Re: [TRNSYS-users] Best Controller for Controlling Slab Surface Temperature?

[Ben Heymer <bheymer@gmail.com>]

Brad,

First make sure that the timestep you are using is small enough. You could start with 1/120 hours, then increase while checking that the system dynamics still make sense.

I recommend starting with a simple proportional controller (Type 1669 or similar) which will simulate quickly and is quite typical for real-world control of radiant slabs. If that doesn't track closely enough, you can try the iterative controller (Type 22) which I find to be a good proxy for real PID controllers (though it will slow down the simulation). There is a PID controller in TRNSYS (Type 23) but that requires the simulation time step to be similar to the real-world controller time step. This is not often the case for HVAC simulations.

Ben Heymer, PE

On Sun, Sep 20, 2015 at 4:52 PM, Bradley Painting <paintingbr@appstate.edu> wrote:

I am attempting to control the surface temperature of a radiant slab by turning flow on and off through an active layer. The active layer receives a fluid of variable temperature. The allowable temperature range of the surface must be pretty small to achieve thermal comfort -- within a couple degrees.

At first I tried using a simple Type2b differential controller, where the heating setpoint is the Upper Temperature and the slab surface temperature is the Lower Temperature. However, it doesn't seem like it is responding. I do anticipate a problem with this regardless because of the thermal lag of the concrete slab. Which controller within the TESS or standard TRNSYS library would work best? Thanks.

--

Brad Painting

Master of Science Candidate, Renewable Energy Engineering

Department of Technology & Environmental Design

Appalachian State University

Boone, NC  28608

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