Back to knowledge
JRC

Heat captured during phase change

Thermal energy storage (TES) systems can  store heat or cold to be used at a later time under varying conditions such as temperature, place, time, or power. The main use of TES is to overcome the mismatch between energy generation and energy use [1]. The key requirements for the design of a TES system are high energy density in the storage material (storage capacity), good heat transfer between the heat transfer fluid (HTF) and the storage material, mechanical and chemical stability of the storage material, compatibility between the storage material and the container material, complete reversibility after a number of cycles, low thermal losses during the storage period, and easy control. Moreover, the most important design criteria are the operation strategy, the maximum load needed, the nominal temperature and enthalpy drop, and the integration into the whole application system. 

 

Integration of active TES systems in a building [10] 

 

Already in 2011, Arce et al. [2] calculated the potential of load reduction (L), energy savings (E), and climate change mitigation (as CO2 emissions reduction – RCO2) of TES in buildings in the EU. The applications considered were seasonal solar thermal systems (L=25,287 MWth; E=46,150 GWhth; RCO2=12,517,676 tons), district and central heating systems (L=1,453,863 MWth; E=2,326,182 GWhth; RCO2=630,957,558 tons), solar short-term systems (L=416,180 MWth; E=319,269 GWhth; RCO2=86,599,153 tons), and passive cold systems (L=9,944 MWth; E=18,148 GWhth; Ee=6,481 GWhe; RCO2=3,085,135 tons). The subscript “th” stands for “thermal” and the subscript “e” stands for electric. 

 

There are three technologies of TES systems, each one with different performance, which will drive for which technology each one is more appropriate. Moreover, each technology is in a different maturity status.  Sensible TES is when the energy is stored increasing or decreasing the temperature of a material (i.e., water, air, oil, bedrock, concrete, brick). Latent TES uses the phase transition, usually solid-liquid phase change, of a material; the materials used in latent TES are called phase change materials (PCMs). The last technology includes sorption and chemical energy storage  and it is usually known as thermochemical TES. 

Integration of PCM in a TABS system: PCM in concrete slab with exchange with air for free-cooling in summer and free-heating in winter [15] 

 

Several reviews can be found in the literature on TES for building applications, i.e., PCM for heating and domestic hot water (DHW) [3], PCM for air conditioning [4], PCM in building envelopes [5], adsorption for cooling in buildings [6], TES in hybrid systems [7], TES for seasonal storage [8], or more general building applications [9–11]. 

 

This factsheet focusses on the use of PCM for heat recovery and free-cooling and free-heating. In this context, core activation, thermally-activated building systems (TABS), suspended ceilings, and ventilation systems are used [10]. In free-cooling, coldness from the night is captured and stored to be used when cooling is needed in the building [12]. Free-heating is a similar concept, when heating from waste heat recovery or available solar energy are captured and stored to be used at a later time, in the heating system. PCMs help in increasing the amount of coolness or heat that can be stored; moreover, PCMs help storing the thermal energy at the desired temperature. These technologies may use ventilation systems to improve their performance [13]. Heat recovery can be done from any waste energy source available in the building. An example is the use of PCMs to recover the rejected heat from air-conditioning equipment [14].  

Phase change materials integration in a ceiling (https://www.building.co.uk/news/phase-change-materials/3111760.article) 

 

Even if these technologies cannot provide thermal comfort by themselves, and some supplementary equipment might be needed, they allow removing/downsizing the mechanical ventilation systems, while providing better thermal conditions, circulating fresh air, reducing energy costs, and improving demand side management. 

 

MATURITY:  

 

TES-based free-cooling and free-heating are mature technologies (TRL=9), heat recovery is at a less advanced stage (TRL=7-8). PCM materials and their technologies are still under development, although some products can be found on the market (TRL=5-8). 

CO-BENEFITS
KEYWORDS
PRE-CONDITIONS & ENABLING CONDITIONS
CONSTRAINTS/BARRIERS FOR IMPLEMENTATION
DRAWBACKS/ADVERSE IMPACTS OF THE SOLUTIONS after implementation
EXTERNAL LINKS
IMPACTS (Indicators + DNSH)
INSTRUMENTS/Processes for implementation
EXAMPLES

In this collection

Passive building design strategies: building orientation, passive heating and cooling

Passive building design means providing passive heating, passive cooling, and natural ventilation to maintain comfortable indoor conditions with no need for energy, by taking advantage of location (climate), orientation, massing, shading, material selection, thermal mass, insulation, internal layout and the positioning of openings to allow the penetration of solar radiation, daylight, and ventilation in the desired amounts [1–8]. When duly applied, passive design strategies are a designer’s first opportunity to increase a building’s energy efficiency, without adding much less front-end cost to a project as compared to active design strategies. Efficient passive design results in smaller heating and cooling loads (so that the building’s mechanical system – if any – can be downsized) and smaller electric loads for lighting through the use of daylighting design strategies.  

 

Beyond local climate, building orientation is a key aspect for passive design. The most energy-efficient designs are facing south or north to allow better solar energy management and better quality of daylighting. Building shape is also very relevant in the design, as an elongated and narrow plant (with south or north facing façade) allows for more of the building to be receive daylight. Shading strategies properly combined with other passive design strategies are also required, especially in hot climates [9,10]. Since the main difficulty in designing natural ventilation systems driven by buoyancy and wind is the simultaneous estimation of ventilation airflows and indoor temperatures, solar chimneys are used [11,12]. A solar chimney is a vertical shaft utilizing solar energy to enhance natural ventilation. 

 

Passive heating can be achieved by capturing the heat from the sun inside the building. Tweaking the window-to-wall ratio and the building exposure to the sun, all the while controlling for the thermal mass, heat flows and insulation allows to effectively store, distribute and retain the heat. The thermal mass defines the capacity to absorb, store and release heat. Heavyweight construction materials like concrete, brick and stone exhibit large thermal mass that can be used to effectively store the heat over peak hours and release it overnight. 

Passive building design. Figure from

 

Passive cooling is a set of design strategies to reduce heat gains and favour heat dispersion. Many methods exist and include using solar shadings as well as designing openings in such a way to allow good ventilation (such as solar chimneys). Shading can either be operable (external louvres, blinds, and deciduous trees) or fixed (e.g. eaves, overhangs, fences and evergreen trees). 

 

 '

Shading devices for north-facing openings. 

Figure from https://www.yourhome.gov.au/passive-design 

 

Passive design strategies are rated in different standards, such as PassivHaus (Passive House), BREEAM, LEED or WELL. 

 

The literature shows that today there are many net-zero, nearly-zero energy, and certified Passive House buildings worldwide, in different climate or geographic regions. Most are in Europe and North America, followed by New Zealand, Kore, Japan, China, and India [1]. Literature also shows that is it possible to achieve at least the Passive House energy standard of performance in all climate zones [13]. 

 

MATURITY:  

 

Although individual passive techniques are already commercial, their holistic implementation in buildings is still at TRL=4-6. 

Citizen Participation Platforms

E-participation [1][2][3][4][5] enables citizens to use digital technologies or platforms, e.g., combination of geographic information systems (GIS), Web 2.0 and mobile technologies (including video, mobile messaging and Internet access), for communication, engagement and deliberation on policy or planning challenges.  

 

Engagement and participation are vital tools in climate adaptation and environmental decision making as these entail increased community acceptance, support for climate actions, and provide new insights based on local knowledge [12]. Citizens can be consumers as well as producers of useful data for policy development and decision making (WeGovNow, Smarticipate, AI4PublicPolicy). 

 

There are multiple degrees of citizen participation ranging from passive, i.e., being simply informed, to responsive, i.e., contribute to consultation, to active, i.e., being fully empowered by having final decisions delegated to them (see Arnstein’s ladder [6]) [7]. In e-participation initiatives, both top-down (i.e., issues identified by public authority) and bottom-up (i.e., citizens led initiative) approaches can be applied. As multiple actors (i.e., different departmental units) are involved in the provision of e-participation, cross-organizational issues related to ownership and accountability may arise [3].  

 

Technologies supporting government processes (GovTech) can add great value to participatory processes (e.g., access to sensor kits, web portals and data), as shown by examples of Madrid (Decide Madrid), Bristol (Bristol Approach to citizen sensing – e.g., air quality, solid fuel burning etc.) [7], and Brussels (Curieuzenair). E-participation is usually considered part of e-government [5]. 

 

E-Government (or Electronic-Government) [1][2][8] refers to the application of Information and Communication Technologies (ICT) to government functions and procedures with the objective to increase efficiency of government agencies, enhance delivery of public services, and facilitate low cost and faster public engagement with public authorities. A comparative survey [8] of global e-government performance of municipalities highlights the best e-governance practices. It uses five categories of measures: privacy and security, usability, content, service and citizen and social engagement. For citizen and social engagement category Shanghai, Auckland, Seoul, Madrid, Paris, and Lisbon are ranked top cities for year 2018-19. 

 

Open Governance [9] is about transparency of and access to government data and decision making process so that innovative forms of collaborative actions (i.e. bottom-up and top-down) can be applied to solve policy problems, raise awareness, increase public participation, change behaviour, promote e-democracy, and revolutionise traditional service provision [10][11]. It is closely associated with open government data that can provide new insights about issues and services as well as offers the opportunities to participate, comment and influence plans and policy agenda to foster greater citizen participation. 

 

 

E-participation solutions range from responding to planning e.g., top-down to bottom-up urban regeneration [Smarticipate] or policy challenge [WeGovNow] or reporting a local problem (e.g., Bristol’s FixMyStreet); or bottom-up budget planning (e.g., Helsinki’s participatory budgeting) or accessing open data (e.g., Hamburg’s Transparency portal).  

 

There are several e-participation initiatives where various ICT tools are used to deliver different public services. For instance,  

Cross border e-governance initiatives such as [ACROSS], [DE4A] and [GLASS] go beyond one city’s public administrative level (even at EU level and beyond [iKaaS]) and deal with cross-border interoperable, mobile [mGov4EU] and privacy-aware public services.  

MATURITY: 

 

Many e-government and e-participation tools are available at higher TRL and are already being used by municipalities for public services and e-participation, e.g., open source Consul platform is being used in 35 countries by 135 institutions; Similarly, Organicity tools are used for over 35 experiments in various cities. 

 

Some of the example solutions fall under validation and demonstration category such as DUET and Smarticipate.  

Flat plate solar collectors

Solar thermal panels are devices that convert solar radiation into heat and transfer it to a heat transfer fluid (typically water or an anti-freeze fluid) to be stored or to reach the point of use.

Source: Jafari S, Sohani A, Hoseinzadeh S, Pourfayaz F. The 3E Optimal Location Assessment of Flat-Plate Solar Collectors for Domestic Applications in Iran. Energies. 2022; 15(10):3589. https://doi.org/10.3390/en15103589 

 

FPC is the main solar collector technology installed in Europe with more that 2 million m2 installed per year [1]. FPCs are suitable for low-medium temperature applications including domestic hot water, heating, preheating and combined systems. In buildings FPC can be used both as a direct system or an indirect system. In the first case, cold water in a storage tank is pumped and heated directly through the collector. However, in passive system (thermosiphon) can be employed avoiding the use of the pump and using the force of gravity and the buoyancy effect of water at different temperatures. In these systems a horizontal tank are employed and placed above the collector. In an indirect system a heat transfer fluid in a closed loop is heated by the collector and used to transfer thermal energy to the water through a heat exchange. FPC can be also used in cities to provide renewable heating at district level being an effective solution when they operate at low temperatures [2] .  FPC consists of tubes carrying a heat transfer fluid placed in an insulated, weather-proof box with a dark absorber material and thermal insulation material. FPC can be installed as a thermosiphon system, in which the circulation of the heat transfer fluid is induced by the density difference caused by the increase of temperature, or as an active system with a pump [3]. The simplicity of construction makes FPCs a relatively low-cost solution, which can be installed as single modules on roofs, or manufactured in a larger format for roof or facade integration or for ground-mounted systems. For the production of FPC, different materials can be used including copper, aluminium, stainless steel combined with a glazing to achieve a high efficiency. 

Source: https://www.onosisolar.com/solar-collectors/flat-plate-solar-thermal-collector/  

 

MATURITY:  

FPC is a mature technology available on the market (TRL 9) suitable for domestic applications such as the production of domestic hot water which represents more than 90% of the global market [3]. FPC can also be used for space heating or space cooling when coupled with liquid desiccant based air conditioning systems [4]. FPC can also be employed in pool heating, drying applications [5], or large scale heating systems including district heating [6] with more than 340 systems installed around the world [2]. 

Comments ()

Authors

JRC

Last update: June 14, 2023

Tags

Energy
Under license CC BY-NC-SA
This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format for noncommercial purposes only, and only so long as attribution is given to the creator. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.