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Why, when and how do HVAC-systems pollute the indoor environment and what to do about it? The European AIRLESS project


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From 1998 to 2000, a European project named AIRLESS was conducted by 12 institutes, universities and companies from seven European countries. The objective was to develop strategies, principles and protocols to improve and control the performance of HVAC-systems and its components for incorporation in codes and guidelines. The first step was to define air pollution caused by and/or originating from HVAC-systems, to investigate ways to prevent this pollution and to define strategies to keep this pollution away. A summary of this first phase of the AIRLESS project is presented. - Copyright © 2002 Elsevier Science Ltd. All rights reserved. -
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Pre-publication version of Building and Environment 38 (2003) 209 – 225
Why, when and how do HVAC-systems pollute the indoor environment
and what to do about it?
The European AIRLESS project
Dr. Philomena M. Bluyssen1*, Christian Cox1, Olli Seppänen2, Eduardo de Oliveira
Fernandes3, Geo Clausen4, Birgitller5, Claude-Alain Roulet6
1TNO Building and construction research, Department Healthy Buildings and Systems,
*Postbus 49, 2600 AA Delft, The Netherlands,, tlf.: +31 15 2695290,
fax: +31 15 2695299
2Helsinki University of Technology, Laboratory of Heating and Air Conditioning, Finland
3University of Porto, Faculdade de Engenharia, Portugal
4Technical University of Denmark, International Centre for Indoor Environment and Energy,
5Technical University of Berlin, Hermann-Rietschel-Institute, Germany
6Swiss Federal Institute of Technology Lausanne, Solar Energy and Building Physics
Research laboratory, Switzerland
From 1998 to 2000, a European project named AIRLESS was conducted by 12 institutes, universities
and companies from 7 European countries. The objective was to develop strategies, principles and
protocols to improve and control the performance of HVAC-systems and its components for
incorporation in codes and guidelines. The first step was to define this pollution, to investigate ways to
prevent this pollution and to . define strategies d to keep this pollution away.. A summary of the first
phase of the AIRLESS project is presented.
Indoor air pollution, HVAC-systems, Performance, Strategies
The energy consumption of ventilated and air conditioned buildings as well as the indoor air quality
are highly dependent on the design and the performance of the systems and components applied. In a
project named “European IAQ-Audit project” [1], 56 audited European office buildings showed in
general rather poor indoor air quality as evaluated by the sensory panels with substantial
dissatisfaction among the occupants. The study showed that the occupants are a less dominant
pollution source and that sources of pollution in the audited European office buildings comprised
mostly building materials and components of ventilation systems.
The research project entitled “European Database on Indoor Air Pollution Sources in Buildings
[2],was initiated to characterise and model mainly the building materials as indoor pollution sources.
A pre-study was done to characterise the origin and causes of the pollution caused by HVAC-systems
and its components. From this study followed that it is a complex process, in which many factors are
candidate for being responsible for the creation of the pollution sources. These factors can be
distributed in three categories:
factors related to the components themselves (design, material);
factors related to the physical/chemical environment around the components (temperature, relative
humidity, airflow);
factors related to the operation and maintenance of the components.
The Database project [2] and the European Audit project [1] as well as other studies, have shown that
the components of the HVAC-system can pollute the passing air considerably. However, its is still
unclear why, how and when these components contribute to the air pollution. Understanding of this
pollution mechanism is important. Only then effective measures to reduce pollution can be taken or
innovative ways of improving the performance of the components can be introduced.
From 1998 to 2000, a European project named AIRLESS was conducted by 12 institutes, universities
and companies from 7 European countries. The objective of AIRLESS was to develop strategies,
principles and protocols to improve and control the performance of HVAC-systems and its
components for incorporation in codes and guidelines. The first step of the European project
AIRLESS (Design, Operation and Maintenance Criteria for Air Handling Systems and Components
for better Indoor Air Quality and Lower Energy Consumption, Pre-Normative Research), was to
define this pollution and to investigate ways to prevent this pollution [3]. In the second step, protocols
were defined to keep this pollution away. And finally, strategies to decrease the pollution caused by a
total HVAC-system together with strategies to lower the energy consumption were defined.
In this publication, the outcome of the first step is reported and strategies for optimal IAQ
performance are presented.
Literature study
From previous studies was concluded that from the perceived air quality point of view (smells,
odours) the main potential pollution sources in HVAC-systems are filters, duct systems, rotating heat
exchangers, coils and humidifiers. For each component therefore a literature study was performed to
collect the knowledge already available and to formulate questions that need to be answered to be able
to pinpoint the reason of pollution of the polluting effect. By experimental studies in the laboratory
and/or in the field these answers were searched for.
Parameters and techniques
For most of the HVAC-components, the most relevant air parameters that were measured were
airflow temperature, air velocity, air relative humidity, and perceived air quality (Figure 1).
Additionally, chemical measurements (VOCs, dust, etc.) and/or biological measurements were
performed, depending on the protocol followed.
According to the protocol developed for the AIRLESS project [4], sensory measurements were
performed with a sensory trained panel. The panel evaluated the air quality at two or more locations.
The minimum requirement was that the air quality is assessed directly upstream of the component and
directly downstream of the component. During the sensory evaluations the temperature and relative
humidity of outdoor air and of the air supplied to the filter as well as conditions in the waiting room
were recorded. The air exhausted from the measurement unit was delivered to the subjects through
exposure equipment with an airflow rate of at least 1 litter per second. A well-ventilated and odourless
waiting room was available for the sensory panel. The environmental conditions in the waiting room
did not differ significantly from the temperature and relative humidity of air evaluated at the
experimental set-up.
If chemical measurements were performed, it comprised of the analysis of the air upstream and
downstream of the component tested. Measurements were performed by using direct reading
instruments or by taking air samples and analysis afterwards. Chemical analyses (VOCs) were carried
out according to the protocol developed in CEN TC264 WG7 [5].
If microbiological measurements were performed, they were performed by contact samples on the
clean and dirty side, and by taking air samples before and after the component.
Strategies for optimal IAQ performance
IAQ strategies for an optimal performance of HVAC-systems and its components can be divided in
several categories:
- Strategies that affect the design of the HVAC-system (Design): design principles and innovative
design strategies.
- Strategies that affect the HVAC-system while in use (Operation): operation, maintenance and
replacement strategies;
For each of the components present in an HVAC-system the two categories of strategies were
inventoried, and additionally the HVAC-system as a whole was considered.
Literature study
In general, air filters of an HVAC-system have two functions:
- To prevent (potential) negative effects on health and comfort of occupants in buildings;
- To clean and protect the HVAC-systems and ducts, building, interior and equipment.
Complete air cleaning may require the removal of airborne particles, micro organisms and gaseous
pollutants. Performance of air filters that remove particles is described with efficiency, airflow
resistance or the dust-holding capacity [6, 7]. In practice, the pressure difference (air resistance) over
a filter is usually the determining factor for the lifetime of a filter. No standard tests are available to
evaluate the potential pollution by a filter. In other words, the chance that a filter starts to pollute
under certain conditions is not determined. However, in several studies is shown that used filters, that
remove particles from the passing air, can pollute the air instead of cleaning it. The pollution by the filters
is expressed by a decrement of the perceived air quality evaluated by a panel of persons [8-13].
A literature review on filters and pollution sources was performed [14]. Comparing investigations
performed was troublesome because of:
- Different conditions to which the filters were exposed (flow rate/face velocity, type of flow
(continuous/intermittent), location of exposure (lab/field), duration of exposure and the location
of the filter in the system);
- Different filter types, filter materials and filter classes were used for the experiments;
- From several studies, not all relevant data were provided in the papers;
- Especially with regard to microbial pollution different measuring methods were used.
From 35 experimental studies reported in literature, it was concluded that it is still unclear what
causes the sensory pollution from filters. In the studies analysed, for most environmental and material
condition factors, an influence as well as no influence on odour or microbial pollution was found
(Table 1). Only humidity, or maybe one should read water content of the filter, came out clearly as an
influencing factor for microbial growth.
It was suggested that micro organisms, particularly fungi, cause the sensory pollution from filters.
However, it has not been proven/shown yet how and when this occurs. A possible explanation for this
uncertainty, which emerges from literature, is the way microbial pollution of filters is measured. It is
possible that, similar to chemical measurements, the used techniques nowadays are not sufficient. Big
differences, up to a magnitude (factor 10), in concentrations of micro organisms were found on
different parts of the same filter. This indicates that one should be cautious when evaluating microbial
measurements. Another reason could be that not the fungi cause the pollution, but other sources, like
bacteria. Another hypothesis is that a reaction with e.g. Ozone plays a major role in polluting the air.
Also, it was not completely clear which effect temperature and humidity conditions in an air-handling
unit have on the sensory emission caused by micro organisms. From the literature study, water
content of the filter and continuity of the airflow through the filter come forward as important factors.
And the microbial treatment of a filter did not seem to have an effect on the growth of micro
organisms in or on a filter.
From the literature review the following major questions emerged, with respect to the pollution effect
of filters:
- Are micro organisms the reason for the polluting effect?
- If yes, under which environmental and material conditions do these organism pollute?
- If no, what is then the reason for the polluting effect?
A series of experiments was performed.
Small pieces of filters in four different relative humidities were tested, but without airflow through the
pieces. The odour intensity of the filters increased over time at high relative humidity (over 85 %) and
decreased with low humidity (44 %), indicating that microbial activity could be the cause for odour
A used filter was tested at three different relative humidities (25, 45 and 55%), at a constant
temperature in a laboratory setting. The results showed that the relative humidity had a significant
impact on the acceptability votes. This effect could also be due to the difference of the enthalpy of air
To ensure poor survival conditions (low humidity) for micro organisms a pre-heater was placed in
front of a filter. A comparison between a filter with a pre-heater and a filter without a pre-heater for
approximately 50 weeks showed that during low outdoor air temperatures (below 0ºC) and high
relative humidities (higher than 80%), the filter without the pre-heater had higher odour intensities of
the air after the filter than the filter with the pre-heater. However, this could be a perception effect
(influence of temperature and humidity on perception of air quality) rather than an effect on emission
(by micro organisms).
The sensory emission of a filter with living micro organisms was compared with a radioactive
radiated filter in which all micro organisms were dead. The results showed no difference in perceived
air quality between the filters, indicating that micro organisms were not the main pollution sources
under these conditions.
Several new filters were investigated and it was found that odour intensity decreased after one week
with continuous flow through the filters. Glass fibre filters seem to have less sensory emissions than
filters made of cellulose (see Figure 2). In another experiment was found that the odour emitted from
new filters (3 days old) was higher than the odour emitted from 33 days old filter, exposed for 33 days
to a continuous airflow.
A long-term experiment of 28 weeks was carried out to investigate the influence of intermittent
airflow compared to continuous airflow on the pollution effect of filters (Figure 3) [26]. No statistical
relevant differences between odour intensity and VOC-emissions of the filter exposed to the
continuous flow and the filter exposed to the intermittent flow was observed. Microbiological growth
did occur on the soiled side of the filters, but also on the ‘clean’ side, specifically for the filter with
the intermittent flow. Despite this growth on filters, no significant increase of the odour intensity of
the air passing the filters was observed. Growth of micro organisms on filters apparently is not always
leading to odour emission.
In another experiment was found that the odour intensity of the air after the filter did not change
significantly with an increase of the airflow.
In an-experiment with ozone, no effect on perceived air quality from filters by changing the ozone
concentration was found. Due to the high air velocity and the short contact time, ozone was not
considered as a factor in HVAC-systems.
Strategies for optimal IAQ performance
From the studies performed with filters it was concluded that filters are one of the main sources of
sensory pollution in ventilation systems. New filters already seem to influence the perceived air
quality negatively, the filter material had a significant influence on the starting pollution effect of new
filters. The pollution of new filters decreased after some time of use, however when filters get older,
i.e. are in use for some time, the pollution increased again. The reason for this is still unclear. It seems
that micro organisms may not be the only pollution source on a filter.
Environmental conditions such as airflow (amount or intermittent/continuous) and temperature did
not have an influence on the odour intensity of air that has passed a filter.
Both new and used filters pollute the air. Filtering of the air is necessary to clean the air (from
particles) for the occupants and to protect the HVAC-system. A new principle of filtering is an
absolute must. The fact that fresh outdoor air is transported through dirt is asking for problems.
Therefore, the filter industry should develop new filter techniques that do not pollute the air.
Because the reason for pollution after the filter is in use for some time is still unclear, the strategies
presented in Table 2 are preliminary advises.
Air Ducts
Literature study
From the Database project [2] followed that duct systems pollute the passing air when they are
unclean, both new and used. Besides a pollution source, ducts may also be a reason for loss of
ventilation efficiency. Most ducts in Europe are leaky and thus increasing the energy use for
ventilation [35].
Typical parameters clarified in the literature study on air duct hygiene, were the surface concentration
of dust and micro organisms (fungi and bacteria) present on the bottom of the duct. But also the
quality of the supply air, in terms of particle concentration, micro organisms, TVOC (Total Volatile
Organic Compounds) and odour. Due to the long operation time (up to several decades) and due to the
large inner surface area of ventilation ducts, estimated to be about 10 % of the floor area in office
buildings [36], a significant amount of dust may accumulate mainly on the bottom surface of
ventilation ducts. The dust layer may promote the survival and growth of micro organisms and results
in release of metabolic products, spores or even viable cells, into the supply air, causing health
problems to occupants of the buildings.
Table 3 shows the factors of influence in the first column and the impact of an increase of these
factors on the surface concentrations of dust and micro organisms in the second and third column as
derived from the literature study. In general, the particle concentration in the air (either gravimetric or
number related) is the basic parameter influencing the dust surface concentration. Other parameters,
such as flow velocity and duct geometry, merely affect the deposition rate, i.e. the fraction of airborne
particles that settles on the duct surface. As a consequence, it is obvious that if more particles pass the
ventilation filters and enter the duct system, the higher the surface dust concentration.
The major question to be answered with respect to the pollution effect of ducts was:
What is the effect of air velocity (airflow), duct length, manufacturing residues and dust?
A series of sensory experiments with a trained sensory panel were performed with new ducts in order
to study effects of air velocity (airflow), duct length, material and manufacturing process [37, 38].
The effect of airflow and the length of duct on the intensity of four different new ducts (glass, spiral
wound and two flexible aluminium ducts of which one was cleaned) was studied. The influence of the
airflow was small, the intensity of the spiral wound duct was higher than for the glass duct (used as a
reference), and the intensity of the non-cleaned flexible aluminium duct was the highest, of the
cleaned flexible aluminium duct the lowest. The length of the duct had an influence on the intensity,
the longer the duct the worse the air quality at the end. The highest influence was seen with the non-
cleaned flexible aluminium duct and the lowest with the cleaned flexible aluminium duct.
The distribution of particles in ducts was monitored. In the ducts and outdoors, particles smaller than
3 µm were found most frequently (Figure 4). At the beginning of a duct, the dust load was higher then
after the filters and at the end.
The effect of oil residue and the effect of airflow was studied by comparing spiral wound ducts
manufactured without processing oil and with traditional manufacturing technology (with oil). The
odour intensity correlated linearly with the surface density of oil residuals (Figure 5). Against
expectations, no saturation effect was observed within the test duct length of 36 m. The effect of
airflow on odour emissions was negligible at the tested velocity range from 1 to 5 m/s.
The effect of debris accumulated into supply air ducts during construction was studied by storing new
spiral wound ducts at two different construction sites for two to three weeks (Figure 6). After the
storage phase the average surface densities varied from 1.6 to 6.9 g/m² depending on the type of duct
and storage site. No simple correlation was observed between the amount of accumulated dust and the
odour intensity, which indicates the dominant effect of oil residue emission. The analysis of dust
samples showed that all samples contained the same kind of debris: mineral wool fibres, mortar or
concrete dust, sand, and tile or flooring tile dust - all materials handled at the construction site.
When supplied with non-humidified air, the odour intensity from metal ducts containing oil residuals
was better than with humidified air. Ducts manufactured without processing oil had no effect on the
odour intensity (Figure 7). When the humidifier was turned on, the odour intensity increased in all
measurement points, but the strongest increase was observed in the case of metal ducts manufactured
without processing oil.
Strategies for optimal IAQ performance
Depending on the machinery used in the manufacturing process, new spiral wound ducts, flexible
ducts and other components of the ductwork might contain small amounts of processing oil residuals.
The oil layer is very thin and invisible, but it emits an annoying odour. From the studies performed it
was concluded that oil residuals are the dominating sensory pollution source in new ducts. Emissions
from dust/debris accumulated in the ducts during construction (mostly inorganic substances) seem to
be less important. However, the organic dust accumulated during the operation period may produce
more severe odour emissions.
Additionally, it was found that if dust has accumulated on the inner surface of the ducts, the relative
humidity of the air in the ducts has an important effect on the odour intensity. Relative humidity has,
however, no effect on the odour intensity caused by oil residuals. The effect of airflow on the
perceived air quality from ducts was relatively small and is probably insignificant in normal
applications. And finally, the length of the duct had a significant influence on the perceived air
quality. The longer the duct, the worse the perceived air quality at the end of the duct.
Some strategies to reach optimal IAQ performance for ducts are presented in Table 4. Source control
should be emphasised for ducts: start with clean ducts, then avoid dirt to get in by encapsulating
during construction and efficient filtering, quality management on the construction site should be
focussed on.
Literature study
From the literature study on humidifiers followed that micro organisms are almost always the reason
of problems with humidifiers, when problems occur. The use of biocides does not guarantee a
sufficient hygienic standard. Methods to disinfect humidifier water are the use of hydrogen peroxide
and the use of UV-radiation. The use of the UV-method does not guarantee germ-free water.
The most important question to be answered with respect to the pollution effect of humidifiers was:
What is the influence on odour intensity of different humidifier systems, microbiological
growth, airflow and water quality?
Experiments were undertaken for three types of humidifiers to answer this question [39]: spray nozzle
humidifier, steam humidifier and ultrasonic humidifier
Spray nozzle humidifier
A series of experiments was conducted with a spray nozzle humidifier on or off, with fresh or with
old water, and cleaned or not cleaned. The results show (Figure 8) that the difference between the use
of old or fresh water is enormously (30%). The air quality was better with an active than with an off-
state spray nozzle humidifier. These results are different from the studies of Fang et al. [34] who
showed in their investigations, that the perceived air quality deteriorates with an increasing humidity
or enthalpy.
Figure 9 shows that periodical cleaning of the spray nozzle humidifier is absolutely needed. After
cleaning of the humidifier the air quality improved with nearly 40%.
Steam humidifier
In a steam humidifier the water is heated above 100°C resulting in a disinfecting effect on micro
organisms. However, when the humidifier is out of use, the water stands in the tank and bacteria and
moulds have time to grow. Shortly after putting the humidifier to work, particles or odour may
therefore get into the air. This effect was shown in an experiment in which the use of old water was
compared with the use of fresh water in a steam humidifier (Figure 10).
In an experiment in which an off-state steam humidifier was compared with an active steam
humidifier, was shown that the active humidifier caused a higher odour intensity than the off-state.
(Figure 11). There are different possible reasons for these high values: old water, pollution of the
steam reservoir, or the water used (contains salts as well as residues of desalting agents). Another
effect can be the influence of the enthalpy: the enthalpy of the working system increased to more than
50 KJ/kg compared to an off-state value of 30 KJ/kg [34].
Ultrasonic humidifier
An ultra sonic humidifier was investigated with fresh water, for an off-state and an active state. Figure
12 shows that the active humidifier caused a higher odour intensity than the off-state, which was
mainly due to the odour emission of the resin cartridge present.
Microbiological investigations
Figure 13 shows the relation between the odour intensity of the investigated humidifier and the
bacteria concentration at the inner surface of the humidifier. With increasing number of bacteria the
odour intensity increased. From this correlation can be concluded that in the humidifier, the surface
concentration of microorganism can be used as an indicator of odour intensity. This is not the case for
the remaining components of the system.
Strategies for optimal IAQ performance
From the experiments performed, the main reasons of pollution were determined, namely:
- Desalinisation and demineralisation devices/agents (if used).
- Disinfecting additions;
- Old water in tanks and/or dirty tanks;
- Microbiological growth;
- Wrong use when the humidifier is off (the water stands too long in the tank);
It was concluded that humidifiers only pollute the air significantly if the humidifier is not used in the
described way and/or if it is not properly maintained. The investigations make it clear that periodical
cleaning of humidifiers is an absolute must, as is the use of fresh water. Under normal conditions, it
was found for all humidifiers that the airflow has no influence on the odour intensity caused by
In humidifiers, pollution sources are mainly living organisms, which can be eliminated by using
clean, new water regularly, UV-radiation and good maintenance. The basic strategy of not
humidifying the air should be mentioned. A lower relative humidity seems to result in a better
perceived air quality. However, eye complaints might occur with a too low humidity. Strategies for
design and operation are presented in Table 5.
Heating and cooling coils
Literature study
From the literature study on coils and pollution sources, it was concluded that there are no specific
references to coils as pollution sources. That may suggest that coils have not been seen as important
pollution sources in what concerns the pollution generated by the HVAC-systems.
The major question to be answered with respect to the polluting effect of coils was:
Is the coil pollution, chemical, biological and/or sensory, relevant?
The effect of the relative humidity, temperature and age on the emission of pollution by coils, was
studied for two test types: "heating mode" and "cooling mode", and with three types of coils: New
coils (as they come from the manufacturer), 1 month old used coils, and 6 month old used coils.
Sensory assessment, chemical analysis (VOCs) on the air sampled upstream and downstream the
component; and micro organisms analysis in the air and on the coil's surface, were performed. The
sensory results of the used coils are presented in Figures 14 and 15.
The results indicated that VOCs are usually not emitted by heating or cooling coils, be it new or used
ones and. Very low odour intensities have been detected in all cases. No specific trend could be
established with respect to the influence of emission of the test conditions (temperature and relative
humidity) on the odour emission.
To study whether oil residuals can be an important factor, an experiment with a new heating coil with
removable fins was carried out. Half of the heating coil was cleaned with a detergent solution spray.
A trained panel assessed the quality immediately before the test coil and after the cleaned and non-
cleaned side of the coil. Both the cleaned and non-cleaned side emitted odour, but no difference
between the two was observed.
Strategies for optimal IAQ performance
The results showed that heating and cooling coils without condense water or stagnating water in the
pans, are components that have small contributions to the overall odour intensity of the air. On the
contrary, cooling coils with condense water in the pans are microbial reservoirs and amplification
sites that may be major sources of odours to the inlet air. What seems to be the most relevant question
in what regards coils, or more precisely cooling coils, is the microbial growth in condense water. The
drains, condense pans, stagnant water and wet fins are potential microbial reservoirs and amplification
sites. The constant airflow through these sites can contaminate the inlet air distributed to the building.
The fungal contamination in office buildings may be a result from poor maintenance of the AHUs
which cause the overflow of the condense drip pans.
Preliminary strategies for design and operation are presented in Table 6.
Rotating heat exchangers
Literature study
Rotating heat exchangers (RHE) are not, in principle, pollution sources, but they may transport
contaminants by adsorption-desorption [40]. The RHE acts like a contaminant sink in the exhaust
flow and a significant pollutant source in the supply airflow. Emission increases with increasing
airflow and turning speed of the wheel. No difference was found between hygroscopic and non-
hygroscopic wheels.
In addition, it was shown that poorly installed RHEs might present single or two-way leakage
between the exhaust and supply part of the air-handling unit [41, 42]. This results in unexpected
recirculation, which contaminates the supply air exactly in the same way recirculation does. These
leakage can occur from leakage between wheel and gasket and is commonly less than 4%. However,
it may be larger if the wheel is wrongly installed, the pressure difference between supply and exhaust
at the wheel level is too high, or when the wheel is not flat and the rubber seal is not air tight.
The major question to be answered with respect to the pollution effect of rotating heat exchangers
was: Which VOCs (Volatile Organic Compounds) and how much VOCs are transferred in an well-
installed RHE, as a function of temperature and air moisture on both sides of the wheel?
Concentrations of various volatile organic compounds (VOCs) were measured up- and downstream of
a rotating heat exchanger [43]. The VOCs (Table 7) were injected in the extract duct, through
evaporation in a hot airflow.
The criteria used to select VOCs were that the compounds should be:
- commonly present in buildings;
- representative of the different organic families with the characteristic of their functional group
and saturation degree, different boiling points and polarity;
- easy to analyse, in order to provide significant results;
- easy to handle, and should not be too toxic.
Experiments were performed in two HVAC-systems, ventilating an auditorium and a laboratory,
under various conditions several times. In order to avoid adsorption in filters, these were taken out
during the experiments. Experiments were performed with the rotating heat exchanger turning in the
correct direction, i.e. with an active purging sector, and in the wrong direction, thus suppressing the
effect of the purging sector (Figure 16).
Experiments clearly showed that part of the VOCs present in the exhaust air may be recycled to
supply air by the heat recovery unit in the absence of purging sector, or when the purging sector is not
well used. The low transfer rates observed in the laboratory unit with purging sector for limonene,
dipropylether, m-xylene, mesitylene, n-decane, hexanal, 1-butanol and benzaldehyde, confirm the
results found by Andersson et al. [44] for formaldehyde, and attest the efficiency of a purging sector.
Some compounds (with highest boiling points) such as dichlorohexane, hexanol and phenol, however,
easily "passed" the purging sector and are recycled in significant quantities to the supply air (Phenol
with 30%).
Strategies for optimal IAQ performance
It was concluded that RHEs are in general, not by themselves pollutant sources, except perhaps dirty
rotating wheels. RHEs may recirculate pollutants, but this can be reduced by the proper use of a
purging sector. RHEs have in principle a better heat recovery than other types of heat exchangers, and
this is the reason why they are used instead of other models (heat pipes, plate exchangers, etc.) that do
not in principle recirculate pollutants. The latter model could therefore be installed when recirculation
is not acceptable, i.e. do not install rotating heat exchanges in systems where some recirculation of
odours cannot be accepted.
Strategies presented in Table 8 are all to prevent recirculation of pollutants, ad/desorption of
pollutants and/or to prevent the rotating heating wheel from becoming dirty.
Conclusions and strategies for optimal IAQ performance of HVAC-systems
From the first phase of the AIRLESS project was concluded that main sources and reasons for
pollution in a ventilation system may vary considerable depending on the type of construction, use
and maintenance of the system. In normal comfort ventilation systems the filters and the ducts seem
to be the most common sources of pollution, especially odours. If humidifiers and rotating heat
exchangers are used, they are also reasonable to be suspected as remarkable pollution sources
especially if not constructed and maintained properly. The pollution load caused by the heating and
cooling coils seems to be less notable.
Additionally, it was found that the effect of airflow on the pollution effect of HVAC-system
components seems to be less important and therefore an increase of the ventilation rate (air supply) is
a strategy that seems to have no effect on the perceived air pollution level caused by the HVAC-
system and its components itself. It is therefore not taken as an option for an IAQ strategy to improve
the performance of HVAC-systems. Of course, it is still possible to use the increment of ventilation
rate to dilute pollutants that are present in or originate from the spaces to which the air is supplied and
Strategies for design and operation of an HVAC system are presented in Table 9. In this table for the
following sources of pollution strategies are presented:
- Pollution from outdoor air: from continuous outdoor air sources and/or discontinuous outdoor air
sources (f.e. traffic).
- Pollution caused by recirculation of air.
- Pollution caused by system settings or operation strategies: such as on/off strategy and
temperature/humidity settings.
Final remarks
The results obtained are clear and encouraging and useful for the future. AIRLESS resulted in better
knowledge of the processes involved around air quality of HVAC-systems. And AIRLESS resulted in
a “new” way of looking at design, operation and maintenance of HVAC-systems. That does not mean
that there is no more need for further clarifications, maybe through more confined experiments were
causes and effects can be better identified and correlated, as for example is the case for filters. But in
general, the goal, “to identify the causes of indoor air pollution and find ways to prevent this”, has
been reached.
The industry of HVAC is expanding very rapidly in Europe. The commercial aggressiveness is quite
high and products and technologies are changing at a quite high pace. The public in general puts high
expectancies on the access to air-conditioning as a symbol and eventually as an opportunity for better
living conditions. However, indoor air quality is not yet a parameter with a strong political relevance
as energy consumption is. The findings of the AIRLESS project can help to initiate the awareness of
the importance of the performance of HVAC-systems with respect to indoor air quality.
The AIRLESS participants hope that their efforts will help to improve today’s’ situation and that this
project was the first international initiatives of many to come.
AIRLESS was partly sponsored by the European Union in the JOULE programme (DGXII) under the
management of Dr. G. Deschamps. The co-ordination was done by Dr. Philomena M. Bluyssen from
TNO Building and Construction Research in The Netherlands. Other participants were: Helsinki
University of Technology and Halton Oy (Finland); University of Porto (Portugal); Technical
University of Denmark (Denmark); Technical University of Berlin and Heinrich Nickel GmbH
(Germany); University of Sevilla (Spain); Swiss Federal Institute of Technology Lausanne, Sulzer-
Infra Labs Ltd, Swiss Federal Institute for Testing Materials (EMPA), and Sorane SA (Switzerland).
The presented experiments in this publication were executed by participants to the AIRLESS project,
in which the following persons had the lead: Birgit Müller from the Technical University of Berlin
(Humidifiers), Olli Seppänen from the Technical University of Helsinki (Air ducts), Dr. Claude Alain
Roulet from the Swiss Federal Institute of Technology Lausanne (Rotating heat exchangers), Prof.
Eduardo de Oliveira Fernandes of the University of Porto (Heating and cooling coils) and Ir. Christian
Cox from TNO Building and Construction Research (air filters).
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C.A.Roulet, 1996, European Audit project to optimize indoor air quality and energy consumption in office
buildings, Indoor Air Journal.
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Buildings, Final report, vol.1., Denmark.
3. Bluyssen, P.M., O. Seppänen, , E. de Oliveira Fernandes, G. Clausen, B. Müller, J.L. Molina, C.A. Roulet,
2001, AIRLESS: A European project to optimise air quality and energy consumption of HVAC-systems,
CLIMA 2000, September, Napels, Italy.
4. Bluyssen, P.M., 1998, Protocol for sensory evaluation of perceived air pollution with trained panels,
October, TNO Bouw, Delft.
5. CEN, 1999, ENV13419, Building products, Determination of the emission of volatile organic compounds,
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6. ASHRAE, 1995, ASHRAE Handbook Heating Ventilating and Air-Conditioning Applications, Chapter
41, Control of gaseous indoor air contaminants, Atlanta, ISBN 1-883413-23-0.
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marking, Central Secretariat: rue de Stassart 36, B-1050 Brussels, Belgium.
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CLIMA 2000, Sarajevo, Aug.1989, vol.3, pp.139-144.
9. Bluyssen, P.M., 1991, Air quality evaluated with the human nose, Air Infiltration Review, vol.12, no.4,
September 1991.
10. Bluyssen, P.M., 1993, Do filters pollute or clean the air?, Air Infiltration Review, Vol. 14, No.2, March
1993, pp.9-13.
11. Finke, U., 1993, Verunreinigingsquellen in Klimaanlagen, Ki Klima Kaelte Heizing 10/1993, pp.392-395.
12. Hujanen, M., Seppänen, O., and Pasanen, P., 1991, Odor emission from the used filters of air-handling
units, IAQ'91 Healthy Buildings, pp. 329-333.
13. Torkki, A., Hotokainen, J., Seppänen, O., 1995, Olfactory emissions of used filters, Healthy Buildings'95,
Milan, September, vol.2, pp.941-946.
14. Bluyssen, P.M., C. Cox, J. Souto, B. Müller, G. Clausen, M. Björkroth, 2000, Pollution from filters: What is the
reason, how to measure and to prevent it?, Healthy Buildings 2000, Helsinki, August, vol.2, pp.251-256.
15. Björkroth, M., Torkki, A., Seppänen, O., 1997, Components of the air handling unit and air quality, Healthy
Buildings’97, Washington DC, vol.1, pp.599-603.
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growth on ventilation filter materials, Indoor Air'90, Toronto, vol.3, pp.203-206.
17. Möritz, M., Schleibinger, H., Rueden, H., 1997, The influence of service life, filter medium, air temperature
and relative humidity on the growth of micro-organisms on air filters in HVAC systems, Healthy
Buildings’97, Washington DC, vol.1, pp.623-628.
18. Björkroth, M., Torkki, A., Seppänen, O., 1997, Effect of particulate filter on perceived air quality, Healthy
Buildings’97, Washington DC, vol.1, pp.557-562.
19. Kemp, S.J., et al., 1995, Filter collection efficiency and growth of micro-organisms on filters loaded with
outdoor air, ASHRAE Transactions, 101, Pt1.
20. Maus, R., Goppelsröder, A., Umhauer, H., 1996, Viability of micro-organisms in fibrous air filters,
INDOOR AIR’96, Nagoya, Japan, vol.3, pp.137-142.
21. Möritz, M., Schleibinger, H., Nipko, Christian, A., Rüden, H., 1999, Influence of service life on the
concentration of viable microorganisms on air filters in heating, ventilating and air conditioning (hvac)
systems, Indoor Air 99, vol. 2, pp. 225-226.
22. Neumeister, H.G., et al., 1997, Fungal growth on air filtration media in heating ventilation and air
conditioning systems, Healthy Buildings’97, Washington DC, 1997, vol.1, pp.569-574.
23. Schleibinger, H., Graf, G., Möritz, M., Rüden, H., 1999, Growth of micro-organisms and production of
mvoc on air filters in hvac systems in two different polluted areas, Indoor Air 99, vol. 2, pp. 231-236.
24. Frydenlund, F., Haugen, E., Kristiansen, Ø, Lysne, H.N. , Ahlén C., Hanssen, S.O., 1999, Composting in
ventilation filters? A possible key to altered thermotolerance in microbial flora of indoor air, Indoor Air 99,
vol. 2, pp. 184-189.
25. Johansson, J.H.P., Rosell, L., 1999, Does the air quality detoriate during the use of air filters?, Indoor Air
99, vol. 4, pp. 31-36.
26. Cox, C.W.J. and Bluyssen, P.M., 1997, Reduction of sensory pollution by air filters: effect of treatment to
inhibit microbial growth, Healthy Buildings/IAQ97, Washington, September 28 October 2, Vol. 1, pp.
27. Hake, W., Neumeister-Kemp, H.G., Kemp, P.C., Martiny, H., 1999, Reduction of micro-organisms by hvac
systems filters and analysis of the micro-organisms passing through the filters, Indoor Air 99, vol. 2, pp. 43-
28. Pasanen, P., Teijonsalo, J., Seppänen, O., Ruuskanen, J., Kalliokoski, P, 1994, Increase in perceived odor
emissions with loading of ventilation filters, Indoor Air 1994, no.4, pp.106-113.
29. Pasanen, P., Pasanen, A.-L. and Kalliokoski, P, 1995, Hygienic Aspects of Processing Oil Residues in
Ventilation Ducts, Indoor Air, Vol. 5, pp. 62-68.
30. Parat, S., et al., 1996, Airborne fungal contamination in air-conditioning systems: effect of filter and
humidifying devices, American Industrial Hygiene Association Journal 57, pp. 996-1001.
31. Teijonsalo, J., Passanen, P., Seppänen, O., 1993, Filters of air supply units as sources of contaminants,
Indoor Air ’93, vol. 6, pp. 553-538.
32. Pasanen, P., et al., 1990, Emissions of volatile organic compounds from air conditioning filters of office
buildings, Indoor Air'90, Toronto, Canada, July-Aug, vol.3, pp.183-186.
33. Kemp, P.C., Carlsson, T., Nickelmann, A., Neumeister-Kemp, H.G., 1999, Comparison of micro-organisms
loading from two air filter materials during the first eight weeks of service life. Indoor Air 99, vol. 2, pp.
34. Fang, L., Clausen, G., and Fanger, P. O., 1996, The impact of temperature and humidity on perception and
emission of indoor air pollutants, Indoor Air ’96, Nagoya, Vol. 4, pp.349-354.
35. Carrie, F.R., et al., 1997, Impacts of air distribution system leakage in Europe, the SAVE-DUCT project, 17th
AIVC conference, Athens.
36. Pasanen, A.-L., Kujanpää, L., Pasanen, P., Kalliokoski, P. and Blomquist, G., 1998, Culturable and total
fungi in dust accumulated in air ducts in single-family houses, Indoor Air, Vol. 7, pp. 121-127.
37. Björkroth, M., B. Müller, V. Küchen, P.M. Bluyssen, 2000, Pollution from ducts: What is the reason, how to
measure and how to prevent it?, Healthy Buildings 2000, Helsinki, August, vol.2, pp.163-168.
38. Björkroth, M., V. Asikainen, The effect of ventilation duct material and dust accumulation on perceived supply
air quality, Healthy Buildings 2000, Helsinki, August 2000, vol.2, pp.157-162.
39. Müller, B., K. Fitzner, P.M. Bluyssen, 2000, Pollution from humidifiers: What is the reason, how to measure
and to prevent it?, Healthy Buildings 2000, Helsinki, August, vol.2, pp.275-280.
40. Pejtersen, J., 1996, Sensory pollution and microbial contamination of ventilation filters, Indoor Air, vol.6,
41. Roulet, C.-A; Foradini, F., and Cretton, P., 1994, Use of tracer gas for diagnostic of ventilation systems,
Healthy Buildings'94, Budapest, Vol 2, pp 521-526.
42. Roulet, C.-A, Foradini, F., and Deschamps, L. 1999, Measurement of Air Flow Rates and Ventilation
Efficiency in Air Handling Units, Indoor Air'99, Edinburgh.
43. Roulet, C.A., M.-C. Pibiri, R. Knutti, 2000, Measurements of VOC transfer in rotating heat exchangers,
Healthy Buildings 2000, Helsinki, August, vol.2, pp.221-226.
44. Andersson, B., et al., 1993, Mass Transfer of Contaminants in Rotary Enthalpy Exchangers, Indoor Air,
1993, no.3, pp.143-148.
Figure Captions
Figure 1 Schematic approach of the test protocols.
Figure 2 Comparison of different new filters (filter class F7).
Figure 3 Odour intensity upstream (before) and downstream of (after) the filters.
Figure 4 Particle distribution in an HVAC-system.
Figure 5 Correlation between the odour intensity and the mass of oil residuals in the tested ducts.
Figure 6 Test ducts at a construction site.
Figure 7 Sensory assessment of contaminated ducts.
Figure 8 Odour Intensity of air after a spray nozzle humidifier.
Figure 9 Odour intensity of the air after a dry spray nozzle humidifier before and after cleaning.
Figure 10 Odour intensities from fresh water and water from a steam humidifier.
Figure 11 Odour intensity of air after the steam humidifier.
Figure 12 Odour intensity of air after the ultrasonic humidifier.
Figure 13 Bacteria concentration at inner surface of a humidifier correlated with the odour intensity.
Figure 14 Sensory results for the first old coil - heating mode.
Figure 15 Sensory results for the second old coil - cooling mode.
Figure 16 Average VOC recirculation rates measured in both units, with and without purging sector.
Airflow [m³/h]
Odour intensity
Cassette Filter
Bag Filter Cellulose
Bag Filter glass fibre
Particle size
Particles per Minute
Outdoor air
HVAC - Entry
Before Filter
After Filter
Duct upper side
Duct end
= 0,8277
00,2 0,4 0,6 0,8 11,2 1,4
Cumulative mass of oil residuals [g]
Odour intensity
1 m/s
3 m/s
5 m/s
All velocities
Airflow [m
Odour Intensity
Test 1 - dry
Test 2 - fresh water - OFF
Test 2 - fresh water - ON
Test 3 - 1 week old water - OFF
Test 3 - 1 week old water - ON
Test 4 - 2 weeks old water - OFF
Test 4 - 2 weeks old water - ON
Airflow [m
Odour intensity
Before cleaning
After cleaning
Fresh water
Water from the steam
Odour Intensity
Test 1
Test 2
Test 3
Airflow [m
Odour Intensity
Test 1 - OFF
Test 1 - ON
Test 2 - OFF
Test 2 - ON
Test 3 - OFF
Test 3 - ON
Odour Intensity
Test 1
Test 2
bacteria at inner surface of humidifier
Odor Intensity
Coil Test Condition
Sensory Evaluation
26/28 ºC
30/22 %
26/28 ºC
45/36 %
26/28 ºC
31/24 %
Odour intensity
60 %
Sensory Evaluation
60 %
50 %
50 %
60 %
50 %
Coil Test Condition
Odour intensity
Table 1 Overview of studies categorised on influence from factors on odour and microbial
Microbial growth
Björkroth et al. 1997 [15]; Torkki et al.
1995 [13]
Martikainen et al. 1990 [16]; Moritz 1997
Björkroth et al. 1997 [18]; Kemp et al.
1995 [[19]; Martikainen et al. 1990 [16];
Maus et al. 1996 [20]; Möritz 1997 [17];
Möritz et al. 1999 [21]; Neumeister et al.
1997 [22]; Schleibinger et al. 1999 [23]
Björkroth et al. 1997 [15]; Torkki et al.
1995 [13]
Frydenlund et al. 1999 [24]
Björkroth et al. 1997 [15]; Bluyssen, 1993
[10]; Torkki et al. 1995 [13]
Neumeister et al. 1997 [22]
Frydenlund et al. 1999 [24]; Johansson et
al. 1999 [25]
Type of flow
Cox and Bluyssen 1997 [26]
Hake et al. 1999 [27]
Frydenlund et al. 1999
Filter type
Pasanen et al. 1994 [28]; Pasanen et al.
1995 [29]
Parat et al. 1996 [30]
Teijonsalo et al. 1993 [31]
Frydenlund et al. 1999 [24]; Pasanen et al.
1990 [32]
Filter class
Teijonsalo et al. 1993 [31]
Parat et al. 1996 [30]
Frydenlund et al. 1999 [24]; Pasanen et al.
1990 [32]
Filter medium
Pasanen et al. 1994 [28]
Björkroth et al. 1997 [18]; Hake et al. 1999
[27]; Kemp et
al. 1999 [33]; Maus et al.
1996 [20]
Kemp et al. 1995 [19]; Möritz 1997 [17];
Pasanen et al. 1990 [32]
Location in
Hujanen 1991 [12]
Frydenlund et al. 1999 [24]
Area of
Hujanen 1991 [12]; Pasanen et al. 1995
Treatment of
Pasanen et al. 1994 [28]
Cox and Bluyssen 1997 [26]
Duration of
Passanen et al. 1994 [28]
Kemp et al. 1999 [33]
Björkroth et al 1997 [15]; Cox and
Bluyssen 1997 [26]; Torkki et al. 1995 [13]
Frydenlund et al. 1999 [24]; Kemp et al.
1995 [19]; Martikainen et al. 1990 [16];
Möritz 1997 [17]
Table 2 IAQ strategies for filters.
Prevent filters from becoming a source of pollution
Select a low-polluting new filter.
Condition new filters before use: out-gass before the filter is
placed in the system.
Use another filtering method like electrostatic filtering or
apply a two or more phase filtering system.
Keep the filter dry (by proper outlay of air intake section,
heating of supply air with pre-
heater or heating filters for a
certain period).
Minimise micro organisms for example with UV-radiation.
Avoid snow penetrating in the HVAC-
system by proper
outlay of air intake section.
Keep filter bags from lying on the bottom of the filter
chamber when the HVAC-
unit is not in operation
(preventing filters absorbing water due to eventual rain or
snow penetration)
Change filter on time: Depending on the situation, traffic and
other loads once in 3 to 12 months, but in general every 6
months for high polluted areas (town) and 1 year for low-
polluting areas (country side).
Check pollution effect regularly in sensory, chemical and
biological terms.
Prevent outdoor air passing the filter:
Make certain the filter frame and sealing seat have no leaks.
Prevent outdoor air impurities from passing the filter itself:
proper choice of filter type.
Make certain the filter frame and sealing seat have no leaks.
Table 3 Factors influencing the concentration of dust and micro organisms on the surface of
ventilation ducts (as derived from various studies).
Influence on the Concentration of:
Increase of:
Micro organisms
Outdoor air concentration of
particles and micro organisms
Filter class
Operation time / age of duct
Availability of water
(relative humidity, water condensation)
Air velocity
= increase;
= decrease
Table 4 IAQ strategies for ducts.
Prevent ducts from becoming a source of pollution
Use duct material that doesn’t require oil during the
manufacturing process.
Use duct material that doesn’t emit pollutants itself.
Interior surfaces shall be smooth.
Avoid sharp-edged curves, transition pieces or self-tapping
screws in walls of ducts.
Inspect and clean ducts if necessary, with regular intervals
(at least once a year).
Prevent dust accumulated during operation or debris from construction
Close end of ducts when not in operation (at construction
site, during transport or in factory, and when installed when
terminal units are still missing).
Keep accessories packed in closed boxes.
Package should be removed just before installation.
Check prior to the first operation, all parts in contact with the
airflow for cleanliness and re-clean if necessary.
Install a filter system th
at cleans the air before it enters the
Inspect and clean ducts if necessary, with regular intervals
(at least once a year).
Check filter system that provides clean air to duct, with
regular intervals (inspect at least once a year).
Prevent condensation points
Add insulation material to exterior of the duct.
Prevent condensation or water from humidifiers
Other recommendations
Limit flexible air ducts (difficult to clean).
Avoid sealant with high emission and do not attach tapes or
Install a service opening for inspection and cleaning.
Install stiffeners and other fittings in such a way that deposits
of dirt are prevented and cleaning can be carried out.
Check location and service openings, especially in spaces
with suspended ceilings. Very often service openings in
ducts are useless, because there is no opening in the
suspended ceiling or there are cables under the service
Table 5 IAQ strategies for humidifiers.
Prevent pollution from water, water tanks and devices/agents to disinfect, demineralise and/or desalinate the water
Remove oil residue before use of humidifier to prevent an oil
film on water.
Take care using disinfecting material (in water for example)
Use UV-handling of water.
Take care when using cartr
idges to prepare soft water, they
can emit VOCs.
Install demineralisation device in disperser to keep the
oscillator circuit board free from mineral precipitation for as
long as possible.
In case there is an oil film on water surface: water must be
drained and humidifier must be cleaned immediately.
Use clean water every week.
Clean tank (not possible for steam: keep them dry/empty
when not in use.
Clean humidifier regularly: every 6 months (dry or wet).
Water must be changed in operation breaks or after one week
of use.
Desalinisation must take place with an agent that does not
Use a control system with which
Humidifier shall automatically shut down when the HVAC-
system is shut down, to prevent humidifier from running dry.
New water is added when t
he water temperature exceeds
20ºC (spray nozzle and evaporative humidifiers, ultrasonic
Check operation of control system regularly.
Other recommendations
Do not use wetted plates of soft material as a humidifier (so-
called evaporative system).
Prevent moisture from a steam humidifier: a steam
humidifier not correctly installed or miss-constructed can
lead to condensation in ducts.
Table 6 IAQ strategies for coils.
Prevent water reservoirs and material of coils to become a source of pollution
Keep outlet of drain free at the lowest point of the drain pan
(include angle).
Water/condense should not stay too long in reservoirs:
change system design.
Remove oil before installation.
Prevent corrosion by selecting the proper material.
Do not place any adsorbing material behind cooling coil.
Maintain on time:
Water collection reservoirs: remove water regularly,
- No visible growth of moulds on coil surface.
Prevent water droplets from being produced
Place a droplet catcher behind coil.
Table 7 List of VOCs used for contaminant transfer experiments.
(current names)
Formula Sources
Boiling point
solvent, fuel
solvent, fuel
hexanal (caproaldehyde)
paper, paints
Cyclic and
1,8-p methadiene
me, detergent
solvent, fuel
solvent, fuel
Table 8 IAQ strategies for rotating heat exchangers.
Select a wheel equipped with purging sector, and install it
with the purging sector on the warm side of the wheel.
Supply and exhaust fans should be located and sized so that a
positive pressure difference of about 200 Pa is achieved
between supply and exhaust ducts at the wheel level.
Avoid hygroscopic wheels when contamination is an
important concern. Hygroscopic materials increase in most
case the efficiency of the heat exchange. However, odours
and other contaminants are also better
adsorbed on such
If wheel is warped: change wheel or use modern seals made
of thin plastic foils between two brushes.
Install filters in both ducts upwind the heat exchanger.
If pressure on supply side is negative compared to exhaust
side: change pressure hierarchy.
If the rotation of wheel is in the wrong direction: change to
proper direction. The wheel should pass from exhaust to
supply ducts in front of the purging sector.
Clean dirty wheels according to instruction of the
manufacturer, with
either compressed air or vacuum cleaner,
or pressurised water.
Check that the wheel control stops the wheel when no heat
can be recovered.
Table 9 General IAQ strategies for HVAC-system.
Prevent pollution from outdoor air coming in the system
Select appropriate filtering system.
Location of outdoor air intake nearby a pollution source:
locate outdoor air intake at a clean site.
Discontinuous outdoor air sources: Match operation strategy
(close system at certain hours or use recirculation with an
appropriate filtering system).
Continuous outdoor air sources: use an appropriate filtering
Prevent pollution from recirculation
Install appropriate filtering system in exhaust part of the
Install possibility for switching of recirculation system at
certain hours.
Avoid recirculation if possible
Discontinuous indoor air sources: no recirculation at certain
Continuous outdoor air sources: use an appropriate filtering
System settings/operation strategies
Room temperature 20°C ((lower air temp. improves PAQ)
(set-point has to be higher because of possible deviations
(control system)).
Room humidity at 30% to 50% (lower RH improves PAQ,
but lower than 30% might affect health negatively).
Daytime – night-time: start system before official business
hours (e.g. 1 hour earlier);
Weekend off: start systems before official business hours.
Off during certain periods during the day: for example when
no one is present (meeting rooms for example).
... Some of the VOCs detected inside the occupied space are volatile aromatic hydrocarbons (VAHs), semi-volatile organic compounds (SVOCs), and volatile aldehydes and formaldehyde (HCHO) [22]. Another study by Bluyssen et al [23] showed that when examining the result from the (European IAQ-Audit project) which included 56 audited European office buildings. The result of the study suggests that the quality of the indoor air is considered very poor as evaluated by the sensory panels with substantial dissatisfaction among the occupants. ...
... This phenomenon is well translated into the result of the ambient temperature inside the FFO during the autumn and spring scenario. When examining the average reading from table(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) it shows that all the monitoring point are showing the same average temperature of 296 °K (22 °C). however, when looking at the chart from figure (5.74) it demonstrates that the ambient temperature around both monitoring 1 and 4 has a slightly high average temperature compared to the average readings from monitoring point 2 and 3. ...
... 23 Eco-House survey question 10 Q 10: Are any of the following items located within your workroom or area? (Check all that apply) ...
There is always a demand for energy and the building sector demands a lot of energy. Consequently, due to the increasing amount of energy used in buildings, it is contributing to the increase of Greenhouse gas emission, and it is also contributing to the depletion of natural resources. The answer to this problem was to develop new kind buildings that will ensure that they would consume as little energy as possible. The term low carbon building was used to identify this type of building. However, since low-carbon building is aimed to conserve as much energy as possible it does not guarantee the indoor air condition inside these buildings. Thus, this thesis has studied indoor air quality in two renowned low-carbon buildings that were built using the latest technologies and building standards. The aim of this research was to study whether the implantation of new energy efficient technologies and low-carbon building standards has affected the indoor air quality inside the space. The result of the study has shown that the implantation of new energy efficient technologies did not compromise the indoor air quality inside the space. In fact, the use of new technologies like MVHR has insured the air quality inside the space and allowed for the pollutant inside the space to reach an acceptable level. However, there some issues that were discovered when analysing the data and performing the simulation for the three selected indoor space for this study. The first of these problems is that in the chemistry building, for example, not all areas inside the building have the same indoor air condition. The data from the Open Space Office (OSO) has much better indoor air quality compared to the First Floor Office (FFO). This could show that when designing a low-carbon building all areas inside the space are important and no certain region should be neglected. The second problem was found in the Eco-House Space (EHS) in which the natural ventilation did not provide an adequate indoor air quality condition. The third problem is overheating. the issue of overheating was present in all three indoor spaces which showed that in cold regions like the United Kingdom, there should a well-developed solution that will ensure that indoor air condition in low-carbon building is well kept in all seasons.
... This comparatively limited record can be explained by several factors including legal, economic, and ethical barriers, as well as practical challenges relating to residential access. [9][10][11] Underlying all these factors, the greatest methodological challenge is the heterogeneity of indoor environ- building tightness 8,18,19 ; heating and cooling systems and operation [20][21][22] ; size, geometry, and available surface area of a space 18,23,24 ; the nature, frequency, and intensity of human behaviors and activities such as smoking, cooking, burning candles, or vacuuming [25][26][27] ; the operation of windows, mechanical ventilation, and air cleaning devices [28][29][30][31][32][33] ; the generation of secondary organic particles through indoor chemical reactions [34][35][36][37] ; and more. Yet, the generalizability of existing studies is limited by their focus on specific geographic areas, episodic duration of measurement, and other constraints. ...
We surveyed literature on measurements of indoor particulate matter in all size fractions, in residential environments free of solid fuel combustion (other than wood for recreation or space heating). Data from worldwide studies from 1990 to 2019 were assembled into the most comprehensive collection to date. Out of 2752 publications retrieved, 538 articles from 433 research projects met inclusion criteria and reported unique data, from which more than 2000 unique sets of indoor PM measurements were collected. Distributions of mean concentrations were compiled, weighted by study size. Long‐term trends, the impact of non‐smoking, air cleaners, and the influence of outdoor PM were also evaluated. Similar patterns of indoor PM distributions for North America and Europe could reflect similarities in the indoor environments of these regions. Greater observed variability for all regions of Asia may reflect greater heterogeneity in indoor conditions, but also low numbers of studies for some regions. Indoor PM concentrations of all size fractions were mostly stable over the survey period, with the exception of observed declines in PM2.5 in European and North American studies, and in PM10 in North America. While outdoor concentrations were correlated with indoor concentrations across studies, indoor concentrations had higher variability, illustrating a limitation of using outdoor measurements to approximate indoor PM exposures.
... Microorganisms are then released into the supply airflow and subjected to blowing air (Pasanen et al., 1997). Studies have shown that the materials and functions of ducts have a significant effect on microbial growth and aerosolization (Bluyssen et al., 2003). Polyurethane foam insulation is more favorable to the breeding of fungi than glass fiber and galvanized iron (Chang et al., 1996). ...
Fungi in indoor environments can cause adverse health effects through inhalation and epidermal exposure. The risk of fungal exposure originates from the aerosolization of fungal spores. However, spore aerosolization is still not well understood. This paper provides a review of indoor fungal contamination, especially the aerosolization of fungal spores. We attempted to summarize what is known today and to identify what more information is needed to predict the aerosolization of fungal spores. This paper first reviews fungal contamination in indoor environments and HVAC systems. The detachment of fungal spores from colonies and the spore aerosolization principle are then summarized. Based on the above discussion, prediction methods for spore aerosolization are discussed. This review further clarifies the current situation and future efforts required to accurately predict spore aerosolization. This information is useful for forecasting and controlling the aerosolization of fungal spores.
... In addition, some portable air filtration systems are also used to maintain IAQ in building environment [4]. Although these systems are applicable in various circumstances, some limitations are still there affecting the air cleaner's efficiency as well as the IAQ [5,6]. Moreover, an increased ventilation through the HVAC system may not always improve IAQ in areas where outdoor air pollution is relatively high [7]. ...
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Life-Cycle Assessment (LCA) is the systematic analysis of the potential environmental impacts of any product or process throughout the life cycle. This work presents the LCA of Active Living Wall Systems (ALWS), an advanced form of living wall, which is a vertical greening system designed to reduce the indoor air pollutants along with several other benefits for occupants and building environment. Although this system is considered as having high potential to improve indoor air quality, ALW has not yet been assessed thoroughly from environmental perspective. Hence, the environmental impact of production, operation, maintenance, and finally disposal phase of ALW systems have been investigated through LCA in this paper. Built as an experimental set-up, two different ALW systems have been investigated extensively for this study including ALW system based on felt layers, and planter box ALW. Life-cycle environmental impacts have been analyzed using ReCiPe environmental impact methodology. Comprehensive study results showed similar environmental burden for both ALW systems for a life span of 10 years, indicating stainless steel and PVC as the most impacting construction materials. Operational energy was responsible for major impacts in climate change and terrestrial acidification category where incorporation of solar energy showed possible reduction of burden. Finally, felt based ALW system and commercially available air purifier have been compared from environmental perspective. Although having few limitations, this LCA study has the potential to help both the manufacturers and built environment experts to improve the balance between benefits and environmental impacts for a more sustainable ALW system that can ultimately lead us to an improved indoor environment.
... Synergy occurs when the efficiency of coupled air ions and UV exceeds the additive effects of using each method separately. 42 As such, the synergy values were then calculated using Equation (2). ...
The efficacy of the in‐duct application of ultraviolet waveband C (UVC) emitting at 254 nm wavelength and air ions against aerosolized bacteria was studied in a full‐scale 9‐m long ventilation duct. Combined positive and negative ion polarities (bipolar ions) and combined UVC and ions were tested. The UVC was generated by a mercury‐type UVC lamp and air ions were generated by positive and negative polarity ionizers. Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium), and Staphylococcus epidermidis (S. epidermidis)were tested at a concentration of 108 to 9 10 cells in 50 ml of sterilized distilled water. The case in which the positive ionizer was placed first, followed by the negative ionizer, demonstrated significantly higher disinfection efficiencies for E. coli (p = 0.007) and S. typhimurium (p < 0.001), but lower efficiency for S. epidermidis (p = 0.01) than the reversed sequence. The combination of UVC (3.71 J/m2) and air ions (1.13 × 1012 ions/m3 for positive ions and 8.00 × 1011 ions/m3 for negative ions) led to higher inactivation than individual disinfection agents operating under the same dose. A synergetic inactivation effect was observed for S. epidermidis under the combined UVC and positive ion case, while the combined UVC and negative ion case showed significant synergy effects for E. coli and S. typhimurium.
... PM 2.5 and PM 10 can also originate from certain indoor sources, such as pollens, dust, pesticides, mold, and human activities, including cooking, welding, smoking, kerosene heaters, and household cleaning [9,[15][16][17]. Further studies are warranted in that the existing HVAC systems are not capable of addressing all aspects of aerosol infection control, and the auxiliary filtration interventions with a proper operation are now required [8,[18][19][20]. Therefore, to prevent occupants' health risks from exposure to indoor air pollution, efficient monitoring and studying the relations between indoor and outdoor air quality are necessary. ...
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The 24 h and 14-day relationship between indoor and outdoor PM2.5, PM10, NO2, relative humidity, and temperature were assessed for an elementary school (site 1), a laboratory (site 2), and a residential unit (site 3) in Gainesville city, Florida. The primary aim of this study was to introduce a biplot-based PCA approach to visualize and validate the correlation among indoor and outdoor air quality data. The Spearman coefficients showed a stronger correlation among these target environmental measurements on site 1 and site 2, while it showed a weaker correlation on site 3. The biplot-based PCA regression performed higher dependency for site 1 and site 2 (p < 0.001) when compared to the correlation values and showed a lower dependency for site 3. The results displayed a mismatch between the biplot-based PCA and correlation analysis for site 3. The method utilized in this paper can be implemented in studies and analyzes high volumes of multiple building environmental measurements along with optimized visualization.
Nearly zero energy buildings (nZEB) are considered a key measure to reduce energy consumption in buildings. However, there is growing evidence that nZEB design strategies may impact indoor environmental quality (IEQ). Most of the current research on nZEB has focused on the energy efficiency and cost-effectiveness of nZEB, with less research on the IEQ of nZEB. This literature reviewed 25 case studies on IEQ assessment to determine the actual IEQ performance in nZEB and the impact of design strategies on IEQ. The results showed that all four parameters of IEQ performance assessment have yet to be included in the scope of IEQ assessment. In addition to physical parameter measurements and criteria, subjective measurements should be the primary determinant of IEQ. Moreover, the analysis shows that overheating, poor air quality, thermal discomfort, and Sick Building Syndrome (SBS) are common IEQ risk factors reported. At the same time, the building envelope, HVAC system, and control system are the main factors contributing to the increase in IEQ risk factors. This review will provide practical reference values and recommendations for building professionals in future studies.
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This experimental study aims to investigate and analyze the performance of a Water-Air Heat Exchanger that functions as passive cooling in a building ventilation system in the tropics. Before being blown into the room, the high-temperature outdoor air will be passively cooled by the lower-temperature water. Air driven by an Inline Duct Fan with a constant mass flow rate of 4.68 cubic meters per minute flows through a PVC hose as a heat exchanger inserted into a full water reservoir with a diameter of 100 cm and a height of 110 cm. A heat exchanger hose with a diameter of 6.35 cm and a length of 4130 cm is installed in a spiral-circular manner with a total of 16 coils with a diameter of 80 cm to increase the heat transfer effectiveness between water and air. The passive cooling effectiveness is analyzed by decreasing the air temperature between the inlet and outlet of the ventilator after passing through the heat exchanger. The temperature, humidity, and daylight measurement data were carried out for 36 consecutive hours using a multichannel data logger at several locations; ventilator inlet, ventilator outlet, water in the tub, and outside air. The measurement results show that the designed water-to-air heat exchanger provides a significant passive cooling effect and can reduce air temperature to 6.88 °C. By utilizing the passive cooling effect, the cooling energy gain obtained during the measurement period in the ventilation system of this building is 8.3 kWh. The methodology and results of this research are expected to make a positive contribution to the development of the concept of energy-efficient buildings by using passive cooling techniques
Pathogenic airborne microbes are the potential source of infectious diseases transmission. This study aimed to investigate and compare the microbial load, composition and prevalence of fungal and bacterial species at hospital sites facilitated with different ventilation systems and having different disinfection frequencies and occupancy levels. For this purpose, sixteen sampling sites were selected in two public hospital buildings including outpatient departments (OPDs), surgical wards, operation theaters (OTs), emergency departments, waiting room, burn unit, intensive care unit, nursing unit and medical laboratory. Results showed highest bacterial (829–4980 CFU/m³) and fungal levels (90–920 CFU/m³) in OPDs and wards respectively, whereas lowest concentration was observed in OTs of both hospitals. Overall, sites facilitated with central/mechanical heating ventilation and air conditioning (HVAC) system, higher cleaning frequency and lower occupant's density showed lower contamination levels. Staphylococcus spp. (53%), Micrococcus spp. (30%) and Bacillus spp. (11%) were found as abundantly occurring bacterial microbiota whereas Aspergillus spp. (67%) and Penicillium spp. (28%) were predominant fungal genera observed.
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Building-related health symptoms are multifactorial, hence a comprehensive study is needed to identify associations of such symptoms with building aspects. Previous studies have identified certain building characteristics as risk factors for both dry eyes and headaches, which are among the most prevalent symptoms suffered by office workers. This study investigated associations of dry eyes and headaches with building characteristics in outpatient areas because these conditions may vary between office and hospital buildings. A survey was performed in six hospital buildings, which included administering a questionnaire to 556 outpatient workers and an inspection of the building locations, services and 127 outpatient rooms. Multivariate regression models were produced for dry eyes and headaches. Both models were adjusted for personal and work-related aspects. The prevalence of self-reported dry eyes and headaches in outpatient areas was related to building-related aspects that affect the indoor air quality and visual quality, and to room types. In general, this study is consistent with previous office studies. However, a specific finding of this study is the association of the most frequently used room types and the presence of a window to the corridor with dry eyes and headaches.
Technical Report
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This project, involving a large number of partners, sought to bring together in one place knowledge relating to the strength of indoor pollution sources, and establish the necessary ventilation rates which would provide both for an energy-efficient operation, and comfortable conditions in buildings. Construction materials only recently were identified as major sources for indoor air contamination. This project aims to work towards a better definition of adequate ventilation rates to guarantee energy-efficient building and good indoor air quality (IAQ). Quantifying the strength of materials as pollution sources and introducing that data in appropriate models will contribute to a better design and management of buildings and systems.
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Abstract A European project started at the end of 1992, in which, in addition to current methods, trained sensory panels were used to investigate office buildings all over Europe. The main aim of this EC-Audit was to develop assessment procedures and guidance on ventilation and source control, to help optimize energy use in buildings while assuring good indoor air quality. In each of nine countries, six or more office buildings were selected. Measurements were performed at five selected locations in each building. The buildings were studied while normally occupied and ventilated to identify the pollution sources in the spaces and to quantify the total pollution load caused by the occupants and their activities, as well as the ventilation systems. The investigation included physical and chemical measurements, assessment of the perceived air quality in the spaces by a trained sensory panel, and measurement of the outdoor air supply to the spaces. A questionnaire for evaluating retrospective and immediate symptoms and perceptions was given to the occupants of the buildings. The building characteristics were described by use of a check-list. The annual energy consumption of the buildings and the weather conditions were registered. This paper presents results and conclusions of the audit in 56 buildings in Europe. However, the analysis and discussions of the results are a summary of the work done, and are focused mainly on comparison between sensory assessments and the other measurements performed. Furthermore, this paper brings the results of the study based on a two-factor analysis. A paper dealing with results on a multifactorial analysis is in preparation.
Fungal spore content in dust accumulated in air ducts was investigated in 24 mechanically ventilated single-family houses of which 15 had also a central air heating system. Dust was collected from the ducts simultaneously with cleaning of the ventilation systems. Besides spore concentrations and flora of culturable fungi, total fungal spore concentrations were determined in dust samples by the aqueous two-phase technique and spore counting with epifluorescence microscopy. Culturable spore concentrations in the dust varied from 10 1 to 10 7 CFU/g and total spore concentrations from 10 7 to 10 8 spores/g. Total spore concentrations in the duct dust were significantly higher in the air heated houses than in the other mechanically ventilated houses. The difference resulted mainly from a higher proportion of recirculation air and a higher age of the air heated houses. Cladosporiiim, Penicillium, Aspergillus and yeasts consisted of >90% of fungal flora in the dust. Although total spore concentrations were at the same level both in the exhaust and in the supply ducts in both types of house, culturable fungal spore concentrations were slightly higher in the exhaust ducts than in the supply ducts. The proportion of culturable spores was <5% of total spores in dust accumulated in the ducts.
Sensory responses to clean air and air polluted by five building materials under different combinations of temperature and humidity in the ranges 18-28°C and 30-70%RH were studied in the laboratory. A specially designed test system was built and a set of experiments was designed to observe separately the impact of temperature and humidity on the perception of air quality/odour intensity, and on the emission of pollutants from the materials. This paper reports on the impact on perception. The odour intensity of air did not change significantly with temperature and humidity; however, a strong and significant impact of temperature and humidity on the perception of air quality was found. The air was perceived as less acceptable with increasing temperature and humidity. This impact decreased with an increasing level of air pollution. Significant linear correlations were found between acceptability and enthalpy of the air at all pollution levels tested, and a linear model was established to describe the dependence of perceived air quality on temperature and humidity at different pollution levels.
The fungal contamination of air processed by an air-conditioning system can be quite high, depending on the technical features of different parts such as filtering and humidifying devices, as well as on their maintenance. The effect of filtration and humidification by sprayed water on the fungal air content was studied by analyzing the total culturable airborne fungi and four mold genera: Aspergillus, Beauveria, Cladosporium, and Penicillium. In four air-conditioning systems air samples were collected simultaneously on either side of the filters and humidifiers, using four single-stage viable particle samplers, on a malt agar chloramphenicol medium. High-efficiency filters (EU7) and lower efficiency filters (EU4) were compared, with actual efficiency calculated for every genus identified. The concentration levels measured below the high-efficiency filters were significantly lower than that measured above the filters. For the EU4 filters, the differences were not significant for Beauveria and Penicillium. For the latter a release of spores was detected, raising the question of the growth of microorganisms within the filters. The EU7 filter efficiency (80 to 97%) was higher than that of the EU4 filters, ranging from 36 to 70% depending on the fungi. This variability between genera raises the questions of how dependent filter efficiency is on the diameter of particles, as stated for inert particles. Finally, the concentration levels below the humidifier were lower than above it. This was related to the low contamination of the water itself (less than 100 colony- forming units per milliliter).
Abstract The development of odor emission rates from EU6 classified glass fiber bag filters was studied in four air-handling units (AHU), and emissions from the same kind of filters with EU3 classified polyester prefilters were studied in two units. The filters were loaded in six AHU in downtown Helsinki. The pressure drop was measured, and the odors of the filters were evaluated by a trained panel under laboratory conditions (T = 20°C, face velocity 1.0 m/s) every sixth week. The odor emissions of simultaneous atmospheric dust samples were also studied. The odor emissions of the filters rose during the first three months to a level where every third person would be dissatisfied. The emissions from coarse prefilters were similar to those from the more efficient filters without prefilters, and the emissions of the main filters were significantly lower if used with prefilters. This result indicates that the prefilters effectively protected the fine filters from odor-causing particles. The results of tests made with atmospheric samples agree with this result. Relative odor emissions were the highest in coarse fractions (> 10.0 m). The pressure drop increased with the particle mass collected on the ventilation filter, but it did not correlate well with the odor emission of the filter. Thus, pressure drop alone is not an adequate criterion for changing supply air filters when hygienic aspects are a concern.
Concerning artificial ventilation of interiors, microbial processes on air filters are assumed to cause pollution of the supply air with possible damage to the exposed persons' health. Therefore, the reaction of microorganisms on air filters was analysed in this project. The analysis focused on the influence ofair temperature, relative air humidity, the filter medium and service life as detenninants for microbial growth on air filters.
The present work is a study of reentrainment of a tracer gas formaldehyde via six rotary air-to-air heat exchangers (all enthalpy exchangers) in the northern part of Sweden. Five exchangers installed in office buildings and one in a day-care centre were included in the study. Formaldehyde in indoor was used as a monitor pollutant and was determined in air samples collected in the ducts at four positions around the rotor of the exchanger, in the supply-air duct and in the exhaust-air duct. Air sampling of homogeneous duct air was performed simultaneously at the four positions using 2, 4-dinitrophenylhydrazine-impregnated glass fibre filters. The sample analysis of formaldehyde was made by high-performance liquid chromatography. The reentrainment of formaldehyde was calculated and found to be 1-9%. These results show that a rotary heat exchanger can be used in buildings where activities produce low levels of air pollutants, provided that the exchanger is properly installed and maintained.
The hygienic properties of two types of processing oils used in the manufacture of galvanised metal air ducts mere investigated. One of the oils was based on mineral oil and the other on vegetable oil. Evaporation of the oil emulsions from the galvanized metal surface was followed for ten months, after which the water-binding capacity of the residues was measured in increasing and decreasing RH at the range of 75-100%. The potential of processing oil residues to act as nutrients for fungi was tested with Penicillium brevi-compactum in the laboratory. The odour emission of oil residues was evaluated with the aid of a trained panel for eight months. After the ten months, the residue of mineral-oil- and vegetable-oil-based products was 60% and 79% of the original amount, respectively. Both oils were able to absorb water but desorption of the water from vegetable-oil-based products was delayed, thus increasing the risk of fungal growth. The residues of both oils provided sufficient nutrients for fungal growth. The odour emissions from the oil residues were high and that of vegetable oil tended also to increase. To attain high indoor air quality, duct manufacturing methods which do not leave residues should be developed.