Effects of HVAC ventilation efficiency on the concentrations of

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					                                          Proceedings: Indoor Air 2002


    Y-Y Li 1,3 *, P-C Wu 2, H-J Su 2, P-C Chou3, C-M Chiang 1
  Dept. of Architecture, College of Engineering, National Cheng Kung University, Taiwan,
  Grduate Institute of Environmental and Occupational Health, Medical College, National
    Cheng Kung University, Taiwan, ROC.
  Dept. of Interior Design, College of Design & Planning, Shu-Te University, Taiwan, ROC.

    Potential sources for emitting formaldehyde and volatile organic compounds are abundant in
    office buildings. Exposure to the above compounds may result in short-term, long-term, or
    carcinogenic effects at concentrations often measured. Our study conducts field
    measurements on six typical office buildings with different HVAC systems to evaluate the
    effects of ventilation efficiency on the concentration of formaldehyde and total volatile
    organic compounds (TVOC). Formaldehyde and TVOC concentrations were measured by
    continuous photo-acoustic Multi-Gas monitor. The air-change rates were estimated by tracer
    gas concentration decay method in every test space. Air Exchange Efficiency (AEE) and
    Effective Ventilation Rate (EACH) were also calculated to characterize the ventilation pattern
    and mixing factor. Our results show that the increase of effective ventilation could reduce
    formaldehyde and TVOC in office buildings. We therefore suggest that increasing ventilation
    efficiency appears to be a plausible solution to diminish both formaldehyde and TVOC
    concentrations in office buildings.

    Office Buildings, Ventilation Efficiency, Volatile organic compounds, Formaldehyde.

    Numbers of potential formaldehyde and volatile organic compounds exist in office buildings.
    These include paint, adhesives, vinyl floor, ceiling, wall coverings, carpets, insulation
    material, composite wood products and some equipment. Serial studies also indicate that high
    concentrations of VOCs were observed when large amount of these products are installed in
    buildings [Etkin, 1994]. Moreover, many VOCs, such as formaldehyde and Benzene, are
    potential human carcinogens that may carry some risk for developing cancers even in low
    levels of exposure [IARC, 1995] [Swenberg, 1983; Heck, 1999]. Therefore, many countries
    such as German, Denmark, USA, Canada, Japan and European Union are promoting programs
    or guidelines to reduce VOCs exposure in indoor environments.

    Taiwan, while located in subtropical region, is also present with high density of population
    and buildings in commercial districts. Over-decoration and large quantity of furniture and
    equipments are likely to have introduced high concentrations of formaldehyde and total
    volatile organic compounds (TVOC) in most office buildings according to (our) field

        Contact author email: hamalee@mail.stu.edu.tw

                                    Proceedings: Indoor Air 2002

investigations. This study measured 6 office buildings with different HVAC (Heating,
Ventilation and Air Conditioning) systems. To clarify the effects of air change rate and air
exchange efficiency on the concentrations of formaldehyde and TVOC, different combination
of ventilation controls were performed in these buildings.

Six office buildings, (3 with RC structure and 3 with SRC structure; 3 with FCU and 3 with
AHU), were selected into the study after walk-through inspection. The detail descriptions of
each building were documented, and 4 of them were shown in Table 1, including the
decoration area of different building materials. Two representative spaces were chosen for
environmental measurement in each building. All test spaces were higher than floor 4 to
avoid the influence of outdoor pollutants from traffic exhaust.

Formaldehyde and TVOC were measured by continuous Multi-Gas monitor Type 1302 (Brüel
& Kjær, Demmark) whose design was based on the photo-acoustic detection principle. Six
samplers with TEFLON tube were distributed in the sampling room for multiple sampling at
the same time. The measurements were conducted continuously for 2-3 working days. The
detection limit of Formaldehyde is 0.04 ppm, and 0.02 ppm for TVOC.

Table 1 The description and characteristics of the test buildings
                          Building A           Building B            Building C            Building D
City                      Kaohsiung City       Taichun City          Taipei City           Taipei City
Building Construction     RC                   SRC                   RC                    SRC
Total floor of building   12 floors            13 floors             17 floors             11 floors
Age of the building       3 years              2 years               13 years              1 year
Standard floor area
                          900                  865                   1480                  820
                          5F          8F       5F          13F       8F          12F       10F         11F
Sampling floor and
                          Small       Large    Small       Large     Large       Large     Large       Large
space                     space       space    space       space     space       space     space       space
Area of test space (m2) 125           125      190         840       1240        780       820         820

Height of the space (m) 2.8           2.8      2.6         2.6       2.4         2.4       3.0         3.0

Number of person          5           54       2           18        164         89        45          38
                          Fan Coil Unit        Fan Coil Unit         Fan Coil Unit         Air Handling
Type of HVAC system
                          System               System                System                Unit system
                                               Heat recovering       Fresh Air Supplied    Inlet of AHU system
Inlet of the outdoor air Open window           system                Ducts in the roof     in every floor

                                               Office automatic
                          Office automatic     system furniture,
                                                                     Office automatic      Office automatic
                          system furniture,    Mineral fiberboard,
                                                                     system, carpets,      system, carpets,
                          Mineral fiberboard   computer, printer
Decoration, furniture,                                               Mineral fiberboard,   Mineral fiberboard,
                          computer, printer,   copy machine, fax
and equipments                                                       computer, printer     computer, printer
                          copy machine, fax    machine,
                                                                     copy machine, fax     copy machine, fax
                          machine, plywood     Gypsum board
                                                                     machine               machine
                          partition, paint     partition, wood

                                Proceedings: Indoor Air 2002

Ventilation Efficiency estimation
Two types of indicators were used to estimate the ventilation efficiency.

1. Air Change Rate Measurement (ACH)
The air-exchange rates were estimated by tracer gas concentration decay method, and
measured by continuous photo-acoustic Multi-Gas monitor Type 1302e (Brüel & Kjær,
Demmark) [Shaw, 1991].

2. Air Exchange Efficiency (AEE)
The air exchange efficiency (AEE) is designated to characterize the airflow pattern and to
discuss the mixing factor of test space [Sandberg, 1996]. AEE is dependent on 2 major
factors for buildings with HVAC system: (1). Relative location of the supply and extract
devices, (2). Momentum of air jet at inlet. Table 2 shows the performance of room ventilation
and the air exchange efficiency. The AEE value was examined with the age-of-air of different

Table 2 Performance of Room ventilation situation and the Air Exchange Efficiency.
  Situation          Air-Exchange Efficiency      The Evaluation with the Age-of-air
  Unidirectional                                 Local mean age-of-air in Exhaust
                     50% - 100%
  Flow                                           =Room average age-of-air 2
                                                    Local mean age-of-air in Exhaust
  Perfect Mixing       50%
                                                    = Room average age-of-air
  Short-                                            Local mean age-of-air in Exhaust
                       0%~50%                       < Room average age-of-air

3. The Effective Ventilation Rate Indicators (EACH)
The airflow pattern and volume of exchanged air should be taken into account when
determining the true ventilation efficiency in test space. A new indicator was therefore
estimated to represent the effective ventilation and used to examine the relationship between
indoor air pollutants and ventilation efficiency. Effective Ventilation Rate (EACH) was
developed to evaluate the ventilation efficiency with greater precision [Li, 2000], namely the

All variables in this study were measured simultaneously to document the real-time variation
of air flow in test space. Figure 1 shows concentration patterns of formaldehyde during 4
days in one test space. Shadowed area of the figure indicates that the HVAC system is in
function. We observe that the formaldehyde concentrations would significantly decay when
HVAC system is turned on, and accumulated again after being turned off. Moreover, the
baseline concentrations appear to be close between working days and weekend.

Figure 2 shows the concentration variations of TVOC over 4 days in one test space.
Similarly, TVOC concentrations significantly decay when HVAC system is on, and also
accumulate again when off. Yet, the baseline of TVOC exposure in working days is higher
than during weekend. It appears that operation of HVAC system might also remove some
TVOC emitting from products and human activities.

                                                                                Proceedings: Indoor Air 2002

                                                                                         HCHO monitoring 10F
                                                                                                                                                                                      wi    eas
                                                                                                                                                                                 HCHO- ndow- t
                                                                                                                                                                                      r   m ddl
                                                                                                                                                                                 HCHO-oom - i e
                                                                                                                                                                                      r   norh- i
                                                                                                                                                                                 HCHO-oom - t s de
                                                                                                                                                                                 HCHO- l
   Concentration (ppm)

                             0.80                                                                                                                                                    m    ne
                                                                                                                                                                                 HCHO- achi




                                 14:24      19:12   0:00   4:48    9:36         14:24         19:12      0:00         4:48                           9:36         14:24      19:12         0:00      4:48          9:36          14:24
                                      Working day                    Working day                                                                                  Weekend                                          Weekend
                                                                                                       Time (hh/mm)

Figure 1. Variation of formaldehyde concentrations in one test space. (Shadowed area: air-
conditioning on)
                                                                                          TVOC Monitoring 10F
                             13.0                                                                                                                                                             il
                                                                                                                                                                                        TVOC -n
                                                                                                                                                                                            wi    eas
                                                                                                                                                                                        TVOC- ndow- t
                                                                                                                                                                                             r   m ddl
                                                                                                                                                                                        TVOC-oom - i e
                             12.0                                                                                                                                                            r   norh- i
                                                                                                                                                                                        TVOC-oom - t s de
    Concentration (mg/m)

                                                                                                                                                                                        TVOC- l

                                                                                                                                                                                            m    ne
                                                                                                                                                                                        TVOC- achi






                                    14:24   19:12   0:00    4:48    9:36         14:24         19:12        0:00        4:48                           9:36          14:24      19:12         0:00          4:48          9:36         14:24
                                      Working day                          Working day                                                                            Weekend                                           Weekend
                                                                                                          Time (hh/mm)

Figure 2. Variation of TVOC concentrations in one test space. (Shadowed area: air-conditioning on)

                                Relationship between HCHO concentration-8hr and (EACH/RtD)                                                              Relationship between TVOC concentration-8hr and (EACH/RtD)
                            0.30                                                                                                                    3.50
                                                                                                       -0.351                                                                                                               y = 1.0356x

                                                                                   y = 0.0771x

                            0.25                                                                                                                    3.00                                                                           2
                                                                                          2                                                                                                                                      R = 0.1845
                                                                                        R = 0.5381
 HCHO concentration (ppm)

                                                                                                                         TVOC concentration (mg/m

                                                                                                                                                    2.50                                                                         P=0.124066
                            0.20                                                        P=0.001274
                            0.05                                                                                                                    0.50

                            0.00                                                                                                                    0.00
                                    0.0     0.1     0.2     0.3      0.4           0.5           0.6            0.7                                         0.0       0.1            0.2          0.3         0.4           0.5           0.6            0.7
                                                                           -1                                                                                                                                       -1
                                                           EACH / RtD (h )                                                                                                                    EACH / RtD (h )

Figure     3. The relationship between                                                                                                              Figure 4. The relationship between TVOC
formaldehyde concentration and Ventilation                                                                                                          concentration and Ventilation efficiency
efficiency indicator of decoration (EACH/RtD)                                                                                                       indicator of decoration (EACH/RtD)

                                         Proceedings: Indoor Air 2002

Having established a preliminary association between the ventilation efficiency and the indoor
concentrations of formaldehyde and TVOC, factors attributable to the sources of these
exposures are further examined. The RtD, ratio of total decorated area to the floor area, was
calculated and taken into account when evaluating the intensity of pollutants, equation 1. In
addition, a comprehensive indicator, integrating effective ventilation rate (EACH) and the
intensity of decoration was defined as CIVD, equation 2.
                                 decorated area, m 2 )
                       Ad (Total¡@
                RtD =                                                                        (1)
                            A (Floor area, m 2 )
                CIVD =                                                                                               (2)

Table 3 The performances of the concentrations and ventilation levels in six buildings.
                                 Total area              HCHO           TVOC                                EACH
    Space               Area         of       RtD     Concentration Concentration   ACH      AEE   EACH
              Volumn             decoration           - 8hr average - 8hr average
    Units      (m3)     (m2)       (m2)       (%)        (ppm)        (mg/m3)       (h-1)    (%)    (h-1)   (h-1)
   A1 (5F)     1147.8    468.5      635.84     136%         0.120         0.800       2.01    33.60 0.675    0.498
   A2 (8F)      338.1    138.0      234.85     170%         0.060           NA        2.12    36.60 0.776    0.456
   A3 (10F)     850.9    347.3      585.00     168%         0.110         1.520       2.37    36.20 0.858    0.509
   B1 (6F)      975.0    390.0      864.17     222%         0.140         2.220       0.84    39.10 0.328    0.148
   B2 (11F)     525.0    210.0      859.82     409%         0.240         2.330       0.74    41.50 0.306    0.075
   B3 (17F)     575.0    230.0      550.01     239%         0.150         2.190       0.66    29.40 0.194    0.081
   C1 (8F)      533.0    205.0      572.43     279%         0.170         2.040       0.97    45.30 0.439    0.157
   C2 (20F)     387.9    149.2      773.89     519%         0.220         1.990       0.84    40.70 0.342    0.066
   C3 (38F)     608.4    234.0      335.27     143%         0.140         1.470       1.77    26.70 0.473    0.330
   D1 (5F)      972.5    389.0      868.00     223%         0.190         1.470       0.81    47.01 0.382    0.171
   D2 (6F)      987.5    395.0      918.22     232%         0.170         1.540       1.10    36.30 0.397    0.171
   E1 (3F)      575.8    235.0      556.43     237%         0.100         1.490       2.84    53.10 1.508    0.637
   E2 (6F)      526.8    215.0      528.92     246%         0.096         1.700       1.83    52.70 0.964    0.392
   E3 (9F)      771.8    315.0      713.83     227%         0.130         1.200       1.34    42.60 0.571    0.252
   F2 (6F)      230.4     96.0      243.62     254%         0.110         0.790       1.31    43.80 0.574    0.226
   F3 (8F)      174.5     69.8      179.16     257%         0.110         1.000       1.60    19.60 0.314    0.122
   G1 (4F)      176.4     72.0      238.32     331%         0.130         1.240       1.41    41.20 0.581    0.176
   G2 (8F)      184.7     75.4      332.93     442%         0.140         1.200       1.83    44.00 0.805    0.182

Table 3 shows the results of formaldehyde and TVOC concentrations and the levels of
ventilation efficiency indicators in six investigated buildings. The relationships between
formaldehyde or TVOC concentrations and CIVD value are shown in Figure 3 and Figure 4.
The decay patterns of formaldehyde and TVOC suggest that the increase of effective
ventilation rate, and control of the decoration intensity could reduce indoor formaldehyde
(R2=0.54, p=0.001) and TVOC (R2=0.1845, p=0.124) concentrations.

The exposure levels of both formaldehyde and TVOC appear to decrease significantly after 1-
2 hrs operation of HVAC system (Figure 1 and 2). Such a phenomenon suggested that the
operation of HVAC system might have removed some formaldehyde and TVOC assuming the
quantity of formaldehyde emission in office was steady and constant. We therefore propose
that having the ventilation turned on about 2 hrs before the occupants come into the building
should effectively reduce the risk of exposure to high-level formaldehyde and TVOC. The
continuous measurements of formaldehyde have shown that human activity does not seem to
be the determining factor of formaldehyde exposure in office buildings because the
concentrations were not significantly decrease over weekend. Such an observation indicates
that the emission from building materials may be the major source for the presence of indoor

                                  Proceedings: Indoor Air 2002

formaldehyde. It can be suggested that the selection and use of building materials should be
placed in a higher priority for an effective control of indoor formaldehyde concentrations.

Our results also suggest that increase of effective ventilation rate could reduce formaldehyde
and TVOC concentrations in office buildings after examining the relationship between indoor
formaldehyde and TVOC levels and a comprehensive indicator of ventilation efficiency, CIVD
(Figure 3 and 4). This finding indicates that proper increase of ventilation efficiency could
lessen exposure levels of formaldehyde and TVOC. Collective results of this study, therefore,
propose that a better strategy in controlling indoor formaldehyde exposure should integrate
the consideration of optimal ventilation efficiency (EACH), and source intensity of decoration

Our study suggests that operating ventilation before working hour could significantly reduce
exposure levels accumulated at night. In addition, the increase of effective ventilation rate
can also lessen the formaldehyde and TVOC exposure inside office buildings.

The authors thank all fellow friends of Archilife Research Center and Graduate Institute of
Environmental and Occupational Health for their endless help in the intensive sampling
activity, and time-consuming laboratory analysis.

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