Updating the program - Home Energy Management System

By Jeff MacKinnon, P.Eng., PE


Back in the fall I finally started programming the ClickPLC to manage the thermal ETS that heats the studio.

There were a couple things that I just didn't bother dealing with:

  • adding space temperature
  • finer control during long periods of low prices (weekends)

The simple reason is that I didn't have an analog temperature probe that I could easily add to the PLC and I didn't want to get into using MODBUS. For the time being I added a manual ON/OFF switch and a AUTO/ON switch.

This way I was able turn off the heater during the weekend, go back down and turn it back on on Sunday afternoon and everything would be great. However, when I came down this morning it was 16C in the studio, I forgot to TURN IT BACK ON!

So, I have it ON manually so that I don't freeze this morning, but it is the kick that I need to update this.

The Plan for today

I still don't have a temperature sensor, but I want to make sure that I give the ETS enough time to charge on Sunday and keep the space warm. The way that I want to do this is based on the room temp, if it is below 19C I want to make sure the ETS is on, during low power, and then off around 22C.

22C is about where I have the dial on the ETS set, which is something that I need to fix but it requires running another control wire.

What will the logic look like?

I'm starting with an expensive clock controller that takes no account of the temperature inside or out.

The existing ETS Contol

My first thought was something like this

First ladder logic alteration

This will work for the outside temperature, but "already warm" doesn't know the day of the week by itself. I will need to add timer to that one.

The timer logic

I'm thinking 4h is a good time to get started, and the way that ClickPLC works, when it's enabled the timer starts and stops when the enable is gone. The T1 only changes state when the timer gets to the setpoint.

So the "final" logic will look something like this.

The final logic sketch

Getting this into the PLC

The first thing that I need to do is get both inside and outside temperature into the PLC. Since I don't have these connected directly into the PLC, I need to get them from VTScada.

Modbus is the "easiest" way to do this, but this post has gotten long enough.

Stay tuned, that post is coming.

This post is part 4 of the "Home Energy Management System" series:

  1. Home Energy Management
  2. Updating Heating Control - Home Micro Grid
  3. Finally programming my ETS
  4. Updating the program - Home Energy Management System