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NAFA Guide to Air Filtration.
Chapter 13Owning and Operating Cost
By Dirk ter HorstApril 19th, 2012
Another Approach….Air Filter Comparison
OUTLINE
Objective Energy Cost Calculation: 2 approaches Calculation Example & Methodology Comparison Total Filtration Cost Tool’s presentation Conclusions
Objective
Present a practical and easy approach to air filter evaluations + operation based on: End user/customer experience (Pressure drop
and filter life) Standardized filter life indicator (ASHRAE 52.2
DHC) All air filtration associated costs Use of software
Assumptions and considerations
NAFA
Customer experience (Pressure drop and Time)
Constant environmental conditions
Average pressure drop Straight Line
New approach
Customer experience (Pressure drop and time)
Constant environmental conditions
Time vs. Pressure Drop Time vs. ASHRAE DHC Air filter Pressure Drop vs.
DHC Signature
Linear Pressure Drop Approach
Considering the pressure drop changes linearly with time the energy consumption is expressed by:
fof tPPQ
E21000
𝐴=∆𝑃𝑜𝑡 𝑓+12
(∆𝑃 𝑓 −∆𝑃𝑜 ) 𝑡 𝑓
Where:ΔP0 = Initial Filter pressure drop [Pa]ΔPf = Final Filter pressure drop [Pa]tf = operating time[hrs] = average pressure drop
Filter Pressure Drop vs. Time Approach
Considering the pressure drop of the filter versus time, the energy consumption is expressed by:
ftdtP
QE
01000
𝐴=0
𝑡 𝑓
∆ 𝑃 𝑑𝑡
Energy Cost
The energy cost is calculated by:
Linear pressure drop vs. time:
Filter pressure drop vs. time:
fof tPPQ
tcosEnergy21000
ftdtP
QtcosEnergy
01000Where:E = energy consumption [kWh]Q = airflow [m3/s]ΔP = pressure Drop across the filter [Pa]t = the time is operating the fan [hrs.]η = system efficiency (fan, motor & drive) [%]
Transposition…
+ =
Assumption:Air filters of the same efficiency and media type
have captured the same amount of dust if they are exposed to identical environmental conditions over
the same period of time
Two filters to work with… Example
Filter A: MERV 14. 24x24x4 Box type. Initial pressure drop: 0.35 inch H2O DHC at 1.5” H2O: 67grams. ASHARE Dust 2000 cfm $70.0/unit
Filter B MERV 14. 24x24x4 Box type Initial pressure drop: 0.3 inch H2O DHC at 1.5” H2O: 143 grams. ASHRAE Dust 2000 cfm $70.0/unit
Linear approach… for 100 filters
Two different filters without DHC considerationLinear approach:
US$ 701.74/year
Two different filters with DHC considerationLinear approach…
US$ 9,682,90/year
Curve approach… for 100 filters
Two different filtersWith DHC considerationCurve approach
US$ 9,173.82/year
Optimization Linear approach..
Pressure Drop of filters at change-out time for financial optimization:
0.85inch w.g.
Cost reduction: $9,712.03/year
(for 100 filters)
Optimization… DHC curves.
Pressure Drop of filters at change-out time for financial optimization:
0.60inch w.g.
Cost reduction: $10,134.13/year
(for 100 filters)
Compare Apples to Apples…
Filter Type Filter depth Frame type Frame material Filter media material Face screen Incinerable Filter brand/make Test standard Air flow Maximum final pressure
drop Efficiency Test dust
Test Laboratory Test filter procurement/source Age of test report UL 900 compliance
Fan type Reasons for change out time Other considerations
Practical approach to TFC
Easy calculation….Let’s see a software tool:
http://filtrationcost.lpdtechnologies.com
Conclusions
Use the ASHRAE 52.2 DHC curve information when evaluating the financial impact of air filters.
Calculate the recommended filter change out pressure drop (optimization).
The cheapest filter nor the filter with the lowest initial pressure drop are necessarily the best solution.
There is a WIN-WIN opportunity for the customers and the industry!