study brochures, detailed information is inlcuded for each building.

The field studies are presented in brochure format. Each brochure contains information in a standardized format. This includes the introduction & climate, building information, resilient cooling, KPI evaluation, design simulation, performance evaluation, discussion, lessons learned, references & key contacts.

This study is framed around two research questions to 1) investigate the probable changes in future climate and 2) evaluate the changes in cooling demand of a studied building when implementing an assemble climate representing mid-term future period (2041-2060). The chosen building is a preschool in central Sweden that fulfills the Nearly-Zero Energy Building (NZEB) requirements based on today’s Swedish National Building Regulations. To assess and cope with the present and future cooling energy needs of the building, a climate file representing present conditions along with a projected future typical climate file are utilized. The future climate is an assembled typical meteorological year climate file using the CORDEX data. 

The present climate file underpredicts the future energy demands therefore verifying to be unsuitable for anticipated energy analysis. It was discovered that the cooling demand for assembled climate file is almost 4 times the present climate file for the studied conditions. 

In this study, the performance of different cooling technologies from energy and economicperspectives were evaluated for six different prototype residential Nearly Zero Energy Buildings(NZEBs) within a planned future city district in central Sweden. This was carried out by assessingthe primary energy number and life cycle cost analysis (LCCA) for each building model and coolingtechnology. Projected future climate file representing the 2050s (mid-term future) was employed.Three cooling technologies (district cooling, compression chillers coupled/uncoupled with photovoltaic (PV) systems, and absorption chillers) were evaluated. Based on the results obtained fromprimary energy number and LCCA, compression chillers with PV systems appeared to be favorableas this technology depicted the least value for primary energy use and LCCA. Compared to compression chillers alone, the primary energy number and the life cycle cost were reduced by 13%, onaverage. Moreover, the district cooling system was found to be an agreeable choice for buildingswith large floor areas from an economic perspective. Apart from these, absorption chillers, utilizingenvironmentally sustainable district heating, displayed the highest primary energy use and life cycle cost which made them the least favorable choice. However, the reoccurring operational cost fromthe LCCA was about 60 and 50% of the total life cycle cost for district cooling and absorption chillers,respectively, while this value corresponds to 80% for the compression chillers, showing the high netpresent value for this technology but sensitive to future electricity prices.

A two-trough parabolic-shaped concentrating photovoltaic solar collector with a vertical half-size ‘phosphorus-passivated emitter rear totally diffused’ bifacial cell string receiver was designed and built for household applications, with the aim of smooth the electrical ‘duck curve’. The study consisted in testing the concentrating photovoltaic solar collector outdoors, under real weather conditions, for its daily electrical peak power and efficiency, as well as for its electrical transversal and longitudinal Incidence Angle Modifier direction. The outdoor testing measurements were conducted in a parabolic trough with low concentration coupled with a central vertical half-size ‘phosphorus-passivated emitter rear totally diffused’ bifacial cell string receiver. Furthermore, the electrical transversal Incidence Angle Modifier showed to be very delicate due to the position and outline of the receiver, which led to an electrical peak efficiency close to 10% at ±25° (i.e., for an electrical power output of around 49.3 W/m2). To validate the measured parameters, a ray-tracing software has been used, where the measured Incidence Angle Modifiers have a very good agreement with the simulated Incidence Angle Modifiers (e.g., deviation of <4%). Consequently, the concentrating solar collector met the objective of lowering the Photovoltaic cell stress and high radiation intensity, by shifting the electrical peak power at normal (e.g., at 0°) to higher incidence angles (e.g., ±25°); this aids the electrical demand peak shaving, by having the highest electrical power production displaced from the highest intensity solar radiation during the day.

This study aims at assessing how well a mechanical night ventilation of today, will cope with delivering acceptable thermal comfort while minimizing the electricity use and the electrical peak power demand for cooling in a historic office building in Sweden at both typical current climate and typical future climate in 2050s. The method includes numerical study in IDA-ICE simulation program using the typical current and future climate profiles. The results show that, for coefficient of performance of 3 and specific fan power of 1.5 kW/(m3/s), it would be possible to lower the electrical peak power demand and the electricity use in cooling machine by up to 2.2 kW (13%) and 1.4 MWh (48%) by night ventilation rate of 2.1 lit/(s·m2) at typical future climate in 2050s. Corresponding figures for typical current climate are 4.6 kW (36%) and 0.9 MWh (72%) owing to cooler nights and more diurnal temperature differences. 

The world is facing a rapid increase of air conditioning of buildings. It is the motivation of Annex 80 to develop, assess and communicate solutions of resilient cooling and overheating protection. Resilient Cooling is used to denote low energy and low carbon cooling solutions that strengthen the ability of individuals and our community to withstand, and prevent, thermal and other impacts of changes in global and local climates. It encompasses the assessment and Research & Development of both active and passive cooling technologies of the following four groups:

Reduce heat loads to people and indoor environments.Remove sensible heat from indoor environments.Enhance personal comfort apart from space cooling.Remove latent heat from indoor environments.The present review sums up the state of the art in cooling solutions which may be regarded as resilient. Its main objective is to systematically describe the available cooling solutions, their physical basis, their benefits and limitations, their technology readiness level, their practical availability, and applicability. Doing so, the State-of-the-Art Review forms the basis for the work of Annex 80.

The building sector accounts for a third of the total energy use in Sweden, and district heating provides half of the heating needs. The peak demand loads within a district heating network occur both regularly and irregularly and impose a burden on the energy company to fulfill the demand, often by using more expensive and less environmentally friendly resources (e.g., fossil fuels) instead of the waste heat from industry or biofuels. Heat storage during hours of less demand and prior to colder periods can be used for load management and sustainable planning of energy supply, as well as reduction of total greenhouse gas emissions. Thus, heat supply to the building can be lowered temporarily during the peak power period to utilize the stored thermal energy within the building thermal inertia. The use of indoor temperature decay and the delivery of heating power to a multifamily building are studied here, and heating storage capacity and thermal inertia are calculated. During the performed decay test, the energy supply was estimated to be reduced by 61% for 5 h, which resulted in only a 0.3 °C temperature decay. Therefore, the suggested method can shave eventual peaks in supplied heat with minimal influence on the thermal comfort.