Cynthia A. Cruickshank

Solar-Assisted Heat Pump Systems: A Review of Existing Studies and Their Applicability to the Canadian Residential Sector

Heat pumps are commonly used for space-heating and cooling requirements. The combination of solar thermal and heat pump systems as a single solar-assisted heat pump (SAHP) system is a promising technology for offsetting domestic hot water, space-heating and cooling loads more efficiently. Task 44 of the Solar Heating and Cooling Programme of the International Energy Agency is currently investigating ways to optimize SAHP systems for residential use. This paper presents a review of past and current work conducted on SAHP systems. Specifically, the key performance data from many studies are highlighted and different system configurations are compared in order to establish insight towards which system configurations are suitable for the Canadian residential sector. It was found that the most suitable configuration for Canadian residential buildings depend on a combination of factors which may include occupant behavior, building characteristics, operation parameters, system components, the performance criteria of interest and climate. A large variety of configurations and parameters exist for SAHP systems and this made analyzing a specific system, comparing differing systems and establishing an optimal design fairly difficult. It was found that different authors used various different performance criterions and this inconsistency also added to the difficulty of comparing the studies of different systems. Overall, a standard performance criterion needs to be established for SAHP systems in order to meaningfully compare different configurations and determine optimal configurations for certain requirements. Copyright

Characterization of a Thermosyphon Heat Exchanger for Solar Domestic Hot Water Systems

This paper presents a simplified test method that was developed to allow preconfigured solar domestic hot water systems that use natural convection/thermosyphon heat exchangers to be characterized. The results of this test method produce performance coefficients for simple empirical expressions that describe the fluid flow and heat transfer in the heat-exchange loop. These empirically derived coefficients can be used as an input to a general simulation routine that allows overall system performance to be determined for various loads and climatic conditions. To illustrate the test procedure, results are presented for a typical heat exchanger under a range of operational conditions.

Non-Isothermal Hydrodynamic Modelling of the Flowing Electrolyte Channel in a Flowing Electrolyte-Direct Methanol Fuel Cell

The performance of a direct methanol fuel cell (DMFC) can be significantly reduced by methanol crossover. One method to reduce methanol crossover is to utilize a flowing electrolyte channel. This is known as a flowing electrolyte-direct methanol fuel cell (FE-DMFC).In this study, recommendations for the improvement of the flowing electrolyte channel design and operating conditions are made using previous modelling studies on the fluid dynamics in the porous domain of the flowing electrolyte channel, and on the performance of a 1D isothermal FE-DMFC incorporating multiphase flow, in addition to modelling of the non-isothermal effects on the fluid dynamics of the FE-DMFC flowing electrolyte channel.The results of this study indicate that temperature difference between flowing electrolyte inflow and the fuel cell have negligible hydrodynamic implications, except that higher fuel cell temperatures reduce pressure drop. Reducing porosity and increasing permeability is recommended, with a porosity of around 0.4 and a porous material microstructure typical dimension around 60–70 μm being potentially suitable values for achieving these goals.Copyright

Model-based predictive control of office window shades

In the automation of interior window shading devices, a control system that relies on a prediction of environmental conditions and a buildings thermal response can provide savings to space-conditioning loads beyond what can be achieved using a reactive approach. The development of these control strategies can be difficult because of the uniqueness of each building. A simplified model-based predictive control (MPC) method for window shades is proposed. To this end, a control-oriented model representing the heat transfer problem in a perimeter office space was developed. The parameters of the model were estimated using the ensemble Kalman filter (EnKF). The energy-savings potential of the EnKF-based MPC approach for window shades was investigated using EnergyPlus simulations. This was accomplished by implementing the control-oriented model into the energy management system application of EnergyPlus. Simulations were conducted to assess the energy saving potential of using the EnKF-based MPC for roller blinds in a south-facing perimeter office space in Ottawa, Canada. The simulation-based results indicate the potential for about 35% reduction in electricity usage for space conditioning over manually operated interior roller blinds.

Nonisothermal Hydrodynamic Modeling of the Flowing Electrolyte Channel in a Flowing Electrolyte–Direct Methanol Fuel Cell

The performance of a direct methanol fuel cell (DMFC) can be significantly reduced by methanol crossover. One method to reduce methanol crossover is to utilize a flowing electrolyte channel. This is known as a flowing electrolyte-direct methanol fuel cell (FE-DMFC).In this study, recommendations for the improvement of the flowing electrolyte channel design and operating conditions are made using previous modelling studies on the fluid dynamics in the porous domain of the flowing electrolyte channel, and on the performance of a 1D isothermal FE-DMFC incorporating multiphase flow, in addition to modelling of the non-isothermal effects on the fluid dynamics of the FE-DMFC flowing electrolyte channel.The results of this study indicate that temperature difference between flowing electrolyte inflow and the fuel cell have negligible hydrodynamic implications, except that higher fuel cell temperatures reduce pressure drop. Reducing porosity and increasing permeability is recommended, with a porosity of around 0.4 and a porous material microstructure typical dimension around 60–70 μm being potentially suitable values for achieving these goals.Copyright

Experimental Investigation on the Performance of a Formic Acid Electrolyte-Direct Methanol Fuel Cell

The performance of a new methanol fuel cell that utilizes a liquid formic acid electrolyte, named the formic acid electrolyte-direct methanol fuel cell (FAE-DMFC) is experimentally investigated. This fuel cell type has the capability of recycling/washing away methanol, without the need of methanol-electrolyte separation. Three fuel cell configurations were examined: a flowing electrolyte and two circulating electrolyte configurations. From these three configurations, the flowing electrolyte and the circulating electrolyte, with the electrolyte outlet routed to the anode inlet, provided the most stable power output, where minimal decay in performance and less than 3% and 5.6% variation in power output were observed in the respective configurations. The flowing electrolyte configuration also yielded the greatest power output by as much as 34%. Furthermore, for the flowing electrolyte configuration, several key operating conditions were experimentally tested to determine the optimal operating points. It was found that an inlet concentration of 2.2 M methanol and 6.5 M formic acid, as along with a cell temperature of 52.8 °C provided the best performance. Since this fuel cell has a low optimal operating temperature, this fuel cell has potential applications for handheld portable devices.

Modeling of an Indirect Solar Assisted Heat Pump System for a High Performance Residential House

Heat pumps are commonly used for residential spaceheating and cooling. The combination of solar thermal and heat pump systems as a single solar-assisted heat pump (SAHP) system can significantly reduce residential energy consumption in Canada. As a part of Team Ontarios efforts to develop a high performance house for the 2013 DOE Solar Decathlon Competition, an integrated mechanical system (IMS) consisting of a SAHP was investigated. The system is designed to provide domestic hot water, space-heating, space-cooling and dehumidification. The system included a cold and a hot thermal storage tank and a heat pump to move energy from the low temperature reservoir, to the hot. The solar thermal collectors supplies heat to the cold storage and operate at a higher efficiency due to the heat pump reducing the temperature of the collector working fluid. The combination of the heat pump and solar thermal collectors allows more heat to be harvested at a lower temperature, and then boosted to a suitable temperature for domestic use via the heat pump. The IMS and the buildings energy loads were modeled using the TRNSYS simulation software. A parametric study was conducted to optimize the control, sizing and configuration of the system. This paper provides an overview of the model and summarizes the results of the study. The simulation results suggested that the investigated system can achieve a free energy ratio of about 0.583 for a high performance house designed for the Ottawa climate. Copyright

Characterization of an Air-PCM Energy Storage Design for Air Handling Unit Applications

In Canada, space heating and cooling accounts for 55 percent of the total energy consumption in the commercial sector (Natural Resources Canada, 2016). Efficiency improvement in this area using energy storage could have a significant impact on the total energy demand. Phase change materials (PCMs) have been shown to be a viable medium for thermal energy storage having larger storage capacity per mass then conventional sensible heat storage materials. However, they generally have low thermal conductivity producing low heat transfer rates, resulting in relatively slow charging and discharging of the material. This paper will discuss the characterization of an air-PCM storage design for commercial air handling unit (AHU) applications during winter.

Sensible Thermal Energy Storage: Diurnal and Seasonal

Abstract Sensible thermal energy storage is the heating or cooling of a material with no phase change present to store either heating or cooling potential. This is most commonly achieved using water as a storage medium, due to its abundance, low cost, and high heat capacity, although other solids and liquids including glycol, concrete, and rock are also used. Sensible storage is typically used to meet the domestic hot water, heating, and/or cooling demands of a building, and can be diurnal, with a typical charge and discharge period of a few days, or seasonal with a charge and discharge period of a year, meeting the seasonal demands of the building. Sensible thermal energy storage systems are most commonly paired with solar thermal systems or heat pump systems, and when paired can allow solar energy to meet a significant portion of a building’s energy requirements.

In-Situ Experimental Validation of THERM Finite Element Analysis for a High R-Value Wall Using Vacuum Insulation Panels

Team Ontario is one of twenty collegiate teams selected to design and build a solar powered, net positive home for the U.S. Department of Energy Solar Decathlon 2013. One aspect of Team Ontario’s competition design entry is a high R-value wall using vacuum insulation panels. This paper details the method used for theoretical evaluation of the high R-value wall, stating all simplifying assumptions made. Theoretical simulations were performed in THERM, a two dimensional finite element heat transfer modelling program. Following a weighted average method used by industry experts, the whole-wall thermal resistance value was calculated. To verify the modelling results, an in-situ experimental validation was conducted. An 8′ × 8′ wall test specimen was built to the specifications of Team Ontario’s wall design. Experimental heat flux and temperature readings were collected from the test specimen in Carleton University’s Vacuum Insulation Test Facility located in Ottawa, Ontario, Canada, with the test specimen exposed to exterior weather elements. The experimental and theoretical results are compared and conclusions drawn to determine the effective thermal resistance of the vacuum insulation panels installed in the wall assembly. Finally the theoretical model is refined based on the previous study and a more accurate whole-wall thermal resistance of Team Ontario’s wall design is determined.© 2013 ASME