Hot-water tankless/zone control question

Steamhead

Looked at a job the other day that was, shall we say, a kludge.

I've spent the afternoon going through wiring diagrams and haven't found a way to do this yet. We don't run into many of these.

House is mid-century slab-on-ground, no basement. Tiny boiler room that can only be accessed from outside. First floor was originally radiant, now baseboard.

Boiler is a Dunkirk Empire, oil-fired w/tankless coil. No gas in house and no room for an indirect. Oil company has this boiler maxed out- 2 GPH!

Three zones with circs. Only the first-floor zone is connected to the triple aquastat so the circ drops out if the water temp gets too low. The other two are ordinary circ relays. This is probably why they have the boiler firing at such a frighteningly high rate.

I'd like to do the following:

1- install an updated aquastat (AquaSmart or HydroStat) to gain control of water temp above that required to operate the coil;

2- wire the circs so they drop out if the boiler drops below the minimum coil temp. I'd prefer to use a zone panel to do this but haven't found one that will let me power the circs, but not the panel's relay logic, through the aquastat. Yes, I could do this with R845 or similar relays but that would be a lot more wiring.

Thanks in advance for any suggestions.

EdTheHeaterMan

Fagabout-it! Look at my second post. No relay needed

This might work. This WILL work.

Whether you use a L1824 or the Aqusmart or the Hydrolevel control, the C1 and C2 will power a 120 V circulator for heat and stop the 120 V circulator when there is insufficient temperature in the boiler for DHW. If you connect a relay with 120V coil to the C1 and C2 terminals you will power the relay coil. If you use a set of NC contacts, when ever the C1 has power the NC contacts will open.

If you wire these contacts to a 4 zone Circulator relay with priority zone, the priority zone will be energized whenever the C1 on the aquastat relay is in DHW priority mode. This will disable all the circulators on the three non priority zones.

Once the boiler has recovered temperature sufficient to supply heat, the C1 on the aquastat will power up and open the Priority zone circuit. Thus allowing the circulators on the 3 space heat zones to operate

Edit: I should have put the X X from the SR504 to the Aqua-Smart TR and TW terminals @Steamhead ... but you already know that.

EdTheHeaterMan

I believe there is another way to do it without the NC relay by using the ZC and ZR on each of the two controls. I'll look at that to see if we can eliminate the need for a relay.

EDIT
It appears that the original Taco SR503 relay has already taken care of your needs.

By removing the factory installed jumper between the ZC and ZR on the SR503 and connecting the ZC from the SR503 to the aquastat ZC and connecting the ZR from the SR503 to the ZR on the aquastat, the problem is solved. All circulators are on the C1-ZC circuit for the DHW priority. The ZR from the SR503 will operate the burner as needed on a call for heat even if the DHW is satisfied and the Hi lim is not yet reached.

HVACNUT

The diagram by Ed would definitely work, but leaving the existing aquastat and adding a 2 zone control panel in lieu of the separate relays and utilizing the ZR,ZC terminals. That will control power to the circulators based on the low limit setting to help ensure sufficient domestic hot water. 
Upgrading to the Hydrostat or Aquasmart wouldn't benefit too much with the tankless coil. You can't use the economy settings and the existing triple has condensate protection because of the low limit.

hot_rod

The Caleffi relays have remote enable contacts that may simplify this. Connect 24- 120VAC to that connection.

Steamhead

Thanks! We'll see how it works.

Steamhead

HVACNUT said:

The diagram by Ed would definitely work, but leaving the existing aquastat and adding a 2 zone control panel in lieu of the separate relays and utilizing the ZR,ZC terminals. That will control power to the circulators based on the low limit setting to help ensure sufficient domestic hot water. 
Upgrading to the Hydrostat or Aquasmart wouldn't benefit too much with the tankless coil. You can't use the economy settings and the existing triple has condensate protection because of the low limit.

@HVACNUT , the existing aquastat on this boiler keeps it at 180°F all the time. I'm pretty sure a more-advanced control like a HydroStat or AquaSmart could maintain a lower temp when there is no call for heat, and ramp up when a call does come in.

Steamhead

@EdTheHeaterMan , do you know if the expandable Taco relays (as SR503-EXP) would work the same way?

109A_5

Hello @Steamhead,
Would this work for what you want to do ?

See manual page 25, there are other examples too.
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Beckett-7610A0001U-Manual.pdf

HVACNUT

Steamhead said:

The diagram by Ed would definitely work, but leaving the existing aquastat and adding a 2 zone control panel in lieu of the separate relays and utilizing the ZR,ZC terminals. That will control power to the circulators based on the low limit setting to help ensure sufficient domestic hot water. 
Upgrading to the Hydrostat or Aquasmart wouldn't benefit too much with the tankless coil. You can't use the economy settings and the existing triple has condensate protection because of the low limit.

@HVACNUT , the existing aquastat on this boiler keeps it at 180°F all the time. I'm pretty sure a more-advanced control like a HydroStat or AquaSmart could maintain a lower temp when there is no call for heat, and ramp up when a call does come in.

A triple acting aquastat will maintain the low setting and only go to the High limit setting on a space heat demand. 

EdTheHeaterMan

The existing L8124 if still working properly should be able to maintain a lower temperature setting by setting the LO LIMIT to a minimum temperature of something like 150° or 160°. and setting the DIFF to something like 10° or 15°. Then you can set the HI LIMIT to 180° or 190°

By using the the aquastat with the SR503 (I believe either one will work) and connecting the ZC and ZR as I indicated above, all the zone circulators will provide DHW priority.

The problem with the L8124 X-XXXX of any style, IS that most oil burner, Gas heat, Plumber, HVAC, and Electricians... don't take the time to read and understand the installation instructions. This leads to insufficient or erratic DHW when adding a second, third, or more space heating zones. But you can fix that with a bigger nozzle obviously... from what you found.

So @Steamhead, the answer to your query about SR503-EXP is YES.

MikeAmann

@Steamhead
from above, you said, Only the first-floor zone is connected to the triple aquastat
Why is it running off of the HI limit?

Steamhead

MikeAmann said:

@Steamhead
from above, you said, Only the first-floor zone is connected to the triple aquastat
Why is it running off of the HI limit?

Got me. We were there to work on another part of the system so I didn't dig into this, just observed it.

EdTheHeaterMan

@Steamhead, You can connect all the zones to a SR503 and no circulators to the C1 on the L8124. You then connect the ZC and ZR as shown. There is no need to connect the XX of the SR503 to the TT of the L:8124. The ZR will bring the burner on, without the need for the TT as designed for use the old way with RA845XXXX. The SR503 will operate the burner thru ZR as needed. The ZC will stop circulators if boiler temperature falls below the Low Limit/Diff. setting as designed.

Only replace the L8124 if there is a problem with it. Sometimes Simple is better than those new fangled electronic thig-a-ma-gigs.