Computer / electronics gurus...

[280plus]

I have an idea for an intermediate card for a control system that offers a LOT of nifty features but ironically not the one I desperately want the most. There is a remote panel that connects via ddc cable to a logic module in the equipment and acts as a brain that oversees the operation of the entire system. It has the capability of operating multiple units simultaneously. I'm wondering if anyone out there thinks they have the expertise to develop a card to go between these two logic modules and add the particular feature I'm looking for. It would involve both hardware and software knowledge. It may involve as much as developing your own schematic for the modules. I'm not sure there's one available.

[TarpleyG]

You talking about something along the lines of an IP KVM switch?

Greg

[280plus]

I have no idea.

What I want is a device that will monitor outdoor air temp and also monitor and control an outlet water temp in relation to it, so that as outdoor temp goes down outlet water temp goes up. And vice versa.

The tough part is interfacing it with the existing DDC controls.

[Harold Tuttle]

a remote ambient temperature water mixing switch, huh...

[280plus]

Yea, kinda, we're not mixing just heating. It already exists for boilers but not this new fangled air source to water heat pump I've been working with.

[charby]

I rented a place a few years ago that had boiler and the thermostat was one that would increase the boiler temperature as the outside temp would drop.

For example you could set it so that at 32 degree outside the boiler would be 160 degrees. at 0 degrees the boiler would be at 175.

[280plus]

Exactly!

[charby]

Is this for that place you showed us pictures of last week?

-C

[280plus]

Yup...

[cfabe]

280, I am a computer engineer and likely have the knowledge to implement this. I am not familiar with this 'DDC Cable' interface, can you provide any more information on that and most importantly is the existing protocol in use open or will reverse engineering of the equipment be necessary?  Is this a hobby type thing or something you could forsee doing a production run of?

[280plus]

I expect reverse engineering would have to take place. I'm thinking if we came up with a quick prototype and patent we might just sell it back to the company as opposed to manufacturing and marketing it. Each piece of equipment has it's own logic board that oversees the operation of that single unit. The DDC board is a device that facilitates the mating and operation of multiple units. It "talks" to one lead unit via signals sent through a shielded "DDC" (Direct Digital Control) cable with three conductors. The subsequent units are piggy backed to the lead unit using the same style cable. Just FYI these are not standard PCs they are logic modules designed specifically for the operation of these units. The problem is not findig a device that will  ramp output temperature in relation to input temperature. I can buy one of those off the shelf. It's adding such a device to the DDC circuit that will function normally with it. Chances are once they hear my request the MFG will revamp the internal design of the DDC board but they might consider an add on if all the work is already done for them. It WOULD be kind of a shot in the dark to be honest.

[280plus]

I'm going to non chalantly ask if I can get ahold of the schematics.

[cfabe]

I did a little quick google searching and it seems like this DDC is  a common term among hvac and energy systems, but I'm not clear as to whether it is a name for a type of control system or an actual communications protocol. For this equipment in question, must one use only the manufacturer's control equipment or is it possible to pair these heat pumps with a third party controller?

I have experience in embedded hardware and software design, and communications protocol design. I know this wouldn't be PC based, it sounds like a simple enough application to use a simple 8-bit integrated microcontroller like an HCS08 or maybe a PIC. I've never tried to reverse engineer a communications protocol before, however. So having some sort of documentation or at least a clue how the thing works would be a huge step forward.

The engineer in me however makes me question that if you want to do temperature adjusting thing on this installation, and other controllers are out there that perform this function for other systems, perhaps the engineers at Robur are also aware of the benefits and either have this capability and you are not aware of it, or it is something they plan on including in a later or higher optioned version of the unit or control system. Is what you're trying to accomplish a common feature of hot water heating systems, and if so, can you think why they did not include this, other than just oversight?

[280plus]

Good questions. I DO feel it's an oversight on their part. That doesn't mean I'm right though. One question I have in to them is whether it would be detrimental to the units to operate them this way. If I were to NOT use the DDC board all I would have to do is hook an existing off the shelf "reset" control across two terminals in each unit to control the temperature of the outgoing water. Which was my original plan. Once I hook in the optional DDC, to the best of my knowledge, those terminals are overridden and there are no similar terminals incorporated into the DDC board. Everything is then controlled by the DDC and, according to the factory, so far, there is no way to achieve what I'm asking through the DDC. They recommended blending the water, well, that's not what I disussed at the outset with them so at this point it's too late to add the necessities for blending. I COULD eliminate the DDC board and get a hefty refund but it does have some nifty features that I like, which is why I bought the thing.

As far as getting an idea of how it works, at this point all I have is the instruction manual that explains all the functions and how to set them up. I'm HOPING I can get some schematics.

All DDC is is the elimination of switches. Instead of relying on a thermostatically controlled switch to turn the unit on and off we're using thermistors and digital circuitry. So instead of a 24V signal calling in relays we're actually sending data back and forth. It gives us much better control over our systems and ways of of monitoring them for example. If I wanted to I could hook this system to a PC with which I could monitor it's function and control it over the internet. It is most widely used in commercial applications where, in a large building here in Hartford, they would have to call Chicago to have the room temperature setting changed.

It may very well be that all I have to do is break the signal to the units until I want them to fire. But I'd need to know which conductor to break and will that foul anything up by doing so.

This particular board will express data in 5 different languages. It has lots of memory so I can scroll back through and see what it's been doing for at least the past few days. I don't recall how far back it goes.

I'm waiting for some replies from the factory on all this. I hope to know more in a few days. Does the email address here get to you? As soon as I know more I'll drop you a line.

[280plus]

Sometimes, when you hash something out with someone else, it helps. I THINK that if I turn my DDC board set temp down to say 85* outlet and then hook my reset across my 2 terminals it MAY override the DDC and achieve said goal. Now to confirm that.

[cfabe]

Yes, my email link should work. Let me know what you find out.