The field of solar energy is growing at an amazing rate. But before new technologies can make it into our homes and businesses, extensive research must be done first. This is precisely what the Rural Renewable Energy Alliance (RREAL) and Apex Solar have done recently with solar thermal air heating for ventilation.
Within every structure, a supply of fresh, oxygen-rich air is required for a variety of reasons, including keeping people comfortable and healthy and preventing moisture buildup and mold growth. This fresh air can be supplied by venting air from outdoors to indoors, while simultaneously pumping exhausted air out. This simple idea gets a little more complicated when you take into account the temperature difference between outside and inside (especially in cold winter months). Recently, RREAL and Apex Solar dedicated themselves to investigating the use of solar air heating in residential structures to make up this temperature difference.
“Ensuring sufficient fresh air in a tightly air-sealed residence is a necessary but energy intensive process,” Principal Investigator, Adam Kutrich of RREAL, explained. He continued, “Heating fresh air from ambient temperature up to the desired building temperature during the Minnesota heating season represents a significant amount of energy use.”
The nuts and bolts of the research involved investigating the use of glazed flat plate solar air heat (SAH) collectors to supply heat for residential make-up air. Kutrich described that, “In a glazed flat plate collector, solar energy passes through a glazing and is collected by a specially coated absorber plate. When the system operates, air is driven into a cavity behind the absorber where it collects thermal energy before entering the house.”
The study compared this use of SAH to the use of heat recovery ventilators (HRVs). Kutrich described the HRVs’ function as “passing the incoming and outgoing streams of air next to each other so that the exhaust air heats up the intake air (or reverse if it is warm out). This way the HRV recycles up to 80% of the thermal energy that would otherwise leave the building.”
The research project modeled the systems at two separate locations, St. Cloud, MN and Boulder, CO to assess performance in multiple climates.
While the experimental data collection ran smoothly, the results were not what the researchers were hoping for. Kutrich conceded, “The only significant challenge we encountered was mild cognitive dissonance associated with the findings.” He expanded by saying, “We were surprised to learn that A) solar air heat is not a highly competitive strategy for meeting residential ventilation make-up loads given current technologies and B) that solar air heat systems installed as residential ventilation make-up heat systems produce more energy than recirculation space heating systems of the same size.” In addition, the examination of the two systems combined provided inconclusive results.
Despite the unexpected results, RREAL and Apex Solar, as well as CERTs, believe the study was a step in the right direction, even if it is away from SAH with residential structures. With advancements in solar technologies happening more and more frequently, a replication of the study could be beneficial. Kutrich concluded that, “We believe there is merit in further study. If the project were to be duplicated, we would encourage a larger study with an applied component […] The modeling and assumptions employed in this study were appropriate, but we certainly generated additional questions that can only be answered through applied research.”
Project Snapshot:
- Location: Pine River, MN
- Technology: Solar Air Heating
- CERTs Funding: $2,500
