Heat Dissipation Limit Research Articles

Thermal Effects on Monolithic 3D Ferroelectric Transistors for Deep Neural Networks Performance

Monolithic three‐dimensional (M3D) integration advances integrated circuits by enhancing density and energy efficiency. Ferroelectric thin‐film transistors (Fe‐TFTs) attract attention for neuromorphic computing and back‐end‐of‐the‐line (BEOL) compatibility. However, M3D faces challenges like increased runtime temperatures due to limited heat dissipation, impacting system reliability. This work demonstrates the effect of temperature impact on single‐gate (SG) Fe‐TFT reliability. SG Fe‐TFTs have limitations such as read‐disturbance and small memory windows, constraining their use. To mitigate these, dual‐gate (DG) Fe‐TFTs are modeled using technology computer‐aided design, comparing their performance. Compute‐in‐memory (CIM) architectures with SG and DG Fe‐TFTs are investigated for deep neural networks (DNN) accelerators, revealing heat's detrimental effect on reliability and inference accuracy. DG Fe‐TFTs exhibit about 4.6x higher throughput than SG Fe‐TFTs. Additionally, thermal effects within the simulated M3D architecture are analyzed, noting reduced DNN accuracy to 81.11% and 67.85% for SG and DG Fe‐TFTs, respectively. Furthermore, various cooling methods and their impact on CIM system temperature are demonstrated, offering insights for efficient thermal management strategies.

An arctic breeding songbird overheats during intense activity even at low air temperatures

Birds maintain some of the highest body temperatures among endothermic animals. Often deemed a selective advantage for heat tolerance, high body temperatures also limits birds’ thermal safety margin before reaching lethal levels. Recent modelling suggests that sustained effort in Arctic birds might be restricted at mild air temperatures, which may require reductions in activity to avoid overheating, with expected negative impacts on reproductive performance. We measured within-individual changes in body temperature in calm birds and then in response to an experimental increase in activity in an outdoor captive population of Arctic, cold-specialised snow buntings (Plectrophenax nivalis), exposed to naturally varying air temperatures (− 15 to 36 °C). Calm buntings exhibited a modal body temperature range from 39.9 to 42.6 °C. However, we detected a significant increase in body temperature within minutes of shifting calm birds to active flight, with strong evidence for a positive effect of air temperature on body temperature (slope = 0.04 °C/ °C). Importantly, by an ambient temperature of 9 °C, flying buntings were already generating body temperatures ≥ 45 °C, approaching the upper thermal limits of organismal performance (45–47 °C). With known limited evaporative heat dissipation capacities in these birds, our results support the recent prediction that free-living buntings operating at maximal sustainable rates will increasingly need to rely on behavioural thermoregulatory strategies to regulate body temperature, to the detriment of nestling growth and survival.

Controlling the temperature build-up in electrode-sealed coin-shaped batteries via designing central heat dissipator

Nowadays, the ever-increasing demand for the computational power in the calculators, watches and LED lights require higher consumption rate from their portable energy source, which is typically coin-shaped batteries. The required power generates and accumulates a large amount of heat, which is a critical safety concern due to flammability of the included organic electrolytes. When heat dissipation is minimal from the electrode surface, the packaging boundary remains the sole heat transfer medium. In such case, although the center carries a minimal real estate compared to the rest of the electrode surface, the heat gets trapped, due to having the lowest reach to the heat-dissipating boundaries. For this purpose, a central heat sink component is anticipated for the coin-shaped batteries and the temperature profile across the cell is analytically derived. Subsequently, the role of the sink thermal conductivity and its scale as well as the thermal conduction of the boundary on the formation of steady state temperature profile has been analyzed. More specifically, the location of the maximum temperature rmax and its value Tmax is obtained and verified versus the extreme values of the thermal conductivities, the areal ratio of the heat sink, and the current density. The obtained results could be useful for the cost-effective design of the packaging materials (i.e. sustainable plastics and bio-degradable) with limited heat dissipation for the rechargeable batteries, particularly during the high power applications, in the presence of highly flammable electrolytes.

A Cutting Force and Hole Geometry Study for Precision Deep-Hole Microdrilling of Magnesium.

Size effects, high thrust forces, limited heat dissipation, and tool deterioration are just some of the challenges that deep microdrilling poses, underscoring the importance of effective process control to ensure quality. In this paper, an investigation performed on a microdrilling process on pure magnesium using a 0.138 mm diameter microdrill to achieve an aspect ratio equal to 36 is proposed. The effect of the variation of the cutting parameters feed per tooth fz and cutting speed vc was studied on thrust force, supporting hole quality evaluation in terms of burr height, entrance, and inner diameters. The results showed that fz significantly influences the hole quality. In fact, as fz increases, the burr height decreases and the inner diameter approaches the nominal diameter. However, optimizing the hole geometry with high feed per tooth values increases the thrust forces, compromising tool life. In fact, a significant dependence of the thrust force on both cutting parameters was found. In this scenario, increasing vc can mitigate the high thrust forces by inducing material softening. The study results improve precision manufacturing by refining parameters, ensuring the quality and reliability of magnesium-based microcomponents.

The abnormal deformation behaviors in commercial pure Ti during high speed compression

The effect of high speed compression on the deformation behaviors of pure titanium (Ti) was investigated in this paper. The results indicated that deformation twinning dominated the entire deformation process. In addition to the commonly observed twinning modes 101̅2<101̅1>,112̅1<112̅6>and 112̅2<112̅3>twinning, the uncommon twinning modes 101̅1<101̅2>, 112̅4<224̅3> twinning, and a rare twinning mode 112̅3<112̅2> twinning which has not been reported in previous literature, were observed. The 112̅3<112̅2> twinning presented an orientation relationship of 87° <101̅0>. Moreover, deviations from the ideal twinning relationship were observed in some twins which might due to the deformation induced dislocation-twin interactions. Alongside twinning, high angle kink bands with a misorientation of 61°<71017̅3> were locally activated to accommodate the deformation. These abnormal deformation behaviors, including the formation of unusual twins and high angle kink bands, occurred in grains that were less favorable for triggering common dislocation and twinning modes, based on the Schmid factor calculations. The high strain rate during high speed compression limited heat dissipation time and generated additional energy, thereby enhancing the flow stress and raising the temperature, which facilitated the occurrence of these abnormal deformation behaviors.

Hygroscopic cooling (h-cool) fabric with highly efficient sweat evaporation and heat dissipation for personal thermo-moisture management

Moisture evaporation plays a crucial role in thermal management of human body, particularly in perspiration process. However, current fabrics aim for sweat removal and takes little account of basic thermo-regulation of sweat, resulted in their limited evaporation capacity and heat dissipation at moderate/intense scenarios. In this study, a hygroscopic cooling (h-cool) fabric based on multi-functional design, for personal perspiration management, was described. By using economic and effective weaving technology, directional moisture transport routes and heat conductive pathways were incorporated in the construct. The resultant fabric showed 10 times greater one-way transport index higher than cotton, Dri-FIT and Coolswitch fabrics, which contributed to highly enhanced evaporation ability (∼4.5 times than cotton), not merely liquid diffusion. As a result, h-cool fabric performed 2.1–4.2 °C cooling efficacy with significantly reduced sweat consuming than cotton, Dri-FIT and Coolswitch fabrics in the artificial sweating skin. Finally, the practical applications by actually wearing h-cool fabric showed great evaporative-cooling efficacy during different physical activities. Owing to the excellent thermo-moisture management ability, we expect the novel concept and construct of h-cool fabric can provide promising strategy for developing functional textiles with great “cool” and comfortable “dry” tactile sensation at various daily scenarios.

The role of ambient temperature and light as cues in the control of circadian rhythms of Damaraland mole-rat

ABSTRACT Light is considered the primary entrainer for mammalian biological rhythms, including locomotor activity (LA). However, mammals experience different environmental and light conditions, which include those predominantly devoid of light stimuli, such as those experienced in subterranean environments. In this study, we investigated what environmental cue (light or ambient temperature (Ta)) is the strongest modulator of circadian rhythms, by using LA as a proxy, in mammals that experience a lifestyle devoid of light stimuli. To address this question, this study exposed a subterranean African mole-rat species, the Damaraland mole-rat (Fukomys damarensis), to six light and Ta cycles in different combinations. Contrary to previous literature, when provided with a reliable light cue, Damaraland mole rats exhibited nocturnal, diurnal, or arrhythmic LA patterns under constant Ta. While under constant darkness and a 24-hour Ta cycle mimicking the burrow environment, all mole-rats were most active during the coolest 12-hour period. This finding suggests that in a subterranean environment, which receives no reliable photic cue, the limited heat dissipation and energy constraints during digging activity experienced by Damaraland mole-rats make Ta a reliable and consistent “time-keeping” variable. More so, when providing a reliable light cue (12 light: 12 dark) to Damaraland mole-rats under a 24-hour Ta cycle, this study presents the first evidence that cycles of Ta affect the LA rhythm of a subterranean mammal more strongly than cycles of light and darkness. Once again, Damaraland mole-rats were more active during the coolest 12-hour period regardless of whether this fell during the light or dark phase. However, conclusive differentiation of entrainment to Ta from that of masking was not achieved in this study, and as such, we have recommended future research avenues to do so.

Simulation of an aircraft thermal management system based on vapor cycle response surface model

The modern aircraft Thermal Management System (TMS) faces significant challenges due to increasing thermal loads and limited heat dissipation pathways. To optimize TMS during the conceptual design stage, the development of a modeling and simulation tool is crucial. In this study, a TMS simulation model library was created using MATLAB/SIMULINK. To simplify the complexity of the Vapor Cycle System (VCS) model, a Response Surface Model (RSM) was constructed using the Monte Carlo method and validated through simulation experiments. Taking the F-22 fighter TMS as an example, a thermal dynamic simulation model was constructed to analyze the variation of thermal response parameters in key subsystems and elucidate their coupling relationships. Furthermore, the impact of total fuel flow and ram air flow on the TMS was investigated. The findings demonstrate the existence of an optimal total fuel flow that achieves a balance between maximizing fuel heat sink utilization and minimizing bleed air demand. The adaptive distribution of fuel and ram air flow was found to enhance aircraft thermal management performance. This study contributes to improving modeling efficiency and enhancing the understanding of the thermal dynamic characteristics of TMS, thereby facilitating further optimization in aircraft TMS design.

Limits to sustained energy intake. XXXIV. Can the heat dissipation limit (HDL) theory explain reproductive aging?

According to the heat dissipation limit (HDL) theory, reproductive performance is limited by the capacity to dissipate excess heat. We tested the novel hypotheses that (1) the age-related decline in reproductive performance is due to an age-related decrease of heat dissipation capacity and (2) the limiting mechanism is more severe in animals with high metabolic rates. We used bank voles (Myodes glareolus) from lines selected for high swim-induced aerobic metabolic rate, which have also increased basal metabolic rate, and unselected control lines. Adult females from three age classes - young (4 months), middle-aged (9 months) and old (16 months) - were maintained at room temperature (20°C), and half of the lactating females were shaved to increase heat dissipation capacity. Old females from both selection lines had a decreased litter size, mass and growth rate. The peak-lactation average daily metabolic rate was higher in shaved than in unshaved mothers, and this difference was more profound among old than young and middle-aged voles (P=0.02). In females with large litters, milk production tended to be higher in shaved (least squares mean, LSM±s.e.: 73.0±4.74 kJ day-1) than in unshaved voles (61.8±4.78 kJ day-1; P=0.05), but there was no significan"t effect of fur removal on the growth rate [4.47±2.29 g (4 days-1); P=0.45]. The results provide mixed support of the HDL theory and no support for the hypotheses linking the differences in reproductive aging with either a deterioration in thermoregulatory capability or genetically based differences in metabolic rate.

Enhancing stability in thin-walled part production with L-DED wire using an adaptive controller

Laser-based direct energy deposition (L-DED) with metal wire is an efficient additive manufacturing process known for its cleanliness, user-friendliness, and cost-effectiveness. Nonetheless, heat build-up, especially in thin-walled parts, leads to geometric deviations and process instabilities due to limited heat dissipation. Closed-loop control of deposition height and local temperature addresses this issue. However, traditional controllers like PID controllers with fixed dynamics cannot adequately handle the long-term drifts inherent in the system dynamics. This study introduces an adaptive controller that dynamically adjusts the parameters for effective L-DED control using optical coherence tomography for the measurement of the deposition height and a coaxial camera for the determination of the temperature from thermal radiation. The control variables include the feed speed of the wire for material input and the laser power to control the deposition height and temperature. Our approach reduces deviations of the wall’s height by a factor of 10 and enables defect-free fabrication of thin-walled parts. This underscores the efficacy of our control system in enhancing L-DED.

Lightweight hybrid lithium-ion battery thermal management system based on 3D-printed scaffold

Electric vehicles have been developed rapidly to alleviate energy shortages and environmental pollution. However, battery thermal management is still challenge to the complex structure, heavy weight, and limited heat dissipation under harsh conditions. To address these issues, a honeycomb hybrid thermal management system, which integrates the multi-layered liquid-cooled channels into a 3D-printed metal scaffold to enhance the thermal exchange effect. The impacts of the coolant inlet and outlet arrangement, channel layer number, porosity, coolant flow rate, and continuous charge-discharge cycle on heat dissipation were numerically analyzed at 35 °C and discharge rate of 3C to evaluate the system cooling performance. The results show that the heat dissipation efficiency of the proposed system is greatly improved compared with that of the system with pure phase change materials. An 85 % porosity of 3D-printed metal scaffold performs excellent heat dissipation and low system weight, the system weight can be reduced by 60 % compared to a conventional system with aluminum solid cold plate with a same volume. The system's maximum temperature and temperature difference are kept at 48.1 °C and 2.6 °C, respectively. Additionally, the system performance was validated in the continuous charge-discharge cycle test. This work will help develop the lightweight BTMS with excellent thermal performance for electric vehicles.

Small increases in ambient temperature reduce offspring body mass in an equatorial mammal.

Human-induced climate change is leading to temperature rises, along with increases in the frequency and intensity of heatwaves. Many animals respond to high temperatures through behavioural thermoregulation, for example by resting in the shade, but this may impose opportunity costs by reducing foraging time (therefore energy supply), and so may be most effective when food is abundant. However, the heat dissipation limit (HDL) theory proposes that even when energy supply is plentiful, high temperatures can still have negative effects. This is because dissipating excess heat becomes harder, which limits processes that generate heat such as lactation. We tested predictions from HDL on a wild, equatorial population of banded mongooses (Mungos mungo). In support of the HDL theory, higher ambient temperatures led to lighter pups, and increasing food availability made little difference to pup weight under hotter conditions. This suggests that direct physiological constraints rather than opportunity costs of behavioural thermoregulation explain the negative impact of high temperatures on pup growth. Our results indicate that climate change may be particularly important for equatorial species, which often experience high temperatures year-round so cannot time reproduction to coincide with cooler conditions.

Real-time temperature prediction of lunar regolith drilling based on ATT-Bi-LSTM network

Lunar drilling is conducted in extreme environments, where limited heat dissipation pathways may cause overheating during drilling, potentially leading to destructive effects on the drill tool. To address the challenge of rapid temperature change in lunar regolith drilling, this paper presents a spatiotemporal feature fusion method for the real-time prediction of drilling temperature inside a lunar regolith simulant. The method aims to accurately predict the temperature of eight positions on the drill tool in the next second based on seven state parameters during drilling from the previous 20 seconds. It utilizes deep learning techniques to combine the Bi-LSTM and self-attention mechanism to fully exploit past and future information to extract spatiotemporal features from time series data and focus on the crucial features for temperature prediction. Additionally, a proposed early stopping-Bayesian hyperparameter optimization method is incorporated to effectively adjust the hyperparameters of the model. Experimental results demonstrate the superior performance of this method on data from drilling experiments with lunar regolith simulant in a vacuum chamber, significantly outperforming other models in statistical terms and meeting real-time prediction requirements. Furthermore, it exhibits robustness and generalization capability in practical applications on two different robotic drills. This research provides reliable support for predicting drilling temperature in future lunar exploration missions and reveals the spatiotemporal relationship in the thermophysical field during drilling. It holds crucial significance in guiding mission planners and operators to proactively implement appropriate measures in advance, ensuring the smooth operation of the drilling apparatus and comprehending the generation, conduction, and dissipation mechanisms of heat during lunar regolith drilling.

Limits to sustained energy intake. XXXIII. Thyroid hormones play important roles in milk production but do not define the heat dissipation limit in Swiss mice.

The limits to sustained energy intake set physiological upper boundaries that affect many aspects of human and animal performance. The mechanisms underlying these limits however remain unclear. We exposed Swiss mice to either supplementary thyroid hormones (THs) or methimazole during lactation at 21 °C or 32.5 °C, and measured food intake, resting metabolic rate (RMR), milk energy output (MEO), serum THs and mammary gland gene expression of females, and litter size and mass of their offspring. Lactating females developed hyperthyroidism following exposure to supplementary THs at 21 °C, but they did not significantly change body temperature, asymptotic food intake, RMR or MEO, and litter and mass were unaffected. Hypothyroidism, induced by either methimazole or 32.5 °C exposure, significantly decreased asymptotic food intake, RMR and MEO, resulting in significantly decreased litter size and litter mass. Furthermore, gene expression of key genes in the mammary gland were significantly decreased by either methimazole or hot exposure, including gene expression of THs and prolactin receptors, and Stat5a and Stat5b. This suggests that endogenous THs are necessary to maintain sustained energy intake and milk energy output. Suppression of the thyroid axis seems to be an essential aspect of the mechanism by which mice at 32.5 °C reduce their lactation performance to avoid overheating. However, THs do not define the upper limit to sustained energy intake and milk energy output at peak lactation at 21 °C. Another, as yet unknown, factor, prevents supplementary thyroxine exerting any stimulatory metabolic impacts on lactating mice at 21 °C.

Experimental research and optimization of a thermoelectric generator excited by pulsed combustion mode under limited heat dissipation for combined heat and power supply

In this paper, a scheme of pulse combustion mode with pulse input of gas is proposed to solve the problems of low output electrical performance and energy conversion efficiency of combustion-based thermoelectric systems under limited heat dissipation conditions, which is based on experiments. The characteristics of the thermoelectric system show that pulse combustion mode can increase the instantaneous temperature difference, so as to achieve the excitation effect on the output power. The relationships among output power, system efficiency, excitation intensity and pulse input parameters, and the geometry of thermoelectric modules are obtained. The influence of pulse input parameters on the excitation intensity is interactive, and top dead center of pulse inlet power is the parameter that has the greatest influence on the performance. Compared to the constant combustion mode, the pulse combustion mode can increase the output power by up to 28.3%. A maximum output power of 7.15 W with air-cooled heat dissipation and a maximum system efficiency of 3.26% were experimentally obtained, which is a 30% increase in efficiency over current air-cooled heat dissipation thermoelectric systems. Therefore, this paper can provide solutions for more practical power supply, provide effective and feasible guidance for the study of thermoelectric systems, and provide useful insights into the electrical properties of thermoelectric systems.

Enhanced capillary performance of hierarchical dendritic copper surface for ultrathin heat-spreading devices

High-performance electronic systems require efficient heat dissipation devices. Vapor chambers (VCs) are practical thermal solutions for lightweight portable electronics that have limited heat dissipation space. A functional VC requires an interior wick to sustain the capillary circulation of the condensed fluid back to the heated region. The capillary wick performance can be indexed by the ratio of liquid permeability to the effective pore size of the wick structure. This study describes the capillary behavior of a thin hierarchical dendritic copper film (&amp;lt;100 μm thick) prepared by electrodeposition and thermal sintering. The effects of the electrodeposition current density, deposition time, and sintering temperature on the capillary performance of the dendritic copper films were investigated. The relationship between the wicking capability and dendritic morphology, tailored by the electrodeposition process, was explored. A post-deposition sintering treatment was found to be beneficial for improving the structural integrity, adhesion, and capillary performance of dendritic copper wicks. A very high capillary performance (0.81 μm) was realized on a 30-μm-thick dendritic copper wick that matches the need for ultrathin VCs used in highly compact electronic systems.

Experimental Research on Heat Dissipation at the Hot End of Semiconductor Refrigeration Chips

TEC1-12705 and TEC1-12706 two types of semiconductor refrigeration chips were designed with different hot-end heat dissipation conditions. At the same time, a test device for heat dissipation of heat pipes for heat sinks with separate current input and two-stage refrigeration was designed, and the influence of hot-end heat dissipation conditions on cold-end temperature was analyzed. The test results show that the cold terminal temperature of the semiconductor refrigeration sheet is related to the heat dissipation capacity of the hot terminal. Under the condition of limited heat dissipation capacity, the cold terminal temperature decreases first and then increases with the increase of the input current; and under the condition of ensuring the heat dissipation capacity, the cold terminal temperature decreases with the increase of the input current and decreases with the decrease of the hot terminal temperature. The two-piece TEC1-12706 semiconductor refrigeration sheet adopts two-stage refrigeration with separate current input, and the minimum temperature of the cold terminal can reach −36,8°С. The test results show that improving the heat dissipation conditions of the hot end can improve the performance of a single semiconductor refrigeration sheet. At the same time, under the best heat dissipation conditions, the use of separate current input two-stage refrigeration can greatly reduce the temperature of the cold end, which is of great significance to improve the working temperature difference of the semiconductor refrigeration sheet.

Lactating SKH-1 furless mice prioritize own comfort over growth of their pups.

Lactation is the most energetically demanding physiological process that occurs in mammalian females, and as a consequence of this energy expenditure, lactating females produce an enormous amount of excess heat. This heat is thought to limit the amount of milk a mother produces, and by improving heat dissipation, females may improve their milk production and offspring quality. Here we used SKH-1 hairless mice as a natural model of improved heat dissipation. Lactating mothers were given access to a secondary cage to rest away from their pups, and this secondary cage was kept either at room temperature (22°C) in the control rounds or cooled to 8°C in the experimental groups. We hypothesized that the cold exposure would maximize the heat dissipation potential, leading to increased milk production and healthier pups even in the hairless mouse model. However, we found the opposite, where cold exposure allowed mothers to eat more food, but they produced smaller weight pups at the end of lactation. Our results suggest that mothers prioritize their own fitness, even if it lowers the fitness of their offspring in this particular mouse strain. This maternal-offspring trade-off is interesting and requires future studies to understand the full interaction of maternal effects and offspring fitness in the light of the heat dissipation limitation.

The travel speeds of large animals are limited by their heat-dissipation capacities.

Movement is critical to animal survival and, thus, biodiversity in fragmented landscapes. Increasing fragmentation in the Anthropocene necessitates predictions about the movement capacities of the multitude of species that inhabit natural ecosystems. This requires mechanistic, trait-based animal locomotion models, which are sufficiently general as well as biologically realistic. While larger animals should generally be able to travel greater distances, reported trends in their maximum speeds across a range of body sizes suggest limited movement capacities among the largest species. Here, we show that this also applies to travel speeds and that this arises because of their limited heat-dissipation capacities. We derive a model considering how fundamental biophysical constraints of animal body mass associated with energy utilisation (i.e., larger animals have a lower metabolic energy cost of locomotion) and heat-dissipation (i.e., larger animals require more time to dissipate metabolic heat) limit aerobic travel speeds. Using an extensive empirical dataset of animal travel speeds (532 species), we show that this allometric heat-dissipation model best captures the hump-shaped trends in travel speed with body mass for flying, running, and swimming animals. This implies that the inability to dissipate metabolic heat leads to the saturation and eventual decrease in travel speed with increasing body mass as larger animals must reduce their realised travel speeds in order to avoid hyperthermia during extended locomotion bouts. As a result, the highest travel speeds are achieved by animals of intermediate body mass, suggesting that the largest species are more limited in their movement capacities than previously anticipated. Consequently, we provide a mechanistic understanding of animal travel speed that can be generalised across species, even when the details of an individual species' biology are unknown, to facilitate more realistic predictions of biodiversity dynamics in fragmented landscapes.

Behavioural responses of a large, heat-sensitive mammal to climatic variation at multiple spatial scales.

Climate warming creates energetic challenges for endothermic species by increasing metabolic and hydric costs of thermoregulation. Although endotherms can invoke an array of behavioural and physiological strategies for maintaining homeostasis, the relative effectiveness of those strategies in a climate that is becoming both warmer and drier is not well understood. In accordance with the heat dissipation limit theory which suggests that allocation of energy to growth and reproduction by endotherms is constrained by the ability to dissipate heat, we expected that patterns of habitat use by large, heat-sensitive mammals across multiple scales are critical for behavioural thermoregulation during periods of potential heat stress and that they must invest a large portion of time to maintain heat balance. To test our predictions, we evaluated mechanisms underpinning the effectiveness of bed sites for ameliorating daytime heat loads and potential heat stress across the landscape while accounting for other factors known to affect behaviour. We integrated detailed data on microclimate and animal attributes of moose Alces alces, into a biophysical model to quantify costs of thermoregulation at fine and coarse spatial scales. During summer, moose spent an average of 67.8% of daylight hours bedded, and selected bed sites and home ranges that reduced risk of experiencing heat stress. For most of the day, shade could effectively mitigate the risk of experiencing heat stress up to 10°C, but at warmer temperatures (up to 20°C) wet soil was necessary to maintain homeostasis via conductive heat loss. Consistent selection across spatial scales for locations that reduced heat load underscores the importance of the thermal environment as a driver of behaviour in this heat-sensitive mammal. Moose in North America have long been characterized as riparian-obligate species because of their dependence on woody plant species for food. Nevertheless, the importance of dissipating endogenous heat loads conductively through wet soil suggests riparian habitats also are critical thermal refuges for moose. Such refuges may be especially important in the face of a warming climate in which both high environmental temperatures and drier conditions will likely exacerbate limits to heat dissipation, especially for large, heat-sensitive animals.