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|Title: ||Simulation - based exploration of the thermal performance of selected multi-storey office buildings in Accra, Ghana|
|Authors: ||Simons, Barbara|
|Keywords: ||Thermal Comfort|
|Issue Date: ||20-Oct-2016|
|Abstract: ||The lack of empirical data and practical advice on thermal performance and efficient use of
energy in buildings are gradually becoming a burden to the country. Amidst the recent
advancement in the usage of curtain walls for office buildings, high consumption of energy and
poor thermal comfort issues have become dominant. Given the warm-humid climatic
characteristics of Ghana, energy needs for cooling of office buildings represent an increasing
burden on the environment and the economy. In many instances, the building design is not
supported by a detailed analysis and evaluation of thermally relevant features as well as options
related to orientation, envelope, glazing ratio, shading devices, and thermal mass. Thus, design
decision making is not sufficiently informed by relevant expertise pertaining to energy efficient
building design methods and technologies.
By adopting subjective thermal comfort models, building performance simulation and
experimental approaches, this research aimed at advancing knowledge on how thermal comfort
conditions could be enhanced and energy-use reduced in Ghanaian office buildings. In this
context, the research had the following objectives:
i. To assess occupants view of their indoor thermal comfort conditions within the selected
ii. To determine the thermal comfort conditions of the indoor environment of the selected
iii. To identify energy reduction strategies for the indoor conditions of the selected buildings
based on validated models.
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iv. To identify overheating reduction strategies (passive case-no air conditioners) of the
Adopting a case study research strategy, a number of data collection methods were employed.
Both quantitative and qualitative data were collected and analysed in line with a framework
designed to examine and extract relevant materials in relation to the research questions. The
research database included 4 multi-storey office buildings (Ridge Towers [R.T.], World Trade
Centre [W.T.C.], Premier Towers [P.T.], and Heritage Towers [H.T.]) and 195 occupants‘
From May, 2012 to April, 2013, indoor and outdoor climatic conditions (mainly temperature and
relative humidity) were monitored, using data loggers. To evaluate the existing indoor climatic
conditions, measured air temperature and relative humidity values were plotted in the
psychrometric and bioclimatic charts. A survey (questionnaire) of 195 occupants was conducted
to record their views on indoor environment, installed systems and energy use.
At a general level, the study provided insight into the character of occupants within the
buildings, their general views and concerns regarding energy use and thermal comfort. It
provided evidence of how the buildings could be made comfortable by means of the
psychrometric and bioclimatic charts. Significantly, the study showed how building cooling
loads could be reduced to the minimum whiles providing comfortable indoors passively. On the
psychrometric chart, the monthly hourly temperature and relative humidity values for R.T. and
P.T. were within the comfort zone. All the values for W.T.C. were outside the comfort zone
whiles H.T. had the months of January, May, June and July inside the comfort zone. This
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suggests that R.T. and P.T. could operate passively all year round while H.T. could do that
within certain months of the year. W.T.C. was found to be very uncomfortable all year round.
Plotting both W.T.C. and H.T. values on the bioclimatic charts, 7 months were within the
comfort zone of Olgyay‘s chart in the H.T. building. This gave an indication of five
uncomfortable months for the same building. Givoni‘s chart suggests that W.T.C. could be made
comfortable by means of comfort ventilation, conventional dehumidication and air-conditioning
for the various months. Olgyay‘s chart suggested that air velocity of between 0.1m/s to 1m/s
could improve the comfort conditions of the spaces within the W.T.C. In the H.T., Givoni‘s chart
recommends high thermal mass and comfort ventilation whiles Olgyay‘s chart proposes air
velocity of 0.1m/s to get the other 6 months within the comfort zone.
Additionally, the analysed data from the questionnaire among others showed that the three most
important parameters for occupants‘ satisfaction in the office spaces studied were air quality,
thermal comfort and fire safety. Again, the respondents (occupants) were interested in receiving
training on the effective and efficient operation of building systems, which could help increase
satisfaction, comfort and reduce energy performance of buildings.
The calibrated simulation results suggested that measures regarding building fabric and controls
could improve buildings‘ energy performance. Particularly, careful combinations of
improvement measures (such as efficient glazing, thermal mass, façade insulation, night
ventilation, efficient electrical lighting, form and orientation) have a significant potential to
reduce buildings' cooling loads (31% – 49%) in the climatic context of Accra.
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When the buildings operated passively, the alternative improvement scenarios considerably
reduced the mean overheating in the offices up to about 2.9K, depending on the reference
overheating temperature assumption. Though not exactly identical, there is a clear
correspondence between the ranking of the scenarios in view of lower cooling demands ( active
building mode) and lower overheating tendency ( passive operation mode ).
A significant contribution of this research to the body of knowledge is the provision of
empirical evidence with respect to improvement of thermal performance in multi-storey office
buildings in Accra, Ghana. Until the current research, the above assertion had not been
supported by any empirical study within the localized climate of the capital city of Ghana.
Another significant contribution of this research to the body of knowledge is the provision of
sufficient evidence to confirm that the procedure for the determination of the comfort zone on
the psychrometric chart could be adjusted for tropical climates where people are generally
adapted to higher relative humidity and moderate temperatures. Validated simulation models
are used in retrofit analysis for improvement in the thermal performance of buildings.
Therefore another significant contribution of this research is the achievement of validated
simulation models for energy assessment in multi-storey office buildings in Ghana. This
provides a reference point for future validated simulation studies involving multi storey office
buildings with curtain walls in Ghana. Moreover, this study is the first of its kind in the climatic
context of Accra, Ghana|
|Description: ||A thesis submitted to the Department of Building Technology, Faculty of Built Environment, College of Art and Built Environment in partial fulfilment of the requirements for the degree of Doctor of Philosophy, 2015|
|Appears in Collections:||College of Architecture and Planning|
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