C.S. Lee is R&D Manager and C. Flaherty is Director of Media Dept. and Laboratory at Circul-Aire, Inc., Montreal, Canada, L. Zhong is a Ph.D. student, D. Farhanyan is a M.A.Sc. student and F. Haghighat is a professor in the Dept. of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada.

Development of a parallel test system for the evaluation of UV-PCO systems

Chang-Seo Lee, PhD Lexuan Zhong Donya Farhanyan

Associate Member ASHRAE Student Member ASHRAE Student Member ASHRAE

Christopher Flaherty Fariborz Haghighat, PhD

Associate Member ASHRAE Fellow ASHRAE

ABSTRACT

Ultraviolet photocatalytic oxidation (UV-PCO) is considered as a promising technology but the complicated PCO reaction mechanisms

and unexpected intermediates still need to be further explored in order that PCO technology can be successfully applied.

Standard test methods for air cleaning systems are mainly for measuring particulate removal, limiting ozone generation. ASHRAE has

developed test methods for gaseous pollutant removal; however, these are mainly applicable for sorbent media like activated carbons. Numerous

papers on UV-PCO technology present the potential of UV-PCO, but the majority of these works were done in bench-top scale reactors under

ideal reaction conditions.

The main objective of this research is to evaluate UV-PCO systems equitably and thoroughly under the conditions relevant to the actual

applications. For this purpose a test rig composed of four parallel test ducts with 0.3m x 0.3m of cross-sectional area each, was designed and

constructed. UV-PCO section was designed to be versatile so that different UV-PCO systems with various geometries can be installed. Each

duct has a fan with a variable speed control so that the test air flow can be controlled regardless of the flow resistances of different UV-PCO

systems. We carried out prequalification tests of the test rig including air leakage test, velocity uniformity test, concentration uniformity test and

sink effect test of the test rig. Then three different UV-PCO systems and one ozone generation system were tested for ethanol removal. The paper

presents the details of the design and the prequalification tests of the test rig, and some preliminary test results of UV-PCO systems.

INTRODUCTION

Modern building ventilation design must take into account the health and comfort of the occupants as well as energy

consumption and the environment. The system needs to protect occupants against chemical contaminants from numerous

internal sources - office equipment, furniture, building materials, appliances, as well as bio-contaminants from the

occupants themselves. To reduce exposure to internal contaminants outdoor air is brought in to dilute the contaminants

and exhaust a portion to outdoors.

The quantity of the outdoor air brought into the building can have a direct negative effect on the energy cost of

ventilation. There is a cost to heat, cool, humidify or dehumidify the outdoor air depending on the location and season.

This leads to a balancing act between Indoor Air Quality (IAQ) and ventilation cost.

The strategy of diluting indoor contaminants with outdoor air assumes that the outdoor air is clean; this is not the case

in many large cities or near industrial complexes. Most ventilation systems have a form of particulate filtration but this is

usually more to protect HVAC equipment from fouling and does nothing to remove outdoor gaseous contaminants.

The need for good IAQ, high energy cost, poor outdoor air quality and the risk of a chemical release have all

increased the need and interest in systems to filter gaseous contaminants from the air. There are the traditional systems for

filtering gases, activated carbon and/or potassium permanganate alumina pellets in trays or deep beds. There are new

technologies, UV, UV with catalyst, ion generating tubes, particulate filters incorporating very thin beds of activated carbon

or alumina pellets, and carbon cloth, becoming available that also claim to filter the air of gaseous contaminants.

ASHRAE Standard 62.1 Indoor Air Quality Procedure (IAQP) allows reduced outdoor air ventilation rates when

proper air cleaning systems are combined (ASHRAE, 2010). Despite this potential to increase IAQ, lower energy cost, and

the added level of protection from a chemical release there is a reluctance to incorporate chemical filtration in HVAC

systems. This reluctance is from a lack of clear performance data showing effective removal of gaseous pollutants.

There are limited applicable standards when it comes to gas-phase air cleaning, especially for new technologies. There

are ASTM standards for activated carbon but these apply to more industrial applications and do not apply to other filtration

systems. ASHRAE has developed test methods (i.e., ASHRAE Standard 145.1-2008 and 145.2-2011) for gaseous pollutant

removal; however, these are mainly applicable for sorbent media like activated carbons and do not fairly evaluate the

performance potential of the new technologies. As a result design engineers only have data from manufacturing done

testing. These test results are often not directly applicable to IAQ. Since each manufacturer designs their own test

procedures the results are not comparable from one manufacturer to another. This lack of standards and convincing proof

of performance greatly limits the use of gas-phase air cleaning by design engineers. The development of a universal test

procedure relevant to IAQ, valid to all forms of gas-phase air cleaning would benefit the industry, the HVAC design

engineer, and all building occupants.

Aiming for the development of such universal test procedure, the project first selected UV photocatalytic oxidation

(UV-PCO) technology for evaluation. Numerous papers on UV-PCO technology present the potentials of UV-PCO in air

cleaning(Chen and Zhang, 2008, and Obee, 1996), and the mechanisms involved in UV-PCO technology is complicated

and different from those of adsorbents like activated carbons.

UV-PCO uses semiconductor materials like titanium dioxide where electrons transit from the valence band to the

conduction band from the absorption of light in the near UV range. The subsequent generation of positive holes and their

interactions with water lead to the formation of hydroxyl radicals. These can act as powerful oxidizing agents and be used in

the mineralization of organic molecules on the surface of titanium dioxide. In addition, claims have been made with respect

to the use of UV-PCO devices in enhanced inactivation rate for the removal and destruction of microorganisms (Lin and Li,

2003). However, it must be noted that in case of incomplete oxidation the pollutants may be transformed to other by-

products that can also pose health hazards. Also deactivation of catalytic surface can take place reducing the efficiency of

UV-PCO devices (Cao et al., 2002). Although a number of such devices are available in the market, no systematic studies

have been carried out regarding their comparative performance. Numerous literatures are available on UV-PCO technology,

but the majority of these works were done in bench-top scale reactors under ideal reaction conditions. Limited data are

available to the user so as to make an informed decision.

Due to these limitations, there is a great need to test different UV-PCO systems under various conditions that an air

cleaning system may encounter in real-life applications. Since a large number of tests have to be conducted, to save time a

new test rig with four parallel test ducts was designed and constructed. The paper presents the details of the design and the

prequalification tests of the test rig, and some preliminary test results of UV-PCO systems.

DESIGN AND CONSTRUCTION OF EXPERIMENTAL SETUP FOR UV-PCO TESTING

The biggest challenge in designing a proper test rig was the space limitation, because the laboratory is located in

downtown Montreal and a full-scale test rig complying ASHRAE Standard 145.2-2010 was already occupying large space in

the laboratory. The maximum available room was only about 1.3m×3.8m. Bench-top scale setup was not considered

because regular sizes of UV lamps cannot be used in such system. Then test results could be questionable and may not be

transferrable to full-scale system performances. With the given limitations the test duct size allowing reasonable scaling-up

was decided as 0.3m×0.3m. To run many tests in time-efficient manner, it was decided to develop four parallel ducts; hence

four tests can run at the same time.

Figure 1 shows the picture of the developed test rig. It has 3.56 m of total length and 1.20 m width. The test rig is

made of aluminum which has the highest reflectance of UV. Pre-filtration (), contaminant gas introduction and mixing

(), followed by upstream temperature and relative humidity measurement station are located in the 1.20m×1.21m main

duct. The main duct is connected to four separate 0.3m×0.3m ducts. Each 0.3m×0.3m duct contains upstream air sampling

and air flow measurement section (), UV-PCO section (), downstream air sampling, air flow, temperature and relative

humidity measurement station (), a cleanup media bed (), a variable speed fan (), and the final filtration.

Air flow rate of each duct can go up to 340 m3/hr (200 cfm), so total of 1360 m3/hr (800 cfm). Due to the size of the

rig, the laboratory air was used as carrier air and air filtration was applied prior to the introduction of challenge air

contaminant. From the challenge contaminant introduction point to the upstream air sampling section is only about 1.2m,

which is not enough to have a good mixing; therefore a fan and a custom designed air mixer were applied. Cross-shaped

averaging air sampling tubes were used for both upstream and downstream air sampling. All the probes and tubing used in

air sampling are either stainless steel or PTFE.

Various geometries of UV-PCO systems are available in the market. The UV-PCO test section was designed to be

able to accommodate different UV-PCO systems, and to be easy to install and modify. Different UV-PCO system can

result in different flow resistance. To be able to control the air flow rate, each duct has a variable speed fan with its own

control.

The designed test rig is for single-pass testing and the carrier air containing challenge air contaminant as well as

potential by-products generated from UV-PCO systems is exhausted into the laboratory. To clean up these potentially

harmful contaminants, a final cleanup adsorbent media bed is installed in each duct before the variable speed fan. The

adsorbent media are regularly changed for safety.

Figure 1 Developed UV-PCO parallel test rig

PREQUALIFICATION TESTS OF THE TEST RIG

To investigate the removal performance of UV-PCO air cleaners in the test rig of four parallel test ducts under

different experimental conditions, apparatus qualification tests have been conducted to quantitatively verify that the test rig

is capable of providing reliable UV-PCO air cleaner efficiency measurements. The prequalification testing of the test rig

includes (1) Test ducts leakage test, (2) Test ducts velocity uniformity, (3) Concentration uniformity, and (4) No filter test.

Test Ducts Leakage Test

The test ducts leakage test was carried out without any devices installed inside the duct system. According to the

proposed draft of ASHRAE 145.2-2011, the duct pressures for the leak test are normally determined by adding the duct

operating pressures with 250 Pa (1 inch of H2O) under different airflow rates. Since UV-PCO systems usually have a low

pressure drop than other adsorbent media beds, 250 Pa is a safe factor to be added. Then the test duct was sealed to be a

closed system by taping hardboards to the duct openings. Compressed air was carefully fed into the test duct. Sulfur

hexafluoride (SF6), a tracer gas, was injected into the four ducts system and the concentration of it was continuously

monitored by a multi-gas detector. Based on the well-mixed single zone model, the equilibrium equation of the compound

SF6 can be established as follows:

C = Co × e−QleakV

∙𝑡 (1)

where C (ppm) is the SF6 concentration inside the duct as function of time (t, sec), Co (ppm) is the initial tracer gas

concentration, V (m3) is the volume of the closed system, and Qleak (m3/s) is the leak flow rate of the whole test rig.

The experiment was performed at approximate 0.066 m3/s (140cfm) airflow rate for each duct. The total airflow was

963 m3/hr (567cfm). The average duct pressure at this airflow rate was 177Pa (0.708 inch H2O). Hence, the duct pressure

for the leak test was adjusted to around 425Pa (1.7 inch H2O) by metering with the compressed air. Figure 2 presents the

SF6 concentration decay inside the ducts.

(a) (b)

Figure 2 Tracer gas test results - SF6 concentration decay with time: (a) the first test (b) the second test

The total volume of the closed part of test rig is 1.67m3. Through equation (1), the computed air leakage flow rate is

8.94 m3/hr (5.26 cfm). Therefore, the leakage rate is 0.93% of the test airflow rate of 963 m3/hr (567cfm), which is below

1.0% leakage limit given in the ASHRAE standard 145.2-2011. The whole procedure was repeated for assurance. The

leakage flow rate of the second test was 7.73 m3/hr (4.55 cfm), which is 0.80% of test air flow. Therefore, the leakage of the

test rig satisfy the requirements.

y = 1.000E-01e-1.487E-03x

R² = 7.956E-01

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 500 1000 1500

Co

nce

ntr

atio

n [p

pm

]

Time [sec]

y = 1.0000E-01e-1.2860E-03x

R² = 8.5920E-01

0

0.02

0.04

0.06

0.08

0.1

0.12

0 500 1000 1500

Co

nce

ntr

atio

n [p

pm

]

Time [sec]

Test Ducts Velocity Uniformity and Stability Test

The velocity uniformity test was carried out to evaluate the velocity performance inside four ducts. This is prerequisite

to guarantee the contaminants evenly dispersed into the four ducts. Also, the air velocity of each duct needs to be stable

during whole test periods. The test was conducted at about 185 m3/hr (109 cfm) and 378 m3/hr (222 cfm) of air flow rates.

Air velocity transmitter was installed in each duct, and the readings were recorded using a data acquisition system. The

velocity test procedure was repeated twice to validate the repeatability. Then the average and the standard deviation of

velocity data were calculated for each duct as presented in Table 1. The coefficient of variation (CV), which is the velocity

deviation of four ducts divided by their average velocity, is used to evaluate the performance of four ducts velocity. At 185

m3/hr airflow rate the CV was 6.07% and 2.59% for two tests. At 378 m3/hr airflow rate the CV was 0.70% and 0.90% for

the corresponding two tests. To validate that air velocity can be constant in case of long-term testing, the air velocity of

each duct was monitored for three days (i.e., Test #2 at 185m3/hr). Figure 3 shows that the air velocities were stable.

Table 1. Velocity Uniformity Test Results

Location Test #1

@ 185 m3/hr [m/s]

Test #2 @ 185 m3/hr

[m/s]

Test #1 @ 378 m3/hr

[m/s]

Test #2 @ 378 m3/hr

[m/s]

Duct #1 0.585±0.0081 0.545±0.0088 1.13±0.0151 1.13±0.0140 Duct #2 0.527±0.0090 0.577±0.0102 1.12±0.0158 1.12±0.0147 Duct #3 0.568±0.0081 0.549±0.0089 1.14±0.0129 1.14±0.0121 Duct #4 0.515±0.0105 0.553±0.0104 1.13±0.0158 1.13±0.0182

Figure 3 Air velocity stability test.

Test Ducts Concentration Uniformity

The concentration inside four ducts should be evenly distributed to exam simultaneously the performance of UV-

PCO system in each duct. P-xylene was used as the challenge gas since among VOCs, p-xylene is relatively heavy; hence

lower diffusion coefficient than lighter compounds. Concentration uniformity test was conducted by generating p-xylene

and measuring the concentration at upstream and each downstream in empty ducts without any UV-PCO system. A multi-

gas photoacoustic analyzer coupled with an automatic multi-channel air sampler was used to monitor the concentration.

Before introducing the challenge gas, the background concentration of p-xylene at each duct was measured. Then p-xylene

was injected into the test rig, and monitoring of its concentration was continued for around 6 hours. The air flow rates were

carried out at about 170 m3/hr (100 cfm) and 340 m3/hr (200 cfm), respectively. Table 2 presents the average and standard

80

90

100

110

120

0 12 24 36 48 60 72

Air

Ve

loci

ty [f

pm

]

Time [hr]

"Duct #1"

"Duct #2"

"Duct #3"

"Duct #4"

deviation of concentrations measured at each duct. The CV, the ratio of the standard deviation to the mean average

concentration of four ducts, was 0.75% and 0.84% at 170 m3/hr flow rate and was 1.28% and 1.13% at 340 m3/hr flow rate.

Hence, reliable concentration uniformity was achieved.

Table 2. Concentration Uniformity Test Results

Location Test #1

@ 170 m3/hr [ppm]

Test #2 @ 170 m3/hr

[ppm]

Test #1 @ 340 m3/hr

[ppm]

Test #2 @ 340 m3/hr

[ppm]

Upstream 1.51±0.033 1.55±0.031 1.16±0.049 1.14±0.019 Duct #1 1.50±0.022 1.53±0.029 1.17±0.048 1.16±0.020 Duct #2 1.47±0.028 1.50±0.031 1.14±0.050 1.13±0.019 Duct #3 1.49±0.029 1.53±0.024 1.14±0.050 1.13±0.033 Duct #4 1.49±0.022 1.52±0.029 1.14±0.051 1.13±0.020

No Filter Test

An upstream-downstream comparison test was performed without a UV-PCO device in place to check the adequacy

of the overall duct in open-loop mode. As there was no PCO filter installed, the calculated single-pass removal efficiency

indicates the loss of the challenged gas resulted from the leakage and the sink effect. Since the test duct material is

aluminum not stainless steel, there might be more sink effect. Based on the results of the concentration uniformity test (the

same experimental setup with no filter installed), the calculated average removal efficiency at flow rate of 170 m3/hr was

between 1.05% and 2.71% for test #1; and between 1.44% and 3.24% for test #2. Similarly, the calculated average removal

efficiency at flow rate of 340 m3/hr was between -1.16% and 1.61% for test #1; and between -1.57% and 1.17test #2.

Hence, leakage/and or sink effect of the test rig is insignificant.

UV-PCO TESTING AND THE RESULTS

Three different commercially available UV-PCO systems and one UV ozone generation system were tested for

ethanol removal at about 0.475 ppm and 1.11 ppm. Each UV-PCO system is consisted of three PCO panels and two UV

lamps between two panels, hence, total of four UV lamps. The configuration of each duct is 1) Duct#1: UV-PCO#1 that

has UVC lamps (i.e., 253 nm wavelength) and PCO-A; 2) Duct#2: Ozone generation system that has vacuum UV lamps

(VUV); 3) Duct#3: UV-PCO#2 that has VUV lamps and PCO-A; and 4) Duct#4: UV-PCO#3 that has VUV lamps and

PCO-B. Due to the confidentiality agreements, the details of the UV-PCO systems cannot be disclosed.

After the fan in each duct is turned on, the background conditions like concentrations, temperature, humidity and air

flows are monitored for minimum 30 minutes or until stabilized. Then the UV lamps in all ducts are turned on. Once UV

outputs become stable, the challenge contaminant generation is started and introduced into the test rig. Since the

concentrations of ethanol tests were low, an automatic syringe pump with gas-tight syringe was used for ethanol generation.

During whole period during the test, the concentrations of challenge contaminant and ozone, and test conditions including

temperature, humidity, air flow and UVC irradiance were continuously monitored. Ethanol was monitored at both

upstream and downstream air sampling ports of each duct using a multi-gas photoacoustic detector (Bruel & Kjaer, Model

1302) connected with eight-channel automatic air sampler (CAI MK3 Sampler). Ozone monitor (Teledyne Instruments

Model 465L) has built-in six air sampling channels, so four downstream ports, one upstream port and one at the exhaust

were monitored. All test condition monitoring sensors (Ebtron ELF, Vaisala HMT100) of each duct were connected to a

data acquisition system (Agilent 34927A ).

Previous works indicated that main byproducts of concern generated from UV-PCO systems are aldehydes. Active air

sampling using DNPH cartridge connected with potassium iodine (KI) ozone scrubber was applied to measure aldehyde

generations. Air samples were taken at 1.3 l/min of sampling flow rate for two hours at four downstream ports and one

upstream port. The first samples were taken from about 30 minutes after ethanol generation was started. The second

samples were taken immediately after the first sampling is finished. The samples were handled and analyzed following EPA

TO-11a method (EPA, 1999) using a HPLC (Perkin Elmer).

The removal efficiency (E) of a UV-PCO system or ozone generation system was calculated when both upstream and

downstream concentrations are steady:

( ) = −

∙ (2)

where, Cup and Cdn are the average concentration under steady state at upstream and downstream, respectively.

Figure 4 presents the removal efficiency results of each duct for both challenge concentrations. UV-PCO systems

have better performance in ethanol removal than the ozone generation system. UV-PCO#3 installed in Duct#4 has the

highest removal efficiency regardless of ethanol concentration. UV-PCO#2 has better performance than UV-PCO#1 at

0.475 ppm of ethanol. When the concentration was increased to 1.11 ppm, however, the performances of both UV-PCO#1

and UV-PCO#2 became similar. The test conditions were 170±8 m3/hr of flow rate for each duct, 22±1oC of temperature,

13±3% of relative humidity. The ozone levels at the downstream sampling ports were 22.6±4.50 ppb for Duct#1,

2200±61.4 ppb for Duct#2, 2390±53.3 ppb for Duct#3, 1060±14.8 ppb for Duct#4 for 0.475 ppm of ethanol test; and

23.2±3.79 ppb for Duct#1, 2140±65.0 ppb for Duct#2, 2310±49.9 ppb for Duct#3, 1060±17.0 ppb for Duct#4 for 1.11

ppm of ethanol test. Laboratory analysis for byproduct measurements are in progress. The details of the results will be

included in the final submission of the paper.

Figure 4 Ethanol removal efficiency results of UV-PCO systems and a ozone generation system

SUMMARY

Gas-phase air cleaning systems applying various technologies are available in the market. Among new air cleaning

technologies, literatures have praised UV-PCO as promising one, and the more complicated mechanisms are involved in

UV-PCO than traditional technologies like physical and/or chemical adsorption. Existing standard test methods for the

evaluation of gas-phase air cleaning systems were mostly developed based on the knowledge of traditional technologies, and

may not be suitable in evaluating other newer technologies. Aiming for the development of a universal test procedure for

the evaluation of gas-phase air cleaning relevant to IAQ, this study focus on the comprehensive evaluation of UV-PCO

systems as a first step.

0

10

20

30

40

50

Ozone Generator UV-PCO#1 UV-PCO#2 UV-PCO#3

Re

mo

val e

ffic

ien

cy [

%]

Ethanol 0.475 ppm Ethanol 1.11ppm

Since many tests have to be carried out, a new test rig consisted of four parallel ducts were designed and constructed.

To ensure that the rig is appropriate for the measurements of UV-PCO system performance, various pre-qualification tests

including air leakage test, air velocity uniformity and stability test, concentration uniformity test and no-filter test were

conducted. Upon successful completion of pre-qualification tests, preliminary UV-PCO performance tests were carried out

for ethanol removal. Three different UV-PCO systems and one ozone generator were tested simultaneously. UV-PCO

systems have much better performance than the ozone generator. Different UV-PCO systems have different performances.

At higher challenge ethanol concentration, the removal efficiencies are lower for all UV-PCO systems. The research is on-

going and more tests will be conducted to have comprehensive understanding of UV-PCO systems.

ACKNOWLEDGMENTS

This study is supported by Natural Science and Engineering Research Council Canada (NSERC) Collaborative

Research and Development Grants.

NOMENCLATURE

C = concentration

= efficiency

Q = flow rate

t = time

V = volume

Subscripts

o = initial condition

up = upstream

dn = downstream

REFERENCES

ASHRAE. 2010. ANSI/ASHRAE Standard 62.1 Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating Refrigeration and Air Conditioning Engineers, Inc.

ASHRAE. 2008. ANSI/ASHRAE Standard 145.1 Laboratory Test Method for Assessing the Performance of Gas-Phase Air-Cleaning Systems: Loose Granular Media. Atlanta: American Society of Heating Refrigeration and Air Conditioning Engineers, Inc.

ASHRAE. 2011. ANSI/ASHRAE Standard 145.2 Laboratory Test Method for Assessing the Performance of Gas-Phase Air-Cleaning Systems: Air-Cleaning Devices. Atlanta: American Society of Heating Refrigeration and Air Conditioning Engineers, Inc.

EPA Method TO-11A. 1999. Determination of Formaldehyde in Ambient Air Using Adsorbent Cartridge Followed by High Performance Liquid Chromatography (HPLC) [Active Sampling Methodology]. Cincinnati: U.S. Environmental Protection Agency.

Cao, L., Gao, Z., Suib, S.L., Obee, T.N., Hay, S.O., and Freihaut, J.D. 2000. Photocatalytic oxidation of toluene on nanoscale TiO2 catalysts: Studies of deactivation and regeneration. Journal of Catalysis, 196: 253–261.

Chen, W. and Zhang, J. 2008. UV-PCO device for indoor VOCs removal: Investigation on multiple compounds effect. Building and Environment, 43: 246-252.

Lin, C.Y. and Li, C.S. 2003. Inactivation of microorganisms on the photocatalytic surfaces in air, Aerosol Science and Technology, 37: 939–946.

Obee, T.N., (1996) "Photooxidation of sub-parts-per million toluene and formaldehyde levels on titanic using a glass-plate reactor", Environmental Science and Technology, vol. 30, pp. 3578-3584.