There are two things you are not considering. First there is pumping of the chilled water, which adds heat to the fluid that the chiller must remove. If you set the pump’s Rated Pump Head to a tiny number this can be removed. Second there is a loop capacitance model which will shift loads over time. If you set the Plant Loop Volume field to a tiny number this can be removed.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Yan Xue
Sent: Wednesday, November 14, 2012 1:16 PM
To: EnergyPlus Support
Subject: [EnergyPlus_Support] How to calcualte "Chiller Evap Heat Trans Rate" in E+
Dear all
I'm trying to figure out how the E+ calculates the chiller electric consumption recently. According to the reference, I learnt that the ratio of "Chiller Evap Heat Trans Rate" to "Chiller Electric Consumption" is COP. And in inputoutput reference, it's said that "Chiller Evap Heat Trans Rate" means the evaporator heat transfer which is the cooling delivered by the chiller. So I think the "Chiller Evap Heat Trans Rate" equals the water enthalpy difference between water inlet node and outlet node of the cooling coil. And it should be the same as the air enthalpy difference between air inlet and air outlet node of the cooling coil. However, when I checked them and found that for most timestep, the difference was very little such as 1%, but sometimes it could be as much as +-20% !
Is there anybody who can explain the problem for me? I have attached the idf file and there are 5 zones in the building, I use one single HVAC system for each zone, we can just focus on one zone for the problem. In the "Output:Variable", I have chosen the related parameters for the North Zone. Thank you so much.
Sincerely
Yan
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