Refrigeration, air-conditioning and cooling technology - 2007.pdf

PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 84E CONOMICAL CONSIDERATION IN THE SELECTION OF FITTINGSMFittings Nominal k V valuediameterShut-off valve 50 80Three-way valve 40 50Non-return valve 45 50Separate machine cooling and room air coolingsystems were selected for economic reasons.For the machine part, 20200.00 kg/h of a water/glycol mixture are to be moved by the circulatingpump. The temperature is controlled by an admixingvalve and the loads adapted. Due to theflow volume, a pump with a connection size ofDN 50 is sufficient. The pipeline is chosen tohave a size of DN 100. In order to keep the buildingcosts down, the isolating valves required beforeand after the pump for maintenance reasonscould be selected to be size DN 50. A k V valueof 40 for the control valve is to be assumed fora valve authority of approx. 70 % for a very goodcontrol. This requires a pump with a deliverypressure of 91 kPa. For operation of approx.3800 hours per year and an electricity rate of€ 0.15, this makes € 604.00 in annual operatingcosts.Alternatively, the installation of shut-off valvesin size DN 100 is possible, with a control valvewith a k V value of 50 and a valve authority of approx.44 %. If a tightly closing valve is selected,the shut-off valve can be omitted. The requireddelivery pressure of the pump is then only 71 kPa.The annual operating costs are then only€ 457.00. This alternative over a time span of12 years means that € 1764.00 can be saved assumingenergy costs stay the same. For approx.€ 300.00 more in investment costs, which paysfor itself in less than 2 years in saved operatingcosts, there is a savings of € 147.00 for everyyear after that.MFittings Nominal k V valuediameterShut-off valve 100 800Three-way valve 100 50Non-return valve – –The other hydraulic circuits are to be consideredunder the same aspects. Usually, higher k V valuescan be selected for control valves and shutoffvalves at high control quality with the bigadvantage of lowered operating costs and amortisationin less than 2 years.The non-return valve is installed so that thereis no incorrect circulation. When tightly closingcontrol valves are used, this can be omitted.In order to prevent undesired circulation withinthe pipe due to gravitational effects, the sensiblepipe dimensioning should be given specialattention.84 Subject to change without prior notice 02/2007 WILO AG