Frank Scholzen

Experimental studies on the development of a solar hybrid module with an aluminum microchannel evaporator

In recent years, the possibility to combine photovoltaics (PV) and solar thermal collectors into one hybrid module (PVT-module) has been increasingly investigated. PVT-modules produce thermal and electrical energy at the same time. As the efficiency of a photovoltaic module decreases with temperature, the temperature of the heat transfer media is often limited to about 30 °C and the PVT-module is combined with a heat pump, which increases the temperature on the “warm side”. This paper deals with a PVT-module, which combines a microchannel based evaporator of a CO2 (R744) heat pump with a PV panel (PVT-direct). The PVT-direct overall system is reduced to the refrigerant circuit due to the direct refrigerant expansion in the PVT-module. A conventional PVT heat pump system has an additional glycol-water circuit. Since a pump and an additional heat exchanger for the secondary cycle were omitted, the system has increased efficiency. Due to lower module temperatures, the increase of the photovoltaic efficiency is a further advantage of the PVT-direct-module. To prove the feasibility of the PVT-direct heat pump system, the Cologne Institute for Renewable Energy (CIRE) is developing and modeling a test facility for this purpose within the research project “PVT-direkt”. Furthermore, a functional PVT-direct-module with a microchannel based evaporator was designed and built. Much importance has been given to experimental studies under laboratory conditions in order to investigate (1) the adjustment of the functionality and layout of the PVT-direct-module for characterizing the joining of brazed joints in aluminum microchannel evaporators and (2) the influence of the backside aluminum plate of the PVT-direct-module regarding leakage currents and parasitic capacitances. The overall results obtained in these experimental studies are analyzed in this paper.

Methodology for Optimally Sizing a Green Electric and Thermal Eco-Village

This paper presents an energy system for a future eco-village, situated in Luxembourg’s city center, whose thermal and electrical energy needs are covered by renewable resources. Specifically, electrical energy is provided by a biogas driven combined heat and power plant, and photovoltaic panels. Lithium-ion accumulators are used for storing the surplus of electrical energy production. Thermal energy needs are mainly covered by a dual source heat pump which draws environmental energy from an ice tank or solar air absorbers. A heat buffer stores heat produced by the combined heat and power plant, a power to heat module and the heat pump. This work focuses on optimally sizing, in terms of power rating, capacity or volume, the energy system components. To this end, a combinatorial simulation-based optimization approach has been developed using MATLAB. The optimal set-up is determined by minimizing the overall cost of the energy system with additional constraints to be respected. Annual needs in thermal and electrical energy, photovoltaic electricity production and the corresponding weather data are based on real data.

Primary energy used in centralized and decentralized ventilation systems measured in field tests in residential buildings

ABSTRACT Ventilation systems can save heat energy by using heat recovery, but use electrical energy to power the fans. In practice, the energy efficiency of those systems can be lower than expected. In this paper, results of field tests with 20 centralised and 60 decentralised ventilation systems for residential buildings and calculations a of the primary energy savings of those devices are presented. Parameters like volume flow unbalances, shortcuts, heat recovery efficiency and specific fan power have been addressed and used as input data to calculate the primary energy balance. Every system showed positive primary energy savings. The mean value for centralised systems was 2.92 Wh/m3 with a high standard deviation of 2.23 Wh/m3, while the decentralised systems showed higher savings of around 4.75 Wh/m3 with a standard deviation of 0.01 to 0.15 Wh/m3. In general, the calculated savings in field tests were significantly lower compared to those calculated from nominal values.