Raising Air Temperature Research Articles

Characteristics of facial electromyography during cold exposure and feasibility of evaluating thermal comfort

A comfortable building environment plays a vital role in enhancing both the physical and mental well-being of its occupants. In recent years, the assessment of building thermal environments has gained significant attention. The assessment methodology is shifting from subjective evaluations to more physiological assessments. However, the exploration of facial muscles in this context has remained largely uncharted territory. The primary objective of this research was to investigate the characteristics of facial electromyography (fEMG) in a cold environment and examine its potential for assessing thermal comfort. The experiment was divided into two parts. The first part focused on understanding fEMG characteristics in the time domain, frequency domain, and phase during activities like speaking, expressing emotions, and exposure to cold conditions. The second part aimed to study the recovery process of fEMG after cold exposure, achieved by increasing clothing insulation and raising air temperature. The findings revealed significant distinctions in fEMG characteristics when subjects engaged in speaking (notably in the low-frequency component of the anguli oris muscle), expressing emotions (with a prominent low-frequency component in the zygomatic muscle), or experiencing cold conditions (highlighted by the high-frequency component of the masseter muscle). Interestingly, augmenting clothing insulation in the body region posed challenges in improving facial muscle electrical activity, while raising air temperature effectively alleviated facial muscle tension. This study represents the pioneering application of fEMG in indoor thermal comfort evaluation. It offers a physiological foundation for assessing thermal comfort based on facial skin temperature and facial expressions. Furthermore, the research contributes valuable data that can support the advancement of wearable devices and smart building systems.

The Impact of Vegetation Canopy on the Outdoor Thermal Environment in Cold Winter and Spring

The current study investigated the impact of vegetation canopy on the outdoor thermal environment in cold winter and spring, a less-explored aspect of its climate effects. Firstly, we conducted on-site observations of meteorology parameters on a campus in a hot summer and cold winter region. Then the ENVI-met microclimate simulation model was utilized to simulate the air temperature, relative humidity, wind speed and direction, and solar radiation of typical winter and spring days. Furthermore, the PET index was calculated to evaluate the thermal conditions. Our findings revealed that during the daytime, the vegetation canopy raised air temperature and relative humidity, reduced wind speed, and mitigated solar radiation. Solar radiation emerged as the primary factor affecting thermal comfort in the cold winter and spring. The presence of deciduous broad-leaved vegetation notably reduced cold discomfort and improved thermal comfort in the cold winter and spring. Finally, we propose replacing evergreen broad-leaved vegetation with deciduous broad-leaved vegetation in hot summer and cold winter regions to ensure year-round thermal comfort, especially in the cold winter and spring.

The use of steam dryer with heat recovery to decrease the minimum exhaust flue gas temperature and increase the net efficiency of thermal power plant

Net power plant efficiency is the ratio of exportable electrical power output to the product of fuel consumption rate and fuel heating value. Conventionally, power plants are designed to attain the maximum net power plant efficiency by using regenerative feed water heating, in which extracted steam from steam turbine is used to increase feed water temperature. An important factor that determines the net power plant efficiency is the temperature of flue gas exhausted from the power plant. Decreasing this temperature increases the net power plant efficiency. However, exhaust flue gas temperature should not be lower than the lower limit in order to avoid the corrosion resulting from condensation of sulfuric acid vapor in flue gas on heat exchanger tubes. The lower limit can be raised by reducing fuel moisture content and raising air temperature at boiler inlet. In this paper, it is proposed that low-pressure extracted steam should be used for fuel drying in steam dryer, and vapor released from steam dryer should be used for air heating in heat recovery air preheater. By doing so, the lower limit of exhaust flue gas temperature is decreased, and the net efficiency of the power plant is increased. A case study of a 600-MW lignite-fired power plant is used to demonstrate that the integration of steam dryer and heat recovery air preheater is economically justified.

Crop response to P fertilizer omission under a changing climate - Experimental and modeling results over 115 years of a long-term fertilizer experiment

• The omission of P had a rather small effect on winter cereal yields. • Sugar beet, clover and potato yields were most affected by P deficiency. • Raising air temperature reduces yield loss caused by phosphorus limitation. Phosphorus (P) is an essential plant nutrient. However, our understanding of the complex interactions between soil P availability, environment, management and crop growth is still limited. We used unique historic and recent soil and crop data spanning more than a century combined with a process-based crop model to analyze the impact of P fertilizer omission and P fertilization on the biomass production of five crops. The long-term field experiment at Dikopshof, Germany, was established in 1904 with a 5-year crop rotation of sugar beet, winter wheat, winter rye, clover and oat/potato (potato replaced oat in 1953) on a fertile Luvisol. Averaged over the period from 1906 to 2018, the yield loss due to P omission was low for winter wheat and winter rye (7–8 %). In contrast, yield losses for sugar beet, clover and potato were relatively high (15–24 %). The yield loss from P fertilizer omission in comparison to the reference treatment (rotation mean excluding oat/potato) increased until the middle of the last century from 7% to 18 %, but subsequently decreased to 13 %. Trend and correlation analyses suggest that this decrease was related to an increase in air temperatures in especial during spring and a lower yield loss under P omission. Crop model simulations showed decreasing topsoil organic carbon concentrations after the 1930ies as manure was discontinued in 1942 but also due to increasing air temperatures. The increase in plant-available topsoil P concentrations during the last decades was one of the main factors offsetting yield losses despite P fertilizer omission. Our study suggests that climate change and, in particular, a marked increase in temperature since the middle of the last century most likely influenced soil P dynamics with a significant impact on crop production.

Impact assessment of common bean availability in Brazil under climate change scenarios

CONTEXTBrazil is one of the main producers of common beans (Phaseolus vulgaris L.), which have high nutritional value as human food. The climate changes predicted in the 21st century might be a possible threat to the planet’s food security, given the expected population increase, and hence, increased demand for food. OBJECTIVEThis study aimed to project the impact of climate change on common bean cropping systems using an upscaling climate approach and crop modeling to represent the Brazilian production regions. METHODSWe considered the representative CO2 concentration pathway scenarios (RCPs) 4.5 and 8.5 presented by the 5th IPCC Assessment Report from 20 atmospheric global circulation models covering the main bean-producing region in Brazil. The well-calibrated CROPGRO-Drybean crop model simulated two representative cultivars of the “black” and “colors” types and three cropping seasons applied by Brazilian farmers. RESULTS AND CONCLUSIONSOn average, we found that yield increased by 5.56% and 9.12% for the RCP 4.5 and 8.5 scenarios, respectively. Increased photosynthetic efficiency due to the increased atmospheric CO2 concentration was identified as the main cause of this yield increase. Crop respiration rates increased due to the raised air temperature, and were responsible for increasing the probability (production risk) of not meeting the future domestic demands for grains to 10.13% and 8.34% for the RCP 4.5 and 8.5 scenarios, respectively. For the national supply of grains, estimates pointed to a future in which crop production will probably rely more on area expansion than yield gains by crop intensification. SIGNIFICANCEOur findings emphasize the need for new policies for land utilization and investments in scientific research programs aimed towards genetic adaptation in all main Brazilian crops in the face of potential climate change.

Warming promotes growth of seedlings of a woody encroacher in grassland dominated by C4 species

Little is known of warming effects on growth and defence of woody seedlings that potentially invade grasslands. We predicted that elevated temperatures would increase growth and spine length of Vachellia sieberiana seedlings growing (1) with or without grass in the dormant season and early growing season, but (2) only when grass cover is absent in the mid-late growing season. To test these predictions, 120 seedlings were grown in 20 field plots in the dormant season, early growing season, middle of the growing and late growing season. Ten plots were warmed with open-top chambers that raised air temperature by 1.0 to 2.5 °C depending on season. Warming generally increased growth metrics regardless of grass cover across seasons and generally increased spine length only when grass cover was absent. The results imply that under a warmer climate, V. sieberiana will thrive irrespective of grass cover.

Control of lettuce big‐vein disease by application of fungicides and crop covers

One of the economically important diseases of lettuce is lettuce big‐vein disease (LBVD), which leads to severe yield losses. LBVD is associated with a complex of two viruses, Lettuce big‐vein associated virus (LBVaV) and Mirafiori lettuce big‐vein virus (MLBVV). These viruses are transmitted by motile zoospores of Olpidium spp. fungi, which persist in the soil for decades through resting spores. In greenhouse and field experiments, this study tested whether changing plant and soil temperatures together with fungicide application would have a significant effect on controlling LBVD in lettuce. Soil fumigation with metam sodium was not effective at controlling the disease, as opposed to treatment with chloropicrin and methyl bromide. Moreover, the fungicides carbendazim and fluazinam were effective in reducing the incidence of Olpidium virulentus. Nevertheless, control of the fungal vector did not seem to be sufficient to control the disease due to the transition ability of the virus under low vector abundance. Crop covers, which affect the favourable environmental conditions for the viruses by lowering soil temperature and raising air temperature, reduced the disease symptoms. Combining fungicides with crop cover had a synergistic effect on reducing disease symptoms, thus providing a sustainable solution for LBVD.

A modelling study of the terrain effects on haze pollution in the Sichuan Basin

The Sichuan Basin (SB), covering 260,000 km2 immediately to the east of the Tibetan Plateau (TP) with a large drop exceeding 3000 m in elevation over a short horizontal distance, is a region of high haze pollution in China. The terrain effects of this unique deep basin on haze pollution have not been well investigated. During 14–19 January 2014, heavy haze pollution engulfed the SB with high PM2.5 concentrations. By using the WRF-Chem model, the topographic effects on haze pollution in the SB and the underlying mechanisms were investigated by two sets of simulation with and without the basin topography. The simulation results show that the SB topography lead to an increase of 48 μg m−3 in the basin-averaged surface PM2.5 contributing about 44% to the PM2.5 concentrations during heavy haze pollution, indicating an important role of the basin topography in worsening air pollution. The surface PM2.5 level enhancements varied spatially from 0 to 30 μg m−3 in the eastern basin to 60–120 μg m−3 in the western basin, respectively corresponding to 0–20% and 50–70% relative to the concentrations simulated without the SB topographic condition, reflecting the stronger topographic effect of the TP in the western SB. The topographic effects intensify the haze pollution via reducing wind speed, raising air temperature and humidity in the lower troposphere, as well as dropping boundary layer height in the basin. Resulted from the impact of TP on mid-latitude westerly winds, a typical leeside vortex of immediately upstream TP over the basin was developed with accentuating PM2.5 accumulations in the basin, implying a strong influence of TP on air quality in the SB.

The Hot Serial Cereal Experiment for modeling wheat response to temperature: field experiments and AgMIP-Wheat multi-model simulations

The data set reported here includes the part of a Hot Serial Cereal Experiment (HSC) experiment recently used in the AgMIP-Wheat project to analyze the uncertainty of 30 wheat models and quantify their response to temperature. The HSC experiment was conducted in an open-field in a semiarid environment in the southwest USA. The data reported herewith include one hard red spring wheat cultivar (Yecora Rojo) sown approximately every six weeks from December to August for a two-year period for a total of 11 planting dates out of the 15 of the entire HSC experiment. The treatments were chosen to avoid any effect of frost on grain yields. On late fall, winter and early spring plantings temperature free-air controlled enhancement (T-FACE) apparatus utilizing infrared heaters with supplemental irrigation were used to increase air temperature by 1.3°C/2.7°C (day/night) with conditions equivalent to raising air temperature at constant relative humidity (i.e. as expected with global warming) during the whole crop growth cycle. Experimental data include local daily weather data, soil characteristics and initial conditions, detailed crop measurements taken at three growth stages during the growth cycle, and cultivar information. Simulations include both daily in-season and end-of-season results from 30 wheat models. Data access via doi 10.7910/DVN/M9ZT0F

Ground-level climate at a peatland wind farm in Scotland is affected by wind turbine operation

The global drive to produce low-carbon energy has resulted in an unprecedented deployment of onshore wind turbines, representing a significant land use change for wind energy generation with uncertain consequences for local climatic conditions and the regulation of ecosystem processes. Here, we present high-resolution data from a wind farm collected during operational and idle periods that shows the wind farm affected several measures of ground-level climate. Specifically, we discovered that operational wind turbines raised air temperature by 0.18 °C and absolute humidity (AH) by 0.03 g m−3 during the night, and increased the variability in air, surface and soil temperature throughout the diurnal cycle. Further, the microclimatic influence of turbines on air temperature and AH decreased logarithmically with distance from the nearest turbine. These effects on ground-level microclimate, including soil temperature, have uncertain implications for biogeochemical processes and ecosystem carbon cycling, including soil carbon stocks. Consequently, understanding needs to be improved to determine the overall carbon balance of wind energy.

Analysis on Photovoltaic Energy-Assisted Drying of Green Peas

A photovoltaic energy-assisted industrial dryer has been analyzed. The dryer has been tested in various weather and working conditions with 3 kg of green peas from 75.6% initial moisture content to 20% final moisture content (w.b.). The effect of various drying air temperatures at three levels (40, 50, and 60°C) and two distinct air velocities (3 m/s and 4 m/s) was examined. Drying performance was assessed with regard to criteria including drying kinetics, specific and total energy consumption, and color and rehydration ratio. The results have proved that total drying duration reduces as air velocity rate and drying air temperature raise. Relying upon the drying durations, the generation performances of photovoltaic panels were between 5.261 and 3.953 W. On the other part, energy consumptions of dryer were between 37.417 and 28.111 W. The best specific energy consumption was detected in 50°C at 3 m/s for 600 minutes with 7.616 kWh/kg. All drying conditions caused darkening as color parameters. Rehydration assays have showed that rehydrated green peas attained higher capacity with raised air temperature and air velocity.

Exploitability of Renewable Resources in Administrative Buildings

The evaluation of energy flow measurements in two very special buildings under the name of Open Gardens, located in Brno, resulted in confirming that the resources of renewable energy in the Czech Republic can be sufficiently utilized. This energy is derived from photovoltaic elements and earth heat pumps and, additionally, it gets also accumulated in building structures. The energy from renewable resources is utilized for heating, cooling, warm water preparation, for raising air temperature, and it also partially covers the demand for electricity in the building. During the summer period, if the solar gains are considerable, the buildings need being cooled. This is ensured by an earth heat pump enabling the storage of waste heat in deep earth bore holes, offering the advantage of recuperating the heat for heating the rooms during the winter months. At the same time all electricity produced in the building gets utilized, covering roughly 1/3 of the consumption. A plan of comprehensive measurements aiming at the optimization of the most demanding electric appliances has been conceived for this compound of buildings, in order to ensure the best possible utilization of the produced electricity.

Development for a Hot-Water Heating System Using Biogas Energy in the Pig Farm

A water heating system which utilized biogas energy as a heat source in farrowing house of pig farm was developed in this study. The hot water which was heated by the biogas-burners flowed through the delivery pipeline to heat the metal panel made of aluminum alloy in the piglet’s incubator. The ambient air temperature in the piglets incubator could be raised by way of the thermal radiation of the aluminum panel and then kept the piglets warm. The simulation tests of the hot-water heating system was aimed to find out the reference conditions of the field tests by measuring the temperature of the hot water under different flow rate of the hot water and investigating the air temperature change rate in piglets incubator. The results of simulation tests showed that the ambient air temperature of the piglets incubator can achieve above 28 °C within 30 minutes in the conditions of 90 °C hot water and 45.3 L/min water flow rate. The influence of flow rate to the ambient air temperature in the piglet’s incubator was not significant. The results of the field tests obtained that the heating panel surface temperature increased significantly with the rising hot water temperature. Under the condition of 85 °C hot water and 45.3 L/min flow rate, the raised air temperature was 5.2 °C within 25 minutes in the piglets incubator where 13-day-age eight piglets stayed. This hot-water heating system can switch by hand to the electric-auxiliary heating device when there is no enough biogas to use. The hot-water heating system can achieve the purpose of saving electric energy and reducing the emissions of the greenhouse gas. It is feasible to operate and adjust the suitable temperature for the growth environment of piglets.

Contrasting growth responses of dominant peatland plants to warming and vegetation composition.

There is growing recognition that changes in vegetation composition can strongly influence peatland carbon cycling, with potential feedbacks to future climate. Nevertheless, despite accelerated climate and vegetation change in this ecosystem, the growth responses of peatland plant species to combined warming and vegetation change are unknown. Here, we used a field warming and vegetation removal experiment to test the hypothesis that dominant species from the three plant functional types present (dwarf-shrubs: Calluna vulgaris; graminoids: Eriophorum vaginatum; bryophytes: Sphagnum capillifolium) contrast in their growth responses to warming and the presence or absence of other plant functional types. Warming was accomplished using open top chambers, which raised air temperature by approximately 0.35 °C, and we measured air and soil microclimate as potential mechanisms through which both experimental factors could influence growth. We found that only Calluna growth increased with experimental warming (by 20%), whereas the presence of dwarf-shrubs and bryophytes increased growth of Sphagnum (46%) and Eriophorum (20%), respectively. Sphagnum growth was also negatively related to soil temperature, which was lower when dwarf-shrubs were present. Dwarf-shrubs may therefore promote Sphagnum growth by cooling the peat surface. Conversely, the effect of bryophyte presence on Eriophorum growth was not related to any change in microclimate, suggesting other factors play a role. In conclusion, our findings reveal contrasting abiotic and biotic controls over dominant peatland plant growth, suggesting that community composition and carbon cycling could be modified by simultaneous climate and vegetation change.

Stream temperature sensitivity to climate warming in California’s Sierra Nevada: impacts to coldwater habitat

Water temperature influences the distribution, abundance, and health of aquatic organisms in stream ecosystems, so understanding the impacts of climate warming on stream temperature will help guide management and restoration. This study assesses climate warming impacts on stream temperatures in California’s west-slope Sierra Nevada watersheds, and explores stream temperature modeling at the mesoscale. We used natural flow hydrology to isolate climate induced changes from those of water operations and land use changes. A 21 year time series of weekly streamflow estimates from WEAP21, a spatially explicit rainfall-runoff model were passed to RTEMP, an equilibrium temperature model, to estimate stream temperatures. Air temperature was uniformly increased by 2°C, 4°C, and 6°C as a sensitivity analysis to bracket the range of likely outcomes for stream temperatures. Other meteorological conditions, including precipitation, were unchanged from historical values. Raising air temperature affects precipitation partitioning into snowpack, runoff, and snowmelt in WEAP21, which change runoff volume and timing as well as stream temperatures. Overall, stream temperatures increased by an average of 1.6°C for each 2°C rise in air temperature, and increased most during spring and at middle elevations. Viable coldwater habitat shifted to higher elevations and will likely be reduced in California. Thermal heterogeneity existed within and between basins, with the high elevations of the southern Sierra Nevada and the Feather River watershed most resilient to climate warming. The regional equilibrium temperature modeling approach used here is well suited for climate change analysis because it incorporates mechanistic heat exchange, is not overly data or computationally intensive, and can highlight which watersheds are less vulnerable to climate warming. Understanding potential changes to stream temperatures from climate warming will affect how fish and wildlife are managed, and should be incorporated into modeling studies, restoration assessments, and licensing operations of hydropower facilities to best estimate future conditions and achieve desired outcomes.

Coating the inner surfaces of pipes with high-viscosity epoxy in annular flow

Applying a thin, protective coating of a nontoxic, chemically resistant epoxy to the interior of existing pipes is an alternative method to pipe replacement. In order to find the controlling parameters in this method, in this study, viscous epoxy was propelled by compressed air through clear polyvinyl chloride (PVC) pipes. Epoxy flow was annular, and it hardened to form a thin, uniform coating on the inner pipe surface. A video camera was employed to record fluid motion, and the thickness of the coating was measured using an image analysis program named ImagJ. Tests were done with varying air temperature, airflow rate, piping configuration, and epoxy temperature. A one-dimensional numerical algorithm was developed to model fluid flow, heat transfer, and epoxy curing. Heating the epoxy makes it move faster because liquid viscosity decreases with increasing temperature. The coating was significantly thicker at the bottom of a horizontal pipe than at the top due to sagging of the epoxy coating after it had been applied, resulting in flow from the top to the bottom of the pipe. Sagging could be reduced by maintaining airflow until curing was almost complete and the epoxy had hardened enough to prevent it from moving easily. The combination of the experimental results and numerical modeling showed that the most important parameters controlling the speed of the epoxy and coating thickness were the air flow rate and temperature, since they determine the shear forces on the epoxy layer and the rate at which the epoxy cures. Raising air temperature increases the reaction rate and therefore decreases the time required for the epoxy to cure inside the pipe. The results of the simulation showed a very good agreement with the experimental results in pipes with 1-in diameter or less.

The effect of periods of high temperature and manipulating fruit load on the pattern of tomato yields

SummaryTo assess whether cycles in the weekly pattern of tomato yields were due to the pattern of fruit load on plants, truss-removal and truss-pruning treatments were applied to individual rows within glasshouse compartments. When the pattern of fruit load was stabilized by pruning all trusses to five fruits, fruit size increased although the pattern of yield was similar to that from control rows. Furthermore, imbalances in fruit load caused by truss removal did not cause cyclical fruit production. The effect of temperature on the pattern of yield was investigated by raising air temperature within compartments by about 4.5 K for one week on two occasions. High yields were initially recorded following the start of the high temperature pulse but low yields were subsequently recorded. Overall, there was no significant effect of the treatment on cumulative yields over the course of the experiment. The results show that changes in air temperature are important in determining the pattern of tomato yields. Fruit temperatures were recorded with thermal-imaging equipment and thermistor sensors inserted into fruits. Fruit temperatures in excess of 35°C were recorded, although fruit temperatures were only slightly above air temperatures when averaged over longer periods. Fruits at the south end of the rows were on average 1.9 K warmer than the air compared with 0.9 K warmer in the middle of the rows. For accurate predictions of the pattern of yield, fruit temperatures should be considered.

THE RESPONSE OF TUNDRA PLANT BIOMASS, ABOVEGROUND PRODUCTION, NITROGEN, AND CO2FLUX TO EXPERIMENTAL WARMING

We manipulated air temperature in tussock tundra near Toolik Lake, Alaska, and determined the consequences for total plant biomass, aboveground net primary production (ANPP), ecosystem nitrogen (N) pools and N uptake, and ecosystem CO2 flux. After 3.5 growing seasons, in situ plastic greenhouses that raised air temperature during the growing season had little effect on total biomass, N content, or growing-season N uptake of the major plant and soil pools. Similarly, vascular ANPP and net ecosystem CO2 exchange did not change with warming, although net primary production of mosses decreased with warming. Such general lack of response supports the hypothesis that productivity in tundra is constrained by the indirect effects of cold temperatures (e.g., low nutrient availability or short growing-season length) rather than by cold growing-season temperatures per se. Despite no effect on net ecosystem CO2 flux, air warming stimulated early-season gross photosynthesis (GP) and ecosystem respiration (ER) throughout the growing season. This increased carbon turnover was probably associated with species-level responses to increased air temperature. Warming increased the aboveground biomass of the overstory shrub, dwarf birch (Betula nana), and caused a significant net redistribution of N from the understory evergreen shrub, Vaccinium vitis-idaea, to B. nana, despite no effects on soil temperature, total plant N, or N availability. Thus, although air warming had no effect on total ecosystem N pools, it did mediate N distribution within the plant community. The early-season stimulation of GP is consistent with warming effects on leaf expansion of dominant shrubs (including B. nana) observed in other studies in tussock tundra. The stimulation of ER probably resulted from maintenance and growth respiration associated with higher aboveground B. nana biomass production and higher root N uptake and/or turnover in the greenhouses. The species responses to warming are consistent with changes in plant species assemblages associated with past warming and suggest that future warming may increase the abundance of B. nana in tussock tundra. We conclude that a 4°C rise in air temperature alone will significantly stimulate carbon turnover in tundra but will have little effect on net carbon balance.

Responses of human skin temperature and thermal sensation to step change of air temperature

1. 1. The purpose of this paper is to clarify the non-linearity of the human physiological and psychological responses to step change of air temperature by impulse response analysis using Discrete Fourier Transformation. 2. 2. Experiments were conducted to investigate the effect of thermal transients on human responses. 3. 3. Experimental conditions were as follows: lowering air temperature from 30 to 20°C and raising air temperature from 20 to 30°C. 4. 4. The responses of local skin temperature on lowering air temperature from 30 to 20°C are not necessarily opposite to the responses found on raising air temperature from 20 to 30°C. 5. 5. From impulse response analysis using Discrete Fourier Transformation, skin temperature responses to the opposite air temperature change do not necessarily coincide with each other whenever the same temperature stimulus is occurred.

Colonial thermoregulation in honey bees (Apis mellifera)

1. Populations of honey bees held at a constant temperature for 24–48 h exhibited diurnal rhythms of metabolic rate (MR) and locomotor activity with peaks during the day and lows at night. The amplitude of the metabolic rhythm decreased as air temperature (Tin) increased. 2. Thermoregulatory behaviors including clustering and fanning occurred in cycles which correlated with the diurnal rhythms of MR and activity. 3. At cold air temperature (10°C), a high rate of thermoregulatory heat production was independent of visible activity, and conversely, at high air temperatures (40°C), MR was low despite increased locomotor activity. 4. Decreasing air temperature from 30 to 10°C day and night resulted in clustering, and metabolic increases proportional to the degree of cooling. Raising air temperature from 30 to 40°C day and night caused a drop in metabolic rate, an increase in locomotor activity, and fanning. 5. Day/night differences in thermoregulatory responses to cooling included a nocturnal reduction of the threshold air temperature for thermogenesis and a decrease in the slopes of the metabolic response curves below this threshold. At 10°C there was more clustering at night than during the day. 6. The presence of capped brood moderates these responses in a quantitative manner, as indicated by the greater metabolic rate when the bee/brood ratio is small and the greater amount of clustering on brood comb than on broodless comb. 7. At cold air temperatures (10°C), capped brood temperature is maintained above 30°C through the combined effects of clustering and thermogenesis. The metabolic responses are inversely correlated with the degree of clustering.