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OVERVIEW | Is HVAC system flexibility linked to energy savings?

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OVERVIEW | Is HVAC system flexibility linked to energy savings?

Shutterstock / Lisa F. Young

by François Durier (CETIAT)


What do we mean by flexibility?


In the context of the energy performance of buildings, the flexibility of a system refers to its ability to adapt to changes, and the ease with which it responds to such changes whilst maintaining or increasing its performance and levels of service.


For example, building flexibility can refer to the building’s ability to adapt over its lifetime to changes in parameters such as occupant needs and activity, weather conditions, or energy sources, whilst maintaining or improving the building's fitness for use, occupant well-being, and energy performance.


The energy flexibility of a building refers to its ability to adapt to its occupants' needs, to make use of different energy sources according to their availability, price or carbon content, or to modulate the building's energy demand according to a signal from the energy network or from the energy supplier in order to adapt to grid needs for demand variations.


Towards a smart readiness indicator?


In its proposal for a revised Energy Performance of Buildings Directive, published in November 2016, the European Commission states that a smartness indicator of the building should be introduced to cover flexibility features, in order to "take part in demand response" and to "contribute to the optimum, smooth and safe operation of the various energy systems and district infrastructures to which the building is connected".


In the position adopted by the Council in June 2017, the word "flexibility" is no more present in the definition of a smartness indicator (which it refers to as the "smart readiness indicator"). Innovative energy flexibility management solutions are presented as a basis for a clean energy transition, and the smart readiness indicator is described as characterising the capabilities of buildings with regard to operation, monitoring and management, interaction with occupants, demand response and interoperability of automation and control systems and technical building systems.


A draft amendment published by the European Parliament in April 2017, suggests that the smartness indicator should rate "the ability of a building or building unit to adapt its operation to the needs of the occupant and the grid and to improve its energy efficiency and overall performance".


An ongoing study on behalf of the European Commission is intended to provide technical support to feed the negotiations and decision process regarding the potential setting up of a "Smart Readiness Indicator" for buildings. This indicator would rate:


  • the readiness to adapt in response to the needs of the occupant and to empower building occupants by taking direct control of their energy consumption and/or generation;
  • the readiness to facilitate maintenance and efficient operation of the building;
  • the readiness to adapt in response to the needs/situation of the grid.

A project on "Energy flexible buildings" (Annex 67) is currently in progress (2014-2019) within the framework of the "Energy in Buildings and Communities" programme of the International Energy Agency (IEA EBC). It defines the energy flexibility of a building as the ability to manage its energy demand and generation according to local climate conditions, user needs and grid requirements.


Energy flexibility of HVAC systems


In its June 2017 report "Opening the door to smart buildings", the Buildings Performance Institute Europe (BPIE) states that a smart building: "(i) stabilises and drives a faster decarbonisation of the energy system through energy storage and demand-side flexibility; (ii) empowers its users and occupants with control over the energy flows; (iii) recognises and reacts to users’ and occupants’ needs in terms of comfort, health, indoor air quality, safety as well as operational requirements".


In a separate report titled "Smart Buildings Decoded" BPIE also states the following: "In the energy system, flexibility will be needed for both supply and demand sides. Increased integration of distributed energy (re)sources, renewables and storage and the growing peak demand for electricity will drive the need for more flexibility, demand response capabilities and empowerment of the consumer to further develop an affordable, reliable and decarbonised energy system. Buildings have the potential to drive the flexibility of the energy system, through energy production and control, storage, demand response as well as through an interconnection with electric vehicles".


Evolution of connected and smart homes (Source: BSRIA) — taken from the BPIE report "Smart Buildings Decoded"


As far as HVAC systems are concerned, these explanations show that flexibility means on-site use of renewable energy sources (e.g. solar thermal, biomass, heat pumps, photovoltaics), energy storage (heat, cold or electricity storage), advanced controls, integration and interconnection, users information and opportunity given to them to act on the system.


Flexibility and energy savings


Numerous studies have assessed the energy savings linked to enhanced controls of HVAC systems.


A study prepared in 2014 for eu.bac (European Building Automation and Controls Association) looked at the potential energy savings from the increased application of heating controls in residential properties across the European Union. Results show that the enhanced adoption of existing heating control technologies (2014) in EU homes lead to peak annual energy savings of over 50TWh per year, nominal fuel bill savings of around €4.3 billion and CO2 savings of nearly 12MtCO2 per year.


From the 2014 eu.bac recport


According to BPIE, building automation can reduce energy consumption by around 27% in households, and smart technology can save an average of 23% of energy consumption in offices.


In a 2013 BUILD UP Overview article, eu.bac recalled that, as a result of the Energy Performance of Buildings Directive (EPBD), about 40 European standards were developed to harmonise the energy calculation methods for buildings. EN 15232 is the standard concerning the energy impact of building automation, controls and building management. It includes a method that allows an assessment of the energy savings for building heating and cooling thanks to building automation and control systems.




The energy flexibility of a building requires that its HVAC systems be designed, controlled and operated appropriately for the intended purpose. If so, the HVAC systems will contribute to the building's ability to manage its energy demand and generation according to the various parameters. Several sources state that enhanced controls of HVAC systems can provide significant energy savings.