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Thermostat Question

 
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Old 02-25-2009, 09:50 AM   #1
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Thermostat Question


My folks recently bought a house, and we want to upgrade the thermostats.

The heating system has a gas-fired hot water boiler, with baseboards throughout the house. There are 2 thermostats controlling 2 zones: One for the basement, and the other for the main living areas of the house.

This house also has a cooling system for the living areas, with a roof-mounted air handler and outside compressor and associated ductwork in the attic.

There are 3 thermostats: One for the heating zone in the basement, and the other 2 are located adjacent to each other in the living room --- one for heating, the other for cooling.

Here is what I want to do:

I want to install a single thermostat for the living areas, combining the 2 existing stats. I understand that the "R" terminal is for the heating system and the "RC" is for cooling. I will remove any jumper in the new thermostat to accomplish this separation of power supplies for each system.

Using a single thermostat in place of the 2 existing stats upstairs prevents both systems from operating at the same time.

The problem I have is the additional heating zone thermostat in the
basement. I want to prevent that zone from operating should someone inadvertantly turn up the basement thermostat during the summer while the upstairs thermostat is in cooling mode. We don't want to be heating the basement at the same time we are cooling the upstairs.

So my question is this: Is there a thermostat available or wiring configuration that allows me to install an interlocking relay that disconnects power to the boiler while the upstairs stat is set for cooling mode? This would have to be active even if the stat was not calling for cooling operation, just be set for cooling mode.

I would rather not have to install a separate heat/cool double-throw switch, but want the internal switch in the stat to do this function.

I'm not sure if the O/B terminal can accomplish this, since the lock-out relay would have to be active all the time the stat was in cooling mode, whether or not the A/C system was operating.

any suggestions you can offer are appreciated.
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Old 02-25-2009, 09:30 PM   #2
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Re: Thermostat Question


You can buy a peanut relay (24v coil) from Jonstone supply, Grainger, or whom-ever is your local hvac supplier (about $15.00). Pull an 18-2 wire from the existing t-stat to your boiler. Install the relay on the boiler wherever possible.

Wiring connections: y + common on t-stat to the coil terminals on the peanut relay. break the wire from the basement t-stat and connect them to the n.c. contacts on the relay.
By doing this, whenever the upstairs stat calls for heat, the n.c. contacts will open. When the cooling is satisfied, the n.c. contacts will close.

You know, another thing you could do is to simply disconnect one of the wires (discconect the wire that is on the w terminal) from the stat during the summer. Simple Simon

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Old 02-25-2009, 11:38 PM   #3
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Re: Thermostat Question


Nope, this will not work properly.

The only thing your scenario will prevent is the downstairs unit from operating while the A/C unit is cooling. What happens when the upstairs unit is satisfied and shuts off? Then the basement heat could start up causing a heating/cooling cycle. This is unacceptable.

I understand that disconnecting the white wire will prevent the downstairs unit from working. This is not the point here. The problem is my folks are in their 80's and are not capable of handling such tasks. I can't be there to baby-sit them all the time, since I live several hundred miles away.

I need to have this system operate automatically, since we already found both the heating and cooling systems running at the same time, due to their misunderstanding of how to set the thermostats.

For now, I have switched off the breakers for the cooling system, but this will have to be dealt with by summer.

A thermostat with aux. contacts in it would be ideal for this type of situation, if I only knew which model to buy. I have no problem installing a separate relay to disconnect the heat while the cooling mode is selected.
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Old 02-26-2009, 01:40 AM   #4
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Re: Thermostat Question


Gotcha, I was kinda wondering why you wanted to disconnect the basement t-stat. I would call the Honeywell and/or White Rogers customer service people. They may have something, good luck. If they don't have an indoor stat that will do what you want, you might use an outdoor temp sensor/t-stat that will open when the temp rises above say 70 degrees. It's just a thought. Johnstone Supply is another good source.
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Old 03-01-2009, 07:08 PM   #5
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Re: Thermostat Question


You were on the right track, you need to find a non heat pump, or single stage heat pump, stat that still offers O and B outputs, and many do. Most will offer a maintained 24vac output on O for cooling or B for heating, whenever the sub base switch is set for that. Then it is a simple matter of adding a relay with a 24vac coil, running the white boiler wire through the normally closed contacts, so that when Mom and Pop's stat is set to cooling, the O terminal opens the relay, and breaks the white boiler wire. I have seen a few all digital stats that are goofy on the O and B outputs, your best bet is a stat, digital or otherwise, that has a mechanical switch for heat off cool in the sub base. These strategies have been used for years on older zone control panels to direct heat or cool operation.
As with any control scheme like this, you need to both test it in all modes, and document in the basement so a service guy will not have figure out what is going on. Post a big note "upstairs stat must be in off or heat mode for boiler heat to work" or something like that, so your solution does not become a problem later-should work ok though.
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Old 03-03-2009, 01:19 PM   #6
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Re: Thermostat Question


turn the power off to the boiler in the summer months.
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Old 03-03-2009, 08:26 PM   #7
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Re: Thermostat Question


Why not just put in an outdoor stat to lockout the boiler at temps above 60F. That should solve your problem.
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Old 03-08-2009, 11:31 AM   #8
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Re: Thermostat Question


Quote:
Originally Posted by kbsparky View Post
A thermostat with aux. contacts in it would be ideal for this type of situation, if I only knew which model to buy. I have no problem installing a separate relay to disconnect the heat while the cooling mode is selected.
Kb,
I wonder if a 24V latching cube relay could work for the situation you described.
I know many of these relays use only momentary, pulse voltage to latch and reset, but I seem to recall something about using a resistor in series with the coil to allow for a continuous voltage to be applied to the without damage, so this might be something for you to look into.
Maybe you could wire the relay to latch when Y terminal on the upstairs T-stat is energized during a call for cooling and interrupt the W wire in the basement T-stat, then have it unlatch when W on the upstairs T-stat is energized on a call for heat.
That way the basement heat would continue to be locked out as long as the upstairs T-stat stays in cooling mode and will only allow the basement to return to heating after the upstairs T-stat is switched back to Heat mode and initiates a call for heat.
Anyway… just a thought.

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