2012-improvement of indor living environment by occupants preferences for heat recovery ventilators...

8/12/2019 2012-Improvement of Indor Living Environment by Occupants Preferences for Heat Recovery Ventilators in Hihg-ris

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Original Paper

Indoor and uiltiltEnvironment Indoor Built Environ 2012;21;4:486502

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 EVentilation rates EOperating schedule E

Residential building

Abstract

This study examined the influence of heat recovery

ventilators (HRVs) on energy savings and indoor airquality (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 wereoperated 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: 10.1177/1420326X11429714

Accessible online at http://ibe.sagepub.com

Figures 323 appear in colour online

Sooyoung Kim,Department of Housing and Interior Design, Yonsei University, Seoul, South

Korea. Tel. 82-2-2123-3142, Fax 82-2-313-3139,

E-Mail [email protected]


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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 ofteneffective 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 [816]. The results of these studies implied that the

annual heating energy could be effectively saved by theapplication 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 [2125]. 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. Energysaving 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 energysavings. 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:

37834N, longitude: 126858E), 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;21:486502 487


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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 [2831]. 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 Ondolduring 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;21:486502 Kim et al.


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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 heatexchange. 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 [3438]. 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 alleight 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 1.2 m 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 1.5 m.

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 Summer

2 A 39 24 h OFF Not exchanged Installed Not passed

3 A 40 24 h ON Not exchanged Removed Passed

4 A 40 24 h OFF Not exchanged Removed Not passed

5 B 10 24 h ON Exchanged Installed Passed Winter

6 B 10 24 h OFF Not exchanged Installed Not passed7 B 11 24 h ON Not exchanged Removed Passed

8 B 11 24 h OFF Not exchanged Removed Not passed

Table 1. Building thermal properties

Properties Building A Building B

Floor area (m2) 207 217

Ceiling height (m) 2.4 2.4

U-value of window (W/m2 K) 3.40 3.34

U-value of wall (W/m2 K) 2.74 2.65

Ratio of window to wall (%) 43 41

Table 2. Conditions of HRVs

Item Bldg. A Bldg. B

Heat exchange type Sensible and

latent

Sensible

Efficiency of latent heat exchange (%) 39.3 N/A

Efficiency of sensible heat exchange (%) 62.5 55.1



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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 12 min. The mean value of CO2 concentration

monitored by the three samplers was used to determine

ventilation rates in the space. The determination wasperformed based on the theoretical background that has

been approved and effectively used in other previous

research [3943].

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 1.2 m 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 waterused 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 occupantsare 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.



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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 23.48C

to 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 CO2decreased 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]

CO2Concentration[ppm]

0.0

0.2

0.4

0.6

0.8

1.0

Ventilarionrate[ACH]

CO2 variation-Case 5CO2 variation-Case 6

Ventilation rate-Case 5

Ventilation rate-Case 6

Fig. 5. Example of measured CO2 concentration and ventilationrates by tracer gas concentration decay method (Room 3, Cases 5

and 6).

20

10

0

10

20

30

40

0 12 24 36 48 60 72

Time [hr]

Temperature[C

]

0

20

40

60

80

100

120

RelativeHumidity[%].

Winter-OA Temp.Winter-10th Temp.Winter-RH

Fig. 4. Variation of temperature and humidity (2224 January).

0

5

10

15

20

25

30

35

40

0 12 24 36 48 60 72

Time [hr]

Temperature[C]

0

20

40

60

80

100

120

RelativeHumidity[%].

Summer-OA Temp.

Summer-39th Temp.

Summer-RH

Fig. 3. Variation of temperature and humidity (24 August).



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The reduced concentration ranged from 40ppm to

292 ppm and 56 ppm to 236ppm for the Cases 5 and 6,

respectively.

Based on the reduction in CO2 concentration for each

data monitoring point, ventilation rates were determined

[3941]. 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 determineventilation 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 beoperated 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

VentilationRates[ACH].

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]

Concentration[g/m3]

Case 1-Room 3

Case 4-Room 3

Case 5-Room 3

Case 5-Livingroom

Case 8-Room 3

Case 8-Livingroom

Fig. 7. Concentration variation of formaldehyde.



8/17

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 offormaldehyde in newly-constructed residential buildings

should not exceed 210 mg/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 137.31mg/

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 37.69mg/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 roomswould 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 33.66mg/m3 in Case 5,

and ranged from 16.15 mg/m3 to 44.42 mg/m3 in Case 8.

After 168h in Case 5, the concentration of formalde-

hyde in the living room was reduced 1.62 times greaterthan that in Room 3, reduced by70 mg/m3 in the living

room and 43.08 mg/m3 in Room 3. In Case 8, the decrease

in concentration was 65.96 mg/m3 in the living room and

45.77mg/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



9/17

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

R

2

= 0.94

0

20

40

60

80

100

0 50 100 150 200

Accumulated Time [hr]

Decreas

edConcentration[%]

Case 1-Room 3

Case 5-Room 3

Case 5-Livingroom

Fig. 8. Correlation between accumulated time and reduced amount

of 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 50 100 150 200

Accumulated Time [hr]

DecreasedConcentration[%]

Case 4-Room 3

Case 8-Room 3

Case 8-Livingroom

Fig. 9. Correlation between accumulated time and reduced amount

of 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) 56.36 0.00

(Constant) 70.95 16.56 4.28 0.02


(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) 44.91 0.01

(Constant) 10.52 10.89 0.97 0.41


(Constant) 6.96 3.08 2.26 0.11


(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) 89.98 0.00

(Constant) 16.07 5.27 3.05 0.06



10/17

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 surfaceareas 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 38mg/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 345mg/m3 and 298mg/m3,

respectively. The concentrations of ethylbenzene and mp-xylene varied from 268 mg/m3 to 344mg/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 30m/g,

1000m/g, 360 m/g and 700m/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-xylene

Pollutant

Concentration[g/m].3

Outdoor

Case 1

Case 4

Fig. 10. Concentration of VOCs (Cases 1 and 4).

0

50

100

150

200

250

300

350

400

Benzene Toluene Ethy lbenzene m, p-xy lene o-xy lene

Pollutant

Concentration[g/m3].

Outdoor

Case 5

Case 8

Fig. 11. Concentration of VOCs (Cases 5 and 8).



11/17

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 shouldbe 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 hexchanging 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 248C

for 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 summerwhen 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

EnergyConsumption[kWh].

Case 1Case 4

Case 5Case 8

Fig. 12. Measured energy consumption.



12/17

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 betweenthese 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) 37.64, p50.05)

and Case 3 (F(1,23)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 energycould 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 20

Measured Energy [kWh]

SimulatedEnergy[kW

h].

Case 1

Case 3

Fig. 13. Correlation between measured and simulated energy

consumption.

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) 37.64 0.01

Slope 0.961 0.16 6.14 0.00

Case 3 (Constant) 0.034 0.97 0.04 0.97 F(1,23) 71.15 0.00

Slope 1.014 0.12 8.44 0.00



13/17

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 energysavings by HRVs for the preferred operation hours. The

majority of operation hours preferred by residents did not

exceed 12h 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 1.8

0.0

1.8

14.0

17.5

1.8

3.5 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

Percentage[%]

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

EnergyConsumption[kWh/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

Profess ional etc

Occupation

Percentage[%]

Highschool

Bacholor

Master

Fig. 17. Participants education level and occupation.

7.0

28.9 29.8

25.4

8.8

0

10

20

30

40

No use


14/17

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 twobuildings 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 majorportion 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 24h continuously

without heat exchange. However, such control schedules

Table 6. Operation schedule for HRVs according to residents preference

Operation Time (124 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 24

6 h g g g g g g

12 h g g g g g g g g g g g g

11.4

3.5

11.4

6.1

30.7

21.9

14.9

0

10

20

30

40

No use etc when

necessary

sleep cooking dining After

cooking

Case for using HRV

Percentage[%]

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


6hr 12hr

Fig. 20. Predicted energy consumption according to operation

schedule (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


6hr 12hr

Fig. 21. Predicted energy consumption according to operation

schedule (Bldg. B).



15/17

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 whenventilation 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-

u o us o p era tio ns o f HRVs e ffe c tiv ely wo uld

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


6 hrs 12 hrs

Case 5 Case 6

Fig. 23. Annual energy consumption according to operation

schedule (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

EnergyCo

nsumption[kWh/m2].

6 hrs 12 hrs

Case 1 Case 2

Fig. 22. Annual energy consumption according to operation

schedule (Bldg. A).



16/17

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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