ENERGY SAVING


and energy consumption, reducing bio- contamination on air handling surfaces which are exposed to HVAC system airflow reduces the possibility for potentially harmful pathogens to be aerosolized and delivered to the buildings breathing zone, garnering improvements in occupant productivity and health. While neither of these technologies is considered a substitute for proper filtration or ventilation, they may certainly help enhance the effectiveness of both. Understanding that UV-C and NPBI are both electrically powered devices that should remain operational continuously throughout the year to produce maximized results, the analysis of associated energy consumption is relatively straightforward once device sizing has been accomplished.


Using the coil shown in the diagram (right) as


our example, we size and analyze the life cycle attributes of both technologies. We are assuming a large commercial air handling system moving 30000 l/s (60000 cfm) of air, for a nominal 525 kW (150 tons) of cooling capacity at an air velocity of 2.5 m/s (500 fpm) through a 12 m2 (120 ft2) cooling coil, with four individual 1800 mm (72”) wide by 1500 mm (60”) tall coils stacked in a 2-high by 2-wide configuration.


UV-C lamp sizing based on ASHRAE


recommendations for 7.5 lamp watts per 0.1 m2 (ft2) of coil surface area would yield a minimum requirement for 900-watts of installed lamp capacity. Because UV-C lamps are only available in specific nominal size increments we might


look at specifying a quantity of (8) high-output lamps, each 1500 mm (60”) long and rated at 155 watts per lamp, with 13,000 rated lamp life hours (1.48 years) which is time allotted until bulb replacement is necessary. (4). If (2) lamps are installed for each individual coil we end up with 1,240 installed lamp watts, slightly more than required but still appropriate. NPBI manufactures have evaluated and


rated their product for the removal of coil bio- contamination, specifying that ionization bars be placed at the top of the cooling coil(s). In this position a single ionization bar can effectively cover 1500 mm (60”) of vertical coil height. The bars are provided in 150 mm (6”)


incremental pieces, which are joined together in the field to assemble the bar length required to cover the length of any cooling coil. In this case we might specify (2) 3600 mm (144”) bars, one bar for 2-coils, with a single power pack providing ionization voltage. The power requirement for this system is a mere 15-watts of total energy consumption, and there are no replacement parts to be concerned with. The diagram also details the NPBI installation for this example. Moving forward with a simple operational cost analysis we will assume both technologies are left running continuously year-round, with an electricity cost of £0.12 pence ($0.10) kilowatt hour (kWh). The following results have been calculated: Q UV-C: £800 ($1086) energy cost per-year Q NPBI: £10 ($13) energy cost per-year.


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Beyond raw energy consumption, certain additional yearly life-cycle costs may also be worth considering. This should include any yearly component or parts replacement and its associated labor costs. UV-C would require approximately £1,775 ($2400) for lamp replacement every 2-years (£887 ($1200) per year). It should be noted that UV-C lamps contain mercury (and perhaps titanium dioxide, as doping to help reduce ozone production) therefore must be disposed of accordingly as hazardous material. UV-C exposure is harmful to humans so


proper system safety precautions must be implemented while servicing, not limited to wearing proper personal protective equipment (PPE) when handing and disposing of lamps. NPBI has none of these concerns or additional ongoing life-cycle costs tied to its value proposition. Revisiting our previous 525 kW (150 ton) air conditioning example, when recognizing that clean cooling coils can potentially result in HVAC energy savings from 10 to 25% each year, we can add an additional £2000 to £6000 ($3000-$8000) in savings to the baseline energy and maintenance cost reductions previously calculated for NPBI. It is clear that this is a technology building owners and operators should seriously consider when striving for healthier, greener, and more cost-efficient buildings (of all types) everywhere.


X www.globalplasmasolutions.com www.acr-news.com • February 2022 31


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