STATISTICAL ANALYSIS OF WEATHER DATA OF EIGHTEEN NIGERIAN LOCATIONS FOR MODELS DEVELOPMENT FOR REFRIGERATION AND AIR CONDITIONING SYSTEMS
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Date
2018-01
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UNIVERSITY OF ILORIN
Abstract
The global increase in ambient temperature is partly responsible for increase in energy consumption of cooling systems. Therefore, there is a need to optimise systems designs which require design codes based on current meteorological data. The aim of this study was to develop models from weather data that will provide useful information for developing new design codes for air-conditioning and refrigeration systems in Nigeria.The objectives were to: (i) evaluate the 1%, 2½% and 5% design conditions for dry bulb temperature (TDB) and the coincident relative humidity (CRH) of the four warmest months (FWMs); (ii) develop the probability density function (PDF) and cumulative distribution functions (CDF) by evaluating TDB and relative humidity (RH) bins and develop models for degree-days; (iii) evaluate the two-dimensional (2D) bin of TDB and RH to establish number of hours per year in the comfort zone per location; and (iv) investigate the effect of TDB on the energy consumption of refrigerators and air-conditioners.
From the hourly data of eighteen stations of Nigerian Meteorological Services Agency, outdoor 1%, 2½%, and 5% design conditions for TDB of FWMs were determined using Gaussian distribution table with their corresponding CRH. Thereafter 0.4%, 1.0% and 2.0% upper percentiles were determined from the CDF curves and the CRH was obtained for the percentiles per location. Models were developed by averaging PDFs and CDFs of TDB. The degree-days models were obtained from CDF models. The numbers of hours that TDB and RH pairs are within the comfort zones and appreciable evaporative cooling can be experienced were estimated per location from 2D bin data. The accuracy of the models waschecked using Mean Forecasting Error (MFE), Mean Absolute Deviation (MAD) and Mean Absolute Percentage Error (MAPE). The effect of TDB on energy consumption was investigated in four ambient temperature conditions for refrigeration systems, and 15days for air conditioning systems.
Results showed that the:
(i) 2½% design conditions for human comfort for TDB were42.7°C for Maiduguri and 32.6°C for Jos being the maximum and minimum,with their corresponding CRH of 14.7% and 17.4% respectively;
(ii) maximum errors obtained for CDF were 0.04, 0.03 and 4.14% for MAD, MFE and MAPE respectively and annual degree-days were below 10% for MAPE for most of the base temperatures when the results from modelsand the weather data were compared;
(iii) highest hours of TDB and RH pair in the comfort and appreciable-evaporative-cooling zones occurred for Kano (2042 hours) and Sokoto (2400 hours) respectively; and
(iv) highest energy consumed by refrigerators (rated 110 W) was 326.5Wh for 3hours at 37.1°C average TDBnear bakery-oven and for AC (of 3.52 - 3.57 kW cooling capacity) was 12.39kWh at 26.5°C outside and 22.0°C inside TDB.
The study concluded that the models and the new design codes were good in predicting energy consumption for refrigeration and air-conditioning systems.Hence, the outside design conditions computed are useful for revising the design code for comfort air conditioning system for various locations in Nigeria.
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Keywords
STATISTICAL ANALYSIS, WEATHER DATA, MODELS DEVELOPMENT, REFRIGERATION, AIR CONDITIONING SYSTEM