Bernard Marie Lachal

Cooling and preheating with buried pipe systems: monitoring, simulation and economic aspects

On basis of extensive monitoring and simulation work, we examine the fundamental difference between winter preheating and summer cooling potential of buried pipe systems under Central European climate, as well from an energetic as from an economic point of view. Care is taken to account for exhaustive energy balances, taking into account sensible and latent heat exchanges, as well as diffusion through soil.

Thermal analysis of five outdoor swimming pools heated by unglazed solar collectors

Abstract We have analysed measurements from five outdoor swimming pools located in Switzerland and heated by unglazed solar collectors. The main contributions to the daily energy balance of the swimming pools are evaluated. They include the active and passive solar gains, as well as the heat losses related to radiation, evaporation, convection, and water renewal (in order of importance). Coherent results are obtained using multilinear regressions in order to determine the best fitting values of the empirical parameters involved in the thermal equations.

Structural instabilities of Chevrel phases: The alkaline earth molybdenum sulphide series

Abstract The low temperature structural phase transition occuring in EuMo6S8 was also detected, by specific heat measurements, in bulk samples of M Mo6S8 with M=Ba, Sr and Ca. Sintered material of EuMo6S8 equally transforms, but in a broad temperature interval. The triclinically distorted phases are characterized by a very low electronic densities of states.

Lattice instability in the non-superconducting compound EuMo6S8

We have performed electrical resistivity and specific heat measurements on bulk Eu1.1Mo6S8 together with low-temperature X-ray powder diffractometry. These investigations revealed a structural phase transition (occuring at 109 K) from the room-temperature rhombohedral structure to a low-temperature triclinic distorted structure in which the compound exhibits a non-metallic behavior.

Heat Capacity Analysis of a Large Number of Chevrel-Type Superconductors

Low-temperature specific heat measurements were performed on a series of binary, pseudobinary, ternary, and pseudoternary molybdenum chalcogenides MxMo6X8. The measurements covered a sufficiently wide temperature range to yield the relevant moments of the phonon spectra in addition to the electronic term. From the data in the superconducting state, strong coupling parameters were also obtained, particularly the gap ratios 2 Δ (0)/kTc. The superconducting transition temperature of the Chevrel-type phases essentially depends on the bare electronic density of states at the Fermi level and, moreover, on the atomic order pertaining to the Mo6 and certain chalcogen sites. For the ordered compounds, the relation λ≃aNbs(EF) holds on the average. The factora≃1.25 eV Mo atom spin is practically equal to that found for Nb-based A15-type compounds.

Thermal analysis of five unglazed solar collector systems for the heating of outdoor swimming pools

The performance and behavior of five unglazed solar collector installations, devoted to the heating of five outdoor swimming pools located in Switzerland, is studied on the basis of experimental data collected in 1988. Due to the low temperatures involved, hourly efficiencies often exceed 80%. The mean daily collector efficiency is of the order of 60% in optimal conditions and is in good agreement with the G3 simulation program.

Direct evidence for the first-order phase transition at the lower critical temperature in Er1?x Ho x Rh4B4

Using a heat-pulse and a relaxation technique, we have performed an extensive calorimetric investigation on the reentrant superconductors Er1−xHoxRh4B4 (x=0.4 and 0.6) around their lower critical temperature. These experiments revealed a supercooling effect and thermal hysteresis, thus establishing the first-order nature of the transition. Based on the measurement of the latent heat, our thermodynamic analysis suggests that the onset of ferromagnetism is lowered by only 55 mK due to the competing superconducting phase. Results of magnetization and ac susceptibility experiments on these compounds are also included.

First-order phase transition to strongly anisotropic ferromagnetism in Tl2Fe6Te6

Abstract The magnetic susceptibility, magnetization, specific heat and electrical resistivity were measured on the new material Tl2Fe6Te6. All the data show a very sharp anomaly revealing a phase transition to ferromagnetism at Tc≈220 K. The presence in the structure of one-dimensional metallic clusters ¦Fe 3 ¦ 1 ∞ is evidenced by a very strong magnetic anisotropy in the ferromagnetic state, showing an interesting intermediate situation between a pure linear chain and 3-dimensional iron. Furthermore, the unusual sharpness of the transition leads us to anticipate a first-order phase transformation, but the lack of detectable thermal hysteresis was surprising. The molecular field model proposed by Bean and Rodbell in order to account for the similar behavior of MnAs gives a close representation of our magnetic data. Thus, a pronounced dependence of the exchange interaction upon interatomic spacing may well be the dominant mechanism leading to the observed phenomena.

Spatial–Temporal Analysis of the Heat and Electricity Demand of the Swiss Building Stock

In 2015, space heating and domestic hot water production accounted for around 40% of the Swiss final energy consumption. Reaching the goals of the 2050 energy strategy will require significantly reducing this share despite the growing building stock. Renewables are numerous but subject to spatial-temporal constraints. Territorial planning of energy distribution systems enabling the integration of renewables requires having a spatial-temporal characterization of the energy demand. This paper presents two bottom-up statistical extrapolation models for the estimation of the geo-dependent heat and electricity demand of the Swiss building stock. The heat demand is estimated by means of a statistical bottom-up model applied at the building level. At the municipality level, the electricity load curve is estimated by combining socio-economic indicators with average consumption per activity and/or electric device. This approach also allows to break down the estimated electricity demand according to activity type (e.g. households, various industry & service activities) and appliance type (e.g. lighting, motor force, fridges). The total estimated aggregated demand is 94 TWh for heat and 58 TWh for electricity, which represent a deviation of 2.9% and 0.5% respectively compared to the national energy consumption statistics. In addition, comparisons between estimated and measured electric load curves are done to validate the proposed approach. Finally these models are used to build a geo-referred database of heat and electricity demand for the entire Swiss territory. As an application of the heat demand model, a realistic saving potential is estimated for the existing building stock; this potential could be achieved through by a deep retrofit program. One advantage of the statistical bottom-up model approach is that it allows to simulate a building stock that replicates the diversity of building demand. This point is important in order to correctly account for the mismatch between gross and net energy saving potential, often called performance gap. The impact of this performance gap is substantial since the estimated net saving potential is only half of the gross one.

Pascool Electronic Metahandbook, PEM

In the PASCOOL research program, which is part of the European research project Joule II, one task was dedicated to the development of an interactive software that would summarise the result of the Pascool research program and show the applicability of passive cooling in Mediterranean countries. The aim was to encourage designers to make use of passive cooling strategies in existing and new buildings. Therefore, a software called PEM, Pascool Electronic Metahandbook was created. A selection of buildings from the southern European countries are presented in this software. These buildings had been previously monitored and simulated as a separate task within the Pascool program. In addition, the software contains a climate database and simple predesign tools for dimensioning insulation and solar protection. Version 1.2 of this software was completed in October 1995 and is available on CD-ROM.