Proceedings of BS2015: 14th Conference of International Building Performance Simulation Association, Hyderabad, India, Dec. 7-9, 2015.
DEVELOPMENT OF PERSONALIZED RADIANT COOLING SYSTEM FOR AN OFFICE ROOM
Vaibhav Rai Khare1 , Anuj Mathur1 , Jyotirmay Mathur1 , Mahabir Bhandari2
1Centre for Energy & Environment, Malaviya National Institute of Technology, Jaipur, India.
2Oak Ridge National Laboratory, Oak Ridge, USA
The building industry nowadays is facing two major challenges – increased concern for energy reduction and growing need for thermal comfort. These challenges have led many researchers to develop Radiant Cooling Systems that show a large potential for energy savings. This study aims to develop a personalized cooling system using the principle of radiant cooling integrated with conventional all-air system to achieve better thermal environment at the workspace. Personalized conditioning aims to create a microclimatic zone around a single workspace. In this way, the energy is deployed only where it is actually needed, and the individual’s needs for thermal comfort are fulfilled. To study the effect of air temperature along with air temperature distribution for workspace, air temperature near the vicinity of the occupant has been obtained as a result of Computational Fluid Dynamics (CFD) simulation using FLUENT. The analysis showed that personalized radiant system improves thermal environment near the workspace and allows all-air systems to work at higher thermostat temperature without compromising the thermal comfort, which in turn reduces its energy consumption.
This manuscript has been co-authored by UTBattelle, LLC under Contract No. DE-AC05- 00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-accessplan).
Interest and growth in radiant cooling systems have increased in recent years because they have been shown to be energy efficient in comparison to all-air distribution systems (Khan et al., 2015). In radiant cooling system, temperature of the structure is reduced by supplying chilled water at lower temperature flowing through the pipes embedded in the structure. The radiant cooling system removes the major part of the sensible load while latent load and remaining sensible load is removed by the ventilation system. The radiant cooling system can provide the comparable comfort level at higher room temperature than the conventional system at lower room temperature in context to human body reaction (Xiang et.al, 2012). Therefore, radiant cooling system, coupled with a smaller forced-air system (for ventilation, latent loads and supplemental sensible loads) can reduce a building’s total energy use by operating at higher set-points. One of the major drawbacks with the Radiant cooling system is condensation. When temperature of panel is below dew point temperature of room air, then the moisture present in the air condenses. This will result into microbial growth which decreases the air quality. Apart from this, temperature control for different systems has very different response times which lead to thermal discomfort of the asymmetrical distribution of the radiant temperature related with panels installed on ceilings and floors (Fred S. Bauman et.al., 1996). In order to overcome this limitation many researchers designed a personalized radiant cooling system. Personalized conditioning aims to condition only a relatively small space around the user. It has been shown that such kind of systems improves an individual’s comfort and reduces the energy consumption when designed and used properly (Melikov AK et.al, 2007). It has been shown that with the use of personalized cooling system, thermal comfort can be well maintained even at the room air temperatures reaching 30 °C and at a relative humidity of 60–70% (Zhai Y et.al, 2013). Personalized convective cooling is applied in all the reviewed studies concerning cooling, often in combination with personalized ventilation. In these studies the most common strategy for reducing the energy use is to increase the temperature set-point for the total volume conditioning while the comfort is still well maintained by the personalized cooling.
The estimated energy savings vary between 4 and 5% when the cooling set-point is increased by 2.5–6 °C (Takehito Imanari, 1999). It has to be noted that the highest energy savings of 51% are achieved by the combination of increased cooling set-point and reduced airflow rate (Schiavon S et.al, 2010). The objectives of the present study are: 1) to localize the effect of cooling in the near vicinity of the occupant to minimize the energy used to condition the unoccupied space, 2) to understand and minimize the condensation problem on the radiant panel. In order to minimize the condensation, both, radiant and conventional cooling systems were operated in various temperature combinations maintaining thermal comfort in the vicinity of the occupant along with the minimum use of the energy. A three dimensional simulation software package, ANSYS v15.0, was used to develop the model, which was validated using test data from an existing experimental facility. CFD simulation provides detailed spatial distributions of air velocity, air pressure, temperature and turbulence by numerically solving the governing conservation equations of fluid flows. It is a reliable tool for the evaluation of thermal environment and air distribution (Khan et al., 2015). These results can be directly or indirectly used to quantitatively analyze the indoor environment and determine system performances. A main reason of using CFD is the excellent pictorial presentations of results which allow engineers to have a better understanding on the indoor environment.
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