1,721,188 research outputs found
New ideas for energy utilisation in combined heat and power with cooling: II. Applications
Full text linkChemical dehumidification can be beneficial in a HVAC plant, both in terms of capital and operating costs. The sorption system can be integrated into a traditional plant, usually satisfying the latent heat load, but it can satisfy even the whole load with particular cycles which also use evaporative cooling.
A number of applications are examined here, both integrated and self-sufficient systems, driven by natural gas or waste heat, working with liquid or solid sorption. Different lay-outs, performance and savings suggest new ideas for better energy utilization in H VAC combined heat and power plants
Experimental measurement of thermophysical properties of H2O/KCOOH (potassium formate) desiccant
No full textThis paper presents the measurement of the thermal conductivity and the dynamic viscosity of H2O/KCOOH (potassium formate) desiccant with a salt concentration from 60 to 80% in the temperature range 1- 80 degrees C. The thermal conductivity measurement gives evidence of a great sensitivity to salt concentration and lower sensitivity to temperature: H2O/KCOOH desiccant shows a thermal conductivity from 23 to 33% lower than water at the same temperature. H2O/KCOOH desiccant exhibits a Newtonian behaviour in all the investigated ranges of temperature and concentration. The relative viscosity shows a great sensitivity to salt concentration and weak or no sensitivity to temperature up to a solution concentration of salt around 70%. For higher solution concentration of salt (75 and 80%) the relative viscosity shows a great sensitivity also to temperature. H2O/KCOOH desiccant presents a dynamic viscosity from 4 to 30 times higher than water at the same temperature. (C) 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserve
Three years experimental comparative analysis of a desiccant based air conditioning system for a flower greenhouse: Assessment of different desiccants
No full textThis paper presents three years experimental comparative analysis of a desiccant-based and a traditional
air conditioning system for a flower greenhouse in the winter season. Two identical neighbouring flower
greenhouses were equipped with a traditional and an innovative air conditioning system respectively.
The innovative air conditioning system is based on the Ventilated Latent Heat Converter (VLHC) AGAM
1020 that consists of a dehumidification and a regeneration unit. Heat recovery is performed on the
desiccant regeneration process to warm up the dehumidified air coming back into the greenhouse.
Comparative analysis was carried out for three years using three different desiccants in the VLHC: H2O/
LiCl in 2010, H2O/KCOOH in 2011 and H2O/LiBr in 2012. The greenhouse equipped with a sorption unit
exhibits an energy saving of 9.6% in 2010, 11.7% in 2011, and 15.1% energy saving in 2012. The comparative
analysis gives the opportunity for the assessment of the hygroscopic salt solutions currently used as
desiccants. Although H2O/LiBr desiccant exhibits the best performance, the solution H2O/KCOOH seems
to be very promising as “desiccant of the future”
Three years experimental comparative analysis of a desiccant-based air conditioning system for a flower greenhouse
No full textModelling and Mapping Thermal Comfort Conditions with Solar Radiation: Comparison of Steady-State and Dynamic Indexes
No full textAIM AND APPROACH Short-wave solar radiation may have a great impact on the indoor thermal sensation of occupants, especially in highly glazed buildings. The dynamic nature of the phenomenon suggests that steady-state approaches such as Fanger’s could be not completely suitable to analyze the performance of building design configurations or management and control strategies. This paper investigates the impact of solar radiation on some commonly used thermal comfort indices. In particular this study contrasts the steady-state PMV with dynamic indices (TSENS, TSV and DTS) based on Pierce’s thermophysiological model. Solar irradiation on the subject has been taken into account by means of an adjusted value of the mean radiant temperature according to La Gennusa et al. (2005) approach, which was originally proposed to correct Fanger’s PMV. The evolution of comfort conditions is mapped on a grid of reference points, which allows us to pay special attention to the irradiated area, closer to the glazing. The indexes capability of describing critical conditions is contrasted. SCIENTIFIC INNOVATION AND RELEVANCE Despite the use of highly glazed facades has become more and more common, the most used thermal comfort models do not account explicitly for solar radiation. The availability of a reliable and computationally efficient approach to include solar radiation contribution in thermal comfort metrics is of great importance for improving indoor environmental conditions either in the early design or during the operation optimization phases. In this work, the effects of short-wave solar radiation contribution have been included into different thermal comfort models by adjusting the mean radiant temperature (MRT) of the environment. The solar-adjusted metrics and the original ones are calculated in an open plan office of 100 m2 with a large window on the South façade, equipped with shading devices and a heating and a cooling system. The environmental variables are obtained by thermal simulation of the space in EnergyPlus. The results are then fed into an original simulation code implementing the traditional and the solar-adjusted comfort models in several reference points inside the space. The comfort conditions and their evolution are presented in detailed comfort maps, to contrast the capability of the solar-adjusted metrics to describe the quality of the thermal environment and highlight the main criticalities. PRELIMINARY RESULTS AND CONCLUSIONS Although under abrupt variations of the environmental conditions steady state indices such as PMV are far from being accurate in describing the occupant sensation, there is little difference between steady and non-steady approaches when considering the typical conditions inside a conditioned space. The four comfort indices, PMV, TSENS, TSV and DTS, seem to be equally suitable to assess the evolution of thermal sensation in conditioned buildings when warm sensation is prevailing and no solar radiation is to be included. Nevertheless, TSV requires a suitable calibration, being very sensitive to the choice of the reference mean skin temperature in the thermally neutral and steady state Tsk,0, and its scale must be resized with reference to the other comfort metrics. TSENS is the less affected by the mean radiant temperature correction when considering cooler conditions. In this respect, either PMV, DTS or calibrated TSV succeed in highlighting criticalities arising from specific positions of the occupants and time of day. In the current implementation, TSENS appears to be insensitive to cool environments. Further investigation is needed. MAIN REFERENCES Cappelletti, F., Prada, A., Romagnoni, P., & Gasparella, A. (2014). Passive performance of glazed components in heating and cooling of an open-space office under controlled indoor thermal comfort. Building and Environment, 72, 131–144. Doherty, T. J., & Arens, E. (1988). Evaluation of the physiological bases of thermal comfort models. ASHRAE Transactions, 94(1), 1371–1385. Fanger, P. O. (1970). Thermal comfort: Analysis and applications in environmental engineering. Copenhagen: Danish Technical Press. Fiala, D. (1998). Dynamic Simulation of Human Heat Transfer and Thermal Comfort (Doctoral dissertation). De Montfort University. Gagge, A. P., & Fobelets, A. P. (1986). A Standard Predictive Index of Human Response to the Thermal Environment. ASHRAE Transactions, 92:2B. La Gennusa, M., Nucara, A., Pietrafesa, M., & Rizzo, G. (2007). A model for managing and evaluating solar radiation for indoor thermal comfort. Solar Energy, 81(5), 594–606. Takada, S., Matsumoto, S., & Matsushita, T. (2013). Prediction of whole-body thermal sensation in the non-steady state based on skin temperature. Building and Environment, 68, 123–133. Tzempelikos, A., Bessoudo, M., Athienitis, A. K., & Zmeureanu, R. (2010). Indoor thermal environmental conditions near glazed facades with shading devices - Part II: Thermal comfort simulation and impact of glazing and shading properties. Building and Environment, 45(11), 2517–2525
Including the effect of solar radiation in dynamic indoor thermal comfort indices
No full textThe use of solar gains is one of the most effective passive strategies to reduce the heating energy demand of buildings. However, solar radiation not only affects the thermal balance of the building, but also that of the occupants. Several approaches have been developed for including solar effects into steady-state thermal comfort models (i.e. Fanger Model) proposing a correction to the calculation of the Predicted Mean Vote (PMV) and validating it experimentally. One of those approaches incorporates solar radiation as an adjustment of the mean radiant temperature (MRT) used in the calculation of the PMV. In this paper the described approach has been integrated in the calculation of three dynamic thermal comfort indices (i.e. TSENS, TSV and DTS). Results have been compared to the corresponding solar-adjusted PMV. The performance of the comfort models has been assessed on 12 different configurations of a shoebox open plan office, given by the combination of two window sizes and two window
orientations in three European locations. Results are presented in detailed spatial and temporal maps for a whole year. Two of the three compared dynamic indices (TSENS and TSV) have been found to perform similar to the solaradjusted PMV in detecting comfort issues
Resilience to Occupancy Profiles of Office Buildings Energy Performance and Potential Energy Savings from Smart Controls
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Comparison of Different Glare Indices through Metrics for Long Term and Zonal Visual Comfort Assessment
Full text linkNowadays different indices are used for the assessment of the visual discomfort related to glare, such as Daylight Glare Index, Daylight Glare Probability, and Vertical Eye illuminance. Regardless of their effectiveness in detecting glare perception, all these indices are intended to be local and instantaneous, not summarizing the long term glare perception through the space (Carlucci et al. 2015). In this work, a set of metrics able to express both the time constancy, i.e. availability, and the spatial uniformity, i.e. usability, has been used for detecting discrepancies and inconsistencies between the glare indices when dealing with time and space distribution. Results confirm that different glare indices can lead to different conclusions not only when considering point and instantaneous values but also when analysing availability and usability. Moreover, the availability and usability representations, indirectly confirm themselves effective in providing a global assessment of the confined space analysed, even when visual comfort is concerned
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