Subcooling with AC and adiabatic gas cooling for energy efficiency improvement: field tests and modelling of CO2 booster systems

In the last decade several plant configurations and components have been proposed to increase the efficiency of CO2 refrigeration systems. Among these, subcooling is considered a simple but effective solution, together with the employment of adiabatic cooling systems at the gas cooler. In this work, a fully instrumented CO2 booster plant installed in a supermarket is considered, to compare parallel compression, subcooling and adiabatic cooling. Subcooling is performed taking advantage of chilled water available from the HVAC system. The experimental data are used to validate a model for the comparison on a yearly basis. Parallel compression and subcooling show to be almost equivalent in terms of yearly energy use, while the adiabatic cooling system gives the best performance. Comparisons reveal that the subcooler cooling capacity should be chosen carefully to avoid oversizing, while the influence of the EER for the chiller appears quite small. Subcooling performed at the expense of an HVAC plant shows to be an interesting solution, while a great benefit was experienced with the employment of an adiabatic gas cooler

Effects of different moisture sorption curves on hygrothermal simulations of timber buildings

Building energy simulations are a key tool to design high performance buildings capable of facing the future challenges and to help reaching the emissions reduction targets. Currently, thermal properties of materials used in most building energy simulations are assumed to be constant and not dependent of moisture content and temperature. Heat and moisture dynamic transfer models allow to simulate building envelope performance considering thermal resistance reduction due to moisture effects. These models are generally considered more accurate than the heat transfer models and they could be used to simulate the heat transfer (increased by water vapour storage) and the moisture buffering effect on the indoor environment. For the simulation to be performed, hygrothermal material properties should be known as functions of moisture content. Nevertheless, hygrothermal material properties are rarely available and correlations from the literature have to be used. In this study, the moisture storage curves of CLT, OSB and two types of wood fibre insulation have been measured with a dynamic vapour sorption analyser. The other hygrothermal properties are estimated from values measured in previous studies or taken from the literature. The simulations of two small single room buildings in four Italian locations are performed with the software EnergyPlus, considering an ideal HVAC system, to calculate the heating and cooling needs of the building. The HAMT (heat and moisture transfer) module of EnergyPlus is used. With the results presented in this study, it is possible to evaluate how an approximated curve affects the results of a whole-building simulation in terms of wall average water content, indoor air relative humidity and heating/cooling loads

Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

We show the distribution of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three genomic nomenclature systems to all sequence data from the World Health Organization European Region available until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation, compare the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2

Demand side management through latent thermal storage in HVAC systems coupled with commercial refrigeration units

The electrical energy demand of an HVAC plant can be better managed by using latent thermal energy storage when time-of-use tariffs or peak tariffs are in force, in a view of Demand Side Management of the electrical grid. Nonetheless, air conditioning systems show a marked use of electrical power during the day, and the peak in the cooling load mostly corresponds to the lowest performance of the chiller due to outdoor conditions, thus giving rise to a marked peak in electricity use. An HVAC plant of a supermarket is supplied with an ice thermal energy storage, with the main aim of shaving the peak in electrical power use. The latent thermal storage is charged at night-time by employing the CO2 commercial refrigeration system of the supermarket, which is considerably part-loaded during the shop closing time. During daytime, the thermal storage can be operated in replacement of or in parallel to a reversible heat pump, operating as a water chiller for air conditioning. The same heat pump operates at wintertime for heating purposes, in parallel with heat recovery from the CO2 commercial refrigeration plant. A model of the whole system is presented, and possible solutions are shown for demand side management purposes

Influence of cooling load profile on the prediction of energy use in commercial refrigeration p

The cooling load of a commercial refrigeration system is affected by the operating conditions of the refrigerated display cabinets and cold rooms, mainly through their mutual interactions with the indoor environment in terms of temperature and humidity. In this paper, the effects of cooling load profiles in the prediction of the annual energy use are investigated, comparing constant and simplified load functions to a more realistic simulation-based approach. The latter is made using a calibrated hourly model of the whole commercial refrigeration system, which includes a transcritical CO2 booster system with its control rules and the simulation of the display cabinets and cold rooms. These user-defined components are implemented in the TRNSYS environment and linked to the dynamic building simulation. The analysis is performed for different system configurations and weather conditions. The results show that the load profile affects the comparison in terms of energy effectiveness among different system configurations, and should be considered for a fair assessmen

Multiyear hygrothermal performance simulation of historic building envelopes

The objective of this work is to quantify the effects of the short-term climate change with a multiyear (MY) approach on the results of the heat and moisture transfer simulations of an historic building located in Udine (Italy) and to evaluate if a single year simulation could be representative of the results obtained with the MY. The hygrothermal performance and the moisture related risk are evaluated for a brick wall with and without insulation, with a MY of 25 years and with three single years selected form the MY. The software DELPHIN is used for the simulations and the damage indicators are calculated using simplified methods (number of days with unfavourable conditions). Depending on the damage considered, the years have different effects on the studied wall. The simulations that use the MY weather file allow to obtain more accurate results than using one-year simulations, but the effort and time required for the interpretation of the simulation results could be not acceptable. It is then shown that the choice of a representative weather file is crucial to the results of the risk analysis and that considering more than one weather file is necessary to obtain representative results for different damages mechanisms

Evaluation of Multiyear Weather Data Effects on Hygrothermal Building Energy Simulations Using WUFI Plus

Transient building energy simulations are powerful design tools that are used for the estimation of HVAC demands and internal hygrothermal conditions of buildings. These calculations are commonly performed using a (often dated) typical meteorological year, generated from past weather measurements excluding extreme weather conditions. In this paper the results of multiyear building simulations performed considering coupled Heat and Moisture Transfer (HMT) in building materials are presented. A simple building is simulated in the city of Udine (Italy) using a weather record of 25 years. Performing a multiyear simulation allows to obtain a distribution of results instead of a single number for each variable. The small therm climate change is shown to influence thermal demands and internal conditions with multiyear effects. From this results it is possible to conclude that weather records used as weather files have to be periodically updated and that moisture transfer is relevant in energy and comfort calculations. Moreover, the simulations are performed using the software WUFI Plus and it is shown that using a thermal model for the building envelope could be a non negligible simplification for the comfort related calculations

Guidelines on retrofitting of shopping malls

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