UZC4 50% rule and Stages feature interaction

[arg]

How do the 50% Rule and Stages features affect each other?

Under current settings I have two problems:
1. The UZC4 will not stage up when multiple zones are calling for heat.
2. The UZC4 will not stage up when the 2-stage tstat energizes W2. (It will stage up when Bank 1, #6 is OFF.)

This is an installation with:
1. One large zone on a 2-stage tstat
2. Three small zones on 1-stage tstats

Objectives:
1. Allow the 2-stage tstat to stage up to W2 as it sees fit when calling for heat.
2. Keep the small zones on W1 unless two or more zones are calling for heat.

DIP switch settings are:
Bank 1
----------
HP system
CONV hp
ON fan prg
180s purge
TMR stages (pot set to zero)
ON 50% r
ON sas
GAS fan

Bank 2
-------------
HC tstats
1 cs#
O rv
OFF zdl
DA aux rly
OFF ras
0 ra limit
Z1 fan ctrl

The manual I have is P/N 090375A0221 December 12 2005. On page 7 the notes for #5 (Stages) include Note 3, "Thermostat demands to stage up will always over-ride the Timer or OAS staging operations, unless the 50% rule has been enabled, or the return air temperature limit has been exceeded."

The notes for #6 (50% Rule) include Note 2, "In Gas mode the 50% rule occurs between W1 & W2."

Q1. With the 50% Rule ON, is the STAGES setting relevant? In other words, if two or more zones are calling for heat, should the UZC4 go directly to W2, or should it only go to W2 when the OAS or TMR settings are beyond threshold?

Q2. If I am reading this correctly, the UZC4 cannot meet the objectives. Am I wrong about this?

Q3. If I'm right, what's the best workaround?

Thanks!

[Eric K.]

Q1. With the 50% Rule ON, is the STAGES setting relevant? In other words, if two or more zones are calling for heat, should the UZC4 go directly to W2, or should it only go to W2 when the OAS or TMR settings are beyond threshold?

The 50% Rule inhibits or prevents the panel from staging up if there is a demand to (Timer, OAS or T'stat) AND less than 1/2 the zones are calling. It will not automatically cause a stage up when 1/2 the zones call, there still must be a demand to stage up from the thermostat, OAS or timer.

Q2. If I am reading this correctly, the UZC4 cannot meet the objectives. Am I wrong about this?

Your 2 objectives cannot both be achieved.

Q3. If I'm right, what's the best workaround?

The only way you can achieve the operation you desire is to add an expansion board (Model ZXM-2) bring your total zones to 6. You now have 2 addition unused zones, which you will parallel to the Thermostat inputs on the Large Zone. This will cause, according to the panel, 3 zones to call at once when the large zone calls, this will put you at 50% therefore allowing the Large zone to stage up. Also, the 3 small zones will not be able to stage up unless all 3 are on or the large zone is also operating. I hope this is clear, if not feel free to call me and we can discuss this in greater detail.

Eric

[arg]

Q1. With the 50% Rule ON, is the STAGES setting relevant? In other words, if two or more zones are calling for heat, should the UZC4 go directly to W2, or should it only go to W2 when the OAS or TMR settings are beyond threshold?

The 50% Rule inhibits or prevents the panel from staging up if there is a demand to (Timer, OAS or T'stat) AND less than 1/2 the zones are calling. It will not automatically cause a stage up when 1/2 the zones call, there still must be a demand to stage up from the thermostat, OAS or timer.
...
I hope this is clear, if not feel free to call me and we can discuss this in greater detail.

OK, so with the 50% Rule ON, no zone can stage up on its own. And a 1-stage stat by definition cannot stage up. That does clarify it. Thank you.

Hmmm. The expansion module idea does not sound all that elegant. I'm thinking about something using AUX RLY and a resistor on the OAS contacts, but at the moment I don't have a good enough grasp on the variables come up with anything remotely coherent.

I'm going biking now. Maybe that will help.

[Eric K.]

That is not a bad idea, but it will not work for 2 reasons. First, once you activate OAS the 50% rule is defeated in heating operations. Second, with the OAS open/shorted and a demand for heat, the panel will activate emergency heating and lock out the compressor. Unfortunately, the easiest way to accomplish the operation you desire is the method I proposed earlier. I know it is not the most elegant solution to your problem, but it works!