Process to integrate new (unreleased) CBUS thermostat

Hi all,

I have been *longing* for the new CBUS thermostat. I have an LG LBUM1081BL - a light commercial reverse cycle A/C that has been 'unsuitable' almost since it was installed due to the large 3 degree setback variance (i.e. it will heat to the setpoint and not heat again until it has cooled down 3 degrees which means you spend some time hot, sometime cold and some time just right) and the lack of automatic setback temperature changes per period per day (i.e. Wake, leave, return and sleep settings).

I have talked to the local LG serviceman and he appears reluctant to look into compatibility or performing the integration of the thermostat into my system, referring me to LG technical support. I have sent off an email to LG support with the information I have about the device (from a post on this forum) to ask them if my unit is compatible and how I go about integrating the thermostat. I am fully expecting them to simply come back with a response to the effect of 'we will not warrant the use of any non LG control unit and in the event of a fault will refuse to service any such system until the original controller has been re-installed' and that I will still have no idea on how to hook this little beauty up.

I'm sure CIS has considered this to be the standard position of most manufacturers and I am interested in what you think peoples avenues are in terms of determing system compatibility and finding someone actually interested in installing it.

I think it would make it easier for me to enlist someone if there were some generic installation / wiring instructions. Does such a thing exist yet?

Thanks,
Brad.

 

my understanding...

All I have to go on is the information in the forums and the product guide, but I think you are going to have a hard time with your system.

A/C systems seem to fall into three broad categories:

1. IR control only
2. Dedicated wall controller (and maybe ir) - This is yours
3. "Traditional" thermostat with separate control circuits for heat/cool, compressor & fan

The new C-Bus thermostats seem to be designed to work with the last option in the list; this is typical in older homes and in many commercial spaces.

For example, my house has an old electro-mechanical Honeywell thermostat on the wall. The thermostat basically switches three circuits;

1. Compressor on/off
2. Reversing valve (to select heat/cool)
3. Inside fan unit

In my case these are all 240V circuits so I will need to use C-Bus relays to switch them based on messages from the thermostat. Other systems use 24V ac rather than 240V (This is very common in North America). There are versions of the thermostats with in-built relays that can control these 24V systems directly.

There are a lot of variations on this basic theme; resistive heat & compressor cool or gas heat & compressor cool, two stage heating and so on, but it call comes down to circuits being switch on or off based on temperature.

From googling your system I think you are going to have to perform some major surgery on your unit to get it to work with the Clipsal unit; in theory the same basic circuits are being switched, you just need to work out how they are wired to the existing controller and re-wire them to C-Bus relays; of course if you get it wrong and let the magic smoke out it may be expensive

Paul

 

Thanks for your comments Paul.

Yes, the wall controller unit definately has some proprietary bus wiring off to 'somewhere' - I think the roof unit - but I was hoping that the 24VAC points that the clipsal unit will want to interface too might be accessible in the roof unit and that I could run the approriate wiring up to it. If it is in the outside unit I will have to re-evaluate my desperation.

If you actually found something on the internet that would indicate where in my system those 24VAC control points reside in my system I would appreciate a link so I can check it out.

I'm pretty desperate to get more control over my HVAC unit. I think can make something work via IR control of the existing controller but its a bit clunky and not so reliable. Also, given the cost of running the unit the CBUS thermostat would also allow me to 'log' the on/off cycles and assist in running it more efficiently.

Again, thanks very much for your feedback.

 

Hey Ashleigh do you remember having a conversation on this point a bit over a year ago ???

The trick is going to be finding someone who knows enough about C-Bus and also knows about HVAC - because "letting magic smoke out" of an AC heat pump/compressor is sure to be very expensive.

Maybe if someone finds a person that fits the bill they could post their details here ???

 

Ashleigh,

The combination of the thermostat, and NIRT interests me. I have already interfaced the A/C unit to CBUS via IR, carefully analysing and constructing IR sequences for various settings (e.g. Heat, 23 degrees, Fan High, etc) and triggering the IR sequences from a PAC that is interfaced to an old mobile phone I had.

An option could be to install the thermostat, leaving the existing wall unit installed (maybe relocated inside the pantry) and I think you're saying the CBUS thermostat would generate CBUS events that I can pick up with the PAC and switch the A/C system on via my NIRT IR sequences. Not elegant but definately an easy install option for me and it leaves the A/C system intact.

Brad.

 

IR Control

Hi Brad,

If you use IR control you will need to send an IR command to turn on the AC with a low set point (if cooling) or high setpoint (if heating) or you will still hit your dead-band issue.

Something else to consider is setting the system to "ventilate" if possible rather than off when in a cooling cycle and the set point is reached. This should operate the indoor fan but turn off the compressor. This will ensure that air flows through your house even when the system is not actively cooling and help to ensure a more even temperature.

Paul

 

For those interested, below is the response from LG. It is exactly as expected.

"Dear Brad Thank you for emailing LG Electronics Australia. With regards to the operating range of the thermostat whereby there is a 3 K differential between the initiation and termination of heating this is predetermined by the factory and can not be altered. The wall controller has a programmable timer which turns the unit on or off based on the customer?s requirements over a 7 day period. With respect to external temperature control there is no means of interfacing such control with our product other than the wall control that is supplied with this unit at the time of initial purchase. Kind Regards."


I intend to go down the route of using the CBUS thermostat interface it to my existing system via CBUS and IR.

The benefit for me is I will (I think) be able to configure multiple setback periods, adjust my setback 'variance' (the degree to which the system will wait until driving the temperature towards the setback again) and this will all be in a cool (pun intended) HVAC User Interface.

To do this I need the thermostat to give me CBUS events that tell me to turn the unit on to heat (or cool) and turn the unit off. Would it be possible for someone to give a brief description of the type of information the unit can transmit onto CBUS?

For example, can my PAC pick up the following data from the unit:
- heat or cool on and off
- the temperature at the unit
- the temperature the unit is currently set to

I'm getting excited now...

 

I am definitely no A/C expert, but I reckon some some care should be taken here - the "deadband" is actually there for a very good reason.

You need to leave some hysteresis (dead band), or the motor will be cutting in/out/in/out continuously once the temperature hits the setpoints. I wouldn't consider 3?K (?C) to be a particularly wide hysteresis figure. If you need better control than that then you might need to change the compressor to an inverter type that can modulate the temperature more "accurately".

You also need to allow for restart delay times, as you are going to kill the compressor motor or trip the circuit breakers by switching it in and out too often (quickly).

Clipsal employees - it might be worthwhile going to have a talk with the local sales office of TAC, as they can help with this kind of control stuff.

 

True, I have definately considered those aspects.

I know that currently my A/C unit has a 50% duty cycle (which is pretty bad and due to insulation problems that I need to resolve). Being big (it costs $1 per hour to run if on all the time) and takes 20 seconds to 'warm up' every time it switches on, so I will be watching it very carefully as my recent power bills have been astronomical and wear and tear on the unit is already occuring.

The good thing about leaving my system intact is that there is already protection from turning it off and on too quickly. Since I will be simulating on/off button presses I know that if I turned it off then turned it on a minute later the unit already protects itself by not doing anything for a period of time. I don't know if this protection is in the main unit or the wall controller but since I am leaving the system intact, I'll be right.

But all the same, like you said, if I'm stupid enough to configure it with a 0.5 degree deadband it will turn on and off all the time costing me easily in excess of $1000 a quarter in power and wear out the unit. A deadband of 3 degrees is a real pain. I can't get comfortable. I have coaxed it to have a deadband of 2 degrees by setting it to divide the temperature measurement between the common zone and the roof thermostat but this gives me other problems.

I believe this unit has a minimum deadband setting which should prevent these issues anyway. Much less risky than individuals making up their own PAC logic and using relays and temperature sensors to drive systems completely.

When I fix my heat loss problem and then can set the deadband to 2 degrees, I reckon I'll be happy.

 

help with thermostats

hello there everyone, just playing around with the 5070thb on a job of mine and have a small issue which may be obvious to some, so hopefully they could fill me in. What I have is a relay unit controlling solinoids for underfloor hot water heating. I want to control the relays via the thermostat which I have done but the on off switch does not seem to prevent the thermostat from cycling.
What i would like is while the thermostat is "on" the thermostat works via the sensor but if the home owner pushes the off button the haeting system stops is this possible or am i missing something obvious.
cheers justin..

 

Is it possible to use AC (IR transmitter) for cooling, water heating (relay controlled) for heating?

Which thermostat mode should be used?