42.<strong>Renewable</strong>Heating & Cooling:Vision,Opportunities<strong>and</strong> Challenges
2<strong>Strategic</strong> <strong>Research</strong> <strong>and</strong> <strong>Innovation</strong> <strong>Agenda</strong> <strong>for</strong> <strong>Renewable</strong> Heating & Cooling<strong>Renewable</strong> Heating & Cooling: Vision, Opportunities <strong>and</strong> Challenges<strong>Renewable</strong>Heating & CoolingEuropean Technology Plat<strong>for</strong>m2.1 Defining heating <strong>and</strong> coolingHeat <strong>and</strong> cold are <strong>for</strong>ms of thermal energy 3 . We heat <strong>and</strong> cool to adjust the temperatureof indoor air <strong>for</strong> com<strong>for</strong>t, to produce domestic hot water (DHW) <strong>and</strong> in industrial productionprocesses.Heat <strong>and</strong> cold present a number of differences with other <strong>for</strong>ms of energy such aselectricity in that:• Heat <strong>and</strong> cold transmitted over long distances are subject to relevant losses 4 .• Heat <strong>and</strong> cold must be supplied at least at the temperature level which matchesthe dem<strong>and</strong> 5 .• Storage of heat <strong>and</strong> cold is generally easier <strong>and</strong> less expensive than electricity storage.The transport problem results in the fact that a heat (or cold) source must be near thesite of usage in order to keep an acceptable relation between heat (or cold) losses to heat (orcold) transferred. Maximum transport distances <strong>for</strong> small capacities are in the rangeof a few tens of meters, while <strong>for</strong> larger capacities they can be up to several kilometres, suchas in a district heating system. Storing heat in the <strong>for</strong>m of phase-change materials (PCMs)or chemical compounds is the only way to transport it over even longer distances 6 . Withouttransport, solutions <strong>for</strong> meeting heat <strong>and</strong> cold dem<strong>and</strong> will have to focus onindividual, decentralised installations from single houses to grids on a municipal <strong>and</strong>regional level.3Following a practice ofengineering <strong>and</strong> energytechnology disciplines, inthis publication the terms“heat” (or “cold”) <strong>and</strong> “thermalenergy” are used interchangeably.However in physicsthese two concepts are welldistinguished. In thermodynamics,heat is alwaysaccompanied by a change inentropy <strong>and</strong> it is defined asenergy in exchange betweentwo systems, or a singlesystem <strong>and</strong> its surroundings.As a process variable, heatis never a property of thesystem, nor is it containedwithin the boundary of thesystem. Thermal energy is astate function <strong>and</strong>, in contrastto heat, it exists on both sidesof a boundary.4The ef<strong>for</strong>t to isolate a heattransmission line is muchhigher than to isolate aelectricity cable5This is the primary purposeof heat pump technology, thatis to trans<strong>for</strong>m low temperaturerenewable energy fromthe air, ground or water to heatat higher temperature thatcan be used <strong>for</strong> space heating,heating water or cooling.6A truly ancient example ofphase change material used<strong>for</strong> storage <strong>and</strong> transport ofcold is ice, harvested in coldareas <strong>and</strong> transported overlong distances <strong>for</strong> use in hotregions <strong>and</strong> seasons, alreadyin the Roman Empire. Ice harvesting,transport <strong>and</strong> storagereached industrial scale in the19th <strong>and</strong> early 20th century.While the trans<strong>for</strong>mation issue in electricity is that of voltage, in heating <strong>and</strong> coolingit is a matter of temperature (Info Box 1). In any case, the temperature of heat or coldsupply must meet the required temperature of the installation. In the heating sector, trans<strong>for</strong>mationof heat to different temperature levels is just a matter of time whenan adjustment towards ambient temperature is desired: heat will eventually cool down(or heat up) to the desired temperature, <strong>and</strong> mixing may be applied to speed up thisprocess when fluids are concerned.Info Box 1Trans<strong>for</strong>mation of voltage in the electricity sectorcan be done with high efficiency using electromagnetic-inductivetrans<strong>for</strong>mers; the principle wasalready discovered by Faraday <strong>and</strong> Henry in 1831<strong>and</strong> be<strong>for</strong>e 1900 numerous types of trans<strong>for</strong>mers<strong>for</strong> many applications were in practical use.The thermodynamic principles of refrigeration <strong>and</strong>heat pumping, allowing <strong>for</strong> a kind of “heat trans<strong>for</strong>ming”to adjust temperature levels, date backto the same era as theoretical work by Carnot(1824), a patent issued to Perkins in 1834, <strong>and</strong> thefirst practical application of heat pumping by Rittinger(1855).These principles laid the foundations <strong>for</strong> the refrigerationcycle in use today. Market uptakehowever, in particular of heat pumps, took almosta century to materialise.Nicolas Léonard Sadi Carnot(1796-1832)Peter Ritter von Rittinger(1811-1872)5
Change language