Jean Lebrun

Experimental analysis and simplified modelling of a hermetic scroll refrigeration compressor

Abstract The first part of this paper presents a detailed analysis of the results obtained in a previous experimental study. In the frame of that study, a hermetic scroll compressor has been equipped with internal sensors by the manufacturer. The analysis reveals the main processes affecting the refrigerant mass flow rate as well as the compressor power and the discharge temperature. Based on these experimental results, a simplified model of the scroll compressor is proposed. It assumes that the refrigerant mass flow rate is affected by a suction temperature increase due to heat gained from a uniform wall temperature. This fictitious wall is supposed to gain heat from the electromechanical losses and from the discharged gas and to loose heat to the suction gas and to the ambient. The compression process is considered to be isentropic up to the “adapted” pressure and then isochoric until the discharge pressure. The model is able to compute variables of primary importance, like the mass flow rate, the electric power and the discharge temperature, as well as secondary variables such as suction heating-up, discharge cooling-down, and ambient losses.

Scroll compressors using gas and liquid injection: experimental analysis and modelling

The first part of this paper presents an experimental analysis of different hermetic scroll compressors using different methods of injection: the first one is without injection, the second one uses vapor injection and the third one liquid injection. The analysis reveals the influence of these methods on the compressor behavior. A simplified model of the scroll compressor is then proposed that takes into account not only the different internal processes but also the refrigerant injection. It assumes that the refrigerant mass flow rate is affected by a heating-up due to a uniform wall temperature. This fictitious wall is supposed to gain heat from the electromechanical losses and from the discharged gas and to loose heat to the suction and to the ambient. The compression step is considered isentropic up to the adapted pressure and then at constant volume until the discharge pressure. The model is able to compute variables of first importance like the mass flow rate, the electric power and the discharge temperature, as well as secondary variables as suction heating-up, discharge cooling-down, and ambient losses. The validation based on 45 experimental results shows excellent results.

Simplified modelling of an open-type reciprocating compressor

Abstract The first part of this paper presents a detailed experimental analysis of an open-type reciprocating compressor equipped with internal sensors. The analysis reveals the main processes affecting the refrigerant mass flow rate as well as the compressor power and the discharge temperature. Based on these experimental results, a simplified steady-state model of the reciprocating compressor is proposed. The refrigerant mass flow rate is supposed to be affected by the clearance volume re-expansion, by a pressure drop occurring through a supply flow restriction and by a temperature increase due to some heat transfer from a supposed-to-be isothermal wall. The friction power loss is supposed to be transferred to this fictitious wall, which is also exchanging heat with the discharged gas and with the ambient. The model is able to determine the ambient losses and so, the exhaust temperature. The compression itself is considered as adiabatic, reversible and therefore isentropic. The friction power loss is decomposed into a constant contribution and another one proportional to the isentropic power.

Experimental analysis of the performances of variable refrigerant flow systems

This paper presents a testing methodology applicable to variable refrigerant flow (VRF) equipment. A test bench is presented: it consists of a set of six calorimeters, each one fully instrumented and controlled in such a way to compensate almost all combinations of sensible, latent, heating and cooling loads. This test bench is used for a three-pipe VRF system with ve indoor units and one outdoor unit. Examples of testing results are presented in the paper, in order to illustrate the methodology and also validate a simulation model. The (heating or cooling) emission of each indoor unit is identi® ed thanks to a very accurate `air’ balance inside each calorimeter. Refrigerant side (pressure and temperature) measurements are used in order to identify the refrigerant flow rate and the characteristics of the compressors (isentropic effectiveness) and of the terminal units (heat transfer coef® cients) in different regimes. Examples of global performance evaluation are also presented in the paper.

From model validation to production of reference simulations: how to increase reliability and applicability of building and HVAC simulation models

Validation of simulation models appears from a long time as a key issue in order to promote a more intensive and more efficient use of simulation models in the field of building and HVAC simulation. IEA Annex 34/43 originally targeted a number of specific applications where a more advanced validation was required: ground coupling problems, multizone building, shading, day lighting and cooling load interaction, HVAC components and ventilated facades. These validation exercises were built on the large methodological experience obtained in previous projects and address sometimes very fundamental problems of heat transfer in buildings. Consulting engineers and practitioners might see these exercises as a bit too far from their objectives and it is the reason why an additional activity was proposed with the specific aim of producing, based upon the results of the validation of models, a set of reference simulations. These applications cover a range of building types (residential, commercial) and systems (production, distribution emission) and run in a variety of climates. The paper will describe how models dedicated to these applications were developed, starting from validation results, going through the selection and consolidation of simulation hypothesises and ending with a number that might be considered as reference for the concerned applications. The paper will concentrate on models required by a residential building application (multizone building equipped with a heat pump or a condensing boiler, heat emitted by radiators or floor heating systems). Simulations make use of both EES and TRNSYS software and both software are applied in parallel as far as possible in the different applications in order to get a better judgment of their potential advantages and drawbacks. The use of reference simulations in view of qualifying normative methods currently in development in the frame of the European Energy Performance in Buildings Directive is also addressed and demonstrated in the paper.

Thermal Model and Experimental Validation of Humidifier Systems as Commissioning Tools in HVAC Systems

This paper presents the results of an experimental study performed to obtain a simplified model applicable to two adiabatic humidification systems: wetted wires and centrifugal atomizing. The aims of this study are to provide a model to be used in situ as a diagnosis tool in the commissioning of air-conditioning systems, and to develop a comparison between “wet” and “therma” effectiveness methodologies that also can be useful for the commissioning process. The model is able to predict the exhaust dry-air temperature, exhaust humidity ratio, and the humidifier effectiveness by using as inputs the supply-air temperature and relative humidity as well as the air and water mass flow rates. Simplicity and accuracy are the crucial factors. A series of tests are performed in order to validate the model.

Re-commissioning of an Air Handling Unit

Publisher Summary The building, the Administrative Center of the Walloon Ministry of Equipments and Transport (CA-MET), is designed for a one thousand occupants and is made of 13 modules. In the building, heating and cooling power is distributed through collectors to 14 substations. Most of the substations, divided in northern and southern parts are feeding two building modules. In each substation, the air handling units (AHUs) are feeding the offices and the atrium are connected to each other in such as way that a fraction of the air extracted from the offices is ventilated in the atrium. The part that is not injected in the atrium AHU is recirculated in the offices or extracted through the toilets. The AHUs are made of the components—mixing box, filter, heating coil, cooling coil, humidifier, and fan. The Building Energy Management system is controlling both the AHUs and the radiators heating circuits. For AHU, the strategy consists controlling the valve of the heating or cooling coil in order to modify the supply air temperature according to the return air and the outside air temperature conditions.