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A sustainable storage solution for the Science Museum Group

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Museums in recent years have sought ways to reduce the environmental impact of their operations. One approach has been to look at ways to cut back on the energy required to stabilise storage conditions, particularly relative humidity, through passive moisture control rather than mechanical systems of heating and air conditioning. To this end the Science Museum Group employed hemp in the form of hemp-lime concrete, to construct a new storage facility for its collections, drawing on research into the buffering ability of hygroscopic natural building materials. The objective was to reduce energy use, to decrease reliance on mechanical systems and to produce very stable levels of relative humidity, in order to ensure the preservation of significant heritage collections. Although a prototype, to date, this building has performed as anticipated despite some initial construction snags and mechanical system malfunctions. The results encourage further investigation into hygroscopic construction materials to design even more energy-saving ways of providing stable storage conditions for museums.
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Science Museum Group Journal
A sustainable storage solution for the Science Museum Group
Th i s a rti cle wa s wri tten by Ma rta Le ska rd
10-12-2015 Cite a s 10.15180; 150405 Re sea rch
A s us ta i na bl e s tora ge s ol uti on for the S cie nce Mus e um Group
Publi s he d i n Autumn 2015, Is su e 04
Arti cle D OI : http://dx.doi .org/10.15180/150405
Abstract
Museums in recent years have sought ways to reduce the environmental impact of their operations. O ne app roach has been to lo ok
at ways to cut back o n the energy required to stabilise storage con ditions, pa rticularly relative hu midity, through passive moisture
control rather tha n mech anica l systems of heating and a ir cond itio ning . To this en d the Science Museum Group employed hemp in
the form of hemp-lime con crete, to construct a new storag e facility for its collections, drawing on research into th e b uffering ab ility of
hygroscopic natural b uilding materials. The objective was to reduce energy use, to decrea se reliance on mechanical systems and to
produ ce very stable levels of rela tive humidity, in order to en sure the preserva tion of significant heritage collection s. A lthough a
prototype, to d ate, this building has performed a s anticipated despite some initial construction snags and mechanical system
malfunctio ns. The results encourage further investigation into hygroscopic construction ma terials to desig n even more energy-saving
ways o f providing stab le storage con ditions for museums.
Figure 1
The Hempcrete Museum Sto re (HMS) at W rou ghton nearing completion
DOI: http://dx.doi.org /10.15 180 /1 504 05/017
Component DOI: http://dx.doi.org/10.15180/150405/001
Keywords
mus eum s tor a ge, h ygroscopic buildi ng ma terials, hemp, hemp-lime con crete, hempcrete, pr eventive cons erva tion, s usta ina ble,
rel ative h umidi ty
Introduction
Heating a nd a ir-conditioning a re prob ably the mo st sign ificant consu mers of fossil fuels by ga lleries and museums. W e n eed to
devise imaginative new so lutions to resolv e the dichotomy between long -term collections care a nd expensive environmental
condition s. (NMDC, 2 008 )
In recen t year s museums ha ve embraced s ustai nabi lity, d evel opi ng pol i cies to reduc e the carbon footpri nt of opera ti ons .
Ini ti a ti ves to less en environmental i mpact b y cutting ba ck on energy a nd wa ter us e and i ncreasi ng recycl ing a nd r eus e have
been introduc ed i nto day-to-day procedures . Larger sca le s chemes incl ude s ourci ng ma teri al s a nd products wi th the l eas t
environmental i mpact (Moore, 200 7) a nd encoura gi ng contra ctors a nd s uppliers to develop environmenta lly preferabl e go od s
and servi ces (Bri tish Museum, 20 07). Government di recti ves to meet ca rbon emission reducti on ta rgets by i mprovi ng overa ll
buildi ng energy performance ha ve res ulted i n mini mum energy performanc e requirements for mech a nica l a nd engineering
sys tems , s uch as heating a nd c ool i ng, i n new and i n exi sti ng bui l dings (EU Di recti ve, 2002). Thes e are al l worthwhil e
endeavou rs to ena ble museums to ‘go green’ a nd a chi eve envi ronmenta l, economic a nd ethical benefi ts . Bu t this pa per a rgues
tha t mu s eums could go even further i n cons ervi ng ener gy and reducing ca rbon emi ss ions whi l e a ctua l l y impr ovi ng their
function as protecti ve structures for c ultural ma teria l. Renewa ble energy sourc es a nd natural construction ma terials could b e
us ed in the des ign of museum repos itor i es whi ch wo ul d not on l y substanti all y ful fil the di recti ves for s usta inabi l i ty a nd
reduc ti on of carbon emi ss ions but might a ls o conti nuous l y mainta in stabl e internal condi tions whi ch would a ss ist i n the
preservation of heri tage col lections. Thi s was the ambi tion that drove the Science Mus eum Group to pi lot a novel form of
sus taina ble storage.
Preventive c ons erva ti on, a ls o known a s col lections care, i s one o f the pri mary r es ponsibi lities of museums tasked wi th
preserving ma terial cul ture for posteri ty. The I nter national Counci l of Mus eums – Committee for Conservation des cri bes it a s
identifyi ng and reducing potential risks and h a za rds to cul tura l a nd heri tage o bj ects while on exhi bit and in storage by
applyi ng appropr i a te mea s ures and a ctions for regi stration, stor a ge, handl i ng, pa cki ng and trans portati on, s ecurity,
environmental ma nagement, emergency planning, staff and publ ic a wa renes s a nd l ega l c ompl ianc e (I CO M-CC, 20 08). By
control li ng light, temperatur e, relative humidi ty, pol lution and pests, the need for i nterventi ve trea tment ca n be forestalled.
Both the level s and fluctua tions of relative humidi ty (hereafter RH) must be modera ted in order to mitigate da mage not only to
orga nic (ani mal and vegetal) materi a l s but a ls o to i norgani cs, parti cul a rly metals suc h as iro n and copper a l l oys . The
pa rameters recommended for stabi l ity i n museum d i s play a nd s torage c onditions, in pa rticul a r thos e of tempera ture a nd RH
ha ve thems el ves recentl y been revis ed to a wider ra nge tha n previ ous l y advised a s a respons e to the need for s usta ina bility
(II C-ICOM-CC, 2 014 ). Propos ed gui dance to arc hi tects a nd engi neer s i s fo r low energy and passive s oluti on s to ma i ntai n the
preservation needs of the col l ections i nstead of c l ose co ntr ol of pres cri bed l evels through mec hani cal a nd engineering sys tems
(NMDC, 2 008 b). Ea rly r es ea rch i n domestic buildi ngs s ugges ts that stabi li ty of temperatur e a nd RH c oul d be c onsider a bly
enhanced by exploi ting the b uffering abi lities of high thermal ma ss , thermal iner ti a a nd moistur e a bsorpti on capa bility of
buildi ng ma terial a nd design (Osanyintola a nd Simon s on, 2006 ); s o far there has been l i mi ted investigation of the potential
benefits to mus eums.
Bui lding materi al s s uch a s steel, concrete, bri ck, mineral wool insul ation, gl as s , gyps um boa rd a nd plastic pa int are commonl y
us ed in the constructio n of mus eum bu i l dings and storage repositories. However, whi l e concr ete, bri ck a nd i nsul ation provi de
thermal capa city, none of them ha ve any significant moi s ture tr a ns fer capa bility (Pa dfield a nd La rsen, 2 004). A few low en ergy
mus eum s tor a ge b uildi ngs ha ve been cons tructed us i ng s uch conventional ma teri al s but passive moi stur e bufferi ng of the
interna l envi ronment ha s been achieved more by the contents of the stores, chi efly pa per, rather than by the hygros copic or
moi sture a bsorbi ng abi li ty of abs orbent wa ll s , c ei l i ngs a nd floors (Pa dfield et al, 200 7).
There do exist more porous constru ction ma terials which have grea ter moi sture a bsorbi ng capa bility than c oncrete, bri ck a nd
gypsum. Among them a re bi o-ba s ed ma terials s uch a s s traw, fl ax and hemp, whi ch also ha ve excellent sus ta i nabl e credenti al s ;
they are n a tur a l (renewabl e) res ourc es, require less energy to produce a nd ma nufa cture (l ow embodied energy), a re rec ycl abl e;
and loc k up carbon dioxide (CO 2) b oth during the growi ng pha s e a nd for the l ifeti me of a bui l ding (Lawrence, 201 4). They have
signi fic ant hygroscopic ca pabi l i ty due to their porous struc tures a nd c a n buffer fl uctuations of RH by releasing moi sture a s
well a s stori ng it, depending on a mbient conditions. W i th the a ddi ti on of l ow energy or passive s ystems of ventilation to and
from ex terna l a ir, porous na tura l materi a l s could potentia l l y contr ol RH to s et poi nts. The u s e of these ma terials for collections
storage i s, however, ex peri mental , and in using them to c reate a new s tor a ge faci li ty, the Sc i ence Mus eum Group needed not
only to be aware of exi sting resear ch, but undertake s ignifi cant tes ti ng a nd monitoring of the new bui ldi ng. Thi s work forms part
of a PhD proj ect by the a uthor i n conj unction wi th the University o f Bath a nd i s descr i bed i n thi s a rticle. The paper reports on
the effecti veness of a natural porous bui ldi ng ma teri al , used in c onj un ction wi th a small ai r ha ndl i ng s ystem, to provide the
stabl e condi tions a nd ver y low energy cons umpti on required for a col l ecti ons s tora ge b uildi ng.
The storage situation prior to the new building
The Sci ence Mus eum Grou p is devoted to the history and contempora ry pra ctice of sci ence, medi cine, tec hnology, i ndustry and
medi a. W i th a n unri valled c ollecti on of historical and cul tura l material, i t i s cons i dered to b e the mos t si gnifi cant group of
mus eums of s cienc e a nd i nnova ti on wo rldwi de (Sc i ence M useum, 2 015). The Group consis ts of: the Science Mus eum (London),
the Mus eum of Scienc e a nd Indus try (Ma nchester), the National Ra ilwa y Museum (York), the National Med i a Mus eum (Br a dfor d)
and the National Ra ilwa y Mus eum (Shi ldon). Its co l l ection i ncl udes fi ne art, a rch i va l, photogr a phi c and l i bra ry ma terials a s
well a s thous ands of obj ects both large and sma ll, rangi ng for exa mple from airfra mes a nd l ocomoti ves to s urgi cal scalpel s
and needles.
As in many s i za ble mus eums, more tha n ni nety per cent of the gr ou p’s co l l ection i s i n storage rather than on d i s play, despi te
ha ving fi ve publ ic loc a ti ons and a dynamic loa ns progra mme. Not a ll obj ects were col lected to be di s played but were acquired
for reference a nd research. Some obj ects remain in s tora ge as they ma y be too l arge, too fr a gi le or too ha za rdous to go on
publ ic di splay but a re retai ned beca use of thei r cultur a l , histor i c or techn i cal va lue.
Figure 2a
Pi cca rd’s hot a i r ba lloon envel ope 1 973 -4 39 is too l arge ever to be displ ayed i n the
Museum
DOI: http://dx .doi .or g/10.151 80/15 0405 /018
Figure 2b
As wel l as being enormous, the r ope i s ma de from asbes tos fi bre a nd the fa bri c of
the envel ope i s begi nn i ng to deteriorate
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Previ ous l y, each museum in the gr oup ha d its own s tora ge faci li ties both at the mus eum site a nd i n externa l wa rehous es . But to
reduc e cos ts to the es tate, by 2015 a ll northern externa l s tores wer e clos ed and col lections tra nsported to the s torage s ite a t
Wroughton , W i ltshi re. Stora ge for the Sci ence M us eum Li bra ry & Arc hives had a lready been moved to W roughton i n 200 7.
Figure 3
The Sci ence Mus eum Grou p at Wro ughton – aeri al vi ew showing object stores
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The W roughton store is near Swi ndon on a former RAF a i rfi el d. The 5 45-a cre site, purc has ed from the Mini stry of Defence i n
19 79 for use a s a la rge objects store, ha s ten Sec on d World War ha ngars (with eight being us ed for c ollecti ons s torage) and one
custom-buil t s tore (s tore A1, opened i n November 199 4). Former maintenance bui ldi ngs have been c on ver ted for use by the
Library & Arc hives, Cons erva ti on a nd Es tates op erations. At almost 200 metr es a bove s ea l evel the s ite i s exposed to wi nds from
all di recti ons a nd i s s usc eptibl e to frequent weather cha nges. Hori zonta l rain is a parti cul ar featur e, resul ting in moi sture
penetra ti on of a geing bui ldi ng fa bri c.
The hangars , bui lt i n the l ate 1930 s to thr ee different designs a l l a pproxima tely 38 ,000 c ubi c metres i n capa city, a re not hea ted.
All are unins ulated concrete a nd s teel s tructur es .
Figure 4
A compilation of ima ges sh owing (from top to b ottom): L-type ha ngars (L2): parabolic
steel framework wi th c oncrete s kin; D-type h a ngar (D4 ): reinforced c a s t concrete
with conc rete bow-s trung roof trus ses; C-type ha ngar (C1 ): s teel fr a mework wi th
conc rete bl ock infill a nd wooden roof (before refur bishment)
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The hangers are i n va ryi ng degrees of disrepa i r, s ome wi th very l imi ted maintenanc e over the pa s t 36 yea rs, which has resul ted
in c racki ng concr ete a nd r us ting s teel elements. Three ha ve been renovated, one mor e full y tha n the other s . However, with the
site often being wet a nd wi ndy, the envi ronment i n all the ha ngars is col d and da mp, wi th temperatures rarel y cl imbing above
13 oC, a nd RH l evels between 6 5–100 per cent, with i nternal fl uctuations mi rrori ng external condi tions. Large i ndustri al,
agricultur a l a nd trans port objects are s tor ed either on the fl oor or on pa l l ets i n the hangars . Long-s pan pall et racking holds
smal l er or disass embled obj ects from the engi neeri ng technol ogies, medica l, computing, medi a a nd s cienc e col lections; thes e
ca n be c rated, c overed with Tyvek or pol ythene, trea ted wi th surfa ce coa tings or unprotected, dependi ng on obj ect type and
condition.
Graph 1a
C1 da ta Marc h–Ma y 20 15: despi te C1 undergoi ng renovation, wi th only i nsu l a ti on i n
the wa ll s a nd no RH b uffering, the envi ronment is only slightl y better tha n tha t i n
one of the una ltered hangars
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Graph 1b
D3 data Ma rch–Ma y 20 15: despi te C1 undergoi ng renovation, wi th only i nsu l a ti on
in the wa ll s a nd no RH bufferi ng, the envi ronment is only slightl y better tha n tha t i n
one of the una ltered hangars
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Figure 5
A compilation of ima ges sh owing (from top to b ottom): Externa l s hot of C1 hanga r,
refu rbi shed i n 201 1–12 ; Interna l s hot of C1 hanga r showi ng repa inted i nteri or a nd
long-s pan racking; Externa l s hot of D3 hangar; I nternal s ho t of D3 hanga r
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Stor e A1 i s an ins ulated s teel framework s tructur e wi th co nc rete foundation a nd fel t roof. I t wa s bui lt i n 19 92–9 3 i n res ponse to
a strategic review of the Scienc e Mus eum storage requirements . Desi gned with envi ronmenta l contro l s pro vi ded by a bui ldi ng
mana gement s ys tem, with origina l s peci fications for temperatur e a t 14±2 oC a nd r el a ti ve humidi ty of 55 ±5 per cent, the bui ldi ng
fail ed to deliver the tight envi ronmenta l para meters due ma inly to the failur e of the dehumidi fi cation s ys tem. Continuous l ow
level heating by oi l-fu el l ed boilers currentl y mainta ins the RH between a n acceptabl e 45–6 5 per c ent in the s torerooms , but the
boilers are a gei ng and require almos t daily maintenance. Stora ge is on mobile a nd s tatic ra cki ng, leavi ng no fl oor spa ce for
over-s ize obj ects, and there i s a lmost no capa city l eft for additional obj ects i n the r a cki ng. Cl earl y a new, eco no mi cally a nd
environmentall y sus taina ble storage s olu tion needed to be found.
Figure 6
A compilation of ima ges sh owing (from top to b ottom): Externa l view of the A1
Collecti ons Storage Fa cility (19 90s); Storeroom s howi ng mobi l e ra cki ng; Storeroom
showi ng s ta tic racking
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Graph 2
A1 envi ronmenta l moni tori ng da ta Marc h–May 20 15. Low l evel hea ti ng keeps the RH
at 50 ±5 per cent
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Com ponent D OI: http://dx.doi.org/10.15180/150405/002
Preventive conservation storage issues
Stor a ge i ss ues for a n extraordi nary col l ection of s cienc e obj ects a re complicated by both s i ze a nd mul ti plici ty of materi al s of
many of the objects . Obj ects suc h as a 1 918 Ammonia Refri geration Compres sor , a sta ti on ga s meter a nd the fi rst hovercra ft,
are l arge a nd robus t and c a n wi ths tand l ess than i deal environmenta l s tora ge c ondi tion s . Many of the other 35,000 objects
stored a t Wroughton are made with materi als wh i ch a re vulner a ble to l ight exposure, duration and wa velength; p a rticulates;
smoke a nd ga seous pol lution; ins ect and rodent pests; and va ryi ng l evel s a nd fl uctuations of tempera ture a nd RH. Many of the
objects in stor a ge a t Wroughton are large and robus t, s uch as the fol lowi ng exa mple i ma ges:
Figure 7a
Lightfo ot Ammoni a Refri gera ti on Compres sor from Uni on Col d Stor a ge, Al exandra
Dock, Liverpool 1982 -3 55
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Figure 7b
Watfor d’s town ha ll-s tyle gas s tation meter; 1979-818
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Figure 7c
SR-N1, the wo rld’s fir s t hovercraft, bu i l t i n 19 59;1968 -5 40
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Ob jects suc h as i n the following images are not i ncons idera ble in size but a re made fro m materi als whi ch c an fade, a re
tempti ng to i nsect a nd other pests and can rea ct disastrous ly to c hanges , especi al l y in RH:
Figure 8a
Model of the clipper shi p Stonehouse, built i n 187 1
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Figure 8b
Three-wheeled motor c a r s upplied i n ki t form by Ka rl Benz a nd a s s embl ed in 18 88 by
Emil e Ro ger, engineer a nd designer
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Figure 8c
19 36 Wurli tzer Si mplex mul ti-s el ector j uke box model 41
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Whi le i t i s true that greater da ma ge and deterioration to the mus eum col lection coul d come from fire, flood, a cci dent, theft,
va nda l ism a nd confl ict, occurrences of thes e are fa r l es s l ikel y due to s ite l oca tion a nd preventi ve measures.
Whi le damage fr om l i ght i ntens i ty and duration wi thi n the h a ngars is eli minated by ex cluding all l ight exc ept duri ng
occupation, the l evels of RH a nd temp erature (herea fter T) withi n the h a ngars do n ot meet the mus eums’ own a greed
rec ommendations for bes t pra ctice c ollecti ons c a re for r obust objects (RH 3 5–65 ±20 per c ent; T 16 oC–24oC±3oC (Bra in and
Bur den, 2 011 )). Thr ou gh the annua l as s es s ment of storage s pac es , the is s ues of inc orrect T and RH a nd pest ma nagement have
been hi ghlighted by the conservation and col lections care team. All i s sues are a res ul t of the agei ng s tructur es wh i ch were n ever
intended either to still be in u s e or to be us ed to s tore obj ects of cultur a l s ignifi canc e. Pests – birds , parti cul arl y jackda ws a nd
pi geons , a nd rats, mi ce and rabbits – fi nd their way i nto the ha ngars through hol es a t the top a nd bottom of the corr odi ng
ha ngar doors. Unl ess food or nes ting ma terial is pres ent, little da mage i s done to the obj ects by rodents . Ho wever, bird
excrement c a n da mage surfa ce fi nis hes so preventive mea sures such a s coveri ng vulnera bl e obj ects wi th Tyvek s heeting a re
undertaken. Moths and mould flouri sh under fa vour a ble co nd i ti ons of high RH and wa rm T but the ha ngars ar e rarel y wa rm;
however, outbr ea ks of both moth a nd moul d ha ve occu rred, es pec ially in r oa d vehicl es with fabric and l ea ther i nteri ors .
In fa ct, serendi pitously, the col d temperatures could slow down the ra te of deteri ora tion i n ma terials. Res earc h ha s s hown tha t
orga nic materi al s uch as paper deca ys more s l owly at tempera tur es under 12 oC (Burge, 20 14; Micha l s ki, 20 02; W ils on , 1995 ).
It is the associated hi gh RH l evel s i n the hangars that ca use mos t of the deterior a ti on to the c oll ection, whether objects are
compos ed of orga nic or i norgani c ma teria ls , or both. It is therefore the i ss ue of co ntrolling humi dity that wa s the pr i ma ry
conc ern that a ny new s torage fa cili ty needed to addres s.
Com ponent D OI: http://dx.doi.org/10.15180/150405/003
Deterioration caused by relative humidity
For each material, there is a level of environmental moisture content, related to th e a sso ciated relative humid ity, which is
consistent with its physical, chemica l o r biolog ical stability. (ASHRAE, 200 7)
Rel a ti ve Humidi ty is the ratio of c ur rent a bsol ute humi dity i n the a ir rel ative to the ma ximum abs olute humi dity a t a parti cul ar
temperatur e. As warm air ca n hold more moisture than c ol d air, RH drops a s temp erature rises and conversely ri ses a s
temperatur e drops . At 100 per cent RH, the air is s a tur a ted and the moi stur e c a n co nd ens e into water d roplets. Changes in RH
ca n ca use phys ical, chemi cal a nd biol ogica l dama ge to the materi al s out of whi ch obj ects are made.
In ma terials der i ved fr om plant a nd a nimal ma tter (or ga nic materi als ), whi ch natura l l y conta in wa ter, moi sture c ontent adj usts
to equi li bra te wi th the RH of the en vi ronment, and there can be s ubsequent c hanges i n di mension or physical cha racter i s ti cs
whi ch ca n res ult in physical da mage. Da ma ge from moistur e ga in can c ompris e s well i ng, cockl i ng, wa rpi ng, plastici si ng,
leaching, di ss olvi ng, fadi ng, s ta i ning, weathering, cr a cki ng and wea kening. Convers ely d a ma ge from moistur e l oss ca n res ult in
shrinking, spl itti ng, cra cki ng, br ea ki ng, cru mbling, del ami nating, stiffening and wea kening. The extent of da ma ge will depend on
the i nterna l physical s tructure of a ma terial, any external constri ctions, the envi ronmenta l RH values a nd rates of cha nge, and
overa ll ti me of ex po s ure.
Chemical da mage ca n also occur to both orga nic and inorgani c ma terials a t high humi dity l evel s. Organi c ma terials ma y lo s e
strength, colour, sha pe and fl exibi li ty when chemi cal bonds are br oken by the a ddi ti on of a water mol ecul e (hydro l ys is ). Wi th
low RH levels , s alt contami nated cera mic s , meta l s and s tone ma y devel op wh i te crys tal s on their sur fa ce (effl ores cence) or even
di sintegra te, and uns tabl e gla ss may turn opa que (c rizzle). I n hi gh RH level s s alts from deterior a ti ng gl as s c a n attra ct moi sture,
with droplets forming on the glass s urface, a nd meta ls c a n co rrode; a la yer of dus t wil l a ccel erate corrosion rates when the RH
ri ses a bove 7 5 per c ent. Bi ologi cal deteri or a ti on i s mos tl y ca used by micr o funga l gr owth (moul d); some moul ds will germi nate
around 65 per cent RH wi th a s uffi cientl y warm temper a ture. Mould ca n gro w on both organi c and i norga nic materi al s i f there
are s uitabl e nu trients a vai la ble.
Figure 9
Moul d growth on a l eather bicycle seat
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For mixed ma terial museum col l ection pr es erva ti on, the museum group RH guidel ines agree wi th the wider guidel ines , set out in
the recent j oint declara tion from the I nterna tiona l I nstitute for Cons erva tion a nd the Intern a ti on a l Counci l of Mus eums
Cons erva tion Commi ttee, a dvoc a ti ng a modera te range of 40 –60 per cent ±5 –10 per cent. W hil e RH l evels in the A1 s tore a t
Wroughton rema i n wi thin the s et poi nts due to cons is tent l ow-l evel heating, RH i n the h a ngars rarely drops to the hi ghest end
point. Even the most extens i vel y renovated hangar h a s higher than acc eptab l e l evels of humi dity for muc h of the year. Repl acing
the old ha ngars with s uitab l e bui ldi ngs for the s tora ge of the group’s col lection i s the ul tima te soluti on. Designing sus taina ble
storage bui ldi ngs to mus eum preventi ve cons erva ti on pol icy gui delines is the cha llenge.
Com ponent D OI: http://dx.doi.org/10.15180/150405/004
The need for a new kind of museum store
In 2010 a n agreement to hous e the inc i pient Rail Indus try Na tional Arch i ve as wel l a s a need for enviro nmenta l ly c ontroll ed
storage for pa inti ngs, s hip models and horse-dra wn carriages [1] prompted the deci si on to bui l d a new stor e a t Wroughton. Th e
collections al l required s tabl e RH l evel s whi ch c ou l d be a ll owed to dri ft modera tely withi n the reco mmended s et-poi nts but the
level s had to be pr ovi ded by l ow ener gy consumption a nd r educed r el i a nce on a mecha nica l a nd engineering sys tem (Moore,
2013). The store woul d be c ons tructed i nsi de one of the r enovated hanga rs (Hanga r D2) whi ch a lready hel d the a rchive s tore;
pl anning per mi ss i on wo uld not be required a nd i t was thought the hanga r i ts el f would provide a n additional l evel of protecti on
from the outs i de elements .
The design pr ojec t team had member s from vari ous mus eum departments : Es tates, Sustaina ble Development, Conservation &
Collecti ons Care a nd Curator i a l (Archi ves). Input from Conservation a nd Sus taina ble Devel opment led the project team to
cons ider the use of a hygros copic buildi ng ma terial which wo ul d buffer RH fl uctuations s uffi cientl y to el imi nate cons tant
rel ianc e on heating or dehumidi fication. Ba sed on researc h from the Universi ty of Bath (Sutton et al, 201 1) a nd resul ts fr om
newl y cons tructed c ommerc i a l warehous es (Beva n and Woolley, 2 009; Betts , 2 010 ), a bi o-ba sed cons truction concr ete ma de
from i ndustri al hemp and l i me bi nd er wa s c hos en, both for i ts bufferi ng a bility a nd i ts ecol ogica l credenti al s .
Com ponent D OI: http://dx.doi.org/10.15180/150405/005
Hemp-lime concrete: what is it?
Hemp-l i me c oncrete or hempcrete is a mi x of the c hopped up woody s tal k (s hiv) of i ndustri al hemp shi v (Cannabis sativa) with a
lime-based bi nd er and wa ter.
Figure 10
Hemp s talk showing the fibre a nd c ore
DOI: http://dx .doi .or g/10.151 80/15 0405 /034
Indu s trial hemp i s a fibrous pl ant simi l ar to flax a nd j ute. It i s a fas t-growing (thr ee to four months) carbon s eques trating
broa d-leafed pl a nt which requires mini ma l fer ti l i s ers , pesticides a nd herbicides a nd onl y modera te amounts of moisture. Hemp
was fi rst ha rves ted by the Chi nese over 8,500 years ago, then intr oduced to west As i a , Egypt and Eur ope between 2 000 and 10 00
BCE (Sma ll and Marc us, 200 2). Ind us trial hemp i s grown for fibre a nd gr a i n: fibres a re us ed to produ ce texti les (the name
‘ca nvas ’ i s deri ved from ca nna bis), s tring a nd r op e, a nd paper ; grain is us ed for food, a nimal feed and oil. Whi le of course it
comes from the same fa mil y as the ca nnabi s drug, breedi ng hemp over centuri es for tall s lender pl ants with l ong fi bres has
reduc ed the tetrahydroc a nna binol (THC) content (the ps ycho a ctive i ngredient) to l ess than 0 .3 per cent, maki ng the pl a nt a po or
sourc e of drug materi a l . China lea ds the world i n the p roduction of i ndustri al hemp; i t is grown i n over thi rty c ou ntri es
incl ud i ng the Uni ted Ki ngdom, where i t mus t be grown under the Home O ffic e Low THC Cannabi s (Hemp) licence.
Figure 11
Indu s trial Hemp Crop in Peasenhal l Roa d, Walpole, Suffolk
DOI: http://dx .doi .or g/10.151 80/15 0405 /035
On ce a crop is cut, the hemp s tal ks ar e l eft i n the field until sufficientl y rotted (retted) by rain and dew; then they are ba l ed and
stored i ndoors to allow dryi ng to ha l t the retting process. The outer fibres a re s epa rated from the inner woody s hiv usi ng a
decor ticator, which a lso shreds the shi v into chi ps. The c hi ps, or i gi nally c on s i dered to be a low-va lue wa s te product of the fibre
indus try, predomi nately ma rketed as ani mal bedding, ha ve begun to be us ed a s a bio-b a s ed cons truc tion ma terial. By 20 04,
about four per cent of the hemp s hiv pro du ced i n the EU wa s used in c ons truction (Karus a nd Vogt, 2004 ).
Figure 12
Hemp s hi v befo re casting
DOI: http://dx .doi .or g/10.151 80/15 0405 /036
Com ponent D OI: http://dx.doi.org/10.15180/150405/006
Hemp as a building material
Hemp s hi v ha s cha racter i s ti cs that make i t parti cul arly s uita ble as a bui lding materi al . I t i s more res is tant to biol ogica l deca y
tha n simi lar bi o-ba sed materi al s s uch as s traw and i ts s i lica content ma kes it fi re-retar dant. Shi v is a very porous ma terial,
bei ng a pproxi ma tely s ixty per cent ai r by vol ume, which ma kes it very hygroscopic, a ttracti ng (a dsorbi ng) mo i s ture qui ckl y and
rel easi ng i t (desor bing) slowly. I t i s hydrophilic, abs orbing water up to four times i ts weight. Th ermal conductivi ty is al s o low
due to the i nternal poros ity, whi ch reta rds the ra te of heat tra nsfer as air is l es s conductive (Ar na ud a nd Go ur l ay, 2 012).
However, the fibres require a bi ndi ng ma terial to produce a mortar. As hempc rete wa s i nitially used as a s ympa thetic repa ir
materi al for hi stori c oa k fra med bu i l dings infi l led with a mixture of s traw a nd l ime (wa ttle a nd daub) (Hi rst et al , 2010 ) l ime-
ba sed bi nders ha ve been us ed in the mi x in preference to Portl and cement. Portl and cement, whi ch s ets hard a nd relativel y
quickly and requi res l es s s kil l to us e, repl aced the use of lime mortars from the middle of the ni neteenth century (Ca rra n et al ,
2011). But, bec aus e cement’s hard nes s a nd dens ity i s i ncompatibl e a nd damagi ng when used with a ny ‘s oft’ a nd porous
buildi ng ma terial s uch a s tradi tiona l brick or porous s edimenta ry s tone, l i me mortar produc ti on has recently been revived for
the c on s erva ti on a nd restoration of heri tage bui ldi ngs a nd for us e with other na tura l bui l ding materi a l s (La bess e, 2005 ).
Commerci al l y ava ilabl e li me binders typica ll y contai n a va ryi ng prop or ti on of natural hydra uli c l i me, h ydrated or slaked lime,
a hydr a ul ic component suc h as Portland cement and/or other s i l i ca-containi ng ma teri al s s uch a s fly a sh, a res idue of c oa l
burning. Fl y as h improves the wor ka bility of the mi x due to its fi ne round gra ins and reduces the requi red water c ontent (De
Brui jn a nd Joha nsson, 201 3).
Com ponent D OI: http://dx.doi.org/10.15180/150405/007
Benefits of using lime
Des pite the potential environmenta l i mpact of limes ton e mi ning and lime pro du ction, there a re ma ny benefi ts to us ing l ime. I t i s
va pour p ermeabl e, which enha nces control of RH and reduces the potential for mould gro wth and condensation; i t has low
thermal conductivi ty and can a ct as a mas si ve thermal heat store; it i s al ka li ne, inhibi ting moul d growth and i nsec t a ctivi ty; i t
is l on g-l as ting; it is fi re and wa ter res is tant; i t can easily be recycled or abs orbed back i nto the land wi thout toxici ty (Rhydwen,
2009). Hydr a ted lime morta r is known for being self-healing’; a s i t cur es s lowly thro ugh c a rbonation[2], it can a djust to earl y
buildi ng movement. If a ppropri ate wet-d ry c yc l es a re ava il a ble, the c a l cium compounds can reprec i pitate into cra cks , then
conti nue the ca rbona tion proces s (Lubelli et a l , 2011 ).
Com ponent D OI: http://dx.doi.org/10.15180/150405/008
The advantages of using hemp-lime concrete
The s ustaina ble credenti a ls of hemp-l ime are s ubs tanti al: renewa ble, r ecyc l a ble, potenti a l l y sea li ng up enough c a rbon di oxi de
to produ ce a negative c a rbon footprint i n constructio n (Lawrenc e et a l, 201 2), but the cr uci al benefi t of using hempcrete for
mus eum s tor a ge i s i ts hygr othermal – heat and mois tur e – buffering b eha viour. I ts l ow ther ma l conductivi ty and good hea t
ca paci ty provides excellent i nsul a ti on. I ts wa ter va pour permeabi l ity, high moisture trans fer and s tora ge capa city modera te the
humidi ty of the a mbient envi ronment a nd provi de the crucial consi s tenc y of environment that objects need.
Hempcr ete has a range of buildi ng us es from roof i nsu l a ti on (l ow dens i ty) to wa ll s (medi um dens i ty) and gr ound s la bs (high
density), produced by va rying the p roportions of binder, hemp and wa ter. Di fferent densities have a si gnifi cant effect on the
movement of hea t a nd moi s ture through the ma terial, wi th lower dens iti es being mor e porous , whi ch r es ults in lower thermal
conduc ti vity a nd therefore better i nsul ating performance (Barcl a y et al, 201 4). There are good c on necti ons between the pores,
whi ch make i t highl y permea bl e and abl e to abs orb moisture a nd s ound. Hempc rete’s overa ll bufferi ng effec t on i ndoor RH ha s
been shown to i mprove res pir a tory comfo rt, ski n humidi ty and per ceived indoor air quality (Collet et al, 201 3). Mois tur e
buffering also reduces condensa tion a nd moul d growth, dec reasing the need for ventil a ti on a nd cutti ng energy cos ts (Col inart et
al, 201 3; Latif, 201 4). Despi te l ow dens i ty hempcrete requiring a loa d bea rin g s tructur e, i ts benefi ts ma ke it a very attra ctive
materi al for constructing mus eum stor a ge.
Figure 13
Interl inked pore structure of hemp s hiv (Photomicrogra ph x500)
DOI: http://dx .doi .or g/10.151 80/15 0405 /037
Com ponent D OI: http://dx.doi.org/10.15180/150405/009
Hempcrete Museum Store design and construction
Ha vi ng s el ected the bu i l ding materi al , the museum appoi nted contra ctors whos e approa ch s uppo rted the intent to produc e a
low cost, l ow-ener gy a nd s usta inabl e s tora ge b ui lding. The bui lding des i gn wa s modelled wi th Integrated Envi ronmenta l
Sol utions (I ES) software us ing environmenta l data from the hangar interior a nd the s i te, a nd the known thermal effi ciency and
hygros copic performa nce o f hempcr ete i n or der to pr oduce a reduc ed air ha ndli ng s ys tem. In fa ct, the software did not
acc ura tely s imul a te the hygro s copic behavi our of the hempc rete an d a nu merical pr ocedure wa s therefore developed to adj ust
the para meters of s i mulated temperature a nd humidi ty to bri ng them clos er to res ul ts from l aboratory tes ts. Thi s r es ulted i n the
des ign of a hea ting and venti l a ti on s ystem wi th no a ctive c on trol of humidi ty a nd no a ctive c ool i ng mec ha nism, but with
expecta tions of meeti ng an RH l evel of 50 ±5 per c ent mos t of the time (Ja nkovic, 20 12) by rel ying o n the pass i ve buffering
perfor ma nce of the hempcrete walls a nd on s eas on a l a mbient humidi ty level s .
A steel-framed three-s torey, six-room repos itor y, providi ng 980 m2 of s tora ge s pace, was pl anned, taki ng ful l a dva nta ge of the
hei ght wi thin the ha ngar.
Figure 14
Arc hi tectural plans for a s teel-fr a med, thr ee-s torey, six-room repos itory, pr ovi di ng
980m2 of s tora ge s pace
DOI: http://dx .doi .or g/10.151 80/15 0405 /038
Cei l i ng height o n each l evel was dicta ted by the needs of the coll ections and the ra fters of the ha ngar; the ground level ceili ng
ha d to be hi gh enough for the tal les t of the h or s e-dra wn ca rri ages , which r edu ced the height of the other two level s to jus t under
average ceiling hei ghts (225 cm). Cros s-l ami nated ti mbers , formed from s pruce pa nels bond ed together perpendi cul a rly to one
another, woul d give the fl oors and cei li ngs high structural strength, exc el l ent dimensional s ta bility a nd vapour per mea bil ity
(Sutton et al, 201 1) The pa nel sections woul d be i nserted i nto the steel framework, s peedi ng up cons truction ti me a nd
elimi na ting s i te wa ste. Before the steel framework wa s er ected, the or i gi nal hangar floor ha d to be removed and a new fl oor
poured with deeper founda tions for the support c olumns as a high fl oor loa d ha d been s pec i fied for the a rchiva l s torerooms.
Becaus e the storage repository was being built ins ide a hanga r which woul d mitiga te wi nd c hill a nd s ome temper a tur e
extremes , the foc us was on thermal i ner ti a a nd humi dity control rather than temp erature regul ation. The contr a ctor fi tted a
prefa bri cated cl a dd i ng s ys tem, Hemcla , coupl ed wi th Hemcrete® i n timber fra med pa nels , over the prima ry s teel frame
structure. Whi le the cl addi ng sys tem norma l ly h a d a thi ckness of 120 mm and i ncl uded a hemp fi bre q ui lt for ther ma l
ins ula tion, the sys tem was modi fi ed to el imi nate the fi bre qui lt a nd i ncr eas e panel thicknes s to 20 0mm to a ugment moi sture
and therma l bufferi ng ca paci ties .
Hemcrete® i s a proprietary blend of lime-based bi nder a nd prepared hemp shi v, mixed wi th water to fo rm a s lurry for casting or
sprayi ng. Hemc rete® p a nels are factory pro duced, force-dried and ava il a ble in b es poke sizes. The pa nels meet curr ent British
Stand a rd fire r es i stanc e tes ts for bu i l ding materi al s . Pre-ca st panel s a re intended for year-round cons truction a nd wh ere time
on si te i s restri cted. W hil e hemp-lime mi x can be pr oduced wet on site and ei ther c a s t i nsi de a framework or s pra yed a ga ins t a
lini ng board, a s there was a ti ght dea dline due to the storage needs of the collections, constructi on of the store had to take
pl ace over the wi nter months a nd pre-c a s t pa nels were the onl y co ns truc ti on choi ce.
Figure 15
Pre-casting pa nels for the Museum store
DOI: http://dx .doi .or g/10.151 80/15 0405 /039
To r educe any potenti al dus t emanating from the unc oa ted hempcrete panel s a nd for fi re pr otec ti on, the inner fa ce of each
Hemcrete® panel was li ned wi th a thi n va pour -permeabl e unpainted ma gnesium silicate board (Mul ti-Pro)[3], even though i t
was l ikel y that this woul d reduce the buffering ca pabi lity of the hemp-l ime. The outer fa ce of the bui ldi ng wa s covered wi th a
va pour p ermeabl e membrane, wood fibreboard a nd r od ent-proof wi re mes h with a n added layer of Multi-Pro boa rd a gai nst
colli s i on dama ge a t floor l evel.
Figure 16
Pre-cast panel s i n D2; ma gnesium si l i cate board (whi te) on upper fa ce
DOI: http://dx .doi .or g/10.151 80/15 0405 /040
Figure 17
Ins ta l l a ti on of the hemp-l ime panel s on the s teel s tructure
DOI: http://dx .doi .or g/10.151 80/15 0405 /041
Acc es s to each of the l a rger object s tora ge rooms i s through both s teel rol ler shutter doors a nd pers onnel doors ; each s tora ge
room also ha s a fir e exit. Fr ee-s tanding stair acc es s, balconi es a nd railings were ins tal l ed front and ba ck a nd a n object-only
lift i nsta ll ed at one front right corn er. Rea ch tr uck acces s i s through gates in the s a fety railings .
Figure 18
Acc es s to up per floor u s i ng forklift a nd pallet ba y
DOI: http://dx .doi .or g/10.151 80/15 0405 /042
Figure 19
Ins ta l l a ti on of M&E sys tem on the exteri or of HMS
DOI: http://dx .doi .or g/10.151 80/15 0405 /043
Com ponent D OI: http://dx.doi.org/10.15180/150405/010
Control of the internal environment
It was a l ways envi si on ed tha t s ome active mec hani cal s ystem would need to be i ncl uded in the envi ronmenta l control of the
store. Thi s was intended to provide very energy-effici ent mana gement of the a mbient en vi ronment in c onj unction wi th the
pa ssive regulation by the bui l ding fabri c. Venti la ti on to outside was consi dered nec es s a ry a s the RH level s wi thin the ha ngar
would alwa ys be hi gher tha n those i nside the repository; moi s tur e s tored in the hemp-lime wa ll s wo uld need to be dried out
periodically. A Tr en IQ3 b ui lding mana gement s ystem (BMS) and two Ai rflow® air-ha ndl i ng units (AHU) wer e i nsta ll ed to
ci rcul a te external cool dr y ni ght-time or warm da ytime air depending on humi dity requirements wi thin the stor e. Ser vi ces were
run externa lly with onl y vents and moni tors i nside ea ch r oom.
It was a l so of grea t impor tanc e to ha ve a ver y acc ura te moni tori ng s ys tem as a s ource of da ta to res earc h the effecti veness of
the s tore, a nd to moni tor the da y-to-day c onditions for mainta ini ng the ca re of the obj ects. In fa ct, two moni tori ng sys tems were
incl ud ed: a Carnego® monitoring sys tem for the BMS (14 combined T a nd RH s ensors – two i n each s toreroom, on e i n the hanga r
and one external) wa s i nstalled a nd ma naged r emotely by the design engi neers . Combined RH a nd T s ensors wer e a l so ins talled
as pa rt of the mus eum’s bes poke envi ronmenta l moni tori ng sys tem[4], mana ged by Co ns erva tion s ta ff.
Com ponent D OI: http://dx.doi.org/10.15180/150405/011
Teething problems
Ini ti a l i ss ues wi th moi sture l evels were detected by the mor e s ensitive Ha nwell® sens ors . Both ex terna l BMS T a nd RH s ensors
were faul ty as wa s the contr ol softwa re runni ng the AHU fa ns, res ulting in warm moi st dayti me ai r bei ng dr a wn i nto the store
rooms ins tead of cool dry ai r at night. Th ere wa s una ntic i pated moisture from both the drying conc rete fl oor ma ss , a ffecti ng
mainl y the ground floor store, and the hemp-l ime panel s. By July 2 012 , l es s than three months befor e the fi rst objects were to be
rel oca ted to the s tor e, RH l evel s were clos e to 80 per c ent on the ground floor, 70 per cent on the fi rst fl oor and 65 per cent on
the top floor – measur ements which fel l outs ide the mu s eums’ own a cceptabl e range.
Figure 20
Ground fl oor after completion
DOI: http://dx .doi .or g/10.151 80/15 0405 /044
Graph 3
HMS ground fl oor environmenta l data fi rst yea r of opera tion. Shows the forced
remo va l of moi s tur e by M&E sys tem unti l May 2 013 when sys tem was turn ed off
DOI: http://dx .doi .or g/10.151 80/15 0405 /045
Thes e teethi ng pr obl ems required the museum to employ un expected a ctive mechani sms to reduc e the RH level s at l east i n the
short term. P orta ble dehumidi fiers a nd a ir cond i ti oners were deployed along wi th a sli ght eleva tion of the ambi ent temperature.
After sens ors wer e repl aced, s oftware upda ted and hea ters rewi red, operation of the AHU s ystem assisted i n reduc ing the RH to
between 40–5 0 per cent on all fl oors (Ja nkovic, 20 13). Fl uctuations in RH were also c ons idera bl y reduc ed through the
replacement of faul ty da mpers , which had c aus ed an i mbalanc e i n the a irflow from the duc twork. However , both fa n and heater
opera tions continued to caus e fluctua tions between 5 –10 per cent/2 4 hours . RH level s a lso rose when the dehumidi fier
condens ate ta nks wen t unemptied[5]; thi s wa s resol ved by c onnecti ng the equi pment to the ha ngar’s drai nage cha nnel to
achieve c ontinuous dra ini ng.
With the s ea s ona l r i s e of tempera ture, the hea ters were turned off i n Ma y 20 13 whi ch resul ted in a sl ow rise of RH to 6 0 per
cent i n the ground floor store room. In order to decrea se RH fl uctuations, i t wa s deci ded to al l ow the buildi ng to d rift passivel y
through the s pri ng and s ummer seasons s o the entire a ir ha ndl ing sys tem was swi tch ed off. The s tore r ema ined i n pa ss i ve mode
until Ma rch 2014 , when the RH l evels, which had dri fted s l owly u pwards a t a rate of around one per c ent per month, ro s e a bove
seventy per c ent on the groun d fl oo r. Thi s was considered to be too hi gh a nd a n attempt was ma de to r ei nstate the HVAC s ystem
with mini mal succ ess a s handover a nd traini ng to run the s ystem ha d never occurred.
Graph 4
HMS ground fl oor environmenta l data second year of oper a ti on . Sp i kes in RH and T
from January–Ma rch a re a resul t of a heatin g s ystem pr ogra mme gli tch. The s i ngle
spi ke in June 2 014 occ urred when the hea ti ng s ystem wa s tur ned on briefl y to reduce
the RH l evel
DOI: http://dx .doi .or g/10.151 80/15 0405 /046
Ini ti a l l y, from August 201 4, the RH was a ga in reduc ed us ing porta ble dehumi difi ers and a i r condi tioners. The o rigi na l designer
was contra cted to reins tate the air h a ndl i ng a nd heating sys tem a nd he also provided tra ining to the s i te’s Es tates team. Ful l
running of the s ystem wa s reins tated five mo nths l ater although mi ld and damp ex terna l condi tions mea nt tha t i niti al l y fou r
hours of daily heating was pri mari l y us ed to reduce the RH l evels . This resul ted i n da il y ra pid fl uctuations of 10–1 5 per c ent.
Fl uctuations were reduced once dr i er externa l a i r could be utilised along wi th hea ti ng. Level s were s ta bilised over three months
on the ground floor to 6 0 per c ent and 55–6 0 per cent on the other two fl oors. In Apri l 2 015 , RH regulation wa s r etur ned to the
pa ssive mode and fl uctuations were vi rtua ll y elimina ted. Again the RH ros e very slowly unti l, by July 2 015, i t was aro un d 68 per
cent on the ground fl oor. Becaus e the externa l a i r wa s rarel y drier outside the hanga r tha n tha t wi thin the s tor e due to the wet
summer, a si ngle dehumidi fier wi th humidi sta t s et to sixty per cent, connected to the hangar’s dra ina ge, was ins tal l ed i n the
ground fl oor s tor e room. This resul ted in s tabi li sation of RH to jus t a bove s ixty per cent wi th vi rtua l ly n o fl uctuation
wha tsoever. RH levels on the other two fl oors ha ve also dropped sli ghtly, i ndi cating moi sture movement through the
interconn ected poros ity of the l ow-densi ty hemp-l i me walls.
Graph 5
HMS ground fl oor environmenta l data thi rd year of oper a ti on . M&E s ystem
opera tion wa s reins tated to reduce the r i s e on RH thro ugh November–April. Al though
the s ystem wa s s uppo s ed to have b een turned off i n Apr i l to al l ow pa ss ive
opera tion, one heater r ema ined func ti ona l , r es ul ting i n continuous sma ll
fluc tua tions i n T and RH
DOI: http://dx .doi .or g/10.151 80/15 0405 /047
Graph 6
Ground fl oor environmenta l data Ma rch–June 201 5. W i th the heater turned off, the
buildi ng returned to ful l passive mode, wi th an a ntici pated s l ow ri se i n RH
DOI: http://dx .doi .or g/10.151 80/15 0405 /048
Com ponent D OI: http://dx.doi.org/10.15180/150405/012
Discussion
To date, the hemp-l i me walls have been s hown to be very effec ti ve moi sture buffers . Even when the mechani cal s ystem wa s
malfunctioni ng, intr oduci ng moisture-l a den a ir into the store rooms i nstead of dry a i r, the i nteri or RH l evel s never rose clos e to
the extent of the enviro nmenta l condi tions i n the hanga r. Once s ta bilised a t an a cceptabl e RH l evel and with the mec hani cal
sys tem s witched off, the buildi ng ha s demons trated c ons i stentl y excellent RH s tabi li ty.
But as the h emp-l i me functi ons a s a buffer not a s a control l er of RH, some method of moi stur e removal fr om the hempcrete
conti nues to be requi red i n order to bring the RH back down to preferred va lues. Moni tori ng data from D2 ha ngar shows RH
level s outs ide the s tore to be generally between 70 –10 0 per cent[6]. As the RH i nside the s tore i s l ower tha n tha t i n the hangar,
moi sture c a nnot be tr a nsported out thr ough the hempcrete walls and i nto the ha ngar; the vapour-per mea ble membra ne fitted
between the h empcr ete wa ll s and the externa l wood fibreboard a l s o prevents moi sture movement from the ha ngar ba ck i nto the
hempcrete ma terial. In order to remove moi stur e, the air ha ndl ing pl ant runs cyc l es of hea ting a nd a ir fl ow, i ntroduci ng dr i er
air into the s torerooms a nd extra cting d a mp a i r. Thi s does gra dua l l y reduce RH level s but c reates continuous fl uctuations
whi ch coul d contri bute to the physical deteri or a ti on of organi c ma terials over time, a l tho ugh the fl uctuations are of short
dura tion thanks to the buffering effect of the hygroscopic materi al s .
As col l ecti ons a re now s tored in the rooms , the RH mus t be controlled withi n the gr oup’s set pa rameters and shoul d not be
allowed to ri se a bove seventy per c ent for a ny extended peri od of ti me. So far, the a i r ha ndling sys tem has onl y reduced the RH
to 5 5–60 per cent during the wi nter months , with the RH then rising to the ma ximum l evel over s i x to eight months of passi ve
opera tion. If the moisture removal pr oces s i s fol l owed a s ori ginal l y intended, cycling dry a ir a nd heat thr ou gh the winter
season to reduce the RH, then allowing a pa ss i ve drift fo r the r ema ind er of the year, thi s s hould provi de an a cceptabl e level of
control . However, a t pres ent the a ir ha ndl i ng cycli ng must be run by an operator wh o moni tor s external condi tions ; the bui lding
mana gement s ys tem softwa re is not s ophistica ted enough to check or predi ct drier externa l condi tions in order to tur n on the
air ha ndl ing units. As dri er condi tions genera ll y occur a t night outside nor ma l working hour s , this mea ns the s ystem does no t
ful ly run as des igned. Using the heating to reduce RH ra ther than ex terna l dry a i r ha s been s hown by the monitori ng to ca use
greater fl uctuations i n RH. Becaus e of the successful (lower RH l evel and fewer fl uctuations) tri a l wi th the c urr ent
dehumi dification equipment, discus s ion i s underway r ega rdi ng the possibl e installation of dehumidi fication uni ts i n the
ducti ng. Thes e coul d be oper a ted duri ng working hours, drying externa l a ir before introduc i ng it i nto the storerooms, mi micki ng
the ori ginal concept but a ddi ng a l ittle more engi neeri ng.
When the mechani cal s ystem ha s been r unning, its opera tion has been very low-cos t. Curr ently i t runs wi th electrical
cons umpti on a t 2 0,39 7.5kWh agains t a predi cted 2 4,32 0kWh, whi ch i s l ess than a thi rd of the runn i ng cos ts a nd emissions of a
conventi onal envi ronmenta ll y contr olled mus eum s tor e of the same s ize (Moore, 201 3). W hen i n pa ssi ve mode, the running
costs a re negligi ble; costs of runni ng the dehumi difi er ha ve yet to be c a l cul ated but it wi ll not c ons ume even clos e to the s ame
power as the ful ly opera ting sys tem.
The hempcrete museum store took a longer time to dr y out tha n anti cipa ted by either the contractors or the museum proj ect
team. But, bec a use the hempcr ete has demonstra ted s uch excel lent hygrotherma l cha racteris tics, objects stored in the bu i l ding
were not put a t risk d uri ng the s tabilisation per i od, a s s hown by the monitori ng da ta. RH fl uctuations ha ve stayed wi thi n
establ i shed para meters for the ma teria ls stored; RH levels have been s li ghtly high but never in the range to s upport mould
growth or promote corrosion.
Conti nued mon i tor i ng of the hempc rete store ma y show that, as the buildi ng ma terials continue to cure over ti me, RH l evels do
not ri se qui te as high s o tha t operation of the a ir ha ndl ing sys tem will be requi red l ess fr equ entl y. Or the hemp-l ime panel s may
now be ‘pre-condi tion ed’, with a memory of an RH l evel of 55 –70 per cent a nd i t may never be pos si ble to prevent the eventua l
drift back up to 70 per cent. However, oper a ti ng the buildi ng as i s done presentl y still ha s given the Sci ence Mus eum Group a
very effecti ve and effi cient envi ronmenta l ly c ontroll ed store a t a mini mal run ni ng cos t and a n exc el l ent prototype for future
storage bui ldi ng projects .
Figure 21
A compilation of ima ges sh owing (from top to b ottom): HMS i n us e; Stora ge of hor s e-
drawn carriages on groun d fl oo r; Art s tora ge o n second fl oor
DOI: http://dx .doi .or g/10.151 80/15 0405 /049
Com ponent D OI: http://dx.doi.org/10.15180/150405/013
Conclusions
The Hempc rete Museum Store i s a step forwa rd i n pr ovi di ng s usta ina ble controlled envi ronment mus eum storage. W hil e
cons truction cos ts wer e a ppro ximately ten per c ent hi gher than a tra ditionally c ons tructed mus eum stor e (Moore, 20 13), i ts
running cos ts a re less than half of a clima te c on trol l ed spa ce of the s ame size. The bi o-ba s ed ma terials us ed ha ve reduced the
ca rbon footprint of i ts cons truction a nd the hemp-l ime will continue to lock up CO2 for the duration of its use. The
environmental condi tions withi n the s tore a re stabl e; when the bu i l ding is in pa ssi ve mode ther e a re vi rtua lly no fl uctuations i n
RH or tempera ture. W hen the mecha nica l a ir ha ndl i ng s ystem i s runni ng, the buffering abi li ty of the hygros copic buil di ng
materi al r edu ces the extent of fluc tuations caus ed by hea ting or fan operation.
The s tore won three ma jor a wa rds in 20 13 for i nnova ti on a nd s usta ina bility both i n the mus eum and the buildi ng indus try
sectors : Greenb ui ld Awa rds , Best Workplace New Bu i l d; Museums and Heri tage Awards, Sus tai na bility; Cha rtered Ins titute of
Bui lding (CI OB) South W est Bu i l t Envi ronment Awards, Innovation[7].
The Hempc rete Museum Store may be us ed as a pro totype for developing further sus taina ble mus eum s tor a ge for the Sci ence
Museum Group. W roughton needs new l a rge s torage bui ldings to repl a ce the ageing ha ngars . Bui l ding storehous es wi th
hygros copic ma teri al s ma y be part of the s olution s i nce they na tura lly provide the s ta bl e envi ronment that col lections requi re
to ensur e l ong-term pres erva ti on. Areas for fur ther res earch i ncl ude l ooki ng at pa ss ive a lterna tives to mecha nica l a nd
engi neeri ng s ystems to reduc e mois tur e s tora ge a nd i nvestiga ti ng more porous materials to coa t i nteri or walls. The possibi li ty
of fine pa rticul a te ma tter[8] dri fting out of uns ealed hemp-l i me also needs to be es tablished as wel l a s the potenti a l effec t that
the a lka li ne na ture of hempc rete might ha ve on aci dic polluti on fr om degra ding paper , plastic and wood. An interna l
environment i n a detac hed bui l ding may rea ct differentl y to that of thi s s tore bui lt i nside a hanga r, or a ltern a ti vel y buildi ng
des ign ma y need to mimi c the ‘b ui lding wi thi n a bui l ding’ c on cept. Some o f these fa ctors ma y be a nswered through c onti nui ng
res earch bei ng underta ken by the a uthor a t the Uni vers i ty of Bath. Others may onl y be a nswered by bui lding another stor a ge
buildi ng.
Acknowledgm ents
I would like to tha nk Loui s a Burd en, Ma tt Moore a nd Dennis Kelles-Kra use, Science Mu s eum Group, for their assistanc e i n
writing thi s a rticl e. I a l s o wi s h to thank my supervisor s , Dr Mi cha el La wr enc e and Dr Stephen Lo, University of Bath, Depa rtment
of Archi tecture a nd Civi l Engineeri ng for thei r support and enc oura gement.
Com ponent D OI: http://dx.doi.org/10.15180/150405/014
Appendix A
The Hempc rete Museum Store proj ect des ign team:
Externa l Contra ctors
Ia n Pr i tchett, Tec hn i cal Di rector and Vi ce Ch a i rman, Lime Technol ogy
Pi ers Ashl ey-Ca rter, P roj ect Ma nager, Hemcrete P roj ects Ltd
Dr Lubo Jankovi c, Di rector, Emi s s ion Zero R&D
Jeremy Col l i ns, Stru ctural Engineer , Syl va Group
Andy Aram, Q ua ntity Su rveyor
Dr Mi ke Lawrence, Cons ulta nt, BRE Centr e for Innova tive Cons truc ti on Materi als
Si mon K i rton, Di rector, Emiss i on Zero A&E
Intern a l SMG Proj ect Ma nagement tea m
John Bevi n, Di rector of Estates (retired)
Louisa Burden, Head of Cons erva ti on a nd Col l ections Ca re
Ma tt Moore, Head of Sus tai na ble Development
Tim Procter, Cur a tor of Archi ves, National Ra il wa y Museum
Ma rta Leska rd, Conservation a nd Col lectio ns Care Ma nager
Da rren Hopkins , Esta tes Mana ger
Si mon Cha mbers , Pro ject Ma nager
Com ponent D OI: http://dx.doi.org/10.15180/150405/015
Appendix B: Manufacturers and suppliers
Software
Integrated Envi ronmenta l So l utions (IES) https ://www.i es ve.com/
Hemp-l i me c oncrete materi al s
Hemcla Limetec Group www.li metec.co.uk/
Tra dica l® Hemc rete® Lhoi st Group www.lhoist.com/
Tra dica l® HB- l i me b i nder
Tra dica l® HF- hemp
Air ha ndl i ng and moni tori ng equi pment:
Trend Bui lding Ma nagement Sys tems https ://www.trendc ontrols .com/en-GB
Airflow Venti l a ti on Sys tems https://www.ai rfl ow.com/
Ha nwell Monitoring Sys tems www.the-imcgro up.com/ha nwell-environmenta l -monitoring-and-control
Ca rnego Monitoring Systems www.carnegosystems.com/
Com ponent D OI: http://dx.doi.org/10.15180/150405/016
Tags
Museum collections
Scienc e museums
Twenty-fi rst centur y
Cons erva ti on
Collecti ons s torage
Footnotes
1. Pa inti ngs a nd s hip mo del s had been on exhi bition si nc e the 19 60s in the Shipping Gal l ery i n the Sci ence Mus eum. They
ha d to be moved into stora ge i n order to develop the spa ce for the new Informa ti on Age Gall ery (o pened 20 14). The
hors e-dra wn carr i a ges had been moved ea rlier from hangars , where they were prone to attac k by moul d and moth, to the
north wi ng of the Engi neering Buildi ng (Conservation); thi s s pace now wa s required for the cons erva ti on of obj ects s uch
as the Rugby Tuning Coil, which was to form the centre of the new ga ll ery.
2. Ca rbona tion i s the chemi cal reacti on between l ime (calci um hydr oxi de) and a tmospheri c carbon dioxide, whi ch
converts the lime back to calci um carbonate.
3. Res i s ta nt Buildi ng Pr oducts www.res i s tant.co.uk
4. A wi reless Ha nwell® (IMC Group) moni tori ng sys tem relays data on tempera ture a nd relative humidi ty from data loggers
situa ted i n exhibi tion galleri es i n the Sc ienc e Mus eum and i n stor a ge a reas in Bl ythe Hous e and a t Wroughton to a
centra l databa se which c a n then be rea d by cons erva tion s ta ff at all three s ites .
5. Ini ti a l l y the dehumi difi ers ha d to be emptied ei ther by the contra ctor or by c ons ervation s ta ff. Usua ll y by Monday
mor ning the ta nks wo uld be full, resul ting in the RH bouncing ba ck to the u pper level .
6. Thi s i s s i mil a r to da ta from a l l the ha ngars on s ite, which r ema in da mp even when outside RH i s l ow.
7. http://www.greenbuildnews .co.uk/n ews -d etail s /2 013 -Greenbuild-Award s -winners -r eveal ed/8 12;
http://www.mus eums a ndheri ta ge.c om/s how/awards /hall -of-fa me/201 3-awa rd-winners; http://www.ci ob.org/nea r-
you/s outh-wes t
8. In other words, dus t – p a rticularly fi ne calci um carbonate pa rticl es.
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Author information
Ma rta Leska rd i s the Cons ervation a nd Col lections Ca re Ma nager a t the Sci enc e Mus eum Group’s stora ge si te at W roughton i n
Wiltshi re. She is a l s o currently a part-time PhD student i n Ci vil Engi neeri ng, University o f Bath, c onducting res earch i nto
sus taina ble co ns truc ti on methods to ena ble the pres ervation of museum col l ections i n stor a ge.
Marta Leskard
Conservation and Collections C are Manage r
Contact t his author >
... The construction based on hemp lime bio-composite material (hempcrete) was specified within a steel frame to facilitate multi-story construction. The main construction types were as follows: The thickness of external walls was chosen to provide a balance between thickness and U-value, consistent with experience from projects by Eberlin and Jankovic [32] and by Leskard [33]. The thickness of internal walls was gradually increased from 100 to 300 mm in order to achieve negative embodied emissions. ...
... As hempcrete is nature-based material [18], there will be potential for recycling at the end of the lifetime of the building. Although other materials may be suitable for this purpose, the choice of hempcrete was based on its well documented properties [18], on the authors' monitoring experiences [32], and design experience [33] of this material. ...
... The use of hempcrete as the main construction material, previously used by a team member on design of a museum artefacts storage facility [33], provides thermally stable and uniform environment. Shallow plan depth, combined with vertical ventilation stacks/light wells, provide natural daylight and natural ventilation. ...
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This article introduces BioZero, a nature-inspired near-zero building proposed for Quay St, Brooklyn, New York. The building is designed for the maximum use of daylight and natural ventilation. This is the result of its shallow plan depth and the inner light wells/ventilation stacks, which also serve the inner circulation space. The light wells/ventilation stacks are created as a result of the organic shape of the internal partitions. The building is constructed from a steel frame and hemp-lime bio-composite material (hempcrete), which smooths out the fluctuations of internal air temperature and relative humidity. The south facing façade is fitted with the Cadmium Telluride (CdTe) photovoltaic array that covers 90% of the opaque surface area of the façade. The design was based on nature-inspired computation, with sustainability principles as guiding constraints. The main findings are that the building achieves −227 tonnes of negative embodied carbon due to sequestration of CO2 in the hemp plant from which the material was harvested, and a net-zero operation. The main conclusions are that in the context of climate emergency, nature inspired design leads to energy efficient buildings with a high level of thermal comfort, which are buildable and sustainable.
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