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Comment by VectorLock | Hacker News Reader

If you build a greenhouse around your outdoor dining area, is it an outdoor dining area any more?

The reasoning I've heard is that greenhouses provide group isolation rather than overall ventilation per se, but there's usually also a trapdoor or partially open roof to vent the air, so it does work in some sense. This is what it looks like in practice in Chicago [0].

Indoor Plexiglass partitions provide isolation too but the level of isolation is more limited. Plus the air in a smaller indoor location is recirculated between partitions, whereas outdoors it is ostensibly exchanged at much higher rates.

Which makes me wonder, can't we build indoor booths?

The catch would be one would also need a HVAC that can exchange air outside the booths at high throughputs like aircraft cabins.

ACPH = air changes per hour = 60 * Q / L where Q = volumetric flow (ft3/min), L = ft3.

Aircraft cabin ACPH are around 20-30 (and through a HEPA filter) [1], while a restaurant dining area is 8-12 [2] (many assumptions here, like airtightness, etc), and no HEPA.

[0] https://www.timeout.com/chicago/news/dine-and-drink-in-a-pri...

[1] https://www.iata.org/contentassets/f1163430bba94512a583eb6d6...

[2] https://www.engineeringtoolbox.com/air-change-rate-room-d_86...

Exactly what's considered "outdoor" in that respect depends on the jurisdiction. For example DC's current regulations allow tents to count as outdoor dining as long as they have no more than one side closed [1]. Other places allow more enclosed tents.

[1] https://coronavirus.dc.gov/page/coronavirus-new-and-expanded...

My family's plan for watching $sportsball together outside this winter is having everyone in their own small ice fishing tents with personal electric heaters. There's going to be a lot of extension cords running out of the garage.

I assume you are aware that each heater will need to be on its own circuit? A garage typically only has 2 or so, so you'll need to run extension cords to various rooms in the house.

Also you'll need 14 gauge extension cords, many regular ones are only 16 or 18 gauge.

So, we tried it this last sunday and we did trip the breakers. The garage only had 1 circuit for the outlets (the other powered ceiling lights and the garage door.

New plan for next time: electrically heated blankets!

Depends on how sealed it is. An actual greenhouse would not be. If the area is draughty and has a lot of air exchange it may actually be close to outdoors.

A CO2 meter can give a quick approximation of whether the greenhouse canopy spacs is more like an inside or outside.

My intuition was you’re right. But I could see it being the other way if it’s just a loose shield.

Following that logic, it seems indoors would also be fine if they open up a bunch of windows?

In a place with wall windows, quite possibly! But it really depends on the airflow.

You can use a co2 meter as a proxy. Outdoor levels are generally around 450 in a city. If your indoor space with open windows is there, you’re probably basically outside. If it is higher, you’re not.

See here for example, co2 is a commonly used tracer gas: https://www.ghdonline.org/uploads/Measuring_Air_Changes.pdf

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To be clear. I think very few restaurants have enough windows to really be like outside with a bunch of people in there.

I had a look at the greenhouses. Key difference from indoor dining: they prevent superspreader events. The problem with indoor dining is you have 30+ unmasked people dining in a poorly ventilated room. One infected person can infect many others.

In a two person tent an infected person can infect at most their dining partner, assuming waiters are provided good sanitary measures.

Under UK law it wouldn't be, once the walls exceed 50% of the perimeter it's no longer classed as outdoor

"But officer, this tiny slit in the wall is a fractal curve with infinite length"

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