Gregor Henze - Academia.edu (original) (raw)
Papers by Gregor Henze
LEUKOS The Journal of the Illuminating Engineering Society of North America
Two simulation methods were developed to model the lighting energy use for a real office building... more Two simulation methods were developed to model the lighting energy use for a real office building and the results of those simulations were compared to submetered lighting energy data from that building. Three deterministic schedules and six stochastic first-order Markov-models were used to assess annual lighting energy density and peak demand density at both the office-level and the building-level. The stochastic simulations, which apply only to the private offices, resulted in much lower annual energy density and peak demand density predictions due to interactions of users with the lighting and shade controls, and widely different daily use profiles. For the whole-building simulations, comparing all three deterministic schedules resulted in an inverse relationship between peak demand density and annual energy density; the closest correlation with the submetered data was found through the most building-specific but least empirically-vetted schedule-based simulation.
at - Automatisierungstechnik, 2009
Journal of Solar Energy Engineering, 2004
ABSTRACT
Journal of Solar Energy Engineering, 2003
Journal of Solar Energy Engineering, 2007
ABSTRACT
Journal of Solar Energy Engineering, 2003
... 1222. Tamblyn, RT, 1990, Optimizing Storage Savings, Heating/Piping/Air-Conditioning, 62(8... more ... 1222. Tamblyn, RT, 1990, Optimizing Storage Savings, Heating/Piping/Air-Conditioning, 62(8), pp. ... Akbari, H., and Sezgen, O., 1992, Case Studies of Thermal Energy Storage (TES) Systems: Evaluation and Verification of System Performance, LBL-30852, Lawrence Berkeley ...
Journal of Architectural Engineering, 2001
HVAC&R Research, 2003
This paper describes a simulation-based investigation of machine-learning control for the supervi... more This paper describes a simulation-based investigation of machine-learning control for the supervisory control of building energy systems. Model-free reinforcement learning control is investigated for the operation of electrically driven cool thermal energy storage systems in commercial buildings. The reinforcement learning controller learns to charge and discharge a thermal storage tank based on the feedback it receives from past control actions.
Energy and Buildings, 2012
ABSTRACT This research study examines the peak energy reduction potential and avoided cost from u... more ABSTRACT This research study examines the peak energy reduction potential and avoided cost from using an automatic thermostat set point control strategy in a residential home which responds to the price variation in a time-of-use tariff. Twelve benchmark homes, composed of three different home sizes in four different geographical locations, are each evaluated under twelve unique control scenarios with systematically varied peak period length, rate ratio, and set point offset. All time-of-use tariffs are designed to be cost neutral with the existing flat rate tariff assuming the same base case operating scenario. Historical real time prices for 2008 and regional specific construction features were used. The total savings potential as well as the additional benefit from increased set point offsets were found to be highly dependent on the climate. For a particular location, savings on a percentage basis were very consistent across home sizes for similar control strategies, meaning the same tariff may be applied to all residential customers without disadvantaging customers in smaller homes. Finally, the utility cost savings varied from 225to225 to 225to9 per home with many time-of-use tariffs resulting in more money given to the homeowner than actually saved by the utility.
Energy and Buildings, 2008
A group of buildings in the pharmaceutical industry located in Southern Germany is experiencing a... more A group of buildings in the pharmaceutical industry located in Southern Germany is experiencing a trend of growing cooling loads to be met by the chilled water plant composed of 10 chillers of greatly varying cost effectiveness. With a capacity shortfall inevitable, the question arises whether to install an additional chiller or improve the utilization of the existing chillers, in particular those with low operating costs per unit cooling, through the addition of a chilled water thermal energy storage (TES) system. To provide decision support in this matter, an optimization environment was developed and validated that adopts mixed integer programming as the approach to optimizing the chiller dispatch for any load condition, while an overarching dynamic programming based optimization approach optimizes the charge/discharge strategy of the TES system. In this fashion, the chilled water plant optimization is decoupled but embedded in the TES control optimization. The approach was selected to allow for arbitrary constraints and optimization horizons, while ensuring a global optimum to the problem.Optimization scenarios have been defined that include current load conditions as well cooling loads that are elevated by 25% from current conditions in order to reflect the expected growth in cooling demand in the near future; both scenarios analyzed the impact of storage capacity by investigating several TES tank capacities. The annual optimization runs revealed that – based on the elevated cooling load scenario – the smallest TES system pays back the incremental investment necessary for the TES system in about three years; based on today’s cooling loads the static payback is approximately six years. As the efficiency and cost of operating the existing chillers vary over a wide range, the TES system allows for a reduction in operating costs for the chilled water plant by avoiding the operation of inefficient chillers (such as the single-stage absorption type) and shifting the demand to more efficient ones (such as the electrically driven centrifugal chillers).The adoption of a TES system will not only provide economic benefits as measured in operating cost savings, but also operational merits such as the avoidance of numerous safety measures necessary for a cooling plant without storage (e.g., always operating at least two chillers), and a cost effective addition of supplemental cooling capacity. Moreover, the overall system reliability and availability will be significantly improved through the addition of a thermal energy storage system.Future work will address the development of near-optimal heuristics suitable for implementation in the actual pharmaceutical industry buildings.
Energy and Buildings, 2003
This study investigates whether thermal storage systems can be controlled effectively in situatio... more This study investigates whether thermal storage systems can be controlled effectively in situations where cooling loads, non-cooling electrical loads, weather information, as well as the cost of electricity are uncertain and have to be predicted. The analysis shows that the reduction in achievable utility cost-savings is small when relying on real-time pricing (RTP) electricity rates that are made available by the utility only 1 h ahead instead of an entire day-ahead. Real-time pricing rate data from two utilities, one in the South and one on the West Coast of the United States, were used in both a day-ahead (24 h rate certainty) and an hour-ahead (1 h rate certainty) fashion. Using measured data for a hotel and an office building in the United States, predictive optimal control strategies delivered greatly superior utility cost-saving performance compared to conventional partial-storage thermal energy storage strategies, even with inaccurate forecasts. The more accurate the prediction becomes, the greater will be the cost-saving performance of cool storage systems under predictive optimal control, and the smaller will be the impact associated with uncertain RTP rates in the hour-ahead RTP tariff case. Consequently, uncertain electrical utility rates do not imperil the superior cost-saving benefits of cool storage when governed by predictive optimal control. #
Energy and Buildings, 2010
This paper studies the natural wind environments in two locations of hot climate regions at Egypt... more This paper studies the natural wind environments in two locations of hot climate regions at Egypt. Aswan and Farafra in south and west Egypt were selected. Two proposed models are simulated by computational fluid dynamics (CFD) in two cases of wind velocities. The two models have different both of dimensions at passages and cavities between buildings and shapes of windward sides of buildings. The wide distances between passages of buildings at the same row and rectangular shapes that have slope exterior wall in two directions at the windward sides are devoted to Aswan. The narrow distances between passages of buildings at the same row and rectangular shapes that have trapezoid courtyards that face wind are devoted to Farafra. The results show that the Aswan model can achieve at the inlet surfaces (windward side of buildings) 1.8-2.4 m/s (60-80% of wind velocity) especially at the second and third rows of indoor air velocity which is the required indoor air velocity for comfort. The Farafra model which uses a courtyard can achieve at the inlet surface 1-1.2 m/s (33-41% of wind velocity) which is less than the required indoor air velocity for comfort. The results can achieve the high rate of wind velocity 38-70% and between two and three times comparing favorably with previous studies that report only 20% of wind velocity at the second row and 15% of wind velocity at the third row.
Journal of Building Performance Simulation, 2012
There are many factors that drive the energy consumption and demand in high-rise commercial offic... more There are many factors that drive the energy consumption and demand in high-rise commercial office buildings. Understanding the effects of individual building parameters and two-factor interactions can be very useful for directing building audits and developing energy simulation models. A fractional factorial analysis was conducted to evaluate a large number of building parameters in an effort to quantify their effect
An optimization module is developed and incorporated within EnergyPlus. As an application of the ... more An optimization module is developed and incorporated within EnergyPlus. As an application of the optimization module, improved controls are determined for building passive thermal energy storage inventory. The paper describes the implementation of the optimization module within EnergyPlus. Moreover, the paper presents results of a comparative analysis to assess the performance of various optimization algorithms evaluated as part of the implementation of the internal optimization module within EnergyPlus. Parametric analyses are carried out to evaluate the effectiveness of the optimization module integrated with EnergyPlus in harnessing the building thermal mass to reduce either energy use or peak-demand associated with cooling a prototypical office building under various operating conditions. Selected results of the parametric analyses are presented in this paper. In particular, the performance of the internal optimization module is compared against that of GenOpt, an external optimization system. The study reveals that the Nelder-Mead simplex method provides an appropriate compromise between computational efficiency, robustness, and accuracy of the optimal solution.
A module for ice-based thermal energy storage (TES) systems has been developed and integrated wit... more A module for ice-based thermal energy storage (TES) systems has been developed and integrated within EnergyPlus. The TES module uses BLAST models for two direct ice systems (ice-on-coil external melt and ice harvester) and one indirect ice systems (iceon-coil internal melt). The TES systems are integrated as part of the EnergyPlus cooling plant components and are able to operate for any charge/discharge rates provided as input data. In this paper, the structure of the TES module as implemented in the EnergyPlus is described. In addition, typical input-output variables from the added TES module are illustrated. Moreover, the operation of the TES systems is discussed for various conventional control strategies.
Journal of Solar Energy Engineering
ABSTRACT
LEUKOS The Journal of the Illuminating Engineering Society of North America
Two simulation methods were developed to model the lighting energy use for a real office building... more Two simulation methods were developed to model the lighting energy use for a real office building and the results of those simulations were compared to submetered lighting energy data from that building. Three deterministic schedules and six stochastic first-order Markov-models were used to assess annual lighting energy density and peak demand density at both the office-level and the building-level. The stochastic simulations, which apply only to the private offices, resulted in much lower annual energy density and peak demand density predictions due to interactions of users with the lighting and shade controls, and widely different daily use profiles. For the whole-building simulations, comparing all three deterministic schedules resulted in an inverse relationship between peak demand density and annual energy density; the closest correlation with the submetered data was found through the most building-specific but least empirically-vetted schedule-based simulation.
at - Automatisierungstechnik, 2009
Journal of Solar Energy Engineering, 2004
ABSTRACT
Journal of Solar Energy Engineering, 2003
Journal of Solar Energy Engineering, 2007
ABSTRACT
Journal of Solar Energy Engineering, 2003
... 1222. Tamblyn, RT, 1990, Optimizing Storage Savings, Heating/Piping/Air-Conditioning, 62(8... more ... 1222. Tamblyn, RT, 1990, Optimizing Storage Savings, Heating/Piping/Air-Conditioning, 62(8), pp. ... Akbari, H., and Sezgen, O., 1992, Case Studies of Thermal Energy Storage (TES) Systems: Evaluation and Verification of System Performance, LBL-30852, Lawrence Berkeley ...
Journal of Architectural Engineering, 2001
HVAC&R Research, 2003
This paper describes a simulation-based investigation of machine-learning control for the supervi... more This paper describes a simulation-based investigation of machine-learning control for the supervisory control of building energy systems. Model-free reinforcement learning control is investigated for the operation of electrically driven cool thermal energy storage systems in commercial buildings. The reinforcement learning controller learns to charge and discharge a thermal storage tank based on the feedback it receives from past control actions.
Energy and Buildings, 2012
ABSTRACT This research study examines the peak energy reduction potential and avoided cost from u... more ABSTRACT This research study examines the peak energy reduction potential and avoided cost from using an automatic thermostat set point control strategy in a residential home which responds to the price variation in a time-of-use tariff. Twelve benchmark homes, composed of three different home sizes in four different geographical locations, are each evaluated under twelve unique control scenarios with systematically varied peak period length, rate ratio, and set point offset. All time-of-use tariffs are designed to be cost neutral with the existing flat rate tariff assuming the same base case operating scenario. Historical real time prices for 2008 and regional specific construction features were used. The total savings potential as well as the additional benefit from increased set point offsets were found to be highly dependent on the climate. For a particular location, savings on a percentage basis were very consistent across home sizes for similar control strategies, meaning the same tariff may be applied to all residential customers without disadvantaging customers in smaller homes. Finally, the utility cost savings varied from 225to225 to 225to9 per home with many time-of-use tariffs resulting in more money given to the homeowner than actually saved by the utility.
Energy and Buildings, 2008
A group of buildings in the pharmaceutical industry located in Southern Germany is experiencing a... more A group of buildings in the pharmaceutical industry located in Southern Germany is experiencing a trend of growing cooling loads to be met by the chilled water plant composed of 10 chillers of greatly varying cost effectiveness. With a capacity shortfall inevitable, the question arises whether to install an additional chiller or improve the utilization of the existing chillers, in particular those with low operating costs per unit cooling, through the addition of a chilled water thermal energy storage (TES) system. To provide decision support in this matter, an optimization environment was developed and validated that adopts mixed integer programming as the approach to optimizing the chiller dispatch for any load condition, while an overarching dynamic programming based optimization approach optimizes the charge/discharge strategy of the TES system. In this fashion, the chilled water plant optimization is decoupled but embedded in the TES control optimization. The approach was selected to allow for arbitrary constraints and optimization horizons, while ensuring a global optimum to the problem.Optimization scenarios have been defined that include current load conditions as well cooling loads that are elevated by 25% from current conditions in order to reflect the expected growth in cooling demand in the near future; both scenarios analyzed the impact of storage capacity by investigating several TES tank capacities. The annual optimization runs revealed that – based on the elevated cooling load scenario – the smallest TES system pays back the incremental investment necessary for the TES system in about three years; based on today’s cooling loads the static payback is approximately six years. As the efficiency and cost of operating the existing chillers vary over a wide range, the TES system allows for a reduction in operating costs for the chilled water plant by avoiding the operation of inefficient chillers (such as the single-stage absorption type) and shifting the demand to more efficient ones (such as the electrically driven centrifugal chillers).The adoption of a TES system will not only provide economic benefits as measured in operating cost savings, but also operational merits such as the avoidance of numerous safety measures necessary for a cooling plant without storage (e.g., always operating at least two chillers), and a cost effective addition of supplemental cooling capacity. Moreover, the overall system reliability and availability will be significantly improved through the addition of a thermal energy storage system.Future work will address the development of near-optimal heuristics suitable for implementation in the actual pharmaceutical industry buildings.
Energy and Buildings, 2003
This study investigates whether thermal storage systems can be controlled effectively in situatio... more This study investigates whether thermal storage systems can be controlled effectively in situations where cooling loads, non-cooling electrical loads, weather information, as well as the cost of electricity are uncertain and have to be predicted. The analysis shows that the reduction in achievable utility cost-savings is small when relying on real-time pricing (RTP) electricity rates that are made available by the utility only 1 h ahead instead of an entire day-ahead. Real-time pricing rate data from two utilities, one in the South and one on the West Coast of the United States, were used in both a day-ahead (24 h rate certainty) and an hour-ahead (1 h rate certainty) fashion. Using measured data for a hotel and an office building in the United States, predictive optimal control strategies delivered greatly superior utility cost-saving performance compared to conventional partial-storage thermal energy storage strategies, even with inaccurate forecasts. The more accurate the prediction becomes, the greater will be the cost-saving performance of cool storage systems under predictive optimal control, and the smaller will be the impact associated with uncertain RTP rates in the hour-ahead RTP tariff case. Consequently, uncertain electrical utility rates do not imperil the superior cost-saving benefits of cool storage when governed by predictive optimal control. #
Energy and Buildings, 2010
This paper studies the natural wind environments in two locations of hot climate regions at Egypt... more This paper studies the natural wind environments in two locations of hot climate regions at Egypt. Aswan and Farafra in south and west Egypt were selected. Two proposed models are simulated by computational fluid dynamics (CFD) in two cases of wind velocities. The two models have different both of dimensions at passages and cavities between buildings and shapes of windward sides of buildings. The wide distances between passages of buildings at the same row and rectangular shapes that have slope exterior wall in two directions at the windward sides are devoted to Aswan. The narrow distances between passages of buildings at the same row and rectangular shapes that have trapezoid courtyards that face wind are devoted to Farafra. The results show that the Aswan model can achieve at the inlet surfaces (windward side of buildings) 1.8-2.4 m/s (60-80% of wind velocity) especially at the second and third rows of indoor air velocity which is the required indoor air velocity for comfort. The Farafra model which uses a courtyard can achieve at the inlet surface 1-1.2 m/s (33-41% of wind velocity) which is less than the required indoor air velocity for comfort. The results can achieve the high rate of wind velocity 38-70% and between two and three times comparing favorably with previous studies that report only 20% of wind velocity at the second row and 15% of wind velocity at the third row.
Journal of Building Performance Simulation, 2012
There are many factors that drive the energy consumption and demand in high-rise commercial offic... more There are many factors that drive the energy consumption and demand in high-rise commercial office buildings. Understanding the effects of individual building parameters and two-factor interactions can be very useful for directing building audits and developing energy simulation models. A fractional factorial analysis was conducted to evaluate a large number of building parameters in an effort to quantify their effect
An optimization module is developed and incorporated within EnergyPlus. As an application of the ... more An optimization module is developed and incorporated within EnergyPlus. As an application of the optimization module, improved controls are determined for building passive thermal energy storage inventory. The paper describes the implementation of the optimization module within EnergyPlus. Moreover, the paper presents results of a comparative analysis to assess the performance of various optimization algorithms evaluated as part of the implementation of the internal optimization module within EnergyPlus. Parametric analyses are carried out to evaluate the effectiveness of the optimization module integrated with EnergyPlus in harnessing the building thermal mass to reduce either energy use or peak-demand associated with cooling a prototypical office building under various operating conditions. Selected results of the parametric analyses are presented in this paper. In particular, the performance of the internal optimization module is compared against that of GenOpt, an external optimization system. The study reveals that the Nelder-Mead simplex method provides an appropriate compromise between computational efficiency, robustness, and accuracy of the optimal solution.
A module for ice-based thermal energy storage (TES) systems has been developed and integrated wit... more A module for ice-based thermal energy storage (TES) systems has been developed and integrated within EnergyPlus. The TES module uses BLAST models for two direct ice systems (ice-on-coil external melt and ice harvester) and one indirect ice systems (iceon-coil internal melt). The TES systems are integrated as part of the EnergyPlus cooling plant components and are able to operate for any charge/discharge rates provided as input data. In this paper, the structure of the TES module as implemented in the EnergyPlus is described. In addition, typical input-output variables from the added TES module are illustrated. Moreover, the operation of the TES systems is discussed for various conventional control strategies.
Journal of Solar Energy Engineering
ABSTRACT