Refrigerant R410A Vaporisation Inside a Small Brazed Plate Heat Exchanger

This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R410A vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature and outlet conditions are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show high sensitivity both to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows high sensitivity to refrigerant mass flux and weak sensitivity both to saturation temperature and outlet conditions. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling: a fair agreement is found

A comprehensive analysis of time influence on floating floors: effects on acoustic performance and occupants\u2019 comfort

Impact noise is increasingly becoming an important issue both in terms of technologies for its reduction and in terms of its perception inside buildings. In fact, a high level of noise clearly affects indoor comfort and liveability of confined spaces. For this reason, this study focuses on the influence which the screed static load has over time on the resilient material of a floating floor and on its final performance. Five different types of resilient materials have been tested for five years and the results are analysed in terms of material type, surface contact and thickness variation, dynamic stiffness measured on 8 different time steps and its application on 6 different bare floors. Obtained parameters values are therefore studied in terms of perceived comfort and compliance with 31 European countries regulations limits. Results clearly show that time has a paramount influence on all types of resilient materials (with the exception of one) in all configurations and that complete floor selection, in time, can greatly change perceived indoor living comfort and compliance with the limits imposed by laws

Development of sets of simplified building models for building simulation

This work proposes a method to manage the complexity of variables involved in building simulation studies and to identify groups of simplified building models suitable to have statistically significant results. The method is described by means of an applicative example, whose aim is the definition of a set of configurations appropriate for the analysis of TRNSYS and EnergyPlus discrepancies in monthly energy needs, hourly peak loads and time of occurrences of hourly peak loads – for both heating and cooling. The proposed procedure for the definition of a reference set of building configurations moves on from the selection of a set of candidate variables describing the building envelope characteristics, paying attention to implications of each choice and to cross-correlations among variables. This is obtained by means of a screening analysis with a simple statistical index (Spearman’s rank correlation coefficient). Two sample sizes are considered in order to evaluate the effects on the selection procedure. For each of the six considered outputs, the most significant group of configuration variables is identified, and the differences among those groups are described

Building Simulation Applications BSA 2013 - Proceedings of 1st IBPSA Italy conference

Building Simulation application 2013 was the first IBPSA Italy regional conference on building performance simulation. The two-day event focused on three main subjects: simulation of building performance, actual perspectives in building physics and simulation tools. The principal mission is to promote and advance the practice of building performance simulation in order to improve the design, construction, operation and maintenance of new and existing building

Evaluation of the Indoor Thermal Quality in high schools buildings: strengths and limits of different assessment methods

Recent studies have pointed out how much the indoor environmental quality in schools\u2019 classrooms is an important factor which could prevent serious adverse effects not only on the students\u2019 comfort sensation, but also on their health and learning potential. However, although standards EN ISO 7726:2001, EN ISO 7730:2005 and EN 10551:2001 give recommendations about how to practically perform objective and subjective measurements, on the evaluation of the level of comfort perceived in buildings, there is the need to define a systematic and standardized way in order to implement the comfort assessment through a methodical and uniform approach. In this work the assessment of the Indoor Thermal Quality of two classrooms in one high school located in Treviso, a town in the North-East of Italy, is presented in order to highlight the strengths and the limits of two different evaluation approaches: field monitoring, survey questionnaires. To reach the aim, two monitoring and surveys campaigns were carried out, one during the spring and one during the heating season. All the four comfort areas were investigated through the questionnaires: the thermal, the visual, the acoustic and the air quality perception.. Afterwards objective and subjective responses on thermal and visual perception have been compared

Multi-stage calibration of the simulation model of a school building through short-term monitoring

The increasing attention on the improvement of new and existing buildings' performance is emphasizing the importance of the reliability of the simulation models in predicting the complexity of the building behaviour and, consequently, in some advanced applications of building simulation, such as the optimization of the choice of different Energy Efficiency Measures (EEMs) or the adoption of model predictive control strategies. The reliability of the energy model does not depend only on the quality and details of the model itself, but also on the uncertainty related to many input values, such as the physical properties of materials and components, the information on the building management and occupation, and the boundary conditions considered for the simulation. Especially for the existing buildings, this kind of data is often missing or characterized by high uncertainty, and only very simplified behavioural models of occupancy are available. This could compromise the optimization process and undermine the potential of building simulation. In this context, the calibration of the simulation model by means of on-site monitoring is of crucial importance to increase the reliability of the predictions, and to take better decisions, even though this process can be time consuming. This work presents a multi-stage methodology to calibrate the building energy simulation by means of low-cost monitoring and short-term measurements. This approach is applied to a Primary School in the North-East of Italy, which has been monitored from December 2012 to April 2014. Four monitoring periods have been selected to calibrate different sets of variables at a time, while the validation has been carried out on two different periods. The results show that even if less than 8 weeks have been considered in the proposed calibration approach, the maximum error in the estimation of the temperature is less than ±0.5 in 77.3% of the timesteps in the validation period

Building Simulation Applications BSA 2013 - Proceedings of 1st IBPSA Italy conference

Building Simulation application 2013 was the first IBPSA Italy regional conference on building performance simulation. The two-day event focused on three main subjects: simulation of building performance, actual perspectives in building physics and simulation tools. The principal mission is to promote and advance the practice of building performance simulation in order to improve the design, construction, operation and maintenance of new and existing buildings

Sound absorption performance of sustainable foam materials: Application of analytical and numerical tools for the optimization of forecasting models

Traditional models used to predict acoustic properties of poroelastic materials are usually applied to fibrous layers or polyurethane foams. However, for new materials like complex cellular foams these procedures may not be applied due to the different cell microstructure. To this aim, the sound absorbing properties of novel sustainable foam materials are investigated as a function of the nature and loading of waste powders and their effects on the microstructure and the acoustic properties. The foams are prepared from naturally occurring alginates that are in situ polymerized. The morphology and the acoustic properties of the foam-cells appear linked to the particle size distribution of the starting powder. Determination of the parameters of Johnson\u2013Champoux\u2013Allard acoustic model (tortuosity, viscous characteristic length, thermal characteristic length, porosity and flow resistivity) was performed using five different forecasting methods, including traditional analytical model for fibrous materials as well as inverse procedure. A new procedure for tortuosity computation of foam is proposed and validated. Transfer Matrix Method calculation of the absorption coefficient was performed and compared with the experimental data, in order to assess the validity of the model. Indirect method technique is demonstrated to be dependent on experimental measurement of thermal characteristic length

A multi-stages approach to the calibration of a school building's simulation model

The calibration process is an important step to improve the reliability of the simulation model and to reduce the differences between simulated and measured building energy performance. This paper presents a methodology to calibrate a building simulation model by means of low-cost monitoring set-up and short term measurements. The proposed method can be defined as a multi-stage calibration. It is based on the assumption that input data affect the simulation results differently according to the considered period of the year. It seems thus possible to calibrate different sets of parameters in different reference periods, with the advantage of using shorter recording times when the calibration periods have been consistently selected