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Abstract For 118 million residential housing units in the U.S., there is currently a gap between the potential energy savings that can be achieved through the use of existing energy efficiency technologies, and the actual level of energy savings realized, particularly for the 37% of housing units that are considered residential rental properties. Additional quantifiable benefits are needed beyond energy savings to help further motivate residential property owners to invest in energy efficiency upgrades. This research focuses on assessing the adoption of energy efficient upgrades in U.S. residential housing and the impact on rental prices. Ten U.S. cities are chosen for analysis; these cities vary in size across multiple climate zones, and represent a diverse set of housing market conditions. Data was collected for over 159,000 rental property listings, their characteristics, and their energy efficiency measures listed in rental housing postings across each city. Following an extensive data quality control process, over thirty different types energy efficient features were identified. The level of adoption was determined for each city, ranging from 5.3% to 21.6%. Efficient lighting and appliances were among the most common, with many features doubling as energy efficient and other desirable aesthetic or comfort improvements. Then using propensity score matching and conditional mean comparison methods, the relative impact on rent charged in each city was calculated, which ranged from a 6% to 14.1% increase in rent for properties with energy efficient features, demonstrating a positive economic impact of these features, particularly for property owners. This was further subdivided into five types of energy efficiency upgrade and three housing types. Single family homes generally demanded higher premiums with energy efficient features, however there was not a consistent pattern across the types of efficient upgrades. The results of this work demonstrate that investment in energy efficient technologies has quantifiable benefits for rental property owners in the U.S. beyond just energy savings. This methodology and results can also be used in other cities and by property owners, utility companies, or others, ultimately encouraging further investment and positive economic impact in residential energy efficiency and in turn improving energy and resource conservation in the building sector.

Abstract This paper discusses the minimization of the fuel consumption of a gasoline engine through dynamic optimization. The minimization uses a mean value model of the powertrain and vehicle. This model has two state variables: the pressure in the engine intake manifold and the engine speed. The control input is the throttle valve angle. The model is identified on a universal engine dynamometer. Optimal state and control trajectories are calculated using Bock’s direct multiple shooting method, implemented in the software MUSCOD-II. The developed approach is illustrated both in simulation and experimentally for a generic test case where a vehicle accelerates from 1100 rpm to 3700 rpm in 30 s . The optimized trajectories yield minimal fuel consumption. The experiments show that a linear engine speed trajectory yields an extra fuel consumption of 13 % when compared to the optimal trajectory. It is shown that, with a simple model, a significant amount of fuel can be saved without loss of the fun-to-drive.

Abstract A high-temperature PEFC system, developed with the aim of delivering 5 kW electrical power from the chemical energy stored in diesel and kerosene fuels for application as an auxiliary power unit, was simulated and tested. The key components of the system were an autothermal reformer, a water–gas shift reactor, a catalytic burner, and the HT-PEFC stack. The targeted power level of 5 kW was achieved using different fuels, namely GTL kerosene, BTL diesel and premium diesel. Using an integrated system approach, operation without external heat input was demonstrated. The overall analysis showed slight but non-continuous performance loss for 250 h operation time.

Applied energy 388, 125530 (2025). doi:10.1016/j.apenergy.2025.125530 Published by Elsevier Science, Amsterdam [u.a.]

Small scale (solar-) thermally driven cooling systems suffer from two important drawbacks: firstly, the systems usually offer no means of adapting the chilling capacity to the actual load; secondly constantly running pumps and fans lead to high auxiliary electricity consumption even when the available driving and cooling water temperatures only allow a reduced chilling capacity. To solve these problems a generic approach for controlling the main parasitic electrical devices – the cooling water pump and the heat rejection fan - as a function of the actual boundary conditions was developed. Different variants of control strategies are analyzed in different system configurations under a variety of climates and load conditions by means of dynamic system simulations in TRNSYS. The most typical combinations of ab- and adsorption chillers with dry cooler and wet cooling tower are covered. The results show that capacity modulation can be realized well by this approach. Additionally electricity savings of up to 25% can be achieved for reasonably sized systems compared to a reference control strategy with fixed pump speed and fixed cooling water set temperature. Yet it becomes obvious that the concrete savings depend strongly on the system configuration and boundary conditions.

Abstract An enhanced TRNSYS simulation model, NEM, of the behaviour of a domestic hot-water (DHW) store, with an immersed heat-exchanger (HX), has been developed and validated. This model simulates the dynamic heat-depletion and recovery processes in the immersed HX and predicts the transient temperature-patterns for various DHW draw-off versus time profiles. Realistic daily profiles (RDPs), based on field studies, were developed to provide representative draw-off patterns for the testing of thermal stores and simulation studies. The effects of these RDPs and five other existing profiles on the store’s performance are analysed using the enhanced model. The simulation results indicate the importance of the HX’s recovery, as well as the number, type and time of occurrence of the draw-offs in the profile, on the thermal store’s performance. It is concluded that RDP profiles should be used in the performance testing of thermal stores to obtain results that reflect conditions experienced in the field.

Abstract A resilient strategy for optimal demand response control based on the management of highly-distributed electric loads is presented to meet transmission-level control aimed at maintaining voltage stability. The proposed load control scheme balances device- and grid-level objectives simultaneously, and is demonstrated for a system comprising a distributed responsive population of 14,000 residential-sized buildings integrated in a transmission system network consisting of six buses. Air-source heat pumps are implemented as the primary heating source in the responsive building population, and are introduced as a dispatchable grid-side energy resource, where aggregated output can be objectively ramped up or down through the use of an optimal centralized control strategy. A two step multi-objective optimization procedure is implemented to simultaneously satisfy balancing of the power system and customer objectives across a multi-scalar system. At the power system-level, the optimal preventive control scheme is obtained based on steady-state voltage stability constraints. At the customer-level, an optimal demand response strategy is proposed, wherein the aggregate power demand from a population of heat pumps is controlled to follow load-shedding requirements. The customer comfort is continuously maintained by constrained regulation of the thermal set-point governing operation of the heat pump device. The proposed demand-side strategy achieves similar goals to conventional approaches to regulation and spinning reserve ancillary services, but with the significant benefit of higher efficiencies. Under the proposed scheme, ancillary services provided by the electric loads effectively become virtual generators that enhance the voltage stability in power systems operating under increased uncertainty, and replace severe or multiple contingency reserves typically supplied by conventional generators. The proposed demand response control scheme can be extended to other potentially responsive end-use appliances, and opens avenues for increased exploitation of intermittent renewable energy resources while reducing operating costs and emissions.

Abstract Attention is devoted to the application of cylindrical-parabolic solar concentrators in the intermediate temperature range for which wide receivers are used. Suitable indices that describe the performance of the concentrator are defined and evaluated. The effect of each individual parameter on total concentrator performance is investigated. The results of the analysis are presented as a set of graphs which can be used easily when designing parabolic concentrators.

Abstract Fuel cell vehicles and carsharing depict two potential solutions with regard to pollution and noise from traffic in cities. They are most effective when combined, and hydrogen is produced via electrolysis using renewables. One major hurdle in utilizing fuel cell vehicles is to size hydrogen refueling stations (HRS) and hydrogen production via electrolysis properly in order to fulfill the carsharing vehicles’ demand at any given time. This paper presents data on refueling behavior in free-floating carsharing, which have not been available thus far. Refueling profiles of hydrogen carsharing vehicles are modeled based on this data. Furthermore, this analysis presents and applies a methodology for optimizing topology of a wind turbine-connected HRS with onsite electrolysis via an evolutionary algorithm. This optimization is conducted for different carsharing fleet sizes, and HRS profitability is evaluated. The results show that larger fleets are capable of decreasing hydrogen production costs significantly. Moreover, adding capacity to the HRS in order to prepare for hydrogen demand from private vehicles in the future does not significantly increase costs. However, overall costs are still high compared to the current market price in Germany, requiring further cost reductions.