Experimental investigation of the steady state behaviour of Breathing Walls by means of a novel laboratory apparatus

Breathing Walls are envelope components, based on porous materials, crossed by a natural or forced airflow. Since they behave both as recovery heat exchangers and active insulation, reducing the conductive heat flux, they represent a promising envelope technology, allowing to reduce energy consumption in buildings. From the modeling point of view, an analytical model can be found in literature, describing heat and mass transfer across Breathing Walls in steady state conditions. However, to the best of the authors' knowledge, the model lacks an exhaustive experimental validation. Therefore, in this paper, the novel laboratory apparatus named Dual Air Vented Thermal Box developed at Politecnico of Milano is presented. The apparatus is used to experimentally investigate the steady state behaviour of a 1 m2 Air Permeable Concrete sample, crossed by an airflow at different velocities up to 12 mm/s. The temperature profile inside the sample, measured in different positions, is compared with the model predictions. While in the central portion of the wall a very good agreement is found, the experimental results at the top and at the bottom of the wall suggest a non-uniform velocity field entering the sample. A qualitative confirmation of this hypothesis is provided by CFD simulations on the apparatus, clearly showing a mixed convection regime on both sides of the wall. The results lead to state the validity of the one-dimensional analytical model in literature, although a careful application should take into account adjusted boundary conditions, consisting in an airflow velocity possibly variable with height

In Situ Measurement of Wall Thermal Properties: Parametric Investigation of the Heat Flow Meter Methods through Virtual Experiments Data

Energy retrofit of existing buildings is based on the assessment of the starting performance of the envelope. The procedure for the in situ measurement of thermal conductance is described in the ISO 9869-1:2014, which provides two techniques for data processing: the average method (AM) and the dynamic method (DM). This work studies their effectiveness using virtual data from numerical simulations based on a finite difference model applied to different wall kinds, considering winter and summer boundary conditions alternatively (Italian Milan-Linate TMY). The estimated thermal conductances are compared to the reference theoretical values. The main purposes are: (i) defining the shortest test duration that provides acceptable results; (ii) assess the reliability of the criteria provided by the standard to evaluate the measurement quality; (iii) evaluate the sensitivity of both methods to variables such as wall properties, boundary conditions and others more specific to the DM (namely, the number of time constants and linear equations). The AM always provides acceptable estimates in winter (-3.1% divided by 10% error), with better outcomes when indoor heat flux is considered, except for the highly insulated wall, but is not effective in summer, despite the fulfillment of the acceptance criteria for the highly insulated wall. The DM provides improvements in both seasons (0.05% divided by 8.6% absolute values of error), for most virtual samples, and requires shorter sampling periods, even below the 3 days limit suggested by the standard. The test on the confidence interval indicated by the ISO 9869-1:2014 is not reliable and measurements are sensitive to the number of linear equations, that is left to the user's discretion without strict indications. This work suggests a possible approach for overcoming this issue, which requires deeper future investigation

Broadband Measurement of Error Vector Magnitude for Microwave Vector Signal Generators Using a Vector Network Analyzer

A frequency-domain method is proposed for the broadband measurement of error vector magnitude (EVM) for vector signal generators (VSGs). The technique is based on frequency-swept narrowband acquisitions performed with a vector network analyzer (VNA) by exploiting a stable (yet unknown) reference signal to obtain phase-repeatable measurements, eventually allowing to refer the residual distortion contribution of the analog VSG output to its digital input. The method leverages on the formulation of a novel measurement-based model, which accounts for the IQ imbalance effect and allows to separate it from the actual distortion within the VSG, ultimately yielding accurate broadband EVM measurements at microwave carrier frequencies without any time-domain waveform reconstruction, completely avoiding the use of broadband receivers and corresponding calibration

Infection by Xanthomonas campestris pv.viticola under temperature increase and carbon dioxide concentrations.

The experiments were carried out under controlled conditions to evaluate the impact of increased temperature and concentration of carbon dioxide on infection of Xanthomonas campestris pv viticola, the causal agent of bacterial canker in Vine seedlings. It proceeded the evaluation of the following epidemiological components: incubation period (PI), severity (SEV) and using that data were calculated the area under the disease progress curve (AUDPC). It used grape seedlings (Italia, Crimson Seedless, Sugraone and Selection 8) inoculated with bacterial suspension (108 CFU mL-1). The experimental design was completely randomized, factorial arrangement 4x4 (cultivar x temperature) and 4x2 (cultivar x carbon dioxide concentration) which was carried out twice. The data were subjected to variance analysis. Increasing temperature reduced bacterium?s incubation period with significant differences between genotypes. For Selection 8 and Crimson temperature increase caused enhancement on severity and AUDPC. For Seleção 8 the incubation period (PI) was extended from 7.93 to 30.18 days when the concentration changed from 390 to 770 μmol/mol. The increased CO2 concentration reduced AACPSD and SEV for Sugraone and Selection 8. The results show that the temperature and carbon dioxide (CO2) concentration of the air may have different effects on bacterial canker of grapevine

Zoo-technical application of Ground Source Heat Pumps: a pilot case study

Ground Source Heat Pumps are energy-efficient HVAC systems usually adopted in residential and commercial buildings. However the control of the thermal environment is required not only in spaces occupied by people, but also in intensive breeding farms, in order to maintain healthy conditions and to increase productivity. In the Italian livestock breedings, heating is usually provided by means of gas or Diesel burners directly installed in the stable. An important part of the heating load is due to the large ventilation rates required for the livestock wellbeing. Cooling is either absent or achieved by evaporative systems that also increase the humidity level in the stables, thus requiring even larger ventilation rates. Therefore the applicability of geothermal heating and cooling in breeding farms was analysed in a research project co-funded by the Lombardy Region and the Italian Ministry of Research and Education. A pilot system for heating, cooling and ventilation was designed and installed in a piglets room at the Experimental and Didactic Zoo-technical Center of the University of Milan. Five Borehole Heat Exchangers (BHEs), installed down to a depth of 60 meters into an alluvial aquifer, were coupled with a Ground Source Heat Pump. The heat pump provides heating and cooling to an Air Handling Unit, including a Heat Recovery system. A monitoring system was installed in order to measure comfort conditions in the piglet room, operating conditions and energy consumption of the HVAC system, together with the spreading of the thermal plume in the ground. In this paper the results of a monitoring campaign carried out in a typical winter period are presented and discussed. The overall energy efficiency of the system, expressed in terms of a COP, results to be equal to 4.04. A comparison between the pilot HVAC system and a traditional one is also carried out, showing that the proposed solution can provide over 40% primary energy saving. Following, cost savings in energy bills for farmers are found, although the ratio between electricity cost and fuel cost is a key parameter

Impacto de alterações da temperatura sobre a severidade do míldio da videira.

Diante dos cenários climáticos futuros, a temperatura do ar sofrerá aumentos, interferindo na distribuição geográfica e temporal de doenças. O míldio, causado pelo fungo Plasmopara viticola, é uma das principais doenças que ocorre na videira. O desenvolvimento deste patógeno pode ser influenciado por vários fatores ambientais, entre eles, a temperatura. O objetivo deste trabalho foi avaliar o impacto do aumento da temperatura na severidade do míldio da videira nas cultivares Crimson, Thompson e Alicante. Para a avaliação, mudas com 4-6 folhas foram inoculadas com uma suspensão de esporos na concentração de 105 esporos/mL + Tween 20 a 0,01%, por meio de pulverização. Após a inoculação, as mudas foram submetidas às temperaturas de 26, 28, 29.1, 30.4 e 31.8 oC, por 24 horas. Posteriormente, as mudas foram mantidas a temperatura de 26 oC, fotoperíodo 12 horas até a avaliação dos resultados. Foi avaliada a porcentagem da área foliar doente, por meio de escala diagramática e o período latente, determinado pelo número de dias entre a inoculação e a produção de esporos. O aumento da temperatura interferiu na infecção do míldio da videira, diminuindo a severidade da doença e aumentando o período latente

Impacto de alterações da temperatura sobre a infecção do óidio da videira.

O Painel Intergovernamental de Mudanças Climáticas (Intergovernanmental Panel on Climate Change - IPCC) descreve um cenário futuro com aumentos da temperatura média no planeta Terra entre 1,8 a 6,4 oC nos próximos 100 anos, contribuindo para aumentar ou limitar o desenvolvimento das doenças em plantas. O objetivo deste trabalho foi avaliar o efeito de alterações da temperatura na severidade do oídio da videira. Mudas das cultivares Alicante Bouschet e Thompson Seedless foram inoculadas com uma suspensão de esporos na concentração de 105 esporos/mL + Tween 20 a 0,01%, por meio de pulverização e submetidas às temperaturas de 26, 28, 29.1, 30.4 e 31.8 oC, por 24 horas, selecionadas com base nos acréscimos de 2,0; 3,1; 4,4; e 5,8 oC sob a temperatura média da região do Submédio do Vale do São Francisco (26 oC) correspondente aos cenários do IPCC. Posteriormente, as mudas foram mantidas a temperatura de 26 oC, fotoperíodo 12 horas até a avaliação dos resultados. A doença foi avaliada por meio de escala diagramática. Nas condições experimentais utilizadas, o aumento da temperatura diminuiu a severidade da do oídio da videira