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NREL is leveraging its understanding of sustainable building science, high-efficiency HVAC, and sorbent chemistry to target research on the most energy-intensive portion of the 9 Quads of energy America consumes for heating and cooling each year.
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 A researcher measures a prototype air cleaner's contaminant removal performance. Proven sampling techniques accelerate by a factor of 50, the measurement of parts per billion VOC contaminant challenges found in indoor air. |
To this end, NREL has developed critical R&D capabilities for advancing IAQ sensing and air cleaning science at its Advanced Thermal Conversion Lab. The facility can challenge prototype air cleaners and evaluate their performance 50 times faster than conventional qualitative methods, accelerating the development of effective approaches. Once their performance is qualified, active air cleaners will ultimately claim ventilation "credits" under building design codes. HVAC systems incorporating direct air cleaning will require less ventilation air to dilute contaminants, and less energy will be consumed to provide the same level of IAQ.
Desiccants are a subset of materials called sorbents. Sorbent systems can be designed to control chemical gases and vapors in the same way desiccants work on humidity. In fact, desiccant component manufacturers have product lines that are used to control solvent vapor emissions for industries ranging from automotive coatings to semiconductor manufacture. Sorbent-based technology can be applied to improve indoor air quality (IAQ) in a number of ways: by enabling the efficient introduction of higher fresh-air ventilation rates, by directly scrubbing recirculated air to reduce the need for ventilation, and by incorporating real-time sensors that limit ventilation air when it's not needed.
IAQ is an elusive parameter to quantify, but is vital to our health and productivity given the amount of time we spend indoors. NREL has produced unique equipment that can map indoor VOC "signatures" and has increased the sensitivity of low-cost VOC sensors by a factor of 100. These technologies will enable a strategy called demand-controlled ventilation in which energy-intensive fresh-air conditioning is optimized by limiting its use when contaminant levels are low.
Reducing IAQ to an output that can be monitored is a complex task because it results from a combination of several different factors, including temperature, humidity, carbon dioxide, volatile organic compounds (VOCs), particulates, and bioaerosols. Low-cost sensors for temperature and humidity are readily available and, in newer buildings, are usually integrated directly into the building ventilation control system. Very recently, inexpensive carbon dioxide (CO2) sensors have been offered commercially. CO2 concentrations are often used as an indirect measure of human occupancy in building spaces as an input to ventilation control systems. They can't sense build-up of VOC's off-gased from building materials, however. Total VOC sensors are also available, but they can only measure the sum of all VOCs present. This approach may not detect when any one VOC is rising to problem levels. A low-cost sensor that can distinguish between key VOC's in real-time would be useful to optimize ventilation air effectiveness and energy efficiency.
Measuring individual VOC concentrations indoors is difficult because they are typically in the parts-per-billion (ppb) range. The commonly used analytical techniques, with detection limits in the parts-per-million (ppm) range, require specialized equipment costing tens of thousands of dollars to measure VOCs. To measure VOC concentration levels at ppb traditionally requires an additional time-consuming collection step, which makes them even more expensive.
A technique that could provide "real-time" data on organic contaminant concentration in indoor environments would allow building operators to actively regulate the building environment, in much the same way that operators now use information on temperature, humidity, and CO2 concentration. The goal of current work at NREL is to develop a low-cost, real-time chemical sensor by combining advanced chemometric analysis with commercially available sensors.
Cyrano Sciences, Osmetech, AppliedSensor, AlphaMOS, and Microsensor Systems.
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