UKC

I've been endeavouring to improve ventilation in publicly-accessible buildings in my LA over the last year; followers of the covid threads might remember some of the discussions we had at that time. There've been lots of successes in improvements both to policies and to actual systems that were informed by discussions here, for which I'm hugely grateful: you've all helped to make public spaces safer for half a million people. But now I'm getting to the point of dealing with the less tractable public spaces: those that are too old or too badly designed to be made safe easily.

I've been using a SAF Aranet 4 to gauge air quality in a number of workspaces that seemed to me to be problematic. Having got the evidence base together using both the C02 readings and Univ. Colorado-Boulder's aersol modelling tool (here: https://docs.google.com/spreadsheets/d/16K1OQkLD4BjgBdO8ePj6ytf-RpPMlJ6aXFg...) and managed to persuade the powers-that-be that the air quality is poor enough to need urgent correction, I've been given a pretty open hand to determine the solution myself.

These spaces have no natural or artificial ventilation barring an openable door to the outside air at one end, & have no scope for architectural alteration or installation of mechanical ventilation. There is no possibility of through-ventilation. Furthermore there's no appetite to spend on any long-term solution as the buildings in this zone are scheduled to be demolished in 18 months' time. The spaces are occupied by workers and freely accessible by the public who, owing to the nature of the service, tend to be the more vulnerable.

Whilst a universal FFP2/3 policy would be very effective in this sort of space, it's just not viable. I've proposed free-standing air purifiers with HEPA filters: this has been accepted and now I have to choose which ones. Other than knowing I need 5 ACH/800 m3h-1 CADR and a reliable & cost-effective supply of replacement filters, I don't have much idea where to start; and I'm wary of making errors owing to over-stepping the limits of my own knowledge, physics being very much not my field.

Has anyone dealt with such problems and acquired any useful know-how about HEPA systems available in the UK? Or has anyone implemented ventilation solutions that they're happy or unhappy with? Would you have recommendations, or warning of pitfalls to avoid? I know these forums are full of people with the most surprising & varied kinds of expertise; maybe we've even got a ventilation engineer or an aerosols physicist lurking here...

In reply to bruxist:

Sorry, bit waffly and no definitive answers.

The OP from this thread might have something scientific to add - https://www.ukclimbing.com/forums/off_belay/ip_licencing-744494

I assume you've seen the CDC guidance [1]?  

I set up HEPA at home in the "good" times when the father in law visited, and also when I got Covid in winter 21/22.  My main concern was "dead zones", mentally visualising the airflow in to and out of the portable unit as a constant volume-flow-rate closed loop, ballooning out in cross sectional area further from the unit as the airflow slowed down, and bunching up as it returns to the filter, forming a "moving air zone".  Easy to imagine how such a closed loop from a single point filter can't flow well through opposing corners in a room for example, so air cleaning in those corners relies more on the moving air zone having a rapid drawdown of particulates (through the HEPA filtration) and then a slower draw-down from the dead zones by net diffusion into the lower density moving air zone.  I'm not an aerosol physicist but it's similar to some detailed modelling of diffusion I did on much smaller scales with point sources, sinks, diffusion and flow.

I didn't do any modelling for the HEPA because it would be so naive as to be noise, although I did get a LIDAR scan of the room including furniture before the pointlessness of modelling dawned on me...

When in doubt, measure.

• It's all a bit cargo cult, but you might look at the room, measure the airflow induced by the portable unit using with a decent airflow meter at various locations, and make sure the main activity areas aren't airflow dead zones, moving the filter(s) if necessary.  Ideally you'd use a thermal mass flow meter for sensitivity regardless of the airflow direction (vs an anemometer).
• You should be able to use synthetic smoke (smoke detector testing, party "smoke in a can") released at various locations to measure draw-down time, particularly with a suitable, logging air quality sensor.  You'd want to compare their particle sizes (if known) with respiratory particle sizes to contextualise the measurements in suspected dead zones.
• I think you’ll find more people have done this sort of airflow testing for cleanroom certification than for infection control; but it’s the same physical problem.  There’s some really nice portable thermal mass airflow units used for cleanroom testing…. Beats my handheld spinning anemometer…

Alternatively, perhaps my intuition on dead-zones is completely wrong and it's a non-issue.   Hopefully this will be a school-day thread for me... 

You didn't say if the people in these rooms are in fixed locations, or if they move about.  If it's mostly fixed locations, there's the possibility of building in-room ducting to remove air from the location of each person to then be in-room HEPA filtered and returned at ceiling level, giving a clean, continuous airflow to each fixed location.  There's a lot of options for the ductwork and ducted HEPA units, although it might be a bit too noisy as it's normally designed for the fans to go in separate plant spaces.

What ever system you use, you want one that measures the pressure drop across the filter to give an indication that it's becoming clogged; for some units this will just be a "change filter" indication; for industrial AHUs there will be proper telemetry. 

[1] https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html

In reply to bruxist:

Thought about something like this?

https://m.vevor.co.uk/portable-utility-blower-c_10374/12-300mm-duct-fume-po...

They're the go-to solution when you run into the dreaded 'confined space' bureaucracy.

In reply to wintertree:

This is tremendously useful. Thank you, Wintertree. I hadn't seen the thread you linked before, but will certainly contact the OP.

I used the CDC guidance early last year when dealing with larger buildings like libraries, and it gave me just enough of a handle on things to be able to talk to the HVAC installation engineers about what was needed. I've been into those sites again recently and have been really pleased about how good the ventilation is now (those sites that had previously been superspreader hotspots haven't seen *any* infections and though it's impossible to know for sure, I'll accept epistemic uncertainty if the results speak for themselves.)

I think I've resolved (at least to my own satisfaction) the problem of dead zones in the spaces with which I'm now dealing, and also the problem of freedom of movement (workers don't tend to be in a fixed position but move around a central area with the public). The idea of synthetic smoke for testing is great - I'd been puzzling over how to deal with demonstrating effect, as once HEPA filters were in use the C02 readings would become redundant for covid, if not for general air quality.

Know what you mean about cargo cult logic. In an ideal world there'd be infection control and H&S specialists sorting this stuff out in public spaces, but I'm not seeing that happen in practice.

In reply to Longsufferingropeholder:

That's a fantastic thinking-outside-the-box solution! But I think it would be too loud at 71dB. The spaces I'm thinking about are more like GP's waiting rooms: below 50dB is probably essential.

In reply to wintertree:

That would be me -

I’ll read through and reply tomorrow when I’m supposed to be working.

In reply to bruxist:

The ducting is the cheap part. You can have the noisy end miles away (and don't ask me how to deal with the aftermath when someone trips over it).

In reply to bruxist:

Hi Bruxist,

so, my two penneth worth. I would look to Rensair for your in-room solution (I’ve no connection, I just know they are good and that their solution is science/Eng based rather than snake oil). They have a proven and tested HEPA product that will work for you and they will do the maths too to prove that the CADR is equal to or greater than that required for the volume of space you are looking to filter.  Ask to see a CFD model of the delivery/extraction process and what their CADR is, along with the particulate matter size they claim to filter (the ‘rona’ is effectively trapped and quickly dedicated by HEPA) These are the holy grail. Filter lifetime should be looooong.

CADR is your primary ask after filter type. That delivery rate should be as high as possible in terms of lph/lpm and you also need to take in to account the velocity of the air exchange as this impacts air circulation/mixing - the entrainment effect so that clean air exceeds dirty air.

you talk about enclosed rooms, no ventilation other than opening a door. The pragmatic reality is that this is a good thing in that with the door closed you control the environment and maintain airborne  particulate matter levels to a given minimum. Open the door, and have an influx of new people and you immediately dirty the air and have to start all over again, ergo the R in clean air delivery rate becomes even more important, it’s not only the LPH of clean air delivery but also the frequency/number of air changes. You need them quick.

supposed dead spots in your room are not always as dead as you think. The Venturi effect and entrainment get everywhere, and human thermal plume also adds to the mixing effect.

research/Google ‘Corsi-Rosenthal’ cubes. There is a lot of maker expertise you can lean on there, and if you DM me I’ll put you in touch with a very respected environmental Prof at Copenhagen Uni who will be more than happy to answer your questions with far more knowledge than I ever can 😀

One last point, ionisation, blue light, chemical, anything other than HEPA is useless at best and detrimental to health at worst. Do not buy a solution that claims to do anything other than filter air (gases are another thing altogether, there you are looking for a combined active/nano carbon filter)

You’re doing a good thing - keep at it 😀

In reply to bruxist:

Similar solution at a different scale: Ducted domestic bathroom fans are very quiet and available in a range of sizes. You might not have the budget for boring inlet/vent holes in the building but perhaps in the door(s) depending on construction/fitting detail? It'd be ugly but it doesn't sound like we're discussing an architectural treasure here.

jk

In reply to BRILLBRUM:

Seconded.  

A sliver lining form Covid if there's broader evidence/understanding that HEPA works for airborne infection control in shared spaces - particularly important if it can get retrofit to spaces like hospital consultation rooms and GP surgeries.

I dropped you a PM after your IP thread; I don't know if it went to trash or if you deliberately filed it in the "ravings of a certified lunatic" folder...  Drop me a line through PM if you want a copy.

In reply to Bruxist:

The cargo cult thinking that went out from HSE > CIBSE > institutional facilities managers in terms of air handling could in some niche cases make things worse I think, particularly where some spaces are under PIV and others under passive ventilation (open windows).  

Just don't forget to have the smoke detectors disabled for the duration...  Also, if you can find Bobcat Goldthwait he might like to help -  youtube.com/watch?v=2kV2EVWNqXQ&

In reply to jkarran:

Worth thinking about where the vented air will go - likely out though other spaces in the building as viable virus laden droplets, rather than rapidly desiccating against the HEPA fabric.  There are ducted biaxial MVHR fans with passively driven exhaust, which would reduce leakage in to the rest of the building; ideally you'd put a separate ducted fan in set to "blow" to compensate the one set to "suck".  (Thanks to this thread, Spaceballs has been on my mind all day.  "We can't stop...")

In reply to wintertree:

@wintertree - must have gone in the spam or I would have def looked and responded. I'm not with that company now unfortunately. The primary money man withdrew his funding and flogged the IP to the company I was trying to work a deal with. Such is the mercenary world of start-up tech and angel investors I guess.

 @wintertree Agree on the smoke test, it's a really good way to show effectiveness over time with different filtration models. Don't use a smoke machine though. They only work in a 1m cubed space, beyond that the smoke is too heavy and sticky (yes sticky). Smoke bombs however work a treat in a large space and if you film it and do so with time-lapse you can clearly see the Venturi effect of the air filter, the removal of the dirty air, and distribution of the clean air.

@bruxist Something I forgot to add earlier is that you need to look at solutions that meet or are aligned with the Chinese (I know, but they are way ahead of us on this) GB-T standards for air filtration. I would also want to see independent validation for the removal of the 'airborne' virus by a trusted lab like Institut Pasteur or the equivalent. There should also be a test cert for airborne particulate matter. 

@wintertree/@jkarran you don't want to vent the air to somewhere else, you need to introduce clean air at the equivalent to which you are removing dirty air. Venting, unless to the outdoors, just moves the problem around and doesn't create good air circulation.

In reply to bruxist:

Does the building have a smoke vent system like a high rise tower typically does? 

In reply to BRILLBRUM:

Not the first time that I've posted a non-climbing query to these forums and found a degree of expertise, directness, and openness you'd be hard pushed to find in many academic depts... Thank you! Am looking at Rensair now, & will

The workplaces I'm dealing with at the moment all have one door that opens directly to the outside air. I'm sure there'll also be ones that are enclosed spaces with only internal doors opening to internal corridors but, for now, the ones that are open to the public are all walk-in from the street, same as shop units would be. Should this make any difference to thinking about the LPH & frequency of ACH? 

I'd never come across Corsi-Rosenthal cubes before; now I'm engrossed in reading & watching videos about them. Very inspiring - I have one Uni/community collaborative project that I think might be usefully redirected temporarily... Will DM you this evening.

And thank you particularly for taking the care to include those warnings about ionisation etc. I had got that far in my research and come to the conclusion that I needed to avoid such 'solutions', but as I said in my OP, this isn't my field and I'm always wary of the limits of my own expertise.

In reply to jkarran:

Generally once the urgency's been acknowledged, LAs run with the principle and don't kick off about budget. The problem with this zone of buildings is I believe that they're stable as is, but need demolishing owing to asbestos. Vents could go in the frontage but would vent directly onto a public area.

In reply to bruxist:

I really liked that when I looked it up after the post.  The circular symmetry feels like it should give a very good airflow for most rooms (vs common rectangular units with more limited flow zones), and the pre-filter should greatly extend service life.  The whole thing looks like it was properly designed by experts rather than thrown together by a general consumer electronics group…

Re: ionic precipitators etc, SAGE had similar to say to BRILLBRUM - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/...

In reply to BRILLBRUM:

I’m sorry to hear that.  I hope that you’re not too discouraged should another opportunity arise; it’s all a learning experience…

Indeed.  I’m just going to skip past my rant about arguing with a brick wall and state that when dealing with a mixture of positive pressure facilities including HEPA filtered, majority recirculated air in the same building space as passively ventilated offices, the relevant UK guidance on covid air handing was highly sub optimal if applied to individual rooms and not holistically.  

In reply to wintertree:

I've been back in one larger building recently which had a cracking HVAC system installed last year. Unfortunately it also had a cut-out which switched it off every hour or so, the default being 'off'. The engineers showed me how to turn it back on, and I then showed the workers how to monitor it & turn it back on themselves. That was a workaround to deal with building managers who were following the basic HSE guidance, then thinking 'job done', without consideration for the fact that a state-of-the-art mechanical ventilation system isn't worth s**t unless it's actually operating... It's quite challenging when there's a Bobcat Goldthwait in charge of a building.

I haven't got the more recent concessions to improve air quality by talking about covid at all, btw. I've monitored air quality during meetings & used the live graphs from the Aranet 4 to demonstrate the impact of the C02 on cognitive capacity. It might be a bit TED-talk showy & exaggerated, but when an hour into a meeting I say something like "Do you all realize that you're now twice as stupid as you were before this meeting started?", then show the deterioration in air quality & explain what it means, the conclusion that full-time wages are being paid for half-time brains seems to cut through in a way that concern about airborne viral threats doesn't.

In reply to Andy Hardy:

I don't think so, but I haven't seen the plans for the whole building, or zone; only for individual units, which I needed for dimensions. All of these buildings are low-rise though.

In reply to wintertree:

Thanks for that EMG paper. The quality & clarity of SAGE papers throughout has been astounding; also astounding, the degree to which UK Gov has disregarded them.

In reply to bruxist:

If it does have a smoke vent system (and it doesn't have to be a high rise) it could potentially be repurposed to provide a serious amount of fresh air!

Systems I've worked on typically have 2 or more risers running up the building to fans on the roof. The vents open on the floor with the fire and the fans either suck or blow depending on where the fire is. Fans are usually variable speed so you can control the airflow

In reply to bruxist:

There is a cracking paper on airborne pollution on cognitive ability where the study subjects are prem league baseball umpires. The study follows them around the circuit from inner city to rural stadiums and maps their ability to make snap/complex judgement calls. Completed over a number of years it shows that there is an 11% drop in capability/accuracy relative to the environment.

will dig around for it when I get a mo - the relevance here is that something similar happens in enclosed environments (lecture theatres/classrooms) over time too as we know, and the answer is - clean air.

In reply to bruxist:

With respect to the ‘Rona’, opening a door to the outside world is no bad thing, it induces a forced air change, and the movement of people will also cause disruption of the static air in the room. The main thing that you need to take in to consideration is that yes you have essentially vented the room, but you have also introduced a new set of contaminants and as soon as you close the door you have a sealed box in which you need to enact a full air change as quickly as possible so as to get back to a safe level of airborne contaminant.

actually - I should say, less dangerous/less potential for contamination. No filter will completely remove all of the airborne virus, it’s always 99.xxx% effective.

Of all the solutions to the airborne virus, the only one the US CDC recommends is HEPA/air filtration and the FDA/EPA shut down sales of any solution that could not prove effectiveness with independent lab test results, and California put in place a bill/requirement called CARB of which the production/by-production of ozone by a technology will render it illegal for sale - so agin HEPA.

In reply to bruxist: on this, HVAC systems are incredibly energy hungry. The more effective the filter, the more energy needed to ‘suck’ the air through the filter and obv’s over time as the filter clogs (and actually improves filtration as it becomes more dense) that power consumption goes up. One way to improve HVAC efficiency is to actually dial it down and introduce a non-mechanical duct/fascia that uses a forced drop in air pressure across the duct opening to cause entrainment, this creates ‘free’ movement of air and has the potential to increase the efficiency of the HVAC rather a lot. Again, human thermal plume also increases the efficiency as your getting free movement of air via hot people.

I’m loosely describing a concept I worked on, but I’d be surprised if the HVAC industry isn’t also looking at this.

In reply to wintertree:I loved what I was doing but our major investor couldn’t see beyond the money, and we were admittedly burning R&D cash somewhat in pursuit of our holy grail. So I get his reticence to splash more cash as he’s not seen the big early win relative to what he thought was possible as a result of the pandemic.

I fell on my feet and am now working for a consultancy and have been pimped out to a big energy/oil company to help them greenwash themselves. I’m partly thrilled to be doing some good, solid, and well funded evidence based work/partly horrified to be working for a company that behind closed doors doesn’t really give two shits for sustainability just so long as it keeps making money whilst at the same time appearing to be all touchy-feely.

Pays the bills though.

In reply to BRILLBRUM:

And this is the paper https://www.journals.uchicago.edu/doi/pdfplus/10.1086/698728

In reply to Andy Hardy:

Thanks Andy. I'm on holiday for a couple of weeks, otherwise I'd be able to find out pretty quickly. But I very much don't want to be sending requests for info into work whilst I'm off; might set a precedent I'd come to regret! I'll look into it when I'm back. Meanwhile I wanted just to get ideas & advice and let it all stew in the back of my mind for a couple of weeks.

I couldn't resist having a peek at the buildings on Google satellite view though. They're early 70s flat-roof buildings, and the roof area is very sparse compared to other buildings in the same area - no visible vents or fans or indeed anything.