Posted by Jeff Wahl on 3/15/2023 to UV System Education
This article examines two different types of residential ultraviolet disinfection systems in an attempt to identify the long term operating costs of each and the environmental impacts associated with their operation. This comparison is not manufacturer specific, and is meant to highlight the differences in technology and implications for residential water treatment applications.
Mercury Arc UV Systems
Emits electromagnetic energy from a mercury arc lamp.
Currently the industry standard for residential uv water disinfection systems.
UV lamps in these systems emit a broad spectrum of radiation that disinfects the water. An important part of this process is the quartz sleeve, which prevents the water traveling through the ultraviolet chamber from coming directly into contact with the electrically charged lamp.
LED UV-C Systems
Utilizes deep-UV light-emitting-diodes (LED).
New emerging technology for residential uv water disinfection systems.
Since the diode is the source for the UV Ray, there is no requirement for a UV lamp or quartz sleeve as there is with traditional UV technology. High-power-density UV-C LEDs and advanced controls allow for easy maintenance and economical space considerations.
Mercury arc systems require replacement of the lamp in approximately one year's time. The quartz sleeve in these systems should be replaced every three years. These are generally accepted intervals for most manufacturer’s systems maintenance requirements. Whether installed vertically or horizontally, space that equals the length of the UV chamber must be left for the removal of the lamp and sleeve for the required ongoing maintenance.
LED systems do not have lamps or sleeves, and instead have recommendations for the diodes to be replaced at either three year or ten year intervals, depending on the system. As a result, there is no need for annual maintenance on an ongoing basis. The LED diodes can be accessed through threaded caps on most systems, which do not have the same distance requirements as mercury arc systems.
Most People do not Consider Maintenance when Purchasing a UV System
An often unknown part of mercury arc uv disinfection is the generation of heat within the uv chamber when the lamp provides rays with no water flow. The heat generated can result in quartz sleeve fouling's as it acts to oxidize iron and/or sulphur present in water, as well as increase calcification adherence if calcium and magnesium (hardness) are present.
Heat generation with no water flow for extended time periods can also dry out the o-rings that are providing a water tight seal on the sleeve. Extreme cases can result in flooding.
Due to the unique properties of UV-C LEDs, fouling is much less of a concern as heat discharge is managed at the back of the system and not on the quartz lamp or sleeve where fouling occurs. “Instant on” LED technology allows for powering the LEDs only when water is flowing, thereby eliminating the heat build-up that results in the fouling found in systems using permanently powered mercury lamps.
Most UV Lamps are NOT RECYCLED when no Longer Required
Conventional UV lamps contain mercury, but UV LEDs are free of any hazardous materials. This eliminates the risk of a mercury spill if a lamp breaks and exposure once lamps reach landfill sites. Mercury is often an unknown component in UV lamps / bulbs and is disposed of without knowledge or intention.
Due to the fragile nature of lamps and sleeves, packaging usually includes protective wrap or insulators within the cardboard boxes or tubes they are shipped in. Repetitive replacement of UV lamps over time will increase volumes in landfills when packaging and lamps are not recycled properly.
Over a ten year period, following recommended manufacturer replacement intervals, there would be 10 uv lamps and 3 quartz sleeves required for a traditional mercury arc system. A ten year LED system would require no replacement components over the same time period.
Watts & kWh
Power is required to operate both systems. Mercury arc systems draw an average of 40 to 60 watts of total power continuously, 365 days a year.
With about 10 to 20% less usage than mercury arc systems and flow activation, UV LEDs operate at significantly less total power consumption. This is due to the systems turning on and off with water flow and the diodes only being on when water is running through the system.
It is reasonable to say that LED systems save
between $60 and $70 dollars per year
in operating costs when compared to mercury arc systems.
Total Power Usage - Yearly Comparison
60 Watts = 0.06 kWh
60 * 24 Hours = 1440 Daily Watts
1440 Watts = 1.44 kWh per day
1.44 kWh * 365 Days = 525.6 kWh
525.6 kWh * 0.15 = $78.84
LED 20% Calculations
1440 Daily Watts * 20% = 228
228 Watts = 0.288 kWh per day
0.288 kWh * 365 Days = 105.12
105.12 * 0.15 = $15.78
LED 10% Calculations
1440 Watts * 10% = 144
144 Watts = 0.144 kWh per day
0.144 kWh * 365 Days = 52.56
52.56 * 0.15 = $7.88
Canada, June 2022: The price of electricity is 0.114 U.S. Dollar per kWh for households.
$0.114 US to Canadian Dollars ($1.34) = $0.15
LED consumes less than 10 - 20% energy depending on the usage requirements.
Total Cost of Operation
The purchase price, including annual costs for maintenance and power consumption, should be considered in order to determine the total cost of operation over a fixed period of time. Some mercury arc systems have lower initial purchase prices, but when factored over a ten year period, have a total cost which exceeds that of LED systems over the same time period with maintenance and power considerations factored in. If maintenance is completed by companies rather than homeowners, the frequency of service calls and fuel usage adds to overall costs and should not be forgotten. Environmental costs are difficult to determine in a quantitative figure, but are part of determining the overall costs of operation as well.
Best Practice Recommendation
Consider both technologies when purchasing a UV disinfection system and make sure to check the manufacturers recommendations for required maintenance. Considering the total cost of operation over the lifespan of the system is a good practice. If you are unsure or have questions, consult a certified water treatment professional who can provide you with the necessary information.
Volume 6 – Issue 8 Wahl H2O - Water Awareness
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