The challenge of introducing an exergy indicator in a local low on energy

Extending the idea of exergy to practitioners and policy makers is still a major challenge. Recently the "Canton of Geneva" in Switzerland introduced a new law governing the procedures of attribution of building permits for new or retrofitted city areas. Authorities were asked to define a procedure including the calculation of an exergy indicator to be quantified in each file submitted for acceptance of large projects. This paper summarizes the problem definition, a clarification of the limits expected from the exergy indicator as well as the excel tool and the tables used to facilitate this quantification both for heating and air conditioning. For simplification the overwhole system was divided into a superstructure formed by four subsystems including the room convector, the plant of the building, a possible district heating and cooling plant and an external power plant. Three temperature ranges were considered for the building distribution networks both in heating and cooling. In a first approach it was accepted that the exergy efficiency would not be indicative of the relative use of renewable versus non renewable. Ten different technology combinations were considered ranking from the lowest heating exergy efficiency with nuclear electricity and joule heating to the best efficiency with hydroelectricity and District heating electric heat pumps using lake water. For nuclear plants the exergy efficiency was assimilated to be the standard electrical First Law efficiency, which we know is misleading (Haldi, Favrat Ecos2004) but it was strategically not the place to generate controversy on that issue. For most technology combinations the net exergy efficiency is the product of the exergy efficiency of the subsystems to be considered. Although the effectiveness of this introduction is not yet fully assessed the major benefit so far has been the renewed awareness of the interest of having low heating and high cooling temperatures of the building network

High Performance Air-Water Heat Pump with Extended Application Range for Residential Heating

A new type of air-water heat pump has been developed with the aim to cover an extended application range in high temperature residential heating (for retrofitting existing oil or gas boilers in hydronic heating systems). The base heat output is about 10 kWth. Based on a commercial heat pump, the refrigerant cycle was modified with two main components: A hermetic scroll compressor with a specially designed vapor injection port and an internal “economizer” heat exchanger. Performance tests were carried out in the laboratory over a wide range of injection mass flow rates and at external conditions covering air temperatures down to -12°C. At A-7°C/W60°C an increase of heat output of 28% and a COP improvement of 15% compared to the tests without injection flow have been observed. The heat output at A2° C/W50°C (standard operating conditions without injection) and at A-12° C/W65°C (extreme heating point with injection) are about the same. Considering these promising results and with the aim to further improve the seasonal COP and the heat output curve, a second compressor prototype based on a different compressor model, is being tested in phase two of this project

Oral vitamin B12 for patients suspected of subtle cobalamin deficiency: a multicentre pragmatic randomised controlled trial

BACKGROUND: Evidence regarding the effectiveness of oral vitamin B12 in patients with serum vitamin B12 levels between 125-200 pM/l is lacking. We compared the effectiveness of one-month oral vitamin B12 supplementation in patients with a subtle vitamin B12 deficiency to that of a placebo. METHODS: This multicentre (13 general practices, two nursing homes, and one primary care center in western Switzerland), parallel, randomised, controlled, closed-label, observer-blind trial included 50 patients with serum vitamin B12 levels between 125-200 pM/l who were randomized to receive either oral vitamin B12 (1000 μg daily, N = 26) or placebo (N = 24) for four weeks. The institution's pharmacist used simple randomisation to generate a table and allocate treatments. The primary outcome was the change in serum methylmalonic acid (MMA) levels after one month of treatment. Secondary outcomes were changes in total homocysteine and serum vitamin B12 levels. Blood samples were centralised for analysis and adherence to treatment was verified by an electronic device (MEMS; Aardex Europe, Switzerland). Trial registration: ISRCTN 22063938. RESULTS: Baseline characteristics and adherence to treatment were similar in both groups. After one month, one patient in the placebo group was lost to follow-up. Data were evaluated by intention-to-treat analysis. One month of vitamin B12 treatment (N = 26) lowered serum MMA levels by 0.13 μmol/l (95%CI 0.06-0.19) more than the change observed in the placebo group (N = 23). The number of patients needed to treat to detect a metabolic response in MMA after one month was 2.6 (95% CI 1.7-6.4). A significant change was observed for the B12 serum level, but not for the homocysteine level, hematocrit, or mean corpuscular volume. After three months without active treatment (at four months), significant differences in MMA levels were no longer detected. CONCLUSIONS: Oral vitamin B12 treatment normalised the metabolic markers of vitamin B12 deficiency. However, a one-month daily treatment with 1000 μg oral vitamin B12 was not sufficient to normalise the deficiency markers for four months, and treatment had no effect on haematological signs of B12 deficiency

Suivi in situ de l'efficacité d'un protocole de nettoyage lessiviel

National audienceLa qualité d'un nettoyage lessiviel repose sur trois critères : l'état physico-chimique de la surface traitée, le coût du nettoyage et l'impact environnemental. Une méthode, basée sur la technique de la microbalance à quartz, a permis d'évaluer in situ l'influence de différents paramètres (degré de contamination, nature et concentration de détergent sur le temps de nettoyage)

Contrôle de la propreté de surface avant traitement (CSP)

Solothurn, Suisse, 30 octobreJournées Techniques SGO-SST, Caractérisation de revêtements métalliques et de surface

The Kelvin probe technique for assessing efficiency of stearic acid removal from gold surfaces using atmospheric-pressure plasma

International audiencePlasma removal is an alternative cleaning method used to avoid effluents and volatile organic compounds resulting from the use of detergents and solvents. An innovative method to estimate residual stearic acid (C18H36O2) after the atmospheric-pressure plasma cleaning process of a gold surface is presented. This method, based on surface potential measurement by a Kelvin probe, enables monitoring of treated samples. The Quartz Crystal Microbalance (QCM) technique is used as a reference technique to specify with precision both initial and residual stearic acid masses. Stearic acid remaining on gold surfaces is proportional to the time of exposure to plasma and initial contamination. Moreover, the results reveal that surface potential evolution post-plasma exposure is a function of residual stearic acid, whatever the degree of initial contamination

An Onset of Nucleate Boiling Criterion for Horizontal Flow Boiling

An extensive database has been collected for the evaporation of two hydrofluorocarbon refrigerants (HFC- 134a and the zeotropic mixture HFC- 407C) and the natural refrigerant ammonia (R-717). A model to predict the onset of nucleate boiling has been successfully developed to differentiate pure convective evaporation from mixed convective and nucleate boiling heat transfer during horizontal evaporation inside a horizontal tube of 14mm I.D. The analysis of the Stratified, Stratified-Wavy and mainly Annular flow patterns during evaporation with differente heat flux ranges showed very accurate results in terms of mean local heat transfer coefficient using this new onset of nucleate boiling criterion

Flow Boiling and Pressure Drop Measurements for R134a/Oil Mixtures Part 2: Evaporating in a Plain Tube.

Intube flow boiling experiments for refrigerant R-134a mixed with a lubricating oil are reported for a plain, horizontal tube. The tests were run at a nominal inlet pressure of 3.4 bar over a wide range of vapor qualities at mass velocities of 100, 200, and 300 kg/m2s (73.5, 147 and 220.5 thousands of lb/h ft2) for inlet oil concentrations from 0-5 wt.% oil. At low to intermediate vapor qualities (0.2 <x< 0.60), the oil tended to increase the local boiling coefficient while significant deterioration in boiling performance occurred at high vapor qualities for the higher concentrations. As opposed to similar tests with a microfin tube, no evidence of oil holdup inside the plain tube test sections was noted. However, the effect of flow pattern appears to be important while also the effect of local physical properties on the heat transfer coefficient at high vapor qualities was confirmed

An analytical void fraction solution for horizontal separated two-phase flows

Separated flow models are of great interest to model two-phase flow such as Stratified, Stratified-Wavy and Annular flow patterns. Taitel and Dukler proposed a model for Stratified flow assuming that the interfacial effects can be neglected and modelled the pressure drop assuming smooth walls. Based on a new definition of hydraulic diameter for two-phase flows in channels and including the effect of shear on the interface, it is possible to obtain a more general analytical solution for Stratified flow. An extension to Annular flow is possible with the same model, but here the roughness of the tube walls and the interface is taken into account. This model allows a comprehensive approach to modelling of two-phase flow phenomena in the form of partial Reynolds numbers, partial pressure drops, partial rates of dissipation and partial rates of interfacial entrainment, and allows a direct comparison to be made between Stratified and Annular flows. This new model is an interesting platform that can be related to experimental data by the friction factors of the four surfaces of contact

Intube Flow Boiling of R-407C and R-407C/Oil Mixtures. Part 2: Plain Tube Results and Predictions

Intube evaporation tests for R-407C and R-407C/oil are reported for a plain copper tube. The tests were run at a nominal inlet pressure of 6.45 bar (93.5 psia) at mass velocities of 100, 200 and 300 kg/m2s (73581, 147162 and 220743 lb/h ft2) over nearly the entire vapor quality range. Pure R-407C performed very similar to pure R-134a run previously in similar tests at all three mass velocities, differing only at high vapor qualities where the peaks in href vs. x were shifted slightly. For local vapor qualities from 10-70%, oil tended to have little effect on local R-407C/oil heat transfer coefficients at the lowest mass velocity while at the higher mass velocities the effect was to increase or decrease the coefficients within ±20% of the pure R-407C values. At vapor qualities higher than 70%, the effect of the oil was very dramatic, decreasing performance by as much as 80-90% even with small amounts of oil. Two-phase pressure drops were increased by the presence of oil, especially at high vapor qualities. Two methods for predicting local boiling coefficients of refrigerant-oil mixtures were presented. Using the refrigerant-oil mixture viscosity in place of the pure refrigerant viscosity in the recent Kattan-Thome-Favrat flow boiling model and flow pattern map without further modification predicted the R-134a/oil and R-407C/oil data quite accurately. The Friedel two-phase friction multiplier was found to work adequately for pure R-134a and pure R-407C. Finally a new local refrigerant- oil viscosity ratio was developed that accurately predicted two-phase pressure drops of R-134a/oil and R-407C/oil mixtures at high vapor qualities