Parametric analysis on the thermal comfort of a cooling tower based thermally activated building system in tropical climate – An experimental study

doi:10.1016/j.applthermaleng.2018.04.077

Applied Thermal Engineering

Volume 138, 25 June 2018, Pages 325-335

https://doi.org/10.1016/j.applthermaleng.2018.04.077 Get rights and content

Highlights

•
Increase in cooling surface advances the maximum and minimum of comfort parameters.
•
In humid regions, shading can be a permanent feature as radiative sky cooling is low.
•
Ventilation increases fluctuation and advances extrema of the comfort parameters.
•
Ceiling fan improves thermal comfort by increasing the adaptive neutral temperature.
•
Among all parameters studied, cooling surface has the highest impact on the comfort.

Abstract

Thermally Activated Building System (TABS) provides not only better thermal comfort but also good indoor air quality. It can be coupled with passive cooling systems as it can operate at a relatively higher water temperature. Even though TABS is a promising energy-efficient and eco-friendly system, the influences of various design and operating parameters on the indoor thermal comfort of a building with TABS are not well understood. Hence, the influences of cooling surfaces (area), shading, natural ventilation and ceiling fan on the performance of cooling tower based TABS were investigated in an experimental room of dimensions 3.5 m × 3.5 m × 3.15 m. The increase in the number of cooling surfaces decreased (favourable) the thermal comfort indices and advanced the time at which their maximum and minimum were reached. The average predicted percentage of dissatisfied was 89% if roof alone was cooling. This reduced to 20% if all the surfaces of the building were cooled. Shading of the roof reduced the maximum operating temperature of the indoor space by 0.9 °C when all the surfaces of the building were cooled with TABS. The use of ceiling fan increased the indoor operative temperature marginally. However, the increase was less than the neutral temperature offset of 2.6 °C that was achieved by higher air movement. Thus, the use of the fan results in a better indoor thermal comfort. Natural ventilation advanced the occurrence of the maximum temperature of indoor air by 1½ and 2¾ hours for fan off and fan on cases respectively. It also advanced the extrema of the other indoor comfort parameters. The cooling tower based TABS was able to achieve thermal comfort even in unfavourable warm and humid tropical climates under certain operating conditions.

Introduction

Thermal comfort improves physical and psychological health, enthusiasm and productivity of the occupants of a building [1]. Hence, from ancient times human beings have put efforts to construct thermally comfortable living spaces. This is evident from the architecture of ancient buildings [2]. In modern days, thermal comfort is achieved predominantly by mechanical air-conditioning systems, which are not only energy intensive and eco-destructive [3] but also responsible for inferior indoor air quality [4], [5] and poor thermal comfort [6]. Concurrently, the demand for air-conditioning for comfort application has increased drastically in recent years and is expected to increase further [7]. This is attributed to the human aspiration for a better thermal environment, increase in time spent indoors, economic growth [8], heat island effect and global warming [9]. The rise in energy demand and increase awareness about environmental issues such as climate change have led to energy conservation measures. Thermally activated building system (TABS), which provides a better thermal comfort and indoor air quality, is a promising energy efficient alternative to the conventional cooling system. One of the important advantages of TABS is its ability to achieve thermal comfort with cooling water at relatively higher temperature. This makes TABS compatible with passive cooling systems such as geothermal cooling and cooling tower (CT) [10]. This paper investigates the influence of cooling area, shading, natural ventilation and ceiling fan on the thermal comfort of a room cooled with CT supported TABS.

Section snippets

Literature survey

TABS operates by circulating cold water through pipes embedded in a concrete slab. The water cools the slab, which in turn cools the indoor space. The major challenges of TABS are leakages in joints and water condensation on indoor surfaces. The former is addressed by switching from metal pipes to flexible crosslink polyethylene (PEX) pipes [11], and the latter is avoided by operating the system at higher water temperature and reducing the absolute humidity of the air supplied to the

Experimentation

Experimental work can be classified into field and laboratory experiments, with each of them having their own advantages and limitations. The former is better in terms of validity, whereas it commonly lacks control of parameters compared to the latter. In the present work, a room of size 3.5 m × 3.5 m × 3.15 m (H) was constructed with TABS, which was supplied with water from a CT (Fig. 1). The standalone room was exposed to solar radiation on all sides, with the surrounding trees and structures

Results and discussion

In this experimental study, the outdoor conditions were not controlled. Hence, the experiments were repeated if the diurnal trend or the average value were very different among the cases compared. In addition, the differences in outdoor conditions were factored in while analysing the results.

Conclusions

From the detailed literature review, it was found that the influence of parameters on the indoor thermal comfort of a building with passive Thermally Activated Building System (TABS) is not well understood. An experimentation room was built to study the performance of passive TABS integrated with a cooling tower. The influences of cooling surface (area), shading, ventilation and ceiling fan on the indoor thermal comfort are summarised below.

The increase in cooling surfaces improved the thermal

Acknowledgment

The authors thank DST, GOI for funding this study (Ref.: SR/S3/MERC/00091/2012).

References (45)

J. Zhao et al.
Productivity model in hot and humid environment based on heat tolerance time analysis
Build. Environ.
(2009)
M.S. Hatamipour et al.
Passive cooling systems in buildings: Some useful experiences from ancient architecture for natural cooling in a hot and humid region
Energy Convers. Manage.
(2008)
M. Xue et al.
Flow, stock, and impact assessment of refrigerants in the Japanese household air conditioner sector
Sci. Total Environ.
(2017)
N.H. Wong et al.
Comparative study of the indoor air quality of naturally ventilated and air-conditioned bedrooms of residential buildings in Singapore
Build. Environ.
(2004)
S.C. Sekhar et al.
Indoor air quality and thermal comfort studies of an under-floor air-conditioning system in the tropics
Energy Build.
(2002)
M. Santamouris
Cooling the buildings – past, present and future
Energy Build.
(2016)
C. Shen et al.
Dynamic thermal performance of pipe-embedded building envelope utilizing evaporative cooling water in the cooling season
Appl. Therm. Eng.
(2016)
D. Song et al.
Performance evaluation of a radiant floor cooling system integrated with dehumidified ventilation
Appl. Therm. Eng.
(2008)
K.N. Rhee et al.
A 50 year review of basic and applied research in radiant heating and cooling systems for the built environment
Build. Environ.
(2015)
J.L. Niu et al.
Energy savings potential of chilled-ceiling combined with desiccant cooling in hot and humid climates
Energy Build.
(2002)

D.O. Rijksen et al.

Reducing peak requirements for cooling by using thermally activated building systems

Energy Build.

(2010)

Z. Tian et al.

A field study of occupant thermal comfort and thermal environments with radiant slab cooling

Build. Environ.

(2008)

G.P. Henze et al.

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

Energy Build.

(2008)

D. Pahud et al.

Geocooling potential of borehole heat exchangers' systems applied to low energy office buildings

Renew. Energy

(2012)

A.H.H. Ali

Passive cooling of water at night in uninsulated open tank in hot arid areas

Energy Convers. Manage.

(2007)

K.A. Antonopoulos et al.

Experimental and theoretical studies of space cooling using ceiling-embedded piping

Appl. Therm. Eng.

(1997)

X. Jin et al.

Numerical simulation of radiant floor cooling system: the effects of thermal resistance of pipe and water velocity on the performance

Build. Environ.

(2010)

P. Ma et al.

Modeling of TABS-based thermally manageable buildings in Simulink

Appl. Energy

(2013)

S. Jahedi et al.

On the advantages and disadvantages of subjective measures

J. Econ. Behav. Organ.

(2014)

B. Olken

Corruption perceptions vs. corruption reality

J. Public Econ.

(2009)

F. Nicol

Adaptive thermal comfort standards in the hot–humid tropics

Energy and Build.

(2004)

A.K. Mishra et al.

Field studies on human thermal comfort — An overview

Build. Environ.

(2013)

Cited by (25)

Summer thermal and energy performances assessment of a modular hydronic thermal barrier wall for ultra-low energy buildings - A field experimental study
2024, Applied Thermal Engineering
Hydronic thermal barriers with ultra-low carbon emission attributes are progressively gaining prominence in the competition of thermal insulation solutions for opaque envelopes of low-energy buildings due to their excellent thermal performance and low-grade energy utilization potential. This paper introduces a novel approach involving a modular hydronic thermal barrier wall (MHTB) that incorporates preset pipe cavities and replaceable filling material. This proposition seeks to address the challenges confronted by conventional hydronic thermal barrier walls (CHTBs), specifically in terms of internal heat transfer enhancement and rapid assembly/dismantling. On-site thermal performance tests and energy-saving evaluations were conducted in summer conditions based on three scaled-down rooms with MHTB, CHTB and a conventional external insulation wall as the south walls. The results showed that the MHTB could significantly reduce heat passing through the south wall in summer, resulting in a decreased cooling load attributed to the wall and subsequently lowering indoor temperatures. At a charging temperature of 17.0 °C, the MHTB exhibited a reduction of 11.3 °C in interior surface temperature compared to the conventional external insulation wall, accompanied by a corresponding increase of 2.76 kWh·m⁻² in cumulative heat flux. In addition, the MHTB could effectively mitigate inhomogeneous heat transfer within the wall, enhancing the overall heat transfer effect. Across the four investigated conditions, the MHTB with a steel grit-sand mixture as the filling material demonstrated an approximate 4.7% increase in cumulative heat flux and a 12.2% enhancement in cumulative cooling quantity compared to the CHTB. Overall, the findings substantiated the efficacy of the MHTB system and offered a crucial point of reference for advancing research in optimizing the performance and modular construction of hydronic thermal barrier walls.
Impact of indoor heat load and natural ventilation on thermal comfort of radiant cooling system: An experimental study
2023, Energy and Built Environment
Construction and operation of buildings are responsible for about 20% of the global energy consumption. The embodied energy of conventional buildings is high due to the utilization of energy-intensive construction materials and traditional construction methodology. Higher operational energy is attributed to the usage of power-consuming conventional air-conditioning systems. Therefore, moving to an energy-efficient cooling technology and eco-friendly building material can lead to significant energy savings and CO₂ emission reduction. In the present study, an energy-efficient thermally activated building system (TABS) is integrated with glass fiber reinforced gypsum (GFRG), an eco-friendly building material. The proposed hybrid system is termed the thermally activated glass fiber reinforced gypsum (TAGFRG) system. This system is not only energy-efficient and eco-friendly but also provides better thermal comfort. An experimental room with a TAGFRG roof is constructed on the premises of the Indian Institute of Technology Madras (IITM), Chennai, located in a tropical wet and dry climate zone. The influence of indoor sensible heat load and the impact of natural ventilation on the thermal comfort of the TAGFRG system are investigated. An increase in internal heat load from 400 to 700 W deteriorates the thermal comfort of the indoor space. This is evident from the increases in operative temperatures from 29.8 to 31.5 °C and the predicted percentage of dissatisfaction from 44.5% to 80.9%. Natural ventilation increases the diurnal fluctuation of indoor air temperature by 1.6 and 1.9 °C for with and without cooling cases, respectively. It reduces the maximum indoor CO₂ concentration from 912 to 393 ppm.
Hydronic flow path analysis on the thermal comfort performance of radiant cooling system
2023, Thermal Science and Engineering Progress
Construction and operation in the building sector account for more than 1/5th of global energy consumption. Moving on to an energy-efficient cooling technology and eco-friendly building material can lead to energy savings and a reduction in associated CO₂ emissions. In the present study, an energy-efficient thermally activated building system (TABS) is integrated with eco-friendly building material, namely, glass fibre reinforced gypsum (GFRG). The proposed hybrid system is termed as thermally activated glass fibre reinforced gypsum (TAGFRG) system. This system is not only energy-efficient and eco-friendly but also provides better thermal comfort. An experimental room is constructed with the TAGFRG roof within the Indian Institute of Technology Madras campus, Chennai, i.e., in a tropical warm and humid climate zone. The TAGFRG roof has reinforcement in every third cavity with cooling pipes, while in the other two cavities, cooling pipes are embedded with air gap and partial reinforcement. The TAGFRG roof has four parallel loops of cooling pipelines, and each loop consists of one reinforcement zone (RZ) and two air gap zones (AZ1 and AZ2) in series. According to the water flow path in a single loop, various combinations of the flow path, i.e., RZ → AZ1 → AZ2, AZ1 → RZ → AZ2 and AZ1 → AZ2 → RZ, have been analyzed. According to the adaptive thermal comfort model, the water flow path has a negligible effect on thermal comfort. The average operative temperature for all the cases investigated varies between 28.1 and 29.2 °C. The operative temperature is always within the 90% band of thermal comfort, as per the adaptive comfort model.
Investigation of changes in Driver's biosignals and thermal comfort according to the heating method in winter
2023, Case Studies in Thermal Engineering
In this study, thermal comfort was studied during actual driving of vehicles in winter with measurement of skin temperature, heart rate variability (HRV), and electroencephalogram (EEG), and the conducting of subjective questionnaires to examine the thermal comfort of the driver. HVAC heating, seat heating mode, and HVAC with seat heating mode were used to investigate changes in biosignals and subjective evaluations with time. As a result, after 30 min of pulse wave measurement, LF/HF showed an increase of 9.2% and 8.4% in heating seat and HVAC with heating seat, respectively, compared to HVAC heating, confirming that concentration was improved. Besides, the concentration of attention showed an increase of 119% and 2.19% in the heating seat and HVAC with heating seat, respectively. In the heating seat mode, because the HVAC system is not operated, the improvement of the car's interior temperature is delayed while driving, which greatly affects TSV. However, in the case of TCV or CLV, it was the highest after 30 min of driving, and concentration and comfort during driving were the highest. In addition, the driver's physiological changes in winter occurred sooner than the environmental changes, and the driver's psychological response was quicker than their physiological responses.
Heat transfer study of green roof in warm and humid climatic conditions
2023, Materials Today: Proceedings
Urban Heat Island (UHI) effect has become one of the major issues due to the increase in temperature the urban areas. Green roofs help to increase the thermal comfort of the building as they can reduce the heat flow through a building envelope. Since the vegetation acts as an insulating layer, the plants cover the roof, providing evaporation and transpiration cooling. In this paper, it has been studied the heat transfer through the conventional roof using experimental data and then constructed a numerical model for a green roof and performed simulations on the atmospheric conditions same as the experimental data, and observed that there is a decrease in the inside room temperature of the building installed with green roof in comparison to a conventional roof. From the simulations, concluded that there was a decrease in temperature during the peak hours. The results indicated that the green layer absorbs large amounts of solar radiation and releases it in the form of evapotranspiration (ET) and photosynthesis thus reducing the amount of heat penetrating the roof. With this inference, it is evident that the thermal comfort for the occupants is favorable and the cooling load and peak demand are reduced. This result is supported by the fact that the green layer absorbs large amounts of solar radiation and releases it in the form of evapotranspiration and photosynthesis thus reducing the amount of heat penetrating the roof.
Impact of placement and design of phase change materials in thermally activated buildings
2022, Journal of Energy Storage
Phase change materials (PCMs) and thermally activated building systems (TABSs) are two candidate technologies for reducing the energy consumption of modern buildings due to their favorable thermal storage features. However, the existing relevant studies do not specify the optimal integration schemes of PCMs when used in radiant cooling systems. Hence, this paper reports the first attempt to parametrically optimize the PCM-TABS system integration, considering typical open office space in the hot and dry climate zone of Cairo, Egypt. Using dynamic system simulations, four system configurations are examined, regarding the relative positions of the activated slab and Bio-PCM layer (ceiling or floor), and compared to active ceiling or floor systems (without PCMs). The results demonstrate the feasibility and favorableness of using PCMs in TABS, with energy and cost saving up to 18.80 and 19.78 %, respectively. The largest cost savings are achieved when PCMs are incorporated into the radiant ceiling, with a melting temperature of 22.0 °C and thickness of 6.0 cm. Energy savings also increase as the volume of PCMs increases, with melting temperatures closer to the building's setpoint. The percentage of comfortable hours decreases slightly from ~100 % to >95.5 % when using some PCM designs due to their thermal inertia, but PCMs result in generally lower variations of indoor thermal comfort. By mapping the performance of such system configurations, the study can be valuable for researchers and practitioners alike to determine the optimal integration scheme of PCMs in radiant cooling systems.

View all citing articles on Scopus

View full text

Research PaperParametric analysis on the thermal comfort of a cooling tower based thermally activated building system in tropical climate – An experimental study

Highlights

Abstract

Introduction

Section snippets

Literature survey

Experimentation

Results and discussion

Conclusions

Acknowledgment

Build. Environ.

Energy Convers. Manage.

Sci. Total Environ.

Build. Environ.

Energy Build.

Energy Build.

Appl. Therm. Eng.

Appl. Therm. Eng.

Build. Environ.

Energy Build.

Energy Build.

Build. Environ.

Energy Build.

Renew. Energy

Energy Convers. Manage.

Appl. Therm. Eng.

Build. Environ.

Appl. Energy

J. Econ. Behav. Organ.

J. Public Econ.

Energy and Build.

Build. Environ.

Research Paper
Parametric analysis on the thermal comfort of a cooling tower based thermally activated building system in tropical climate – An experimental study