Load modulation strategies of residential heat pumps for demand-response programs with different thermal storage options

This research work presents a methodology to assess the potential of load modulation strategies of HVAC systems for demand response programs at different scales. Two different demand response programs are considered: feed-in tariff signals for renewable production load matching and signals from the distribution grid operator for operational planning and congestion management at the distribution level. The resulting control problems are solved using optimal control formulations. First, the strategies are applied to four typical Belgian houses to match on-site PV production. Different thermal storage options are considered: on the one hand, thermal storage in the building envelope and in water tanks for domestic hot water, and, on the other hand, additional water tanks for space heating needs either in a parallel four-pipe or in a parallel two-pipe configuration. According to the type of house and the modulation strategy considered, a ranking of the most suitable storage option is proposed. Secondly, the method is extended to the scale of a distribution feeder with 50% PV penetration rate. Results show that with 20% heat pump penetration with suitable storage options, residual load reduction reach 28 to 73.4% with ADR#1 and 43.7 to 51.4% with ADR#2. ADR#1 outperforms ADR#2 for short modulation intervals, but can lead to up to 70% additional overconsumption if the chosen thermal storage option is not adapted to the house insulation level

Technological and Economical Survey of Organic Rankine Cycle Systems

peer reviewedThis paper presents an overview of current R&D in the field of small and middle scale Organic Rankine Cycles (ORC’s). Major ORC’s applications are described and their technical and economical maturity is analyzed. The paper also emphasizes the selection criteria for the expander and for the working fluid

Comparison of moving boundary and finite-volume heat exchangers models in the Modelica language

When modelling low capacity energy systems such as a small (5–150 kWel) organic Rankine cycle unit, the governing dynamics are mainly concentrated in the heat exchangers. As a consequence, accuracy and simulation speed of the higher level system model mainly depend on the heat exchanger model formulation. In particular, the modelling of thermodynamic systems characterized by evaporation or condensation, requires heat exchanger models capable of handling phase transitions. To this aim, the finite volume (FV) and the moving boundary (MB) approaches are the most widely used. The two models are developed and included in the open-source ThermoCycle Modelica library. In this contribution a comparison between the two approaches is performed. Their performance is tested in terms of model integrity and accuracy during transient conditions. Furthermore the models are used to simulate the evaporator of an ORC system and their responses are validated against experimental data collected on an 11 kWel ORC power unit

Importance of the reconciliation method to handle experimental data in refrigeration and power cycle: application to a reversible heat pump/organic Rankine cycle unit integrated in a positive energy building

Experimental data is often the result of long and costly experimentations. Many times, measurements are used directly without (or with few) analysis and treatment. This paper therefore presents a detailed methodology to use steady-state measurements efficiently in the analysis of a thermodynamic cycle. The reconciliation method allows to correct each measurement as little as possible, taking its accuracy into account, in order to satisfy all constraints and to evaluate the most probable physical state. The reconciliation method should be used for multiple reasons. First, this method allows to close energy and mass balances exactly, which is needed for predictive models. Also, it allows determining some unknowns that are not or that cannot be measured precisely. Furthermore, it fully exploits the collected measurements with redundancy and it allows to know which sensor should be checked or replaced if necessary. An application of this method is presented in the case of a reversible HP/ORC unit. This unit is a modified heat pump which is able to work as an organic Rankine cycle by reversing its cycle. Combined with a passive house comprising a solar roof and a ground heat exchanger, it allows to get a plus energy house. In this study case, the oil mass fraction is not measured despite of its strong influence on the results. The reconciliation method allows to evaluate it. The efficiency of this method is proven by comparing the error on the outputs of steady-state models of compressor and exchangers. An example is given with the prediction of the pinch-point of an evaporator. In this case, the normalized root mean square deviation (NRMSD) is decreased from 14.3 % to 4.1 % when using the reconciliation method. This paper proves the efficiency of the method and also that the method should be considered more often when dealing with experimentation