@article {77,
	title = {Energy flexibility of domestic thermal loads{\textendash}a building typology approach of the residential building stock in Austria},
	journal = {Advances in Building Energy Research},
	volume = {13},
	year = {2019},
	pages = {122{\textendash}137},
	publisher = {Taylor \& Francis},
	abstract = {Due to a high share of fluctuating renewables in the energy system and many grid-connected heating systems, Austria is facing a growing problem of peak loads in electric and thermal grids [E-Control Austria (2015). Market Report {\textendash} National Report to the European Commission, Retrieved from https://www.econtrol.at/documents/20903/443907/EC_Marktbericht15_ENGL.pdf/e22b1ce5-a8c9-44bf-a701-0a73af678735]. Based on the research done in the framework of EBC Annex 67 Energy Flexible Buildings [Jensen, S. (2015). IEA EBC Annex 67 Energy Flexible Buildings {\textendash} Annex Text. www.annex67.org], theoretical and practical considerations about the potential contributions of domestic heat loads to energy flexibility are drawn for building typologies in Austria TABULA. (2009{\textendash}2012). Typology approach for building stock energy assessment/IEE EPISCOPE Project. Retrieved from http://www.episcope.eu/ieeproject/tabula/]. In order to explore the potential of energy flexibility of residential buildings that can be used without jeopardizing building comfort, various building models have been simulated in IDA ICE. Connections between energy flexibility related to the building{\textquoteright}s technical equipment, its construction period, physical characteristics, climate and user comfort are analysed. The evaluation shows which individual technologies and parametric optimizations are recommended for load management. The results show that in buildings built according to Austrian standards after 1980 at least 50\% of domestic heating peak loads can be shifted to off-peak periods.},
	keywords = {Demand response, Demand-side management, energy efficient architecture, Energy flexible buildings, load control, residential building typology, thermal mass},
	doi = {10.1080/17512549.2017.1420606},
	author = {Tobias Wei{\ss} and Anna Maria Fulterer and Knotzer, Armin}
}
@article {67,
	title = {Predictive rule-based control to activate the energy flexibility of Norwegian residential buildings: Case of an air-source heat pump and direct electric heating},
	journal = {Applied energy},
	volume = {237},
	year = {2019},
	pages = {500{\textendash}518},
	publisher = {Elsevier},
	abstract = {The building energy flexibility potential of a Norwegian single-family detached house is investigated using predictive rule-based control (PRBC) and building performance simulation (using IDA ICE). Norwegian timber buildings are lightweight and four different insulation levels are considered. Both on-off and modulating air-source heat pumps are analyzed and compared to direct electric heating which is the most common heating system for Norwegian residential buildings. A detailed model for both the heat pump system and the building is implemented, a level of detail not found in previous research on building energy flexibility. The three PRBC investigated have the following objectives: reduce energy costs for heating, reduce annual CO2eq. emissions and reduce energy use for heating during peak hours. This last objective is probably the most strategic in the Norwegian context where cheap electricity is mainly produced by hydropower. The results show that the price-based control does not generate cost savings because lower electricity prices are outweighed by the increase in electricity use for heating. The implemented price-based control would create cost savings in electricity markets with higher daily fluctuations in electricity prices, such as Denmark. For the same reasons, the carbon-based control cannot reduce the yearly CO2eq. emissions due to limited daily fluctuations in the average CO2eq. intensity of the Norwegian electricity mix. On the contrary, the PRBC that reduces the energy use for heating during peak hours turns out to be very efficient, especially for direct electric heating. For air-source heat pumps, the control of the heat pump system is complex and reduces the performance of the three PRBC. Therefore, results suggest that a heat pump system should be modeled with enough detail for a proper assessment of the building energy flexibility. First, by varying temperature set-points there is a clear interaction between the prioritization of domestic hot water and the control of auxiliary heaters which increases energy use significantly. Second, the hysteresis of the heat pump control and the minimum cycle duration prevent the heat pump from stopping immediately after the PRBC requires it. Finally, the paper shows that the influence of thermal zoning, investigated here by cold bedrooms with closed doors, has a limited impact on the building energy flexibility potential and the risk of opening bedroom windows.},
	keywords = {Building energy flexibility, CO2eq. intensity, Demand response, Direct electric heating, Heat pump, Predictive rule-based control},
	doi = {10.1016/j.apenergy.2018.12.074},
	author = {Clau{\ss}, John and Stinner, Sebastian and Sartori, Igor and Georges, Laurent}
}
@article {72,
	title = {A standardised flexibility assessment methodology for demand response},
	journal = {International Journal of Building Pathology and Adaptation},
	year = {2019},
	publisher = {Emerald Publishing Limited},
	abstract = {Purpose
The purpose of this paper is to standardised four-step flexibility assessment methodology for evaluating the available electrical load reduction or increase a building can provide in response to a signal from an aggregator or grid operator.

Design/methodology/approach
The four steps in the methodology consist of Step 1: systems, loads, storage and generation identification; Step 2: flexibility characterisation; Step 3: scenario modelling; and Step 4: key performance indicator (KPI) label.

Findings
A detailed case study for one building, validated through on-site experiments, verified the feasibility and accuracy of the approach.

Research limitations/implications
The results were benchmarked against available demonstration studies but could benefit from the future development of standardised benchmarks.

Practical implications
The ease of implementation enables building operators to quickly and cost effectively evaluate the flexibility of their building. By clearly defining the flexibility range, the KPI label enables contract negotiation between stakeholders for demand side services. It may also be applicable as a smart readiness indicator.

Social implications
The novel KPI label has the capability to operationalise the concept of building flexibility to a wider spectrum of society, enabling smart grid demand response roll-out to residential and small commercial customers.

Originality/value
This paper fulfils an identified need for an early stage flexibility assessment which explicitly includes source selection that can be implemented in an offline manner without the need for extensive real-time data acquisition, ICT platforms or additional metre and sensor installations.},
	keywords = {Demand response, Demand side management, Demonstration study, Energy flexible buildings, Smart grid, Smart readiness indicator},
	issn = {2398-4708},
	doi = {10.1108/IJBPA-01-2019-0011},
	author = {O{\textquoteright}Connell, Sarah and Reynders, Glenn and Seri, Federico and Sterling, Raymond and Marcus M. Keane}
}
@article {79,
	title = {Characterizing the energy flexibility of buildings and districts},
	journal = {Applied energy},
	volume = {225},
	year = {2018},
	pages = {175{\textendash}182},
	publisher = {Elsevier},
	abstract = {The large penetration rate of renewable energy sources leads to challenges in planning and controlling the energy production, transmission, and distribution in power systems. A potential solution is found in a paradigm shift from traditional supply control to demand control. To address such changes, a first step lays in a formal and robust characterization of the energy flexibility on the demand side. The most common way to characterize the energy flexibility is by considering it as a static function at every time instant. The validity of this approach is questionable because energy-based systems are never at steady-state. Therefore, in this paper, a novel methodology to characterize the energy flexibility as a dynamic function is proposed, which is titled as the Flexibility Function. The Flexibility Function brings new possibilities for enabling the grid operators or other operators to control the demand through the use of penalty signals (e.g., price, CO2, etc.). For instance, CO2-based controllers can be used to accelerate the transition to a fossil-free society. Contrary to previous static approaches to quantify Energy Flexibility, the dynamic nature of the Flexibility Function enables a Flexibility Index, which describes to which extent a building is able to respond to the grid{\textquoteright}s need for flexibility. In order to validate the proposed methodologies, a case study is presented, demonstrating how different Flexibility Functions enable the utilization of the flexibility in different types of buildings, which are integrated with renewable energies.},
	keywords = {Demand response, Energy flexibility, Flexibility function, Flexibility index, Smart building, Smartness},
	doi = {10.1016/j.apenergy.2018.05.037},
	author = {Rune Gr{\o}nborg Junker and Armin Ghasem Azar and Rui Amaral Lopes and Karen Byskov Lindberg and Reynders, Glenn and Relan, Rishi and Madsen, Henrik}
}
@article {78,
	title = {Energy flexible buildings: An evaluation of definitions and quantification methodologies applied to thermal storage},
	journal = {Energy and Buildings},
	volume = {166},
	year = {2018},
	pages = {372{\textendash}390},
	publisher = {Elsevier},
	abstract = {As demand response and energy flexibility are often suggested as key principles to facilitate high levels of renewable energy sources into energy markets, different studies evaluated the potential impact of energy flexibility in buildings. Nonetheless, due to differences in definition and quantification methodologies for energy flexibility, comparing results between such studies is difficult. With a review and applied evaluation of existing definitions and quantification methodologies this paper aims at assessing the applicability, benefits and drawbacks of each quantification methodology.

The conducted review shows that energy flexibility definitions found in the literature have their particularities despite sharing the same principle that energy flexibility is the ability to adapt the energy profile without jeopardizing technical and comfort constraints. The survey of quantification methodologies reveals two main approaches to quantify energy flexibility. A first approach quantifies energy flexibility indirectly using past data and assuming a specific energy system and/or energy market context. The second approach directly predicts the energy flexibility that a building can offer to the energy system in a bottom-up manner. While applications for both approaches were identified, this paper focuses on the latter. By applying methodologies that follow this second approach to a common case study, three common properties of energy flexibility were observed: i) the temporal flexibility; ii) the amplitude of power modulation; iii) and the associated cost.},
	keywords = {Demand response, Demand side management, Energy flexible buildings, load control, Smart grid},
	doi = {10.1016/j.enbuild.2018.02.040},
	author = {Reynders, Glenn and Rui Amaral Lopes and Marszal-Pomianowska, Anna and Aelenei, Daniel and Martins, Jo{\~a}o and Saelens, Dirk}
}
@article {81,
	title = {Heating system energy flexibility of low-energy residential buildings},
	journal = {Energy and Buildings},
	volume = {180},
	year = {2018},
	pages = {95{\textendash}108},
	publisher = {Elsevier},
	abstract = {Energy flexibility is proposed as a cost-effective solution facilitating secure operation of the energy system while integrating large share of renewables. With strict building regulations in Denmark, newly built buildings are low-energy buildings. In order to identify the role of low-energy buildings in the energy system, we investigated the physical potential for flexibility and analysed the thermal storage capacity existing inherently in the structural mass. Two building types were studied: single-family house and apartment block. The aim is to quantify the energy that can be added to or curtailed from each building during a time period without compromising thermal comfort. Different scenarios (starting time and duration), building design characteristics and boundary conditions were studied. The findings showed that low-energy buildings are highly robust and can remain autonomous for several hours. Although for individual buildings the available energy for curtailment is limited, if many buildings are aggregated energy flexibility becomes significant. The potential for storage in the thermal mass is considerable. The analysis presented high dependence of flexibility potential on boundary conditions (ambient temperature, solar radiation, internal gains) and underlined the importance of envelope insulation. Heat losses govern the potential for flexibility, while the walls{\textquoteright} thermal mass has a secondary influence.},
	keywords = {Building thermal mass, Demand response, Energy flexibility, Low-energy building, Thermal energy storage},
	doi = {10.1016/j.enbuild.2018.09.030},
	author = {Foteinaki, Kyriaki and Li, Rongling and Heller, Alfred and Rode, Carsten}
}
@article {90,
	title = {Aggregation potentials for buildings{\textemdash}business models of demand response and virtual power plants},
	journal = {Energies},
	volume = {10},
	year = {2017},
	pages = {1646},
	publisher = {Multidisciplinary Digital Publishing Institute},
	abstract = {Buildings as prosumers have an important role in the energy aggregation market due to their potential flexible energy consumption and distributed energy resources. However, energy flexibility provided by buildings can be very complex and depend on many factors. The immaturity of the current aggregation market with unclear incentives is still a challenge for buildings to participate in the aggregation market. However, few studies have investigated business models for building participation in the aggregation market. Therefore, this paper develops four business models for buildings to participate in the energy aggregation market: (1) buildings participate in the implicit Demand Response (DR) program via retailers; (2) buildings with small energy consumption participate in the explicit DR via aggregators; (3) buildings directly access the explicit DR program; (4) buildings access energy market via Virtual Power Plant (VPP) aggregators by providing Distributed Energy Resources (DER)s. This paper also determines that it is essential to understand building owners{\textquoteright} needs, comforts, and behaviours to develop feasible market access strategies for different types of buildings. Meanwhile, the incentive programs, national regulations and energy market structures strongly influence buildings{\textquoteright} participation in the aggregation market. Under the current Nordic market regulation, business model one is the most feasible one, and business model two faces more challenges due to regulation barriers and limited monetary incentives.},
	keywords = {aggregators, Building energy flexibility, business model, Demand response, energy flexibility potential, virtual power plant},
	doi = {10.3390/en10101646},
	author = {Ma, Zheng and Joy Dalmacio Billanes and Bo N{\o}rregaar J{\o}rgensen}
}
@article {89,
	title = {IEA EBC annex 67 energy flexible buildings},
	journal = {Energy and Buildings},
	volume = {155},
	year = {2017},
	pages = {25{\textendash}34},
	publisher = {Elsevier},
	abstract = {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: {\textquotedblleft}Energy Flexible Buildings{\textquotedblright} 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.},
	keywords = {Demand response, Demand side management, Energy flexible buildings, Flexibility indicators, load control, Smart Energy Networks},
	doi = {10.1016/j.enbuild.2017.08.044},
	author = {S{\o}ren {\O}stergaar Jensen and Marszal-Pomianowska, Anna and Roberto Lollini and Wilmer Pasut and Knotzer, Armin and Engelmann, Peter and Stafford, Anne and Reynders, Glenn}
}
@article {88,
	title = {Space heating demand response potential of retrofitted residential apartment blocks},
	journal = {Energy and Buildings},
	volume = {141},
	year = {2017},
	pages = {158{\textendash}166},
	publisher = {Elsevier},
	abstract = {In future and smarter energy systems, time varying energy prices enable indirect demand response (DR) to assist the electricity supply system to meet demand. This simulation-based study investigates how economic model predictive control (E-MPC) schemes for space heating operation can utilize the thermal mass in an existing multi-story apartment block and eight retrofit scenarios to provide DR. The performance of the E-MPC scheme was evaluated in terms of its ability to enable end-user cost savings, reduce CO2 emissions and to perform load shift of the heating demand compared to a conventional PI controller. Two E-MPC approaches were considered: centralized E-MPC where inter-zonal effects were considered and decentralized E-MPC that neglected heat transfer between adjacent apartments. The E-MPC schemes led to increasing cost savings (up to approx. 6\%) and reduced CO2 emissions (up to approx. 3\%) as a function of increasing energy efficiency of the retrofit scenarios. The absolute amount of shifted power from peak load periods was rather consistent (approx. 2 kWh/m2 heated net area) across all retrofit scenarios compared to the existing building. The centralized E-MPC scheme led to marginally better results than the decentralized E-MPC. The added complexity involved in establishing a centralized E-MPC compared to a decentralized E-MPC may therefore not be worth the effort.},
	keywords = {Demand response, Economic model predictive control, Energy flexibility, Residential space heating, Structural thermal storage},
	doi = {10.1016/j.enbuild.2017.02.035},
	author = {Theis Heidmann Pedersen and Rasmus Elb{\ae}k Hedegaard and Petersen, Steffen}
}
