Patrick Tebbe

A Numerical Model for Thermal Performance of an Unglazed Transpired Solar Collector

In this paper, we will present a numerical model for estimating the thermal performance of unglazed transpired solar collectors located on the Breck School campus in Minneapolis, Minnesota. The solar collectors are installed adjacent to the southeast facing wall of a field house. The collectors preheat the intake air before entering the primary heating unit. The solar collector consists of 8 separate panels (absorber plates). Four fans are connected to the plenum that is created by the absorber plates and the adjoining field house wall. All fresh air for the field house is provided by the solar collectors before being filtered and heated by four, independent two stage natural gas fired heaters. Moreover, the following data were collected onsite using a data acquisition system: indoor field house space temperature, ambient air temperature, wind speed, wind direction, the plenum exit air temperature, the absorber plate temperature, and the air temperatures inside the plenum. The energy balance equations for the collector, the adjacent building wall, and the plenum are formulated. The numerical model is used to predict the air temperature rise inside the plenum, recaptured heat loss from the adjoining building wall, energy savings, and the efficiency of the collectors. The results of the numerical model are then compared to the results obtained from the onsite measurements; which are in good agreement. The model presented in this paper is simple yet accurate enough for architects and engineers to use it with ease to predict the thermal performance of a collector.Copyright

Work in progress — Engaging students in thermodynamics with Engineering Scenarios

This NSF CCLI Phase II project is focused on addressing improvements in student pedagogy and educational materials for the thermodynamics curriculum. The project intends to complete the development of the “Engineering Scenario” concept as a textbook supplement based on actual engineering facilities and real-world problems. The material is based on an expanded case study format and constructed in a web based format, allowing extensive integration of narrative, pictures, video, and web links to expand the background material. The Phase I project allowed for the development and testing of a single Scenario based on a local plant. Lessons learned from the previous assessment are guiding current development and expansion to include multiple facility types and locations for Phase II. This will be supplemented by input from student focus groups and readability test results. Assessment will occur at multiple institutions and will make use of engagement surveys, concept inventories, and student focus groups.

The Magnitude of the Thermal Energy Stored in a Building Wall Adjacent to an Unglazed Transpired Solar Collector

In this paper, we will present a method for estimating the stored thermal energy in a building wall that is adjacent to an unglazed transpired collector. We also discuss how this value should be incorporated in the collector efficiency calculations. An unglazed transpired collector is made of a relatively thin, dark, perforated metal wall that is installed approximately 14 inches (35.5 cm) away from a south facing building wall to create an enclosed plenum. Typically, the outside air is drawn into the collector by fans that are located on the top of the collector. These types of solar collectors are used to preheat the intake air using solar energy before the air enters existing HVAC systems. They are generally used in situations and buildings where large ventilation volume flow rates are required. Most of the studies related to unglazed transpired collectors deal with estimation of air temperature rise due to solar gain and recaptured heat loss from the adjoining building wall. In the past, studies have neglected the amount of thermal energy that is stored in the building wall. However, as shown in this study, the stored thermal energy is of significant amount, and if incorporated correctly in the collector efficiency calculations, it would lead to higher efficiency values.Copyright