Supply/Return with Mixing Valve - Failsafe mode issue

[SteveJ]

System is plumbed as shown below - storage tank not online. Thanks for all the help and comments.

Controller board not installed.

Looking to finish failsafe mode before controller is added.

All circulator (C-1 through C-5) are Grundfos 15-58 with internal flow checks. All are set to low speed.

All zone valves are Honeywell 3/4" normally closed except the one from the Seton to the storage tank.

Failsafe mode definition - mode that system runs in if computer controller fails.

Failsafe issue is the C-5 circulator pulling through the AM-102R mixing valve - set at position 13 - about 125F.

If there is a heat source on - right now only the Seton, then everything is fine. If the Seton circulator is off (set by Seton aquastat on Seton supply at 145F) then the mixing circulator C-5 continues to run and will pull hot (or cold) water through any of the heat sources. The propane boiler happens to be the shortest route and I have a cutoff to prevent flow through it now.

So, my options as I see it are:
1. Only allow the mixing circulator (C-5) to run if one of the other circulator are on.
2. Place aquastat on main supply and shutoff C-5 if the temp falls below a threshold - allows for heat scavenging.
3. Place zone valve on each heat source to prevent flows when not operating.

So, for failsafe (no computer controller), what would you suggest for controlling C-5.

I guess this is similar issue to a primary/secondary system when the primary loop circulator is off?

Thanks,
Steve

 

[Nofossil]

If it were me (and it's not), I'd use three 110vac relays, one in parallel with each of C1, C3, and C4. I'd wire the contacts in parallel with each other and in series with C5 so that C5 can run only if one of the others is running.

 

[SteveJ]

nofossil,

Thanks for the reply - I wish it were you

What about scavenging heat from one of the supplies? Wouldn't it be nice to be able to run the mixing pump C-5 while any source was still hot?

Also, with the three relays - shouldn't the coils be wired in series (rather than parallel) with each of the C-1, C-3 and C-4 with the contacts all in parallel and then in series with C-5? That is, switch closes when either C-1, C-2 or C-4 are on?

Please forgive my ignorance - trying to learn...
Steve

 

[Nofossil]

nofossil,

Thanks for the reply - I wish it were you

What about scavenging heat from one of the supplies? Wouldn't it be nice to be able to run the mixing pump C-5 while any source was still hot?

Also, with the three relays - shouldn't the coils be wired in series (rather than parallel) with each of the C-1, C-3 and C-4 with the contacts all in parallel and then in series with C-5? That is, switch closes when either C-1, C-2 or C-4 are on?

Please forgive my ignorance - trying to learn...
Steve

I think to scavenge, you'd still need the relevant source circ to be running.

Relay coils are very high resistance (low load) devices. Never wired in series. The coils should each be in parallel with the associated circulator motor. Of course, if the circulator is powered by a double pole relay that has a spare pole, you could just use that. I don't know how your circs are powered so I just drew in a black box labeled 'controller' for each of them. All I need to know is that they provide 110vac to run the circ.

You have the contact configuration right.

Here's a drawing.....

 

[SteveJ]

nofossil,

Thanks (as always) for setting me straight...

Question about wire size to C5:

If the 120V relay is about a 40ft (each way) wire run from C5 and C5 is a UP15 run on low speed (about 0.5A @ 120V), then will Cat 5E be okay? Maybe twist a few pairs together? The ampacity rating is at http://www.powerstream.com/Wire_Size.htm - 24AWG chasis rating of 3.5A - seems kind of close.

What is the largest current you run through your ethernet runs?

Thanks,
Steve

 

[Nofossil]

I don't use cat5 for anything bigger than a 24vac zone valve. In your case, I'd do one of two things:

1) Make a high voltage relay box and run all circulators from it

2) Put a high voltage relay in or near C1, C2, and C4, but use the contacts to switch 24vac rather than 110vac. Use the 24vac to drive an additional relay that's mounted in or near C5.

High voltage relays should be in an enclosure. If there's not enough room in the circulator housing, use a standard electrical junction box nearby (about a buck at your unfriendly Home Despot or equivalent).