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Mohamed, Chun Kwon is correct in his comments. I thought I would just add some other things that I noticed. 1. As Chun Kwon mentioned, you need to add some thermal capacitance (probably in the form of a tank) in the cooling water loop. You also need to reduce your timestep to something on the order of 5 minutes. Make sure that all of the storage tanks in the simulation can hold at least 1 timestep of fluid in them. The two tanks in your simulation are rather small (1m3 and 0.3m3) given the flow rates on your chiller. 2. You have used the same flow rate equation to set all three flow rates on the absorption chiller (hot water, cooling water, and chilled water). All of the machines that I have seen have a certain ratio of these flow rates. I have never seen a machine where all three rated flow rates were the same. This might be skewing the performance of the chiller. 3. The thermal capacitance of your building zones is left at the default value of 1.2*ZoneVolume, which accounts only for the thermal capacitance of the air in the zone, not for any of the furnishings. A better value would be approximately 1.2*5*ZoneVolume 4. The chiller's capacity is left at its default value of 1500kW which seems rather high, especially given the size of the cooling coil. 5. You correctly caught that you have to set the number of Type4 tank nodes on both the parameters and the outputs tab of the Type4 proforma. However, be careful, the question that you have to answer is slightly different. In one case it asks how many nodes there are and in the other case it asks how many nodes there are in addition to the top and bottom nodes. What is specifically going on in your simulation is that the long time step, the lack of capacitance in the cooling loop, and the very large chiller capacity are causing one of the flow streams to not only freeze but to drop well below -273C at which point the psychrometrics routine generates an error. Kind regards, David On 9/10/2013 07:38, Mohamed Adel wrote:
-- *************************** David BRADLEY Principal Thermal Energy Systems Specialists, LLC 22 North Carroll Street - suite 370 Madison, WI 53703 USA P:+1.608.274.2577 F:+1.608.278.1475 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com |