Minimize Heat Loss Research Articles

Design, Fabrication, and Performance Evaluation of Portable and Large-Area Blackbody System.

In this study, a portable and large-area blackbody system was developed following a series of processes including design, computational analysis, fabrication, and experimental analysis and evaluation. The blackbody system was designed to be lightweight (5 kg), and its temperature could exceed the ambient temperature by up to 15 °C under operation. A carbon-fiber-based heat source was used to achieve a uniform temperature distribution. A heat shield fabricated from an insulation material was embedded at the opposite side of the heating element to minimize heat loss. A prototype of the blackbody system was fabricated based on the design and transient coupled electro-thermal simulation results. The operation performance of this system, such as the thermal response, signal transfer function, and noise equivalent temperature difference, was evaluated by employing an infrared imaging system. In addition, emissivity was measured during operation. The results of this study show that the developed portable and large-area blackbody system can be expected to serve as a reliable reference source for the calibration of aerial infrared images for the application of aerial infrared techniques to remote sensing.

Investigation of PM10, PM2.5, PM1 in an unoccupied airflow-controlled room: How reliable to neglect resuspension and assume unreactive particles?

It is now well recognized that Particulate Matter (PM) is one of the main air pollutants affecting both ambient and indoor air quality. While ambient PM mass concentration measurements are often performed by air quality monitoring networks, current regulations do not address their indoor concentrations. The latter can be estimated nonetheless from a mass balance analysis accounting for (i) the transfer of particles from outdoor and (ii) their typical indoor sources (emissions, resuspension) and sinks (deposition, removal by air exchange). Inherently, the mass balance analysis is valid with inert atmospheric species, i.e. mass is conserved and described by sources and sinks, thus assuming no physicochemical transformations. To check that the relative imbalance (RI) is not significant over different size fractions, a series of careful measurements were conducted in an unoccupied room within a building incorporating an energy-efficient design (minimal heat losses, negligible air leaks, etc.). We show that by carefully characterizing the room properties, i.e. the air exchange rate, penetration factors and deposition rates for sized-resolved particles, the PM10 and PM2.5 fractions, which are typically regulated outdoors, as well as PM1, can be well estimated indoors (with RI between measured and expected values < 19%) under moderate ambient temperatures (<22 °C in this study). However, RI increases significantly, especially for submicron particles, at higher temperatures, indicating possible transformations in the particulate phase, which are not accounted for by the mass balance model. Therefore caution is recommended regarding the mass balance analysis to estimate PM fractions indoors, especially for PM1.

КОНСТРУКТИВНА ТА ЕКОНОМІЧНА ЕФЕКТИВНІСТЬ ЗОВНІШНЬОГО УТЕПЛЕННЯ СТІН БУДИНКІВ

The article considers several different options for materials for external wall insulation and their advantages from an economic and structural point of view, taking into account the characteristics of some of the most popular insulation and the feasibility of use in a given case. Currently, energy saving and reducing the use of fuel resources is one of the most pressing issues, both in the construction of new buildings and in the case of reconstruction of the existing building stock and means the need to have structures that will minimize heat loss. It is understood why high-quality thermal insulation is an investment for many years in the conditions of unstable energy prices and the economic advantages of reliable insulation from different directions are described. The comparative technical characteristics of the most popular materials of polyfoam and mineral wool in thermal insulation of walls are given, features of their use in different conditions are analyzed, the average prices for the device for the city of Kiev are compared. For a cheaper option, the calculation of the economic effect for the city of Kyiv is performed. It is determined that one of the most important factors of comfortable life is maintaining a comfortable microclimate in the building for many years, regardless of the weather outside, where you can feel as safe and comfortable as possible, and its direct dependence on quality protection of structures outside. Emphasis is placed on the fact that reliable protection of structures is also an investment in the peace of mind of the building owner and the confidence that the structures will not require repair in a short period of time. Whatever new forms of buildings and structures are invented today by developers, high-quality and modern insulation is an integral part of modern and comfortable housing, a part that should not be neglected and first of all perform all work qualitatively and pay special attention to joints of sheets of insulation material, to have as little chance as possible of external influences on warming which action can reduce service life not only of a design of warming, but also of the building as a whole.

Influence of geometry on the thermal performance of water pit seasonal heat storages for solar district heating

The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating. A TRNSYS component model for a truncated cone water pit was developed based on the coordinate transformation method and validated by experimental results from the water pit heat storage in Huangdicheng in 2018. The thermal performance of 26 water pits with different heights and side wall slopes was calculated for 10 consecutive years. It takes four to six years for the water pit to reach steady-state operation. The operation data from the tenth year was selected to evaluate the thermal performance of each configuration. The results show that because of the thermal insulation on top of the water pit, the height to diameter ratio of a water pit with minimum annual heat loss was always smaller than 1.0. The annual storage efficiency of a water pit increases with side wall slope due to the reduced side wall area. There is an almost linear increase in the thermal stratification number of a water pit with height. With an increase in the height, thermal stratification in water pits with a steeper slope increased more gradually than water pits with a lower slope. The findings in this paper are relevant for the design optimization of water pits as seasonal thermal energy storages.

Strengthening effect of microwave on spark ignited spherical expanding flames of methane-air mixture

The Microwave Assisted Spark Ignition system is a novel and potential ignition method to improve efficiency of spark ignition engines. To better understand the coupling mechanisms/characteristics between microwaves and spark plasma, experiments were conducted to visualize spark discharge and flame development with microwave emitted in a Constant Volume Combustion Chamber. The operation parameters varied included equivalence ratio, ambient pressure, microwave pulse repetition frequency, and peak power. To clearly illuminate the coupling mechanism between microwave and spark plasma, a small-diameter antenna device was specifically designed to minimize heat loss. The microwave assisted spark ignition and flame propagation characteristics of methane-air premixed spherical flames were studied first. Subsequently, non-reactive discharge was experimented to exclude the effects from combustion. Results showed that microwave increased the development speed of an early flame kernel by 60% with 1 kHz microwave pulse repetition frequency and 1000 W peak power under the condition of equivalence ratio 0.6 and ambient pressure 0.1 MPa. The enhancement was believed to be the result of enhanced chemical reaction and the induced flame deformation by collisions between high energy electrons and other particles. As the ambient pressure increased, the enhancement effect of microwaves on flame kernels was found to diminish. In this situation, non-reactive discharge and related MAI experiments showed that a higher pulse repetition frequency or peak power was beneficial to strengthen the effect of microwave as much higher energy absorption efficiency was achieved.

Performance of Biodrying Process based on Temperature Profile and Cumulation

The biodrying process of solid waste is an approach to the use of biomass energy, where solid waste is dried using the heat generated from aerobic degradation of organic matter. Temperature profile and cumulation of the solid waste biodrying process are the success factors in drying solid waste. The reactor used is made of plywood with dimensions of (30 × 30 × 100) cm equipped with a heat sink using Thermoshield Universal to minimize heat loss. Aeration discharge at the biodrying process reactor is 0.023 m3/kg/h. The results showed a maximum temperature of 61°C produced from the bottom layer of the biodrying reactor (addition of 6 l / min air flow) on the first day at 10:00 pm. Cumulation temperature in the bottom layer of the biodrying reactor for 21 days of research reached 186.9°C. This value is a source of heat generated from the decomposition of waste under aerobic conditions. Based on the three layers, it can be concluded that the bottom layer produces higher temperature cumulation than the top or middle layer. This research can be a reference for determining temperature monitoring points and knowing Temperature cumulation generated from the waste decomposition process using biodrying technology.

УСТАНОВКА ДЛЯ ДОСЛІДЖЕННЯ ТЕПЛОПРОВІДНОСТІ ЕНЕРГОЕФЕКТИВНИХ ТЕПЛОІЗОЛЯЦІЙНИХ МАТЕРІАЛІВ РОСЛИННОГО ПОХОДЖЕННЯ

One of the key point criteria of any thermal insulation material that determine its energy efficiency is thermal conductivity. Determination of thermal conductivity of materials of plant origin, as well as any other, can be reliably determined only experimentally. The proposed original design of an inexpensive installation for studying the thermal conductivity of heat-insulating materials of plant origin contains a heat-insulated empty body for placing the test sample and a heat source. The heat flow is created by a heating element, which consists of an upper and lower metal plate of a given thickness with a known coefficient of thermal conductivity. The volume created between the plates is filled with a layer of quartz sand to create additional homogeneous heat flow. This design of the heating element provides a homogeneous distribution of heat flux over the cross-sectional area of the test sample of the insulating material. To register the change in the magnitude of the heat flux, thermocouples are used, which are located on the inner surface of the upper plate of the heat source and on the cold side of the investigated sample of heat-insulating material. Data on temperature changes are registered by the automatic registration block. A tubular electric heater of appropriate configuration is symmetrically attached to the lower plate along the cross-sectional area. The tubular electric heater is connected to the voltage control unit. Between the lower plane of the lower plate and the housing of the installation there is an air layer to minimize heat loss from the heating element. The coefficient of thermal conductivity, which characterizes the efficiency of the insulating material, is calculated by the known Fourier formula for the steady-state temperature regime from the input information about the temperature difference in the characteristic cross sections of the sample.

Physical and thermal insulation properties of the composites based on seawater-neutralised bauxite residue

The objective of this study is to evaluate the possibility of using bauxite residue (BR), which is a highly hazardous waste, as a filler in thermoset polymer matrices for applications in insulating construction materials to minimise heat loss in buildings. Unsaturated polyester resin (UPR) blended with the seawater-neutralised BR in a ratio of 0–60 vol.% was transformed into a solid via a crosslinking process at room temperature. The pristine polyester and BR–UPR composites were characterised to ascertain their structural, physical and thermal properties. The results indicate that BR is a good filler that can be used with UPR to develop thermal insulation/construction materials. The UPR composite containing 40 vol.% BR is considered to be the optimum mixture with respect to the tested physical and thermal properties because it utilises a large amount of filler and shows promising thermal insulation characteristics with a thermal conductivity of 0.096 W/(m∙K), a thermal diffusivity of 0.161 mm2/s, a 24–h water retention of 0.15 % and a bulk density of 1484 kg/m3. Furthermore, the thermal stability of the prepared composites is positively influenced by the incorporation of BR. The overall weight loss upon heating to 900 °C decreased from 99.85 % (pristine polyester) to 46.68 % (60 vol.% BR composite).

Enhanced solar desalination by delignified wood coated with bimetallic Fe/Pd nanoparticles

In this paper, a new cost-effective method has been developed to utilize solar energy for steam generation. For the first time, the delignified wood was chosen as a self-regenerating substrate coated with Fe/Pd bimetallic nanoparticles (NPs) as either single or double-layer solar photoabsorbers. The results revealed that in the case of single-layer, the optimum wood thickness, the thickness at which maximum evaporation rate and minimum heat loss occur, is 10 and 5 mm for the deionized water and seawater, respectively. Under the radiation of 3 sun (3 kW m−2), the evaporation efficiency was enhanced up to 103% using the wood with a thickness of 5 mm coated with Fe/Pd NPs compared to the case in which evaporation happens from the seawater surface without any absorber on the surface (conventional case). In order to increase the evaporation rate, a double-layer substrate was utilized. The lower layer was composed of either wood or polystyrene foam with a thickness of 5 mm while the upper layer was composed of wood with 5 mm thickness coated with Fe/Pd NPs. The results showed 126% and 167% enhancement in evaporation efficiency for Fe/Pd W5W5 (wood with a thickness of 5 mm coated with nanoparticles in the upper layer, and wood with a thickness of 5 mm in the lower layer) and Fe/Pd W5F5 (wood with a thickness of 5 mm coated with nanoparticles in the upper layer, and foam with a thickness of 5 mm in the lower layer), respectively, compared to that of the seawater. Moreover, the economic analysis indicated that using two-layer photoabsorber (Fe/Pd W5F5) is an affordable technique for solar steam generation compared to some previously reported methods in the literature.

Novel Porous Refractory Synthesized from Diatomaceous Earth and Rice Husk Ash

Refractory materials are products used in thermal equipment to protect the fire and prevent heat loss to the outside environment. Thermal equipment such as driers, ceramic kilns, glass or metal furnaces and others always consume high heat in the combustion of the fuel. If the thermal equipments have high heat loss which cause wastes of fuel and increases production costs. Therefore, researchers are always looking for a solution to minimize heat loss for the kiln. In which, refractory materials significantly influence to the heat loss of the kiln and they have been studied a lot in recent years.This study focused on utilization of locally available raw materials to product the novel porous refractory composites. The products have high porosity based on chosing the suitable raw materials and forming process. The refractory has high porosity and low thermal conductivity reponded to requirements of saving energy for the thermal equipments. More important, the novel porous refractory products have high shape stability when observed by heating microscope in a range of room temperature to over 1400 o C.

Impact of Flow Blowing and Suction strategies on the establishment of an aerodynamic barrier for solar cavity receivers

This study compares two aerodynamic approaches to minimize convective losses from cavity receivers, namely blowing and suction. A laboratory-scale cavity receiver was operated in a large wind tunnel at varying wind speed and tilt angle. The inner surface of the cavity was heated to a constant temperature of 300 °C by finely controlled electrical heaters. The measured electric energy required to maintain the heaters at the same temperature was used to provide a direct measure of losses from the receiver. An air curtain was engineered to provide curtain of air blown either downward or upwards across the aperture. Suction was alternatively applied through a nozzle positioned below the aperture for a series of suction flowrates. A numerical study was also conducted using a commercial CFD package and validated with available data. It was found that the upward blowing air curtain performs better than the downward curtain for the buoyancy dominant conditions. Moreover, the measured effectiveness of the downward blowing air curtain at tilt angle of the cavity of 45° showed that the application of air curtain with higher velocities increases the convective heat losses over the case with no air curtain. When comparing the performance of air curtain with air suction, it was found that for the low range of relative momentum ratio of curtain to wind flow, suction performs better than blown air. Finally, this study highlights the need for adaptable strategies, based on operating condition, to minimize heat losses and improve the thermal efficiency of cavity receivers.

Room without a view-Den excavation in relation to body size in brown bears.

Hibernation is an adaptive strategy to survive harsh winter conditions and food shortage. The use of well‐insulated winter dens helps animals minimize energy loss during hibernation. Brown bears (Ursus arctos) commonly use excavated dens for hibernation. Physical attributes of excavated dens are expected to impact the bear's heat retention and energy conservation. The objective of this study was to examine the determinants of cavity size of excavated dens and the impact of physical attributes of excavated dens on energy conservation in hibernating bears, hypothesizing that bears excavate dens in a way to minimize heat loss and optimize energy conservation during hibernation. We predicted that den cavity size would be determined by the bear's body size and that older bears would excavate better‐fitting cavities to minimize heat loss, due to their previous experience. We further predicted that physical attributes of excavated dens would affect the bears’ posthibernation body condition. Our results revealed that bears excavated a den cavity in relation to their body size, regardless of sex, and that older bears tended to excavate better‐fitting den cavities compared to young bears, as we expected. Older bears excavated better‐fitting den cavities, suggesting a potentially experience‐based shift with age in den‐excavation behavior and an optimum cavity size relative to a bear's body size. Our key finding is that insulation of excavated dens provided by wall/rood thickness and bedding materials had a significant positive effect on bears’ posthibernation body condition. We believe that our study provides new insight into how not only the quality of denning habitat, but also the quality of dens may affect hibernating animals, by presenting a potential adaptive aspect of den preparation (age effect on efficiency in den excavation) and effect of den attributes on the posthibernation body condition of brown bears.

Nocturnal dispersal flight of crickets: Behavioural and physiological responses to cool environmental temperatures

Abstract Flight of nocturnal insects may be limited by cool nighttime environmental temperatures. We used laboratory and field experiments to explore the thermal basis of nocturnal flight in wing‐polymorphic Gryllus lineaticeps crickets consisting of long‐winged (LW), flight‐capable morphs and short‐winged (SW), flight‐incapable morphs. These crickets are a model for life history evolution and loss of flight, but their thermal requirements for flight have been unknown. We hypothesized that LW crickets achieve warm body temperatures required for flight through a combination of behavioural thermoregulation, producing heat endogenously (either by initiating muscular thermogenesis or increasing resting metabolic rate) and minimizing heat loss (by circulatory adjustments or insulation). Summer evening air temperatures in the field gradually declined from 25 to 18°C during the hours of nighttime cricket activity. Laboratory LW crickets did not fly at a body temperature of 18°C, and 60% flew at 25°C. In an experimental thermal gradient, spontaneous flight did not occur until body temperature exceeded 35°C, confirming that nocturnal field air temperature limits flight in this species. In a thermal gradient, LW crickets preferred higher temperatures (~36°C) than SW crickets (~32.5°C). In the field, all crickets were warmer than air temperature but considerably cooler than their preferred temperatures. LW crickets had higher field body temperatures (24.3°C) than SW crickets (22.3°C). LW crickets spontaneously initiated muscular thermogenesis through wing vibrations, increasing body temperature to a pre‐flight maximum of 35°C. Muscular thermogenesis was limited below 25°C. LW crickets cooled more slowly and had higher metabolic rates than SW crickets. We conclude that LW crickets prepare to fly on cool nights by gaining heat from warm substrates, activating endogenous muscular thermogenesis and reducing their cooling rate. These mechanisms are absent or less pronounced in SW crickets. The overall thermoregulatory strategy we report represents a previously unrecognized component of insect dispersal polymorphism. We suggest that thermal constraints on nocturnal flight may have contributed to evolutionary loss of flight in other insect groups. A free Plain Language Summary can be found within the Supporting Information of this article.

14-3-3ζ mediates an alternative, non-thermogenic mechanism in male mice to reduce heat loss and improve cold tolerance

ObjectiveAdaptive thermogenesis, which is partly mediated by sympathetic input on brown adipose tissue (BAT), is a mechanism of heat production that confers protection against prolonged cold exposure. Various endogenous stimuli, for example, norepinephrine and FGF-21, can also promote the conversion of inguinal white adipocytes to beige adipocytes, which may represent a secondary cell type that contributes to adaptive thermogenesis. We previously identified an essential role of the molecular scaffold 14-3-3ζ in adipogenesis, but one of the earliest, identified functions of 14-3-3ζ is its regulatory effects on the activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of norepinephrine. Herein, we examined whether 14-3-3ζ could influence adaptive thermogenesis via actions on BAT activation or the beiging of white adipocytes. MethodsTransgenic mice over-expressing a TAP-tagged human 14-3-3ζ molecule or heterozygous mice without one allele of Ywhaz, the gene encoding 14-3-3ζ, were used to explore the contribution of 14-3-3ζ to acute (3 h) and prolonged (3 days) cold (4 °C) exposure. Metabolic caging experiments, PET-CT imaging, and laser Doppler imaging were used to determine the effect of 14-3-3ζ over-expression on thermogenic and vasoconstrictive mechanisms in response to cold. ResultsTransgenic over-expression of 14-3-3ζ (TAP) in male mice significantly improved tolerance to acute and prolonged cold. In response to cold, body temperatures in TAP mice did not decrease to the same extent when compared to wildtype (WT) mice, and this was associated with increased UCP1 expression in beige inguinal white tissue (iWAT) and BAT. Of note was the paradoxical finding that cold-induced changes in body temperatures of TAP mice were associated with significantly decreased energy expenditure. The marked improvements in tolerance to prolonged cold were not due to changes in sensitivity to β-adrenergic stimulation or BAT or iWAT oxidative metabolism; instead, over-expression of 14-3-3ζ significantly decreased thermal conductance and heat loss in mice via increased peripheral vasoconstriction. ConclusionsDespite being associated with elevations in cold-induced UCP1 expression in brown or beige adipocytes, these findings suggest that 14-3-3ζ regulates an alternative, non-thermogenic mechanism via vasoconstriction to minimize heat loss during cold exposure.

Optimization of Multilayered Walls for Building Envelopes Including PCM-Based Composites.

This work proposes a numerical procedure to simulate and optimize the thermal response of a multilayered wallboard system for building envelopes, where each layer can be possibly made of Phase Change Materials (PCM)-based composites to take advantage of their Thermal-Energy Storage (TES) capacity. The simulation step consists in solving the transient heat conduction equation across the whole wallboard using the enthalpy-based finite element method. The weather is described in detail by the Typical Meteorological Year (TMY) of the building location. Taking the TMY as well as the wall azimuth as inputs, EnergyPlusTM is used to define the convective boundary conditions at the external surface of the wall. For each layer, the material is chosen from a predefined vade mecum, including several PCM-based composites developed at the Institut für Werkstoffe im Bauwesen of TU Darmstadt together with standard insulating materials (i.e., EPS or Rockwool). Finally, the optimization step consists in using genetic algorithms to determine the stacking sequence of materials across the wallboard to minimize the undesired heat loads. The current simulation-based optimization procedure is applied to the design of envelopes for minimal undesired heat losses and gains in two locations with considerably different weather conditions, viz. Sauce Viejo in Argentina and Frankfurt in Germany. In general, for each location and all the considered orientations (north, east, south and west), optimal results consist of EPS walls containing a thin layer made of the PCM-based composite with highest TES capacity, placed near the middle of the wall and closer to the internal surface.

Research on regeneration performance of the solar steam method for absorption air-conditioning system

Solar absorption air-conditioning system is a hot spot for solar energy application. The key to high system performance lies in the improvement of energy utilization efficiency. On this purpose, the solar steam regeneration method has been proposed: adopting material with special structure, it locates solar energy in the event of evaporation and minimizes heat loss. However, this method has only been applied on evaporation of pure water, no researches have yet been made on absorbent solutions. To reveal the actual performance of this method for absorption system, both theoretical and experimental work have been done in this paper. Models have been developed and some important parameters have been investigated. Preliminary test of the regeneration process has been carried out. Through analysis, the paper exposes the influences of the solution concentration and absorbent variety. With the solar steam method, the efficiency has been increased by 2 or 3 times, approached 40% in experiments. Beyond higher performance, this new method also has advantages on cost and stability, making it a competitive choice for future application.

Simple structural indocyanine green-loaded microbubbles for dual-modality imaging and multi-synergistic photothermal therapy in prostate cancer

As problems with the overuse of radical prostate cancer (PCa) treatment are increasingly exposed, focal therapy represents the direction of low- or intermediate-risk PCa management in the future. However, inaccurate diagnosis and low controllability of focal therapy hinder its clinical translation. In this study, we develop simple structural cyclic arginine-glycine-aspartic (cRGD) peptide-modified and indocyanine green (ICG)-loaded microbubbles (cRGD-ICG-MBs) for ultrasound-photoacoustic imaging and multi-synergistic photothermal therapy (PTT) to address the above problems. Precise PCa diagnosis is achieved by molecular ultrasound imaging. cRGD-targeting and low-frequency ultrasound with an amplitude of 500kPa convert MBs into nanoparticles for enhanced ICG delivery. Alow frequency2500 kPa amplitude ultrasound enables temporary vasculature destruction, which minimizes heat loss during PTT. Specifically, ICG in the tumor region is 14-fold higher than the control, resulting in satisfactory PTT. Our study highlights that this theranostic strategy possesses considerable clinical translational potential, especially in mini-invasive and individualized PCa therapy.

The determination of isobaric heat capacities of liquid by the new flow calorimeter

A new flow calorimeter is developed to analyze the isobaric heat capacity of liquid. The characteristics of calorimeter have been studied at temperatures from 293 K to 353 K and pressures from 0.1 MPa to 15 MPa. The design of the calorimeter includes the innermost part of the calorimeter with two thick-walls, aluminum shields and microheater. The function of thick-walls with aluminum shields is to replace the conventional constant temperature bath for minimizing heat loss and precisely controlling the temperature of calorimeter. In order to verify the feasibility and reliability of the apparatus, the heat loss is checked by pure water under given pressure and various temperatures. The heat capacity of toluene, heptane and cyclohexane are measured at various temperatures and pressures. The experimentally measured data as a whole is in good agreement with the literature values available. Compared with the literature data, the experimental results by using the new calorimeter show that the deviations are less than 2%.

A multi-scale material model for the estimation of the transversely isotropic thermal conductivity tensor of fired clay bricks

Fired clay bricks are employed in increasingly demanding application domains, such as multi-storey buildings and façades allowing only minimal heat loss. The latter requirement is often met by the use of pore forming agents. Then, pore size and morphology, as well as the thermal conductivity of the solid constituents of fired clay, govern the material's overall thermal conductivity tensor. We here quantify corresponding structure–property relations in the framework of random homogenization theory, introducing ellipsoidal shape and orientation distributions of material phases (including pores) at three different organizational levels. The model is validated by experimental techniques, such as scanning thermal microscopy, micro-computed tomography, and scanning electron microscopy. A final sensitivity analysis reveals that four design parameters heavily contribute to the overall thermal conductivity of fired clay bricks; namely the thermal conductivity of the fired clay matrix as well as the porosity of each of the three organizational levels.

Seasonal shifts in activity timing reduce heat loss of small mammals during winter

All activity imposes costs, but animals can often alter the timing of their activity to reduce these costs. Metabolic costs of activity are especially high during seasons of energy deficits (such as winter), but the extent to which animals can adjust their activity timing to reduce metabolic costs is unclear. Here, we test the hypothesis that the timing of small mammal activity during winter minimizes heat loss. Using motion-activated cameras deployed under snow, we show that a widely distributed nocturnal small mammal species (white-footed mouse, Peromyscus leucopus) shifted to diurnal activity in early winter, which reduced potential heat loss by 4%. The southern red-backed vole, Myodes gapperi, also avoided cold temperatures, but did so by adjusting its activity timing at a broader temporal scale by minimizing activity on cold days. We conclude that plasticity in activity timing – at both 24 h and multiday temporal scales – is an important means of conserving energy during winter and may need to be accounted for when forecasting species distributions, abundances and interactions.