UV Dose and Dwell Time

[darkbluesky]

Hi,

I was reading the detailed information and argumentation in AAP about UV filters, and doing my own calculations in order to better understand it. I have to admit that I agree with most of the approach explained, but there is one thing it seems I can't understand. To put it simply I'll use an example:

Let's take two UV Filters which are the same in everything except in the length of the bulb (so filter length too), for example (I take simple values to ease the reasoning):

Filter A:

P = 55W HO LP Lamp
EffUVC = 33%
L (lamp length) = 50cm
Dq (Quartz sleeve diameter) = 4.5cm
Dt (Body tube internal diameter) = 10.0cm
S (section) = 63.6cm2 = 0.00636m2
Flow = 1200 gph

Filter B:

P = 55W HO LP
Lamp
EffUVC = 33%
L = 100cm
Dq = 4.5cm
Dt = 10.0cm
S (section) = 63.6cm2 = 0.00636m2
Flow = 1200 gph

So the single difference is the length of the lamp (connections distance); filter A is a compact version and B the long version. The rest of parameters are the same.

Note: I take the distance between pipe connections as the lamp length. I could have added another parameter for the distance between pipe connections, but it'd have been proportional to lamp length and close to it, and morevoer it would not change the conclusion.


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I calculate the final dose for each filter under the same conditions. Please note that if you redo the calculations with the data written here you could find very small differences, these are just rounding errors:

gph/w (the same for both):

A: 1200/55 = 21.8 gph/w
B: 1200/55 = 21.8 gph/w

Dwell time (in seconds):

A: 2.49s
B: 4.97s

Calculation example:

Q=1200 gph*3.78l/g=4536 l/h = 0.00126 m3/s -> v=Q/S=0.00126/0.00636=0.2012 m/s -> L/v = 0.5/0.2012 = 2.49s (and for B, 1/0.2012= 4.97s)

Spectral Irradiance (at quartz sleeve surface):

A: 25.68 mW/cm2
B: 12.84 mW/cm2

Calculation example:

Spectral Irradiance (at quartz sleeve surface for UVC wavelength)=P*EffUVC/(pi*Dq*L)=1000*55*0.33/(3.141592*4.5*50)=25.68 mW/cm2

Note: Here I calculate the irradiance in a simplified way, considering the lamp to be concentric with sleeve. Some lamps are 2G11 format (sometimes, in compact filters), which changes that. I have calculated it correctly in that case (it is a longer calcualtion) and the result is similar although a bit higher (~27/28 instead of 25). For this example I stay with the direct calculation as shown here, which imo is enough for our objective.


Dose (at quartz sleeve surface):

A: 63.9 mJ/cm2
B: 63.9 mJ/cm2

Calculation example:

Dose=Dwell_time * Spectral_Irradiance (at quartz sleeve surface) = 2.49s*25.68mW/cm2=63.9 mWs/cm2 (=mJ/cm2). And for B filter 4.97*12.84=63.9 mJ/cm2.
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As you can see both produce the same dose, because although one dwell time is half the other, the irradiance is the double (same watts apply to half surface).

This comparison could have been done with data/filter characteristics that yields two smaller dwell times, for example 0.75 & 1.5s. And also with two different UV filters which, for different installations/flows, give the very same gph/w but very different sterilizing doses (ratio > 5...), etc.

As the dose is what matters to kill microorganisms (in general, but more evidently when all other parameters are just the same, including tank/pond recirculation, cleaniness of quartz sleeve, etc) what I wonder is, which filter deserves a "High Dwell Time" UV Filter designation? or what matters more, is really important the Dwell Time in the case two filters produce the same dose at the end, so they will clarify/sterilize the same ? (Of course considering equivalent cleaniness, filter gap, and leaving aside turnover, which is important but independent of dose: it is more related to size for a given dose capabality).

I'm tempted to say that the most important parameter in a UV filter is the dose for a given flow and the filter gap / maximum distance/radius from lamp (then turnover ratio, installation, cleaniness of sleeve, cleaniness of water, etc. comes later).

If so, then which is the dose (mJ/cm2) to consider Level 1 sterilization and which is the dose (mJ/cm2) to consider Level 2 sterilization, (assuming a good turnover ratio and considering a gap less than 3cm)?

Thanks,

[Carl]

If I understand the point of your post, I would say that "dose" is similar if not the same as "dwell time".
This is where width of the chamber comes in and why a T8 UVC lamps can actually provide better dwell time than a T8 UVC lamp of equal UVC output

See:
www.americanaquariumproducts.com/UVSterilizerDwellTime.html

A good way to test (which is what I did to test) is to use exact same flow rates with different UV configurations on the same size aquariums. Then mark the time to clear something such as Potassium Permanganate.

[Carl]

As well, level 1 and 2 sterilization are determined the way they are is for simplicity.
As noted in the UV Sterilization article, the formula has many flaws. We are for one assuming all lamps are equal, the gap in the chamber is the same (which actually varies considerably), & much more.
In fact as per chamber design, this is where I found with the early Nektonics UVs fell short in actual use and where common canister filter UVs also fall short as much of the water that passes through fails to have adequate contact with UVC energy

www.americanaquariumproducts.com/AquariumUVSterilization.html

[darkbluesky]

Yes, although technically (or better, conceptually) I can't agree about dose and dwell time (seconds) as being equivalent or the near the same, I indeed agree that from a practical point of view (I guess this is your point) dwell time could be a first order (or rough) id or selection criteria (although at the end dose per given flow should be, imo, definitive in case of doubt, as in my example). This is why I wondered the mJ/cm2 for different effects. But anyway, with a table like www.rk2.com/uv-information.php or similar we could guess the level of sterilization needed/wished.

BTW, aside of all calculations the way you describe to test with PP is really practical and definitive, I like it. And well, in fact is a good way to clarify it (pun intended ).

When you mention in your articles -point (B) and under "Flow Rate & Turnover Rate Table" part-, level 2 can control also the algae on side of pond, not in water, what does it mean? How it is going to control it and how much effect could be expected, etc? Could you please elaborate about that (your experience) etc? I am very interested on that.

About the distance to wall in UV filter (I call it gap), in your article it is said to have maximum a distance of 3cm between the bulb or quartz sleeve and the filter wall. The distance between actual lamp and sleeve is not counted/not so important? 

Tx

[Carl]

I have read the article you cited several times now. I certainly do not argue its accuracy, however the point of the AAP UV Sterilization article is for practical application. In fact this AAP UV Sterilization article is one that get among the most complaints as to being too complicated, so I certainly am not going to make it even more difficult for the average UV sterilizer to determine the optimum UV since the formula has proven itself to be quite accurate in practical applications when all exceptions are properly accounted for.

As for the gap, this counts the lamp to the outer wall of the chamber as some quartz sleeves are more "loose" than others. I will also note that this 3 cm number again is admittedly rather vague from my own experience, but is meant to provide outer limits. Frankly a tighter fit (as low as just 3 mm in a custom UV with no sleeve yielded some of my best test results.
www.americanaquariumproducts.com/UVSterilizerDwellTime.html

As for algae, if I understand your question, a UV Sterilizer can control algae that is not in the water column by lowering spores in water column. So this is an indirect benefit, but only a minor one as er actual application.
QUOTE: "It is important to have a flow rate that will turn over the pond or aquarium at least once every 2 to 3 hours for green algae control, once every 1 to 1.5 times per hour for disease prevention (Level One Sterilization), or 2.5 to 3 times per hour for stage 2 sterilization (I have achieved effective level one disease sterilization as tested with a bacterial cloud with as little as once per two hours with a good installation in an otherwise well maintained aquarium).
It is also noteworthy that turnover can even be higher yet than 3 times per hours, however both my own observations and professional consultations have shown that increasing flow rate beyond 3 times per hour does not proportionally increase the benefit in a healthy established aquarium (or pond), this includes for algae control on the side of ponds or seasoned live rock in a marine aquarium"

Further Reading:
www.americanaquariumproducts.com/PondAlgae.html

[darkbluesky]

Yes, I see, thanks for the info. I thought it could be because of increased redox potential, not only spores. Not sure if there is an evident increased redox potential due to the use of an UV filter.

BTW, I have seen another topic here about an AquaMedic HelixMax upgraded with a better lamp. Anyway, I have been trying to find information about the original lamp of these AquaMedic HelixMax units without success. Do you know if the original lamp these units mount, are low pressure / HO lamp or instead a medium pressure one? I ask because some time ago I had an AquaMedic 36W.

Thanks!

[Carl]

Jun 23, 2020 1:17:24 GMT -5 darkbluesky said:

BTW, I have seen another topic here about an AquaMedic HelixMax upgraded with a better lamp. Anyway, I have been trying to find information about the original lamp of these AquaMedic HelixMax units without success. Do you know if the original lamp these units mount, are low pressure / HO lamp or instead a medium pressure one? I ask because some time ago I had an AquaMedic 36W.

Thanks!

The AquaMedics originally cam with a medium pressure low output UVC lamp, Upgrading without a ballast upgrade may result in inability to light or short life since high output UVC lamps require a higher surge voltage to start.
In fact this is where many if not most electronic ballasts fail as they are simply not designed to deliver this surge voltage, rather they are designed for standard fluorescent lights of matching wattage ranges.
When magnetic ballasts were banned in the USA back in 2014, ti drove many UVs to be made in China and ended production fo several models of higher end UV Sterilizers (including some of the TMC Vectons & Advantages AAP sells)

www.americanaquariumproducts.com/TMCUVSterilizer.html

Regards;
Carl

[darkbluesky]

Thanks. I have also asked AquaMedic and the "technical consultant" has answered just this: "we are using PL lamps. That´s low pressure". I suspect he is mixing things up. AFAIK PL means Plugin Lamp (PL-L for Long lamps, and PL-S for Short version, according to Philips definition). I have asked him to double check.

On the other hand, I do not understand, some manufacturers make two versions of their UVC Filters, the long and the short one, with the same power (for example www.aqua-forte.com/uv-c/, the two first 75W models the SB621 vs SB387). If they use the same lamp type/technology, then the lamp has a given W/m (m of arc length, so ~lamp length), so if the lamp is shorter, the power must be lower (except if they use amalgam lamps, but normally they state clearly that it is an amalgam lamp if so). As they do not explain they are amalgam lamps I think they are not. But then, how is it possible? The only answer I could think, is that the longer lamp is just not optimized (for the same length the lamp manufacturer could put more power). Do you know if it is possible/normal?

Regarding dwell time, although it is different (in seconds), if they have the same UVC power output and the filter have the same section (as in the case of these 75w models), then the irradiance is the same and they are equivalent in sterilizing power for a given flow, but I have a hard time believing they have the same UVC Power in watts.

Thanks!

[Carl]

Jun 24, 2020 1:41:09 GMT -5 darkbluesky said:

Thanks. I have also asked AquaMedic and the "technical consultant" has answered just this: "we are using PL lamps. That´s low pressure". I suspect he is mixing things up. AFAIK PL means Plugin Lamp (PL-L for Long lamps, and PL-S for Short version, according to Philips definition). I have asked him to double check.

My understanding too is for PL-L for Long lamps, and PL-S for Short version

As per AquaMedic. These are a common Chinese made UV Sterilzer, which many now sold are (and all from discounters)

As a seller of a couple of Chinese made UVs and have worked with Chinese manufacturers many times (with a bit of a learning curve on my part), it is noteworthy that they do not deal in business the same way we do in North America or Europe. If I strike a deal for 100 widgets at a certain price, I get 100 widgets at this price. With China, if I order 100 widgets that are say normally $10 each but get them for a price of $9, they make the widgets cheaper and at the same value as $9 (in other words, not the same widgets).
My point is at the price point of these AquaMedic UVs, you cannot be getting a high output UV Sterilizer either in lamp, ballast or both

[darkbluesky]

Yes, I suspect it too. I have received a "confirmation" from AquaMedic, just for info, they say: "It´s low pressure comparable with the Philips PL-lamps. ". So it seems confirmed they are Low pressure, and this would mean that these filters would be quite good (with HO lamps, they would fall at Level 1 Sterilization and close to Level 2 regarding dosing, according to my calculations with 700gph and 1200gph , 11w and 36W respectively), although...

...I have a feeling of lost confidence; if he's mixing up PL (Plugin Lamp) with LP (Low Pressure) how can I be sure he knows what he's talking about? I think he is still mixing things up (willingly or not), maybe to conceal his last wrong answer. So, without better confirmation and adding your comment about these designs/manufacturing, I'll have to fail in the safe side and guess that they came with a medium pressure lamp (just as you told me)...which, btw, in that case, they fall a bit short as Level 1 (close, but they do not reach it for the above mentioned gph). 



For the subject of short and long lamp versions, I still don't get the differences, or reason to make a long one when you can have the same power shorter.

In the example of Aqua-forte I mentioned, it is interesting to note that for the long version they state the efficiency of lamp (25W of UVC Power with the 75W lamp, so around 30%), but they do not say anything like that for the short version...I know that it is a -very unhappy- commercial practice to list different characteristics of products that are alternatives so to guide customer interests and preventing him to compare them, becoming confused, but in this case maybe it is done so to hide something too. Who knows. I still would like to understand if the short and long versions lamps are really equivalent (who would like a longer version of same power? you get higher dwell times but less irradiance/intensity).

I note that the Aqua-Forte design is shared (or 99% close) to other brands design (BlueLagoon, Aquaking, etc), so it seems to me a brandless standard design (chinese) which is licensed. Maybe for the long version Aqua-Forte has asked to work with low pressure lamps, and for the short version they are going a more economical way? But both products are under $200...

But still, who knows? It is hard to be sure and they can't expect customers to buy them just to test. I would prefer for example, a more expensive Sera.de UVC-55X one, which at least it uses a quality lamp (Amalgam), and it uses its own design... not a standard chinese one! It is really complicated when you can't test side by side...

[darkbluesky]

BTW, what are the TMC Pro UV110 quartz sleeve diameter, internal filter/body diameter and length between inlet and outlet? I can't find these infos, and it is a pity: I need these datas to evaluate it, but I can't find these infos around.

[Carl]

Jun 27, 2020 1:23:34 GMT -5 darkbluesky said:

BTW, what are the TMC Pro UV110 quartz sleeve diameter, internal filter/body diameter and length between inlet and outlet? I can't find these infos, and it is a pity: I need these datas to evaluate it, but I can't find these infos around.

I do not have any TMC 110 UVs in stock to check.
As for the sleeve, it is 1" ID and 1-1/8" OD

This UV has a wider gap since it is intended for pond use which volume is generally considered more important.

I do know that years ago I ran a test between it and the Aqua 114 watt and the TMC cleared potassium permanganate faster

[darkbluesky]

Thanks. What a pity not to have confimed the other dimmenions. I have guessed that the inlet body diameter is 4" (10 cm) and that the length between connections is 30" (77 cm). If the sleeve diameter is 1-1/8" (so, the closest the water can be to the lamp), then if performs very well, better (and cheaper) than 2xSera 55X. They are the same at the body internal wall, but the TMC gives almost double dose at quartz sleeve (the sleeve is much thinner than Sera's, which is 4.5cm of diameter instead of 2.9cm). I would have a hard time choosing among these two options. But the TMC seems to be longer than 39" (1 meter), the Sera are just 26", which fits in my available space.

[devonjohnsgard]

Here's a video done with some of the measurements. Some of this conversion went over my head, but this video might be helpful. It's comparing the TMC UV to the Aqua UV.

www.youtube.com/watch?v=EqHfYl2JFog

[darkbluesky]

Thank you very much for this link. I have seen several AAP videos but I missed this one. There they give the needed measurements. I have checked more precisely and I have to correct my last post: the TMC performs very well, but not better than 2xSera 55X, they give higher dose (but they are still more expensive). Thanks

BTW, in that video there is a mistake, for the Aqua it is said 55 mm perimeter when if you calculate it is around 72mm, nevertheless it does not change the conclusions. Nice video!