Controlling dual boilers

nate379 · 12:26AM

Aside from fairly expensive controllers, is there an easy solution to setting up 2 boilers?

Would something just as setting one to run 160-180* and the other 140-180* work? 1 boiler would run normally and the other would only kick on if water temp gets too low.

Heat load currently doesn't require 2, but in the future it may, especially if I do a heated parking pad (snow melt)

EBEBRATT-Ed · 12:37AM

You can do that but you're wasting some fuel keeping the idle boiler hot. I have a drawing of a simple lead-lag system where you can run #1 boiler on lead (higher temp) #2 on lag (lower temp) or have them both on lead or both on lag. Of course, you can always shut 1 boiler off if you don't mind needing a back up.

If you wan't the drawing I will look for it. You need 2 relays and 2 aquastats in addition to what you have and some wiring.

hot_rod · 1:30AM

A solar differential control would work nicely.

Basically it has two sensors, two relay outputs.

So if the first boiler cannot keep up it fires the second. It watches the first boiler and if it can catch up to the load it drops off the first.

Temperatures and differentials are all adjustable. VS pumping is on board, basic data logging reads out on the screen.

I like the Resol brand, but others are available. Resol still import through Canada.

https://shop.modularhydronics.com/resol-deltasol-sl-solar-controller-full-kit-4-sensors

109A_5 · 2:49AM

The Tekmar 257 possibly could be utilized to do the boiler staging control. Since it does not have a demand input, the heat demand thermostatic control would have to interrupt the T-T to both boilers from the Tekmar 257 controller. The Tekmar 257's literature would have to be read, and understood to verify it will do what is actually needed for your application.

109A_5 · 7:57AM

You may be able to use the Tekmar 257 like this.

When the 24 Volt relay is de-energized (no call for heat) the 820 Ohm resistor is connected to the Tekmar 257's sensor terminals so the Tekmar 257 thinks the water temperature is about 200 degrees shutting the boiler(s) down.

When there is a call for heat the 24 Volt relay is energized connecting the Tekmar's normal sensor to the Tekmar 257's sensor terminals for normal boiler operation as per the Tekmar 257's programming.

The 820 Ohm resistor is not critical, it just has to be a value that represents a temperature that is above the Tekmar 257's target temperature. The connections to the 820 Ohm resistor should be very secure, no poor quality crimps.

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/42659-source/070-dl-06

Controlling dual boilers

Comments

Categories