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HOMMA, Yoko

MOROOKA, Toshiro

NORIMOTO, Misato

Kyoto University Research Information Repository

Title<Preliminary>The Influence of the Temperature Change Rateon the Humidity Control Effect of WoodAuthor(s)HOMMA, Yoko; MOROOKA, Toshiro; NORIMOTO, MisatoCitationWood research : bulletin of the Wood Research Institute KyotoUniversity (2000), 87: 32-33Issue Date2000-09-30URL http://hdl.handle.net/2433/53148RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityPreliminaryThe Influence of the Temperature Change Rateon the Humidity Control Effect of WOOd*lYoko HOMMA*2, Toshiro MORooKA*2 and Misato NORIMOTO*2(Received 31 May, 2000)Keywords: B-value, C~value, step temperature, humidity contn)l effectIntroduction Results and Discussion0.005Fig. 1. The relationship between the C and B values forsugi wood.1.00.4 0.6 0.8C-value0.2-0.020-0.0250.0Q)-0.005~......--tCI:$;>-0.010I~-0.015 • •0.000When the sinusoidal temperature changes are applied,sinusoidal relative humidity curves result. In this case,the ratio of humidity amplitude in the box lined with amaterial to that in the empty box can be introduced as anindex to estimate humidity control effect of materials.This index, called the C-value, exhibits directly how theextent of the humidity change is reduced by the presence ofmaterials in the box. Fig. I shows relationship betweenthe C and B values for sugi wood obtained in all theconditions employed. Since the C-value was closelyrelated to the B-value, we adopted in this report the C-value instead of B as a measure of humidity control effect.In addition to the C value, the shift of the time atmaximum absolute humidity from the time at maximumtemperature can also be used as an index of the humiditycontrol effect. The r which was defined as this time shiftdivided by period was found to be proportional to C.Both C and r values will depend on temperature changerate as in the B-value. When the temperature changessinusoidally, the rate of the temperature change in thechamber is made by changing (temperature) amplitude atthe constant period or by changing period at the constantamplitude. In the range of period and amplitudeexamined, both the C and r values were found to changeMaterials used are sugi flat grain wood with Icm thick.Porous ceramics wall materials were also used forcomparison. After a steel box with a base 20X 20 cm anda height of 25 cm was lined with above materials, it wassealed carefully to prevent air leakage. The extent oflined area is expressed as the ratio of lined area A (m2) tothe volume of steel box V(m 3),A/V(m- 1). Seven A/V'sfrom 0.25 to 3.0 were adopted in our experiment. Toobtain the Band C-values, temperature and relative·humidity inside the box were measured with time in theclimatic chamber whose temperatures vary sinusoidallyaround 25°C at four amplitudes of 2.5 to lOoC, each ofwhich has four wave periods of6 to 48 hrs. To predict theC-value, we also measured absolute humidity variation byapplying four step temperatures from 5 to 20°C around15°C.Materials and Methods*1 A part of this work was presented at the 50th AnnualMeeting of the Japan Wood Research Society in Kyoto.*2 Laboratory of Property Enhancement.In a treasury of museums or galleries, huge amount ofelectric power is consumed to keep its temperature andhumidity constant. It seems, however, possible to reduceelectric power since almost all the walls inside standardtreasuries are usually lined with wood which hasremarkable humidity control effect; To estimate thehumidity control effect of wood and other materials, it isneceSsary first to establish a useful index for this effect.The B-value I) is known to be an effective measure for thispurpose. It is obtained from the relationship between thelogarithm of relative humidity and temperature measuredin a closed steel box lined with a wall material under thespecified variation of ambient temperature. However,this index is known to be different at different rates oftemperature change even when lined area in the box is thesame.In the present paper, we introduce first an index Cwhich is simpler than B, and then discuss how the C-valueis affected by the temperature change rates. We furtherpropose a method to predict the C-value withoutinformation on temperature change rates.- 32-HOMMA et al.: The Influence of the Temperature Change Rate on the Humidity Control Effect of Wood1.00.8 IIA/V=1.0Q) 0.6 g;:l•~ ~>I 0.4U I0.2 II0.00 10 20 30 40 50Period (hr)Fig. 2. The change in C value for sugi wood with periodmeasured at A/V= 1 at different temperatureamplitude. Temperature amplitude: 2.SoC(0), SoC (0), 7.SoC (.6.), WOC (0). Cal-culated value (.).markedly in the latter. For example for the specimen withA/V= I, the C value fell from 0.6 to 0.2 as the periodincreased from 6 hr to 48 hr. In the former, on the otherhand, both the C ilnd r values remained almost constantirrespective of the temperature amplitude.Based on these findings, an attempt was made to predictC and r by assuming following relation between tem-perature and absolute humidity. (I) When the steptemperature eo is applied at a time t=O, the correspondingabsolute humidity h(t) at a time t (t>O) is proportional tothe absolute humidity lJI"(t) obtained at a step temperatureof IC (i.e. h(t) = eo lJI"(t)). (2) h(t) at any time t, due to theprevious application of step temperatures de in succession,is the sum of the dh which would arise at that time if eachde had been applied independently. From these assump-tions, we may express h(t) at the time t as follows:JI de(u)h(t)= olJl"(t-u)~du.From this equation, when the temperature e(t) is subject tosinusoidal wave, we can easily obtain h(t) from which bothC and r are derived. Fig. 2 shows the change in C valuefor sugi wood with period measured at A/V= I attemperature amplitude of 2.S to WOC. Calculated valuesare also plotted in the figure. As for the measured Cvalues, they decreased markedly with increasing periods,though they remained almost unchanged when comparedat the same period. As for the calculated values, theywere in good agreement with measured ones, except for theresult at 6 hr. Similar results were obtained for othercases with different A/ V. We further observed that themeasured r values at various temperature change rateswere corresponded well with calculated ones within therange of A/V examined. From these consideration, wemay conclude that the C, r, and thus B at anytemperature change rates can be predicted from simplestep ternperature experimen ts.References1) H. MAKI, M. NORIMOTO and T. AOKI: Wood Industry, 36, 476(1981).- 33-

<Preliminary>The Influence of the Temperature Change Rate on the Humidity Control Effect of Wood

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<Preliminary>The Influence of the Temperature Change Rate on the Humidity Control Effect of Wood

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