# Literature review and Objective

Modeling of Radiant mullions

No literature about modeling and performance evaluation of mullion heating and cooling has been found in open publication. Because the mullions are actually radiators and are so close to the window glazing, the heat transfer processes between the mullions and the window glazing, window frames, room surfaces and inside air are complicated. Understanding these principles is important for an accurate simulation of the performance of the mullions in the IW. The heat transfer process of window mullion radiators is defined in the performance study of the mullions. One model has been developed for the mullion heating and cooling simulation. This model has been verified by measured data. The simulated results match the measured data very well. Detailed results and references can be found in the report Performance study Radiant Panels (pdf).

Modeling of Radiant panels

Significant research has been done regarding the heat transfer models, and the thermal comfort and efficiency of ceiling radiant panels. Chen and Kooi (1988) developed a radiant panel simulation model which considered the radiant ceiling panel as an indoor surface exchanging heat with room air by convection and other room surfaces through radiation. Kilkis et al. (1994) proposed an in-slab type panel model. They pointed out that the heat transfer in a panel-cooled room and the cooling panel itself might be represented by a quasi-steady state natural convection model by assuming uniform panel surface temperatures. Stetius and Feustel (1995) developed a 2-D radiant panel model by simplifying heat diffusion equations for an in-slab type panel. Conroy and Mumma (2000) derived an analytical model for a top insulated metal ceiling radiant panel. This model was based on the study of solar collectors conducted by Duffie and Beckman (1991). The basic methodology in this model was to determine the panel cooling capacity by finding the unknown mean panel surface temperature in an iterative process. However, the detail structure of radiant panels varies greatly; it is hard to use one general model to estimate the ceiling panel capacity in the IW.

The objective of the performance study of the radiant panels is to develop a specific model to estimate the heating and cooling capacity of the radiant panels used in the IW (without topside insulation) with a focus on the impact of thermal contact resistance between the tubes and aluminum panels.

Some researchers (Awbi and Hatton 2000, Jeong and Mumma 2003), in recent years, have proposed a mixed convection heat transfer coefficient to calculate the radiant panel capacity, because the ventilation diffusers near the ceiling panels create a forced air flow across the ceiling panels. However, the air velocity near the panel surfaces is related to the diffuser locations. In the IW, the ventilation diffusers are either on the occupants’ desks or on the floor, and thus have little impact on the convection heat transfer across the radiant panels. The references cited above can be found in the detailed report: Performance study Radiant Panels (pdf).

Additional research topics

- Infiltration investigation of a radiantly cooled and heated office (pdf)
Air infiltration has a significant impact on the heating and cooling loads of small office and residential buildings. In a radiantly heated and cooled office, air infiltration normally determines whether this type of system can operate without condensation on the radiant cooling surface in summer, because infiltration may bring considerable moisture into the space. The office studied experiences infiltration that seriously limits the effectiveness of the radiant cooling system and active desiccant dehumidification system. Earlier infiltration measurements using the tracer gas procedure showed infiltration levels of 0.78 – 1.12 ACH, while CO2 concentration measurements gave values from 0.1 – 0.2 ACH. This paper reports the results of infiltration levels determined from blower door measurements and logged humidity data from the ventilation unit as well as a reanalysis of the CO2 data. There were still significant discrepancies that are resolved by combining the measured results with a calibrated simulation and additional site measurements. It is found that infiltration in the studied office is from two sources: one is outdoor air; the other is the indoor air from the floor below the studied office. The total air infiltration for the studied space may vary from 0.74ACH in the summer to 1.5ACH in the winter, while the under floor space air leaking into the studied office may range from 0.46-1.03ACH.

Additional information can be found in the thesis report of Xiangyang (Gary) Gong "Investigation of a Radiantly Heated and Cooled Office with an Integrated Desiccant Ventilation Unit"(pdf).

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