Adsorption cooler design, modeling, and dynamics and performance analyses

This paper presents an adsorption cooler (AC) driven by the surplus heat of a solar thermal domestic hot water system to provide cooling to residential buildings. A cylindrical tube adsorber using granular silica gel as adsorbent and water as adsorbate is considered. The AC is modelled using a two-dimensional distributed parameter model that was implemented in previous adsorption heating and cooling studies. The performance coefficients of the resultant thermally driven colling system are obtained for a broad range of working conditions. The thermally driven AC has a coefficient of performance (COP) of 0.5 and a specific cooling power (SCP) of 44 W.kg--1, considering condenser, evaporator, and regeneration temperatures of 15 oC, 18 oC, and 70 oC, respectively. Moreover, results show that the AC can be used for refrigeration purposes at temperatures as low as 2 oC, and that it can also operate during hotter days under temperatures of 42 oC.This work was supported by the grant SFRH/BD/145124/2019 and the projects UIDB/00481/2020 and UIDP/00481/2020 - FCT - Fundação para a Ciência e a Tecnologia; and CENTRO-01-0145-FEDER-022083 - Centro Portugal Regional Operational Programme (Centro2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund. The present study was developed in the scope of the Smart Green Homes Project [POCI-01- 0247-FEDER- 007678], a co-promotion between Bosch Termotecnologia S.A. and the University of Aveiro. It is financed by Portugal 2020 under the Competitiveness and Internationalization Operational Program, and by the European Regional Development Fund

The role of the compressor isentropic efficiency on non-intrusive refrigerant side characterization of transcritical CO2 heat pump water heaters

Characterizing the refrigerant side of heat pump water heaters (HPWHs) can be intrusive and expensive. On the other hand, direct external measurement techniques can be unfeasible, particularly in commercial HPWHs for residential applications. Non-intrusive in-situ characterization methods have already been successfully implemented in subcritical heat pumps, providing the refrigerant mass flowrate and the equipment energy performance, by using contact temperature sensors and electric power meters. Subcritical suction and discharge specific enthalpies necessary to apply the method can be obtained from the measured temperatures and their corresponding saturation pressures. Nevertheless, this approach does not apply to the transcritical CO2 HPWHs. In the supercritical region, temperature and pressure are independent variables, and an iterative process regarding the compressor isentropic efficiency has to be considered. However, when isentropic efficiency data is not available, an additional procedure is required, using a validated gas cooler model to verify the physical reliability of the numerical solutions.The present study was developed in the scope of the Smart Green Homes Project [POCI-01- 0247-FEDER- 007678], a co-promotion between Bosch Termotecnologia S.A. and the University of Aveiro. It is financed by Portugal 2020 under the Competitiveness and Internationalization OP, and by the European Regional Development Fund (ERDF). This work was funded by the grant SFRH/BD/148378/2019 and the projects UIDB/00481/2020 and UIDP/00481/2020 – FCT-Fundação para a Ciência e Tecnologia; and CENTRO-01- 0145-FEDER-022083 – Centro2020, under the PORTUGAL 2020 Partnership Agreement, through the ERDF

Simulation models for tankless gas water heaters

There is a growing concern about to the scarceness of natural resources and the emissions problematic. Water heating is a relevant part of a household’s energy use, and tankless gas water heaters (TGWH) are widely used. There are design and engineering challenges to develop more efficient devices, with lower emissions of pollutant gases and providing comfort improvements from the user point of view. The main objective of the present work is to provide mathematical models to evaluate and support the development of different TGWH configurations. By simulation, different hardware configurations and advanced control strategies can be tested and optimized regarding energy saving, reducing of harmful environmental emissions and increase of comfort indices by reducing temperature undershoots and overshoots. The TGWH individual components are modelled, laboratory tests are performed and the heat cell is parametrized with experimental data. Configurations with and without bypass function are performed for several water flow rates and setpoint temperature patterns in open loop and with feed-forward control.publishe