I would like to model a gas absorption heat pump and have run into a problem. My first approach was to model it as a regular air-to-water heat pump WaterHeater:HeatPump object, and set the fuel to NaturalGas. I didn't get very far with this since EnergyPlus throws an error if the COP is too low. The absorption heat pump I'm modelling will have a COP of between 1.15 and 1.25 which is low enough to fail.

So my second approach was to search for gas absorption in the documentation, which turned up ChillerHeater:Absorption:DirectFired - link. This looks like it may be a possibility, but it's set up as a chiller which also provides hot water while I just want the hot water. This means I'll have to set up a condenser loop and a cooling loop, neither of which will actually be used which seems like a waste of time.

My question is is the ChillerHeater:Absorption:DirectFired a valid way of modelling a gas absorption heat pump if I can set it so that the chiller is never activated? Am I missing a better way of doing this?

Edit I've set this up and it's running, and with the chiller and condenser loops having operation schemes that are set to always of I think it's OK. A lot of extra lines in the IDF but it's working.

I'm still interested to know if this is the correct way to model this system or if I've missed a simpler alternative.