«Technical Guide on Energy Reduction by Choosing The Right Air Filter Includes: MERV References Filter Application Guidelines Handy HVAC Formulas ...»
Technical Guide on Energy Reduction by
Choosing The Right Air Filter
Filter Application Guidelines
Handy HVAC Formulas
HVAC Rules of Thumb
Clean Air Solutions
Energy - The Driving Force 3
Maintaining the Building Intent 4 Types of Air Filters 5 Selecting the Right Filter 6 HVAC Components on the Air Side 8 Energy Calculation 9 Energy Cost Index 11 Handy Industry Conversions 12 Industry Terms 30 Industry Abbreviations 34 Handy Tidbits & Formulas 36 Camfil - Clean Air Solutions 39 Publications with additional detail on items referenced in this
ASHRAE - American Society of Heating, Refrigeration and AirConditioning Engineers (www.ashrae.org), Various Handbooks and Standards
HVAC Equations, Data & Rules of Thumb, Arthur A. Bell, Publisher:
McGraw Hill Institute of Environmental Sciences & Technology, Various published Recommended Practices (www.iest.org)) Industrial Ventilation, Manual of Recommended Practices, ACGIH Historical materials as published by Camfil, the Cambridge Filter Company and Farr Company.
For the latest copy of this publication in hard copy or PDF form contact Camfil at email@example.com.
The information in this pamphlet is for reference purposes only.
Camfil makes no warranties, expressed or implied, concerning the application of this information.
© 2014 Camfil, USA Energy - The Driving Force Heating, ventilating and air conditioning systems (HVAC) account for more than 40% of the total energy used in North America and 30% worldwide. While each building will have varying costs based upon geography, climate and utility cost for each Kilowatt hour, we are all feeling the effects of global economics and the ever fluctuating prices of fuels.
Commercial Building Primary Energy Consumption Breakdown (from BTS, 2001;
ADL, 1999; ADL, 2001) Additionally, as we all know from a personal standpoint, energy prices are predicted to increase without a leveling in sight. The following chart notes the predicted energy increase in all forms through 2030. If we are going to practice sustainablity and move towards the ‘green’ concept, we need to reduce energy consumption in any area feasibly possible.
Energy Information Administration (EIA), International Energy Annual 2004 (May-July 2006), web site www.eia.doe.gov/iea.
In a standard HVAC system a filter may be responsible for up to 60% of the energy cost to move air through the system. An air filter creates resistance to airflow which makes the fan work harder to move the air required to heat and cool the building.
As the air filter becomes dirty it will increase in resistance thus requiring the fan to work even harder using even more energy.
Some systems are further energy challenged because they require multiple stages of filtration to protect a process, such as a semiconductor or pharmaceutical manufacturing facility where higher grades of filtration are used because of the cleanliness requirement of the end product. These facilities use HEPA filters which have very dense media and require three to four times the power to move air through the filters. Hospital operating suites would also have these high efficiency filtration requirements and would use similar amounts of energy.
Maintaining the Building Intent To control future expenditures it is important that a building’s HVAC system be maintained and operated under the intent of the original design engineer. When a building undergoes major modification, or use changes, the HVAC system is often overlooked. Before any major modification, or building use change, the HVAC system should be examined by an HVAC engineer to ensure that cooling and heating demand may be met and that the comfort of the occupants is not compromised because of reduced ventilation air, or a reduction in the removal of contaminants by air filtration. Additional ventilation, or filtration, may be required if additional pollution generating components are added to the structure (IE: high volume laser printers or copiers).
The HVAC system should also be maintained as close as possible to its original pristine condition where the duct work and coils are free of contamination, sludge, or fouling. Moisture control is also paramount in maintaining the performance of the system and ensuring the proper indoor air quality (IAQ) of the building. A coil should be protected from airborne contaminants by a filter that has at least a minimum efficiency reporting value of 6 (MERV 6) per ASHRAE Standard 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size.
The filter should also fit securely in the frame so filter air bypass is all but eliminated. Dirty systems are often the result of poorly fitting filters, not the filters themselves, as a 1/4˝ gap around a 24˝ by 24˝ filter can equal as much as 18% bypass.
We also need to remember that air filters were originally installed in equipment to protect the equipment, not the environment or people. We have learned the hazards of poor environments so our HVAC systems were the natural choice to install higher efficiency filtration to protect building occupants.
The chart above notes the percent of reduction of heat transfer (R-22 type AC coil) with minimum scaling contamination.
Types of Air Filters Given the multitude of building uses, varying climates and geographical environmental air quality, it is no wonder there are so many different types of filters. What type of filter should you apply in your building to protect the integrity of the HVAC system and of course, the building occupants?
The filter on the left has 6 pockets, the filter on the right has 8 pockets, and both are the same length. The filter on the right has 30% more media area and will last longer and use less energy in its life within the system. At 10¢ a kilowatt hour the filter on the left will cost $95.00 per year to operate and the filter on the right will cost $56.00 (2000 cfm per filter & 60% fan efficiency). Some bag filters can cost up to $227.00 per year in energy.
Are you selecting a filter to control contaminants from an industrial process? Are you selecting filters to protect an office building and reduce absenteeism of employees? Are you protecting a critical process that requires ultra-clean air? Will you change your filters on a preventative maintenance schedule, or will you use increasing pressure drop as a barometer?
Your filter supplier can provide guidance. Their representatives work with filtration every day. Filters are a small part of your overall responsibility, so capitalize on their experience.
The American Society of Heating, Refrigeration and AirConditioning Engineers recommends specific filter efficiencies for certain types of buildings and has assigned values to allow easier selection of the appropriate filter. The following chart notes some common filter applications.
Application MERV Light duty residential for coil or heat exchanger protection, light 1 to 4 commercial for protection of HVAC and industrial equipment.
Superior residential for removal of allergens, light duty commer- 5 to 8 cial, split systems and roof tops.
Superior residential for removal of allergens, commercial office 9 to 11 buildings and institutional.
Superior commercial office buildings, superior institutional, 12 to 13 removal of respirable particles.
General hospital areas, low-level surgical suites, smoke removal, 14 to 15 superior commercial buildings.
High risk surgical suites, hazardous material capture, clean rooms, 16 to HEPA HEPA level protection.
General recommendations. Consult ASHRAE Systems & Equipment Handbook or www.camfil.com for specific application guidance.
The following chart allows you to compare the current MERV values from manufacturers’ literature to other standards that may be referenced in other literature or specifications.
Filter Efficiencies & Corresponding Values of Current Filter Testing Standards
MERV is Minimum Efficiency Reporting Value per ASHRAE 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size Dust Spot Efficiency and Arrestance are values from ASHRAE 52.1, Gravimetric & Dust Spot Procedures for Testing Air Cleaning Devices Used in General Ventilation for Removing Particulate Matter EN779 is the European Filter Testing Standard, Particulate Air Filters for General Ventilation.
Selecting the Right Filter Once the required filter efficiency has been established through guidance from cognizant authorities, how do you select from the multitude of configurations available? Do you select a flat panel pad, a fiberglass throw-away, or a pleated panel as a prefilter?
For your final filter, do you select an extended surface pocket filter (bag) and, if so, how many pockets, what length and what type of media? If you select a rigid box style filter, do you select one with glass mat media, or high-lofted media, in a deep pleat or mini-pleat design, with fine fiber media which removes particles through a mechanical process, or coarse fiber media that enhances its performance with an electret charge?
The answers are not always straight-forward as each filter manufacturer probably has a system somewhere where it may prove to be the best selection. You should always review your options, for your unique application, with your filter supplier, or preferred filter manufacturer.
We will concentrate herein on recommendations for selecting a filter based upon its actual cost of ownership. This includes the cost of the filter, the amount of time it will last in the system, if it will maintain particle capture efficiency throughout its life, and perhaps the most critical factor, the amount of energy that it will use in its period of operation.
For product considerations we should always look at the amount of media area, the type of media used to capture the contaminant and the configuration of the media and filter pack. From a low efficiency panel filter to the highest grade HEPA filter the more media area exposed to the airflow in a given space, the more value the filter will have in terms of lasting longer and using less energy in its lifetime. The concept is analogous to duct selection. When a larger duct is selected to move a given amount of air, the resistance to airflow though the larger duct will be less, resulting in less required horsepower to move the air. As an example, a 6˝ round supply duct will offer 110 cfm of air per 100 feet of duct with a resistance to airflow of 0.10˝ w.g. An 8˝ round duct under the same parameters will have a resistance to airflow of only 0.025˝ w.g., only 25% of the 6˝ round duct. The fan will require less horsepower to move air through the 8˝ duct as opposed to the 6˝ duct.
An air filter with 15 pleats per linear foot exposes over 30% more media to the airflow than a filter in the same configuration with only 10 pleats per linear foot. The filter with the increased media area has more paths for the air to move through the media, creating less resistance to airflow over its lifetime thus requiring less horsepower and less energy.
A 2˝-deep pleated panel filter with 10 pleats per linear foot will not last as long as another pleated panel filter with 15 pleats per linear foot. The filter with fewer pleats will also use more energy while in operation as it will increase in resistance at a much faster rate with dirt loading.
Final filters are available with as little as 40 square feet of media to well over 200 square feet of media. Without considering the Both filters are 24˝ by 24˝ by 12˝, the filter on the right has double the media area of the filter on the left. The filter on the right will last longer and offer significant energy savings. At 10¢ a kilowatt hour the filter on the left will cost $127.90 per year to operate and the filter on the right will cost $53.50 (2000 cfm per filter & 60% fan efficiency). Some bag filters can cost up to $238.60 per year in energy.
extended life of the product with the higher amount of media, the additional energy cost to move air through the filter with less media can be well over $100 per year.
Another determining factor for longer life and lower energy usage relates to configuration losses. Each filter has construction components that restrict airflow. A properly manufactured filter does not have air pockets that can cause turbulent airflow and increase resistance. Additionally, media spacing must be dynamically optimized so air flows through the filter freely even as the filter loads with contaminant. It is also important to maintain media exposure while loading with contaminant through the use of
• tapered pockets on bag filters
• tapered deep pleats on box filters
• and, radially configured pleats as opposed to v-style pleats on medium efficiency prefilters.
Filters are only one component of an HVAC system, albeit one of the most important. Reducing the pressure drop through the air filters can increase airflow to the space and save energy while ensuring that the occupants of the building are protected from contaminants.
Reducing energy and maintaining efficiency will contribute to the requirements of LEED certification. LEED is a registered trademark of the United States Green Building Council. Please refer to www.usgbc.org for additional information on LEED.
Filters will use additional energy as they become loaded with contaminants. If allowed to operate to published final resistance levels, a MERV 14 filter may use up to 50% of the total energy required to operate the fan. Operating to a filter’s published final pressure drop rarely has an economic advantage as the energy penalty to move air through a dirty filter far outweighs the cost of replacing the filters. Final recommended pressure drop, as published in manufacturers’ literature is a maximum.
Ideally filters should always be evaluated using pressure drop versus the actual air velocity of the system. Your manufacturer can provide additional guidance here because your actual values, in your system, can vary widely.