Controlling (2) Weil-McLain Ultras (JohnNY)

JohnNY

Thanks, Glenn.
You're $.02 is very valuable to me.

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JohnNY

Multiple Boiler System

I'm looking for some input for controlling 2 Weil-McLain Ultra boilers with outdoor reset.
I've been advised by WM to use two Honeywell AM4 modules together with a Tekmar 265.

While I'm at it, I'm thinking of using 4 way valves (manual or automatic) to control temps to 6 radiant zones on the same system.
It is a large residential system serving hydro-air, radiators, DHW and cast iron radiation.

Thanks to all who can offer helpful advice.

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Glenn E Sossin

Control Prefer TK4

My opinion, unless your trying to eek out the best possible performance, I would use either Tekmar 261 or the 423. Then you don't have the AM4 cables. The boilers already have the mechanism to modulate. Using the AM4 ribbons in my mind, is like giving your MCBA board a lobotomy. Your paying for a function twice.

The Tekmar 265 is approximately $575 - $650 more with the AM4 cables than the 261. I haven't read or heard anything to suggest there is a substantial energy savings by having 2 boilers say at 30% instead of 1 boiler at 60%, which is the kind of alternate step firing this control (or the heatimer) would do.

Conceptually, I believe adjusting modulation of each boiler back and forth is better than letting 1 boiler fire up to it's max.

I think your customer would be better served with the system control TK4 will offer, especially with the synchronizing of heating zone circulators. It addresses micro-loading. See attachment.

My $.02

Home Depot Employee

Done that!

"Conceptually, I believe adjusting modulation of each boiler back and forth is better than letting 1 boiler fire up to it's max."

I would agree Glenn. Boiler circs remaining the same with a lower fire rate = higher efficiency.

Only argument I have heard to that theory is the increased current consumption by running second boiler circ and exhaust. (He was a church council member and electrical engineer).

Glenn Sossin_2

System Delivery versys Burner efficiency

I was thinking of the overall picture, considering both overall system efficiency and delivery cost rather than just combustion efficiencies.

Is it worth the additional cycling all the system components, and the additional electrical consumption of running two boilers at 30% capacity rather than one boiler at 60%. How big could the savings be?

Hypothetically just throwing out some numbers - assume the boilers are staged with a Tekmar 261 or 423, and $2,000 was spent on fuel for the heating season.

What might the savings be by using the Tekmar 265? By adjusting the modulation of two boilers back and forth, could we save an additional 1%- 2% on fuel consumption?

What about consumption of electricity? He is going to run a second circulator, a 2nd blower, and increase the cycles for all the heating components by 50% or more shortening their useful life.

Is it smart to spend another $600 on controls for the privilege of modulating 2 boilers to save $20 -$40 a year? Is my concept flawed somewhere? I don't see the savings.

I wonder if Tekmar has looked into this. They try to squeeze every ounce of heat out of a system with their control features. It would be an interesting test case.

Floyd_45

If it were me...

I'd be going with the AM-4 and the 265... getting the best comb. eff. possible. My test equip shows me 5-7% diff. from low to high fire... at that rate with the minute amount of elec. that the boiler and the pump pull, I feel I'm saving more with cutting the fuel as much as possible.

Have heard also that the AM-4 will be obselete very soon with the series three Ultra coming out....

Floyd

Glenn Sossin_2

If the percentages are

really that high, than I agree the 265 would have some merit.

That just seems like a really big difference to me. I would think that a high target temperature versus a low target temperature would have a substantial impact on that value. If the boiler design temp was set to 140, as opposed to 180 , wouldn't we see a big difference in the efficiency numbers?? When you ran this test, what was the operating temp of the boiler?