[Etaz]

If you take a look here: Honeywell VisionPro Thermostats - iaqsource.com

There are a number of stats. What's interesting is that Honeywell offers a gizmo that will provide and interlock the 120 control relays and, I think, provide the 24 VAC to their FAN coil stat.

This fan coil stat does offer an speed control.

KISS,

Would this model work in my application? It uses 120V AC input but I am not sure if it would work in my application. It is made by CAS.

Model No. System Fan Function
T202-G5B63 Heat/Off/Cool Auto/on 3 speed

Here is the wiring diagram. I just am not sure where the pipe sesnsor connections would go.
Wiring

1 stage Heat / 1 stage Cool
-------------------------------
1- Input (L1)
2 -Common
3 - Heat
4 - Cool
5 - Lo fan
6 - Med fan
7 - Hi fan
8 - Rev. Valve heat
9 - Rev. Valve cool

1 Heat / 1 Cool
Heat Pump
------------
Compressor, add Jumper to 3,4

1 - Input (L1)
2 - Common (Neutral)
3 - Heat 1 stage
4 - Cool 1 stage
5 - Lo fan
6 - Med fan
7 - Hi fan
8 - Rev. Valve heat (damper)
9 - Rev. Valve cool (damper)

Is this stat even applicable to 2-pipe heat/cool system? I am going to attach pics for you to enjoy of my lovely system. I have also attched a PDF of the CASD stat I was looking at.

To answer MB's question, there are two independent systems in each corner of the condo. The 2-piping water source (see pic) is common piping to all units so if bldg "boiler" or "chiller" goes down then all units in bldg suffer. But thermostatic controls are per unit. A guy in a nother unit replcaed his mechanical (original IEC) t-stat with the non-programmable honeywell T6575 but I was looking for a programmable option.

Thx.

[Etaz]

Actually, take peek at this http://www.ntsupply.com/files/products/62-0278.pdf

I would have places to put all my wires incl. the sensor wries. Which wiring scenario would be most applicable and can I rig the T202 with this wiring in mind?
I know... I'm all over the road but bear with me I really appreciate your time.

[Etaz]

I am still unclear on how to attach pics/files. Infraview seems to be just a freeware image viewer. Is there a site I can attach images to and just post the links in this forum?

[KISS]

Page 2 is very similar to your stat. In fact the lower link is identical.

http://l.b5z.net/i/u/6065183/i/T202_Rev_A_6-29-05.pdf

I may have an idea. Let me think a little bit.

Is Heat/Cool used on the original stat? Somehow I don't think so.
So, I think all we may have to do is prevent Heating or Cooling based on the pipe temperature. Does this seem reasonable? Now what bothers me is the contact ratings. Is it possible to read any info off the fan motor? Like HP or FLA and LRA?

Here: http://www.ntsupply.com/files/products/62-0278.pdf

Page #5 is interesting.

[KISS]

Pictures:

Use "Go advanced" and then "Manage Attachments"

Irfanview is an image resizer if it does fit the size requirements.

[KISS]

Any possibility you can get a wiring diagram of the FAN coil and get it scanned?

[KISS]

Ah. Ideas coming to life.

http://controlsdepot.ca/siebe/pdfs/REDPDF/TC2931.PDF

Available at:

South Side Control Supply Co Invensys Barber Colman TC2931 Strap On Changeover Stat 75F TC-2931

Now we are getting somewhere.

[Etaz]

Yep, that's it. But that works! I don't need another one of those. Ohhhhhh... I see you were thinking out load ;-). Is all my psycho-blabber starting to "connect"?

[KISS]

Yep. Thinking outloud.

I need a question answered:

Am I correct that the fan is not allowed to run to just circulate air, because if it did it would blow hot or warm air, correct?

I think I can make it work "correctly" with one contactor and 1 additional relay + the Changeover switch above.

I need to sleep on it.

[Etaz]

You are correct. Fan has to blow whatever the temp of water is running through the pipes.
"chat" later...

[KISS]

The "pipe sensor" is probably like the TC2931 switch and not a temperature sensor at all.

[KISS]

I think by adding the following logic, the t-stat will work.

If (water hot) and (call for heat) Motor is allowed to run.

If (water cold) and (call for cool) Motor is allowed to run.

(allowed to run) means t-stat controls the speed of the motor from off to high.

[KISS]

A few comments at this point:

To those reading, some pics were too big and sent privately.

The possible stat CAN be made to work with some effort. I'm waiting for the mfr to reply concerning what Auto means. It can be Auto-changeover because of the pipe temp or auto-changeover because of a heat and cool setpoint.

There may be other stats available. I didn't have a chance to look at another promising one. Now that I know what I'm looking for, it should be a bit easier.

The changeover sensor is probably an SPDT switch and it would have to be used.

The energy savings may not be as steep as you would think because you may only be paying for electricity to run maybe a 1/3 HP motor. Maybe 300 W when running.

The changes required, which I would like to avoid, in words would be:

A junction box or enclosure would have to be put in the FAN COIL enclosure to protect the suggested additional controls.

HEAT and COOL wires would have to be used in the tstat box. You probably can use 2 of the 3 wires from the changeover sensor that are running to the current stat.

A contactor would have to be placed on the Neutral side of the motor. (Motor allowed to run). [Need nameplate data to size]

A DPDT relay (120 V coil) would also be used. It would be designed such that when OFF, heat is the default mode. The Changeover sensor (2 of the 3 wires) will be used to provide the switch to energize this coil when the loop water is hot.

What this relay will do is select the HEAT or COOL output of the stat and power the coil of the added contactor. If chatter occurs a small time delay relay can be added.

Standard DIN rail construction techniques can be used. Bushings would have to be used for the penetrating wires.
I'm not real happy about the wire nutted motor connections not in a junction box.

So, in theory, it's possible.

[KISS]

This was a Carrier stat I found http://www.docs.hvacpartners.com/idc.../33cs-56si.pdf

But there is one major gotcha. The fan has to run on Low all the time unless off.

It's a low voltage stat and a relay interface board is required.

The necessity of the fan running all the time makes this one impossible to use

[Etaz]

All this EE talk of throwing new relays and contactors into the witch's brew is making my headspin. Let's step back and scale back.

What if I lose the ability to auto-changeover<grimace>, make it a manual step from the stat. Cap off the sensor wires. Now what do we have? Given the T202 stat that I would like to work in the existing framework, what would have to happen. Refer back to the wiring diagram earlier. Having 3 speeds on fan is overkill, so only have LO or MED speed available when energized? My head is still spinning. :-|

[hvac1000]

Actually a 3 speed manual selector switch for 8.00 bucks on Ebay does the trick. Got one on my unit a camp. When playing cards with the guys I just dial it down to the next lower speed. Nice and quiet. I just bolted it to the furnace in a 4x4 handy box.

[Etaz]

Addendum. Let me reflect on my original obective: Replace archaic manual stat with programmable digital stat for energy savings and more presice temp control.

Now I have walked into a realm where I should just boil water over a flame and watch the hamster on the wheel chase the Cheezit to run the gernerator to power my girlfriend's hair dryer.
Your screenname says it all, KeepItSimpleStupid. Let's hover over this acronym and apply it here. Or because of the archaic system, in order to achieve long term energy savings do I HAVE to throw money at the solution up front? Re-engineering cost savings is also paramount due to budgetary constraints.
Fire when ready... :-/

[Missouri Bound]

Etaz... would you consider moving? Seems like a lot less of a headache. And somehow the phrase "keep it simple stupid" doesn't apply to this anymore. Hmm... Well thanks for opening up the doors Etaz, once in a while it's nice to have our interest peaked. As I said early on you are on the right track. But it would behoove you to have someone you personally know and trust look at the system and advise you rather than make any changes based on comments made on this informative but alas long distance information forum.

Keep the faith.

[Etaz]

Don't blame you a bit, MB. Thanks for your input. It has been enlightening and I will pursue the suggestions rendered in this forum. Cheers.
Nowwww where did I put my analog TV antenna...

[hvac1000]

Don't blame ya a bit, MB. Thanks for your input. It has been enlightening and I will pursue the suggestions rendered in this forum. Cheers.
Nowwww where did I put my analog TV antenna...

Here is part of your system. It was built for a prison but something like this will work for you. Now all you have to do is figure it all out.