Predicting Energy Use & Operation Cost of HVAC Air Filters

Supervisor: Steven Rogak
Researcher: James Montgomery

Introduction

The standard method of testing and classifying air filters is to determine the particle removal efficiency, which is the percentage of particles removed from the air stream at a certain air flow rate for various particle sizes. Existing standards do not account for air filter energy use in classifying filter performance.  As energy reduction in building operation becomes more prevalent a means to accurately determine the energy use of air filters and to improve filter energy efficiency is required. The methods currently proposed to compare filter energy efficiency do not allow for an accurate means of calculating energy use or operation cost under varying air flow rates which precludes them as reliable standards for filter comparison.

Method

To allow for comparison of filtration solutions for any application we endeavoured to develop a model to calculate energy consumption utilizing results from standard filter performance tests and knowledge from filtration theory. This ensured that the resulting model could be easily implemented while maintaining sufficient accuracy to differentiate between like filters. The model was then used to predict the energy and performance of primary filters (box, bag and V-type) from various manufacturers installed in conditions simulating Vancouver. The model was also used to compare the relative performance of system conditions such as electricity price, atmospheric aerosol concentration and system flow profile, among others.

Results

The comparison of the model results for filtration solutions in Vancouver illuminated the relative cost and energy performance for the three types of primary filters investigated. The general trend, across all manufacturers, was that bag type filters are the least costly solution due to low initial cost and energy efficient performance. V-type filters were found to generally be more costly solutions than bag filters because of a higher initial cost. They were, however, found to be the most energy efficient option. Box filters were found to be the most costly filtration solution do to moderate initial cost and high energy consumption.

Electricity prices were shown to have a large effect on the annual cost of filter operation. Increased electricity prices raises the cost of filter operation and widens the performance gap between energy efficient solutions such as bag filters and energy intensive options such as box filters. The particle concentration in the filter airstream was shown to also increase the cost of filter operation. A comparison of filter operation under variable-air-volume (VAV) versus constant-air-volume (CAV) operation showed that VAV operation was more energy and cost intensive than CAV operation for the same average flow rate. The assumption of CAV operation was shown to provide accurate relative ranking of filter performance for filters to be installed in a VAV system and provided for a simpler modeling and calculation method for filter comparison.

Conclusion

The model developed allows for accurate comparisons of the energy use and operation cost of different filtration solutions using knowledge from existing filter testing. The model will allow for the installation of the most energy efficient and least costly filters subject to any building’s unique operation allowing for a reduction in the overall building energy use.

Future work will focus on experimental validation of the model using full scale and laboratory testing.

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Predicting the Energy Use and Operation Cost of HVAC Air Filters Under Variable-Air-Volume Operation: James F. Montgomery, Sheldon I. Green, Steven N. Rogaka