Hybrid heating and cooling system optimisation with TRNSYS

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Hybrid heating and

cooling system

optimisation with

TRNSYS

Submitted in partial fulfilment with the requirements of the degree

MSc in Energy Systems and the Environment

DEPARTMENT OF MECHANICAL ENGINEERING

Lucas Lira

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Copyright Declaration

The copyright of this dissertation belongs to the author under the terms of the United Kingdom Copyright Acts as qualified by University of Strathclyde Regulation 3.49. Due acknowledgement must always be made of the use of any material contained in,

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Acknowledgements

I wo uld li ke t o t hank a se r ie s of pe o pl e t hat , i n t he ir o wn ma nne r , made t his i mpor t ant m om e nt of m y li fe be c ome r e al it y :

M y su per vis or , Dr . M i chaë l K um me r t , f or hi s cons tant gu idan ce a nd val uab le s up por t th r oug h the de ve l opm ent of t his pr oj e ct .

D r . Paul S t ra cha n, r e p re s ent i ng al l t he me m be rs of t he st af f, f or r evi vi ng m y pass i on f or e ngi ne er i n g.

C at he r ine C oope r fr om S c ot ti s h a nd S o ut he r n E ne rg y , f or t he v al uab le i nf or mat i o n pr ov i de d .

M y pare nt s , f or t he ir cons t ant pre se n ce , c ar e and s up por t , e ve n fro m so far awa y . F or s h owin g m e t hat t he r e is no li mi t whe n one wor ks wi t h the he ar t .

M y sist e r s , f or be in g the bes t in the w or ld a nd f or m aki ng my wh it e hair co me out s o one r.

M y fl at mat e s a t Jam e s Go old Hal l , f or s ha r in g the a dv e nt ur e of l iv in g in a s tr an ge c ou nt r y.

K at he r i ne Wall ace , f or m aki ng a st ran ge count r y not s o s tr a nge and al l t he adv i ce , s upp or t a nd a fe w whit e hai r s.

M y “ E ne rg y Sy st e ms a nd t he E n v ir on me nt ” cour s e c ol l e ag ue s , f or al l t he g o od and bad mo me nt s: t he lon g da ys w or ki ng a t the com mu nal r oo m , t he F rida y pr es e nt ati ons , t he par tie s , the f ood, t he ne v e r endi ng dis cus s io n ove r ho w to m ake the wor ld a be t t e r pla ce .

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4 "E ar t h pr ovi de s en oug h t o s ati s f y e ve r y m an 's nee d , b ut not e ve r y man' s gr e e d. "

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Abstract

T he aim of t hi s pr oje ct is t o opt im is e the des ig n of a he at i ng and coo li ng s yst e m f or a ne w bui l din g de ve l o pm e nt , b as e d o n a r eal ca se st u dy .

T he di ffe r ent s ys te m confi gur at io ns we r e s i m ul at e d us i ng T R N SY S , a t r ans ie nt e ne rg y s yst em s si m ul at io n pr og r am dev e lo p ed at t he Uni ve rs it y of W is consi n-M adis on . De tai l ed si mul at i ons we r e us ed t o ass e ss t he ad va nt age s and i ncon ve nie nt of hy br i d s yst e m co nf ig urat io ns i n cl ud i ng com bine d heat and po we r ( C H P) e ngi ne s and wate r -s our ce he at pu mps ( WS H P) . T he com par is on l oo ke d at CO2 em i ssi ons , re ne wable e ner g y s har e , an d ec on om i c pe rf or m an ce .

T he re s ult s sh ow t hat hy br i d s ys te ms wit h a dapte d c ont r ol st r at eg i es al lo w t o m axi mis e t he be nef i t s fr om t he di ffe r ent t e chn ol ogi es i nvo lve d. T his wa s par ti c ul ar l y i m po rt an t whe n a t arge t for on- sit e r ene wa ble e ne r gy pr od u ct i on i s int r odu ce d, as it of t en t he ca se in sust ai nab le bui ld in g co de s and p lan ni ng r e qu ir e me nt s t hr o ug h out the UK. I n s ome case s , i ncre a si ng t he r ene wa ble e ne rg y s har e o f sin gl e -te chn ol o gy s ys te ms wo ul d ha ve r e quir e d s igni fi cant e xt r a inve s t me nt c os t s , while t hey c ou ld be obt a ine d s i mpl y by m od if yi ng the c ont ro l s tr a te g y of a h ybr id s ys te m .

T he the sis al so poi nts out t he ne ed t o e st a bl is h a cle ar def i nit i o n of so me of t he t ar ge t s oft e n r eq uir e d by l o ca l a ut h or i t ie s. S o me r ul es cur r e nt l y us e d t o as se ss CO2 sa vi ngs of mi cr oge ne r at i on in re si de nti al bui ldi ng s ar e un cle ar and ca n e asi l y be m isi nt er pre t ed . O n t he ot he r ha nd, t h e de f in i t ion of t he r e ne wabl e e ne r g y s ha r e of he at p um ps use d f or cooli ng si mp ly coul d not be fou nd .

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6

Figures

F i gur e 1 - E le ct r i cal co ns umpt ion a nd e ne rg y s our ce ... 13

F i gur e 2 : He a t p um p cy cle ... 15

F i gur e 3 - Car not cy cl e ... 16

F i gur e 4 - O pe n l oop conf ig ur at i on ... 17

F i gur e 5 - Cl os ed l oo p con fig ura t i on ... 18

F i gur e 6 - Gas bo ile r e ne rg y fl ow ... 18

F i gur e 7 - CH P e ne rg y flo w ... 19

F i gur e 8 - H yb rid s y st e m e ne r g y fl ow ... 20

F i gur e 9 - CO2 cal cul at io n ... 28

F i gur e 1 0 – Case s tu d y ... 31

F i gur e 1 1 - Da il y l oa d be ha vi our ... 32

F i gur e 1 2 - Heat i ng lo ad pr ofil e ... 33

F i gur e 1 3 - Heat l oa d dur at i on cur ve ... 33

F i gur e 1 4 - C o ol ing l oa d pr of ile ... 34

F i gur e 1 5 - E l e ctr i cal l oad pr of ile ... 35

F i gur e 1 6 - An nua l l oa d pr ofi le ... 35

F i gur e 1 7 - B ase cas e ... 36

F i gur e 1 8 - C ash fl o w exam ple ... 38

F i gur e 1 9 - Heat i ng cir cuit ... 42

F i gur e 2 0 - C o ol ing cir cui t ... 43

F i gur e 2 1 - C H P s uppl i e d di s tr i ct ... 44

F i gur e 2 2 - E ne r gy cos t vs . A ux. bo ile r gas c ons um p ti o n ... 44

F i gur e 2 3 - Loa d d ur at i on cur ve ... 45

F i gur e 2 4 - C H P e le ct r i ca l ge ne r at io n ... 45

F i gur e 2 5 - C H P C O2 sa vi ngs ... 46

F i gur e 2 6 - C ash fl o w CHP ... 46

F i gur e 2 7 - C H P IR R vs . C O2 re d uct i o n ... 47

F i gur e 2 8 - HP su ppl ie d di st ri ct ... 48

F i gur e 2 9 - HP CO 2 r e du ct i on v s. Re ne wabl e s hare ... 49

F i gur e 3 0 - HP cash fl ow ... 50

F i gur e 3 1 – Hea t p um p: I RR vs . CO2 r e duct i on ... 50

F i gur e 3 2 - C H P an d H P IRR vs . CO2 r e du cti on ... 51

F i gur e 3 3 - H ybr id s ys t e m supp lie d di st ri ct ... 52

F i gur e 3 4 - S am e shar e config ur at i on ... 53

F i gur e 3 5 - C H P le a di ng conf igu rat i o n ... 54

F i gur e 3 6 - HP le ad in g confi gur at i on ... 55

F i gur e 3 7 – 5.1 M W he at pum p: HP l ea din g conf ig urat io n ... 56

F i gur e 3 8 - 5.1 M W heat pum p: C H P le a di ng c on fig ura t i on ... 56

F i gur e 3 9 – 5.1 M W C HP: HP le ad in g conf i gur ati o n ... 57

F i gur e 4 0 - 5.1 M W C H P: CH P le adi ng confi gu rat i on ... 58

F i gur e 4 1 - H ybr id s ys t e m: re ne wa bl e vs . C O2 par t i cip ati on ... 59

F i gur e 4 2 – H y br i d s ys te m: C as h fl o w ... 59

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F i gur e 4 4 - Di st r i ct and P V ar r ay are a ... 61

F i gur e 4 5 - H ybr id s ys t e m wit h PV : IR R vs. R e ne wable s ha r e ... 62

F i gur e 4 6 - H ybr id s ys t e m: Cas h fl o w wi t h a nd w it ho ut phot o volt ai c ... 62

F i gur e 4 7 - H ybr id s ys t e m no cool i ng pr i or it y : I R R v s. Re ne w able shar e ... 63

F i gur e 4 8 - M odi fie d l oad dur ati on cu r ve ... 65

F i gur e 4 9 – TR N S Y S m ode l ... 66

F i gur e 5 0 - T hr ee s ou r ces : s ame s har e co nfi g urat i o n ... 67

F i gur e 5 1 - T hr ee s ou r ces : HP le ad ing conf ig urat i on ... 68

F i gur e 5 2 - E ne r gy dis t r ib ut i on ... 70

F i gur e 5 3 – Th r ee s our ces : IR R v s. r e ne wable part i ci pat i on ... 72

F i gur e 5 4 - E ne r gy cos t vs . he at t r ans m iss i on l os se s ... 73

F i gur e 5 5 - IRR vs. he a t t r ans mis si on lo sse s ... 74

F i gur e 5 6 - CO 2 e mis s i on r e du ct i on ... 74

F i gur e 5 7 - C H P e le ct r i ci t y des ti nat ion ... 76

F i gur e 5 8 – Th r ee he at s our ce s : C O2 re duct i o n vs . r e ne wable pa r ti c ipat io n ... 76

F i gur e 5 9 – Th r ee he at s our ce s : IR R v s. r e ne wable s har e ... 77

F i gur e 6 0 - C H P le a di ng conf igu rat i o n ... 79

F i gur e 6 1 - CO2re d ucti on vs . re ne wa bl e par t i ci pat io n ... 79

F i gur e 6 2 - CO2 r ed u ct i on pe r e ner gy t y pe ... 80

F i gur e 6 3 - H ybr id s ys t e m ne w con fig urat i on: I RR vs. re ne wa bl e s har e ... 80

F i gur e 6 4 - HP--> C H P-- >H P c on fi gur at i on ... 82

F i gur e 6 5 - H ybr id s ys t e m wit h ph ot o vo ltai c: IR R v s . r e ne wab le s ha r e ... 83

F i gur e 6 6 - H ybr id s ys t e m wit h ph ot o vo ltai c: C as h fl ow ... 84

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Tables

Table 1 - Primary energy savings ... 20

Table 2 - Example C O2 emission ... 25

Table 3 - C O2 emission including gas turbine ... 26

Table 4 - C O2 emission including local generation ... 27

Table 5 - CO2 emission no surplus ... 27

Table 6 - Energy price ... 37

Table 7 – CHP: capital, operational and maintenance costs ... 38

Table 8 - Heat pumps: capital, operational and maintenance costs ... 39

Table 9 - CHP & HP heating capacity ... 52

Table 10 - Non hybrid: energy distribution ... 69

Table 11 - Hybrid same load share: energy distribution ... 69

Table 12 - Hybrid heat pump leading: energy distribution ... 70

Table 13 - Renewable participation ... 71

Table 14 - electricity selling price ... 75

Table 15 - purchased electricity price ... 75

Table 16 - emission coefficients ... 75

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1. Introduction and objectives

W it h t he intr odu ct i on of e ner gy p ol i ci es t hat t ar ge t e ve r in cr e as i ng CO2 e mi ss i on sa vi ngs and a s ign if i cant s har e of on -sit e r e ne wable e ner g y ge ne rat i on , a ne w se r i es of ch alle nge s and con ce rns a r e pr es e nt e d t o e ner g y s up plie r s a nd e nd-use r s.

S ys te m de s ig ns t hat pr o vi de t he be st a ns we r t o t hes e e co nomi ca l and t e chni cal cha lle nge s ofte n r e quir e a com bi nat i on of t e c hn ol og ie s , e .g . Gr o un d-S o ur ce H e at Pump ( GS H P) and C o mbi ne d He at an d Po wer ( C H P) , or s ol a r the r ma l / phot ov ol t ai c i n co mb inat i on wi t h C H P o r a conve nt i ona l s yst e m. T he se hy br id s yst e m s are m ore co mpl e x t o de si gn a nd opt im ise t han s in gle -t e chnol o gy s yst e ms , be cause o f t he n e ed to inte gr ate de t ai le d cont r ol s tr at eg i es i n t he des i gn pr ob le m . An d s i nce t he y in te gr at e re ne wa bl e e ner gy s ou r ce s a nd oft e n a s i gni fi ca nt am ou nt of st ora ge , t he de si gn mu s t al s o t a ke i nt o acc ount t he a nn ual or mul ti- an nua l pe r f or mance ( up t o 2 5 ye ar s for GS H P s yst e ms) .

T he obje ct ive o f t his dis se r t at i on is to pre s e nt th e de s i g n a nd op ti mi sat i on of a h ybr id s yst e m de s i g ne d t o s up pl y the he a t ing an d cool i ng l oa ds of a la rge -s cale bui ld ing de ve l o pm e nt b a-se d on a re al ca-se -s tu d y. T he t h e -si-s p re -s ent -s and dis c us se s t he re s ult s obt aine d i n de s ig ning t he s ys te m a nd com par ing it t o “ s i ngl e -t e chno l og y ” , or no n- h ybr id , s ys te m conf ig ur at ions.

C hapt e r 2 pr e se nt s t he br oa d conte xt o f t hi s s t ud y , i n cl udi ng t he his t or i ca l e ve nts t hat le d t o t he act ua l con ce r n o ve r t he im pact of e ne r gy g ene rat i o n at t he e nv i r onm ent , i ncl udi ng a n e xam ple o f t he kin d of a ct i on be i ng t a ke n t o c ont ro l th os e im pa ct s . T he ne xt s ub - se ct i ons g o t hr oug h t he basi c i nf or mat i o n re l at e d wi t h the t wo mai n t e chn ol og i es ut il ize d i n t he ca s e st ud y : W at er s our ce he at pum ps a nd com bine d he at a nd p ower . T he co ncept of hy bri d s yst e ms i s t he n pre se nte d a nd i ts pot ent ial ad va nt a ges ar e dis cusse d . C hapt e r 3 e xp lai ns t h e me t hod ol o gy ut ili ze d t o si m u lat e t he e ne r g y s yst e m s pe rf or m an ce e v alu ate the out put s of the si m ul at i ons an d pr o vi des s ome de t ai l s on t he mo de ls use d in t he si m ulat i ons . . F i r st , t he de fin it io n of CO2 e mi ss i on sa vi ngs a nd r ene wab le e ner gy f r act io n is d is cu ss ed , an d the ne ed for clar i fi cat i on of b oth de fi ni ti ons in bu ild in g c o des an d l oc al pla nnin g do cume nt s i s p oi nte d out . T he case st udy and t he ba s e case c onf ig ur at i on ar e t he n des cri be d an d s ome ke y sim ula t i on assu mpt i ons ar e pr e se nte d . The base case config ur at i on i s the s yst e m t hat wi ll s e r ve as a basi s t o ass es s t he pe rf or m an ce o f al l othe r conf ig urat ions. Ec onom i c cal c ula t i o ns are t he n pr es e nt e d a nd app lie d t o t he ba s e case syst e m. C ap it al , ope r at ional and m ai nt e na n ce cos t use d i n t his st ud y ar e pr ov i de d. T he l ast p art of ch apt e r 3

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12 i s de di cat e d t o t he he ati ng and co ol i ng s ys t e ms , an d t he dif fer e nt c on fig ur a t i ons i ncl ud i ng he at pu mp s an d c om bi ned he at an d po we r are de s cr i be d.

I n chap t er 4 t he re s ult s fr om a se r i es o f s i mu lati on s are pr es e nt e d and anal yse d. T he s i m ul at io ns we re di vi de d i nt o t wo ma in gr ou ps : f i r st with o ut l im it at i on o n t he de si gn capa cit y of t he di ffe r ent s ys te m com po ne nts , t hen usi ng c omp one nt s i ze s obt ai ne d fr om t he de sig n t e am in vol ve d in t he r e a l ca se s tudy . T he se cond gr ou p of s im ula ti ons is als o us e d to pe rfo rm a s e ns it i v it y anal ys i s t o ass es s t he i m pa ct o f the m et h od ol og y e mpl oye d to as se ss t he si mul at i on out put s .

T he m ost r e le vant fi ndi ng s a nd re su lt s ar e t hen s umm e d up in t he l ast c hapte r , “C o ncl us i ons ”.

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2. Background

2.1. Historical motivation

T hr oug h hi st or y , di ffe r ent s our ces o f ene rg y have bee n e xp lore d in or de r to s up pl y hum an ne ed s. S ince the beg i nnin g, t his e ne r g y e xt r a ct i o n, e ve n t hough i n a s m al le r s cale , has fo ll o we d s o me ki nd of e n vir o nme nt al de pre dat i on. I ni t ial l y t he bu r ni ng c oal , uti l ize d in la rge s cale t o fe ed s te am ma chi ne s , in t he e arl y 19t h ce nt ur y , ga ve p la ce t o t he oil t hat , wit h t he e ne r g y cr is i s of 1 9 7 3 and t e chno logi cal de ve l opme nt , ope ne d s pa ce t o a br oa de r vari et y o f s ou r ce s , i ncl udi ng he r e a hi ghe r pe ne tr at i on of e le ctr i ci t y ge ne rat ed b y r e ne wabl e s our ce s i nt o the mar ke t . ( 1 )

A lt hou gh ne w t e chno lo gi es h ave be e n cr e at e d t o a ll o w and opt im ize t he e xt r acti on of ene r gy f r om a large a mo unt of natur a l so ur ce s , i t s a vai lab il it y i s not e ve nl y s pre a d ar ound t he g lo be , m a kin g ma ny nati ons s ti l l de pe nde nt on t he tr a diti onal fo ssi l f ue ls , w hi ch ca n be t ra nsp or t e d an d st or e d c on ve ni ent ly . A dde d t o t his , i s t he act ual g ro wt h of e ne r g y co ns u mpt i on. B e i ng a ble t o ge ne rat e or e xtr a ct e ne r gy fr o m ne w so ur ce s i s not e nou gh. I t i s n eces s ar y t o fol lo w the co nt i nuou s e xpa ns i on of cons um pt i on . T he pi ctu r e be l o w (1 ) c om pare s t he e le ct r i ca l de mand at 19 9 5 and t he pr e di cte d o ne at 2 01 0 , dis cr i m in atin g t he or i gin of that e ne r gy .

F i g u r e 1 - E l e c t r i c a l c o n s u m p t i o n a n d en e r g y s o u r c e

I f class i ca l ec on om i c t heor y was appl i ed t o e ne r g y ge ne r at i o n , it w ould i nd i cat e t hat s oc ie t y woul d be f ol low in g t he lo we r cost ge ner a ti on m et hod. A nd it d id ha ppe n fo r a pe r i od of t ime , but i s not t he ca s e a n ym or e . One o f t he r ea s ons is t he re du ct io n of t he avai la bi l it y of s ome s our ce s, s u ch as oi l and gas , not j ust nat ur al l y r a isi ng t he p ri c es but als o ma ki ng cons ume r s of t his kin d of e ner g y p os si ble h ost age s of t he p ro vi d er . A not he r point is t he r e sult ant a m ou nt o f pol lut ants t hr o wn i nt o t he a tm o sp he r e a s cons e que n ce of thi s kind of ge ner ati on. S ome cit ie s ha ve r e ache d po ll uti on le ve ls t hat

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14 m ake li v in g i n t hes e a r e as as d an ge r ous a nd unhe al t hy as bei ng e xpos e d t o a nu cle ar le akage l i ke C he rn oby l (2 ) .

T he gove r nme nts of di ffe re nt c ou nt r ie s , at t his poi nt , fel t t he ne e d t o st ep i n and cre at e s tr i ct e r r ul es and t ar ge ts re ga rd i ng the e ne r gy ge ner at i on , ai mi ng t he re d ucti on of poll u tant s a nd t he de pe nde nce o f f ossi l f ue ls .

O ne e xam ple is t he E din bur g h code fo r s us tai na ble bui ld in gs whi ch s tat e s t hat “ a m ini m um of 1 0% ( 20 % in Ar e as of M ajor C han ge de ve l op me nt s of 2 0 0 0 s qm or 2 0 re side nt ial unit s or mo r e) of it s r e mai ni ng e ner gy r e qu ir e me nt s t o be s uppl ie d by o n s it e r e ne wa ble e ne r g y gene r at i on. Th is on -s it e re ne wa bl e e ne rg y ge ner at i on mu-st pr o v ide at le a-st a f urt he r 1 0% ( 2 0% i n A M C ’s ) re duct io n i n t he de ve l opme nt ’s CO2 e mis s io ns ” ( 3 ) .

T w o te ch nol ogie s t h at ha ve be e n g ai ni ng i m por t an ce wit h t hi s ne w r e al it y are e xp lai ne d in t he ne xt sub -s e cti ons : Heat pum ps and comb ine d he at and po we r sy s te ms .

2.2. Heat pumps

H eat p um ps are e qu i pm e nt t hat d o e xa ctl y what t hei r na me s ugge st s . T he y pu mp heat fr om o ne so ur ce whe re i t is abundant or n ot ne ce ss ar y , a nd de li ve r t o a s e c ond point , t he he at s in k. N o e ne r gy is ge n er ate d , ju st r e pl a ce d , ma kin g t he he at p um ps di ffe r e nt fr om m ost of the he at i ng t e chnol og ie s , w hi ch u t ili z e a co mb us ti on pr o ce ss t o conve rt a pr i mar y s o ur ce of e ne r g y i nt o he at an d is ve r y oft e n r e late d wi t h s e nsi t ive a m ou nt of los se s. W it h a mo ist ur e co nt e nt of 2 0 % , one ki l o of har dw oo d wood chip ma y pr o du ce i n a co mp le te co mbu st io n p r oce ss , 1 5.1 M J* of e ner g y . J us t 8 0 % of t his i s usua ll y con ve r t e d int o he at at a bio mass bo il er , gi ve n it s us ua l e ff i cie n cy . W it h he at pum ps , o ne unit of ene rg y is us e d t o e xt r a ct ar ound 3 un it s fr om t he s our ce and de li v e r at t he si n k. T her e is no e ner g y co nv e r sio n a nd c or re ct l y s el e ct in g t he sour ce s a nd t e chnol ogi es m ay fur t he r i m pr ove t hi s r e lat i on sh ip. In t he case of uti l i zin g a r en e wa ble s ou r ce t o dr i ve t he heat pu mp, t he he ati ng or co o lin g pr oce s s ma y ha ppe n alm ost fr e e of CO2 e mi ss i ons.

T he h ig h e ff i cie n cy o f t he he at pum ps , inc l udi ng e n vir onme nt s of e xtr e me ly c ol d or wa rm we athe r ( 4 ) , the ca pa cit y t o a dd re ne wa ble e ne rg y t o a he at in g l oa d a nd the poss i bi li t y t o w or k com bine d wit h e le ct r i cit y ge ne r at e d t hr ough r e ne wabl e s our ces ma ke the he atp um ps att r act i ve op ti ons w he n de alin g wi t h

*

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15 a s us t ai na ble de ve lo pm ent . M or e de t ail s ab out t he h e at pum p t e chnol og y are s ho w n be ll o w.

2.2.1. Heat pump principle

C hangi ng t he r ma l ene rg y at low t e m per at u r e to t he rm al e ne r g y at a hig her t e mper at ur e i s t he m ain pr in ciple of a he at pu mp . T o a chie ve i t , t he wo r kin g fl uid i s su bm i tt e d t hr ough dif fer e nt pre s s ur e le ve l s an d chan ge o f st ate s . T he pi ct ure be l o w is a si m pl i fie d il lust rat i on of what hap pe ns wit h t he w or ki ng fl uid dur in g t he he ati ng pr o ce ss .

F i g u r e 2 : H ea t p u mp c y c l e ( 5 )

A t lo w p re ss ur e an d t empe rat ure , the r e fr ige r ant li qui d i s dr ive n t o the e vap or ato r , w he r e he at e xcha nge ha ppe ns wit h t he he at s our ce . Be in g at a l owe r t e mpe rat ur e t h an the s our ce , he at fl ows t o the w or ki ng l i qui d , whi ch r e sult s int o a change of phase fr om l i quid t o va por s tat e . The r e fr ige r ant i s t he n dri ve n thr oug h a co mpr e ss or , w he r e a p r es su re ri se t ake s pl a ce , fol lo we d by a r ise of t he li qui d te mpe rat ur e . The no w he ate d r e fri ge r ant pass es t hr ou gh a s e c ond he a t e xcha nge r , t he e vaporat or , w he r e e ne rg y f lo ws fr om t he w or kin g fl u id t o t he he at s in k. W it h t he e ne r gy r e du ct i on , t he r e fri ge r a nt ch ange s s t at e on ce m ore , be co m ing li qui d a nd be i ng pum ped ba ck t o war ds t he e va por at or , pa ss i ng fi r st t hr ou gh an e xpa ns i o n val ve , whe re t he pr es s ure i s r e du ce d . As a cons eque n ce , t he t empe r at ure of t he w or ki ng fl uid al so re d uces . T he cy cl e , t hen , s tar t s ag ain .

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16

2.2.2. Coefficient of performance

T he pe r f or man ce p ar ame te r f or a he at p um p i s kno wn as co e ffi cie nt of pe rf or m an ce , C O P, w hi ch com pare s t he qua nt it y of heat t ra nsfe r r e d be t we en s ou r ce a nd si n k wit h t he ne t wor k in put t o t he c y cle , us ual l y i n t he f or m of e le ct r i cit y , s upp lie d t o t he c ompr e s so r. T he defi nit i o n is :

= _ℎ ℎ

I t is de s ir a bl e t o del i ve r or e xtr a ct a ce rt a in a m ou nt of ene r g y f ro m a gi ve n amb ie nt wi t h t he mi nim u m ex pe ndit u re of wo r k. I n or de r t o unde r st a nd wh i ch condit ions ma y impr o ve the CO P of a s yst em , one must under st and t hat , fo ll o wi ng t he s e c on d l aw of t he rm o dy nam i cs , t he C O P of a c y cl i c de v i ce ope r at i ng be t wee n t w o gi ve n re se r v oi r s , wit h dif fer e nt the r mal e ne r g y s tor e d , ca n ’t be gre at er t ha n a de vi ce o pe r at in g on t he re ve r se C ar not c y cle . T his cy cl e co ns ist s int o t wo re ve rs ibl e is ot he r ma l pr oce ss e s, and t wo r e ve rs ibl e adia bati c pr o ce ss es .

F i g u r e 3 - C a r n o t c y c l e

I ma gi ni ng a he at pu mp w or kin g in s u ch co nd it i ons , w it h th e isot he r ma l pr oce s s ha ppe ni ng a t t he he at so ur ce a nd s i n k, a nd t he e xpans io n and c om pr es s i on hap pe n in g in an adi abat i c p ro c e ss , the C O P m ay be d e fi ne d b y :

= | !"#$|

%&$!'(# !#% − %&*(+,#%

A fte r s ome si mpl if i cat i ons , le ads t o :

=_- -.!"#$

.!"#$− -./+0

F r om t he r e i s e as y t o obse rve t hat , t he s ma lle r the di ffe r en ce i n t empe ra t ure be t we e n the re se r voi r s , t he g r e at e r wil l be t he C O P.

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Give n t o pr a ct i cal di ffi c ult ie s as s oci at e d wit h t he r e ve r se d

mo di fi cat i ons are ma de in p ra cti ce a t t he heat pu mp s . F or e xa mp le , t he e vapor at i on pr o ce s s is al l o we d t o

An ot he r m odi fi cat i on i s the fa ct that

t hr ot t li ng v al ve w her e t he r e fri ge r a nt und e rgoe s a n i rr e v er s ible i se nt ha lpi c pr o ce ss.

2.2.3. The ground source heat pump

He at p um ps ca n be cl assi fi e d a ccor din g t o it s fun ct i on ( heat i ng , c ooli ng , do me st i c hot wat e r , et c) , h

wor ki ng fl uid s ( b ri ne /wat er , wate r /wat e r , ai r/ air , et c) [2 ]. he at pu m ps use t he s oil or

de pe ndi ng of t he de s i r ed a pp li ca ti on .

a s ink or so ur ce i s i t s st ab ilit y an d e le vat e d t e m p er at ur e t hr ou gh t he ye ar whe n com pa r ed w ith , for e xam ple , t he air . T his at tr i bute al lo ws a hi ghe r CO P dur in g se ver e cl i m ati c s it u at i ons ( su mme r or wi nt e r) w he r e t h e di

be t wee n i nte r nal a nd e xt e r nal t e mpe r at ure i s m or e

If wat e r i s a va ila ble a t a r e as ona bl e de pt h and t em pe rat ure , sour ce a ll ows t he ac hie ve me nt of t he hig hes t CO P.

also wo r k wit h ce r t ai n su rfa ce wat er , li ke fro he at r ej e ct i on s ys te m s .

O ne of t he p os si ble co nfi gur ati ons is kn ows as

or l oop) . Wat e r i s p um pe d fr om t he s ou rce ( wate r be d, l ake , r ive r , e t c) , ci r cu lat es t hr ou gh a h eat e xcha nge r and t he n r e tu rn s t o t he or i gin .

F i g u r e

If wat e r is n ot a va ila b le , t he gr o un d ca n wor k as a n e ffe cti ve hea t so ur ce or sin k . H or iz ont al or ve r ti cal colle ct or s , dep e ndi ng o f t he a vai la b le ar ea , a re bur ie d int o t he g r oun d an d a wor kin g f lu id

e ne r g y t hat wi ll be us e d i nt o t he he at i ng p r o ce ss ( or de l ive r s t he he at i n t he ca se of c ooli ng ) . T hi s config ur at i on ma y a

Give n t o pr act i cal d i ffi cult ie s as s oc iate d wit h t he r e ve r se d C ar n ot cy c le , modif i cat io ns ar e ma de in pr a cti ce a t t h e heat pu mp s . F or e xa mp le , the ap or at i on p r oce s s is all o wed t o cont in ue t o t he s atur at e d vapor li ne . An ot he r m odi fi cat i on is t he f a ct t hat t he e xpans i on pr o ce s s is r epla ce d b y a thr ot tl i ng v al ve whe r e t he re fr i ger a nt un de r goe s an i rr e v er s ible i se nt hal pi c

The ground source heat pump

Heat pum ps ca n be cl ass i fie d a ccor din g t o it s fun ct i on ( he at i ng, co oli ng , w ate r , e t c) , heat s ou r ce ( g r ou nd , gr ound- wate r , air , e t c) an d wor ki ng fl uid s ( br ine /wat e r , wat er /wate r , a ir/ air , et c) [2 ]. T he g r ound s o ur ce he at pu m ps us e the s oil or t he wate r pr e se nt in it as t he he at s o ur ce o r s in k , de pen di ng o f t he de si r e d a ppl i ca t i on . T he a dvant a ge of ha vi ng th e gr ound as a si nk or s our ce is it s st ab il it y and e le vat ed t e m p er at ur e t hr ou gh t he ye ar whe n com pa re d wit h , for e xam pl e , t he ai r . T his at t ri bute al lo ws a hi ghe r CO P dur i ng s e ve r e cl im at i c s i tu at i ons ( s umme r or wi nt e r) w he r e t h e di

t we e n i nt e rn al a nd exte r nal te mpe r at ur e is m or e se nsit i ve .

If wat e r i s ava il a ble a t a re aso na ble de pt h and t em pe rat ure , it s uti l iz at i on as sour ce a ll o ws t he a chie vem e nt of t he hig he st CO P. W at e r he a t pu mp s ca n al so wor k wi t h cer t ai n su r fa ce wat e r , li ke fro m r i ver s or la ke s , and wat e r in

One of t he poss i bl e confi gur at i ons i s kn ows as ope n s yst e m ( als o ope n sour ce . W ate r i s pum pe d fr om t he so ur ce ( wate r be d, l ake , r ive r , e t c) , ci r cul ate s t hr ou gh a h e at e xc ha nger an d t he n r e tu r ns t o t he o r i gin .

F i g u r e 4 - O p e n l o o p c o n f i g u r a t i o n ( 5 )

If wate r is n ot a vai la bl e , t he gr ound ca n wor k as a n e ffe ct i ve hea t so ur ce or sin k . H or i z ont al or ver t i cal c oll e ct or s , de pe ndi ng o f t he a vai la b le are a , a r e g ro und and a wo r kin g f lu id , ci r cu lat i ng i nt o t he m , e xt r a ct s t he ene rg y t hat wi ll be us e d int o t he he at ing p r o ce ss ( or de l ive r s t he heat i n the T hi s c on fig ur a ti on ma y a ls o be ut i l iz e d at wate r sour ce he at

17 ar not cy cle , mo dif i cat io ns ar e ma de in pr a cti ce a t t h e heat pu mps . F or e xa mpl e , t he cont in ue t o t he s at ur at e d vap or l i ne . t he e xpans i on pr oce s s is r e pla ce d b y a thr ot t li ng v al ve w he r e t he re fr i ger a nt un de rgoe s a n i r r e ve r s ible is ent ha lpi c

He at pum ps ca n be cl ass i fie d a ccor din g t o it s fun ct i on ( he at i ng , co oli ng , wat e r , ai r , et c) an d T he g r ou nd s our ce it as t he heat s o ur ce or si nk , e of ha vi ng t h e gr ou nd as a s ink or s our ce is it s st ab il it y and e le vat ed t e m pe r at ure t hro u gh t he ye ar , whe n c om pa re d wit h , for e xam ple , t he ai r . T his at tr i but e al lo ws a hi ghe r C O P dur ing s e ve r e cl im at i c s itu at i ons ( su mme r or wi nt e r) whe re t he dif fer e nce

it s util izat i on as Wat e r he a t pu mps ca n m r i ve r s or la ke s , and w ate r i n

(al s o ope n s our ce . Wat er i s p um pe d fr om t he sou r ce ( wate r be d, l a ke , ri ver , e t c) ,

If wat er is n ot a vai la bl e , t he gr ound ca n wor k as a n e ffe ct i ve he a t s our ce or sin k . H or iz ont al or ver t i cal c oll e ct or s , dep e ndi ng o f t he a vai la bl e are a , a r e e xt r a ct s t he e ne r gy t hat wi ll be us e d int o t he he at ing p r o ce ss ( or de l ive r s the he at i n t he ls o be ut i l ize d at wate r s ou r ce he at

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18 pu mps , i n p la ce s whe re t he ope n s yst e m i s n ot de s ir a ble . I n t his cas e , the he at col le ct or w ill be pla ce d i ns i de the wat e r be d .

F i g u r e 5 - C l o s e d l o o p c o n f i g u r a t i o n ( 5 )

2.3. Combined heat and power

T he m ost con ve nt io n al f orm s of e le ct r i cit y ge ne rat io n wor ks t hro ug h the c on ve rs ion o f he at i nt o me c ha ni ca l pow e r, wh i ch is t hen conve r te d to e le ct r i cit y . T he pr o ce ss us uall y pr e se n ts ov er a ll eff i ci e n cy ar ou nd 40 % , n ot c ou nti ng l osse s r e lat e d wit h t he t r a ns m is s ion of t he ge ne r ate d e le ct r i cit y unti l it s fi nal point of cons u mpt i o n.

T he l ow e f fi ci e n cy com es fr om t he fact t hat pa rt of the a va il able i nit i al e ne rg y i s lost i n t he f or m of he at . C re at i ng s che me s th at m ay use t his u nus e d he at wi ll r aise the syst e m ef fi cie n cy. A l so , ha vi ng the ge ne r at i on and c ons u mpti o n poi nt s lo cate d cl os e fr o m e ach ot he r w ill re duce t he t r ans mis s i on l os s e s.

C om bi ne d he at an d p owe r pla nt s w or ks e xact l y ove r th os e po int s. E l e ct r i cit y and heat ar e ge ne r at e d t oge t he r , wit h t he s yst e m us ual ly s uppl yi ng p art of t he heat r e qu ir e me n ts and im p or ti ng an y e xt r a e ne r gy ne e d ed. A ls o , at m ome nts of lo w e le ct ri cal c onsu mpt io n, e l e ct r i cit y ma y be s ol d t o t he gr i d. S i nce t he C H P pl ant s nee d t o be cl ose t o t he he at i n g l oad , in or de r t o av oid t he rm al l oss es , el e ct r i cal l oss e s ar e al s o r e du ce d. Us in g t he h eat that at ot he r s cheme s of e l e ct r i cal gene r at i on wou ld be l ost ma ke s pos si ble the ac hie ve me nt of a 9 0 % ove ral l e ffi cie ncy .

T he pi ctu r e be ll o w s ho ws t wo opt io ns for a gi ve n l o cat io n t hat n ee ds he at i ng and el e ct r i cit y su pp ly . F i rs t one , e le ct ri cit y and he at ar e ge ner at e d i nde pe n de nt l y , t he s e c on d, t hr ou gh C HP ( st i l l conne ct ed t o the gr i d) .

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19

F i g u r e 7 - C HP en er g y f l o w

T w o e ff i cie ncy fi gur e s ar e us e d f or C H P. T he fir st one , a lr e a dy com m ent e d be for e , is t he o ver all e ne rg y e f fi cie n cy. It com pare s t he a mount of t he e ner gy s up plie d t o t he load w it h t he tot al of e ne rg y i n t h e fue l cons ume d.

1 =

₂234₅₆₇₈; Q = He at s up pl ie d t o t h e lo ad

E = E l e ct ri ci t y su pp li e d t o t he l o a d QF u e l = T ot a l e n e rg y su p pl ie d b y t h e f u e l

O t her wa y t o q uant if y the e ffi c ie ncy of the CHP pl a nt is t hro ug h the i ncre me nt al el e ctr i ca l effi ci e n cy. I t co mpar e s t he e le ct ri ci t y ge n e rat e d wi th t he tot al of he at t hat was a ct ua ll y us e d fo r that ge ne rat io n (6 ) .

14 = 9

:";− ₁_.

Q = Heat sup pl i ed to t he lo ad E = E l e ct ri ci t y su pp li e d t o t he l o a d QF u e l = T ot a l e n e rg y su p pl ie d b y t h e f u e l

ηS= T h e rm a l e f f i ci e n c y o f ste a m p rod u ct i o n wit h a co n ve n t i o n a l b o ile r

I t is al s o i m po rt ant t o sa y t hat CH P ge ne rat i on ma y be d iv id e d i nt o t wo diffe re nt gr ou ps of s y st e ms. T he fi r st one u t ili z e s the he at ge ne r ate d b y t he fue l t o f ir st pr o du ce e le ctr i ci t y an d t h en t he t he r m al e ne r gy at l o wer t e mper at ur e i s ut i li ze d t o pr o duce st e a m. T he se are cal le d T o pp i ng S yst e ms . T he y are mor e comm on whe re t he he at i ng r e qu ir e m ent s do not ne e d hig h t e mper at ur e s .

T he B ott om i ng S yst e ms uti l ize t he he at fr om b ur n ing t he f ue l f ir st t o s ati s fy t he he at in g ne e ds a nd t hen t he re si du al hea t i s use d t o pr o duce e l e ct r i cit y . S e ve r al dif fe re nt s ch e mes m ay be use d t o ac hi e ve a co mbi ne d he at and po we r ge ne rat i on. T he y d iffe r fr om t he kin d o f p ri mar y e ne r g y s our ce ut ili z ed ( bi oma ss , coal , liq ui d fue l , gas ) , t he dr i vi ng e n gi ne ( st eam t ur bi ne s , gas t urb ine s , re cipr ocat in g e n gi ne , e t c) or e ve n of ho w the the r m al e ne r g y i s use d .

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T he t ab le be l l ow co mp are s t ypi cal confi gur at io ns a nd i ts e ne r gy cons umpt ion.

Table

An im p or t ant po int at this m ome n t is to hi g hli ght what has be en said be fo re abo ut t he el e ctr i cal ge ne ra t i on. It was s up pos ed t hat t he e le ct r i cit y ge ne r at e d an d n ot us e d w ould be s ol d to t he gri d. S o me ti m es and l ocat io ns su ch o pt i on ma y no t be a vai lab le , or e ve n ma y not be e cono mi cal l y inte r e st ing ( wi t h t he pri ce of t he el e ct r i cit y be in g s ol d be l l ow t he pr i ce f or t he i mpor te d e le ct ri c it y) . T he com binat ion of t he C H P sy st e m wit h heat pu mps ma y be a n i nt e re s tin g opt i on t o e n s

be ge ne ra t e d w hen t her e is a r eq uire me n t for it . I n ot he r w or ds , m ay be inte r e st ing to cr e at e a s yst e m whe re par t o f the t he r mal l oad wi ll be su pp li ed by a C H P pl ant a nd t he ot he r pa rt w il l be s up pl ie d by a he at p ump s ys us i ng t he e le ct r i cit y g e ne r ate d b y t he co mb i ned he at a nd po wer p ro ce ss . T he t her mal l os se s re l at ed wit h the se pr o ce ss es ma y be a pr oble m .

F i g u r e

The t able be l l ow com par es t ypi c al co nfi gur at io ns a nd i ts e ne r g y consu mpt i on.

Table 1 - Primary energy savings (6)

An i m por ta nt poi nt at t hi s mom en t i s t o hi g hl i ght what has bee n said be for e abo ut t he e le ct r i cal ge ne r at i on . It was suppos ed t hat t he e le ct ri cit y gene rat e d and not us ed wou ld be s ol d t o t he gr i d. S o me ti m es a nd l ocat io ns u ch opt i on ma y n ot be avai lable , or eve n ma y not be e cono mi ca ll y int e re s t in g ( wit h t he pr i ce of t he e le ct r i ci t y be in g s ol d be l l ow t he pr i ce for the imp ort e d el e ctr i c it y) . T he co mbi nat io n of the C H P sy st e m wit h he at pu mps m ay be a n i nt e r e st ing opt io n t o en sur e t hat e le ct ri cit y a nd heat wi ll be ge ner a te d w he n t he re i s a r e quir e m en t for it . I n ot he r w or ds , m ay be int e re s t in g t o cre at e a syst e m whe r e par t o f t he t he r mal l oad wil l be su pp lie d by a C H P pl ant and t he ot her pa rt wil l be s up plie d by a he at pu mp s ys us i ng t he e le ctr i ci t y ge ne rat ed b y t he c omb i ned he a t a nd po wer p ro ce ss . The t he r mal l oss es r e l at e d wit h t he se pr o ce ss es ma y be a pr obl e m .

F i g u r e 8 - H y b r i d s y s t e m e n er g y f l o w

20 T he t abl e be l l ow com par es t ypi c al co nfi gur at io ns a nd i t s ene r g y c onsu mpt io n.

An im por ta nt poi nt at t hi s mom en t i s to hi g hli ght what has be e n s aid be fo r e abo ut t he e le ct r i cal ge ne r at i on . It was s up pos ed t hat t he e le ct r i ci ty ge ne rat e d an d n ot us ed wou ld be s ol d t o t he gri d. S o me t i me s a nd l o cat ions u ch o pt i on ma y n o t be avai lable , or e ve n ma y not be e con om i ca ll y inte r es t i ng ( wit h t he pr i ce of t he e le ct r i ci t y be in g s ol d be l l ow t he pr i ce f or the im port e d el e ctr i c it y) . T he co mbi nat io n of t he CH P s y st e m wit h he at ure t hat e le ct ri c ity a nd he at wi ll be ge ner a t ed w he n t he re i s a r e quir e me n t for it . I n ot he r wo rds , m ay be inte r es t i ng t o cre at e a syst e m whe r e par t o f the t he r mal l oad w ill be s uppl ie d by a C H P pl ant and t he ot her pa rt wil l be s up pl ie d by a he at pu mp s ys te m , us i ng t he e le ct r i cit y ge ne rat ed b y t he co mb i ned hea t a nd po we r pr o ces s .

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21

2.4. Hybrid systems

A t a big t r ans mi s si on s yst em , t he p o we r dr awn b y t he cu st ome r s os c illa t e s e xp r es si ve ly duri ng a da y. T a ki ng a cit y as e xa m ple , w hi le at l a te ho ur s of nig ht , o r e ar l y m or ni ngs , a s mo st pe opl e ar e sl ee pi ng , t he e ner g y c ons u mpti o n i s m ost l y fr om st r e e t li ght s , d ome st i c e q uip me n t on idle m ode , e t c. At e ar l y eve ni ng, t hi s consu mpt i on r i s es noti ce ab ly whe n pe ople r e t ur n t o the ir ho me s , and com me r c ial and i ndust r ial faci lit ie s ar e st il l ope r ati ng . It i s i mpor ta nt t o h ave t his inf or mat ion t o mi nd whe n, for e xamp le , it i s pla nne d t o r ai se t he par ti cip ati on of r e n e wa ble e ner g y s our c es int o the e ne rg y pr odu ct i on , as mat chi ng de ma nd a n d ge ne r at i on ma y be a pro ble m. S un ene rg y i s o nl y av aila ble a fe w h ou r s a da y and the win d l e ve ls ma y dr op e xa ct l y whe n t he de m and f or e ne r gy i s hi g h. B io mass b oi le r can r api dl y bu rn m or e fue l t o f ol lo w t he de m and va r iat i on , but its r e l ati v el y l o w tu r n do wn r at i o* ma ke s i t har d t o mat ch the pea k de mands or t he hot wa t er de mand dur i ng s um m er m o nt h s.

C om bi ni ng di ffe r e nt r e ne wable t e chn ol og i e s, o r e ve n t r ad it i o nal e ner gy ge ne rat i on met h ods , ma y r ai se e xpr es s i ve l y the r e l ia bi l it y of a s yst e m , s ti l l r e du cin g it s fi na l C O2 fo ot p rint . T he se a r ra ngeme nts , whe re t he e ner g y fr om diffe re nt so ur ce s is com bi ne d in o rde r t o achie ve t he s a me e nd , ar e call e d hy bri d s yst e ms . I n th e pre ce d ing e xam ple , the b iom as s b oile r could ha ve a t r adi t i onal gas b oi le r run ni ng as ba ckup, s uppl y ing t he pe a k lo ad dur i ng t he wi nt er or t he h ot wat er de m an d du r ing t he sum me r , wit h the ba s e l oad be i ng s up plie d by t he b iom as s. T h is i s a s mal l e xam ple of a h y br i d s y st e m.

F or he at pu mps , t he e xpr e s si on h yb ri d s yst e m i s ofte n r e lat e d wit h t he pr es e nce of di ffe re nt he at s i n ks ( or s ou r ce s) , a i m ing t he re du ct io n of t he i mbal an ce be t we e n he at e xt r a ct i on a nd re je ct i on dur in g t he yea r , at l ocat io ns wi th a pr e dom ina nt weat her ( 7) . A num ber of s t ud ie s wer e ma de i n t his are as i n cl udin g ut il iz in g s i m ul at io n t oo ls in o r de r t o opt imi z e t he se s yst e ms (8 ) ( 9 ) . I n t he se cas e s , t he o pt i miz ati on p r o ce ss co mpa re d heat e xc han ger opti o ns an d si ze s , als o o bse r vi n g t he bes t cont r ol me tho do lo gie s for a s pe ci fi c a ppl i cat i on. What we p lan t o do at t his dis se rt at i on is o bs e r ve t he op t im iz at i on pr o ce ss whe re t he he at pum p w ill be de al in g not wit h an e xt r a he at si nk/s our ce , but an e nt ir e l y di ffe r ent t e chnol og y.

T he opt im iz at io n of s uch s yst e m s w ill de pend on n ot ju st knowi ng t he par ti c ul ar it ie s of e ach t e chnol o gy in v ol ve d , but als o t he cre at i on of a spe ci fi c

*

Turn down ratio is the relationship between the maximum and minimum power output of the boiler. The minimum output is defined by the minimum value at which the boiler will work with high efficiency.

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22 c ont ro l s yst e m t o c oord in ate ho w the y w i ll re lat e be t we e n t he mse l ve s and t he obje ct i ve s t o be ac hie ve d .

T he pr ob le m of de alin g wi t h re ne w abl e t e chnol og y i s t hat t he si te e nv ir on me nt , re s pons ible by t he co nsum pt i o n beh av io r , has al so gr eat i nf lue nc e o ve r t he g e ne r ati o n ca pa cit y. T his ma ke s it mo re di ffi cul t f or a de sig ne r t o wor k wit h pr e pre par e d t e m plat e s. The sol uti on foun d at lo cati on A ma y not be a ppli cabl e at l o cati on B , eve n t houg h bot h ut il i ze s i mi l ar s yst e ms. The ca pa cit y t o si m ulat e h ow a ll t he var ia nts w ill beha ve is a po we r ful t ool d uri ng t he des i gn of the se s ys te ms , gi v in g e n ou gh fl exi bi lit y to t he des ig ne r t o pl ay wi t h t he v ar i ants , co mpa rin g t he obt ai ne d re s ult s a nd t hr ough t hat , opt i m iz i ng t he s yst e m .

D ur in g the opt i miz at io n pr oces s , t he c on tr ol sy s te m must be ver y wel l de fi ned , s i nce i t wi ll i nfl ue nce t he r e qu ir e d s ize o f e qui pme nt , st or a ge t anks , e t c. Ci r cu it conne ct i ons and f lu id t e mpe rat ure s m ay cha nge e xp re ss i ve ly de pen di ng o n ho w t he contr ol wi l l co ord in at e t he di ffer e nt t ec hn ol ogie s . The s tar t -up pe r i od of a bi oma ss boile r ma y be r educed usi ng t he ba ckup ga s bo ile r to pre he at i ts i nte r nal l i ni ng . This m a y ha ve i m pa ct ove r t he ne ce ss ar y s t or a ge t an k. O ne ca n’t de f ine i f t he st or age t an k is o ver or unde r si z ed wit hout kno wi ng t he de t ail s about t he he a t ing cir cui t. Ju st lo o king f or t he s yst e m l oa d an d b oil e r s wo n’t g i ve an a ccur ate ans wer .

A not he r as pe ct t hat w ill de f ine the e ffi cie nc y of a s yst em i s i ts fin an ci al dat a . G ive n t he co mp le xit y of t he e ne r g y chan g es that may ha ppe n in a h ybr id s yst e m , it ma y be com ple x t o get a pr e ci se fee dba ck a bout t he f ina ncia l s av in gs t hat ca n be a chi e ve d wit h out t he pr es e nce o f a s im ulat i on t oo l.

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23

3. Methodology

T his cha pte r wi ll be d e alin g wit h the assu m pti ons ma de an d m et h ods ut i li z ed dur i ng t he ana ly s is of t he r e su lt s , at ch apt e r 4.

I t s tar ts di s cuss i ng t he C O2 e mi s si on and r e ne wab le en e rg y fr a ct i on ca l cu lati ons. B e i ng i nt rod uce d f or t he firs t t ime t o t he e mi ss i on fact or s ta ble i n t he g ove r nme nt ’s S t andar d Ass e ss m e nt Pr o ce dur e f or the e ner g y pe rf or m an ce of d we l l i ngs ( SA P) ( 1 0) some pe ople m ay fe e l unsu r e how t hose v al ue s m us t be us e d . S e ct i on 3. 1 ut i li ze s s imp le e xa mpl e s an d for mul as e xp lai n ho w S A P w as ut il ize d at the pr e se nt di sse r tat i on an d t he re aso ns f or i t.

I n se ct i o n 3. 2 , t he i m por tan ce of h ow t o d e fine a s yst e m r ene wable e ne r g y fr a ct i on is dis cus se d. T he mai n poi nt of t hi s s ub-t o pi c i s t o h i ghl ig ht t he i mpor t an ce t o ha ve a be tt e r de fi nit i on o f t he capa ci t y of a he at pu mp t o s up pl y r e ne wab le e ne r g y an d h o w it m us t be cou nt e d.

T he r e mai ni ng se ct i o ns i ntr odu ce t he s tu di ed s yst em , it s l oa ds , he ati ng ci r cui ts ’ co nfi gu rat i on and h ow t he dat a re ce ive d was ma ni pul at e d i n o rde r to be ut il i ze d at TR N S Y S. T he base case , fr o m whe re t he re s ult s wil l be use d as r e fer e nce for co m pa rin g t he out pu t s at t he si mu lat i on st a ge , is als o pr es e nt e d.

I n a dd it i on, in t h is ch apt e r can a ls o be fo u nd t he me t ho d uti l ize d t o de fi ne t he f ina nci al ga ins de li ve r e d by e ach st udie d s ys te m , in clu di ng he r e t he e qui pme nt , ope rat i onal and mai nt ena nce cos ts .

3.1. CO

2

emission, conversion factor and savings

D ur in g t he r e s ult a nal ys is , a n im p ort a nt o utp ut is the C O2 e m is s ion r e lat e d wit h t he e ner gy pr odu ct io n.

T able s r el at in g t he a mo unt of C O2 e m iss i o n wit h t he us ed e ne r gy s our ce can be fou nd at dif fe re nt li te r at ure , s u ch as D e fr a’s gr een ho u se ga s co nver si on f a ct o r g u i d e li n e ( 1 1) or t h e go ve r n me n t St an d a rd A s se ss me n t Pr oc e d u re f o r t h e e n e rg y pe rf o rm a n ce o f d we l li n g s , SA P 20 0 5- 2 0 08 (1 0 ) , b ot h u se d a s r e fer e nce i n t hi s st udy. F or he at i ng , t he pr o ce ss is q uite s i mpl e , on ce it doe s not i n vol ve a com ple x and la rge ne t wor k, s u ch as wit h e le ct r i cit y. T he t ot a l amo unt of CO2 e mi tt e d wil l be t he t ot a l of fue l co ns ume d mult ip lie d b y r e lat ed co nve r si on fa ct or .

T he CO2 e m it te d , alt ho ugh i mp ort a nt i nf or mat ion , d oe s no t gi ve a pr e cise i de a of ho w e ffe ct i ve t he ge ne rat ion pr o ce s s r eal l y is . A g o od i de a is t o di vi de t he t ot al C O2 e mis s i on by t he t otal ene rg y de li ver e d, r e s ul t i ng i nt o t he

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24 amo unt of C O2 pe r kW h of e ner g y made a vai lab le (w hat is b asi call y t he l o cal c on ve rs ion f a ct or ) .

I n t he case of e le ctr i ci ty , t he dis cuss ion be come s a m or e co mp le x. O nce the e le ct r i cit y i s ge ne r ate d , t her e ar e t wo pos s ibi li tie s : i t wi ll be l o call y uti li ze d or s ol d t o the gri d.

T he fir st opt i on w ill re duce t he l oa d s e en by t he g r id as i f e n e rg y sa vi ngs m et h ods wer e app lie d, l i ke h ig he r buil din g i nsu lati on or ef fi ci ent li gh tin g i ns ta ll e d.

T o cal c ul at e t he l ocal em iss i ons , S A P s ug ges ts t he f ol lo wi ng m et hod :

• T h e t ot a l e mi ssi o n o f t he g e n e ra te d e le ct ric i t y m u st b e ca lc ul a t e d ;

• I n c a se o f e le ct r icit y e x po rt e d t o th e g r i d , t he to t al e ne rg y mu st b e m u l ti pli e d b y a b a se co n ve r si on va lu e a n d t he n su b t r a ct e d f ro m th e pre vio u s re su l t;

• E n e rg y c o n su me d m u st b e mu lt ipl ie d b y th e g ri d e mi s s io n c oe f f ic i e n t . A n inte r es t i ng poi nt i s that S AP ap plie s a diffe r e nt con ver s i on val ue t o t he e le ct r i cit y d isp la ce d fr o m g ri d ( 0 .5 68 kg C O2 pe r kW h) a nd i mpor t e d fr o m t he gr i d ( 0.4 2 2 kg C O2 pe r kWh) . T his ma y c aus e so me di s com for t t o who is fir st i nt r od uced t o t he for m ul a s i nce co ns um pt i on and pr o du ct i on ar e co mpl et e l y r e lat ed a ct i v it ie s and one mi ght e xpe ct th a t b ot h ha ve t he s a me con ve rs i on v al ue .

T o a voi d inst a bi lit y p robl em s in t he g ri d, pro duct i on and gene r at io n m ust m at ch . W he n a ne w s our ce of e ne rg y is ad ded t o t he g rid , mai nt ain in g t he l oa d , s om e w he r e one or m ore pla nt s m ust re d uce the ir pr o du ct io n. T he amo unt of CO2 be i ng pro du ce d cha nge s , a nd i ts m ag nit ude wil l de pe n d of ho w mu ch CO2 t he ne w s our ce is pr od uci ng t o ge ner at e t he d isp l a ce d po we r . A n e xam ple i s gi ve n b el ow.

F i rs t le t ’s ima gi ne t he C O2 e m itt e d by t he en erg y pro ducer :

Po we r is be i ng ge ne r at e d b y t he ma in p r od ucer s co nne ct e d t o t he gr id, e a ch one wit h it s r el a te d e mis s io n coe ffi cie n t , whi ch mu lt i pl ie d b y t he e ner g y pr odu cti on gi ve s t he t ot al CO2 e mis s i on. It can be sa id t hat t he t o tal e m iss i on wi l l be the t ot al pr od uct io n ti me s a co nver si on fa ct or .

9<∗ <+ 9?∗ ?+ 9@∗ @+ ⋯ + 9+∗ += B∗ C 9* +

*D<

W her e En r ep r es ent s t he e ne r gy ge ner at e d by t he p ro du ce r n and Cn t he r e lat ed e mis s i on coe ffi cie nt . F or e xa m ple , i f 10 M W h was ge ne r at e d b y a g as t urb ine wit h e ffi cie n c y of 4 0% , t he e miss i o ns w o uld be : 1 0 0 0 0 x ( 0 .1 94 /0 .4) kg o f CO2. T he val u e i ns i de the bra cke t can be i nt e r pre t e d as p r oduce r

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25 e mi ss i on c oe ffi cie nt . O n ce t he le ft si de of the e qu at io n ab ove in kn own , _B ca n be def ine d.

N ow le t ’s obse rve t he CO2 e m it te d fr o m t he pe r s pe cti v e of t he energ y c on su m pt ion :

S ince t he ene rg y gen e rat e d wi ll be c ons u me d so me whe re , can be said t hat t he C O2 e mi s si ons re lat ed wi t h the ge ne r at ion m ust mat ch t h e e mis si o ns r e lat ed wit h t he co ns um pt i on. B ei ng the l eft s ide d e fi ne d b y the e ner g y pr odu cti on , t he r i ght m ig ht r e pr es e nt t he C O2 e mi ssi o n fr om t he de ma nd s i de whe r e ∑+_*D<9_* ca n be se e n as t he t ot al e ner g y f ro m t he gr i d cons ume d a nd ca v t he gr i d e mi s si on coef fi cie nt .

A base case can be t h en buil t , i mag in in g a s yst e m wit h a he at i ng de ma nd of 5 0 kWh and t he e le ct r i cal one of 2 0 kWh . T hi s e ne r g y wi l l be s up pl ie d b y the gr i d an d a gas boil er wit h 80 % e ffi c ie ncy :

Load ( kW h) Effi ci en cy Us ed ene rg y E miss ion coe f. ( kg pe r kW h) K g of C O2 e mi tt e d He at i ng 5 0 8 0% 6 3 0 .1 9 4 12 .1 E l e ct r i cit y 2 0 10 0 % 2 0 0 .4 22 ( ca v) 8 .5 T ot a l 20 .6

Table 2 - Example CO2 emission

I t is assu me d n o w t ha t this same consu me r has a gas t ur bi ne , wit h e ff i cie n cy of 4 0 % conne c te d t o the gri d, not s up pl y i ng any ene rg y dir e ct l y t o hi s bui ld in g. T he l oad on sit e d oe s not de pe nd of t he g e ne r at io n. S ome whe re , l es s e ne r gy wi ll be p r odu ce d t o bal ance th i s s ur pl us a dde d t o t he gri d. T hi s r e du ct io n can be c on ce nt r ate d at a spe cif i c p lant or spre ad at s e ve r al ones . F or si mpl if i cati on re as ons , it wi l l be ass um e d t hat jus t o ne pl ant wi ll have t o r e du ce it s pr od ucti o n. E 3, f or e xa mple . T he ne w C O2 e mi ss i on wi l l defi ne d be as sh own bel ow : 9<∗ <+ 9?∗ ?+ (9@− 9+G) ∗ @+ ⋯ + 9+∗ ++ 9+G∗ +G= B?∗ C 9* + *D< W hi ch can als o be wr i t t en as : 9<∗ <+ 9?∗ ?+ 9@∗ @+ ⋯ + 9+∗++ 9+G∗ (+G− @) = B?∗ C 9* + *D<

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26 En e w and cn e w r e pr es en t s t he am ou nt of e ne r gy an d the e m iss i on c oe ff i cie nt of t he ne w s ou r ce ( g as t urb ine in t he e xam ple ) .

I s i nt e re st i ng t o ob se r ve th at "9_+G∗ (_+G− _@)” does not represent the CO2 e mi ss i on of t he ne w s our ce , but i ts cont ri bu ti on ove r t he cha nge s at the t ot a l C O2 le ve l , gi ving cre d it t o the “ cl ean ” p r oducer ove r the ne w e mis s io n. It s i mpor t an ce be come s mor e e vi dent whe n t he cal culat io n d one a t t able 2 i s r e pe at e d.

I t i s unde r st oo d t hat t he ne w e ner g y s our ce chan ge d t he e mi s sio n fa ct or v al ue , but w oul dn ’t b e pr acti ca l to kee p t h e t abl e co ns ta nt l y up dat e d. W hat hap pe ns is t hat mo st of t he t i me th is val ue i s chan ge d a t ye arl y base s . T hi s m eans t hat if a c ons ume r ca l cu late s it s C O2 e mis si on, t he t abl e 2 woul dn’t c han ge. W hat h appe ns is t hat , n ow , t he cr e di t f r om t he c le an e r pr od ucer m us t be a ppl i ed . T he r i ght si de o f t he pr e vi o us f or mul a can be r e w ri tt e n as : B∗ C 9* + *D< + 9+G∗ (+G− @) = - 2 K LL O r , s ho wi ng t he e nt ir e s yst e m 9<∗ <+ 9?∗ ?+ (9@M9+G) ∗ @+ ⋯ + 9+∗++ 9+G∗ (+G) = B∗ C 9* + *D< + 9+G∗ (+G− @)

S A P de fi ne s c3 ( the emi ss i on coe f fi ci ent o f t he e le ct r i cit y di spl a ce d fro m t he gr i d) as 0 .5 68 . L oo kin g for t he ne w con su m er t hat n ow i s als o a p rodu ce r , t he fol lo w ing tab le is bu il t :

Load ( kW h) Effi ci en cy Us ed e ne r gy E miss ion coe f. ( kg pe r kW h) K g of C O2 e mi tt e d He at i ng 5 0 8 0% 6 3 0 .1 9 4 12 .1 E l e ct r i cit y 2 0 10 0 % 2 0 0 .4 22 ( ca v) 8 .5 Ga s tur bine -2 6 0% 3. 3 (0 .1 9 4-0 .5 6 8) -1 .2 T ot a l 19 .4

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27 T he s it e is re ce i vin g cre dit s for t he ge ne r at i on of a cle ane r e ne r gy . But h ow w oul d be the sa me t able if t he e ne rg y p ro d uce d was ut il i ze d on s it e , not s ol d t o t he gr i d? Load ( kW h) Effi ci en cy Us ed e ne r gy E miss ion coe f. ( kg pe r kW h) K g of C O2 e mi tt e d He at i ng 5 0 8 0% 6 3 0 .1 9 4 12 .1 E l e ct r i cit y 1 8 10 0 % 2 0 0 .4 22 ( ca v) 7 .6 Ga s tur bine -2 6 0% 3. 3 0 .1 94 -0 .56 8 -1 .2 T ot al 1 8 . 5

Table 4 - CO2 emission including local generation

O bse r ve t hat t he em is si ons r el ate d w it h t he gas t ur bi ne di d n ot chan ge . The que st i on t hat co me s i n mi nd i s : W hy t he sa me cas e i s g iv in g di ffe r ent r es ul ts ? T he ans we r is be ca us e t he ca l cu lati on of t he gas t u r bine e mi ss i on, at t ab le 3 , de fi nes its con t ri but i on t o ma ke t he e le ct r i cit y pr e se nt o ver the g rid cle a ner or n ot , rat he r t han it s r e al e mi s si on. T he r e st of the C O2 wi l l b e s pr e ad al l ove r t he gr i d, be t we e n all t he ot he r co ns ume r s ( tha t wi ll be us i ng t he 0 .42 2 as e mi ss i on fa ct or) .

W hen the t urb ine was conne cte d t o t he lo ad, t he des t i nat ion of t he e le ct r i cit y be came know n, s o n ow what shou ld be de f ine d is t he r e al e mi ss i on , an d not t he cont rib uti on ove r ma king t he g r id cle a ne r or n ot . T he re i s n o e le ct ri cit y g oi ng i nt o t he gr i d. A nd t he r e is t he mi st ake : T he dis pl ace me nt fa ct or w as us ed w ro ng . Ut il i zi ng S A P t able cor r e ct ly w ould g ive m e: Load ( kW h) Effi ci en cy Us ed e ne r gy E miss ion coe f. ( kg pe r kW h) K g of C O2 e mi tt e d He at i ng 5 0 8 0% 6 3 0 .1 9 4 12 .1 E l e ct r i cit y 1 8 10 0 % 2 0 0 .4 22 ( ca v) 7 .6 Ga s tur bine -2 6 0% 3. 3 0 .1 94-0 .56 8 0 .6 T ota l 2 0 .3

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28 T he dis pla ce me nt coe ffi ci e nt ju st can be a ppl ie d i f t he t ot a l g r i d l oa d doe s not de pe nd of t he a mount of e ne r gy bei ng s ol d. If e l e ct r i cit y t hat could be i nt e r nal ly use d st a r ts t o be s ent t o t he gr id, t he t ot al gr i d lo ad wi ll change , m aki ng t he pr e v i ous f or mul a i na ccur ate . T his o bse r vat io n is i m port a nt s in ce m is unde rs ta ndi ng wh at S A P t able me ans or usi ng it wi t h mal i ce ma y s h ow l owe r e mi s si ons t han the re al o ne s. S o m e one pr odu ci ng 1 M W h fr om a n e mi ss i on f re e s our ce and co ns umi ng 1 M Wh wou ld cal cu la te ne gat ive e mi ss i on , i nst e a d of t he r e al z er o, if a ll the pro d uct i on wa s so ld t o t he gr i d. T he i mp or t ant p oi nt t o be awa re her e is t hat no e ne r g y pr od u cti on fr o m ot he r so ur ce s w il l be re duce d whe n e le ct ri cit y is be ing s ol d t o t h e gr i d wh ile t he re i s st il l i nte r nal l oad t o be su pp lie d . It is be in g r e du ce d (9_"#(;"+ 9;!,) and then required 9;!,. O bs er ve t hat t his e ne rg y c onsu me d fr om t he gr i d wi l l have t he sam e e miss io n coe ffi cie nt of t he s o ur ce t hat e n ded up n ot be in g re pl a ce d ( her e r e pr e se nte d by C3 or 0 .5 6 8 fr om S A P data) , and n ot t he gr i d a ve ra ge .

T he pi ct ur e be l o w re pre se nt s 3 poss ibl e s it uat io ns a nd il lust rat es h ow t he ca l cu lati ons s houl d pr oce e d. T he g r id e mi ss i on coe f fi c ie nt i s 0.4 2 2 , t he dis pl ace me nt coef fi ci ent is 0. 56 8 a nd t he ge ne rat i o n coe ffi cie nt is 0 .

F i g u r e 9 - C O2 c a l c u l a t i o n

T he se e xam ple s ma y al so s ho w t he im por t an ce of de fin in g h ow much of the pr odu ced e ne rg y was act ua ll y use d on s i t e or not , w hi ch, s ome h ow , wil l de pen d of t he i ns ta nt ane ous val ue s of pr o du ct i on a n d ge ne r at i on . A t pa r t 4 .2 t his re le v ance is e xp lo re d us in g t he cas e st udy .

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29

3.2. Renewable energy fraction

I n part ca use d b y t he ri se ove r t he pr i ce of foss il fue l s and t he e xhaust i on of i ts l ocal s our ce s , g ove r nm ent s al l a r ou nd the gl obe are r e aliz ing t he i mpor t an ce of up dat ing the ir e ne r gy i nfr as tr uct ur e . UK g o ver nme nt , for e xa mp le , a dopte d a poli c y t o a chie ve a 1 0 % of re ne wa ble par t i ci pat io n ove r t he el e ctr i ci t y ge ne r ate d ( 12 ) . I n M ar ch 2 0 07 , t he E ur o pean Co unci l c om m itt e d the E U to a bin di ng t a r ge t of a 20 % s hare of r e ne wab le e ne r gi es i n ove ral l E U cons um pt i o n by 2 0 2 0 (1 3 ) .

T he se poli cie s all have i n com m on the f ocus not j us t on C O2 e m is si on , but t he s har e of re ne w able e ne r gy ove r t he t otal e ne r gy ge ne r at e d ( or co ns um ed) . E ne rg y pr odu ce rs now ne e d to le ad wit h r e ne wab le pr odu ct i on t arge t s a nd , of cou rs e , be ab le t o de al w it h the m.

T he “ Lon do n des ig n a nd c onst ru ct io n pl an n ing gui da n ce ” ( 1 4) , for e xa mp le , s tat e s t hat “M aj or de ve lo pment s a re requi r ed to sho w ho w t he y wi l l gene r at e a pr opo rt io n o f a sc h e me ’s e ne r g y d e m a n d f ro m re n e wa b l e e ne r g y so u rc e s , wh e re t e ch no lo g i e s a re f e a si b le . T h e Ma yo r’s E ne r g y S t rat e g y st at e s t h at t hi s pr opo rt io n sh o ul d b e a m i n i m u m o f 10 pe rce n t ” .

T he fi r st poi nt i s to m ake cl ear w hat is t his pro po r ti o n is cal culat ed. B a si ca l l y , t he re ne wab le e ne r g y fa ct io n can be s e e n as the share of e ( 14 ) ner gy s up plie d b y a r e ne wable so ur ce ove r t he tot al of e ne r gy co ns um e d. T his ca l cu lati on can be quit e st ra ig ht f or wa r d whe n l oo kin g f or e le ct ri cal ge ne rat i on but w he n t he e ne r g y i s i n t he for m of he at , s ome p r ob le ms ma y o ccu r , s pe cif i cal l y whe n de a li ng wit h he at pum ps.

A publi c c ons ult ati on he ld i n 2 00 6 by the E U Ini t i at i ve o n he ati ng and c oo li ng fr om re ne wabl e e ne r g y s our ce s poi nt e d o ne of t he mai n obst acle s t o a wi de -s pr e a d of -s uch t e chn o logy t he f ol low in g pr o bl em :

• H ea t pu m p st a t u s ( r en e wa b le e n e rg y t e c h n o l o g y o r n o t) no t h a rm on i sed i n al l M e mbe r St a te s

A t U.K , heat pu mps are ac ce pt e d as r ene wable he at sour ce s and it s i mpor t an ce ove r t he E U t ar ge t of r e ne wab le sha re i s h ighl i ght e d ( 1 3 ) ( 15 ) . B ut s om e po int s are n ot y et cl ea r .

I s eas y t o de fi ne t he r e ne wable heat s har e duri ng t he he ati ng cy cle . T he t otal he at s up plie d by t he gr ou nd wi l l be t he t ot al l oa d min us t he t ot al e le ct r i ca l cons um pt i o n. B ut w hat hap pen s whe n t he l oa d i s not he at b ut c oo li ng?

Hybrid heating and cooling system optimisation with TRNSYS