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Enyuan, The total cooling rate is the sensible and latent energy being removed from the air stream by the active section of the heat pump. It is computed as the mass flow rate of air multiplied by the difference between the enthalpy of air leaving the heat pump and the enthalpy of the mixed air (return + ambient) entering the evaporator. The heat pump does not have any kind of economizer controls built into it. The amount of outdoor air being mixed with return air is simply a function of how you have set the outdoor air damper position input. It could be that your heat pump is cooling because there is no ambient air being mixed in and the heat pump is working only with return air. If your concern is that the heat pump would not operate when the ambient temperature is so low (because of freeze up in the condenser) then you have to be careful of your external data file. Performance is interpolated within the range of data given in the file but it is not extrapolated beyond the range. If the heat pump asks for cooling (because of the way you have set the cooling signal input and fan control signal) then the performance (cooling capacity and COP) will be returned for the closest ambient temperature found in the data file. Regards, David On 11/19/2014 14:26, Enyuan Hu 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 |