Sky temperature estimation by : three metallic plates method | |
| Author | Nuttapol Limjeerajarus |
| Call Number | AIT Thesis no.ET-03-17 |
| Subject(s) | Temperature measurements Temperature -- Forecasting |
| Note | A thesis submitted in pa1tial fulfillment of the requirements for the · degree of Master of Engineering. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. ET-03-17 |
| Abstract | Sky temperature is defined to be the temperature of blackbody radiation having the same flux as the downward atmospheric radiation. It is an important parameter for calculating radiative heat transfer between an object at temperature above absolute zero (0 K) and the sky. The sky temperature is used in the design of solar applications (e.g. solar collector and nocturnal cooling system). Hence, the accurate sky temperature needs to be estimated. The objective of this research is to develop and verify a model to be used to predict accurately the sky temperature. A three metallic plates method (3MP) has been proposed as a new method to estimate sky temperature. To achieve this aim, absorptivities of each plate were determined by using spectrometers. Then, by applying an energy balance for each plate of 3MP, the sky temperature could be estimated based on absorptivities, ambient temperature, and plate temperatures. This result was used to develop a model of sky temperature estimation. The experiments of 3MP were conducted d during June 25th to July 3rd, 2003 at INSA-Lyon, France. Pyrgeometer was employed to measure directly the sky temperature during June 5th to 16th, 2003 at AiT and thus to validate the developed model. The comparison of the results of the sky temperature estimated was· by using the proposed model with those obtained by using pyrgeometer and models of earlier studies. The ambient temperature, dew-point temperature and solar radiation were taken into consideration in the developed model. The developed models are During day time (Ta 18-28 °C) During day time (Ta 28-37 °C) During night time J:ky = 0.181+3.175xl0-2 E + 0.721Ta J:ky = 15.979 + 2.751xl0-2 E + 0.268Ta J:ky = -5.221+0.445Td + 0.743Ta The results of the study show that the model can predict the sky temperature very satisfactory during night time and satisfactory during day time. For the night time, the model predicts precisely the sky temperature comparing with AIT's data and the other models. For the day time, the model predicts accurately the sky temperature at low ambient temperatures (25-27 °C) but the difference is more when the ambient temperature is above 27 °C. This might be caused by the convective heat transfer assumption. In this experiment, the convective heat transfer coefficient is assumed to be the same for every plate even though they are not the same since the temperatures are much different between each plate especially at high temperature. This causes higher error during day time than that for night time. |
| Year | 2003 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. ET-03-17 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Kumar, S. |
| Examination Committee(s) | Bhattacharya, S. C. ;Surapong Chirarattananon |
| Scholarship Donor(s) | Government of France |