Impact of Office Buildings Environmental Systems Control Strategy on Indoor Environment
Quality and Energy Use in Different Climatic Regions
Jana Bartonova 1, Karel Kabele 2, Kwok Wai Tham 3
Czech Technical University In Prague, Faculty Of Civil Engineering, Department of
Microenvironmental and Building Services Engineering Czech Technical University In Prague,
Faculty Of Civil Engineering, Department of Microenvironmental and Building Services Engineering
National University of Singapore, School of Design and Environment, Department of Building
SUMMARY
This paper presents the impact of temperature setpoint and thermal control material on energy
use and indoor environmental quality in two different climates using the case study of an
office room. The study is conducted in two stages. The first stage focussed on energy
consumption for cooling, heating and ventilation of the office whilst maintaining thermal
comfort determined from the Predicated Percentage Dissatisfied (PPD) and Predicted Mean
Vote (PMV). The second part evaluates the influence of thermal control materials – Vacuum
Insulated Panels (VIP) and Phase Change Materials (PCM gypsum plasters) on thermal
comfort and energy saving. Comparison of indoor environment condition is performed using a
computer simulation tool (ESP-r) and assessed according to the standards requirements in the
selected regions. Computer simulation was verified by in situ measurements.
KEYWORDS
Energy savings, dynamic simulation, indoor environmental quality, impact of climatic
conditions, case study;
1 INTRODUCTION
Buildings consume more than 40 % of all energy production. Office buildings are significant
consumers of this energy. Modern approaches, such as natural ventilation, using of the
modern materials, day-lighting or demand controlled ventilation, are used to reduce energy
use in the office buildings with impact to indoor environmental quality mainly on thermal
comfort and indoor air quality. This paper focuses on the case study of the office room,
investigating of the impact of indoor air temperature and the influence of modern materials
on, thermal comfort and energy consumption. Questions which this paper aims to answer are:
Is the influence of indoor air temperature on thermal comfort and energy consumption the
same for the offices placed in the different climatic regions? What is effect of using modern
materials on indoor environmental quality and energy saving for cooling, heating and
ventilation?
2 MODELLING AND SIMULATION
The case study is focused on the comparison of indoor environment conditions and energy
consumption in the offices with different environmental systems control strategies (heating,
cooling and ventilation) using computer simulation. Energy consumption refers to energy
utilised for heating, cooling and ventilation of the office, thermal comfort is evaluated from
Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD). For purposes of
the analysis, the office room was chosen which was located in two different climatic regions in Singapore and in the Czech Republic.
Climatic Regions:
Climatic classification was determined on the basis of the Köppen–Geiger climate
classification system. The Czech Republic is located in a temperate continental climate with
relatively hot summer and cold, cloudy and snowy winter. Most rain falls during the summer.
The average annual air temperature usually ranges from 5.5 °C to 9 °C and relative humidity
averages around 40 % and 70 %. Singapore is located in a tropical rainforest climate with no
distinctive seasons, uniform temperature and pressure, high humidity, and abundant rainfall.
Temperatures usually range from 23 to 32 °C and relative humidity averages between 70 %
and 90 %.
Software ESP-r
Dynamic simulation software ESP-r was used for the analysis of influence of indoor air
temperature setpoint on thermal comfort, for determination of values PMV and PPD and for
determination of energy use for heating, cooling and ventilation (Kabele and Dvořáková,
2006).
Model
A reference office room was selected. This office is situated in an existing building of the
Faculty of Civil Engineering CTU in Prague. The room is located in a sixteen-storey threetract building with active heating, cooling and ventilation.
The evaluated office room is 5 m x 3 m in size and the ceiling height is 3.3 m. The room has
one external wall with a window a size 3 m x 1.6 m, floor, ceiling, interior wall separating the
room from the corridor, and partitions with adjoining offices and the hall door. Because the
office is on the second floor, heat losses by transmission are expected to occur only through
the perimeter wall. The facade is oriented towards the southwest.
The schedule for working hours in the office building is 8:00 a.m. to 6:00 p.m. Monday
through Friday.
For heating (only in the Czech Republic) the setpoint temperature is 22 °C, and the heating
elements are available in the range of 0 - 2000 W. Heat energy is distributed 25 % by
radiation and 75% by convection. Heating is controlled at 22 °C during the weekdays from
6:00 a.m. to 10:00 p.m. On the weekdays from 10 p.m. to 6 a.m. and on the weekends and
holidays, heating is set at 16 °C. Humidity is controlled during the working hours.
Cooling - the performance of the cooling elements is available in the range of 0 - 2500 W.
Just as heating, cooling is controlled according to the indoor temperature. The office is cooled
only on the weekdays in the working hours with the same schedule as heating. On the
weekdays from 10 p.m. to 6 a.m. and on the weekends and holidays, cooling is turned off.
Ventilation is mechanical, with a fixed fresh air change rate: 50 m3/h (approximately 1 air
change per hour [ACH]) during working hours and 20 m3/h outside the normal working hours.
Infiltration of old windows constitutes a considerable proportion of the ventilation, it is
assumed to be 0.5 ACH.
Determination of the indoor gains - the model reckons the presence of one person in the office
during working hours. Office facilities (computers, printers, etc.) were also reckoned with.
Lighting operates during working hours throughout the year (illumination intensity is
500 lux). It is assumed that people produce 150 W/person, computer set (PC and printer)
produces 250 W and lighting produces 35 W/m2.
All values (indoor air temperature, humidity, amount of fresh air and air velocity) were
determined according to the standards requirements in the selected regions. For the Czech
Republic - Government Regulation No. 361/2007 Coll. and for Singapore - SS 553:2009.
Verification of the model
Measurement was carried for verification. The measurement consisted of outdoor air
temperature, humidity, solar radiation intensity, speed and wind direction and indoor air
temperature in the reference room (Kabrhel et al., 2011). The measured temperature
fluctuated in the range of ± 0.2 °C around the setpoint temperature selected in the simulation
programme. This difference was deemed as acceptable and model has been considered as
satisfactory.
Simulation
The simulation was performed over a period of a year and was based on the following
boundary conditions and simulation set-up:
• Prague climate data and Singaporean climate data according to ASHRAE;
• Integrated simulation with time step of 0.5 hour;
• Initial start-up period of 10 days.
The first part of the case study - for investigation of impact of indoor air temperature on
thermal comfort and energy consumption, simulation was performed for both regions with
5 equally spaced temperature setpoints between 22 °C to 26 °C.
The second part of the case study - for assessment of impact of the modern thermal control
materials on indoor environmental quality and energy consumption, simulation was
performed in 3 scenarios:
• Scenario 1 - the perimeter wall was additionally insulated by Vacuum Insulated Panels (VIP
panels) from inside of the perimeter wall
• Scenario 2 - using of PCM gypsum plasters on partitions between the offices
• Scenario 3 - combination of first and second scenario
3 RESULTS
Assessment of indoor environment quality:
Desirable thermal environment for the space can be chosen from among the three categories
A, B and C (see Appendix A.1 - BS EN ISO 7730). For office room category, thermal
comfort is guaranteed, if the value of the index PPD < 6%, corresponding to thermal sensation
in the range -0.5 < PMV < +0.5. Thermal comfort is deemed permissible, if the index PPD
exceeds 6% but lower than 20% dissatisfied corresponding to PMV value in the range -1 <
PMV < +1. However, if these values are exceeded then thermal stress occurs. To compute
PMV and PPD the thermal resistance of clothing is set to correspond to the normal wear in the
office environment (0.7 clo), with metabolic rate of 70 W/m2 and air velocity 0.1 m/s.
Results of the first part of the case study - The first part of case study was focused on the
assessment of impact of the indoor air temperature on indoor environmental quality and
energy consumption for cooling, heating and ventilation of the office. From the results of,
the optimal temperature was chosen for cooling of the office.
Figure 1. The Czech Republic - Distribution of PPD (A) and PMV (B) in the working hours
during the year
From Figure 1. it is observed that the best state of the indoor environment in year-round
operation in the Czech Republic is when the temperature setpoint is 23 °C. The indoor
environmental quality decreases more markedly when the cooling temperature is set above
25 °C. It is observed that the influence of temperature setpoint on thermal comfort is not as
large as in the case when the office is placed in Singapore.
Figure 2. Singapore - Distribution of PPD (A) and PMV (B) in the working hours during the
year
When the office is placed in Singapore, optimal temperature is 22 °C (at the setting of the
temperature of 23 °C, a mild discomfort arises but the condition is still deemed to be
allowable). At setting of the temperature of 24 °C and higher, indoor environmental quality
decreases dramatically and during the year-round operation of the office thermal comfort is
not achieved (see Figure 2.).
Table 1. Annual energy consumption (kWh) at different temperature setpoints
Region
Temperature [°C]
Cooling*
Heating*
Humidification*
Dehumidification*
TOTAL [kWh]
THE CZECH REPUBLIC
22
23
24
25
26
1357
1171
999
849
718
2849
2849 2849 2849 2849
71
77
83
90
98
4
1
1
0
0
4281
4098 3932 3788 3665
22
5280
0
0
1057
6337
SINGAPORE
23
24
25
4944 4612 4286
0
0
0
0
0
0
960
859
748
5904 5471 5034
26
3967
0
0
627
4594
* All values are given in kWh, heating (in the Czech Republic) is set on the temperature 22°C
Considering total energy consumption (see Table 1.) and thermal comfort indices PPD and
PMV, the temperature setpoint of 24 °C for cooling appears as the optimal temperature for the
office in the Czech Republic. For the office in Singapore, the temperature setpoint of 23 °C is
evaluated as optimal. In comparison with the temperature of 22 °C, the energy saving is 433
kWh (7%).
Results of the second part of the case study - The optimal temperature, which was determined
in the first part of the case study, was used for the next simulations in this second part of the
case study. In this part the influence of modern thermal control materials (VIP panels and
PCM gypsum plasters) on thermal comfort and energy saving was evaluated.
Figure 3. Distribution of PMV in the working hours during the year
The influence of VIP and PCM gypsum plasters on indoor environmental quality is depicted
in Figure 3. For the office in the Czech Republic using VIP panels or PCM plasters achieves
a 5 % increase in the frequency of occurrence of “contentment” thermal vote (PPD < 6 %).
By using of combination of VIP panels and PCM plasters the percentage increase is
augmented by 7 %.
For the office in Singapore using of VIP panels has negligible impact showing that the
application of VIP panels is not useful for the improvement of thermal comfort in this climatic
region. Using the PCM plasters appears as a suitable solution because they can achieve
increase the frequency of occurrence of “contentment” thermal vote (PPD < 6 %) by 10 %.
Table 2. shows energy consumption for cooling, heating and ventilation corresponding to the
use of modern thermal control materials. By using VIP panels, the office in the Czech
Republic achieved energy saving in winter season, however in summer season, the insulating
panels increase energy consumption for cooling. It is useful to use the combination of VIP
panels and PCM plasters to achieve a balance between energy saving and improvement
of thermal comfort. For the office in Singapore, it makes sense to use only the PCM plasters.
With the PCM plasters thermal comfort is improved but energy saving is small
(approximately 1%).
Table 2. Annual energy consumption (kWh) of the scenarios studied
Region
Variant
Cooling*
Heating*
Humidification*
Dehumidification*
TOTAL [kWh]
THE CZECH REPUBLIC
Initial
VIP
PCM
Combistate
panels plasters nation
999
1123
909
1029
2849
2660
2794
2610
83
86
83
87
1
1
1
1
3932
3870
3787
3727
Initial
state
4944
0
0
960
5904
SINGAPORE
VIP
PCM
panels plasters
4935
4884
0
0
0
0
960
960
5895
5844
Combination
4874
0
0
960
5834
* All values are given in kWh, heating (in the Czech Republic) is set on the temperature 22°C
4 DISCUSSIONS AND CONCLUSION
The presented study based on computer simulation confirmed that the influence of air
temperature and modern thermal control materials on thermal comfort and energy
consumption is different for the two climatic regions. In the Czech Republic, the change of air
temperature does not have so the great influence on thermal comfort as in the office placed in
Singapore. The office placed in the Czech Republic has higher variability in the choice of air
temperature with the smaller impact on thermal comfort. This may be attributable to the
higher humidity conditions experienced in Singapore.
In the Czech Republic the use of modern thermal control materials has positive effects for
energy saving and thermal comfort, although VIP increased energy consumption for cooling
in summer season. For Singapore, only the use of PCM gypsum plasters produce an
improvement in thermal comfort with a marginal reduction (1%) in energy consumption.
5 ACKNOWLEDGEMENT
This paper was supported by 7. FP EU grant NMP2-LA-2008-211948 Clear Up.
6 REFERENCES
EN ISO 7730: Ergonomics of the thermal environment - Analytical determination and
interpretation of thermal comfort using calculation of the PMV and PPD indices and local
thermal comfort criteria (ISO 7730:2005); European Standard.
Government Regulation No. 361/2007 Coll. of 12 December 2007, determining conditions for
occupational health protection; Collection of Laws, Czech Republic.
Kabele, K. and Dvořáková, P.: Indoor Air Quality in Sustainable Architecture. In: Proceedings
Healthy Buildings 2006. Porto: Universidade do Porto, 2006, vol. 3, p. 1-4. ISBN 98995067-1-0.
Kabrhel, M. and coll.: Testing of new technologies for indoor environment in buildings.
Workshop CTU in Prague, 2011.
SS 553:2009 CODE OF PRACTICE FOR Air-conditioning and mechanical ventilation in
buildings; Singapore Standard.