Close to the first burn...that said, miles from the finish line!

i'm no einstein but i would put the heat exchanger on the cold return to the boiler. that way you heat your boiler first so it will only fire when it gets cold water flowing in.

EKLawton said:

i'm no einstein but i would put the heat exchanger on the cold return to the boiler. that way you heat your boiler first so it will only fire when it gets cold water flowing in.

Click to expand...

Foolish to heat the Burnham boiler with the garn, but this has already been covered.

As far as controls:
Does the Burnham stay hot all the time or only run on call for heat?
Is there a control system in place for the Burnham now?
Is there a free set of contacts on the Garn that open on rise above set temp you can use to kill power to the Burnham?
Does the Garn even come with any control for pumps or is it all up to you.?

These will help determine which route to take.

One of the more simple routes would be to use an aquastat on the garn to throw a relay/relays to hand off control to the Burnham when the Garn is to cool
to use. If you just want emergency backup treat them as two separate systems with separate thermostats and set the Burnham TT well below the Garn so
it will only come on if the house gets cold. Downside to this is the boiler may stay hot anyway depending on the type of existing setup.

Work backwards from your house thermostat, TT controls zone valves, zonevalves control the BH or heat exchanger pump(depending on mode oil or wood) and
if heat exchanger pump then also control the pump on input side of exchanger. Wood to oil mode could use a relay kill power to BH, another relay to switch from BH
pump to flate plate pump.

I am not familiar with the Garn or it's controls but this is not that difficult if you work through what needs to run and when. There is a recent thread on relays
and there applications, check it out if you are not familiar.

Kris

my asumption was that the boiler was always on so it is always at a constant temp. so runing thru it first it will not run until no heat comes out of the garn. you would not be wasting any thing and the controls would be alot eas.ier

Use the same controls, just have the injection pump turn on also.

Tim

The key question is what does the BH do when it does NOT have a call for heat? Does it stay turned off and cold? Does it try to cycle periodically to keep it's water hot?

Assuming that it stays turned off and cold, then there are essentially two control strategies to control the three relevant pumps.

Pumps -
P1 - pump on Garn side of HX, should run when house calls for heat, and Garn is hot enough
P2 - pump on house side of HX, should run when house calls for heat, and Garn is hot enough
P3 - pump on Burnham, should run when house calls for heat, and Garn is NOT hot enough

Strategies -

1. Have two thermostats - T1 & T2. T1 is wired to turn on P1 & P2, and set for desired house temp. Put aquastat (or other sensor) on Garn side HX supply pipe, wired to interrupt T1 signal (thus keeping P1 & P2 from running) T2 is wired to Burnham thermostat inputs, and set to approx 5* or more LESS than T1. P3 is wired to Burnham pump control outputs

Method - If Garn is hot, T1 turns P1 & P2 on and off as needed to meet house demand. If Garn supply water drops below minimum required, aquastat prevents T1 signal from reaching pumps. House gets colder, until T2 turns on Burnham, which runs P3 as needed for heat - Wife gets cold & grumpy, sends rvtgr8 out to build fire in Garn... :coolsmirk:

2. One thermostat, set for desired temp. Aquastat or other sensor on Garn side HX supply pipe, wired to coil of DPDT relay. Thermostat wired to common terminals of relay. NC set of relay contacts wired to Burnham thermostat inputs, NO set wired to P1/P2 control. P3 wired to Burnham circ control.

Method - If Garn is hot, sensor closes, tripping relay, thermostat signals go through NO contacts to control for P1 & P2, turning them on and off as needed. If Garn cools down (or there is a failure in the sensor circuit, I wired this way as a fail-safe) the relay returns to off state, sending thermostat signal to Burnham, which again controls P3... Note that some signal may be appropriate to alert house that they are now running off the BH instead of the Garn, as both will be trying to maintain the same temperature setting.

The control logic for P1 & P2 can be very simple, just a relay or two as needed to turn the thermostat signal into on / off switching of the supply for the circs.

One can get much fancier, and spend a lot more money and effort, but IMHO the two approaches above are both workable, simple, and probably the cheapest way to go...

Gooserider

Goose has a good handle on the situation.

I like option #2, option #1 may be a problem because i THINK there are zone valves involved here. If so the TT signal to the Burnham probably comes
from the zone valves so the second thermostat would be tricky.

So.....think in terms of a complete separate system for the Garn. on a call for heat(from the zone valves?) you want to run the pumps on each side of the
flat plate. Like Goose said, insert DPDT relay in the thermostat line to the BH control, and from normally open contacts to the Garn side pump relay. Then all
you need is a signal to control the relay. could be line voltage or low voltage, depends on whats on the garn. If you hook it like goose suggested you will need
contacts on the Garn that CLOSE on temp rise. When the Garn heats up contacts close and energize relay, sending TT signal to Garn side pumps.

You will need some type of relay(24VAC coil?) for the garn side pumps, the thermostat signal will close this relay and run both pumps.
You may want a relay to kill power to Burnham boiler so it does not stay hot all the time, if it only fires on a call for heat it will NOT be needed.
If none of this makes any sense I may have to break out the kids crayons a make a schematic.

As far as football I'm a Ravens fan so I didn't care who won as long as the Steelers lost. Bummer... :down:

Edit: Remember the wiring is the easy part as long as you TURN OFF THE POWER, you don't get wet when you mess this up. Just don't let the smoke out
of anything, It's a bi%@$ to get back in.