Geary Pacific Supply

Geary Pacific Supply

Frequent UV and Filtration Questions in Schools

Posted on Tuesday Sep 01, 2020 at 11:26AM in General


Q: Can the UV lights be powered by the HVAC unit transformer?

Most standard UV power packs use about 16va. Some a little less, some a little more. Most older HVAC units contain a 40va transformer which is enough to control a standard unit with a standard thermostat. If there are a lot of additional controls or ventilation items added, then it is suggested that the transformer be increased to a 50 or 60va transformer with a built-in circuit breaker, or a separate transformer be used for the UV.

Q: Does the light have to stay on 24/7 or can it be cycled with room occupancy?

Per the manufacturers recommendation, the UV system should be powered on 24/7. With UV we are accomplishing two goals, cleaning the air, and cleaning the coil. While cycling it on with the fan will help treat the air, it will limit the amount of UV exposure time on the coil. Evaporator coils are prone biological growth which can also become airborne and potentially cause negative health effects. Having the UV shine 24/7 will not only protect the air while occupied, it will protect the coil and continue to breakdown biologicals after the business or school has closed for the day. 

Q: Does the UV light kill all contaminants on the filter or do techs still need to change filters with caution?

The UV light is very effective at breaking down surface and airborne biologicals. It is also intense enough that it can eat through the fibers in an air filter. Because of this, the UV should not be shining directly on an air filter. So, air filters will still need to be changed at the frequency required to maintain system efficiency and cleanliness. Techs should practice caution while changing air filters. Using proper PPE and by disposing of the air filter directly into a bag that will contain any contaminants that can fall from the air filter, will provide a safer environment for the servicing technician. 

Q: How high of a MERV rated filter can I put in my HVAC unit?

ASHRAE recommends that MERV 13 air filters should be the minimum used, unless the system cannot handle the added resistance that is present with a high efficiency filter. There are several different factors that determine if using a MERV 13 filter is possible. Things like the blower performance, filter rack size, size and design of ductwork, number and type of registers, or additional factory installed accessories (ventilation, smoke detectors) all add to the total amount of airflow resistance in the system. Each HVAC equipment manufacturer publishes how much resistance a unit can handle. As long as the air filter doesn’t cause the overall system to exceed the manufacturer’s specification, higher MERV rated filters can be used.

Q: What is a filter MERV rating?

MERV is an abbreviation for Minimum Efficiency Reporting Value. The MERV rating tells you how effectively the filter traps small particulates you do not want to circulate through your HVAC system such as dust, pollen, mold, and other irritants. The higher the MERV rating, the more efficient the filter will be in trapping the airborne particles as shown below.


Q: Do filters have the same pressure drop (resistance) as they used to have?

The media used in air filters today tends to allow for higher MERV ratings with the same or less restriction than older, less efficient filters.

Q: Should my UV light have a door shut off switch?

It is not required, but strongly suggested to ensure the light is off during service. Do not look directly at the UV light bulb during service. 



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