Selection of low GWP participating gas for a passive cooling skylight
Bibliographic record
Abstract
Rising temperatures as a result of climate make the cooling of building envelopes and creating thermal comfort for more and more people a challenge while energy use must become more efficient.In addition to active (electricity-driven) systems, passive cooling methods are being developed for night-time as well as day-time cooling of buildings.A passive cooling skylight under development at Åbo Akademi has demonstrated a night-time passive cooling effect of ~100 W/m 2 .Its performance depends strongly on the gas used inside the skylight, that will pick up thermal radiation (at long wavelengths, LW) via a lower window and after a natural convection transfer inside the skylight, release the heat to the sky via an upper window.Proof-of-concept work at ÅA involved comparing the use of air with the performance when using carbon dioxide CO2, ammonia NH3 or pentafluoro ethane, i.e. hydrofluorocarbon refrigerant HFC-125.Best results reported were obtained with the latter, but as a result of the 2016 Kigali Amendment to the 1986 Montreal Protocol on HFCs, an alternative for HFC-125 needs to be found, because of its global warming potential (GWP).With GWP = 1 for CO2, = 0 for NH3, for HFC-125 the GWP = 3500.Since a passive cooling skylight can be ranked as a refrigeration installation it cannot contain a gas with a GWP >150 after 2030 under European regulation.The prime material property of a suitable gas is a high emissivity / absorption in the LW range 8-14 µm, also known as the atmospheric window, where, apart from water vapour, nothing prevents radiative heat transfer from Earth directly to space.The hypothesis was that HFC-152a or HFC-41, with GWP values < 150 could replace HFC-125 for this skylight application.Besides GWP, other features that must not prevent the widespread use of the technology are flammability and chemical / physical stability in general, toxicity and, of course, costs.CFD simulations (Ansys Fluent) were used the calculate the passive cooling (LW) heat fluxes, temperatures, the convection flow field, and the transported heat inside the skylight, comparing the mentioned gases.and The results show that the performance of HFC-152a (117.8W/m 2 ) and slightly less so HFC-41 (115.4W/m 2 ), both with a GWP < 150, can match the performance achieved so far with HFC-125 (117.3W/m 2 ), compared to 100.5 W/m 2 with air.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".