Modelling a hot box to get heating and cooling loads

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Hi, I am trying to model a very simple building (just a 10x10x1 box) with no windows, and model the heating and cooling loads required to meet set point temperatures as the energy from the weather data (Gatwick,London) heats the internal space. Is there a simple way to do this? I tried using a VRF system but it doesn't show cooling loads...

There is a warning Calculated design cooling load for zone=THERMAL ZONE: SPACE 101 is zero. Check Sizing:Zone and ZoneControl:Thermostat inputs.

I don't have values for these inputs because I have used the HVAC template thermostat to set set points.

Any ideas? Any help greatly appreciated!