Thanks! Yeah the swimming pool should do the trick. But i'm still struggling with the vegetation. Can I model it as a green roof material?

I would think that depends on what aspect of the trees you are trying to model. Shading? CO2 consumption?

Mainly their evapotranspiration to see what affect trees and grass have on air temperatures and comfort.

Hmmmm. For that purpose you may be able to model them as People with a low Sensible Heat Fraction. You will probably have to mess around with some other settings also. It looks like nobody has asked a related question before, which is somewhat surprising. Congrats, you're the guinea pig! Please circle back and post the solution you ended up using.

Can someone please share how you modeled the effect of the trees and grass? I'm trying to model a greenhouse and I suspect the plants will have a huge impact on the air temperature. Tried to use the green roof material but I'm afraid it is only to be used for roof type surfaces with sun exposure, as I think my current model only takes into account the soil heat exgange from the results of various scenarios.