Energy and Buildings 42 (2010) 845–852

Hygrothermal analysis of a stabilised rammed earth test building in the UK

David Allinson a,*, Matthew Hall b

a Department of Civil and Building Engineering, Loughborough University, Leicestershire LE11 3TU, UKb Nottingham Centre for Geomechanics, Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK

A R T I C L E I N F O

Article history:

Received 21 July 2009

Received in revised form 4 December 2009

Accepted 17 December 2009

Keywords:

Stabilised rammed earth

Hygrothermal

Whole building simulation

A B S T R A C T

This paper describes the analysis of the hygrothermal behaviours of stabilised rammed earth (SRE) walls

used in a building in the UK. The analysis was achieved by computer simulation using WUFI Plus v1.2

whole building hygrothermal analysis software. To validate the model, an unoccupied test room in an

unheated SRE building was monitored for 10 months. The hygrothermal properties of the SRE material

were measured in the laboratory. It is shown that the SRE walls significantly reduced the amplitude of

relative humidity fluctuations in the room air and reduced the frequency of high humidity periods at the

wall surface. By adapting the model to represent an occupied and conditioned space, it is demonstrated

that SRE walls have the potential to reduce the energy demand for humidification/dehumidification

plant.

� 2010 Elsevier B.V. All rights reserved.

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1. Introduction

Hygrothermal behaviour describes the interrelated heat andmoisture transfer between a material and its environment. In thispaper we consider the walls of a room in a building constructedfrom stabilised rammed earth (SRE). The SRE walls weremanufactured from moist earth materials mixed with cementand compacted into formwork. At the outside surfaces, the wallsinteract with the outside environment through the exchange ofheat (convection and radiation) and moisture (wind driven rainand vapour exchange). Similarly, at the inside surfaces the wallsinteract with the indoor environment through the exchange of heatand water vapour (see Fig. 1). The temperature and relativehumidity of the indoor air can be greatly influenced by itsinteraction with the walls [1] and the transport and storage of heatand water in the wall depends on the properties of the constructionmaterials.

Some materials have high thermal mass and can absorb, storeand release large amounts of heat, helping to maintain stableindoor air temperatures, e.g. dense concrete and natural stone.Similarly, some materials have high ‘hygric mass’ and can absorb,store and release significant amounts of water, helping to maintaina stable indoor air relative humidity, e.g. desiccants and clays. SREmaterials have been identified as having a high thermal mass and ahigh hygric mass [2]. They also have the advantage that the inside

* Corresponding author. Tel.: +44 0 115 846 7132.

E-mail addresses: D.Allinson@lboro.ac.uk (D. Allinson),

matthew.hall@nottingham.ac.uk (M. Hall).

0378-7788/$ – see front matter � 2010 Elsevier B.V. All rights reserved.

doi:10.1016/j.enbuild.2009.12.005

surfaces are traditionally left uncovered (i.e. no internal plaster,paint, wallpaper etc.) and are therefore in direct contact with theroom air. More significantly, the hygrothermal properties of SREcan be adjusted through modification of the pore structure bychanging the particle size distribution (PSD) [2,3]. The modifica-tion of soil PSD is already practiced for enhancing density andstrength in earth building materials but, in the absence of reliableresearch data, is not yet commercially practiced to modify thermaland/or hygric properties. Based on prior experimental evidence [2],the authors hypothesise that the optimisation of SRE hygrothermalfunctional properties could be used to build walls that offerbuilding-integrated, passive air conditioning to the indoorenvironment.

The use of exposed thermal mass in buildings is well known andcommonly accounted for at the design stage using calculation toolsand building simulation. It is used chiefly to suppress indoor airtemperature variation and reduce peak cooling loads. Rammedearth walls are known to possess high thermal and hygric mass, thelatter being for passive suppression of indoor relative humidityvariation, air quality, condensation and mould growth. The focus ofthe analysis in this paper is to better understand and quantify howthe hygric mass of SRE can improve indoor environmentalconditions when hygrothermal behaviour is considered.

Other advanced building modelling tools such as ESP-r, EnergyPlus and TAS are restricted to heat storage and transfer and do notsimulate the transient coupled behaviour of simultaneous heat andmass transport/storage. However, following the leading researchconducted by Hens, Kunzel and Karagiozis, Pedersen et al., andothers, there are an increasing number of computer models thatwill model heat and mass transfer in building materials [4]. The

Fig. 1. Hygrothermal behaviour of external building fabric, e.g. a wall (from [22]).

Fig. 3. Schematic of the test room in the SRE building.

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852846

commercially available PC software tool WUFI Plus v1.2 waschosen for the analysis in this paper. The extensively validatedsoftware was developed by the Fraunhofer Institute for BuildingPhysics in Germany, for ‘‘. . .the calculation of transient internal

climatic conditions and heat losses by combination of energetic whole-

building simulation with hygrothermal component calculation’’ [5].While others have looked at whole building hygrothermalsimulation (e.g. [6–8]) the technique has never, to the authors’knowledge, been applied to SRE materials.

2. Test building and data collection

The SRE building, shown in Fig. 2, is located in a village near toMarket Harbrough in the county of Leicestershire, UK. It wasconstructed by Earth Structures (Europe) Ltd. [9] using well-established, patented SRE formwork and pneumatic compactiontechniques developed in Australia by the parent company EarthStructures Pty Ltd. The internal dimensions of the isolated testroom are given in Fig. 3. The walls of the room are of solid cavitywall construction with the inner and outer leaves made of 175 mmSRE and a 50 mm layer of extruded polystyrene insulation. The SRE

Fig. 2. The south facade of the test room in the SRE building.

was manufactured from a blend of MOT type 1 crushed ironstonequarry waste and grit sand with 7 wt% white Portland cementincorporating a non-pore blocking hydrophobic chemical admix-ture that retains the majority of vapour permeability whilstsignificantly reducing capillary potential (i.e. liquid water absorp-tion). The south wall contained the window (650 mm wide by960 mm high) and a floor-to-ceiling timber door. The ceilingconsisted of a layer of hardboard with 75 mm of low density glassfibre batt insulation, whilst the floor was a 125 mm thick concreteslab with no insulation or vapour barrier.

Tinytag1 sensors were used to record the temperature andrelative humidity of the air inside the room, and in the adjoiningbuilding, at 30 min intervals for the period 4/7/2008 to 1/4/2009.The data from the adjoining room was averaged for each hour andused as a boundary condition in the computer model. The ‘Ultra 2’sensors incorporate data logging in a small portable batteryoperated unit with a stated accuracy of �0.5 8C and �3% RH. Theywere positioned above the door and above head height on the backwall of the building, as shown in Fig. 3. In the computer simulation, airtemperature and relative humidity is represented by a single node inthe middle of the room while in reality spatial variations, due to bothtemperature stratification (air temperature increasing with height)and boundary layers (air temperature decreasing across a thin layerclose to the wall surfaces), complicate the measurement ofrepresentative values. Furthermore, sensors could not be placed inlocations were they would interfere with the use of the buildingwhich precluded lower wall positions and suspension from the ceiling

Table 1Hygrothermal properties of the SRE material.

Property Symbol Value Units

Dry density r 1900 kg/m3

Porosity n 0.295 m3/m3

Specific heat capacity cp 868.0 J/kg K

Dry state thermal conductivity l 0.643 W/m K

Vapour diffusion resistance m 14.34 –

Water content at 80% RH w80 61.5 kg/m3

Free water saturation wf 253.47 kg/m3

Moisture heat conductivity supplement b 4.39 %/% RH

Fig. 4. Measured moisture storage isotherms for the SRE material.

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852 847

in the centre of the room. Therefore, the sensors were calibrated in thelaboratory and the difference between air temperature measured inthe centre of the room and air temperature measured above 2 mheight when attached to the wall was found to be less than 5%difference. It was concluded that locating the sensor toward the top ofa wall was a good compromise when sensor placement is restricted,as was the case in this investigation.

The computer modelling period was 1/4/2008 to 1/4/2009 andhistorical weather data were obtained from a personal weatherstation, located approximately 7 km due south of the SRE building[10]. These data consisted of observations of temperature,pressure, relative humidity, wind speed, wind direction, rainfalland solar radiation, recorded at approximately five minute periods.They were averaged for each hour and then converted into a WUFIweather file format.

The weather file was used as the outer boundary condition forthe south, west and east walls. The solar radiation measurementswere applied directly to these walls. This consisted of only thedirect and diffuse radiation, since ground reflected radiation islargely insignificant compared to these terms and so is ignored bythe software. Direct and diffuse radiation were not separated ashigh humidity periods were of particular interest in this study andthose are typified by cloudy days such that the solar radiation isentirely diffuse and was assumed to be isotropic. The only windowwas on the south facade and therefore exposed to the total solarradiation during the peak sunlight hours.

3. Determining the functional properties of the SRE material

Before starting the hygrothermal analysis, a range of detailedmaterial functional properties must be known or measured. Whilethe database included with the software contains some commonbuilding materials, and properties can be found in the literature[11], there is little data available on earth materials. Also, previouswork by the authors has shown that the hygrothermal materialproperties, especially those related to moisture transport andstorage, can vary considerably between different SRE mix types [2]and so it was necessary to characterise the specific SRE materialused for the building. Samples were manufactured from the samematerials and mix design that was used in the construction [12].The ironstone waste (2/3 volume), sand (1/3 volume) and cement(7 wt%) were gravimetrically proportioned and a mixture of waterwith admixture (1.5% Rheomix 790) were added to achieve theoptimum moisture content (15%) which was determined experi-mentally using the Proctor light compaction method after BSBS1377-4:1990 [13]. Samples, comprising 1 l cylinders with105 mm diameter, 1/3 l discs with 105 mm diameter, and a300 mm square slab of depth 53 mm, were manufactured usingidentical compaction energies (�596 kJ/m3), achieved by repeateddropping of a known weight from a given height (dynamiccompaction or ramming). The 1 l cylinders were manufactured inthree layers while the slab and disc were rammed in a single layer.All were cured for a minimum of 28 days at 23 8C and 75% RH.Testing and measurement included specific thermal and hygricproperties (described below) and a summary of the averagedresults is included in Table 1.

3.1. Thermal properties

Thermal conductivity measurements were carried out on the300 mm � 300 mm � 53 mm SRE slab using the heat flow metermethod after ISO 8301:1991 [14] and using a Hilton B480 heat flowmeter apparatus. To determine the relationship between themoisture content of the SRE sample and its thermal conductivity,tests were carried out at a number of moisture contents inaccordance with ISO10051:1996 [15]. Similar tests have been

reported by the authors elsewhere [16]. The software requires a‘moisture-induced heat conductivity supplement’ that was calcu-lated to be 4.39 kg/kg, from the percentage increase in thermalconductivity per percentage increase in moisture content. Thespecific heat capacity of the SRE material was calculated to be868 J/kgK, using the mass-proportioned specific heat capacities ofits constituent parts and the equation given in [17].

3.2. Hygric properties

Moisture storage isotherms (equilibrium moisture content vsrelative humidity) were measured using the method described inBS EN ISO 12571:2000 [18]. The equilibrium moisture content wasmeasured at five points on each isotherm as well as at saturation.The resulting moisture storage isotherm is shown in Fig. 4. Theaverage moisture content at each relative humidity was entered asa table in the software.

Water vapour transmission was measured through the 1/3 l discSRE samples by applying a humidity gradient across the faces of thediscs using the wet cup method after BS EN ISO 12572:2001 [19]. Thewater vapour resistance factor, m, was calculated as the ratio of thevapour permeability of air to the vapour permeability of thematerial. The average value of m for the 4 test samples was 14.34.

The software will approximate the liquid transport coefficientfrom the water absorption coefficient and the moisture content at80% relative humidity. The former was measured by partialimmersion after BS EN ISO 15148:2002 [20] and latter wasestimated from the averaged moisture storage isotherm.

4. The hygrothermal model of the building

The building model consisted of a single zone, representing theroom, and a single attached zone adjacent to both the partition

Fig. 6. Test room: comparison of measured and simulated air temperature.

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852848

wall and ceiling, representing the SRE building. An optionalclimate, generated from the temperature and relative humiditymeasurements in the adjoining SRE building, was used to describethe climate of the attached zone and the external climate wasgenerated from the historical weather data. Ventilation rate wasestimated to be 1.5 air changes per hour and the walls were all setat 80% relative humidity at the start of the simulation period. Themodel was run from 1/4/2008 00:00 to 1/4/2009 00:00 in 1 h timesteps.

The building was ‘leaky’ by design, having a loosely fitted doorand a louvered window that could not be sealed. It was in anunsheltered position and the door and window were regularlyopened to aid ventilation. In the absence of a blower door airtightness test, the figure of 1.5ACH was chosen as it representedthe expected upper limit for a leaky, single story, dwelling. Toassess the choice, sensitivity analysis of the simulation was carriedout by varying the air change rate about the selected mean value.As could be anticipated, the magnitude of air change rate wasinversely related to the variance in diurnal air temperature swings.By direct comparison with the measured temperature data, theinitial estimate of 1.5ACH was found to be the most suitable valuefor simulating air infiltration in this test building. The additionalinfiltration that resulted from door and window opening was notincluded as it was unpredictable.

The temperature and relative humidity of the underside of thefloor slab were defined as an optional climate within the softwaresuch that relative humidity beneath the slab was constantthroughout the year and the temperature varied sinusoidallyabout a mean value, being highest in mid-summer. As the valuescould not be easily measured, the model was back-calibratedagainst the air temperature and humidity data recorded in theroom. For the relative humidity beneath the slab a value of 98% wasfound, which seemed reasonable for a slab on ground. Thetemperature profile beneath the slab was given a mean of 10 8C andan amplitude of �6 8C. This also seemed reasonable as the averagetemperature recorded in the room was 10 8C.

The resulting room air humidity and temperature profiles,generated by the model, compared well with those measured onsite as shown in Figs. 5 and 6. There are a number of factors whichare believed to contribute to the minor discrepancies, above andbeyond those attributable to the mechanics of the model and itsaccuracy settings (�0.5 8C and �0.5% RH). Effects due to changingpatterns of ventilation due to periodic daytime opening of thewindow and door by the building owner, as well as the relationshipbetween ventilation and wind speed/direction, were not considered.The contribution of the contents of the room (e.g. coats, horse saddles,boots etc.) to the thermal and hygric mass were not included. The

Fig. 5. Test room: comparison of measured and simulated air humidity.

measurements of air temperature and relative humidity taken in theroom, and the adjoining SRE building, may not have beenrepresentative of the air as a whole due to poor mixing (stratification)and boundary layer effects. The historical weather data may not havebeen entirely representative due to any local micro-climatephenomena. Taking all of these factor into consideration, the resultswere deemed to be acceptable and the model was used for furtherpredictive analysis.

5. Analysis of indoor moisture buffering

The moisture buffering of the room air by the SRE walls wasexplored, using the model, by changing the vapour resistance atthe surface of the walls to represent different coverings:plasterboard (gypsum board), painted plasterboard and metalfoil. These provided additional surface resistances described by avapour diffusion thickness of 0.1 m, 1 m and 100,000 m, respec-tively. The thermal properties of these walls was unchanged. Theresults in Fig. 7 show that increasing the vapour resistance of thewall surface by the application of wall coverings significantlyincreased the magnitude of the fluctuations in indoor relativehumidity.

The number of hours per day that a wall surface is above 80%relative humidity greatly increases the likelihood of mould growth[21]. The frequency histogram in Fig. 8 indicates the averagenumber of hours each day (i.e. the number of hours per yeardivided by 365 days) that the inside surface of the North wall iswithin given relative humidity ranges. The surface of the plain SRE

Fig. 7. Test room: the effect of wall coating on simulated air humidity.

Fig. 8. Test room: the effect of wall coating on the frequency of simulated humidity

at the inside surface of the north wall.Fig. 9. Unconditioned bedroom: simulated air humidity in summer.

Fig. 10. Unconditioned bedroom: simulated air humidity in winter.

Fig. 11. Unconditioned bedroom: simulated moisture fluxes.

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852 849

and plasterboard covered walls are in the higher ranges forsignificantly less time than the painted plasterboard and foilcovered walls, and it is expected that this would reduce thelikelihood of mould growth significantly. This is further supportedby observational evidence of the test room over a period of oneyear when no mould growth occurred on any of the indoor surfacesdespite the room having no mechanical ventilation.

It can be observed that the relative humidity at the wall surfaceis always very high for the painted plasterboard and the foilcovered walls. This may be due to the fact that (i) the building isunheated providing a high RH in the winter and (ii) the highthermal mass of the wall makes the surface temperature muchlower than the mean air temperature in the summer. It isimportant to note that the test building was unfurnished, and thatin a real occupied building the presence of furniture, carpet,curtains etc. can reduce the RH.

6. Analysis of operational energy saving potential

To consider the potential of SRE materials to improve thermalcomfort and reduce energy demand in occupied buildings, themodel was adapted to represent a bedroom with daily occupationunder three different cooling, heating, dehumidification andhumidification scenarios. The bedroom model was created fromthe model of the room by increasing its width to give a floor area of12 m2, reducing the ventilation to 0.5 air changes per hour,removing the external door, increasing the size of the south facingwindow and upgrading it to double glazing. The new window was2 m wide and had a U-value of 2.73 W/mK and a SHGC(hemispherical) of 0.6. The insulation above the ceiling wasincreased to 250 mm and a further 250 mm of expandedpolystyrene insulation was added beneath the floor slab. Theceiling and floor slab were both made vapour impermeable. Theroom was occupied by two adults from 22:00 h to 06:00 h the nextday providing a moisture load of 86 g/h during those 8 h. Resultsfor the SRE walls were compared with those covered inplasterboard, painted plasterboard and metal foil, as discussedin the following sub-sections.

6.1. Unconditioned scenario

The results were initially examined for the room with noheating, cooling, humidification or dehumidification. Figs. 9 and10 show the daily fluctuations in relative humidity for the first 7days of August 2008 and the first 7 days of January 2009. It can beseen that the SRE walls significantly reduce the periodic

fluctuations in relative humidity of the air in the room, duringboth these summer and winter periods. Fig. 11 shows the rate ofmoisture generated by the people in the room (kg/h) as well as themoisture flux between the room air and the walls (kg/h). It can beseen that the walls absorbed and desorbed moisture in harmonywith moisture generation such that the walls typically absorbed aproportion of the generated moisture during occupation andreleased some of that moisture while the room was unoccupied. It

Fig. 12. Unconditioned bedroom: simulated air temperature.

Fig. 14. Constantly conditioned bedroom: simulated latent heat of

dehumidification.

Fig. 15. Constantly conditioned bedroom: simulated latent heat of humidification.

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852850

should be noted that external weather conditions can modify thisbehaviour as seen on 5/8/2008 when desorption rates from thewall into the room air were significantly lower during a period oflower temperature and higher relative humidity. Increasing thediffusion resistance at the surface of the wall produced asignificant decrease in the rate of moisture transfer. FromFig. 12, it can be seen that this moisture buffering has very littleeffect on the temperature evolution of the inside air as thetemperature profiles generally overlap.

6.2. Constantly conditioned scenario

As living spaces are usually conditioned to improve the thermalcomfort of the occupants, the models were re-run with the innerclimate carefully controlled to give constant year-round designconditions of 18–20 8C and 40–60% relative humidity. Oversizedheating, cooling, humidification and dehumidification plant werespecified so that equipment limitations would not be a factor in theanalysis. The moisture flux between the walls and the room isshown in Fig. 13 where the extent to which increased diffusionresistance of the walls reduced the overall moisture bufferingcapacity can be seen. By looking at the energy demand (latent heat,kW) of the dehumidification, shown in Fig. 14, it can be seen thatthe walls cannot effectively buffer the additional moistureproduced during occupation in the summer (cooling) and thedehumidification plant operates during high humidity periods.From Fig. 15 it can also be seen that periodic humidification of the

Fig. 13. Constantly conditioned bedroom: simulated moisture fluxes.

room also occurred outside of the occupied period in the winter(heating). The energy requirement for both humidification anddehumidification increased significantly when the vapour diffu-sion resistance of the wall was increased. The annual energydemand for conditioning the space is shown in Table 2. While theheating and cooling loads are almost identical a significant savingwas made in the energy required for humidification anddehumidification when compared with the non-moisture buffer-ing case (metal foil covered walls).

6.3. Intermittently conditioned scenario

As it is common to only condition the indoor space periodically,rather than constantly, the same results were examined for the casewhere the temperature and relative humidity controls were only inplace between 06:00 and 08:00 h and then again between 16:00 and22:00 h, each day. From Fig. 16, it can be seen that significantamounts of moisture were desorbed from the walls at the start of themorning conditioning period (the spike). From Fig. 17, it can be seenthat this corresponds with an increased energy demand from thedehumidification equipment. In this way the moisture bufferingbehaviour of the walls increased the energy demand for dehumidi-fication as moisture absorbed during the unconditioned period wasdesorbed into the room air when the conditioning was switched on.From Table 3 it can be seen that again there was little differencebetween the annual energy demand for heating and cooling and thatthere was a significant reduction in the energy required for

Fig. 17. Intermittently conditioned bedroom: simulated latent heat of

dehumidification.

Table 2Energy use and savings for the constantly conditioned scenario.

T 18–20 RH 40–50 all day SRE Plasterboard Foil

Unpainted Painted

Heating power kWh 1313.7 1313.7 1313.8 1314.1

Cooling power kWh �135.0 �135.0 �135.0 �135.0

Latent heat humidification kWh �1.9 �7.0 �26.2 �35.0

Latent heat dehumidification kWh 41.2 58.7 86.2 89.5

Total humidifying and dehumidifying kWh 43.1 65.7 112.4 124.5

Total energy kWh 1491.8 1514.4 1561.2 1573.5

Saving (cooling) % 0.0 0.0 0.0 0.0

Saving (humidification) % 94.5 79.9 25.3 0.0

Saving (dehumidification) % 54.0 34.4 3.6 0.0

Saving (humidifying and dehumidifying) % 65.4 47.2 9.7 0.0

Saving (heating) % 0.0 0.0 0.0 0.0

Saving (total) % 5.2 3.8 0.8 0.0

Fig. 16. Intermittently conditioned bedroom: simulated moisture fluxes.

Table 3Energy use and savings for the intermittently conditioned scenario.

T 18–20 RH 40–50; 06:00–08:00 16:00–22:00 h SRE Plasterboard Foil

Unpainted Painted

Heating power kWh 1060.6 1060.8 1061.0 1061.2

Cooling power kWh �89.9 �90.0 �90.0 �90.0

Latent heat humidification kWh �1.3 �4.6 �16.5 �22.3

Latent heat dehumidification kWh 23.3 14.0 19.0 22.0

Total humidifying and dehumidifying kWh 24.6 18.6 35.5 44.3

Total energy kWh 1175.2 1169.4 1186.5 1195.4

Saving (cooling) % 0.1 0.0 0.0 0.0

Saving (humidification) % 94.1 79.3 25.8 0.0

Saving (dehumidification) % �5.8 36.3 13.7 0.0

Saving (humidifying and dehumidifying) % 44.4 57.9 19.8 0.0

Saving (heating) % 0.1 0.0 0.0 0.0

Saving (total) % 1.7 2.2 0.7 0.0

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852 851

humidification. However the energy requirement for dehumidifica-tion is higher for the unmodified SRE walls when compared with themetal foil covered walls. Interestingly, the plaster board walls showa significant reduction in dehumidification energy and performslightly better overall. This suggests that the hygrothermalproperties of the plaster board are more optimised than SRE, forthe given scenario. Therefore, it may be possible to specify thehygrothermal properties of exposed construction materials by usingpredictive modelling techniques at the design stage. The SRE wallsstill show a reduction in energy, compared with the metal foilcovered walls, when humidification and dehumidification areconsidered together.

7. Conclusions

The indoor climate of a room within a building, constructedwith SRE walls, was modelled using WUFI Plus v1.2 buildingsimulation software. The hygrothermal material properties of theSRE building material were characterised by experimental testing.The simulated temperature and relative humidity profiles of thetest room indoor air were successfully validated against thoserecorded on site.

The simulated results showed that the SRE walls significantlyreduced the amplitude of relative humidity fluctuations duringboth the summer and winter, when compared to walls covered

D. Allinson, M. Hall / Energy and Buildings 42 (2010) 845–852852

with materials that increased surface diffusion resistance (e.g.unpainted plasterboard, painted plaster board, and aluminiumfoil). The SRE walls also reduced the frequency of high humidityperiods at the wall surface and were therefore judged to be highlybeneficial in reducing mould growth in buildings.

The results of the model, when modified to represent anoccupied space, showed that the SRE walls were responsive toperiods of internal moisture gain, absorbing moisture for laterrelease. When the temperature and relative humidity of thespace were controlled constantly, this provided a significantreduction in humidification and dehumidification energy de-mand when compared to the vapour impermeable wall, thoughheating and cooling energy were not significantly different. Whenthe temperature and relative humidity of the space werecontrolled intermittently, there was still an overall reductionin humidification and dehumidification demand, but dehumidi-fication demand for the plain SRE walls was higher than theimpermeable case. This was because the walls absorbedsignificant amounts of water vapour while the plant wasinoperative and that moisture then had to be removed whenthe dehumidification restarted.

It is evident that materials that absorb moisture can bufferrelative humidity changes (hygric mass) in the same way thatmaterials that absorb heat buffer temperature changes (thermalmass). Covering materials with less permeable layers (e.g. paints)dramatically reduces that moisture buffering behaviour. SREmaterials are good moisture buffering materials and are normallyleft uncovered inside buildings and are therefore ideally suited topassive humidity control. It is concluded that SRE walls have thepotential to improve thermal comfort, improve indoor air qualityand reduce the energy demand in buildings but care should betaken with the system design including conditioning strategy andventilation.

Future work should focus on how SRE materials might beintelligently optimised for moisture buffering to suit the givenscenario, and how improvements in thermal comfort due to SREwalls may allow a relaxation of design conditions inside ofbuildings and the possibility to further reduce energy.

Acknowledgements

The authors wish to acknowledge the support of the Engineer-ing and Physical Sciences Research Council, Mr. Bill Swaney ofEarth Structures (Europe) Ltd. for giving access to, and technical

information on, the SRE test building, and Simon Smith atwww.NorthantsWeather.com for the use of weather data.

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[18] British Standards Institute, BS EN ISO 12571:2000 Hygrothermal performance ofbuilding materials and products, Determination of hygroscopic properties, 2000.

[19] British Standards Institute, BS EN ISO 12572:2001 Hygrothermal performance ofbuilding materials and products, Determination of water vapour transmissionproperties, 2001.

[20] British Standards Institute, BS EN ISO 15148:2002 Hygrothermal performance ofbuilding materials and products, Determination of water absorption coefficientby partial immersion, 2002.

[21] Chartered Institute of Building Service Engineers, CIBSE Guide A: Design Data:Chartered Institute of Building Service Engineers, 2006.

[22] ASHRAE, Handbook—Fundamentals, 2009.