Vol.4 No.3 2012

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Research paper : Demonstration test of energy conservation of central air conditioning system at the Sapporo City Office Building (H. Takeuchi )−140−Synthesiology - English edition Vol.4 No.3 (2012) 5.3 Water quality adjustmentWhen 1000 ppm of the agent was added and stirred with the sampled circulating water, cotton-like precipitate was formed. This was thought to be a hydrate formed by the reaction between the anionic rust inhibitor in the circulating water and the cationic one that was used. Therefore, if this agent were injected in the circulating water directly, the hydrate would form and clog the narrow parts of the pipes. To prevent this, the cationic rust inhibitor was used. The circulating water was replaced the total of four times using the off-days to reduce the concentration of the anionic rust inhibitor to several tens of ppm, and the set volume of cationic rust inhibitor was added. The hydrate did not form when the readjusted circulating water and the agent were mixed.The injection of the agent was done near the ejection point of the circulating pump on the 2nd basement. The plunger pump was used to pressure inject a certain amount of agent placed in the agent tank into the circulating water.For the sampled circulating water, the calibration curve of the agent concentration and electric conductivity was obtained beforehand to calculate the agent concentration of the circulating water after injection. During the demonstration test, the circulating water was sampled from the 2nd basement, air conditioning equipment room on the 8th floor, and expansion tank on the 19th floor. The mixing state of the agent for the whole building was estimated from the distribution of the agent concentration. 6 Demonstration test6.1 Appearance of the flow performanceThe demonstration test for winter was conducted in November 2006. The details are described in reference[8]. The heating system of the office building started operating in early morning and was stopped at 17:30. Therefore, the actual circulating water was sampled at 9:00 when the entire circulating water system became thermally steady. The calibration curve for the electric conductivity and agent concentration was obtained from the samples. Since the agent had high viscosity, unevenness in concentration occurred in the system when it was bolus injected, and in extreme cases, the high concentration of the agent might cause clogging in the narrow channels. Therefore, the agent was initially injected at a slow speed of 10 kg/h. Then circulating water was sampled, concentration measured, and abnormalities were checked at the 8th and 19th floors. Slight bubbling was observed in the expansion tank on the 19th floor, but the amount was not problematic, and there was no further increase of the bubbles. A total of 100 kg of the agent was injected over three days. The estimated agent concentration at this point was 3000 ppm.To even out the agent concentration further throughout the system, the second injection was conducted after one week. Two days were taken to inject 80 kg of the agent, and the injection was completed when the estimated agent concentration reached 5400 ppm, which was sufficient to generate the flow drag reduction.In the series of maneuvers described above, the inverter frequency was changed at the agent concentrations of 0 ppm, 3000 ppm, and 5000 ppm, and the values for the flow rate and power consumption of the pump were measured. It was found that 65 % of energy conservation could be achieved by setting the agent concentration to 5000 ppm and the inverter to 35 Hz to match the rated flow during the winter period.The flow drag reduction was studied for the period of cooler use (summer period). It was found that 47 % of energy conservation could be achieved by agent concentration of 3500 ppm and inverter frequency of 40 Hz. The results of the demonstration test for the cooling and heating periods are shown in table 2. The calculated amount of saved energy for the cooling and heating periods in a year was 52,000 kWh, and this amounted to conservation of over 1 % of power usage for the entire city office building. 6.2 Maintenance of the heat transfer propertyAs shown in Fig. 5, for the reduction of the heat transfer performance in the heat exchanger used in the winter period, it was thought that the reduction of both the flow drag and heat transfer performance would not occur due to the great turbulence in the flow due to the complex channel of circulating water, because the high temperature steam supplied by the regional heat travelled through the heat exchanger tube while the circulating water flowed inside the shell-side separated by the segmental baffle plate.The heat exchanger of the evaporation unit of the absorption refrigerator used during the summer period is composed of 414 U-shaped copper tubes of the length of 6 m and an inner diameter of 16 mm. The circulating water flows inside this hairpin tube, and flow drag reduction is expected to occur in the straight section. If the reduction of heat transfer performance is also occurring, the circulating water will circulate the building with insufficient cooling, and the cooling capacity of the entire building will be compromised. For the heat transfer coefficient of the tubes of the heat exchanger, the value obtained from the empirical equation[9] Table 2. Demonstrated operation condition and energy saving rate for summer and winter periods65660035about 5000Heating47660040about 3500CoolingEnergy conservation rate (%)Rated flow (L/min)Set frequency (Hz)Agent concentration (ppm)Air conditioning mode

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