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Parisch P.,Institute fur Solarenergieforschung Hameln GmbH ISFH | Mercker O.,Institute fur Solarenergieforschung Hameln GmbH ISFH | Oberdorfer P.,University of Gottingen | Bertram E.,Institute fur Solarenergieforschung Hameln GmbH ISFH | And 2 more authors.
Renewable Energy | Year: 2015

The short-term behavior of borehole heat exchangers (BHE) is investigated using three 2h test sequences each with constant inlet temperature and constant mass flow rate. Three models of the transient systems simulation program (TRNSYS) have been compared to these measurements. In order to assess the deviations a 3D-FEM model, built in COMSOL Multiphysics®, is compared to the measurement as well.The "Erdwärmesonden" model (EWS) shows a very good accuracy with a deviation less than 10%. The superposition borehole model (SBM) and duct ground heat storage model (DST) neglect the internal borehole heat capacity of fluid and grout. In order to improve their short-term behavior, the models are modified with an adiabatic pipe model with wall capacity in front of the BHE model. Different parameter sets for the pre-pipe are investigated. The optimum parameter set reduces the error between simulation and measurement of the injected heat from 50% to about 5%. With this model modification, all investigated models SBM, DST, and EWS perform as accurate as the COMSOL model. © 2014 Elsevier Ltd. Source


Parisch P.,Institute fur Solarenergieforschung Hameln GmbH ISFH | Mercker O.,Institute fur Solarenergieforschung Hameln GmbH ISFH | Warmuth J.,Institute fur Solarenergieforschung Hameln GmbH ISFH | Tepe R.,Institute fur Solarenergieforschung Hameln GmbH ISFH | And 2 more authors.
Applied Thermal Engineering | Year: 2014

The operation of ground-coupled heat pumps in combination with solar collectors requires comprising knowledge of the heat pump behavior under non-standard conditions. Especially higher temperatures and varying flow rates in comparison to non-solar systems have to be taken into account. Furthermore the dynamic behavior becomes more important. At ISFH, steady-state and dynamic tests of a typical brine/water heat pump have been carried out in order to analyze its behavior under varying operation conditions. It has been shown, that rising source temperatures do only significantly increase the coefficient of performance (COP), if the source temperature is below 10-20 C, depending on the temperature lift between source and sink. The flow rate, which has been varied both on the source and the sink side, only showed a minor influence on the exergetic efficiency. Additionally a heat pump model for TRNSYS has been validated under non-standard conditions. The results are assessed by means of TRNSYS simulations. © 2013 Elsevier Ltd. All rights reserved. Source

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