Grantee Research Project Results

2013 Progress Report: Heating Attic Air for Space Heating and Dryer Applications Using Solar Thermal

EPA Grant Number: SU835329
Title: Heating Attic Air for Space Heating and Dryer Applications Using Solar Thermal
Investigators: Tam, Kawai , Brisk, Philip , Alcaraz, Christian , Mak, Samantha , Rolf, Julianne , Schoeman, Ryan
Current Investigators: Tam, Kawai , Vu, Samantha , Leyva, Juan , Coria, Vanessa , Rodriguez, Giancarlo , Sanders, Brandon , Parker, Jonathan , Kim, Ji Hwan
Institution: University of California - Riverside
EPA Project Officer: Hahn, Intaek
Phase: II
Project Period: August 15, 2012 through August 14, 2014 (Extended to August 14, 2017)
Project Period Covered by this Report: August 15, 2012 through August 14,2013
Project Amount: $89,933
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2012) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Air Quality , P3 Challenge Area - Sustainable and Healthy Communities , Sustainable and Healthy Communities

Objective:

The solar thermal closet is an alternative unit for drying clothes that runs on sustainable energy. Hot air from the attic is funneled through a solar thermal collector on the roof which consists of metal pipes that are exposed to the sun through a transparent plastic cover. Using a series of in-line duct fans, the hot air is channeled to the bottom of the solar thermal closet, where it dries the clothes and then escapes from the top of the closet.  In collaboration with the community of Victory Gardens in Moreno Valley, California, the dryer unit is being tested on-site for collection of thermal data and implementation of optimized designs. The objectives in Phase 2 include continued data collection of the system throughout the different seasons, optimization of the unit for both clothes drying and space heating through improved design features such as drying efficiency, broad functionality, safety and ergonomics and implementation of touch-screen user-friendly controllers.  

Progress Summary:

After taking over this project from the previous team, the new team familiarized themselves with the Phase 1 design and prototype currently on site at Victory Gardens. Continued data acquisition from the prototype unit was invaluable in the design of the next generation of the solar thermal closet. From thermocouple sensors in the prototype, a temperature discrepancy of approximately 10°C was noticed between the heated air exiting the solar thermal collector and entering the closet. The duct that the heated air travels through was completely insulated and thus the two temperatures should have been similar when the solar closet was not actively drying clothing. Upon further inspection it was found that the in-line fan blowing the air towards the closet was broken. It had been running continuously for approximately a year for data acquisition of thermal capacities twenty hours a day. A new fan was installed and the temperature probes were recalibrated, but this action did not resolve the problem. Insulation materials were added to the bottom of the closet floor, and improvements to the insulation on the closet doors and walls were implemented. This dramatically reduced the temperature discrepancy to within 2°C and provided insight for the next design.

The previous solar thermal closet also used large box fans to help circulate the air within the closet in conducting the proof-of-concept tests. Not only were the fans unattractive, but their high energy demand made them impractical. An alternative solution was to mount a second in-line fan at the top of the solar closet. As the air travels from the solar collector to the closet through ductwork, the air undergoes a sudden expansion decreasing the velocity to approximately zero. Maximum turbulence is needed within the closet to help with the drying effect. Although the addition of the inline fan at the exit on top of the closet was inadequate, this provided information for the new design which will include a chimney stack configuration with a chimney vacuum cap that will facilitate the siphon effect to assist in air circulation in the closet. A mathematical model was created to ensure the design specifications for air circulation would be sufficient. Replacing the box fans with a more energy efficient fan is also being evaluated for the next generation of the closet. If the fan can be controlled by the user control system, the fans will not need to be running constantly like they were with the prototype closet. 

The user control system is a new addition to the design of the closet dryer.  When the closet will be used as a space heater, the user will have control over the temperature and humidity of the air coming into the home. The closet will be run by a microcontroller which allows for control over the system and the various safety features mentioned below. The microcontroller will directly interface both the user-controlled LCD and the fans to vary the speed of the air through the system. The LCD is programmed using software that takes the data and transfers them directly to the LCD. The LCD screen will allow the user to be able to operate the closet dryer much like a conventional dryer and the space heater like a typical heating unit. The speed of the fans will determine the temperature that exits the solar thermal collector. A slower fan speed results in more time in which the air parcel spends inside the collector, thus increasing the temperature. The user inputs the desired temperature and the fan will adjust its speed to output the air at the set temperature. Safety features will also be integrated into the programming of the control system. A light will turn on when the doors open and the fans will turn off automatically and must be restarted through the LCD control panel so that if anyone happens to get inside the closet, the hot air will not be blown into the closet. Proper lighting in the closet will also facilitate the hanging and placement of laundry when the doors are opened.

Continued data acquisition from the revised Phase 1 prototype has provided valuable information on the range of temperatures that we can expect and areas for improvement in the design. With the updated fan design and increased floor insulation, the closet temperatures were recorded for different weather patterns throughout the months of April to September 2013. The dates of May 6, July 21, and August 15 were chosen to illustrate the closet performance for rainy, cloudy, and sunny weather. Thermocouples were placed at the exit of the solar thermal collector, in the entry duct to the solar thermal closet and at the outlet of the closet. In addition, a relative humidity sensor was placed at the outlet of the closet. Representative plots and the ambient weather data are provided in Figures 1 to 3. Results from Figures 1 to 3 demonstrate that closet temperatures reached approximately 22°C (72°F), 34°C (93°F)and 45°C (113°F) on a rainy day (Figure 1), partly cloudy day (Figure 2) and a sunny day (Figure 3) respectively. All plots start at midnight represented by time at zero hour.

Figure 1: Temperature and relative humidity data from the solar thermal closet prototype on a rainy day with a maximum ambient temperature of 14.6°C (58.3°F).

Figure 2: Temperature and relative humidity data from the solar thermal closet on a partly cloudy day with a maximum ambient temperature of 28.1°C (82.6°F).

Figure 3: Temperature and relative humidity data from the solar thermal closet on a warm and sunny day with a maximum ambient temperature of 37.5°C (99.5°F).

In all three scenarios the interior temperature of the closet was greater than the ambient temperature in the afternoon. However, to reach our desired working closet temperature of approximately 68°C (155°F), improvements to insulation and circulation of the heated air in the closet will be required. These were all considerations taken into account in the new design of the solar thermal closet which will be constructed as a faux chimney in Victory Gardens.

Contractors have been selected after solicitation of bids. Preliminary blueprints have been submitted to the city of Moreno Valley and we are in the process of waiting for the building permit to begin construction of the chimney and closet. The solar thermal collector design was also optimized by increasing the surface area for solar heating and improving the fabrication and construction process which substantially reduced its weight. This new design will allow for the air to have a longer duration in the collector to heat up and will reduce the load of the unit which will be mounted on top of the roof. The newly designed solar thermal collector has been machined and built and is ready for installation.

Future Activities:

This experience provided invaluable insight that will be applied in the construction of the next solar thermal closet. Improved designs to the solar thermal closet and the solar thermal collector will capture and harness more heat for better drying efficiency of clothes and potential space heating in cooler months. The next closet will have insulation foam inserted into the interior spaces of the closet doors resulting in better insulation and a more aesthetically pleasing look. Lastly, automated control will be implemented to give the user control over the heat leaving the closet. Overall the knowledge gained from designing and conducting research for the first closet was insightful and invaluable. It helped lay the foundation for the next improved solar thermal closet.  

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

Process control, PYTHON software, sustainability, conventional dryer, alternatives, residential, home improvement, green construction, innovative technology, pollution prevention, ambient air, renewable, public good.

Progress and Final Reports:

Original Abstract

2014 Progress Report

2015 Progress Report

2016 Progress Report

Final Report

P3 Phase I:

Heating Attic Air Using Solar Thermal Energy for Space Heating and Drying Applications  | Final Report