Cooling Load Increased When Switching to Water Source Heat Pump in OpenStudio?

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I trying to modify the office-medium prototype building model to use water source heat pump instead of vav with dx cooling and gas preheat electric reheat, but after I made the change, the cooling electric usage increased a lot, and it seems like it was because of the increase of cooling load. I didn't make any change to the thermal zone settings or the thermostat settings , have no idea why it happens. The modification was suppose to bring savings, but now it actually increases the energy use...Anybody can figure out why? I'll try to upload both baseline model and the new model with heat pump system. Not sure if I have enough..points..to do so.