🧵The search for ventilation.
Hotel & COVID-19 Edition.

I stayed yesterday at brand name hotel. Here are some observations about shared air, outdoor air, and maintenance issues.
The room I stayed in does not have shared air. This is typical for hotel rooms. Air in your room gets recirculated and conditioned within your room only - by design.

Pic for unit in my room: window unit with fan and cooling/heating coil.
Indoor air gets recirculated on the side, conditioned and then blown from the top - as shown by my infrared camera. Blue = cold air. orange = "hot" air.
Hint: to know the intake of air on the unit, look where there is dust.
This unit only provides recirculated indoor air - NO outdoor air. I double checked with the brand name manufacturer.

Ok. Where is outdoor air coming from?
Typically, you will see a supply air in the corridor like the picture here.
In the hotel I stayed in, no outdoor air unit is found on the hotel premises and no sign of any supply of outdoor air in the room.
Other method to get outside air is to supply it to the corridor and then get outside air from the door to the room. However, the door is this room was sealed shut and I verified (three different methods) there was no air coming from the corridor.
The only other way is outside air brought in from the windows. However, I could not open them as there were sealed shut. I called the operator and asked her "how do I open these lovely windows", she said she worked at the hotel for a long time and never got asked this question.
In the bathroom, there was exhaust fan (fan taking air from bathroom and room and exhausting to the outside) continuously.

(it does not look pretty as it is never cleaned).
Because of the exhaust fan, taking air from room to outside, room pressure is <0. Meaning that air is being sucked in from corridor or adjacent room. For this room, there was air (small quantity) coming from an ill-sealed door from adjacent room.
My go-to-solution is duct tape.
(unrelated to this thread, if you ever watched forensic files, you would know to always check that this door between two rooms to be always closed)...
I noticed that the air conditioning system in my room has back mold. Unfortunately this is typical as the model is "design and forget".
I took bio-sampling and will be sending the sample to a lab to get the results of what I was breathing. (will share the results).
I also took CO2 data and particulate matter samples from 0.3 um to 10 um in size (will share the results when i graph the data and compare to other environment).

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More from @marwa_zaatari

27 Sep
@JudahWorldChamp @kprather88 @CorsIAQ @jljcolorado @HuffmanLabDU @Poppendieck Hotels do not have shared air by design with 1 caveat.
- In your room, you will have a unit that circulates and conditions only your room air (not shared).
- This unit might be under a window, next to a window, or in corridor of your room next to the bathroom.

See pictures below
@JudahWorldChamp @kprather88 @CorsIAQ @jljcolorado @HuffmanLabDU @Poppendieck Typically, for outside air, hotels (like Hilton and Marriott) have an outside air unit on the roof that brings the air into the building.

So far so good.
Your room air is not shared air with other rooms.
@JudahWorldChamp @kprather88 @CorsIAQ @jljcolorado @HuffmanLabDU @Poppendieck There are two ways to get outside air to the room:
1- Supply outside air directly into the room. That is the preferred method. See picture below. You will see a diffuser above the ceiling, next to the bathroom.

If that is the case, your room is isolated from other rooms.
Read 6 tweets
18 Sep
📢📢New! Air Cleaners Comparison:
1- Selection graph: 1.a. all + 1.b. only HEPA
2- Data download link
3- Request data link
4- Where to place air cleaner?
5- Calculate reqs
6- CADR and noise
7- Letter about unproven tech.

@CleanAirCrewOrg @DavidElfstrom
@kprather88
1a - Selection Graph - All (includes ionizers = unproven tech)
- X axis first cost + first year filter replacement cost in USD
- Y axis: Clean Air Delivery rate = volume of clean air in CFM (cubic feet per min) = ~efficiency x airflow
1b - Selection Graph - only includes HEPA
- X axis first cost + first year filter replacement cost in USD
- Y axis: Clean Air Delivery rate = volume of clean air in CFM (cubic feet per min) = ~efficiency x airflow

Fun Fact:
On average, for each 1 cfm of clean air you pay $1.8
Read 10 tweets
25 Aug
🧵 Answers to what the different strategies will result in term of air change rate

Example used throughout the thread:
👉Classroom: 960 ft2: 30' x 32’
👉Number of occupants: 30 (this is the design number, taking into account average classroom density).
Ventilation by code, this classroom should have 415 CFM airflow of outside air or 14 CFM/person.

👉This airflow is being forced through the HVAC system (unit in classroom or mechanical room).
When we check ventilation, the answer is not “yes” or “no”, the answer should be how much?
Read 9 tweets
23 Aug
📢📢📢 Updated Air Cleaner Chart:

I added the DIY CR box as optimized by @DavidElfstrom.

Look at this beauty!! @kprather88 @JimRosenthal4
It is the most cost effective purifier on the chart.

See below 🧵 comparison to intellipure(tm) /Blueair (tm)/needle point bp ionization Image
How it compares to Intellipure?
DIY CR/DE Box is 9 times cheaper and 2 times more effective and less noisy than Intellipure! @Mssarahmssarah Image
How it compares to Blue air?
DIY CR/DE Box is ~5 times cheaper and 1.55 times more effective than Blue Air 211+ @smartrestartaps Image
Read 4 tweets
20 Aug
🧵 Is it enough?

"We did ventilation school assessment, we bought 2 air purifiers for each room for $40 million" "we conclude, it is safe to return."

A lot of time and money was spent. The school ventilation assessment is a great starting point, but what was the outcome?
Ventilation assessment reports can be found here: survey.nycsca.org/files/

I looked at many classrooms. Similar findings. Most do not have outside air and problems with exhaust fans of bathrooms (unless I am missing something - no reports it was fixed?).
Most schools have windows that can be open but windows are not a reliable method to get you a specific air change rate. For more information about ventilation:

Because mechanical ventilation is not available, a good option is to add air purifiers.
Read 7 tweets
17 Aug
🧵Following-up: I did incognito testing at a famous casino last Aug. On my there, I felt uneasy - casinos were open and schools were closed.

However, this experience opened my eyes: if casinos can open safely and do it right, so can schools..

@HuffmanLabDU @DrEricDing
COVID Safety Plan (1/2)
- People density was at 50% (by design)
- Other measures below.
Everything was followed properly, except social distancing.

Masks were enforced, even outside. One might ask how can you enforce masks if people are drunk? I saw 2 people holding a person to his room while a third person holding by two fingers his mask in place.. commitment!
Read 7 tweets

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