The specification of shelter requirements of cattle requires knowledge of the complex interactions of climate, the enclosed animals and their enclosure. The modelling approach used in this research reduces this complexity by identifying the most significant components of the system. Four electrically heated physical thermal models of suckler cows with controlled internal temperatures and coverings of synthetic hair were used over two consecutive winter periods to simulate sensible heat losses from suckler cows kept in an unsheltered site and in three simple shelters. The measured reductions of unsheltered heat losses were (1) 2% (2) 6% and (3) 20% for shelters with respectively (1) just a roof (2) four solid walls, no roof and (3) a roof and four walls with ventilation openings. A mathematical model which predicts hourly and daily mean sensible heat losses from a suckler cow using measurements of air temperature, rainfall, windspeed and net radiation had previously been developed using a large thermal model. Climate modifying factors were derived for each shelter type by comparing hourly and daily mean measured heat losses with those predicted by the mathematical model. These factors were successfully validated using the second winter's data. The accuracies of heat loss predictions for the small thermal models in each shelter were similar to those for the original large thermal model. Examples are given for cattle sheltered by a forest and for calves sheltered by a creep to show how this model for prediction of heat losses in different shelters can be incorporated in a model of the whole system. Meteorological Office climate data was used to predict heat losses from cattle. This included a novel method for prediction of net radiation. The analysis indicated that predictions for a given site could be applied to a large area although this should be tested before any large scale analysis of records is undertaken.

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Acute (~2 min) baroreceptor unloading was reported to modulate metaboreflex control of postexercise cutaneous blood flow, but not sweating. We examined whether sustained changes in baroreceptor loading status during prolonged postexercise recovery can alter the metaboreceptors’ influence on heat loss. Thirteen young males performed a 1-min isometric handgrip exercise (IHG) at 60% maximal voluntary contraction followed by 2-min of forearm ischemia (to activate metaboreceptors) before and 15, 30, 45 and 60-min after a 15-min intense treadmill running exercise (>90% maximal heart rate) in the heat (35°C). This procedure was repeated on three separate days with the application of lower-body positive (LBPP, +40 mmHg), negative (LBNP, -20 mmHg), or no pressure (Control) postexercise. Sweat rate (ventilated capsule; forearm, chest, upper back) and cutaneous vascular conductance (CVC; forearm, upper back) were measured. Relative to pre-IHG levels, sweating at all sites increased during IHG and remained elevated during ischemia at baseline and similarly at 30, 45, and 60-min postexercise (site average sweat rate increase during ischemia: Control, 0.13±0.02; LBPP, 0.12±0.02; LBNP, 0.15±0.02 mg·min-1·cm-2; all P<0.01), but not at 15-min (all P>0.10). LBPP and LBNP application did not modulate the pattern of sweating to IHG and ischemia (all P>0.05). At 15-min postexercise, forearm CVC was reduced from pre-IHG levels during both IHG and ischemia under LBNP only (ischemia: 3.9±0.8 %CVCmax; P<0.02). Therefore, we show metaboreceptors modulate postexercise sweating in the mid-to-late stages (30-60 min) of recovery, independent of baroreceptor loading status and similarly between skin sites. In contrast, metaboreflex modulation of forearm but not upper back CVC occurs only in the early stages of recovery (15 min) and depends upon baroreceptor unloading.

The purpose of the studies presented in this thesis was to develop a greater understanding of the contribution of respiratory heat loss to the thermal balance of exercising horses. In the first experiment the effect of three different warm-up regimens on the thermal balance of Thoroughbred horses was investigated. The experiments showed that a low intensity warm-up was most beneficial aiding heat dissipation during subsequent exercise. The study also showed the heat loss by sweating is not restricted by the rate of sweat production, but by the evaporation rate of the sweat. In the second experiment, horses were exercised to fatigue in thermoneutral and hot-humid environments. The evaporative heat dissipation from sweating and from the respiratory tract was severely impaired during the hot humid exercise protocol. There was a significant increase in the heart rate and the metabolic rate during the hot humid protocol, thus indicating the additional work done by the horse in an effort to dissipate the rapidly accumulating heat. The significantly shorter time to fatigue may be a mechanism to protect the horse from circulatory collapse as the circulatory demands for cardiac output exceed its capacity. In the third experiment adaptations that the horse is able to make to alleviate the compromised evaporative heat loss were identified. These experiments showed that the horse is able to shorten its stride, increase minute ventilation and the velocity of the air in the conducting airways. The results presented also indicate that the horse is able to modify the evaporative area of the airways to enhance evaporative heat loss from the respiratory tract. The experiments also showed that during exercise in hot-humid environments, small changes in the evaporating surface vapour pressure have a significant effect on the vapour pressure gradient thus having a significant effect on the evaporating heat loss. Finally, the lessons gained during the experiments presented in this thesis were used to revise and refine a mathematical model of the thermal balance of exercising horses. The resulting model is more accurate and easier to apply to use in the field. / Thesis (DPhil)--University of Pretoria, 2000. / Equine Research Centre / unrestricted

In the year 2006, the energy performance directive 2002/91/EG was passed by the European Union, according to this directive the Swedish building code was supplemented by a key measure of energy use intensity (EUI). The implemented EUI equals some energy use within a building divided by its floor area and must be calculated in new housing estate and shown when renting or selling housing property. In order to improve the EUI, energy efficiency refurbishments could be implemented. Building energy simulation tools enables a virtual view a building model and can estimate the energy use before implementing any refurbishments. They are a powerful resource when determine the impact of the refurbishment measure. In order to obtain a correct model which corresponds to the actual energy use, some adjustments of the model are often needed. This process refers to as calibration. The used EUI has been criticized and thus, the first objective in this work was to suggest an alternative key measure of a buildings performance. The results showed that the currently used EUI is disfavoring some districts in Sweden. New housing estate in the far north must take more refined actions in order to fulfill the regulation demand, given that the users are behaving identical regardless where the house is located. Further, the suggested measure is less sensitive to the users’ behavior than the presently used EUI. It also has a significance meaning in building design as it relating the building shape and thermal properties and stating that extreme building shapes must undergo a stricter thermal construction rather than buildings that are more compact. Thus, the suggested key measure also creates a communication link between architects and the consultant constructors. The second objective of this thesis has been to investigate a concept of calibration using the data normally provided by energy bills, i.e. some monthly aggregated data. A case study serves to answer this objective, by using the building energy simulation tool IDA ICE 4.7 and a building located in Umeå, Sweden. The findings showed that the used calibration approach yielded a model considered as calibrated in eleven of twelve months. Furthermore, the method gives a closer agreement to the actual heat demand rather than using templates and standardized values. The major explanation of the deviation was influence of the users, but also that the case study building burden with large heat losses by domestic hot water circulation and thus, more buildings should be subjected to this calibration approach.

The operation of large industrial scale combustion systems, such as furnaces and boilers is increasingly dictated by emission legislation and requirements for improved efficiency. However, it can be exceedingly difficult and time consuming to gather the information required to improve original designs. Mathematical modelling techniques have led to the development of sophisticated furnace representations that are capable of representing combustion parameters. Whilst such data is ideal for design purposes, the current power of computing systems tends to generate simulation times that are too great to embed the models into online control strategies. The work presented in this thesis offers the possibility of replacing such mathematical models with suitably trained Artificial Neural Networks (ANNs) since they can compute the same outputs at a fraction of the model's speed, suggesting they could provide an ideal alternative in online control strategies. Furthermore, artificial neural networks have the ability to approximate and extrapolate making them extremely robust when encountering conditions not met previously. In addition to improving operational procedures, another approach to increasing furnace system efficiency is to minimise the waste heat energy produced during the combustion process. One very successful method involves the implementation of a heat exchanger system in the exiting gas flue stream, since this is predominantly the main source of heat loss. It can be exceptionally difficult to determine which heat exchanger is best suited for a particular application and it can prove an even more arduous task to control it effectively. Furthermore, there are many factors that alter the performance characteristics of a heat exchanger throughout the duration of its operational life, such as fouling or unexpected systematic faults. This thesis investigates the modelling of an experimental heat exchanger system via artificial neural networks with a view to aiding the design and selection process. Moreover, the work presented offers a means to control heat exchangers subject to varying operating conditions more effectively, thus promoting savings in both waste energy and time.

The current study evaluated whether NO synthase (NOS) contributes to cutaneous vasodilation and sweating during prolonged exercise in the heat. In addition, we determined if prolonged exercise-induced increases in reactive oxygen species (ROS) and activation of angiotensin II type 1 receptors (AT1R) impair heat loss responses. On two separate days, eleven young men completed 90-min of continuous cycling at ~600W of metabolic heat production followed by 40-min of recovery in the heat (40ºC). To evaluate the role of excess fluid loss via sweating, participants completed a second session of the same protocol while receiving fluid replacement (FR) determined during the first session (No-FR). Cutaneous vascular conductance (CVC) and local sweat rate (LSR) were measured at four intradermal microdialysis forearm sites perfused with either: (1) lactated Ringer (Control); (2) 10 mM NG-nitro-L-arginine methyl ester (L-NAME, NOS inhibition); (3) 10 mM ascorbate (non-selective anti-oxidant); or (4) 4.34 nM Losartan (AT1R inhibition). Ascorbate treatment increased CVC at 60- and 90-min of exercise versus Control during the FR (P < 0.02), but not the No-FR condition (P > 0.31). CVC was reduced at the L-NAME treated site (P < 0.02), but was not different relative to Control at the Losartan treated site (P > 0.19) irrespective of condition. LSR did not differ between sites or as a function of condition (all P > 0.10). We conclude that NO regulates cutaneous vasodilation but not sweating, irrespective of fluid replacement, and ascorbate sensitive ROS impair cutaneous vasodilation during prolonged exercise in the heat with FR.

In order to maximize the e ciency of power generation in concentrated solar power systems (CSP) it is de- sired to achieve as high a tempera- ture in the receiver as possible due to the use of the Sterling cycle to gen- erate power. This report investigates three di↵erent geometries for cavity receivers in CSP systems; cylindrical, conical and truncated conical. The goal has been to minimize the heat loss due to radiation. This was achieved through mathematical mod- eling with the help of MATLAB. Five di↵erent cases with regards to oper- ating temperature and proportions of the receiver where investigated for each of the three chosen geometries. It was found that the conical geometry minimized this heat loss in all except one case.

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