Energy Consumed by Filters- Easy and Expensive to Miss

2018-05-21

The most obvious consequence is a HVAC system breakdown, usually a fan failure from the increased load. This is very expensive but also hard to not attribute to the deferred maintenance. Much harder to catch but much more common is the increased energy consumed from a filter that is in use beyond its ideal changeout point.

In the example below, we look at common standard capacity pleat changed out at 3, 4 and 6 months respectively. Standard capacity pleats should be changed out every 3 months in most applications. You can see in both the 4 month and 6 month intervals, the TCO increases despite fewer dollars spent on filters, changeout labor and disposal.

Deferred Maintenance

NAFA, the National Air Filtration Association, estimates that 81% of the TCO of a filter is the cost of energy. In the example above, the cost of energy is 79%, 86% and 94% respectively. In other words – the 4 and 6-month changeout intervals reduced non-energy costs by 25% and 50% respectively, while increasing energy consumption 25% and 110% respectively, on a much bigger base.

Filter Resistance Over Life

The longer a filter is installed, the quicker the DP will increase. This is explained by simply agreeing that a filter is a controlled leak with a very high, but fixed number of tiny holes in its media that allow air to pass through while catching particulates. As the filter catches dust/dirt, the filter’s holes get plugged up one by one, and each incremental plugged hole is more significant in terms of remaining unplugged holes than the previous one. This means that filters seem to load linearly with time to start, but their dust loading to time relationship is actually curved, as shown here.

Total Pressure Drop

This exponential relationship causes deferred maintenance on air filters to be particularly damaging to a building’s energy bill.

Finding the right filter and changeout point is critical to managing your total maintenance and energy budget – be careful not to fall into the common trap of deferred maintenance on HVAC filters!

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