Scoring Thermoelectric Wood Stoves
Updated: October 2018.
The judges will use five categories to assess the stoves. They are, listed in order of importance:
- PM emissions
- CO and Safety
- Thermal Efficiency.
Each of the five scoring categories are weighted differently, with many points in the top category – Thermoelectric Innovation – and very few in the last category – Thermal Efficiency. This is partly so that we do not disadvantage prototypes that are not market ready.
Scoring is based on a scale from 1 to 100 and more than 80 of those points are solely based on instrumentation and objective criteria. In a few areas, scores by each judge may vary, but they are still judging based on agreed upon criteria. One of the main roles of the judges is to establish those criteria, approve the test method and oversee the testing and scoring.
- Thermoelectric Output: The greatest number of points is awarded to thermoelectric output because that is the primary objective of this category and many of these stoves are prototypes. The two criteria that will be used to assess thermoelectric output are:
- Peak Watt: Measured as the maximum net power output minus accessories (e.g., pump and fan) 30 minutes after ignition and stove is running in a steady state.
- Watt-hour: Measured over 2-hour period as net energy output (watt-hour) minus accessories (e.g., pump and fan) 30 minutes after ignition and stove is running at a steady state.
While emissions and safety are a high priority for these stoves, the impact of thermoelectric generators on emissions has not been fully evaluated, and all stoves will need to meet EPA PM emission standards before being commercialized.
- Thermoelectric Operation: These criteria will be used to evaluate the overall usability of the TE system and electricity output for what it is designed to accomplish. For example, how easily can the power from the thermoelectric generator (TEG) can be accessed? Does the TEG have a USB port or a 110-volt outlet, and does it have a voltage regulator so that power can easily be accessed by the user. In addition, most TEGs use a water-cooled heat exchange to cool the thermoelectric modules. This heat exchange will be evaluated for user convenience and effectiveness in helping to heat the home.
- PM Emissions
Points will be determined by the instrumentation used to measure PM and individual judges will not have discretion to alter points in this section. Hydrocarbons will also be measured. Since the focus of this category is on power output, the emissions test will focus on emissions during start-up (approximately 30 minutes), reloading and steady state (approximately 2.5 hours). While emissions is a high priority, many of these stoves are prototypes and all of them will have to meet EPA emission standards before they can be commercialized.
- CO & Safety
Half the points in this category is simply CO readings in parts per million through the entire test burn. Judges will assess other potential safety issues that may arise from the stove or the TE system.
The degree of automation to optimize and manage combustion will be assessed by the judges. Complete automation, where no operator engagement is required, and combustion performance is well controlled throughout the test will receive more points than stoves where some level of operator engagement is required. The judges may also record the PM impact of reducing desired heat output right after reloading to see if automation successfully prevents the stove from smoldering.
- Delivered efficiency
The efficiency of heat transfer to the room will be measured using a stack loss method.