Loading strategy for measuring relative humidity and temperature gradient for winter season in ventilated classrooms

Transcription

1 Loadng strategy for measurng relatve humdty and temperature gradent for wnter season n ventlated classrooms drd. ng. SEBASTIAN DORHOI, prof. dr. ng. IOAN BORZA, conf. dr. ng. MIHAI CINCA Department of Buldng Servces Unversty POLITEHNICA Tmşoara Street Traan Lalescu, nr. 2A ROUMANIA, TIMIŞOARA sebastan.dorho@ct.upt.ro; oan.borza@ct.upt.ro; mha.cnca@ct.upt.ro ct.upt.ro Abstract: - The loadng strategy presented n the paper wants to present the relatve humdty and ar gradent temperature for classrooms smulated n laboratory condtons. The study wll take place only for wnter season; the ar humdty wll be ncreased wth an electrcal steam humdfer and the ar temperature by the heatng col of the ar handlng unt. The suppled ar s provded wth an ar handlng and swrl dffusers wth adjustable blades for a better dstrbuton n the room. For exhaust s used one ventlator, matchng the suppled ar flow by the ar handlng unt. The thermal comfort sensaton wll be evaluated by questonnares flled out by occupants for wnter tme n sessons of three hours and analytc calculaton based on SR EN ISO 7730 (2006). Key-Words: - relatve humdty, ar gradent temperature, mxng ventlaton, operatve temperature, supply, exhaust, velocty 1 Introducton The ndoor ar qualty n classrooms t s an mportant factor for the thermal sensaton and acceptablty for the occupants. The parameters that defne the ndoor ar qualty are: dry ar temperature, ar velocty n the room, turbulence ntensty, relatve humdty, the mean ar temperature, the occupant actvty, and the cloth thermal resstance. Also the ndoor parameter depends on the exteror parameters as: dry ar temperature, outdoor humdty, atmospherc pressure and the velocty of the wnd. It s very hard to defne a general ndoor envronment because the judges are dfferent from people to people and as we know, not everybody perceve these parameters the same way. The ASHRAE standard 55 (2003) [1], CR 1752 (1998) [2] and SR EN ISO 7730 (2006) [3] ndcated a range for the comfort zone where the occupant s consdered as a passve subject of thermal exchange. The predcted mean vote can be calculated, but also made wth test fll by the occupants regardng the general thermal comfort. The occuped zone s n the centre of the room. For sedentary occupants the measurement sensors are on three levels: knees 0,1 meter; abdomen 0,6 meter and head 1,1 meter. Am of the paper s the evaluaton of thermal comfort condton n unversty classrooms for wnter season for heatng wth statc radators, mxng ventlaton wth recrculaton and wth 100% fresh ar. The temperature and relatve humdty wll be set for smulatng dfferent ambent condtons whch wll be measured by sensors and evaluated by occupants wth questonnares. 2 Lterature revew The expermental measurement n unversty classrooms (3 classrooms) wth ventlaton systems was reported n research work [5] where the thermalhygrometry comfort where the data measurements where made n 2, 3, 4 ponts dependng on the classroom sze. The nsde parameters measured were: dry bulb temperature, wet bulb temperature, ar velocty, globe thermometer temperature, atmospherc pressure, ar temperature at the neck (1,10 m from floor), floor temperature, radant asymmetrc temperature, carbon doxde concentraton CO 2. The outsde parameters were: ar temperature, relatve humdty, atmospherc pressure and carbon doxde concentraton CO 2. Wth these measured parameters mentoned were calculated : relatve humdty, mean radant temperature, operatve temperature, PMV(predcted mean vote), PPD(Predcted Percentage of Dssatsfed), turbulence ntensty, PPD for thermal gradent, PPD for floor temperature, PPD for radant asymmetry and PPD for current of ar. The occupants from classrooms were men and women. The adaptaton from the occupants was behavoural, physologcal and psychologcal. Also s a dfference between men and women percepton regardng the thermal comfort, because women have a lower metabolsm and the hotter envronment s accept better lke men. Envronment was analyzed by these crtera: ISSN: / ISSN: ISBN:

2 Thermal sensaton; Comfort; Thermal preference; Acceptablty; Tolerablty; Indvdual mcroclmate control; Satsfacton of ndvdual control; Classrooms wthout wndows produce also dssatsfacton. Another envronmental problem was the low ar movement and the occupant related a dssatsfacton regardng the vertcal gradent. Also f the ar velocty n the room s to hgh the percent of dssatsfacton ncreases presented n fgure % r.h. reduced the number of complans of dryness of the skn and eyes compared to 20-30%. Fg. 3 Sensaton of ar temperature for low humdty (15%) and normal humdty(43%) Fg.1: Dssatsfacton caused by room velocty In the fgure 2 s presented the evoluton between dry bulb temperature and relatve humdty from classrooms for average values measured [5] : Dry bulb temperature Classroom 1 Classroom 2 Classroom Relatve humdty Fg.2: evoluton between dry bulb temperature and relatve humdty From research work n offces [8] low relatve humdty lke 15% produce uncomfortably dry ar and symptoms of the face and mucous membranes compared to 43% r.h. The humdfcaton of dry ar reduces the number of these symptoms, and reduces dscomfort arsng from low ar humdty. In fgure 3,4,5 are presented the effect of temperature, dryness of ar and draught for 39 offce workers. Also the relatve humdty should not exceed 60% n order to avod bactera growth n ventlaton ducts. Renkanen et al [9] found that humdfcaton of Fg. 4 Sensaton of ar dryness for low humdty (15%) and normal humdty(43%) Fg. 5 Sensaton of draught for low humdty(15%) and normal humdty(43%) 3 Problem Formulaton The space has 47 m 2 and a volume of 178 m 3 and the number of occupants s 12. The fresh ar supply must be n accordance wth CR 1752 (1998) for occupancy of 0.5 persons/m 2 s 6 l/s m 2. We had half of the occupancy number recommended by CR 1752 and wth nterpolaton t result 3 l/sxm 2, and n the room the smoke was not allowed: 3 l m q fa = 47 3 = 141 = 507,6 (1) s h ISSN: / ISSN: ISBN:

3 The space s placed at the ground level surrounded by other classrooms wtch are heated. The heat demands of the room for wnter s 2.65 kw calculated for Tmşoara at -15 C. For the study the mxed ventlaton ar flow used s q SUP =1350 m 3 /h correspondng to 7.5 h -1 necessary for heatng up the room. For settng the mentoned ar flow of the ar handlng unt t wll be use an adjustable frequency drve unt. The suppled ar flow can be calculated wth the formula: Q qsup = 3600 (2) ρ c t t p ( ) SUP where: q SUP - Flow rate of supply ar [m 3 /h]; Q - Heat demand [kw]; ρ - Densty of ar [kg/m 3 ]; t SUP - Supply temperature [ C]; - Room temperature [ C]; t The fresh ar quantty must be provded for the occupants comfort and t s recommended that the rest of ar to be recrculaton for savng heatng energy. The draught n the room s determned by the average velocty v a (x,t) at a x poston and t tme and the turbulence ntensty (Tu). The nstantaneous velocty at a moment s composed of a mean velocty v and fluctuatng component, v' : 0,62 DR = ( 34 t ) ( va 0,05) ( 0,37 va Tu + 3,14 ) (3) v a = v + v' (4) The temperature dstrbuton n the room was studed by Cox and Elkhuzen [6] whch defned the temperature effectvty dependng on the temperature of exhaust, supply and at a pont x n the room as: ( tex tsup ) ET = (5) ( t t ) x sup t ex Exhaust temperature [ºC]; t sup Supply temperature [ºC]; t x Temperature at x pont [ºC]; The vertcal temperature gradent s determned by the heat load n the room, the ar change rate and the dffuson flow. Fgures 6 and 7 shows the classroom n 3D vew and top vew wth the ventlaton system where the fresh and recrculated ar s treated by the ar handlng unt and t s suppled by 4 celng dffusers wth plenum box n the room. The dffusers are swrl type permttng the possblty to have horzontal and vertcal jet patterns. The exhaust s made by a roof fan mounted outsde. On the exhaust ppe are mounted two duct grlls. Fg.6 3D vew of the ventlaton system for the laboratory (exhaust and supply) Fg.7 Top vew of the ventlaton system for the laboratory (exhaust and supply) Legend: 1- Ar handlng unt wth fresh and recrculated ar, q supply =1350m 3 /h; 2- Exhaust roof ventlator, q exhaust =1350m 3 /h; 3- Electrode steam humdfer, steam output q steam =10kg/h; 4- Damper wth flow meter for supply; 5- Damper wth flow meter for exhaust; 6- Supply swrl dffuser wth adjustable blades for changng ar pattern; 7- exhaust duct grlle The operatve temperature shall apply to a locaton n the centre of the room at a heght of 0,6 m above the floor. ISSN: / ISSN: ISBN:

4 The mean room temperature specfed by CR 1752 for classrooms s 22±3 C, but ASHRAE (1992) lmt the mnmum operatve temperature at 18 C. t o t 10 va + t = v a mr ; (6) Where: t o Operatve temperature [ºC]; t Indoor temperature [ºC]; v a Ambent velocty [m/s]; The questonnares for the occupants (men and women) have contaned the followng questons regardng the thermal comfort sensaton: - Occupant clothng type(clothng ensembles) - Occupant actvty level - Predcted mean vote(pmv) - The occupant locaton n the classroom The calculaton of PMV(predcted mean vote) wll be made by fllng the measured values from the classroom needed to be substtuted n the analytc formula and after compared wth the results from the questonnares. 4 Loadng strategy The study was conducted durng the heatng perod(january-aprl) n a laboratory from the unversty wth controlled ndoor clmate. The ndoor temperature used for the measurements wll between 20 C and 28 C and the ndoor relatve humdty wll be set from 20% to 50% wth a humdty sensor whch commands the steam humdfer. For every temperature step wll be four measurement wth relatve humdty ncreased wth 10%. These measurements wll be made on recrculated ar and 100% fresh ar. The duraton of a measurement t s from 1 to 3 hours. Also the temperature of the walls, celng and floor wll be measured wth an nfrared camera for verfyng the values measured by the black globethermometer. The steam humdfer maxmum steam output s 10 kg/h whch s set by the desred ndoor relatve humdty. The ar temperature and relatve humdty n the room wll be measured n the room n ffteen ponts dsposed at three levels. The mean radant temperature and the velocty wll be measured n the mddle of the room at 0,6 m. The measurng ponts wll be chose consderng the poston of students, the poston of cold and warm surfaces (.e. wndows - mnmum 1 meter dstance from them [7], laboratory equpment). The measurement wll be made for mxng ventlaton wth recrculated ar, wth 100% fresh ar and heatng provded by statc radators wthout ventlaton. The fresh ar and recrculated s heated up tll the desred supply ar temperature wth a heatng col placed n the ar handlng unt. The hot water whch pass through the col s provded by the central heatng system of the school and the hot water temperature s set by a 3 way valve wth servomotor whch mxes the water for the desred temperature. Ths temperature s nfluenced by the exteror parameters lke dry bulb temperature and relatve humdty of the ar whch are also measured. The ndoor measured values wll be: - dry bulb temperature [ C]; - relatve humdty [%]; - ar velocty n the classroom [m/s]; - mean radant temperature [ C]; - celng, wall and floor temperature - CO 2 concentraton The outdoor measured values wll be: - dry bulb temperature [ C]; - relatve humdty [%]; 5 Concluson The measurng strategy n ths paper respects the evaluaton procedure of thermal moderate envronments currently n use. The questonnares wll be flled by the occupants and compared wth the ones from expermental measurements to gve an mage about the value of PMV. The dmenson of the laboratory smulates at small scale a classroom from our unversty. The classrooms from the unversty have only statc radators wthout ventlaton that s why t wll be made a comparson between the two systems and evaluated by the occupants. Also very mportant s the vertcal gradent because n research work [5] the ar velocty n the classroom was to low and ths problem occurred. Because n the classroom are measurng ponts on dfferent heghts t can be measure the vertcal gradent and calculate the effectveness of the ventlaton system. References: [1] Ashrae 55 Standard, Thermal Envronmental Condtons for Human Occupancy, Thrd Publc Revew, 2003, Atlanta, Amercan Socety of Heatng, Refrgeratng, and Arcondtonng Engneers,Inc., USA. [2] CR 1752 Standard, Ventlaton for buldngs, Desgn crtera for the ndoor envronment, 1998, European Commttee for Standardzaton ISSN: / ISSN: ISBN:

5 [3] SR EN ISO 7730 Standard, Ergonomcs of the thermal envronment - Analytcal determnaton and nterpretaton of thermal comfort usng calculaton of the PMV and PPD ndces and local thermal comfort crtera, 2006, European Commttee for Standardzaton [4] ISO 7726 Standard, Ergonomcs of the thermal envronment, Instruments for measurng physcal quanttes, 2001, European Commttee for Standardzaton [5] C. Buratt, P. Rccard, Thermal hygrometry comfort n unversty classrooms: Expermental results n north and central Italy unverstes conducted wth new methodologes based on the adaptve model, Research n Buldng Physcs and Buldng Engneerng Fazo, Ge, RAO & Desmaras (eds), 2006 Taylor & Francs Group, London, ISBN [6] Cox, C.J.W. and Elkhuzen, P.A Dsplacement ventlaton system n an offce, TVVL Magazne, 9, pp [7] CEN/TC 156 pren 13779, Ventlaton for nonresdental buldngs Performance requrements for ventlaton and room-condtonng systems, 2006 [8] Desree Gavhed, Lena Klasson, Percved problems and dscomfort at low ar humdty among offce workers,envronmental Ergonomcs, The Ergonomcs of Human Comfort, Health and Performance n the Thermal Envronment, Vol. 3, pp , 2005 [9] Renkanen, L.M., Jaakkola, J.J. and Seppanen, O The effect of ar humdfcaton on symptoms and percepton of ndoor ar qualty n offce workers: a sx-perod cross-over tral. Arch. Envron. Health, 47: ISSN: / ISSN: ISBN: