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© 2017 enVerid Systems, Inc. All Rights Reserved. enVerid Systems Confidential 1
The Relationship between Filter Pressure Drop, Indoor Air Quality, and Energy Consumption
in Commercial HVAC Units
Marwa Zaatari, PhD
NAFA, August 2017
NAFA 2017
History Quiz What was the original job of the filter? 1. To protect cooling coils from particulate contamination. 2. To prevent furnaces from catching fire caused by
fibers stuck on the furnace. 3. To protect human health. 4. No job other than to look cool.
NAFA 2017
Conventional Wisdom
“A dirty filter will slow down air flow and make the system work harder to keep you warm or cool – wasting energy.”
“Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly…. Keeping the filter clean can lower your air conditioner's energy consumption by 5 - 15%.”
http://ecomerge.blogspot.com https://www.servicechampions.net
What is the impact of increased pressure drop on HVAC units performance?
NAFA 2017
We started by collecting field data. 15 RTUs with and without fan speed control: 8.5à24 Tons
Nominal Capacity
[kW]
Number of Units Tested
84 1 70 7 62 3 53 1 35 2 30 1
NAFA 2017
We Measured system parameters for at least 4 different pressure drops by blocking an area of the filter.
NAFA 2017
For each pressure drop, we measured filter + coil pressure drop and fan pressure rise.
NAFA 2017
For each pressure drop, we measured airflow using calibrated orifices + supply static pressure.
NAFA 2017
For each pressure drop, we measured fan power.
NAFA 2017
Results: Units with no fan speed control: Pressure drop across filters x 2à airflow decrease 15.9%, fan power decrease 12.8%
Residential units: Airflow decrease: 8.6%, Fan power decrease: 4.7% Stephens et al. 2010
NAFA 2017
Results: Units with no fan speed control: Pressure drop across filters x 2à airflow decrease 15.9%, fan power decrease 12.8%
NAFA 2017
Results: Units with fan speed control: Pressure drop across filters x 2à fan power increase 12.5%
Higher Fan Speed
Calculated Fan Efficiency=23%
NAFA 2017
Results: filter pressure drop and fan power versus change in airflow rate.
NAFA 2017
After measuring system parameters for different pressure drops, we modeled cooling capacity, compressor power, duty cycle, EER.
Cooling capacity
Compressor power
Measured inputs: fan power, airflow rate temperature, relative
humidity
Input from units specs:
Other inputs: compressor empirical model based on
ASHRAE 540
• Duty Cycle
• Energy efficiency ratio (EER)= net cooling capacity/total power
NAFA 2017
Results: Cooling capacity and compressor power decrease with decreasing airflow rate.
NAFA 2017
Results: Doubling the pressure drop across filters minimally impacted EER.
Rodriguez et al. 1996
How does pressure drop and particulate efficiency changes with MERV?
NAFA 2017
We collected ASHRAE Standard 52.2 test data for 75 availably commercial filters with MERV 8,11,13,14.
NAFA 2017
We established a relationship between pressure drop and airflow for the 75 filters.
y = 4E-05x2 + 0.1026x
0
100
200
300
400
500
600
0 1000 2000 3000
PRES
SUR
E D
RO
P (P
A)
AIRFLOW (CFM)
FILTER A - LOADED y = 2E-05x2 + 0.0478x
0
50
100
150
200
250
300
0 1000 2000 3000
PRES
SUR
E D
RO
P (P
A)
AIRFLOW (CFM)
FILTER A - CLEAN
NAFA 2017
Results: High MERV does not necessarily means higher pressure drop.
NAFA 2017
We calculated PM2.5 and PM10 efficiency for the 75 filters with MERV 8,11,13,14.
ASHRAE Standard 52.2
Manufacturer data
Calculation: Integrated PM2.5
and PM10 efficiency
ASHRAE RP-1596
Calculation: Integrated PM2.5
and PM10 efficiency
NAFA 2017
Results: Replacing MERV 8 by MERV 11 may not be necessarily advantageous to decrease PM2.5 particle concentrations. This is not true if you replace MERV 8 with MERV 13/14.
What happens to power and clean air delivery rate when you switch MERV 8 to MERV 13/14?
NAFA 2017
Application: MERV 8 as base case
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Results: MERV 8àMERV 13 No fan speed control: Direction of power change depends on the operation mode of the RTU.
Total power increase 2.4% Fan power decrease 8.4%
Cooling mode Fan-only mode
Filter1 Filter2 Filter3 Filter4 Filter5 MERV 8
Filter1 Filter2 Filter3 Filter4 Filter5 MERV 8
NAFA 2017
Results: MERV 8àMERV 13 Fan speed control: Power draw increased during all modes.
Fan power increase 11%
Filter1 Filter2 Filter3 Filter4 Filter5 MERV 8
NAFA 2017
Results: MERV 8àMERV 13 Despite the decrease in airflow for units with no fan speed control, high efficiency filters offer higher CADR
No fan speed control Fan speed control
Filter1 Filter2 Filter3 Filter4 Filter5 MERV 8
Filter1 Filter2 Filter3 Filter4 Filter5
MERV 8
NAFA 2017
Results: clean vs fouled filter, MERV 8 à MERV 13 At fouled conditions, MERV 13 filters offers air quality advantages and higher energy consumption than those observed at clean conditions.
-25-20-15-10-50
Flow
Cha
nge[
%]
Clean Loaded
234567
Pow
er C
hang
e[%
]
Clean Loaded -20
-15
-10
-5
0
Pow
er C
hang
e[%
] Fa
n-O
nly
Mod
e
Clean Loaded
100200300400500600
PM
2.5 C
hang
e[%
]
Clean Loaded 102030405060
PM
10 C
hang
e[%
] C
ADR
Clean Loaded
Coo
ling
Mod
eC
ADR
what What if filters that are insensitive to load build-up existed?
Is this your next Filter-Uber?
NAFA 2017
MPA (Micro-Pneumatic Array) filtration
• A transformative new technique of PM filtration • Sheet arrays of many thousands of millimetric
separation cells • Applying principles of “Moore’s law” to air filtration
• A platform technology that • Can be designed to different PM size threshold • Unlimited lifetime by design, even under high
filtration load • Constant and stable filter performance, insensitive to
load / buildup
0
10
20
30
40
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60
70
80
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100
0.10 1.00 10.00
Arre
stan
ce (%
)
Particle Diameter (µm)
NAFA 2017
MPA: a vast new technology platform
• Can be produced roll-to-roll at almost any cell size • Capacity / longevity can be dialed in per application • Unlimited lifetime, by design
• Can be constructed from recyclable low cost materials • Rapid progress continues:
• Manufacturing techniques and performance • New configurations and systems utilizing this technology • More fundamental breakthroughs still to come, eventually deliver HEPA performance
NAFA 2017
• ASHRAE RP-1596 Team • Dr. Jeffrey Siegel, University of Toronto • Dr. Atila Novoselac, University of Texas at Austin • Store managers • Dr. Nabil Nassif, North Carolina A&T University • Dr. James Braun, Purdue University • enVerid Systems
Acknowledgment
Thank you! [email protected]
