Search

A versatile meteorological index for predicting heat stress in dairy cattle remains elusive. Despite numerous attempts at developing such indices and widespread use of some, there is growing skepticism about the accuracy and adequacy of the existing indices as well as the general statistical approach used to develop them. At the same time, precision farming of high-yielding animals in a drastically changing climate calls for more effective prediction and alleviation of heat stress. The present paper revisits classical work on human biometeorology, particularly the apparent temperature scale, to draw inspiration for advancing research on heat stress in dairy cattle. The importance of a detailed, mechanistic understanding of heat transfer and thermoregulation is demonstrated and reiterated. A model from the literature is used to construct a framework for identifying and characterizing conditions of potential heat stress. New parameters are proposed to translate the heat flux calculations based on heat-balance models into more tangible and more useful meteorological indices, including an apparent temperature for cattle and a thermoregulatory exhaustion index. A validation gap in the literature is identified as the main hindrance to the further development and deployment of heat-balance models. Recommendations are presented for systematically addressing this gap in particular and continuing research within the proposed framework in general. [ABSTRACT FROM AUTHOR]

Controlling air leakage through the building envelope remains a challenge, especially in light of the imperative to transition to a net-zero energy building sector and the increasing importance of indoor air quality during extreme weather events such as wildfires. The British Columbia Energy Step Code is a performance-based compliance option in the British Columbia Building Code which is intended to provide a transition pathway to net-zero energy ready construction by 2032. For small residential buildings, performance targets entail thresholds for the measured air leakage rate through the building envelope. This paper reports on the airtightness of the first 145 single- and two-family dwellings built under the Energy Step Code in Richmond, BC. Although the first phase of the implementation of the Energy Step Code in Richmond entailed no airtightness targets (only testing), results indicate improvement compared to the historical levels of airtightness in the region. [ABSTRACT FROM AUTHOR]

Preventing and alleviating heat stress remain an enormous challenge in dairy farming. Although enhanced air distribution techniques have been developed and deployed in many barns, ventilation alone is no longer sufficient even in regions with historically mild climates. There is an increasing need for cooling of the intake fresh air. Evaporative cooling is a cost-effective sustainable technique used in many applications, including livestock farming. This paper presents a graphical method for preliminary evaluation of evaporative cooling as a viable and effective solution. Thermodynamic principles are combined with models for heat transfer in dairy cattle to develop a set of criteria on the psychrometric chart. The proposed method is demonstrated for a naturally ventilated dairy barn located in the continental central European climate and in two locations with hot climates, a semi-arid/Mediterranean and a humid subtropical climate. • Thermoregulation models combined with thermodynamic principles. • Limits for effectiveness of evaporative cooling derived. • Developed criteria mapped onto psychrometric chart. • A graphical method to assess effectiveness of evaporative cooling proposed. • Proposed method demonstrated for sample barn in Europe. [ABSTRACT FROM AUTHOR]

Laminar free convection in a vertical channel with isothermal walls is a classical heat transfer problem. In general, the channel walls may be at different temperatures, leading to a difference in the rate of heat transfer at the walls. Although numerical and experimental results are often presented in terms of average wall Nusselt numbers, separate correlations for heat transfer at each wall are rarely available. The few existing relations are complex in form due to the extra parameters introduced to facilitate the correlation of results. Moreover, the existing correlations do not reflect the physics of the problem in full. In this work, the three-temperature problem of laminar-free convection of air in a tall vertical channel with isothermal walls is studied in a new theoretical framework, namely the extended Newton formulation. This formulation eliminates the need for an effective temperature difference, hence simplifying the presentation and correlation of the results. The dQdT technique was utilized along with computational fluid dynamics to calculate the average paired Nusselt numbers that characterize the extended Newton formulation of the problem. The dQdT results were then used to derive heat transfer correlations which are both simpler in form and more accurate than the existing correlations. The proposed correlations are applicable to cases of both channel walls hotter or both colder than the ambient air. [ABSTRACT FROM AUTHOR]

This paper examines engineering students' misconceptions of thermodynamics. A summary of the pedagogical theories of misconceptions is presented and the cognitive roots of misconceptions are briefly reviewed. Concept tests are discussed as one of the most effective tools for diagnosing misconceptions, followed by a summary of the available thermodynamics concept tests. Finally, an overview is presented of the most frequent thermodynamics misconceptions among engineering students. [ABSTRACT FROM AUTHOR]

Many convection problems entail more than two isothermal boundaries. In previous work, a resistor-network model was proposed for this class, multi-temperature convection problems. A technique dubbed dQdT was also developed to obtain the paired convective resistances that characterize the thermal network of a multi-temperature convection problem. In the present paper an extension of the Newton law of cooling is proposed as a general formulation of multi-temperature convection in terms of multiple driving temperature differences. Most notably, the proposed formulation eliminates the need for an effective temperature difference. The formulation is characterized by functionality coefficients which give the relation between a heat transfer rate and one of the temperature differences. These coefficients can be obtained using the dQdT technique. The new formulation and the application of the dQdT technique are demonstrated for classical three-temperature convection problems. The connection between the extended Newton formulation and the resistor-network model of multi-temperature convection is also discussed. It is shown that dQdT can be used to determine the applicability of the resistor-network model of convection. [ABSTRACT FROM AUTHOR]

For decarbonization of the building sector to happen at scale, net-zero energy levels of operational efficiency must be achieved. A global consensus is emerging around the Passive House energy performance level (15 kWh/m2/a thermal energy demand) as "net-zero energy ready". Given the imperative to rapidly transform buildings and shortcomings of the traditional prescriptive approach, a growing number of building energy regulations are adopting the performance-based or outcome-based approach, seeking to mandate net-zero energy performance with ambitious timelines. Some such regulations are based on the Reference Building Approach (RBA) where the energy performance of a building is assessed based on a hypothetical building of the same design but meeting a set of minimum prescriptive requirements. More commonly, performance targets are defined in absolute terms, based on energy intensity metrics. Although the European version of the RBA reconciles the absolute and relative performance targets through mandatory statistical performance baselines, the RBA in North America is used as an independent alternative to absolute energy use/demand intensity metrics (kWh/m2/a). This paper examines the North American Reference Building Approach, focussing on its implementation in the British Columbia Energy Step Code as an instructive example. It is shown that the RBA has serious flaws. Most importantly, by creating a sliding scale, the RBA does not deliver net-zero energy performance, while incentivizing inefficient designs and poor energy modeling practices. Despite the regional focus of the data, the conclusions are applicable to the RBA in general. Based on the results, it is recommended that the use of the RBA in building energy codes and standards be discontinued. [ABSTRACT FROM AUTHOR]