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Evapotranspiration from Spider and Jade structural damage, but there are cur- rently no building humidity lower limits. Plants Can Improve Relative Humidity in an Therefore, many commercial and most residential buildings do not control hu- Interior Environment midities in the low humidity range (<40% RH) during heating season. 1,3 1,4 2,5 Low humidities can have adverse Eric W. Kerschen , Caleb Garten , Kimberly A. Williams , health consequences on building occu- and Melanie M. Derby1,6,7 pants (Sterling et al., 1985), such as increased eye irritation (McCulley et al., 2006) and skin dryness (Sunwoo et al., ADDITIONAL INDEX WORDS. Chlorophytum, Crassula, interiorscape, passive 2006). The survival of many pathogens humidification, transpiration and their transmission are sensitive to SUMMARY. Plants in the interiorscape have many documented benefits, but their humidity levels, with increased trans- potential for use in conjunction with mechanical heating, ventilation, and air mission at lower humidities (Lowen conditioning (HVAC) systems to humidify dry indoor environments requires more et al., 2007; Shaman and Kohn, 2009; study. In this research, evaporation and evapotranspiration rates for a root medium Yang and Marr, 2011). control, variegated spider plants (Chlorophytum comosum), and green jade plants Due to the impact of low humid- (Crassula argentea) were measured over 24 hours at 25% and 60% relative humidity ity on building occupants and the (RH) and 20 C to generate data for calculation of the leaf surface area and number desire to reduce building energy con- of plants necessary to influence indoor humidity levels. Evaporation and evapo- transpiration rates were higher for all cases at 25% RH compared with 60% RH. At sumption, passive or low-energy humid- 25% RH during lighted periods, evapotranspiration rates were 15 g hL1 for spider ification approaches are of increasing plants and 8 g hL1 for jade plants. Spider plants transpired during lighted periods interest. Plants can influence the humid- due to their C3 photosynthetic pathway, whereas jade plants had greater evapo- ity of an interior environment through transpiration rates during dark periods—about 11 g hL1—due to their crassulacean transpiration (water movement through acid metabolism (CAM) photosynthetic pathway. A combination of plants with a plant and water vapor emission from different photosynthetic pathways (i.e., C3 and CAM combination) could con- foliage) and evaporation (conversion tribute to greater consistency between evapotranspiration rates from day to night of water to vapor at the surface of root for humidification of interior spaces. Using the measured data, calculations medium), the combination of which indicated that 32,300 cm2 total spider plant leaf surface area, which is 25 spider plants in 4-inch-diameter pots or fewer, larger plants, could increase the humidity of is evapotranspiration. Many low-light an interior bedroom from 20% RH to a more comfortable 30% RH under bright plant species can grow indoors under interior light conditions. existing lighting conditions (DelPrince, 2013; Manaker, 1997; Pennisi and van Iersel, 2012), reducing or eliminating roviding a comfortable and healthy of residential spaces consumes nearly the need for additional energy for environment for building occu- 50% of that energy (Energy Informa- lighting. Light can also be supplemen- pants is critical, as people spend tion Administration, 2009). During P ted in interior environments to opti- more than 90% of their time indoors heating season, HVAC systems use mize plant longevity (DelPrince, 2013). (Moschandreas, 1981). In the United energy to increase indoor air tempera- Researchers have examined the States, buildings consume 40% of pri- ture while subsequently reducing RH. humidification effects of plants on mary energy annually, and conditioning Without supplemental humidification, indoor office environments (Lohr, indoor RH may be as low as 10% in 1992; Lohr and Pearson-Mims, 1996; This manuscript has been assigned Contribution no. cold climates (Kalamees et al., 2009; Wolverton and Wolverton, 1996; 16-373-J from the Kansas Agricultural Experiment € Station (KAES). Nordstrom et al., 1994; Reinikainen Wood et al., 2006). Lohr (1992) stud- We gratefully acknowledge Leigh Murray and Ye Li at et al., 1991). Acceptable building hu- iedtheeffectsonplantsintwooffices the Kansas State University Statistics Consulting Lab midity levels are governed by American and Steven Eckels and the Institute for Environmental with room temperatures of 22 C: one Research for the use of the facilities. Society of Heating, Refrigerating, and office contained a variety of plants, in- Mention of a trademark, proprietary product, or Air-Conditioning Engineers (ASHRAE) cluding varieties of Peperomia (Pip- vendor does not constitute a guarantee or warranty Standard 55; upper limits on humid- eraceae family) and chinese evergreen of the product by Kansas State University or KAES and does not imply it approval to the exclusion of ity are imposed to prevent mold and (Aglaonema sp.), and one control office other products or vendors that may also be suitable. 1Department of Mechanical and Nuclear Engineer- ing, Kansas State University, 3002 Rathbone Hall, Units Manhattan, KS 66506 To convert U.S. to To convert SI to 2Department of Horticulture and Natural Resources, SI, multiply by U.S. unit SI unit U.S., multiply by Kansas State University, 2021 Throckmorton Plant Sciences Center, Manhattan, KS 66506 0.3048 ft m 3.2808 3 3 3Undergraduate research assistant. 0.0283 ft m 35.3147 2.54 inch(es) cm 0.3937 4 Graduate research assistant. 6.4516 inch2 cm2 0.1550 5Professor. 16.3871 inch3 cm3 0.0610 6Assistant professor. 28.3495 oz g 0.0353 33.9057 oz/yard2 g m–2 0.0295 7 Corresponding author. E-mail: [email protected]. 6.8948 psi kPa 0.1450 doi: 10.21273/HORTTECH03473-16 ( F – 32) O 1.8 F C( C · 1.8) + 32
• December 2016 26(6) 803 RESEARCH REPORTS contained no plants. The plants in- low-humified Canadian sphagnum small holes for air flow. Air velocity at creasedofficehumidityto30%com- peatmoss: 30% perlite [v/v (Sun Gro thewallvariedfrom0.5to1ft/s,with pared with 25% RH in the control Horticulture, Agawam, MA)] initially an average value of 0.73 ft/s. Air veloc- office. Further work examined the ef- moistened to match moisture levels in ity directly above the test objects was fects of potted plants in a computer the pots containing plants. Variegated found to be 0 ft/s; therefore, the test laboratory; humidity was not signifi- spider plant, a member of the Aspar- objects were in quiescent conditions. cantly altered, but particulate matter agaceae family with a C3 photosyn- TEST STAND. The test stand con- accumulation decreased by as much as thetic pathway, and green jade, a sisted of a precision scale, soil mois- 20% in the presence of plants (Lohr and member of the Crassulaceae family ture probes, temperature probes, and Pearson-Mims, 1996). In a residential with a CAM photosynthetic pathway, a hygrometer for data collection (Fig. study, the presence of plants in a home were selected because they are com- 1) as well as fluorescent bulbs as the increased RH by more than 10% and monly found in interiorscapes and light source in the dark environmen- decreased airborne microbes by more because they have different photosyn- tal chamber. Experiments were con- than 30% (Wolverton and Wolverton, thetic pathways. The spider and jade ducted for groups of five test objects 1996). Peace lily (Spathiphyllum ‘Sweet plants were transplanted into round, (i.e., pots of root medium, spider Chico’) and dracaena (Dracaena ‘Janet green pots [4 inch diameter, 370 cm3 plants, or jade plants). An electronic, Craig’) plants were field-tested in Aus- volume (Landmark Plastic Corp., precision scale [±0.1 g accuracy (GP- tralian offices during the heating season Akron, OH)], and filled with the same 30KS; A&D, Tokyo, Japan)] recorded (Wood et al., 2006). The plants did not root medium as the control pots. Re- total weight of the five objects. All significantly influence room humidity sults obtained represented moisture loss weight loss was assumed to be water but they reduced total volatile organic from five pots for each of the three and was used to determine evaporation compounds levels. treatments at two RH levels. Each treat- or evapotranspiration rate. Root me- Plant-based systems show poten- ment combination was replicated twice dium moisture content was controlled tial for humidifying, removing indoor at a constant temperature of 20 C. and monitored. Each pot contained pollutants, and providing psycholog- E NVIRONMENTAL CHAMBER. a soil moisture probe (Decagon ical benefits (Dravigne et al., 2008; Runs were conducted in a 570-ft3 5TM Soil Moisture and Temperature Fjeld, 2000; Laviana et al., 1983). environmental chamber at the Insti- Probes; Decagon Devices, Pullman, The majority of previous plant-based tute for Environmental Research at WA). Probes were calibrated according humidification research was field tests Kansas State University, Manhattan. to the Decagon manual (Cobos and conducted in offices or residences. Air at the desired temperature and Chambers, 2010): a known amount of This study quantifies evapotranspira- moisture content flowed into the root medium was completely dried, tion rates from two common indoor chamber via an air system supply on and soil moisture probe output was plant species with different photosyn- one side of the chamber and a return recorded. Known volumes of water thetic pathways in a controlled environ- on the opposite side (Fig. 1). With were also added to obtain a calibration, mental chamber. The research objectives the exception of these air ducts, the include 1) quantification of evapora- chamber was completely sealed. To q =5:031 10 4x 0:0143 ½1 tion rates from a root medium, and verify that chamber conditions were evapotranspiration rates from varie- identical to set conditions, tempera- where q is the volumetric water con- gated spider plants and green jade ture and RH measurements were taken tent (cubic centimeters per cubic cen- plants, at two indoor humidity levels; 1.8 m from the test objects using timeter), and x is the raw output of 2) evaluating the impact of the diurnal thermocouple probes (TMQSS-125U- the sensor. The calibration was linear light cycle on transpiration for two 6; OMEGA Engineering, Stamford, with an R2 value of 0.997. Tempera- plant species with different photosyn- CT) and a digital humidity probe ture and RH were measured 8 inches thetic pathways; and 3) calculation of (PCMini52 Humidity/Temperature above the root medium surface using the plants’ potential impact on RH of Mini Probe; Michell Instruments, two temperature probes (TMQSS- a single interior bedroom, such as in Ely, England). Before each test, cham- 125U-6) and a hygrometer probe a skilled nursing facility (SNF). ber air pressure was also measured (General Eastern Optica Series Chilled Materials and methods using a handheld barometer (Druck Mirror Hygrometer; GE Measure- DPI 740; GE Measurement and ment and Control). TREATMENTS AND EXPERIMENTAL Control, Billerica, MA). Measured E XPERIMENTAL LIGHTING APPARATUS. A root medium and plants chamber pressure ranged from 97 to CONDITIONS. Plants of each species were tested in an environmental cham- 99 kPa. All sensors were monitored by were obtained from stock maintained ber to determine their evaporation and a computer located outside the envi- in the Kansas State University evapotranspiration rates. The six treat- ronmental chamber; computers and Throckmorton Plant Sciences Center ment combinations were 1) pots of investigators were not present in the greenhouses. The plants were accli- root medium with no plants (control), environmental chamber during test- mated indoors for 2 months to adjust 2) pots of root medium with varie- ing. Because air velocity impacts mass to prescribed lighting conditions. gated spider plants, and 3) pots of root transfer, an anemometer (AIRFLOW Light was provided by two fluores- medium with green jade plants. Each AV2; TSI, Shoreview, MN) with a re- cent bulbs (T5; Sunblaster Lighting, experimental unit of five test objects mote vane probe (A15961) was used Kelowna, BC, Canada) and the same were subjected to 25% or 60% RH at to determine air velocity. The probe light schedule was used in the envi- a constant temperature of 20 C. The was moved along the chamber wall ronmental chamber and acclimation root medium control consisted of 70% surface, which contains a pattern of area, with synchronized light on/off
804 • December 2016 26(6) Fig. 1. Test objects (root medium control, spider plants, and jade plants) and sensor positions in the environmental chamber at Kansas State University’s Institute for Environmental Research, Manhattan, to quantify the effect of root medium evaporation and plant transpiration on relative humidity. This layout was used for each of 12 runs of the experiment. All measurements are in feet; 1 ft = 0.3048 m. times (Fig. 2). Each test began with at plants (three treatments) at two hu- plant were measured following exper- least 5.5 h of light (Light 1) followed midities (25% and 60% RH), all at imental testing. All leaves were re- by 11 h of darkness (Dark) and then a constant temperature of 20 C. Be- moved from the plants and sealed light (Light 2). This 24-h testing pro- fore testing, the order of the 12 runs between transparent laminating sheets. cedure allowed the experiments to was randomized. For each run, root The transparent sheets were scanned to capture the effects of diurnal lighting medium moisture content was pre- determine total surface area of each changes on the test objects. The lights pared to a target range of 0.28 to plant’s leaves using a leaf area meter did not interfere with plant foliage. 0.35 cm3 water per cubic centimeter (LI-3000C, LI-COR). To quantify the amount of light of root medium. Initial soil moisture STATISTICAL ANALYSES. The the test objects received, photosyn- content measurements were then evaporation/evapotranspiration rate thetic photon flux (PPF) was measured taken, and water was slowly added to data for the steady-state portion of each (model LI-250 light meter; LI-COR, each pot to raise the moisture content lighting period (Fig. 2) was statistically Lincoln, NE). A PPF of 81 mmol m–2 s–1 to the desired level. After root medium analyzed. For Light 1, the analyzed time was measured at the top of the root moisture reached equilibrium, the five frame was the period between 2.5 and medium (1 ft from the light source) pots were moved into the environmen- 4.5 h after the experiment began. Dur- and 129 mmol m–2 s–1 at foliage can- tal chamber and placed on the precision ing Dark conditions, data were analyzed opy (7 inches from the light source). scale; a root medium moisture probe 8 to 10 h after the light was turned off. Using unit conversions (Thimijan was inserted into each pot. Chamber For Light 2, data were analyzed from and Heins, 1983) to allow for com- air speed and pressure measurements 2.5to4.5hafterthelightwasturned parison, these light levels would be were taken. The chamber was sealed on. Analysis of variance test was con- considered in a ‘‘high’’ category in an and reached steady state in 20 to 40 ducted using SAS software (version 9.3; interior environment (DelPrince, 2013; min, after which automated data col- SAS Institute, Cary, NC) to evaluate Manaker, 1997) that may require sup- lection commenced, measuring tem- interactions of treatment variables of plemental lighting to achieve. The test perature, humidity, root medium the two RH conditions, three treat- objects were subjected to lighting con- moisture content, and weight of the ments (i.e., control, spider plants, and ditions comparable to a bright interior five pots. Data were logged for 24 h, jade plants), and three lighting condi- environment that would maximize plant after which the environmental chamber tions (i.e., Light 1, Dark, Light 2) for evapotranspiration rate. was opened to obtain posttest air speed interactions (Fig. 2). F-tests were calcu- EXPERIMENTAL PROCEDURE. The and pressure measurements. Data were lated for simple effects, and means were experiment consisted of a total of then compiled and analyzed. separated with Tukey’s pairwise com- 12 runs; runs were replicated for six LEAF AREA MEASUREMENTS. Be- parison at a 95% confidence interval treatment combinations: the root me- cause plant transpiration is dependent (a = 0.05); thereby, P < 0.05 is consid- dium control, spider plants, and jade on leaf surface area, leaf areas of each ered statistically significant.
• December 2016 26(6) 805 RESEARCH REPORTS
Results and discussion
EVAPORATION AND EVAPOTRANS- PIRATION. Only evaporation occurred in the root medium control due to the lack of transpiration from any plants. The control showed the least varia- tion in evaporation rate during light- Fig. 2. Lighting schedule for root medium control, spider plants, and jade plants ing periods with evaporation rates tested in an environmental chamber for each of 12 runs in the experiment to between 5 and 9 g h–1 at 25% RH quantify the effect of root medium evaporation and plant transpiration on relative and 2.5 and 5 g h–1 at 60% RH (Figs. humidity. A dark period occurred between Light 1 and Light 2, the first and 3A and 4A). Both plant species second lighted periods, respectively, to which test objects were exposed. showed a distinct change in evapo- transpiration between lighting inter- vals due to evaporation from their root medium and transpiration from the plants themselves. For the spider plants, maximum evapotranspiration occurred during the lighted period, up to 16 g h–1 (Figs. 3B and 4B). In contrast, the jade plants exhibited more constant evapotranspiration levels. During dark periods, jade evapotranspiration exceeded that of the spider plants (Figs. 3C and 4C). At 25% RH, evapotranspiration rates were 11 g h–1 for the group of five jade plants and 6 g h–1 for the group of five spider plants in the dark period (Fig. 3). Evapotranspiration rates were even lower in the dark at 60% RH, around 4.5 g h–1 and 3 g h–1 for jade and spider plants, respectively (Fig. 4). This trend is due to differences in their photosynthetic mechanisms. EFFECT OF LIGHT AND DARK ON EVAPORATION RATES. Lighting condi- tions significantly impacted evapora- tion rates of the plant species in this study. The spider and jade plants experienced transient evapotranspira- tion rates related to the change from dark to light and light to dark. The effect was more pronounced in the transition from Dark to Light 2 for the spider and jade plants (Figs. 3B, Fig. 3. Measured evaporation rates for both runs (1 and 2) of (A) root medium control, and measured evapotranspiration rates for (B) spider plants and (C) jade 3C, 4B, and 4C). Transient changes plants over a simulated 24-h day at 25% relative humidity and temperature of 20 C in observed evapotranspiration rates (68.0 F) in an environmental chamber; N = 1 with five pots per experimental unit; are likely due to stomatal opening and 1g= 0.0353 oz. behavior. The 25% RH environment re- plants, evaporation rates dropped periods (P = 0.01); this may have been sulted in statistically different evapo- sharply, by 62%, during the dark pe- a result of changing volumetric water ration rates across lighting conditions riod and rebounded within 10% of the content over the course of the run for the root medium (P = 0.01) and initial value during the second light (Fig. 6). There was not a difference differing evapotranspiration rates period. However, the jade plants between Dark and Light 2 (P =0.13) across lighting conditions for the exhibited the highest evapotranspira- or Light 1 and Light 2 (P =0.28). spider plants (P < 0.01) and jade plants tion rate during the dark period, 28% In the 25% RH environment, the (P < 0.01). At 25% RH, steady-state higher than the first light period (Fig. spider and jade plants exhibited op- evaporation rates from the control 5A). Since this effect of light was posing evaporative trends (Fig. 5A). decreased by 27% from the first light noted, further pairwise comparisons The spider plants increased evapotrans- period to the darkness, returning to were conducted. For the root medium piration during lighted conditions, and within 12% of their initial value during control, there was a difference be- a difference occurred in evapotranspi- the second light period. For the spider tween evaporation in Light 1 and Dark ration rates between Dark and Light 1
806 • December 2016 26(6) first lighted period at 60% RH were 46%, 59%, and 48% lower than those observed at 25% RH for root me- dium, spider plants, and jade plants, respectively. An influence of light at the 60% RH was observed for the spider plants, indicating the occur- rence of transpiration. In addition, a statistically significant difference was shown between Dark and Light 1(P < 0.01), Dark and Light 2 (P < 0.01), and between Light 1 and Light 2(P < 0.01). In contrast, evapotrans- piration rates of the jade plants at 60% RH were statistically similar during all light and dark periods. In the Dark period, jade evapotranspiration rates were higher than the control’s evap- oration rates, suggesting that the jade plant was transpiring a modest amount. Lower evapotranspiration rates were observed for the root medium control, spider plants, and jade plants at 60% RH compared with 25% RH (Fig. 5) due to decreased driving vapor pressure difference for evaporation with in- creased humidity. This created a nega- tive feedback system that moderated the amount of water released to the environment as RH increased, and could be advantageous to limit indoor Fig. 4. Measured evaporation rates for both runs (1 and 2) of (A) root medium humidification at higher humidities. control, and measured evapotranspiration rates for (B) spider plants and (C) jade E STIMATED TRANSPIRATION plants over a simulated 24-h day at 60% relative humidity and temperature of 20 C FLUXES. Immediately following test- (68.0 F) in an environmental chamber; N = 1 with five pots per experimental unit; ing, total leaf areas of five plants per 1g= 0.0353 oz. species were measured to be 6466 and 4582 cm2 for spider and jade plants, (P < 0.01) and Dark and Light 2 (P < species’ photosynthetic mechanisms. respectively. It should be noted that 0.01), but not between Light 1 and Plant stomata govern gas exchange the spider plants had variegated white Light 2 (P =0.06).Thespiderplants during photosynthesis. Spider plants and green leaves with a white strip also had higher evapotranspiration open their stomata during light pe- down the middle of each leaf blade. rates during light periods compared riods to allow carbon dioxide to enter Research has shown that stomata in with the evaporation rate of the root the plant to be fixed, similar to most white portions of leaves do not re- medium control and similar evapo- plant species with a C3 photosynthetic spond to photosynthetically active transpiration to the root medium con- pathway. However, jade plants exhibit radiation (Roelfsema et al., 2006). trol during Dark periods. In the 25% CAM photosynthesis, as is typical of Total leaf area was reported in the RH environment with jade plants, a dif- succulent plants native to arid climates. results, but the effective spider plant ference was observed between Dark These plants leave their stomata closed leaf area for photosynthesis was less andLight1(P = 0.01) and Dark and during the day to conserve water and than the reported total area. Light 2 (P < 0.01), but not between reduce transpiration. Plant stomata Steady-state transpiration fluxes Light1andLight2(P = 0.11). The then open at night to access carbon were estimated to account for differ- jade plants demonstrated identical dioxide, allowing transpiration to oc- ences in leaf area between spider and evaporation rate to the root medium cur (Taiz and Zeiger, 2006). There- jade plants. The evaporation rate only during light periods, indicating fore, maximum transpiration occurs from the root medium control was negligible transpiration from the jade forspiderplantsinlightedperiods, subtracted from the plants’ measured plants (Fig. 5A). The jade plants had and jade plants undergo substantial evapotranspiration rates to estimate higher evaporation rates than the root transpiration during dark periods. transpiration, and transpiration flux medium control during Dark periods EFFECTS OF RH ON EVAPORATION was calculated using total leaf area. At (P < 0.01), indicating that the plants RATES. In this study, moisture trans- 25% RH, transpiration fluxes for spi- transpired in the darkness. port rates were lower for all treat- der plants during Light 1 and Light 2 Differences in evapotranspira- ments with 60% RH compared periods were 12 and 11 g m–2 h–1, tion rates between spider and jade with 25% RH (Fig. 5). Evaporation/ respectively. During the Dark period, plants can be explained by the plant evapotranspiration rates during the the evaporation rate from the root
• December 2016 26(6) 807 RESEARCH REPORTS
plant leaf surface area of 32,300 cm2 is needed to increase humidity from 20% RH to a more comfortable 30% RH. This is equivalent to 25 spider plants in 4-inch-diameter pots that could be accommodated in a small, automated greenwall, or on a light cart or windowsill display. A few, large plants would most likely result in very similar impact on humidity as this large number of small plants. Therefore, for example, three variegated spider plants in 10-inch hanging baskets with a sim- ilar total leaf surface area could also be used. Use of nonvariegated species of spiderplantswouldalsoreducethe required number of plants. Depending on the climate, an Fig. 5. Steady-state evaporation/evapotranspiration rates from the root medium control, spider plants, and jade plants at (A) 25% relative humidity (RH) and (B) SNF resident may desire the psycho- 60% RH in replicated runs in an environmental chamber. logical benefits of plants without cor- responding increased room moisture levels. Therefore, an interior plant- media and evapotranspiration from Cohen, 1999), the recommended scape could be rotated seasonally, spider plants were not different, ventilation rate is two air changes with spider plants during low-hu- therefore negligible transpiration oc- per hour (ASHRAE, 1999), requiring midity seasons and jade plants for curred. In contrast, jade plant transpi- an air exchange rate of 45.3 m3 h–1 high-humidity seasons. For example, ration flux was 10.3 g m–2 h–1 in the (26.7 ft3/min). The molar air-flow 25 spider plants (32,300 cm2 leaf Dark period, with negligible transpi- rate, n_, can be obtained through the surface area) could be replaced with ration during lighted periods. Tran- ideal gas law, 20 jade plants (18,330 cm2 leaf sur- spiration fluxes decreased for all face area). The maximum evapotrans- PQ –1 species at 60% RH, with fluxes of n_ = ½2 piration (4.5 g h ) occurs during dark 3.2 and 9.1 g m–2 h–1 for the spider RT conditions. According to Eq. [2] and plants during Light 1 and Light 2 Eq. [3], the jade plants would add where P is pressure, Q is volumetric periods, respectively, with negligible 1mol h–1 water. This moisture addi- flow rate, R is ideal gas constant, and transpiration in the Dark period. For tion would increase the 60% indoor T is temperature. Using atmospheric the jade plants, transpiration fluxes of RH by a modest 2.3%, primarily at pressure and a temperature of 20 C 4.4 g m–2 h–1 were observed during night. These two cases demonstrate in Eq. [2], a molar air-flow rate of the Dark period, with negligible tran- the potential efficacy of a natural plant- 1,833 mol h–1 air was obtained. RH, spiration during the lighted periods. based system for passive humidifica- f, is defined as Transpiration fluxes were similar dur- tion. Further design work could yield ing the period that each plant species ! superior plant species; however, study y had stomata open (i.e., light for spider f = v ½3 results suggested that a combination y ; plants and dark for jade plants). Dur- v sat T ;p of plants with different photosynthetic ing periods where stomata were not pathways (i.e., C3 and CAM) might be open, transpiration was negligible, and where yv is the molar fraction of water used to manipulate evapotranspiration moisture transport was almost entirely vapor, and yv;sat is the molar fraction of rates so that they are relatively con- a consequence of evaporation from the water vapor at saturation at a given sistent through the diurnal cycle or root medium. These results may help temperature and pressure. Therefore, fine-tuned for the appropriate season. in the estimation of required plant leaf additional moisture required to increase Although beyond the scope of this surface area needed to humidify in- RH can be determined. study, future research could include terior rooms. During heating season or dry evaluation of evaporation rates from I MPLICATIONS FOR INDOOR conditions, an interior plantscape at various plant media. HUMIDIFICATION. Evapotranspiration an SNF could be augmented with In summary, lighting significantly from plants represents a method to potted spider plants to increase day- impacts plant evapotranspiration be- humidify with minimal energy expen- time RH and potentially improve pa- havior. Transient evaporative behav- diture. Plant-based indoor humidifi- tient well-being due to the presence of ior was observed for jade and spider cation could be especially beneficial in plants. To increase humidity by 10% plants as lighting changed from dark SNFs because plants in an indoor RH, 4.3 mol h–1 water must be intro- to light and light to dark. This tran- environment have been shown to duced into the room. For spider plants sient behavior is likely due to stomatal improve quality of life for the elderly at 25% RH under tested light condi- opening and closing. (McGuire, 1997; Stein, 1997; Tse, tions, a constant evapotranspiration rate Plants with different photo- 2010). For a typical resident room of 15 g h–1 was estimated, based on the synthetic mechanisms, such as jade (22 m3) in an SNF (Ninomorua and datashowninFig.5.Variegatedspider and spider plants, exhibit opposing
808 • December 2016 26(6) to humidify low-humidity indoor en- vironments while negligibly affecting indoor humidity levels at higher hu- midities. Future work could identify additional plant species and combina- tions as well as root media to humidify and improve indoor air quality in re- lation to various indoor environmental conditions.
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