Post by SteveW on Apr 7, 2016 1:52:58 GMT -5
Carl - Thank you for your articles on UV Sterilization. Unfortunately, I must disagree with your analysis of the comparison between T5 and T8 based sterilizer lamps. You wrote:
I agree that T5 lamps are roughly 16% more efficient at converting electrical energy into light energy. But, given two lamps of equal length, equal light output (including identical spectra) and equal flow rates, then the dwell time will be the same, and the germicidal effectiveness will be practically indistinguishable, regardless of the number of electrical watts pumped into each one. (Its sort of like saying that if my car goes 140mph with a 200hp engine, and 160mph with a 300hp engine, then a 300hp HYBRID engine (using 16% less gas) will make my car go 180mph.)
Also - if the manufacturer uses a 5/8" diameter T5 instead of a 1" diameter T8, and reduces the tube sleeve diameter by 3/8" (compared to a T8 fixture), and then reduces the reaction chamber diameter by 3/8" (to stay within 3cm of the tube sleeve) - in that case, the T5 fixture will have a smaller cross section area, which will REDUCE the dwell time for any given volume flow rate.
So, in your example, the T5 produces 12% more output. But you can't add the 16% savings from the electric meter. However, at any given volume flow rate (and assuming identical cross section area), the double length chamber will provide double the dwell time - 100% more, not (as you said) 50% more.
Finally - I have no proof of this next item, but I believe that the UV sterilization process is very closely analogous to heat pasteurization. In the case of heat pasteurization, I found a graph of dwell time required as a function of process temperature. The graph is at www.redpostltd.com/images/lethalgraph.gif. The diagonal line represents equal sterilization effectiveness. Notice that the dwell time scale is logarithmic! At 65c, a certain kill rate is achieved in one minute of dwell time. Reducing the temperature to 56c requires 10 minutes of dwell to achieve the same kill rate. Reducing the temperature to 52c increases the required dwell time to 100 minutes. So, reducing the temperature by 13c would mean removing a 100gph pump and replacing it with a 1gph pump. Small changes in process energy (in this case, heat - but I believe this applies to UV energy in the same way) produce dramatic changes in dwell time requirements. And I mean VERY small changes in process energy - 65c is 338K (Kelvin, an absolute temperature scale), 52c is 325K. A 4 percent increase in temperature here (338/325 = 1.04) from 52c to 65c, results in a 99% decrease in required dwell time. I believe the UV sterilization analog of temperature, is the luminous power rate, watts/cm^2. I believe that the most important design consideration is maximizing light intensity - the last tenth of a watt means more than all the watts before it, and I can't say enough about the importance of premium quality, fresh lamps. Controlling volume flow rates to maintain dwell times, is secondary to maintaining proper light intensity. Of course, once a system achieves a kill rate greater than the target population's reproductive rate (largely a function of the population size when UV is started - its a function of the tank, not the sterilizer) any further increase in light intensity serves mainly to permit (dramatic) increases in flow and reductions of dwell. Some excess intensity is necessary to preclude the effects of lamp aging and chamber fouling.
Anyway - as I said, I have no proof of this last item. But this is how it makes sense to me. If you have any questions, or wish to discuss it further, you can reach me at steve66.oh@att.net
As a rough generalization, the T5 lamp is 16% more efficient, watt per watt of energy used.
This means a T5 25 watt UV Bulb of EQUAL length to a T8 25 Watt Bulb is going to provide more dwell time and thus be a more effective UV Sterilizer.
HOWEVER, many higher wattage UV Sterilizers that use T5 bulbs, also utilize bulbs/lamps that are much shorter.
As an example, a 57 watt T5 as used in the Aqua 114 watt UV is 17.5 inches long (two lamps are used), while the 50 watt T8 UV bulb used in the TMC 110 is 36 inches long (two lamps are used).
So factoring in the higher output (57 versus 50 watts), we have 12% more raw output, then add another 16% for more UVC efficiency (watt per watt of energy consumed), we have 28% more effective.
But next we have to figure an exposure time that is spread over twice the length of bulb and this is 50% more dwell time. So 50 minus 28 and we get 22% more effective for the 50 watt T8 used in the TMC 110 UV!!!
[http://www.americanaquariumproducts.com/UVSterilizerDwellTime.html]
This means a T5 25 watt UV Bulb of EQUAL length to a T8 25 Watt Bulb is going to provide more dwell time and thus be a more effective UV Sterilizer.
HOWEVER, many higher wattage UV Sterilizers that use T5 bulbs, also utilize bulbs/lamps that are much shorter.
As an example, a 57 watt T5 as used in the Aqua 114 watt UV is 17.5 inches long (two lamps are used), while the 50 watt T8 UV bulb used in the TMC 110 is 36 inches long (two lamps are used).
So factoring in the higher output (57 versus 50 watts), we have 12% more raw output, then add another 16% for more UVC efficiency (watt per watt of energy consumed), we have 28% more effective.
But next we have to figure an exposure time that is spread over twice the length of bulb and this is 50% more dwell time. So 50 minus 28 and we get 22% more effective for the 50 watt T8 used in the TMC 110 UV!!!
[http://www.americanaquariumproducts.com/UVSterilizerDwellTime.html]
Also - if the manufacturer uses a 5/8" diameter T5 instead of a 1" diameter T8, and reduces the tube sleeve diameter by 3/8" (compared to a T8 fixture), and then reduces the reaction chamber diameter by 3/8" (to stay within 3cm of the tube sleeve) - in that case, the T5 fixture will have a smaller cross section area, which will REDUCE the dwell time for any given volume flow rate.
So, in your example, the T5 produces 12% more output. But you can't add the 16% savings from the electric meter. However, at any given volume flow rate (and assuming identical cross section area), the double length chamber will provide double the dwell time - 100% more, not (as you said) 50% more.
Finally - I have no proof of this next item, but I believe that the UV sterilization process is very closely analogous to heat pasteurization. In the case of heat pasteurization, I found a graph of dwell time required as a function of process temperature. The graph is at www.redpostltd.com/images/lethalgraph.gif. The diagonal line represents equal sterilization effectiveness. Notice that the dwell time scale is logarithmic! At 65c, a certain kill rate is achieved in one minute of dwell time. Reducing the temperature to 56c requires 10 minutes of dwell to achieve the same kill rate. Reducing the temperature to 52c increases the required dwell time to 100 minutes. So, reducing the temperature by 13c would mean removing a 100gph pump and replacing it with a 1gph pump. Small changes in process energy (in this case, heat - but I believe this applies to UV energy in the same way) produce dramatic changes in dwell time requirements. And I mean VERY small changes in process energy - 65c is 338K (Kelvin, an absolute temperature scale), 52c is 325K. A 4 percent increase in temperature here (338/325 = 1.04) from 52c to 65c, results in a 99% decrease in required dwell time. I believe the UV sterilization analog of temperature, is the luminous power rate, watts/cm^2. I believe that the most important design consideration is maximizing light intensity - the last tenth of a watt means more than all the watts before it, and I can't say enough about the importance of premium quality, fresh lamps. Controlling volume flow rates to maintain dwell times, is secondary to maintaining proper light intensity. Of course, once a system achieves a kill rate greater than the target population's reproductive rate (largely a function of the population size when UV is started - its a function of the tank, not the sterilizer) any further increase in light intensity serves mainly to permit (dramatic) increases in flow and reductions of dwell. Some excess intensity is necessary to preclude the effects of lamp aging and chamber fouling.
Anyway - as I said, I have no proof of this last item. But this is how it makes sense to me. If you have any questions, or wish to discuss it further, you can reach me at steve66.oh@att.net