Search

This article provides an overview of short time-scale validation of the duct storage model (Hellström 1989) for the simulation of ground source heat pump performance using experimental data acquired from two operational systems. The error in the temperature change across the ground heat exchanger in the first system was within measurement error, but it was larger than the measurement error in the second sytem due to uncertainty in the thermal properties of the ground. A sensitivity study determined that the thermal conductivity and heat capacity have the greatest impact on the model accuracy. An assessment of the error in the model using ASHRAE handbook (ASHRAE 2007) values for thermal conductivity and heat capacity provided a measure of acceptable error. The difficulties of using real-world operational systems for model validation are discussed. [ABSTRACT FROM AUTHOR]

Abstract: One innovation to ground-source heat pump (GSHP, or “geothermal”) systems is the hybrid GSHP (HyGSHP) system. A HyGSHP system can dramatically decrease the first cost of GSHP systems by using conventional technology (such as a cooling tower or a boiler) to meet a portion of the peak heating or cooling load. We monitored and analyzed three buildings employing HyGSHP systems (two cooling-dominated, one heating-dominated) to demonstrate the performance of the hybrid approach. The buildings were monitored for a year and the measured data was used to validate models of each system. Additionally, we used the models to analyze further improvements to the hybrid approach and established that it has positive impacts, both economically and environmentally. We also documented the lessons learned by those who design and operate the three systems, including discussions of equipment sizing, pump operation, and cooling tower control. Finally, we described the measured data sets and models from this work and have made them freely available for further study of hybrid systems. [Copyright &y& Elsevier]

This article presents an investigation on the impact of year-to-year weather variability on the optimal design of a system for heating and cooling a building using a ground-source heat pump. The designs of a boiler-ground-source heat pump hybrid and a cooling tower-ground-source heat pump hybrid were optimized using a typical meteorological year (TMY2) weather file and also using 15 years of actual weather data. The results indicate that a design based on a TMY2 weather file may be undersized for a severe weather year; this is particularly true if the severe weather year is encountered during the first year of system operation. A cooling tower-ground-source heat pump hybrid model was developed, which includes the use of a backup boiler placed on the building side (rather than the loop side) of the system. It was found that the use of a boiler backup mitigated much of the negative impact of a severe weather year. The boiler supplied the heating during periods of particularly severe weather so that the ground loop length could be maintained at a reasonable value. [ABSTRACT FROM AUTHOR]

Dynamic simulation tools that could accurately simulate operational data for both the fault-free and faulty dynamic operation of heating, ventilation, and air conditioning (HVAC) systems and equipment are needed for developing and evaluating advanced control and automated fault detection and diagnosis strategies. Among various HVAC subsystems, fan coil units (FCUs) are relatively simple, inexpensive devices that are used extensively in commercial, institutional and multifamily residential buildings. However, very little has been reported in the literature to improve FCU design and operation. There has also been a lack of dynamic simulation tool development focusing on FCUs. The work reported in this study aims at developing and validating a software tool to simulate operational data generated from FCUs that are operated dynamically under both faulty and fault-free conditions. A comprehensive and systematic validation process, using data collected from real FCUs in a laboratory building, is used to validate the tool under both faulty and fault-free operating conditions in different seasons. The validated tool not only is able to predict real-world FCU behaviors under different control strategies, but it is also able to predict symptoms associated with various faults, as well as the effects of those faults on system performance and occupant comfort. [ABSTRACT FROM AUTHOR]

Efficiently, robustly and accurately solving large sets of structured, non-linear algebraic and differential equations is one of the most computationally expensive steps in the dynamic simulation of building energy systems. Here, the efficiency, robustness and accuracy of two commonly employed solution methods are compared. The comparison is conducted using the HVACSIM+ software package, a component based building system simulation tool. The HVACSIM+ software presently employs Powell’s Hybrid method to solve systems of nonlinear algebraic equations that model the dynamics of energy states and interactions within buildings. It is shown here that the Powell’s method does not always converge to a solution. Since a myriad of other numerical methods are available, the question arises as to which method is most appropriate for building energy simulation. This paper finds considerable computational benefits result from replacing the Powell’s Hybrid method solver in HVACSIM+ with a solver more appropriate for the challenges particular to numerical simulations of buildings. Evidence is provided that a variant of the Levenberg-Marquardt solver has superior accuracy and robustness compared to the Powell’s Hybrid method presently used in HVACSIM+. [ABSTRACT FROM AUTHOR]

• This paper reviews strategies in commercial buildings for grid service delivery. • Review and technical papers are searched by Sub-keyword Synonym Searching Method. • Primary limitations, gaps, and future trends are identified. The modern power grid faces multiple challenges due to an increase in the adoption of renewable generation, such as dynamically balancing supply and demand at different time scales. Demand side management in buildings plays a vital role in achieving this balance because buildings can provide grid services through a variety of building assets. However, the development of grid-interactive, efficient buildings is still in its infancy, and a systematic and holistic understanding of grid service delivery strategies in terms of energy efficiency, load shifting, load shedding and load modulating is still limited. This paper is a comprehensive review of the development and application of building-level control strategies for utilizing heating, ventilating, and air conditioning systems to provide grid services. These strategies have been investigated through numerical and experimental studies. Control algorithms, such as heuristic rule-based control and model-based control, have been used to enable the automatic control delivery of grid services. The advantages and disadvantages of the strategies are summarized and discussed. Research trends are also identified, which include considering predicted mean vote-based and occupant-based thermal comfort, modeling of occupant behavior, integrating power grid operations with building control, and combining different demand flexibility modes in the control design. [ABSTRACT FROM AUTHOR]