Recently there have been a lot of accidents by Legionella disease originated in bath water. It is very important matter as measures for Legionella disease to control free residual chlorine concentration exactly. In this report, it is examined that the different value of measurement of free residual chlorine concentration between usage of these two reagents, DPD (N,N-Diethylphenylene-diamine) and SBT (Sulfo-benzyl-tolidine), in terms of its chemical structure, oxidation reduction potential and the results of measuring in bath water.

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An optimum control of heating and cooling plant with thermal storage tanks and refrigerators operated at discrete points is a large-scale mixed integer plan problem. In the previous paper, we proposed a practical approximation method using the linear programming. However, in the previous method, we could not deal with nonlinear operation characteristics about refrigerators operated at discrete points and ON/OFF control pump. In this paper, we propose a method to get a strict optimal solution using the mixed integer programming by replacing refrigerator operated at discrete points with two or more virtual refrigerators. And we describe the optimum control of heating and cooling plant including pump power. We compared the simulation results of this method and those of the previous method and showed the advantages of the new method presented in this paper.

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