Thermal Mass Research Articles

Modeling apparent Pb loss in zircon U–Pb geochronology

Abstract. The loss of radiogenic Pb from zircon is known to be a major factor that can cause inaccuracy in the U–Pb geochronological system; hence, there is a need to better characterize the distribution of Pb loss in natural samples. Treatment of zircon by chemical abrasion (CA) has become standard practice in isotope dilution–thermal ionization mass spectrometry (ID-TIMS), but CA is much less commonly employed prior to in situ analysis via laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) or secondary ionization mass spectrometry (SIMS). Differentiating the effects of low levels of Pb loss in Phanerozoic zircon with relatively low-precision in situ U–Pb dates, where the degree of Pb loss is insufficient to cause discernible discordance, is challenging. We show that U–Pb isotopic ratios that have been perturbed by Pb loss may be modeled by convolving a Gaussian distribution that represents random variations from the true isotopic value stemming from analytical uncertainty with a distribution that characterizes Pb loss. We apply this mathematical framework to model the distribution of apparent Pb loss in 10 igneous samples that have both non-CA LA-ICP-MS or SIMS U–Pb dates and an estimate of the crystallization age, either through CA U–Pb or 40Ar/39Ar geochronology. All but one sample showed negative age offsets that were unlikely to have been drawn from an unperturbed U–Pb date distribution. Modeling apparent Pb loss using the logit–normal distribution produced good fits with all 10 samples and showed two contrasting patterns in apparent Pb loss; samples where most zircon U–Pb dates undergo a bulk shift and samples where most zircon U–Pb dates exhibited a low age offset but fewer dates had more significant offset. Our modeling framework allows comparison of relative degrees of apparent Pb loss between samples of different age, with the first and second Wasserstein distances providing useful estimates of the total magnitude of apparent Pb loss. Given that the large majority of in situ U–Pb dates are acquired without the CA treatment, this study highlights a pressing need for improved characterization of apparent Pb-loss distributions in natural samples to aid in interpreting non-CA in situ U–Pb data and to guide future data collection strategies.

A comparison between grey-box models and neural networks for indoor air temperature prediction in buildings

Model Predictive Control has gained much attention due to its potential to improve building operations by reducing costs, integrating renewable energy sources, and increasing thermal comfort. This paper aims to compare the accuracy of grey-box models based on resistance–capacitance (RC) networks and Long-Short-Term Memory (LSTM) neural networks in the prediction of the buildings’ thermal response, which is a key feature for the successful implementation of predictive controllers. Indoor air temperature prediction tests have been performed on simulated and measured data from buildings with different thermal insulation and thermal mass during both heating and cooling seasons. Results show that neural networks have, on average, a better prediction performance than grey-box models. Both modelling approaches are affected by the building characteristics and by the season considered. The grey-box models require less training data, although the latter seems to play a role only in the worse-performing tests. When user setpoint changes in the testing phase, the LSTM neural network shows a significant drop in the root mean square error. In conclusion, although LSTM outperforms grey-box models on average, the reduced training data and higher reliability under normal operating conditions, as well as their linearity, make RC models a strong alternative for predictive controllers.

Holistic design of energy-efficient temporary houses: Meeting ventilation, heating, cooling, and lighting demands

Recent disasters around the world have brought attention to the challenges faced by the homeless. Energy-efficient container houses (EECHs) offer a comfortable, sustainable, and temporary solution. A holistic design of EECH was conducted for mixed and hot climates using DesignBuilder software. The design, performed initially according to design criteria derived from ASHRAE Standards and previous studies, was subsequently examined for five passive strategies: envelope layering, WWR, windows opening ratio, glazing type, and shading. Optimal conditions were determined by the trade-off between heating and cooling demands, ventilation rate, and minimum daylight factor (DF) and uniformity (UDF). Results reveal that in mixed climates, using insulation materials and thermal mass is recommended, while in hot climates, it is advisable to avoid using them and instead rely solely on internal finishing layers. Complete reliance on natural ventilation is achieved by combining an opening ratio of 35 % with a WWR of 9%–25 % for south and north facades, and 6%–12 % for west façade. In mixed climates, argon gap double clear glazing is suitable, while a low-e layer is added for hot climates. Installing overhangs on south windows enhances UDF, unlike vertical fins on north and west windows. The designed EECHs consume 176 kWh/m2 of electricity annually.

Late Kungurian Radioisotope Age of the Boundary Between the Balakhonka and Kolchugino Groups in the Kuznetsk Basin (Western Siberia, Russia) – Additional Evidence for the Validity of the Ufimian Stage of the East European Permian

This article discusses the Late Kungurian radioisotopic age (276.9 ± 0.4 Ma) of the middle part of the Starokuznetsk Formation (Kuznetsk Subgroup, Kolchugino Group) of the Kuznetsk Basin determined by chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS). The analysis of the biostratigraphic data confirms that the layer dated belongs to the interval in which the Balakhonka Flora (cordaitoid) was replaced by the Kolchugino Flora (fern-pteridosperm-cordaitoid). This indicates that the change from the Balakhonka Flora to the Kolchugino Flora in the low latitudes of Angaraland took place during the Late Kungurian. The data obtained were used for direct correlation of the lower part of the Kolchugino Group with the Upper Kungurian of the International Chronostratigraphic Chart. Similar sequences of non-marine bivalve assemblages in the Permian successions of Angaraland (giant Prokopievskia, Khosedaella-Redikorella-Palaeomutela, and dominant Palaeomutela) and Eastern Europe (giant Sinomya, Palaeomutela-Khosedaella-Redikorella, and dominant Palaeomutela) further support the validity of the correlation of the Kuznetsk Subgroup with the Ufimian Stage. The placement of the lower boundary of the Kolchugino Group in the upper part of the Kungurian Stage of the International Chronostratigraphic Scale raises the question of the continuation of the Ufimian Stage as an independent straton in the East European Stratigraphic Scale. Its lower boundary coincides with the beginning of the change in the Balakhonka and Kolchugino Flora in the low latitudes of Angaraland, as well as with the faunal exchanges between the Euramerican and Angarian non-marine bivalve assemblages.

Geochronological and geochemical effects of zircon chemical abrasion: insights from single-crystal stepwise dissolution experiments

Abstract. Chemical abrasion in hydrofluoric acid (HF) is routinely applied to zircon grains prior to U–Pb dating by isotope dilution thermal ionization mass spectrometry (ID-TIMS) to remove radiation-damaged portions of grains affected by Pb loss. Still, many chemically abraded datasets exhibit evidence of residual Pb loss. Here we test how the temperature and duration of chemical abrasion affect zircon U–Pb and trace element systematics in a series of 4 h, single-crystal stepwise dissolution experiments at 180 and 210 ∘C. Microtextural data for the zircon samples studied are presented in a companion paper by McKanna et al. (2023). We find that stepwise dissolution at 210 ∘C is more effective at eliminating material affected by open-system behavior and enriched in U, common Pb (Pbc), and light rare earth elements (LREEs); reduces the presence of leaching-induced artifacts that manifest as reverse discordance; and produces more consistent and concordant results in zircon from the three rocks studied. We estimate that stepwise dissolution in three 4 h steps is roughly equivalent to a single ∼ 8 h leaching step due to the insulating properties of the PTFE sleeve in the Parr pressure dissolution vessel, whereas traditionally labs utilize a single 12 h leaching step. We conclude that a single 8 h leaching step at 210 ∘C should remove Pb loss effects in the majority of zircon and that this can be used as an effective approach for routine analysis. Further, we calculate time-integrated alpha doses for leachates and residues from measured radionuclide concentrations to investigate (1) the alpha dose of the material dissolved under the two leaching conditions and (2) the apparent minimum alpha dose required for Pb loss susceptibility: ≥ 6×1017 α g−1.

An equivalent circuit approach for remnant thickness evaluation and flaw sizing using pulsed thermography

Active thermography using pulsed heating is a fast and reliable method for detecting flaws in composite and metallic materials. This paper analyzes the temperature decay that occurs immediately after flash heating the front surface of stainless steel specimens as a function of time, based on a novel application of the equivalent circuit approach (ECA). The temperature decay from the front surface is equated to the discharge of a capacitor. The ECA is based on the charging (temperature rise due to flash heating) of a capacitor, followed by its discharge (temperature decay) through a series of resistors (which depends on the conductivity of the material) and capacitance (which depends on the thermal capacitance of the layers) through which the heat is dissipated. The proposed approach analyzes the sequences of temperature data obtained at each pixel location during cooling from a step wedge and a specimen with multiple flat-bottom holes. Time constant maps derived from the analysis are used to ascertain the thickness of the step wedge, detect the flaws, and evaluate the remnant thickness of the flaws. A correlation has been established between the thickness and the time constants. The above approach has been used to estimate the diameter of the flat-bottom holes.

Effect of cryogenic feed line thermal mass distribution and orientation on chill-down performance

Chilldown performance of cryogenic systems is highly influenced by parameters like feed line orientation, thermal mass of the feed system and its distribution, mass flux of the cryogen and heat in-leak. In this work, the impact of feed line orientation and mass flux of cryogen on chilldown is evaluated through a parameter defined as Chilldown Performance Index. A set of experimental data generated with Liquid Nitrogen employing a test section insulated with poly-isocynurate foam is used for this study. Chilldown Performance Index is found to be lower with downward inclination upto 60° downward orientation of test section as compared to that of horizontal orientation. Beyond this, at 90° downward orientation, it is seen to be better as compared to 60° orientation. Chilldown performance improves significantly with upward inclination of test section. Chilldown time is found to be highly sensitive to mass flux, whereas effect on Chilldown Performance Index is not so significant. Experiments also show that chilldown performance is significantly influenced by the distribution of feed line thermal mass. Chilldown is faster in experiments with higher thermal mass distributed near to the inlet to the test section as compared to the case wherein they are distributed near to the exit of the test section. Flow visualisation studies are also conducted employing a vacuum jacketed view glass made of borosilicate material to capture the flow structure prevailing in experiments with different upward and downward orientation and to assess its influence on chilldown. Flow structure is observed to be significantly different in experiments with upward inclination, compared to those with horizontal and downward orientation. Observations made with upward inclination, show the existence of plug or slug flow in the test section, leading to faster chilldown. Flow pattern observed in experiments with 30° and 45° downward orientation is also different compared to other orientations, as liquid flow is mostly confined to the core of the test section, due to gravity effects.

A Novel Quick Temperature Prediction Algorithm for Battery Thermal Management Systems Based on a Flat Heat Pipe

Predicting the core temperature of a Li-ion battery is crucial for precise state estimation, but it is difficult to directly measure. Existing quick temperature-predicting approaches can hardly consider the thermal mass of complex structure that may cause time delays, particularly under high C-rate dynamic conditions. In this paper, we developed a quick temperature prediction algorithm based on a thermal convolution method (TCM) to calculate the core temperature of a flat heat pipe-based battery thermal management system (FHP-BTMS) under dynamic conditions. The model could predict the core temperature rapidly through convolution of the thermal response map which contains full physical information. Firstly, in order to obtain a high fidelity spatio-temporal temperature distribution, the thermal capacitance-resistance network (TCRN) of the FHP-BTMS is established and validated by constant and dynamic discharging experiments. Then, the response map of the core temperature motivated by various impulse heat sources and heat sinks is obtained. Specifically, the dynamic thermal characteristics of an FHP are discussed to correct the boundary conditions of the TCM. Afterwards, the temperature prediction performances of the TCM and a lumped model under different step operating conditions are compared. The TCM results show a 70–80% accuracy improvement and better dynamic adaptivity than the lumped model. Lastly, a vertical take-off and landing (VTOL) profile is employed. The temperature prediction accuracy results show that the TCM can maintain a relative error below 5% throughout the entire prediction period.

The analysis of occupants' thermal comfort in a residential building in Tangier, Morocco

Bioclimatic design is currently one of the most important steps in passive building design adapted to outdoor climatic conditions. However, the Moroccan Thermal Building Regulations (RTCM) primarily focus on the building envelope and its energy performance, often overlooking occupant comfort. To address this gap, a bioclimatic analysis of the Mediterranean climate in Tangier was conducted to determine the percentage of thermal comfort naturally provided by this climate and to identify suitable passive strategies for buildings in the region. The results indicate that Tangier's climate can provide up to 28% thermal comfort. Consequently, the most effective passive strategies for buildings in Tangier include shading techniques, high thermal mass, internal heat gains, and direct passive heating. Furthermore, implementing these strategies can enhance occupant comfort by 6% and reduce the building's energy demand by 11.74%.

Effects of Faraday cup deterioration on Sr and Cr isotope analyses by thermal ionization mass spectrometry.

By comparing data from an extensive set of Sr and Cr isotope measurements performed on two different thermal ionization mass spectrometers (TIMS), using three sets of Faraday cups with different usage histories, we assess the effects of Faraday cup deterioration on high-precision isotope measurements by TIMS. We find that dynamic 84Sr/86Sr and 87Sr/86Sr measurements provide stable and reproducible results over the entire 56 months of this study, regardless of which set of Faraday cups is used. By contrast, static 84Sr/86Sr and 87Sr/86Sr measurements lead to deviant results, drifts over time, and in general exhibit larger scatter. For the most part, these differences can be attributed to changing Faraday cup efficiencies. For the instruments of this study we find that the center cup is most affected, consistent with this cup often receiving the highest ion beam intensities during measurements conducted in our laboratory. For Cr isotopes, we find that the correlation between mass fractionation-corrected 53Cr/52Cr and 54Cr/52Cr ratios observed for static measurements in several prior studies also reflects different Faraday cup efficiencies. Again, the changing efficiency of predominantly the center cup can account for the observed drift and correlation in 53Cr/52Cr and 54Cr/52Cr. Multi-static Cr isotope measurements reduce this drift, but still result in a residual correlation between the two ratios, suggesting this correlation in part also reflects unaccounted mass fractionation effects.

Comparative temperature and consumption data measurement of model buildings with different thermal time constants

In this study, three identically designed model buildings and their heating energy consumption was compared. Those pilot scale buildings are equal by size and were located on the same location. During the measuring campaign both external and internal temperatures were recorded, beside the energy consumption. The model buildings were labeled as A (constant baseline), B (baseline varying according to a time program), and C (unheated, blank). During the measurements, the thermal mass of the buildings was altered. The same amount of thermal mass was installed in all three model buildings during all measurements. According to our results under real weather conditions, the intermittent heating requires less energy than maintaining a constant temperature, and the energy saving is inversely proportional to the time constant at intermittent heating. Instead of specific heat mass, a thermal time constant was used to compare intermittent and constant heating. It was established that as the thermal constant of the model building increases, the energy savings between maintaining a variable base temperature and maintaining a constant base temperature decrease. The expected savings are between 4% and 7%.

Implications for new particle formation in air of the use of monoethanolamine in carbon capture and storage.

Alkanolamines are currently being deployed in carbon capture and storage (CCS) technology worldwide, and atmospheric emissions have been found to coincide with locations exhibiting elevated concentrations of methanesulfonic acid (MSA). It is thus critical to understand the fate and potential atmospheric reactions of these chemicals. This study reports the characterization of sub-10 nm nanoparticles produced through the acid-base reaction between gas phase monoethanolamine (MEA) and MSA, a product of organosulfur compound oxidation in air, using a flow reactor under dry and humid (up to ∼60% RH) conditions. Number size distribution measurements show that MEA is even more efficient than methylamine in forming nanoparticles on reaction with MSA. This is attributed to the fact that the MEA structure contains both an -NH2 and an -OH group that facilitate hydrogen bonding within the clusters, in addition to the electrostatic interactions. Due to this already strong H-bond network, water has a relatively small influence on new particle formation (NPF) and growth in this system, in contrast to MSA reactions with alkylamines. Acid/base molar ratios of unity for 4-12 nm particles were measured using thermal desorption chemical ionization mass spectrometry. The data indicate that reaction of MEA with MSA may dominate NPF under some atmospheric conditions. Thus, the unique characteristics of alkanolamines in NPF must be taken into account for accurate predictions of impacts of CCS on visibility, health and climate.

A WILLIAMSON NANOFLUID WITH MOTILE MICROORGANISMS ACROSS A VERTICAL EXPONENTIALLY STRETCHING POROUS SHEET WITH VARYING THERMAL CHARACTERISTICS

The present work demonstrates a boundary layer movement of an incompressible non-Newtonian Williamson nanoliquid. The boundary layer is around an exponentially stretching permeable vertical surface. Moving motile microorganisms are implicated in the movement throughout a permeable medium considering modified Darcy law. The buoyancy-driven flow is presumed, where the density is expressed as being multiplied by gravity and chosen as a linear function of heat, nanoparticle, and microorganism concentrations. Analogous to the exponentially stretching sheet, an exponential variable magnetic strength is taken normal to the surface. Variable thermal conductivity and mass diffusivity are considered together with chemical reactions. The motivation for this study arises from the involvement of microorganisms in the flow and the contribution of its density equation with the velocity, temperature, and nanoparticles system of equations with suitable boundary restrictions. The fundamental governing scheme of nonlinear partial differential equations (PDEs) is transferred to ordinary ones (ODEs) by employing convenient similarity transforms. These equations are analyzed by the homotopy perturbation method (HPM). Therefore, a major objective graphical formation of the distributions is concluded to recognize the impacts of the produced nondimensional physical factors. Some important physiognomies are concluded from the results. The nanoparticle distribution enhances most of the effective parameters and in turn improves heat transmission, which is a good finding that can be useful in several applications. Microorganisms tend to collect with the growth of the Lewis number and infinity value, whereas its condensation damps with the rise of the bioconductivity and the Peclet number. Those results can be useful in identifying factors that help to get rid of microbes, viruses, and harmful bacteria from surfaces.

A low-cost and high precision determination method of 87Sr/86Sr ratios for red wine using thermal ionization mass spectrometry without column separation

Thermal ionization mass spectrometry is considered as the “gold standard” for obtaining precise 87Sr/86Sr isotopic ratios.

Rapid detection of aflatoxin B1, zearalenone and ochratoxin A in grains by thermal desorption dielectric barrier discharge ionization mass spectrometry.

Dielectric barrier discharge ionization is increasingly used for rapid detection in ambient mass spectrometry, although more often for gaseous and highly volatile samples than for solids and liquids. In this project, we present a rapid and sensitive method for detecting mycotoxins and demonstrate its capability for the detection of aflatoxin B1, zearalenone, and ochratoxin A in food samples. Our method is based on thermal desorption coupled to dielectric barrier discharge ionization mass spectrometry (TD-DBDI-MS), which we show generates minimal interferences and produces almost exclusively molecular ions. We detected mycotoxins in various food samples, including corn, peanuts, millet, and rice. Our method has a linear dynamic range of 1 μg kg-1 to 100 μg kg-1 for all three mycotoxins and a limit of detection (LOD) of 0.31 μg kg-1, 0.28 μg kg-1 and 0.43 μg kg-1, respectively. It is simple, rapid, reduces the pretreatment steps and has significant potential for practical applications.

An exploratory study of “large‐n” detrital zircon geochronology of the Book Cliffs, UT via rapid (3 s/analysis) U–Pb dating

AbstractDetrital zircon (DZ) U–Pb geochronology has improved the way geologists approach questions of sediment provenance and stratigraphic age. However, there is debate about what constitutes an appropriate sample size (i.e., the number of dates in a DZ sample, n), which depends on project objectives, sample complexity, and, critically, analytical budget. Additionally, there is ongoing concern about bias introduced by zircon grain size. We tested a recently developed rapid (3 s/analysis) data acquisition method by multicollector laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) that incorporates an automated selection routine and calculates two‐dimensional grain geometry from polished sample surfaces. Eleven samples were analysed from below and above the Late Cretaceous (Campanian) basal Castlegate unconformity of the Book Cliffs, Utah, in a down‐depositional‐dip transect including Price, Horse, Tusher, and Thompson canyons. 12,448 new concordant dates were generated during two measurement sessions. Results are consistent with recent studies suggesting there is no major provenance change and little time (1–2 Myr) represented across the unconformity. Grain size and sample size both exert a strong control on sample dissimilarity. Age distributions constructed from subsamples of large grains are systematically less similar to whole samples; age distributions composed of small grains are overall more similar to whole samples. As such, North American sediment sources that produce large grains such as the Grenville and Yavapi‐Mazatzal belts can bias age distributions if only large grains are analysed. A sample size of n = 100 is inadequate for characterizing age distributions as complex as those of the Book Cliffs, whereas a sample size of n = 300 provides good characterization. Sample size of n ≈ 1000 or more is unnecessary unless project objectives include scanning for subordinate age groups, such as when identifying the youngest grains for calculating a maximum depositional age (MDA). Dates used in MDA calculations acquired with rapid acquisition are best re‐analysed with longer LA‐ICP‐MS acquisition methods or isotope dilution thermal ionization mass spectrometry for increased accuracy and precision. We include new MATLAB code and open‐source software programs, DZpick and DZmda, for automated spot picking and calculating MDAs.

Parâmetros térmicos do UHPC em situação de incêndio: uma abordagem à norma brasileira ABNT NBR 15200

Abstract Ultra-high-performance concrete (UHPC) has exceptional mechanical properties at room temperature. However, there are no standardized thermal procedures proposed by ABNT NBR 15200 to characterize UHPC at high temperatures, such as in the case of fire. This is due to the lack of research on the subject, leaving gaps for experimental and numerical investigations. Based on experimental analyzes on standardized, small-scale specimens, this research collects a set of parametric data for UHPC at high temperatures. Thermal diffusivity, thermal conductivity, thermal expansion and specific heat as thermal parameters were defined for different temperature ranges. The results were compared with other structural concretes proposed in the literature (NSC, HSC and UHSC). The UHPC exhibited a particular fire behavior. Compared to NSC, HSC and UHSC, the thermal expansion and mechanical parameters of UHPC are less affected at high temperatures, but its thermal conductivity and mass loss are higher. UHPC also has the highest specific heat compared to other concretes. The thermal field of UHPC tends to be higher compared to the other concretes.

U–Pb zircon–rutile dating of the Llangynog Inlier, Wales: constraints on an Ediacaran shallow-marine fossil assemblage from East Avalonia

The Llangynog Inlier of south Wales contains an assemblage of Ediacaran macrofossils from a shallow-marine environment, including discoidal morphs of Aspidella and rare examples of Hiemalora , Palaeopascichnus and Yelovichnus . These are taxa found at other sites in the Avalonian microcontinent (e.g. Charnwood Forest and eastern Newfoundland) and in the younger White Sea Ediacaran assemblages. As the Charnwood fossils reflect a deep-water environment, and no macrofossils have been found in the Ediacaran rocks of the Long Mynd, the fossils of the Llangynog Inlier represent a unique glimpse of shallow-marine life in southern Britain (East Avalonia). However, the lack of absolute age constraints has hampered direct comparison with other assemblages. Here, we report in situ zircon and rutile U–Pb dates from a rhyolitic ash-flow layer of the Coed Cochion Volcaniclastic Member, Llangynog Inlier, which constrains the age of the fossiliferous strata. A weighted mean single grain zircon isotope dilution thermal ionization mass spectrometry U–Pb age of 564.09 ± 0.70 Ma is interpreted as the rhyolite's crystallization age. This age is consistent with in situ laser ablation inductively coupled plasma mass spectrometry zircon and rutile U–Pb dating. The Llangynog age temporally correlates these fossils to dated horizons within East Avalonia at the Beacon Hill Formation, Charnwood (565.22 ± 0.89 Ma) and the Stretton Shale Formation, Long Mynd (566.6 ± 2.9 Ma). Correlations to West Avalonia include the time-equivalent Fermeuse Formation, St John's Group, eastern Newfoundland (564.13 ± 0.65 Ma). The data presented here establish the biota of the Llangynog Inlier as a lateral equivalent to the similarly shallow-marine, tidally influenced ecosystem of the upper Fermeuse Formation. Intra-terrane depositional environmental variability also affects what is preserved in Avalonian fossil sites. Further, time-constrained geochemical data reinforce the Llangynog Inlier's classification within the Wrekin Terrane. Supplementary material : U–Pb data, reference material and figures showing sedimentary structures are available at https://doi.org/10.6084/m9.figshare.c.6965642

Extraction of the Thermal Resistance and the Thermal Capacitance of GaN Power HEMTs by Using Pulsed I–V Measurements

Extraction of the Thermal Resistance and the Thermal Capacitance of GaN Power HEMTs by Using Pulsed <i>I</i>–<i>V</i> Measurements

Energy flexibility using thermal mass for Swedish single-family houses

This paper characterised the potential of energy flexibility in relation to building envelop properties, heat emitters and ventilation for the Swedish context. Simulation results indicated that the potential was higher for newer houses with floor heating and lower for older houses with radiators in winter. Older houses with different levels of insulation showed a similar ability of conserving heat due to different extents of heat losses from ventilation. A house with balanced ventilation tended to be over-ventilated especially if the house was not airtight. The flexibility was decreased with increasing outdoor temperatures, and it was higher in winter and lower in spring/autumn.