Modeling And Predictive Control Of High Performance Buildings With Distributed Energy Generation And Thermal Storage

Building-integrated photovoltaic-thermal (BIPV/T) systems replace conventional building cladding with solar technology that generates electricity and heat. For example, unglazed transpired solar collectors, known as UTCs, can be integrated with open-loop photovoltaic thermal (PV/T) systems to preheat ventilation air and/or to feed hot air into an air source heat pump, thus satisfying a significant part of the building’s heating and/or hot water requirements while also generating electricity. In the present study a model for a BIPV/T system with a two-stage prototype UTC integrated with PV panels has been developed and used to create a new component in TRNSYS. An open plan office space at Purdue’s Living Lab is used as a test-bed to explore system integration approaches with building HVAC systems and thermal storage mechanisms. The BIPV/T system is coupled with the building through a thermal storage tank, which serves as the heat source, and is connected to the air-to-water heat pump, for the radiant floor heating. The building ventilation system is coupled with the air outlet of the BIPV/T system. A detailed building energy model is developed in TRNSYS, which is used to evaluate the annual performance with the results showing significant energy savings. The objective is to develop models that can be implemented within a predictive control framework for the optimal set-point trajectory of the thermal storage tank. In the MPC formulation, the cost function is the integral of the electric energy consumption over the prediction horizon (48 hrs) subject to thermal comfort and equipment constraints. The study also investigates the impacts of the uncertainty in weather forecast (solar radiation) on MPC performance robustness for the integrated solar system. In our methodology, the TRNSYS model is used as a true representation of the building to identify the parameters of a 3rd order linear time invariant state-space model. The sum of squares minimization was used to identify model parameters that minimize the root-mean-squared error (RMSE) of time series predictions for the three state variables (floor surface temperature of the room; room air temperature; building envelope interior surface temperature) between the reduced order and the TRNSYS model. Known inputs to the system include the ambient temperature, solar radiation (absorbed by the envelope or transmitted through the south-facing glazed façade), internal heat gains (occupancy schedule, equipment, mechanical ventilation and infiltration) and the tank set point temperature. A pattern search optimization algorithm has been used over the training data space to identify the parameter values. Parameter bounds were set to constrain the solution space to physically plausible values. The training and calibration data sets includes 2351 (from Jan 4 to Feb 22, 7 weeks) and 1823 (from Feb 23 to Mar 30) data points, respectively. The simplified 3rd order model shows satisfactory performance with the RMSE for the three state variables within 0.5 °C. Model predictive control relevant identification methods such as 4SID (black-box identification) are also considered and the results will be compared with those using grey-box techniques

Numerical Study of Convective Heat Transfer for Flat Unglazed Transpired Solar Collectors

Convective heat transfer coefficients (CHTC) for flat unglazed transpired solar collectors have been computed using high-resolution 3-dimensional steady RANS CFD simulations. The Standard k-ε, Renormalization Normal Group k- ε (RNG k-ε), Realizable k-ε and Shear Stress Transport k-ω (SST k-ω) turbulence closure models were used and the results were compared with experimental data from the literature. The validation study showed that both the Standard k-ε and the RNG k-ε model performed better in terms of matching the experimental data and showing consistently faster convergence. Local CHTC along the plate were evaluated with the validated model for different suction flow rates (0.0448 to 0.0688 m/s) and free stream turbulence intensity (0.8% and 20%) at 6 m/s approaching flow velocity with the results showing that the turbulence intensity has a more profound impact on the overall convective heat transfer process. The local CHTC in the solid surface region of the collector remains constant after a certain length for the cases considered; however, the starting length was found to be longer compared to the values reported in previous analytical studies

Chondrogenic potential of human articular chondrocytes and skeletal stem cells: a comparative study

Regenerative medicine strategies have increasingly focused on skeletal stem cells (SSCs), in response to concerns such as donor site morbidity, dedifferentiation and limited lifespan associated with the use of articular chondrocytes for cartilage repair. The suitability of SSCs for cartilage regeneration, however, remains to be fully determined. This study has examined the chondrogenic potential of human STRO-1-immunoselected SSCs (STRO-1+ SSCs), in comparison to human articular chondrocytes (HACs), by utilising two bioengineering strategies, namely ‘‘scaffold-free’’ three-dimensional(3-D) pellet culture and culture using commercially available, highly porous, 3-D scaffolds with interconnected pore networks. STRO-1+ SSCs were isolated by magnetic-activated cell sorting from bone marrow samples of haematologically normal osteoarthritic individuals following routine hip replacement procedures. Chondrocytes were isolated by sequential enzymatic digestion of deep zone articular cartilage pieces dissected from femoral heads of the same individuals. After expansion in monolayer cultures, the harvested cell populations were centrifuged to form high-density 3-D pellets and also seeded in the 3-D scaffold membranes, followed by culture in serum-free chondrogenic media under static conditions for 21 and 28 days, respectively. Chondrogenic differentiation was determined by gene expression,histological and immunohistochemical analyses. Robust cartilage formation and expression of hyaline cartilage-specific markers were observed in both day-21 pellets and day-28 explants generated using HACs. In comparison, STRO-1+ SSCs demonstrated significantly lower chondrogenic differentiation potential and a tendency for hypertrophic differentiation in day-21 pellets. Culture of STRO-1+ SSCs in the 3-D scaffolds improved the expression of hyaline cartilage-specific markers in day-28 explants, however, was unable to prevent hypertrophic differentiation of the SSC population. The advantages of application of SSCs in tissue engineering are widely recognised; the results of this study, however, highlight the need for further development of cell culture protocols that may otherwise limit the application of this stem cell population in cartilage bioengineering strategies