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Hello,
I have a question about the issue I am facing in my simulation. I am modeling a greenhouse energy system in TRNSYS, which includes a cooling and heating control system as part of the system. My question is very specific, as it is not related to software knowledge, but rather an issue with a component. Specifically, the simple thermostat component from the TESS library for cooling. As you may know, this component is very straightforward to use with requiring mainly a setpoint temperature and a monitoring temperature to provide a 0 or 1 control signal. My problem in the simulation is that, despite setting a setpoint of, for instance, 24 and a temperature variation of 4 to 40, the control signal sometimes outputs incorrect values. For example, for cooling, it should output 0 when the temperature is below 24 (with headband of 0), but there are time steps that it gives 1 for temperatures like 16, 22, 19, etc. It mostly provides a correct signal, but this should always be the case, and it is affecting my results. The same applies to the temperatures above 24, where it should always give one, while there are times when it provides 0.
Let me assure you that the logic is very simple, and I am 100% certain that the input data is correct, as I am outputting everything for debugging purposes. I am suspicious of the component itself and a bug in the system. Please advise me in this regard.
Best wishes,
Amir
What timestep are you using for your simulation? It should be on the order of 1-5 minutes. Lately I have been using 0.02 or 0.05 hours as my timestep.
The behavior that you describe sounds like the simulation is not converging at certain timesteps. When that happens the components can't all get to a state on which they agree and the simulation simply moves on to the next timestep after issuing a warning. If that situation happens too often then the simulation will error out. Almost always the cause of non convergence is too long a time step or too little thermal capacitance in the loop that is being controlled.
With greenhouses there is also a lot of moisture transfer between the plants and the air. I would recommend that you put a time delay (Type150 in the controllers folder or Type661 in the TESS Controllers library) on the air temperature of the zone before you pass that input to the evapotranspiration model. Since you'll have a short time step a slightly delayed air temperature won't impact your results.
kind regards,
david
