Projet européen Keep Kool II. Conserver ou assurer le confort d'été lors de la réhabilitation de bâtiments de bureaux

Article accessible gratuitement en ligne à l'adresse http://aicvf.org/la-revue-cvc/n%C2%B0867-janvierfevrier-2011/National audienceL'usage de la climatisation en Europe est aujourd'hui en très forte augmentation. À titre d'exemple, environ 3,5 millions de climatiseurs individuels ont été vendus en 2005 contre 1,6 million en 1996 (120 % d'augmentation en dix ans). L'existant n'échappe pas à cette tendance, l'isolation des bâtiments lors d'une réhabilitation thermique, nécessaire pour réduire les consommations de chauffage, peut notamment se traduire par des inconforts d'été détectés après coup et favoriser l'installation ultérieure de systèmes de rafraichissement mécanique

Survey of the existing approaches to assess and design natural ventilation and need for further developments

ISBN : 978-0-947649-40-1 Disponible à l'adresse : www.ibpsa.org/proceedings/BS2009/BS09_0220_227.pdfInternational audienceIn the last years many building designers have turned their attention to natural ventilation, due to the potential benefits in terms of energy consumption related to ventilation and air-conditioning, especially in mild and moderate climates. Consequently, several calculation techniques have been developed to design and predict the performance of natural ventilation. This article presents a review of the existing approaches to predict natural ventilation performance, including simple empirical models, nodal models (mono-zone and multi-zones), zonal models and CFD models. For each approach, we analyse the physical basis, the main modelling assumptions, the necessary input data and the area of applicability. Thus, the integration of these methodologies in the available simulation programs is examined, with reference to the different phases of the natural ventilation design process and some examples of application are given. The aim of the review is to identify the main practical limits of existing programs in designing natural ventilation and in predicting its performance and the consequent need for further developments

An evaluation of ground thermal properties measure accuracy by thermal response test of horizontal ground heat exchangers

International audienceThis study aims to present a comparison between temperature measurements relative to horizontal ground heat exchangers with predicted values using thermal response test. A scale 1 test facility of horizontal ground heat exchangers has been implemented in BRGM (Orleans - France) to test performances in real conditions. The heat exchanger is divided in four parts of 100 m² each with different characteristics: - a sunny grass - a shaded grass - a sunny car-park - a shaded car-park These different configurations have been chosen to compare the performances of ground heat exchangers in different environments (surface state, boundary conditions). Furthermore, the temperature in the soil is measured continuously at 3 different levels (-0.5 m, -1 m, -1.5 m). To cartography the temperature field at these 3 depths, optical fibers are distributed in the underground and the use of a distributed temperature sensor (DTS) allows to accurately measure the temperature in the soil surrounding the ground heat exchanger. A thermal response is carried out on the horizontal ground heat exchanger. A monitored constant heating power is injected at a constant mass flow. The temperature measurements at the 3 different levels of a threedimensional numerical model of ground heat exchanger. The thermal response test gives in particular the noticeable differences between the 4 different conditions of each part of the ground heat exchanger. The conclusion will give indications on the consequences of uncertainty about soil thermal properties on sizing

Energy Consequences of Non-optimal Heat Pump Parameterization

The substitution of low-performance gas and fuel boilers by air to water electrical heat pumps is a solution to meet the energy challenge to reduce GHG dwellings emissions. Indeed, most dwelling emissions in Europe are due to heating and DHW generation with fossil fuels. Apart from low carbon emissions, high energy savings are expected from rated performances, but an AWHP may not deliver the expected efficiency because of a bad commissioning. Nowadays, these machines present a high number of parameters – over 40 on average – to be set during the installation, which makes this process very complex. Unfortunately, the parameter setting is a crucial step for the proper operation of the system throughout its life cycle. A non-optimal choice of AWHP parameters may lead to severe performance losses or discomfort. The first part of the paper describes the functions and parameters that the installer must adjust for the commissioning phase. In a second step, the consequences of a non-optimal parameterization of an AWHP are evaluated. This analysis is based on a computer model using Modelica language. The model consists of a heating system, installed in a typical detached dwelling. Simulations are run by pairing the heat pump with the dwelling and the heating system. Simulations show the potential energy savings and the accuracy of indoor air control when control parameters, in particular the heating curve, are adapted to the dwelling and to the heating network. Final results confirm that an optimization of the parameterization of an AWHP makes a significant difference, in both energy savings and indoor air temperature control accuracy

Influence Of Building Zoning On Annual Energy Demand

Simulation tools are widely used to assess the energy consumption of a building. In the modeling process, some choices should be made by the simulation tool user such as the division of the building into thermal zones. The zoning process is user dependent, which results in some difference in energy consumption results and model set-up and computational times. The aim of this work is to assess the influence of building zoning on the results of the dynamic thermal simulation including airflow and thermal transfers between zones For this purpose, several different building zonings are applied to the same office building, and then the results of the dynamic thermal simulations are compared in terms of energy consumption (heating, cooling, and auxiliaries) and computational and set-up times. To assess the impact of thermal zoning, five cases are studied (from the most to the least complex): - 1) *49-zone model* : each zone gathers the premises with the same air handling system, the same occupancy profile, at each floor and building orientation. - 2) *44-zone model* : the premises containing the same air handling system are gathered at every floor, even though their occupancy profile is different. - 3) *26-zone model*: all floors are merged, except for the first and the top floors (under-roof). - 4) *21-zone model* : the first and the under-roof floors are merged with the others if the premises have the same occupancy profile and handling system. - 5) *11-zone model* : the premises with a different orientation but with the same occupancy profile and handling system are gathered. The importance of airflow coupling is evaluated by using the most detailed model (49 zones) and comparing the cases with or without considering air transfer from offices to corridors and toilets (from which air is extracted). Then, to study the impact of thermally connecting juxtaposed zones, the “21-zone model” with and without thermal transfer are compared. Finally, the impact of merging the floors is analyzed by considering different roof and floor insulations and the impact of merging the orientations is studied by using different glazed surface ratio

Non-Intrusive Performance Assessment Method For Heat Pumps: Experimental Validation And Robustness Evaluation Facing Faults

Thanks to their high theoretical efficiency, residential heat pumps (HP) are a promising technology when attempting to reduce the energy consumption of heating in dwellings. Evaluation of their real performances on-field is thus crucial to promote their development and deployment. However, measuring accurately real heating capacity of air-to-air HP is not easy, since measuring air enthalpy and mass flow rate is challenging. A previously developed non-intrusive internal method based on the compressor energy balance has been improved. It can calculate the coefficient of performance (COP) of different HP types, including air-to-air, on field, thanks to real-time measurements, without interfering with normal operation of the system, and without technical data of the specific heat pump. In this study, a complete validation of this method has been led on a test bench, using an air-to-water HP in order to compare the results of the method with the water-side measurements. This internal refrigerant method was tested for various climatic conditions and heating needs, in stationary and dynamic conditions, including starting and defrosting phases. Different faults were simulated to analyse the behaviour of the method in these conditions, including refrigerant undercharging and exchanger fouling. The analysis also extends to identifying which parameters need to be observed to early detect these faults. The method proves to be robust and its uncertainty to remain low, although it varies with the different working phases. The precise knowledge of real-time performances obtained with this method can help to assess the performance impact of faults and thus to improve associated fault detection and diagnostic methods. On a longer-term scale, the comparison of measured field performances and performances obtained via simplified models, such as regulatory models for instance, could give interesting indications to improve these models

Integral and Differential Model of Hermetical Compressor Heat Losses Including Experimental Validation

The current evaluation of heating and cooling system performances has become a major issue in European buildings sector. A promising method for measuring heat pump performances on-field has been previously developed and published. However, the accuracy of the method is strongly dependent on the evaluation of heat transfer from compressor towards the ambient air. In this paper a developed compressor heat transfer model that couples integral and differential formulations is presented. The model consists of three fundamental steps: thermodynamic analysis of the compression process, detailed thermophysical flow analysis using a CFD software, and finally compressor thermal network analysis consisting of integral equations that describe heat transfer of solid-fluid interfaces. Temperature distribution of the compressor shell is the main output of the model. Internal and external thermal profiles obtained from the numerical model and experimental measurements are compared in one operating condition at two compressor speeds. The RMS errors of external profiles are 3.20 °C and 1.96 °C, at 30 rps and 60 rps, respectively. The model can be used to determine the minimum number of surface temperature sensors and their locations on the compressor shell necessary to measure heat losses on-field. More accurate evaluation of compressor heat losses towards the ambient air will improve the accuracy of the performance measurement method

On side refrigerant measurement of heat pump seasonal performances

International audienceHeat pump systems have become very popular for space heating in the residential sector in Europe. However, there is no data available on the in situ seasonal heating performances of air-to-air heat pumps. This is due to the difficulty of measuring their thermal capacity on field over a long period. Several methods relying on air flow rate and enthalpy measurements are being considered for in-situ measurement for air-to-air heat pumps. But accuracy and reliability of these methods are still unknown. In this paper, we show the results of a method based on intrusive measurements (on the refrigerant side) adapted to the dynamic behavior. This method uses Coriolis flow meters measures for the refrigerant flow rate and for enthalpies. Results confirm that the refrigerant density measurement with a Coriolis flow meter can help to predict the refrigerant vapor quality with a satisfying accuracy if the quality is not too high. The method is validated by testing an air-to-water heat pump in laboratory and by using the water enthalpy method as a reference. The experimental results show that the method is reliable in dynamic conditions (including during the defrosting periods). This internal method can be used as a reference to check the air enthalpy method for air-to-air heat pumps

Seasonal Coefficient of Performance of Heat Pumps

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Heat-and-mass transfers modelled for rotary desiccant dehumidifiers

International audienceA desiccant-wheel behavioural model has been developed. This model fulfils several criteria, such as simplicity of parameterization; accuracy; ability to characterize the equipment behaviour under all operation conditions; and short computation time. The method of characteristics has been applied to the heat-and-mass transfer partial-differential equations. This transformation provides equations which are similar to those of a rotary heat-exchanger. Then, the model is described by the effectiveness-NTU method and identified from only one nominal-rating point. The model predictions have been compared with experimental and manufacturers' data for a broad range of operating conditions. Good agreement has been found