Phillips said "Starlink has pushed LEO to the brink of Kessler syndrome."[0]
This is an ESA collision rate prediction, based on... something. It has no known connection to Starlink. Are the assumptions in the ESA paper representative of Starlink (altitude, disposal, collision avoidance system, etc)? Who knows!
If the airflow isn't balanced, there's little point to using an ERV. If half the air is escaping elsewhere, none of that heat is being recovered. You might as well delete the ERV and just use half the airflow, because that will get the same positive pressure for the same energy loss.
My recommendation was mostly for the practical, not functional benefits.
An ERV comes with installation instructions, has a warranty, was designed to run continuously, and an HVAC contractor can install it for you. 3D printing brackets and cutting holes in your own walls isn’t for everyone.
Then it's 100x oversized for the purpose of pressurizing the structure. ;)
ERVs are great for increasing air exchange (two-way flow), but unnecessary when pressurizing because that's one-way flow by definition.
If you already bought an ERV it makes sense to combine the functions, simply because you already bought the expensive ERV hardware. But if you weren't planning to install an ERV anyway, it doesn't make sense to install one just for this project, because it won't do anything to reduce the heating/cooling loss from this type of system.
The one-way component of flow is still 100% non-recuperated. If you install a cheap 100 CFM positive pressure system and it burns an extra $100, then setting your ERV to be unbalanced by 100 CFM will cost that same $100. Same leak rate, same heat loss, same cost!
This is one of those deceptive math problems where it seems like it should work, but really it works out "six of one and half-dozen of the other."
I didn't understand the purpose as pressurising the structure. I understood the purpose as ventilating the interior, providing a central place to attach a filter, and preventing air from coming in from other places.
Yes, exactly! If you're ventilating the interior then using an ERV makes sense. If you're preventing air from coming in from other places, then the ERV doesn't save anything, because (intentionally) 100% of the incoming airflow is leaking out somewhere, so there's nothing for the ERV to do.
I edited my post above to hopefully make it a bit more clear, but it seems you get it right away! Cheers
They did, though! The entire point of positively pressurizing a structure is that any small leaks will instead result in clean air leaking out, which prevents dirty air from leaking in. This is how (most) cleanrooms work.
The neat thing is, if you're already accepting this heat loss penalty anyway (in the service of positive pressure), it greatly reduces or even eliminates the ERV you need to maintain good indoor CO2. So in addition to better indoor AQI, positive pressure can greatly reduce total equipment cost.
Seems like a win/win to me!
Buckminster Fuller proposed a similar scheme in his Dymaxion House (even removing dust via baseboard vents), but it used passive heating and cooling so there was little penalty.
Do ground technicians (exposed to the same contaminants, and for engine techs at much higher levels) have the same cancer risk elevations?
I was aware of the LRD risks associated with bleed air,[1] but I hadn't heard about contaminant introduction in regular service before. Very interesting, thanks.
AirFanta creator Adam Wong has a version using a 3D-printed adapter to 8" circular duct.[0]
In newer builds he places the purifier box indoors and simply reverses the orientation of the fans and filters. This keeps the box protected from weather, and the duct can be run in such a way as to keep out rain or dripping.
The AirFanta is actually rated as EPA E11 (95%) not HEPA H13 (99.97%), so if you're trying to keep out everything in one single pass like a clean room then AirFanta might not be best. It may be a good idea to check the real-world interception performance with a particle counter.
Unfortunately the data doesn't have the required time or space resolution. The drag term is averaged over many orbits, and you can't even use perigee/apogee drift to localize it since the atmosphere rotates so it gets averaged over all longitudes.
You can do some rudimentary localization by latitude, however, by comparing satellites in different inclinations. You also get data by altitude, of course.
What you want is realtime accelerometer records from satellites in flight, exposing their drag factors over specific parts of the planet. The only tricky variable would be their orientation, but that is certainly recorded too.
Based on losing "a few meters of altitude per day," if we assume 5 meter/day at 500 km that's 3 nano-gee. Sensitive piezoresistive accelerometers seem to run in the single digit micro-gee range.[0]
Easier to look at the altitude loss and infer the acceleration indirectly. With access to the raw higher time-resolution altitude data, mapping should be possible.
SpaceX has in the past gone above and beyond to expose TLE data for scientists and astronomers[1], so it's possible that people inside SpaceX would be open to collaborating on such a project.
The air exchanges in seconds, yes (as evidenced by the post-door-closing suction), but the air doesn't stop flowing through the fridge as soon as the air changes once, and the air enters warm and leaves cold, so (by conservation) heat is being robbed from internal surfaces. So you're still losing more heat by leaving the door open longer.
Door open --> Door close --> Suction --> No further heat loss afterwards
These comments are oddly common, but I've never understood the value of simply repeating the definition of uncertainty words like "may." Who is being informed here?
I am being informed about the public opinion. Which I value more than articles. (Don't come me at with AI, I'm well aware that it makes all human communication bad and pointless in theory and more and more in practice, thx.)
Not every correlation deserves to be published in the press. If you think about it, it is weird that they even make articles out of statements that only "may" be true.
It is a matter of thresholds, of consequential bets over provisional non-trivial assessments, and of journalistic duty (taking note - the idea is not from the analyst but from sources; journalists take note that sources made statements).
Analysts work speculatively. And the results of the speculation are not trivial when supported by strong elements.
Errors are fine when they are due to a random process. When the press pick up claims because they are likely to attract readers it's a different story. Errors are not random, they are the result of an optimization process and are very unlikely to happen on the other side of the claim. (For example consider the overwhelming number of articles that have been published with the title "Scientist may have found life on mars" over the past 30 years)
For this reason, "may" in a press article, doesn't carry the same meaning regarding uncertainty than "may" in common language. Which is why I disagree with your comment:
> I've never understood the value of simply repeating the definition of uncertainty words like "may."
In the contrary, I think it is worth reminding people what may actually means here.
Now, I agree with what you and others have said about the usefulness of discussing uncertain claims, and I don't think there is a real disagreement here.
Can we change the link to point there instead?
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