• Energy Research

The increasing global energy demand, the foreseen reduction of available fossil fuels and the increasing evidence off global warming during the last decades have generated a high interest in renewable energy sources. However, renewable energy sources, such as wind and solar power, have an intrinsic variability that can seriously affect the stability of the energy system if they account for a high percentage of the total generation. The Energy Flexibility of buildings is commonly suggested as part of the solution to alleviate some of the upcoming challenges in the future demand-respond energy systems (electrical, district heating and gas grids). Buildings can supply flexibility services in different ways, e.g. utilization of thermal mass, adjustability of HVAC system use (e.g. heating/cooling/ventilation), charging of electric vehicles, and shifting of plug-loads. However, there is currently no overview or insight into how much Energy Flexibility different building may be able to offer to the future energy systems in the sense of avoiding excess energy production, increase the stability of the energy networks, minimize congestion problems, enhance the efficiency and cost effectiveness of the future energy networks. Therefore, there is a need for increasing knowledge on and demonstration of the Energy Flexibility buildings can provide to energy networks. At the same time, there is a need for identifying critical aspects and possible solutions to manage this Energy Flexibility, while maintaining the comfort of the occupants and minimizing the use of non-renewable energy. In this context, the IEA (International Energy Agency) EBC (Energy in Buildings and Communities program) Annex 67: “Energy Flexible Buildings” was started in 2015. The article presents the background and the work plan of IEA EBC Annex 67 as well as already obtained results. Annex 67 is a corporation between participants from 16 countries: Austria, Belgium, Canada, China, Denmark, Finland, France, Germany, Ireland, Italy, The Netherlands, Norway, Portugal, Spain, Switzerland and UK.

Abstract Draft is defined as unwanted local convective cooling. Existing draft risk models, developed in the 1970s, focus on air movement at the neck. The purpose of the present study is to experimentally evaluate ankle draft risk for women with uncovered ankles because of current widespread use of displacement ventilation and underfloor air distribution systems and changes in dress customs. Thirty female university students participated in nine double-blind randomized tests. The subjects wore sandals with lower legs, ankles and feet uncovered. Exposures occurred in an environmental chamber resembling an office environment. The operative temperature at 1.1 m above the floor was maintained at 24.1 °C. The measured air speeds at the ankle varied between 0.16 and 0.59 m/s and the air temperature at the ankle varied between 18.0 and 21.7 °C. Subjective responses were obtained to assess these parameters: thermal acceptability, comfort, preference and sensation, air movement acceptability and preference, local thermal sensation and comfort, and perceived air quality. Subjects were more sensitive to ankle draft than expected. For all the tested conditions, between 20 and 37% of the subjects found the overall thermal environment not acceptable, while between 23 and 57% of the subjects found air movement at the ankle unacceptable. These dissatisfaction percentages are higher than those of international, American and European standards, indicating the need to develop a draft risk model for displacement ventilation and underfloor air distribution systems.

Towards a carbon-neutral society, the building sector has a pivotal role with still a great potential for improvement. A new generation of buildings is rising but, to set a more ambitious shift in the paradigm and to fully justify the additional efforts (technological and economic) needed to fill the gap between net zero and plus energy performances, it is essential to consider not only the direct effects, but also all the indirect impacts. However, research conducted in the last decade solely focuses on the direct effects, mainly energy savings, while the indirect impacts neither have a clear identity nor terminology and a defined list of the impacts and methodologies for their quantification is still missing. With these premises, a systematic literature review on the current state of the art was performed in this work, with the aim of (i) investigating the heterogeneous terminology used for such indirect effects, (ii) identifying a final potential list of impacts both at the household and at the community level and (iii) their macro-categorizations, and (iv) exploring the current implemented methodologies and indicators for an economic quantification. As a final result of the analysis, the authors propose a unique terminology for addressing the indirect effects of high-performance buildings. This paper sets the needed basis and common ground for future research in this field, meant to economically quantify the indirect effects in the building sector.

Abstract An office equipped with personal footwarmers was maintained at cooler-than-normal indoor temperatures in the winter, producing great energy savings. The occupants’ thermal comfort was not affected. The footwarmers provide individual heating control over a segment of the body that most strongly influences comfort perception when one is cool overall. If cooler ambient indoor temperatures could be made comfortable, savings in central heating energy would be possible. During a six-month winter period in Berkeley California, knowledge workers with low-energy footwarmers experienced a lowering of room heating set point from 21.1 °C (70 °F) to 18.9 °C (66 °F). Surveys showed equal thermal comfort in the original ‘higher heating setpoint no-footwarmer’ condition and the ‘lower heating set point plus occupant-controllable footwarmer’ condition. Heating energy was closely monitored throughout. It dropped 38–75% depending on the setpoint reduction and outdoor conditions. The added plug load energy from the low-energy footwarmers was much less than the central heating energy saved by lowering the heating set point (3–21 W vs 500–700 W average power per occupant during occupied hours). A few subjects had ergonomic issues with the particular footwarmers used, so usage was not universal. Additional foot- and leg-warmer design options would help.

Radiant heating and cooling (RHC) systems are being more widely adopted considering the well-known technical advantages: increased thermal comfort, space saving, and reduced energy use. Since the building sector is currently one of the largest consumers of fossil fuels, many directives and regulations have been enacted to address the intense concern about energy use for space conditioning. Even though radiant systems are considered as an energy efficient technology for building heating and cooling, more effort is needed to fulfil the zero energy requirements outlined by recent standards and directives. Renewable Energy Sources (RES) are an effective solution to avoid using finite fossil fuels and related geopolitical issues enhanced by the recent world conflicts. Despite being primarily intermittent and subject to economic and regional constraints, RES offer suitable temperature levels to supply low temperature heating and high temperature cooling operation, a major advantage of RHC system. Although a limited number of studies directly report energy savings or CO2 emission reduction as the main outcomes of the research related to this combination, valuable insights have been obtained for the present review. Primary energy can decrease between 40% and 80% with different integration of RHC, photovoltaic, heat pumps and district heating. TABS can lead to load shifting up to 100%, allowing an increased self −consumption of renewable energy. This paper provides evidence on whether coupling radiant systems with renewables is a promising strategy for achieving nearly-zero annual energy balances in building stocks. It investigates recent trends, limitations and potential to support decarbonization goals.

Abstract ARX models are an effective instrument to evaluate continuous building performance from insufficient monitoring data. However, selecting the right model features is NP-hard. The problem of finding a minimal subset of informative inputs has been studied extensively in various fields but automatic, fast, and reliable procedures for finding optimal models for building performance evaluation are still missing. We propose a novel feature selection algorithm named Greedy Correlation Screening (GCS), which identifies a possible solution at a time by greedily maximizing the correlation between inputs and output and minimizing cross-correlations between inputs. These two objectives are competing, thus leading to best tradeoffs. Among these, the best model is automatically selected by applying filters and quality criteria such as the adjusted coefficient of correlation and non-correlation of residuals. The performance of the proposed heuristic method is compared to two of the best algorithms used in the field, such as GRASP for feature selection and NSGA-II (Non-dominated Sorting Genetic Algorithm). The application on a real case study demonstrates that the proposed method solves the problem of feature selection in building performance estimation efficiently and reliably. Moreover, the model creation is automatic, making it ideal for integration into a Building Management System (BMS) in order to detect faults and perform short-term predictive control.

A novel heated/cooled chair was evaluated for its effect on thermal sensation and comfort. The chair is exceptionally efficient, allowing standalone battery operation over long periods. Its capabilities at providing comfort needed to be established. Twenty-three college students participated in 69 2.25-hour tests. Four heated/cooled chairs were placed in an environmental chamber resembling an office environment. The chamber temperatures were 16°C, 18°C and 29°C. During the tests the subjects had full control of the chair power through a knob located on the chair. The heated/cooled-chair results could be compared to those of conventional mesh and cushion chairs tested in the same three environmental conditions in a previous study, as well as to a thermoelectrically heated and cooled chair. Subjective responses for thermal sensation and comfort were obtained at 15-minute intervals. The results show that the heated/cooled chair strongly influences the subjects’ thermal sensation and improves thermal comfort and perceived air quality. No significant differences were found between men and women. The chair provided comfortable conditions for 92% of the subjects in a range of temperatures from 18°C to 29°C.