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Study on Thermal Load Calculation for Ceiling Radiant Cooling Panel System

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Study on Thermal Load Calculation for Ceiling Radiant Cooling Panel System Study on Thermal Load Calculation for Ceiling Radiant Cooling Panel System Sei Ito1, Yasunori Akashi2, Jongyeon Lim2 1Shimizu Corporation, Tokyo, Japan 2University of Tokyo, Tokyo, Japan This study uses the thermal network model simulation Abstract program “Nets” (H. Okuyama (1999)); a form of HB. The ceiling radiant cooling panel (CRCP) system affords This paper has three sections: (1) Evaluation of Nets, (2) a comfortable environment for occupants with reduced Modeling method for a ceiling radiant model, and (3) cooling energy consumption. However, it seems that the Case study of thermal load calculations for CRCP sys- thermal load calculation for CRCP systems is uncon- tems. firmed. Therefore, this study was conducted to propose a In the first section, comparative testing, namely the thermal load calculation method for the CRCP system ASHRAE Standard 140-2011 (ASHRAE (2011)) is based on the thermal network simulation model using conducted for Nets. Also, AS140 is used to compare the “Nets”. The case study results show that the cooling load simulation program with the standard building simula- on the CRCP system is higher than the general air condi- tion tools to evaluate the validity of Nets. tioning system because the CRCP removes not only the The second section presents the results of the experiment room’s cooling load but also the ceiling plenum’s cool- to evaluate the heat transfer phenomena in the CRCP ing load. Finally, this study clarifies the necessity of system, as well as determine the thermal conductivity of considering the ceiling plenum when calculating the the CRCP. The necessity to consider not only the influ- thermal load for the CRCP system. ence of cooling load caused by the room, but also the Introduction plenum, is shown. Furthermore, we identified thermal conductivity between chilled water and the CRCP sur- Energy conservation technology has been in high de- faces. Therefore, these values are available for the sim- mand regarding efforts to realize (net) zero-energy build- plified CRCP modeling method for the thermal network ings (ZEB). Ceiling radiant cooling panel (CRCP) sys- model. tems represent a key energy conservation technology that can yield high efficiency, since it uses moderately The third section presents a case study that was conduct- chilled water (16−18°C) and does not require energy to ed to clarify the difference between the thermal load propel a fan to remove the cooling load. Generally, a calculation for the CRCP system and the general air- CRCP system provides a high degree of comfort to oc- conditioning system. Finally, this study shows the neces- cupants because it does not induce any draughts. sity of a thermal load calculation for the CRCP system. There are several examples of CRCP system applications, Evaluation of simulation program however it seems that the thermal load calculation for CRCP systems is unconfirmed. The design procedure for Outline of “Nets” simulation program the CRCP system described in the ASHRAE handbook Figure 1 shows an example model of Nets. The model is (ASHRAE (2016)) shows how to determine a CRCP constructed to simulate air, surface and solid tempera- specification that satisfies the design conditions. Howev- tures of the building with a single room and an air- er, the method of determining the design condition, i.e. handling unit. The thermal network model consists of the thermal load, was not referenced in the design proce- nodes and thermal resistances connecting each node. dure. Previous research (J. Feng (2013)) compared the There are three types of node: (1) thermal mass node is sensible cooling load for a radiant system calculated using the heat balance (HB) method with one using the AHU radiant time series (RTS) method. They concluded that RA the HB method was more accurate than RTS in terms of Plenum calculating the thermal load for a radiant system. How- Ceiling ever, the target system in the previous study was limited SA W indow : Thermal resistance to radiant systems without ceiling plenums, such as a (Conduction, Radiation, Convection) radiant cooling panel with insulation on the panel, an : Thermal resistance (Advection) : Thermal mass node embedded surface cooling system and a thermally acti- Room : Surface node vated building system. Therefore, this study was con- Slab : Fixed temperature Node ducted to propose a proper method of calculating the thermal load for a CRCP system with a ceiling plenum. Figure 1: Network model in Nets Proceedings of the 15th IBPSA Conference 555 San Francisco, CA, USA, Aug. 7-9, 2017 https://doi.org/10.26868/25222708.2017.144 set as the heat capacity of each material, which enables the inside of the material to be calculated, (2) surface 8.0 2.7 node is set as the surface and border of materials, which 0.5 N should be set in order to calculate the surface and border Window 2.0 Window temperature of materials properly, and (3) fixed tempera- 0.2 Unit: m ture node is set as a boundary condition, such as weather 0.5 3.0 1.0 3.0 0.5 data. There are four types of thermal resistance: (1) con- duction, (2) convection, (3) radiation, and (4) advection. Figure 2: Isometrics for Case 600 Heat balance equations for each node are determined using this modeling. Therefore, each node temperature is Outdoor Air calculated by solving the equations. Outdoor Air Simulation case based on AS140 For the purpose of evaluating the validity of Nets, com- parative testing was conducted as per the ASHRAE Standard 140-2011 (AS140) (ASHRAE (2011)). AS140 Window Window was developed to validate the building energy simulation Ground Plan Elevation program, determined in many test cases. The building models for the test cases are very simple, as shown in Fig. 2 for example. The calculated results of many simu- Figure 3: Thermal network model for test case lation programs are prepared for comparison with the results calculated by the target program. Then the target ESP BLAST DOE2 SRES/SUN SERIRES S3PAS TRNSYS TASE Nets program can be validated comparatively. 7 7 In this study, basic tests were conducted on the building6 6 thermal envelope and fabric load for Nets. Table 1 5 5 shows the input conditions for the test cases. The varia- ble input parameters are window orientation, sunshade,4 4 heat capacity and the thermal insulation performance of3 3 the building. 2 2 1 Annual Annual Heating Load[MWh] 1 Annual Load[MWh] Heating Table 1: Building conditions for test cases 0 0 600 600 610610620 630 640620650 900 910630920 930 940640 950 650 Low mass basic test Heavy mass basic test 10 5 Case Window Sunshade Case Window Sunshade 600 south ×2 - 900 south ×2 - 8 4 610 south ×2 Overhang 910 south ×2 Overhang 6 3 620 east, west - 920 east, west - [MWh] Overhang Overhang 630 east, west 930 east, west 4 2 Fin Fin Load 640 south ×2 - 940 south ×2 - Annual Cooling 2 1 650 south ×2 - 950 south ×2 - 0 0 600 610 620 630 640 650 900 910 920 930 940 950 Table 2: Control strategies for test cases Case Heating Cooling Ventilating Figure 4: Annual heating and cooling load 600, 610, 620, 0:00~24:00 0:00~24:00 0:00~24:00 630, 900, 910, <20°C: on >27°C: on Off 920, 930 Otherwise: off Otherwise: off setback and Cases 650 and 950 are night ventilation 23:00~7:00 0:00~24:00 0:00~24:00 respectively. <10°C: on >27°C: on Off A thermal network model was developed for Nets to Otherwise: off Otherwise: off 640, 940 7:00~23:00 meet the building conditions of the test cases as shown <20°C: on in Fig. 3. In addition to these conditions, operational Otherwise: off conditions were set to meet control strategies of the test 0:00~24:00 0:00~24:00 18:00~7:00 cases. Then heating and cooling loads are calculated 650, 950 Off >27°C: on On using the models for each case. Otherwise: off 7:00~18:00 Off Evaluation results Figure 4 shows the results for all cases calculated by Table 2 shows the thermostat control strategies for the Nets. The annual heating and cooling loads are within test cases. It is assumed that the control strategies for the range of results calculated by other programs. There- Cases 600, 610, 620, 630, 900, 910, 920 and 930 are fore, Nets is shown to be valid as a thermal load calcula- continuous operation, Cases 640 and 940 are thermostat tion tool. Proceedings of the 15th IBPSA Conference 556 San Francisco, CA, USA, Aug. 7-9, 2017 Modeling method for ceiling radiant panel Heating element 2125 Fundamental experiment for CRCP A fundamental experiment was conducted to understand Ceiling plenum chamber how the CRCP removes the cooling load and to identify Ceiling radiant panel the thermal conductivity of the CRCP. Figure 5 shows 1800×600×3 Water Heating element the device for the fundamental experiment. In order to Corrugated plastic chiller simulate the actual build environment of the CRCP sys- 1720 tem, an insulated box was divided into two chambers: a Room chamber Units: mm room and plenum chamber. The CRCPs, as shown in Fig. 2125 4, were set between the two chambers and assumed to be Numeric values show inside dimensions the actual ceiling. The CRCP is composed of an alumi- num punched panel, metal-reinforced polyethylene pipes Figure 5: Experimental device and heat sinks. The heat sink promotes heat transfer between the chilled water in the pipe and the panel sur- 1787 face. The chilled water was supplied by the water chiller 1453 to keep the water temperature within certain parameters.
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