Technical definition for nearly zero energy buildings

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1 Artcles The full length verson of ths artcle s avalable at the journal webste: -> REHVA Journal Techncal defnton for nearly zero energy buldngs REHVA launched 2013 verson n cooperaton wth European standardzaton organzaton CEN for unformed natonal mplementaton of EPBD recast. REHVA has revsed ts nzeb techncal defnton, snce now the only avalable methodology sutable for the mplementaton n natonal buldng codes for the prmary energy ndcator calculaton. The 2013 verson was prepared n cooperaton wth European standardzaton organzaton CEN and t replaces 2011 verson wth the ntenton to help the experts n the Member States to defne the nearly zero energy buldngs n a unform way verson s complemented wth specfcatons for nearby renewable energy and for the contrbuton of renewable energy use. A set of the system boundares and equatons are gven for energy need, energy use, delvered and exported energy, prmary energy and for renewable energy rato calculaton. Wth these defntons and energy calculaton framework, prmary energy ndcator and renewable energy rato can be calculated as requred by the drectve. Calculaton prncples are explaned wth worked examples n order to assure unform understandng of the defntons. Full report s avalable at the REHVA webste -> REHVA Journal. Jarek Kurntsk Professor, Vce-presdent REHVA Tallnn Unversty of Technology Background EPBD recast (2010/31/EU) launched nearly zero energy (nzeb) target n 2010 wth the need for the Member States to defne what nzeb for them exactly consttutes. REHVA experts realzed the problem that varous defnton of nzeb may cause n Europe and establshed a task force to prepare techncal defntons and system boundares for energy performance calculatons. Startng pont for techncal defntons s the requrement of nzeb n EPBD recast formulated as buldngs wth a very hgh energy performance and where energy need s covered to a very sgnfcant extent by energy from renewable sources. Snce EPBD recast does not gve mnmum or maxmum harmonzed requrements as well as detals of energy performance calculaton framework, t wll be up to the Member States 22

2 Artcles to defne what a very hgh energy performance and to a very sgnfcant extent by energy from renewable sources for them exactly consttute. REHVA techncal defnton for nearly zero energy buldngs nzeb defnton shall be based on delvered and exported energy accordng to EPBD recast and pren 15603:2013. The basc energy balance of the delvered and exported energy and system boundares for the prmary and renewable energy calculatons, are shown n Fgure 1 and 3 (for on ste and for nearby assessment), and descrbed wth detaled system boundary defntons n Fgures 4 and 5. Accordng to EPBD recast, all components of the energy use are mandatory except the energy use of applances (households, elevators/escalators and outlets) whch may or may not be ncluded. Wth the ncluson of applances, energy use n the buldngs ncludes energy used for heatng, coolng, ventlaton, hot water, lghtng and applances. Accordng to Fgure 1, for delvered electrcty and thermal energy t apples: Edel, el Eexp, el Eren el E us, el, and (1) Total energy use of the buldng System boundary of energy use Delvered energy on ste Exported energy on ste Buldng ste = system boundary of delvered and exported energy on ste Fgure 1. System boundares for on ste assessment (nearby producton not lnked to the buldng) connectng a buldng wth on ste renewable energy (RE) sources to energy networks. System boundary of energy use of buldng techncal systems follows outer surface of the buldng n ths smplfed fgure; system boundary of delvered and exported energy on ste s shown wth dashed lne. In the case of nearby producton, the nearby system boundary wll be added, as shown n Fgure 3. Edel, T Eexp, T Eren T E us, T, (2) where E us s total energy use kwh/(a); E del s delvered energy on ste (kwh/a); E exp s exported energy on ste (kwh/a); E ren s on ste renewable energy wthout fuels (kwh/a); Subscrpt el refers to electrcty and T to thermal energy. An example n Fgure 2 explans the use of Equaton 1. An all electrcal buldng wth energy use of 100 has a PV system generatng 20, from whch 10 s used n the buldng and 10 s exported. Wth these values, delvered energy on ste becomes: E E E E del, el us, el exp, el ren, el In order to be able to take nto account a new nearby renewable energy producton capacty contractually lnked to the buldng and provdng the real addton of the renewable capacty to the grd or dstrct heatng or coolng mx n connecton wth constructon/development of the buldng(s), the system boundary of Fgure 1 has to be extended. (If not contractually lnked to the buldng, nearby Fgure 2. An example of an all electrcal buldng explanng the use of Equatons 1 and 2. producton s calculated wth prmary energy factors of the network mx as shown n Fgure 1.) To calculate delvered and exported energy nearby, the energy flows of nearby producton plant contractually lnked to buldng are to be added/subtracted to the delvered and exported energy flows on ste, Fgure 3. Prerequste to apply ths nearby assessment, s the avalablty of natonal legslaton allow- 23

3 Artcles ng to allocate such new capacty to the buldng/development wth a long term contract and assurng that the nvestment on that new capacty wll lead to a real addton to the grd or dstrct heatng or coolng mx. Prmary energy ndcator sums up all delvered and exported energy (electrcty, dstrct heat/coolng, fuels) nto a sngle ndcator. Prmary energy and prmary energy ndcator are calculated from delvered and exported energy wth natonal prmary energy factors as: Total energy use of the buldng System boundary of energy use Nearby producton plant Delvered energy nearby Exported energy nearby On ste Nearby Dstant Edel, fdel, nren, Eexp, fexp, nren E P, nren, where EP P E A P, nren net (3) (4) Fgure 3. Nearby assessment boundary to be used n the case of nearby energy producton lnked contractually to the buldng. Compared to on ste assessment boundary, delvered and exported energy flows on ste are replaced by delvered and exported energy flows nearby. The followng defntons were prepared for unformed EPBD recast mplementaton: 1 EP P E P,nren E del, E exp, s the prmary energy ndcator (kwh/(m² a)); s the non-renewable prmary energy (kwh/a); s the delvered energy on ste or nearby (kwh/a) for energy carrer ; s the exported energy on ste or nearby (kwh/a) for energy carrer ; f del,nren, s the non-renewable prmary energy factor (-) for the delvered energy carrer ; f exp,nren, s the non-renewable prmary energy factor (-) of the delvered energy compensated by the exported energy for energy carrer, whch s by default equal to the factor of the delvered energy, f not natonally defned n other way; A net useful floor area (m²) calculated accordng to natonal defnton. Net zero energy buldng defnton has an exact performance level of 0 kwh/(m² a) non renewable prmary energy. The performance level of nearly zero energy s a subject of natonal decson takng nto account: techncally reasonably achevable level of prmary energy use; how many % of the prmary energy s covered by renewable sources; avalable fnancal ncentves for renewable energy or energy effcency measures; cost mplcatons and ambton level of the defnton. net zero energy buldng (net ZEB) Non-renewable prmary energy of 0 kwh/(m² a). nearly zero energy buldng (nzeb) Techncally and reasonably achevable natonal energy use of > 0 kwh/(m² a) but no more than a natonal lmt value of non-renewable prmary energy, acheved wth a combnaton of best practce energy effcency measures and renewable energy technologes 2 whch may or may not be cost optmal 3. Detaled system boundares for delvered and exported energy calculaton The set of detaled system boundares are extended from the assessment boundary of pren 15603:2013. As stated n EPBD recast, the postve nfluence of renewable energy produced on ste s taken nto account so that t reduces the amount of delvered energy needed and may be exported f cannot used n the buldng (.e. on ste producton s not consdered as part of delvered energy on ste), Fgure 4. reasonably achevable means by comparson wth natonal energy use benchmarks approprate to the actvtes served by the buldng, or any other metrc that s deemed approprate by each EU Member State. Renewable energy technologes needed n nearly zero energy buldngs may or may not be cost-effectve, dependng on avalable natonal fnancal ncentves. The Commsson has establshed a comparatve methodology framework for calculaton of cost-optmal levels (Cost optmal). 24

4 Artcles Fgure 4. Three system boundares (SB) for on ste assessment (nearby producton not lnked to the buldng), for energy need, energy use and delvered and exported energy calculaton. System boundary of energy use apples also for renewable energy rato calculaton wth ncluson of RE from geo-, aero- and hydrothermal energy sources of heat pumps and free coolng as shown n Fgure 5. Renewable energy rato (RER) calculaton In order to calculate the share of renewable energy use, renewable energy rato RER, all renewable energy sources have to be accounted for. These nclude solar thermal, solar electrcty, wnd and hydro electrcty, renewable energy captured from ambent heat sources by heat pumps and free coolng, renewable fuels and off ste renewable energy. Ambent heat sources of heat pumps and free coolng are to be ncluded to the renewable energy use system boundary, because n RER calculaton, heat pumps and free coolng are not only taken nto account wth delvered energy calculaton based on COP, but also by the extracted energy from ambent heat sources. Renewable energy use system boundary s shown n Fgure 5. The renewable energy rato s calculated relatve to all energy use n the buldng, n terms of total prmary energy. It s taken nto account that exported energy compensates delvered energy. By default, t s consdered that the exported energy compensates the grd mx or n the case of thermal energy, the dstrct heatng or coolng network mx. For on-ste and nearby renewable energy the total prmary energy factor s 1.0 and the nonrenewable prmary energy factor s 0. Total prmary energy based RER equaton s the followng: RER P where E E ren, ren, fdel, tot, fdel, nren, Edel, Edel, fdel, tot, Eexp, fexp, tot, RER P s the renewable energy rato based on the total prmary energy, E ren, s the renewable energy produced on ste or nearby for energy carrer, kwh/a; f del,tot, s the total prmary energy factor (-) for the delvered energy carrer ; (5) 25

5 Artcles Fgure 5. Renewable energy use system boundary for renewable energy rato RER calculaton. In addton to energy flows shown n Fgure 4, renewable thermal energy from ambent heat pump and free coolng sources (heat exchangers) s accounted. f del,nren, s the non-renewable prmary energy factor (-) for the delvered energy carrer ; f exp,tot, s the total prmary energy factor (-)of the delvered energy compensated by the exported energy for energy carrer ; E del, s the delvered energy on ste or nearby for energy carrer, kwh/a; E exp, s the exported energy on ste or nearby for energy carrer, kwh/a. Calculaton example Consder an offce buldng located n Pars wth followng annual energy needs (all values are specfc values n kwh/(m² a)): 3.8 kwh/(m² a) energy need for heatng (space heatng, supply ar heatng and DHW) 11.9 kwh/(m² a) energy need for coolng 21.5 kwh/(m² a) electrcty for applances 10.0 kwh/(m² a) electrcty for lghtng Breakdown of the energy need s shown n Fgure 6. The buldng has a gas boler for heatng wth seasonal effcency of 90%. For the coolng, free coolng from boreholes (about 1/3 of the need) s used and the rest s covered wth mechancal coolng. For borehole coolng, seasonal energy effcency rato of 10 s used and for mechancal coolng 3.5. To smplfy the calculaton, emsson and dstrbuton losses of the heatng and coolng systems are neglected n ths example. Ventlaton system wth specfc fan power of 1.2 kw/(m³/s) and the crculaton pump of the heatng system wll use 5.6 kwh/(m² a) electrcty. There s nstalled a solar PV system provdng 15.0 kwh/(m² a), from whch 6.0 s utlzed n the buldng and 9.0 s exported to the grd. Energy calculaton results are shown n Fgure 6, n the buldng techncal systems box. Gas boler wth 90% effcency results n 4.2 kwh/(m² a) fuel energy. Electrcty use of the coolng system s calculated wth seasonal energy effcency ratos 10 and 3.5 respectvely. Electrcty use 26

6 Artcles Fgure 6. Calculaton example of the energy flows n nzeb offce buldng. 27

7 Artcles Fgure 7. Some nzeb offce buldngs are calculated and reported accordng to REHVA defnton that makes t possble to compare the results. See n Journal 3/2011, 2/2012 and 5/2012 for these buldngs from France, the Netherlands, Swtzerland, Fnland. of free coolng, mechancal coolng, ventlaton, lghtng and applances s 39.8 kwh/(m² a). Solar electrcty of 6.0 kwh/(m² a) used n the buldng reduces the delvered electrcty to 33.8 kwh/(m² a). The rest of PV electrcty, 9.0 kwh/(m 2 a) s exported. The delvered fuel energy (calorc value of delvered natural gas) s 4.2 kwh/(m² a). In ths example, t s consdered that 20% of the grd electrcty s from renewable sources wth the non-renewable prmary energy factor of 0 and the total prmary energy factor of 1.0. For the rest of 80% of the grd electrcty the total and non-renewable prmary energy factor of 2.5 s used. Therefore, the non-renewable prmary energy factor of the grd mx s = 2.0 and the total prmary energy factor s = 2.2. It s assumed that exported electrcty compensates the grd mx. Acknowledgment REHVA nzeb Task Force and CEN EPBD project group members are greatly acknowledged for ths work: Francs Allard, Derrck Braham, Dck van Djk, Jacquelyn Fox, Jonas Gräslund, Per Heselberg, Frank Hovorka, Rsto Kosonen, Jean Lebrun, Zoltán Magyar, Lvo Mazzarella, Ivo Martnac, Vojslav Novakovc, Jorma Ralo, Oll Seppänen, Igor Sartor, Johann Zrngbl, Mchael Schmdt, Maja Vrta, Karsten Voss, Åsa Wahlström. 28