Two-way Thermostat

An Online Tutorial

The RCS TX15b Two-Way Thermostat
or
Does the phrase "utility bill" mean anything to you ?

If you've ever thought about incorporating Heating and Cooling controls into your home automation system,
you really should consider the RCS TX15 bi-directional thermostat.

It's been a couple of years now since Steve Fyfe offered the plug-in for the TX15,
but recent changes in XTension make it even more compelling to add
this very reliable HVAC thermostat to your system.

Why do I want to do this ?

Aside from the fact that the TX15 is a very attractive and simple to use replacement for an old thermostat, being able to control it from XTension can save you money on your utility bills.

You can send X-10 commands from XTension to set all of the modes and temperature settings that can be set manually. Plus, the TX15 sends the current temperature to XTension.

So not only can you control the temperature setpoint according to the changing 'modes' of your home, but you can also keep track of how well the HVAC is performing.

Integration with XTension means that you can call in to the house and tell XTension that you're going to be two hours late, and thus the warm up or cool down should be also delayed.

Another nice thing is that if you have door open/closed sensors, you can announce that the doors need to be closed, and if the situation is not corrected, adjust the HVAC so that you're not heating or cooling the neighborhood !

Is this really difficult ?

If you're already familiar with X-10 modules, and XTension, and can use a screwdriver, you can do this yourself.

Except for what logical elements you may want to add to your system that respond to changes or control the settings, the only things you have to do are :

A few wire strips and screw-downs
Download and Import of a plug-in
Paste of a text file into your Attachment Script
(Maybe) change the house code in 9 different places.

The TX15 has been around for several years, and the documentation that comes with it is well-developed. The most common thing that can cause problems is that your system was wired by someone who did not adhere to the industry standard of wire colors.

But even if you're color-blind, you can probably read the labels on your existing thermostat, and carefully label and record the proper connections on the wiring diagram that comes with the unit.

Where to begin ? (after you've bought it)

The TX15 will work just fine in a 'stand alone' mode. You do not need XTension or a computer to make it work.
So the first thing is to set it up according to the included instructions.

The most difficult thing is that the TX15 is really TWO units, where your old wall controller is just one. There is a WDU (wall display unit), must be connected to a separate 'Control Unit'. The problem is that you must find a place to mount the control unit where you also have access to a normal electric socket.

The wall display unit connects to the control unit, which is then connected to the HVAC system with the same wires that previously connected to your old wall controller.

Even if the old cable is buried in the walls, you can probably find where it comes out near the HVAC unit itself.

Since the connection between the wall display unit and the controller requires only 4 conductors, you can just cut the cable near the HVAC unit, and connect the old cable wires from the HVAC to the control unit, and then use the same wires to run from the control unit to the wall display unit.

BUT, wherever you decide to mount the Control Unit, you must have access to an electric socket. The Control Unit needs power, and also needs to connect to a TW523 (X-10 interface) which also must be plugged in to the powerline.

Here's the big picture :

Follow the instructions in the Installation and Operation Manual

There are several different settings for the SW1 switches, and the manual is quite adequate for making these decisions according to the specific type of HVAC unit you have.

My only mistake was that I didn't read all of the instructions before trying it out... :-)

AFTER following the instructions, and making all of the connections, you should be able to make changes to the settings at the Wall Display Unit, and see 'normal' behavior of your HVAC, without any interaction with XTension.

Do make sure that you can change the Mode (Heat, Cool, Off), and that the temperature 'setpoint' does cause the heater or air conditioner to come on appropriately. (Just like your old thermostat.)

Now let's set up the 'computer control'

Having done all of the steps above, and verified the proper operation in 'manual' mode, you should download the plug-in:
CLICK here to download the CLASSIC TX15 plug-in

CLICK here to download the OS X version of the TX15 plug-in
The 'plug-in' includes all of the elements that are needed to monitor the behavior of your new TX15, as well as some basic functions that you will need to control it.

But it does not include any of the 'logic' that you may want to incorporate into other parts of your system to 'decide' when you want to change the HVAC settings. But once this is installed and operational, the database units are available for testing by any of your scripts.

After importing the 'plug-in', and making a single change to the 'attachments script' handler, XTension will be able to report the current temperature, as well as any manual changes that you make from the Wall Display Unit.

The 'fun' part is that you must still add elements that determine whether and when you want to set the 'temperature setpoint'; switch between 'cooling' and 'heating'; and things like turning off the system when a door has been open for too long...

What the 'Plug-In' installs

After downloading the plug-in, you must tell XTension to 'import' it.
You will find this function under the "Database" Menu.

There will be one new "List" named "TX15", which includes a set of new Units, which will manage the different functions of the TX15.

CHANGES you need to make to the 'plug-in'

The plug-in includes a 'text' file that must be copied and pasted into your currently existing (OR new) Attachments Script.

Just pull down the "Scripts" menu, and select "Edit Attachments".

Find an opportune location in the script, and Paste all of the "tx15attach.txt" text into the window, and then SAVE.

Control and monitoring of the TX15 requires that you dedicate almost an entire 'house code' of addresses to the purpose.

To make it simple, just assume that you must 'eat' the whole housecode, and thus you must decide which house code you want to use.

If you just look at your "Master List" in XTension, you should be able to identify either an 'empty' house code, or one that is least used, and thus requires the fewest number of changes to your database and modules.

Once you decide on which house code to use, you must also make sure that the Attachments handler you just pasted reflects that same House Code :

OH ! There is also one Global Script that is installed...

On Startup of XTension, you should already have a 'Startup Script', and you'll want to add a line there that executes the new Global Script "Initialize Thermostat".

This script causes the initialization of the TX15 control unit so that it remembers that there is a computer listening, and a few esoteric elements that you can study if you want. (If you do, please take notes and offer your comments to the XTension discussion list...)

What else do I want to do ?

At this point, you can open the TX15 List menu, and make changes to the "Thermo Setpoint", and the TX15 will start using that temperature as the 'temperature that you want to maintain in the home'. But, there are many things yet that you may want to do with your new toy:

Set the temperature of your home according to the 'mode' of your changing lifestyle.
Disable the HVAC whenever some condition occurs, such as a door is left open for 'too long'.
Add a 'watchdog' scheduled script that keeps track of the 'duty cycle' of the HVAC. By watching the amount of time that it takes to lower or raise the temperature, you can announce the fact that the unit is working 'too hard', and may need service. You may want to look at a sensor that can verify that air is moving in the ducts.

Unfinished things

There is an 'external' temperature probe that you can attach to the Wall Display Unit, but so far I've not found any documentation about how it is used, or if it is really a 'second' sensor, or just replaces the one in the WDU.

Also, some folks have multiple HVAC units in their larger homes, and the plug-in must be modified to allow for this. If there is much interest in this, I'm sure we'll come up with an improved version.

This tutorial is still 'in work', and in need of feedback from YOU.

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Last modified: February 17, 2006
Michael Ferguson, help@shed.com