Post on 17-Jul-2020
Original Paper
Indoor and BuiltuiltEnvironment Indoor Built Environ 2012;21;4:486–502 Accepted: October 17, 2011
Improvement of IndoorLiving Environment byOccupants’ Preferencesfor Heat RecoveryVentilators in High-RiseResidential Buildings
Sang-Min Kima Ji-Hyun Leeb
Hyeun Jun Moonc Sooyoung Kimd
aInstitute of Technology & Quality Development, Hyundai Engineering & Construction Co., Ltd.,
Yongin, Kyeonggido, South KoreabGraduate School of Culture Technology, Korea Advanced Institute of Science and Technology,
Daejeon, South KoreacDepartment of Architectural Engineering, Dankook University, Yongin, Kyeonggido South KoreadDepartment of Housing and Interior Design, Yonsei University, Seoul, South Korea
Key Words
Heat recovery ventilator E Energy savings E Indoor
air quality E Ventilation rates E Operating schedule E
Residential building
AbstractThis study examined the influence of heat recovery
ventilators (HRVs) on energy savings and indoor air
quality (IAQ) in high-rise residential buildings. Field
measurements were performed in four residential
units, which were validated by computer simulations
and estimated the total annual energy consumption.
The operation schedules for HRVs were determined by
a survey of residents. Field measurement results
indicate that HRVs could effectively improve IAQ and
afford effective energy savings. The indoor concentra-
tions of formaldehyde were reduced by 54.6% after
HRVs were operated for 24 h. The initial concentration
was reduced by 82% after 168 h. Toluene was the
dominant volatile organic compounds (VOCs) in the
indoor air. Its initial concentration was reduced by 50%
and other VOCs were also reduced by 40.1% to 53.1%
after HRVs were operated. Annual energy savings of
up to 20.26% were predicted when HRVs were
operated for 24 h continuously, exchanging sensible
and latent heat. HRVs could save energy more
effectively in winter than in summer due to the greater
temperature difference between outdoor and indoor
air. Based on the preferred operation schedules of
homes surveyed, an annual energy savings could be
as high as 8.52%.
� The Author(s), 2011. Reprints and permissions:http://www.sagepub.co.uk/journalsPermissions.navDOI: 10.1177/1420326X11429714Accessible online at http://ibe.sagepub.comFigures 3–23 appear in colour online
Sooyoung Kim,Department of Housing and Interior Design, Yonsei University, Seoul, SouthKorea. Tel. þ82-2-2123-3142, Fax þ82-2-313-3139,E-Mail sooyoung@yonsei.ac.kr
Introduction
Material with high thermal resistance is generally
applied to building envelope with air-tightness to save
energy in high-rise residential buildings that have higher
window to wall ratios on their facade. These building
envelopes with appropriate shading devices are often
effective in utilising daylight to control electric lighting
systems in buildings [1,2]. The tightly sealed envelope
would be effective to save energy, but it could reduce air
infiltration and deteriorates indoor air quality [3].
Insufficient ventilation rates could increase the concentra-
tion of harmful air pollutants such as formaldehyde and
volatile organic compounds (VOCs) and this is now an
important part of building environmental assessment of
green building certification together with the appropriate
building services [4].
In high-rise residential buildings where natural ventila-
tion through envelopes is limited due to tightly-sealed
material, ventilation is primarily dependent on mechanical
systems. Due to this, ventilation strategies are required to
improve indoor air quality and save energy effectively
[5,6]. Alternatively, heat recovery ventilators (HRVs) that
recycle the heat ejected from indoor space could effectively
be applied to buildings in some European and Asian
countries [7].
Various studies were performed to examine the applic-
ability and contribution of HRVs to building energy
savings [8–16]. The results of these studies implied that the
annual heating energy could be effectively saved by the
application of HRVs, and the energy savings would vary
according to the outdoor climatic conditions that affected
sensible and latent heat. The recovery of sensible and
latent heat could reduce annual energy consumption of up
to 40%, and the optimum control strategies depended on
the ratio of latent to sensible heat [17,18]. The application
of HRVs has been demonstrated by previous studies and
would reduce heating energy consumption, but the
operation of HRVs in cold climate may not be economical
when the cooling set-point was above 248C [8,17].
A study, which was performed to examine the applic-
ability and energy saving by HRVs in several cities, have
shown that heating energy could be saved by 20%,
although this study was limited to heating season only
[19]. Other study that was conducted to investigate the
energy performance of HRVs in high latitude regions
showed that the energy savings achieved by the use of
HRVs would exceed the operational costs of the ventila-
tion system [20]. The contributions of HRVs to the
improvement of indoor air quality were also examined
under a variety of conditions [21–25]. These studies
showed that the application of HRVs in buildings can
contribute to improve ventilation rates with significant
energy savings.
Although the effects of HRVs in energy consumption
and ventilation in buildings have been examined in a
variety of studies, they were considered separately. Energy
saving effects with improved indoor air quality according
to the variations of controls for HRVs need to be studied
simultaneously when HRVs are applied to high-rise
residential buildings in real-world situations. It is well
known that effective applications of HRVs are to optimise
air supply and minimise energy consumption keeping IAQ
within ranges recommended by guidelines [26,27].
However, HRVs are usually controlled individually by
residents according to their personal preferences.
Continuous operation of HRVs would improve IAQ
effectively, but HRVs are usually operated only during
limited hours, when residents are at home. Therefore, this
study examined the effect of HRVs on IAQ and energy
savings under various control schemes in high-rise
residential buildings. The HRV operation schedules
preferred by real high-rise residents were examined to
determine the associated energy savings and most appro-
priate control options for HRVs in real-world settings.
Annual energy savings, according to preferred operation
schedules, are estimated and discussed.
Field measurements were performed in high-rise resi-
dential building, and computer simulations were con-
ducted to validate field results and predict annual energy
savings. A survey was also performed for high-rise
building residents to determine frequently-used operation
schedules for HRVs. Additional computer simulations
were then performed to assess the energy savings of HRVs
under these preferred operation schedules.
Research Methods
Field Measurements
The high-rise residential buildings examined in this
study were located in Seoul, South Korea (latitude:
37834’N, longitude: 126858’E), and were built in 2003
with steel reinforced concrete structures. The building that
used for summer measurements (Building ‘A’) has 69
floors, and two identical units on the 39th and 40th floors
were used for measurements. The building used for winter
measurements (Building ‘B’) has 46 floors, and meas-
urements were performed in two identical units on the 10th
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 487
and 11th floors. The floor plans of the units used for the
measurements are shown in Figures 1 and 2.
All units were prepared for general residential use.
Built-in wooden cabinets and bookshelves were installed in
kitchens and living rooms, respectively. The cabinet and
bookshelves were manufactured by a particular company
according to a standard specification for general
application to residential units. Hence, approximately
equal chemical compounds were embedded in them, and
the emission rates of chemical compounds from them were
considered to be equal, although the rates were not exactly
monitored. The cabinet and bookshelves were installed in
each residential unit on the same day of the field
measurements. There were no neighbouring buildings
along the main facades of this residential building, and
no shadows cast over the building by any nearby
structures. Venetian blinds with 2.54 cm between slats
were installed in all windows. The floor was furnished with
flooring on top of the Ondol, which is a radiant floor
heating system commonly used in Korea [28–31]. The
thermal properties of the buildings that are relevant to
energy consumption are summarised in Table 1.
A ceiling-mounted individual air-conditioning system
was used in each unit during the summer, and a district
heating system was used for the Ondol during the winter to
keep the indoor temperature within comfortable ranges as
suggested by the guidelines [32]. The air-conditioning
system supplied air to each room of each unit, and a
centralised ventilation system was applied to return the air
to the outdoors.
Sensible and total heat exchange types of HRVs were
installed in units and controlled to modulate ventilation
rates. The HRV control conditions are summarised in
Table 2. Air supply diffusers were installed in the living
rooms and the four bedrooms of each unit. Diffusers for
returning air were installed in the kitchens, dining rooms,
Fig. 1. Floor plan (Building ‘A’).
Fig. 2. Floor plan (Building ‘B’).
488 Indoor Built Environ 2012;21:486–502 Kim et al.
and living rooms of all units and connected to the HRVs
by ducts. The layouts of the ducts and diffusers are shown
in Figures 1 and 2.
To examine the influence of HRVs on energy savings
and IAQ, the HRVs installed in buildings A and B were
operated according to the control settings shown in
Table 3. In Case 1, both the supplied and returned air
passed through the HRV and participated in heat
exchange. The ventilation rate by the HRV was set at
0.5 air change rate per hour (ACH), satisfying the national
building code of Korea, 2003, during the time period when
the field measurements were performed [33].
Different countries have different ventilation rates set
for buildings [34–38]. In Korea, the recommended
ventilation rate set in the Building Codes, 2003 for the
residential buildings was 0.5 ACH, when this study was
performed. It should be noted that the revised Building
Code, announced in 2006, would require the rate to be not
less than 0.7 ACH, not including natural ventilation [38].
Since this study was performed in 2003, the ventilation
rate controlled in measurements was based on 0.5 ACH.
For Case 2, the HRV was shut off, so that no air passed
through it. Thus, infiltration through envelopes was the
only source of ventilation. For Case 3, the HRV was
operated without a core part where heat exchange occurs.
Accordingly, outdoor and indoor air passed through the
HRV without exchanging heat. The ventilation rate was
set at 0.5 ACH. For Case 4, the HRV was shut off for 24 h
and the core part was removed. Thus, no air passed
through the HRV, and no heat exchange occurred. The
source of ventilation was equal to that of Case 2. For all
cases, the indoor temperature was kept at 268C.The HRVs for Cases 5, 6, 7 and 8 in building B were
controlled according to the same settings that were applied
to Cases 1, 2, 3 and 4, respectively, except that the indoor
temperatures were kept at 238C for all four cases. For all
eight control cases, natural ventilation rates through
windows were measured in Room 3 and in the living
room of each unit using the tracer gas concentration decay
method, which has been used effectively to determine
ventilation rates by infiltration and mechanical systems in
buildings [39,40].
In this study, the ventilation rates by the tracer gas
concentration decay method were measured using a multi-
gas monitor and multi-point samplers. In this study, the
tracer gas concentration decay method was used to
determine ventilation rates in the space. A multi-gas
monitor and multi-point samplers were used to monitor
the concentration variation in CO2. Three samplers were
installed at the height of 1.2m in the Room 3 and living
room. One sampler was positioned at the centre of each
room, and the other two samplers were positioned along a
diagonal line of the Room 3 and living room. The distance
between each sampler was 1.5m.
Before data monitoring procedures for the concentra-
tion began, CO2 gas was sprayed and introduced into the
Table 3. Control settings for heat recovery ventilators (HRVs)
Case Bldg. Floor HRV control condition Season
Operation Heat Exchange Core part Air passed
1 A 39 24 h ON Exchanged Installed Passed Summer2 A 39 24 h OFF Not exchanged Installed Not passed3 A 40 24 h ON Not exchanged Removed Passed4 A 40 24 h OFF Not exchanged Removed Not passed5 B 10 24 h ON Exchanged Installed Passed Winter6 B 10 24 h OFF Not exchanged Installed Not passed7 B 11 24 h ON Not exchanged Removed Passed8 B 11 24 h OFF Not exchanged Removed Not passed
Table 1. Building thermal properties
Properties Building ‘A’ Building ‘B’
Floor area (m2) 207 217Ceiling height (m) 2.4 2.4U-value of window (W/m2 K) 3.40 3.34U-value of wall (W/m2 K) 2.74 2.65Ratio of window to wall (%) 43 41
Table 2. Conditions of HRVs
Item Bldg. ‘A’ Bldg. ‘B’
Heat exchange type Sensible andlatent
Sensible
Efficiency of latent heat exchange (%) 39.3 N/AEfficiency of sensible heat exchange (%) 62.5 55.1
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 489
tested rooms and mixed by a fan. Once the CO2 gas
was mixed completely with the air in the space, the
reduction in CO2 gas concentration was monitored. The
data monitoring was performed for 6 h with a monitoring
interval of 12min. The mean value of CO2 concentration
monitored by the three samplers was used to determine
ventilation rates in the space. The determination was
performed based on the theoretical background that has
been approved and effectively used in other previous
research [39–43].
The concentrations of indoor air contaminants were
monitored for Cases 1, 4, 5 and 8 to examine the effects of
HRVs on the dilution of air pollutants. The concentration
of formaldehyde was measured in Room 3 and in the
living room of each unit. The concentrations of VOCs
were monitored in the living room of each unit. The
measurement was performed at a height of 1.2m in the
centre of each room.
Data monitoring began 1 month after construction was
completed in each unit. Data monitoring intervals for
formaldehyde were: 5 h, 10 h, 1 day, 5 days and 7 days
after the conditions for HRVs outlined in Table 3 were
initiated. The concentrations of VOCs were monitored
once, 5 h after the initiation, based on Korean building
codes used to assess indoor air quality [33,38].
To examine cooling and heating energy consumption,
the total amount of electricity consumed by the air-
conditioning system, fans, and HRV controllers was
measured. The energy used by the Ondol was also
calculated based on input calories of district hot water
used for heating in each unit. Data monitoring in Building
A was performed from June 1 to August 30, 2003, and
monitoring in Building B was performed from January 1
to February 28, 2004.
Computer Simulation
In this study, field measurements were performed for
Building A in summer and Building B in winter. No
measurement data are available for either building for the
remainder of the year. Therefore, computer simulations
were used both to validate the results of field meas-
urements and to predict energy savings by HRVs in
seasons when measurements were not performed.
TRACE 700 was used in simulations to determine
energy consumption under various control conditions for
HRVs. TRACE 700 uses analyses of dynamic load
calculations to simulate heating and cooling loads
according to design alternatives, systems, equipment and
economic analysis. TRACE 700 was pre-programmed with
common design parameters for construction materials,
equipment, base utilities, weather conditions and sched-
uling [44].
Loads were calculated using the response factor
method, which considers heat storage effects occurring
on sealed environmental envelopes. Infiltration rates,
irradiance and heat generation by lighting and occupants
are also considered in the computation algorithms. Due to
these features, TRACE 700 was considered an effective
tool to perform energy analysis for buildings [45,46].
The input data for simulations were equal to the
conditions applied in both buildings used for field meas-
urements. The area and height of each unit, heat transfer
coefficients of windows and walls and lighting loads were
considered. Standard weather data for Seoul, Korea were
used as input data [47]. The specific conditions used to
control HRVs during field measurements were applied
across all simulations to determine the effects of HRVs on
energy savings. Under these conditions, monthly simula-
tions were performed for Cases 1, 3, 5 and 7 during a
period from January to December.
Survey of High-rise Residents to Determine Operation
Schedules
A survey was conducted with the high-rise residents to
determine practical operation hours of HRVs, since HRVs
installed in the buildings are controlled individually by
residents according to personal preferences. A total of 72
female and 42 male high-rise residents, living in apartment
units fitted with HRVs, participated in the survey. Their
education levels ranged from high school to postgraduate
education. The number of family members in each unit
ranged from one to six.
Surveys were conducted personally by interviews
with the residents. The surveys included both
general and specific questions. The general questions
were intended to collect participants’ information such
as gender, age, number of family members, education
level, occupation and which floor of the building they
lived on. The specific questions solicited information
about the participants’ preferences for using HRVs,
including operation hours, situations in which they
typically used HRVs, usual operating modes, and satisfac-
tion levels.
Survey data were analysed to determine frequently-used
operation schedules for HRVs in real-life contexts. Levels
of HRV energy consumption were calculated according to
these operation schedules using TRACE 700.
490 Indoor Built Environ 2012;21:486–502 Kim et al.
Results
Variation of Temperature, Humidity and Ventilation
Rate
The measured outdoor air temperatures and humidity
during data monitoring periods varied but remained
within typical summer and winter ranges for Korea.
Figures 3 and 4 show examples of such variation during a
3-day period in August and January, 2003, respectively. In
general, temperature was significantly influenced by solar
altitude, remaining high during the day and decreasing as
the sun set.
The measured outdoor temperature ranged from 23.48Cto 31.58C in summer. The temperature typically remained
above 268C at night, and reached 29.68C in some cases,
which implies that cooling systems must be continuously
operated during the summer to keep indoor temperatures
within a comfortable range. In winter, the temperature
varied from 12.58C to 4.48C, and remained below 08C for
the majority of the time. This range indicates that heating
must be provided continuously both day and night during
the winter to keep indoor temperatures within a comfor-
table range. The difference between outdoor air tempera-
ture and comfortable indoor temperatures was greater in
winter than in summer. Accordingly, more energy was
used in winter than in summer to keep indoor air within
comfortable ranges as recommended by guidelines [32].
Outdoor relative humidity varied from 63% to 99% in
summer, such that outdoor air needed to be dehumidified
before being supplied indoors to ensure resident comfort.
However, dehumidification is not always required in
winter, since humidity remained between 25% and 41%.
This means that the HRVs function less effectively during
the summer in terms of latent heat exchange between
outdoor and indoor air.
Indoor air temperatures, controlled by HRVs, ranged
from 25.38C to 26.48C in the summer, and from 19.68C to
23.68C in winter. These ranges meet the target temperature
ranges set for both seasons in this study. The effects of
HRVs in terms of energy savings were expected to be
weaker during the summer than winter, since the
difference between outdoor and indoor air temperature
could have an effect on the reduction of energy consump-
tion when HRVs are used.
Figure 5 shows an example of measured CO2 concen-
tration in the Room 3 for the Case 5 and Case 6 in Table 3,
and the ventilation rates which were determined using the
gas concentration decay method based on the monitored
CO2 concentration. Overall, the concentration of CO2
decreased significantly for the two cases over the time
period after data monitoring began. The concentration of
CO2 decreased from 4572 ppm to 1070 ppm and from
4745 ppm to 1363 ppm for the Cases 5 and 6, respectively.
After the test began, the reduction in concentration during
each time interval was greater for the Case 5 than that
of Case 6 due to the influence of HRVs on ventilation.
0
1000
2000
3000
4000
5000
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336
Accumulated time [minutes]
CO
2 C
once
ntra
tion
[ppm
]
0.0
0.2
0.4
0.6
0.8
1.0
Ven
tilar
ion
rate
[AC
H]
CO2 variation-Case 5CO2 variation-Case 6
Ventilation rate-Case 5Ventilation rate-Case 6
Fig. 5. Example of measured CO2 concentration and ventilationrates by tracer gas concentration decay method (Room 3, Cases 5and 6).
–20
–10
0
10
20
30
40
0 12 24 36 48 60 72
Time [hr]
Tem
pera
ture
[°C
]
0
20
40
60
80
100
120
Rel
ativ
e H
umid
ity [%
].
Winter-OA Temp.Winter-10th Temp.Winter-RH
Fig. 4. Variation of temperature and humidity (22–24 January).
0
5
10
15
20
25
30
35
40
0 12 24 36 48 60 72
Time [hr]
Tem
pera
ture
[°C
]
0
20
40
60
80
100
120
Rel
ativ
e H
umid
ity [%
].
Summer-OA Temp.Summer-39th Temp.Summer-RH
Fig. 3. Variation of temperature and humidity (2–4 August).
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 491
The reduced concentration ranged from 40 ppm to
292 ppm and 56 ppm to 236 ppm for the Cases 5 and 6,
respectively.
Based on the reduction in CO2 concentration for each
data monitoring point, ventilation rates were determined
[39–41]. The ventilation rates for the Cases 5 and 6 ranged
from 0.40 ACH to 0.49 ACH and 0.18 ACH to 0.20 ACH,
respectively. For the entire monitoring period, the mean
ventilation rates for Cases 5 and 6 were 0.44 ACH and
0.19 ACH, respectively. These procedures were equally
applied to the 8 cases summarised in Table 3 to determine
ventilation rates using the tracer gas concentration decay
method.
Figure 6 shows the measured ventilation rates using the
tracer gas concentration decay method for all eight cases
in relation to the HRVs and natural ventilation used. In
each case, ventilation rates were similar for Room 3 and
the living room in each unit. For all cases, the differences
between these two rooms ranged from 0.01 to 0.1 ACH.
The natural infiltration rates ranged from 0.19 ACH to
0.32 ACH for Cases 2, 4, 6 and 8, in which HRVs were
shut off and no air passed through them. The differences
between Room 3 and the living room in each unit ranged
from 0.01 ACH to 0.04 ACH, indicating that the
recommended ventilation rate was not satisfied fully by
natural infiltration alone, and that HRVs must be
operated in order to achieve the recommended rates.
This result also indicates that natural infiltration rates
were not equal for different apartment units located on
different floors due to fluctuations in outdoor air pressure
and unpredictable airflow.
Under those natural infiltration conditions for the all
residential units, the HRVs were operated according to the
control settings given in Table 3, and provided additional
ventilation rates to meet the required ventilation rates of
the Korean Building Code. When HRVs were operated for
24 h, the ventilation rate would vary from 0.44
ACH to 0.58 ACH and rarely failed to meet the ventilation
rate requirement as given by the Korean Building Code in
2003 [33].
The differences between the ventilation rates of the odd
and even numbered-cases in Figure 6 were the contribu-
tions of the HRVs to the final ventilation rates in Room 3
and living room of each unit. The ventilation rates
provided by the HRVs ranged from 0.16 ACH to 0.30
ACH. The minimum contribution occurred in Room 3 for
Cases 3 and 4, and the maximum contribution was in the
living room for the Cases 1 and 2.
Concentrations of Air Pollutants
The concentrations of indoor air pollutants showed
noticeable differences according to ventilation rates and
the volume of space in each unit. The concentrations of
formaldehyde for Cases 1, 4, 5 and 8 are shown in
Figure 7. Overall, the concentrations of formaldehyde
were stronger when HRVs were shut off and the
ventilation was depended on natural infiltration only.
The slope of the decrease for a given interval was not
steeper under this condition. Therefore, more time was
required to dilute the concentrations of formaldehyde
when HRVs are not operated.
For all cases, the concentrations of formaldehyde in
Room 3 were expected to be stronger than in the living
room due to the surface to volume ratio of each space,
assuming equal ventilation rates. However, the concentra-
tions of formaldehyde were stronger in the living room
than in Room 3 for the entire data monitoring period,
probably because unpredictable amounts of formaldehyde
0.51
0.26
0.48
0.32
0.44
0.19
0.51
0.23
0.56
0.26
0.58
0.3
0.45
0.23
0.47
0.26
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1 2 3 4 5 6 7 8Case
Ven
tilat
ion
Rat
es [
AC
H].
Room #3 Livingroom
Fig. 6. Ventilation rate by tracer gas concentration decay method.
0
20
40
60
80
100
120
140
160
5 10 24 72 120 168Time [hr]
Con
cent
ratio
n [µ
g/m
3]
Case 1-Room 3Case 4-Room 3Case 5-Room 3Case 5-LivingroomCase 8-Room 3Case 8-Livingroom
Fig. 7. Concentration variation of formaldehyde.
492 Indoor Built Environ 2012;21:486–502 Kim et al.
molecules were emitted from the built-in furniture such as
cabinet and bookshelves.
When HRVs were shut off, the strongest concentrations
of formaldehyde were detected in the living room in Case
8. These concentrations were still lower than those given
by the National Building Code in Korea in 2003.
According to the Building Code, the concentration of
formaldehyde in newly-constructed residential buildings
should not exceed 210mg/m3 [48]. However, formaldehyde
should still be diluted to prevent any potential hazards to
residents who will be exposed to the pollutants continu-
ously as long as they live in the building.
The concentrations of formaldehyde in each space
decreased gradually with time up to 168 h. When the
ventilation rate by natural infiltration in Case 8 was 0.26
ACH, the initially measured concentration was 137.31 mg/m3 in the living room, which was reduced by 65.96 mg/m3
after 168 h. Meanwhile, the concentration in Room 3 was
reduced by 45.77mg/m3 during the same period. This
suggests that the dilution occurred faster in the living
room within this limited time period.
The concentrations of formaldehyde appeared to be
diluted continuously beyond 168 h due to lower infiltration
rates, which were not sufficient to dilute the air and
decrease the concentration. The differences between the
concentrations in the living room and in Room 3 became
smaller as time passed, varying from 37.69 mg/m3 to
17.50mg/m3 after 168 h. This suggests that the concentra-
tions in both rooms continued to become lower beyond
that time point, and that the difference between the rooms
would continue to decrease.
In cases in which HRVs were operated, the concentra-
tion of formaldehyde began to reduce significantly after
24 h. Compared with Case 8, the dilution of air in both
Room 3 and the living room was more effective, and
formaldehyde molecules were removed more quickly. The
concentration did not appear to continue to decrease
noticeably after 168 h. However, the concentration was
expected to decrease stably beyond this point, showing
very narrow decreasing ranges.
In Case 5, in which the ventilation rate was 0.45 ACH,
the initially monitored concentration was 86.16 mg/m3 in
the living room and 52.50 mg/m3 in Room 3. After 168 h,
the concentrations in the living room and Room 3 were
reduced by 81.1% and 82.1%, respectively. This result
suggests that more formaldehyde was removed from the
living room than from Room 3, although the ratio of
initial concentration to final concentration was not
significantly different between the two rooms. The initial
concentrations in the living room and Room 3 in Case 5
were narrower than in Case 8. The differences in
concentrations during the initial stage in both cases were
reduced with time. The difference between monitoring
periods varied from 6.73 mg/m3 to 33.66 mg/m3 in Case 5,
and ranged from 16.15mg/m3 to 44.42mg/m3 in Case 8.
After 168 h in Case 5, the concentration of formalde-
hyde in the living room was reduced 1.62 times greater
than that in Room 3, reduced by70 mg/m3 in the living
room and 43.08mg/m3 in Room 3. In Case 8, the decrease
in concentration was 65.96mg/m3 in the living room and
45.77 mg/m3 in Room 3. This result implies that smaller
ratios of surface area to volume could help to dilute the
concentrations.
These results may be explained by differences in surface
area and volumes of spaces. The ratio of surface area to
volume in each room was a critical factor that had an
effect on the concentration of pollutants under approxi-
mately equal ventilation rates. Space with larger floor area
and therefore greater surface areas, would have a higher
amounts of pollutants emitted from the surfaces. In
addition, larger spaces would require more air to be
supplied by the ventilation rates.
Room 3 was smaller than the living room, which was
open to the dining room and kitchen. The ratios of surface
area to volume were 1.92 for Room 3 and 1.47 for the
living room. This means that the surface area per amount
of air supplied to the living room was less than that
supplied to Room 3. Accordingly, this resulted in more
effective reduction of formaldehyde molecules in the living
room than in Room 3.
In general, the concentrations of formaldehyde and
VOCs in indoor space are determined by the emission rates
from the material and ventilation rates which should be
controlled to maintain comfortable environments. In this
study, the emission rates from the materials, such as the
built-in cabinet and book shelves were assumed to be equal
since they were manufactured by the same manufacturer
according to standard specifications for them.
In addition, they were installed in each residential unit
on the same day, and without being altered or changed
during the field measurements of this study were
completed. Due to these assumptions, the emission rates
from the material were not measured in this study. This
point might be considered as a research limitation, but the
assumption provided reliable grounds for the reduction of
formaldehyde and VOCs concentrations when the ventila-
tion rates were controlled by the HRVs.
Logarithmic regression models were developed for
Cases 1 and 5 to predict the relationship between
formaldehyde concentration and the accumulated time
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 493
which can be applied to the amount of air supplied to
each space. The time elapsed from the beginning of
data monitoring was considered an independent
variable in the model. The difference between initial
formaldehyde concentration and the formaldehyde con-
centration at each time point was considered as a
dependent variable.
The predicted relationship is shown in Figures 8 and 9
and Table 4. Each data point represents the decrease in
formaldehyde concentrations. Overall, a strong relation-
ship was demonstrated between the two variables for all
cases considered in the regression analysis.
The concentrations monitored in Cases 1 and 5
appeared to decrease, showing stable patterns within
limited ranges, and forming a plateau beyond 168 h. This
suggests that the decrease in concentration would stop at
some time beyond that point when a constant volume of
air was supplied to the space continuously under a
constant ventilation rate. As discussed previously, the
decrease in the living room in Case 5 was more efficient
than in Room 3. The coefficients of determination were
0.9442 and 0.94 for Room 3 and the living room,
respectively. This means that the variation of the decreased
concentration of formaldehyde was reduced by 94.42%
and 94% over the time period during the monitoring. The
relationship for Room 3 in Case 1 was also strong.
The regression model was tested using ANOVA to
determine whether a logarithmic relationship existed
between elapsed time and formaldehyde concentration.
Table 4 demonstrates that the logarithmic regression
models were acceptable under the significance level of
0.05, since the levels calculated for all cases were less than
0.01. These models imply that the formaldehyde emitted
from indoor spaces could be removed completely after
260 h when ventilation rates were maintained at 0.45 ACH
by HRVs.
Case 1, Room 3
R2 = 0.948
Case 5, Room 3
R2 = 0.9442
Case 5, Livingroom
R2 = 0.94
0
20
40
60
80
100
0 50 100 150 200Accumulated Time [hr]
Dec
reas
ed C
once
ntra
tion
[%]
Case 1-Room 3Case 5-Room 3Case 5-Livingroom
Fig. 8. Correlation between accumulated time and reduced amountof formaldehyde concentration (Cases 1 and 5).
Case 4, Room 3
R2 = 0.9424
Case 8, Room 3
R2 = 0.8793
Case 8, Livingroom
R2 = 0.9641
0
20
40
60
80
100
0 50 100 150 200Accumulated Time [hr]
Dec
reas
ed C
once
ntra
tion
[%]
Case 4-Room 3Case 8-Room 3Case 8-Livingroom
Fig. 9. Correlation between accumulated time and reduced amountof formaldehyde concentration (Cases 4 and 8).
Table 4. ANOVA test results for model
Model Variable Unstandardised coefficients T Sig. ANOVA test
B Std. Error ‘F’ test Sig
Case 1, Room 3 ln (Time) 30.54 4.07 7.51 0.00 F(1,4) ¼ 56.36 0.00(Constant) �70.95 16.56 �4.28 0.02
Case 5, Room 3 ln (Time) 26.81 3.79 7.08 0.01 F(1,4)¼ 50.13 0.01(Constant) �49.05 15.41 �3.18 0.05
Case 5, Living room ln (Time) 17.93 2.68 6.70 0.01 F(1,4)¼ 44.91 0.01(Constant) �10.52 10.89 �0.97 0.41
Case 4, Room 3 ln (Time) 5.09 0.76 6.73 0.01 F(1,4)¼ 45.24 0.00(Constant) 6.96 3.08 2.26 0.11
Case 8, Room 3 ln (Time) 8.44 1.79 4.71 0.02 F(1,4)¼ 22.16 0.02(Constant) �2.19 7.30 �0.30 0.78
Case 8,Living room ln (Time) 12.27 1.29 9.49 0.00 F(1,4)¼ 89.98 0.00(Constant) �16.07 5.27 �3.05 0.06
494 Indoor Built Environ 2012;21:486–502 Kim et al.
In Cases 4 and 8, the formaldehyde concentrations in
each space were reduced by approximately 50% after
168 h. This result occurred despite the fact that HRVs were
not operated and ventilation was depended on natural
infiltration only. Ventilation rates were not high enough to
dilute the formaldehyde molecules that were being
accumulated in the space after emissions from surface
areas such as wall, floor and ceiling. The reduction in
concentration occurred effectively in the living room
within a given time interval. This result is consistent with
those of Cases 1 and 5.
The coefficient of determination varied from 0.8793 to
0.9641. This implies that the variation in the decrease of
formaldehyde concentration was reduced from 87.93% to
96.41% when the elapsed time changed. Table 4 demon-
strates that the models used were acceptable under the
significance level of 0.05. Unlike Cases 1 and 5, a period of
at least 12,831 h was necessary to dilute all formaldehyde
molecules emitted from indoor spaces. The results for
Room 3 in Case 4 were even worse than those results.
The concentrations of VOCs measured in the living
room of each building are shown in Figures 10 and 11.
Outdoor air contained toluene up to 38 mg/m3, and the
concentrations of other pollutants were weaker. The
concentrations of VOCs in the living room were affected
by the ventilation rates of HRVs and infiltration.
For Cases 4 and 8, when HRVs were not operated and
infiltration was the only source of ventilation, the
concentration of toluene was 345 mg/m3 and 298 mg/m3,
respectively. The concentrations of ethylbenzene and mp-
xylene varied from 268 mg/m3 to 344 mg/m3 in both cases.
Benzene does not seem to be a very critical pollutant.
As with formaldehyde, no VOC pollutants exceeded the
concentration given by the National Building Code of
Korea, 2003, which specifies permissible concentrations of
benzene, toluene, ethylbenzene and xylene as 30 m/g,1000m/g, 360 m/g and 700 m/g, respectively [48]. Although
the monitored concentrations did not violate these codes,
they should still be diluted to improve indoor air quality.
In particular, attention should be paid to reduce the
concentration of ethylbenzene.
The concentrations of all VOC pollutants were reduced
significantly as HRVs were operated. In Case 1, the
concentrations of toluene, ethylbenzene and mp-xylene
were 59.6%, 46.9% and 49.3%, respectively, in Case 4.
The concentrations of the three VOCs in Case 5 were
reduced by 50.1%, 60.1% and 50.5%, respectively, as
compared with the concentrations in Case 8.
The amounts of each pollutant that were removed were
not equal in Cases 1 and 5 due to the differences in initial
concentrations and ventilation rates. In Cases 1 and 5,
benzene was completely removed from the space with the
aid of ventilation by HRVs. However, the concentration of
o-xylene was reduced by only 3%.
It appears that the decreases of pollutant concentra-
tions were influenced by the ratio of surface area to
volume in the living room and by ventilation rates. Under
equal ventilation conditions, the decreases in concentra-
tions occurred more efficiently when the ratio of surface
area to volume was smaller. Those ratios for the living
room were 1.75 in Building A and 1.47 in Building B.
Therefore, decreases in concentrations occurred more
effectively in the living rooms of Building B than in
Building A.
Although the ventilation rates for Building A were
greater than for Building B by 0.11 ACH, the ratio of
surface area to volume of the living room was a more
influential factor in reducing the concentrations of VOCs.
This implies that the removal of pollutants emitted from
indoor surfaces was influenced critically by this ratio when
ventilation rates were not significantly different.
0
50
100
150
200
250
300
350
400
Benzene Toluene Ethylbenzene m, p-xylene o-xylenePollutant
Con
cent
ratio
n [µ
g /m
].3
OutdoorCase 1Case 4
Fig. 10. Concentration of VOCs (Cases 1 and 4).
0
50
100
150
200
250
300
350
400
Benzene Toluene Ethylbenzene m, p-xylene o-xylene
Pollutant
Con
cent
ratio
n [µ
g/m
3].
OutdoorCase 5Case 8
Fig. 11. Concentration of VOCs (Cases 5 and 8).
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 495
In summary, the pollutants emitted from various
materials are important factors in deteriorating IAQ.
They should be removed or diluted by ventilation to
maintain indoor air quality. However, when ventilation
rates are set to maintain the required quality of indoor air,
more energy consumption would occur. Under these
circumstances, the HRVs considered in this study should
be a good alternative for improving IAQ with associated
energy savings.
Energy Consumption Measurements and Validation
Energy consumption in each assessed residential unit of
the high-rise buildings was reduced by the operation of
HRVs to maintain ventilation rates in each unit. Figure 12
shows the monthly energy consumption required to keep
indoor air temperatures within target ranges. Overall, less
energy was consumed in Cases 1 and 5 than in Cases 4 and
8, because outdoor air passed through the HRVs and
exchanging heat with exhausted indoor air at the target
temperatures, which were maintained during the monitor-
ing period.
Heat exchange by HRVs was a meaningful factor in
energy consumption when the temperature difference
between outdoor and indoor air was large. When the
HRVs were shut off and no heat exchange occurred
between exhausted air and outdoor air (Case 8), the
amount of heating energy consumed in January and
February was 1996 kWh and 1864 kWh, respectively.
However, the heating energy consumption was saved by
11.55% on average when the HRVs were operated for 24 h
exchanging heat in winter (Case 5). This result occurred
since the sensible heat that is expressed in terms of
temperature difference between air and air was a
significant contributor to the energy savings.
While the energy saving effect in winter was effective,
the savings in summer was not efficient. In particular, the
HRVs had contributed to save cooling energy up to 3.76%
in the summer. Since the temperature differences in
summer were smaller than that during the winter, less
efficient energy savings were achieved by HRVs during the
summer. In this study, the indoor air temperature was set
at 268C in summer, and the temperature difference
between outdoor and indoor air did not exceed 78C.It appears that the contribution of latent heat recovery
was not significant in energy savings in winter. The
portion of latent heat exchange for heat recovery
ventilators should be considered to improve energy
savings. In general, the results of this study were consistent
with previous studies which were conducted to examine
the influence of heat recovery systems on energy savings in
buildings located in two different climatic conditions [19].
The result showed that the operations of heat recovery
systems saved heating energy effectively in winter when the
outdoor air temperature ranged from �12 to �88C.However, the use of heat recovery system was ineffective
when the cooling set-point in indoor space was above 248Cfor a particular climatic region where outdoor temperature
was 338C.Other study showed undesirable influence of uncon-
trolled heat recovery systems on cooling loads in mild and
cold climate region [17,49]. The results revealed that
temperature-based control strategies should be necessary
to reduce cooling energy consumption. Additional
research also proved that higher cooling energy demand
occurred for particular outdoor conditions during summer
when indoor temperature is higher than the outdoor
temperature and cooling is still necessary to meet thermal
comfort for residents [50]. Although the heat recovery
ventilators were not effective for particular outdoor
conditions in summer, they significantly reduced heating
energy consumption in winter.
Total energy consumption was lowest in June and
highest in August. For Case 1, the energy consumed in
June was 40.54% of that consumed in August. The solar
altitude is highest in June, and the influence of solar
radiation on the cooling load is significant. However, the
mean temperature profile in Korea indicates that the
outdoor temperatures and humidity are greater in August
than in June. This resulted in more cooling energy
consumption in August.
In this study, the energy consumption by HRVs in high-
rise residential buildings was measured during a limited
period, not year-round. To examine the influence of HRVs
on energy savings for entire seasons, computer simulations
were performed using TRACE 700. Experimental data
0
500
1000
1500
2000
2500
Jan. Feb June July AugMonth
Ene
rgy
Con
sum
ptio
n [k
Wh]
.
Case 1Case 4Case 5Case 8
Fig. 12. Measured energy consumption.
496 Indoor Built Environ 2012;21:486–502 Kim et al.
were used as input data in the simulations to predict
energy consumption for periods during which measure-
ments were performed. Standard weather data were also
used for simulations [47].
The results of both experimental measurements and
simulations were examined using linear regression analysis
to validate simulation results. The relationships between
these data are shown in Figure 13. ANOVA tests were
performed to identify significant relationships. A summary
of the tests is shown in Table 5.
The test results indicate that an acceptable linear
relationship existed between measured and simulated
energy consumption for Case 1 (F(1,23)¼ 37.64, p50.05)
and Case 3 (F(1,23)¼ 71.15, p50.05). The coefficient of
determination was 0.8862 for Case 1 and 0.8887 for Case
3. This implies that the variation in simulated results was
reduced by 88.62% and 88.87% for Cases 1 and 3,
respectively, when measured results were used to predict
simulated results. Since the validation was acceptable, the
energy consumption for the rest of the year was predicted
using simulations.
The predicted energy consumption for each month
under various control settings is shown in Figures 14 and
15. Positive and negative values indicate heating and
cooling energy consumption, respectively. Overall, the
energy consumption for each month was less for Cases 1
and 5, when the HRVs were operated to exchange heat
between outdoor air and the exhausted air from indoors.
Specifically, Cases 1 and 5 resulted in annual energy
savings of 23.29% and 18.25% as compared to Cases 3
and 7, respectively. These results were consistent with
previous research, which revealed that heating energy
could be reduced by 20% when heat recovery ventilators
were employed during winter [17,19].
In summary, efficient energy savings were achieved
when heating was necessary, since heat exchange occurred
effectively in the HRVs due to the temperature differences
between outdoor and indoor air. The HRV systems could
achieve effective energy savings and ventilation rates with
improved IAQ in high-rise residential buildings, where
natural ventilation is limited due to tightly-sealed
envelopes.
Determination of Preferred Operation Schedules and
Energy Savings
A total of 72 female and 42 male residents of a high-rise
building participated in the survey. The ages of partici-
pants ranged from 18 to 80. Overall, 87.7% of participants
were older than 40, and 54.4% of those were females.
A detailed distribution of participants’ ages is shown in
Figure 16.
A total of 43% of the survey participants were women
who did not work outside the home and who spent the
majority of their time in their residential units. A total of
37.7% of the participants were professional or self-
employed, and the rest of the participants were students
and salaried persons who commute regularly. Their
education levels ranged from high school to graduate
degrees. A detailed distribution of occupation and educa-
tion levels is shown in Figure 17.
The survey participants preferred to operate HRVs
between 6 and 12 h per day. The operation hours fell into
the range was 55.2% of all the residents surveyed. A total
of 8.8% of the participants preferred to use HRVs
continuously for 24 h per day, but 35.9% of the
Case 1
R2 = 0.8862
Case 3
R2 = 0.8887
0
5
10
15
20
25
0 5 10 15 20Measured Energy [kWh]
Sim
ulat
ed E
nerg
y [k
Wh]
.
Case 1
Case 3
Fig. 13. Correlation between measured and simulated energyconsumption.
Table 5. ANOVA test results for validation
Model Variable Unstandardised coefficients T Sig. ANOVA test
B Std. Error ‘F’-test Sig.
Case 1 (Constant) 0.591 1.10 0.54 0.60 F(1,23)¼ 37.64 0.01Slope 0.961 0.16 6.14 0.00
Case 3 (Constant) 0.034 0.97 0.04 0.97 F(1,23)¼ 71.15 0.00Slope 1.014 0.12 8.44 0.00
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 497
participants preferred to use HRVs less than 1 h per day.
The preferred operation hours for HRVs are shown in
Figure 18.
The survey participants particularly preferred to use
HRVs while they cooked, dined and rested after dining,
with 67.5% indicating such a preference. A total of 6.1%
of the participants preferred to operate HRVs while they
slept. A total of 11.4% of the participants preferred to use
HRVs only when they felt it was necessary. The preferred
cases for operating HRVs are shown in Figure 19.
In this study, preferred operation schedules for HRVs
were determined based on survey results to predict energy
savings by HRVs for the preferred operation hours. The
majority of operation hours preferred by residents did not
exceed 12 h per day, and HRVs were used primarily
around cooking, dining and resting times. Accordingly, it
was determined that operation schedules of 6 and 12 h
were assigned for those three activities to perform com-
puter simulations. The determined operation schedules are
shown in Table 6, and the shaded areas indicate that the
HRVs were operated for the designated time.
The procedures used to predict monthly energy
consumption discussed in the previous section were
applied to the simulations under the determined operation
schedules shown in Table 6. Predicted monthly energy
consumption under two operation schedules is shown in
1.8 1.80.0
1.8
14.0
17.5
1.83.5 3.5
19.3
28.1
7.0
0
5
10
15
20
25
30
< 20 21-30 31-40 41-50 51-60 > 60Age
Per
cent
age
[%]
male
female
Fig. 16. Participants’ age.
–8
–6
–4
–2
0
2
4
6
8
10
12
1 2 3 4 5 5 6 7 8 9 10 11 12
Month
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
Case 5 Case 6
Fig. 15. Predicted energy consumption (Building ‘B’).
1.80.0 0.0 0.0 0.0 0.0
30.7
1.8
5.3
14.9
5.33.5
10.5
0.01.8
3.5
14.0
7.0
0
10
20
30
40
Housewife Student Salaryman Self-employed
Professional etc
Occupation
Per
cent
age
[%]
HighschoolBacholorMaster
Fig. 17. Participants’ education level and occupation.
7.0
28.9 29.8
25.4
8.8
0
10
20
30
40
No use <1 1-6 7-12 24Operation hour [hr]
Per
cent
age
[%]
Fig. 18. Preferred operation hour for HRVs.
–8
–6
–4
–2
0
2
4
6
8
10
12
1 2 3 4 5 5 6 7 8 9 10 11 12
Month
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
Case 1 Case 2
Fig. 14. Predicted energy consumption (Building ‘A’).
498 Indoor Built Environ 2012;21:486–502 Kim et al.
Figures 20 and 21. Positive and negative values indicate
heating and cooling energy consumption, respectively.
Overall, slightly less energy was consumed when HRVs
were used for at least 12 h in the two buildings. Compared
with energy consumption during summer, more energy
was consumed from December to February when heating
was necessary. This result was similar to that for the two
buildings in which the two types of HRVs were controlled
in Cases 1, 3, 5 and 7.
In particularly, the amount of energy consumed in
winter was 2.6 times greater than that consumed in
summer. The energy consumed by the total heat exchange
type of HRVs was slightly greater than that consumed by
the sensible heat exchange type of HRVs. This means that
the sensible heat had an influence on energy consumption
in the season.
In summary, the amount of annual energy consumption
under operation schedules preferred by residents and the
other three cases discussed in the previous section is shown
in Figures 22 and 23. Overall, heating energy was a major
portion of the energy consumption, ranged from 71.90%
to 75.93% of the total energy consumption when HRVs
were operated according to various control settings.
The HRV operated 24 h continuously in Cases 1 and 5
saved energy more effectively than other operation
schedules. In particularly, heating energy consumption
was reduced by 9.54% and 8.09% compared with Cases 2
and 6, respectively. Cooling energy in Cases 1 and 5 was
reduced by 10.63% and 3.39%, respectively. This means
that annual energy consumption can be reduced by
20.17% when HRVs are operated for 24 h continuously,
exchanging sensible and latent heat.
When the total heat exchange types of HRVs were used
according to operation schedules preferred by survey
participants, total annual energy consumption was
reduced by 8.49%. The sensible heat exchanging HRVs
reduced energy consumption by 5.64% annually. The
worst case scenario for energy savings happened in Cases 3
and 7 when HRVs were operated 24 h continuously
without heat exchange. However, such control schedules
Table 6. Operation schedule for HRVs according to residents’ preference
Operation Time (1–24 h)
schedule 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 246 h œ œ œ œ œ œ g g œ œ œ g g œ œ œ œ g g œ œ œ œ œ12 h œ œ œ œ œ g g g g œ œ g g g œ œ g g g g g œ œ œ
11.4
3.5
11.4
6.1
30.7
21.9
14.9
0
10
20
30
40
No use etc whennecessary
sleep cooking dining Aftercooking
Case for using HRV
Per
cent
age
[%]
Fig. 19. Preferred case for operating HRVs.
–8
–6
–4
–2
0
2
4
6
8
10
12
1 2 3 4 5 5 6 7 8 9 10 11 12
Month
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
6hr 12hr
Fig. 20. Predicted energy consumption according to operationschedule (Bldg. ‘A’).
–8
–6
–4
–2
0
2
4
6
8
10
12
1 2 3 4 5 5 6 7 8 9 10 11 12
Month
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
6hr 12hr
Fig. 21. Predicted energy consumption according to operationschedule (Bldg. ‘B’).
Indoor Living Environment in Residential Buildings Indoor Built Environ 2012;21:486–502 499
are not found in reality, since real HRVs supply untreated
outdoor air into indoor spaces.
Conclusions
This study was performed to examine the influence of
HRVs on energy savings and IAQ in high-rise residential
buildings. The summary of findings is as follows.
1. The use of HRVs would enable the apartment units to
meet the mandatory ventilation rates given by the
National building Codes of Korea and effectively
improved IAQ. More formaldehyde molecules would
be removed from large spaces than from small spaces,
since the ratio of surface area to volume of each room
is a critical factor that can have an impact on
pollutant concentration under equal ventilation
rates. A smaller ratio of surface area to space
volume would be much more effective for diluting
pollutant concentrations.
2. Logarithmic regression models that were developed to
predict the decrease of formaldehyde concentration
were acceptable under the significance level of 0.05. It
is expected that all formaldehyde molecules emitted
from indoor spaces are removed after 260 h when
ventilation rates are kept at 0.45 ACH continuously
by HRVs. This implies that the operation of HRVs
would simultaneously contribute to improve indoor
air quality and maintain ventilation rates within the
mandatory requirement of the Building Code.
3. Linear regression models developed to validate the
results of simulations and measurements were accep-
table under a lower significance level. Predicted
annual energy consumption indicates that heating
energy accounted for up to 75.93% of the total energy
consumption under various operation schedules. It
was shown that HRVs could save energy up to
20.17% annually in high-rise residential buildings
when they were operated continuously for 24 h per
day, exchanging sensible and latent heat. In par-
ticularly, the contribution of sensible heat was
effective when HRVs were applied in a region where
the exchange of latent heat would influence the energy
consumption insignificantly. In summary, the contin-
uous operations of HRVs effectively would
save energy and improve indoor air quality and
maintain the necessary ventilation rates for residential
buildings.
4. The survey results showed that the residents in high-
rise residential buildings would primarily preferred to
operate HRVs when they cooked, dined, and rested
after dining. They also preferred to use HRVs up to
12 h per day when those three types of activities were
performed. Under this condition, annual energy
savings by HRVs was as high as 8.49%.
Limitations and Future Work
The results of this study were based on field meas-
urements in high-rise residential buildings taken over a
limited time period. The measurements were performed
during summer and winter only, due to logistical limita-
tions. Measurements for much longer time periods are
necessary in a future study to compensate for these
shortcomings. The emission rates of formaldehyde and
VOCs from the material were not measured in this study
46.91
20.58
45.93
20.17
43.73
19.92
47.58
20.62
0
10
20
30
40
50
60
70
gnilooCgnitaeHEnergy Type
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
6 hrs 12 hrs
Case 5 Case 6
Fig. 23. Annual energy consumption according to operationschedule (Bldg. ‘B’).
52.56
17.08
51.08
16.40
48.25
15.30
53.34
17.13
0
10
20
30
40
50
60
70
gnilooCgnitaeHEnergy Type
Ene
rgy
Con
sum
ptio
n [k
Wh/
m2 ].
6 hrs 12 hrs
Case 1 Case 2
Fig. 22. Annual energy consumption according to operationschedule (Bldg. ‘A’).
500 Indoor Built Environ 2012;21:486–502 Kim et al.
since the rates were assumed to be equal for the spaces
where the concentrations of air pollutants were measured.
Precise measurement for the rate would be useful to
determine the contribution of HRVs to high-rise residen-
tial buildings.
The measurement results were compared with simula-
tion results to validate simulation software and predict
energy consumption for the time when measurements were
not performed. Although the validation was found to be
acceptable under a low significance level, the software has
limitations peculiar to its own computation algorithms. As
different software would provide different results, further
computer simulations by a variety of software packages
would benefit a future study.
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