Boiler protection with a variable delta T pump

SuperTech

As a service technician I have the tendency to become obsessed with trying to make my boiler as efficient as possible. And I like to have all the bells and whistles that the latest technology offers, because it gives my coworkers and I a good topic of discussion.

Currently I have an oil fired Peerless boiler, single zone monoflow system. It's currently equipped with a Honeywell L7224U digital aquastat with a Honeywell outdoor reset module. Anyone who read my other posts might remember that I recently down fired the boiler. I went from a .85 nozzle and over 500 degree gross stack temperature to 415 degree stack temperature courtesy of a .65 nozzle and low fire baffle.
My only concern is the possibility of developing flue gas condensation.
Now my aquastat when equipped with the outdoor reset module is capable of a sort of boiler protection. It can be programmed for a low boiler temperature setting. During a call for heat the burner will operate until the boiler reaches this temperature before it brings on the pump. I have this set for 140 degrees.

But that makes me wonder about a new toy I've been eyeing. A VT2218 ECM pump. I've read that this pump can be used as a boiler protection device against flue gas condensation. So on my boiler I imagine that this would offer increased protection over the aquastat by pumping slowly until the return temperature rises.

Seems interesting. But would anyone recommend this pump as a boiler protection device? It's certainly easier to install and less expensive than a thermostatic bypass valve. And I should save on electricity as well.
Or am I worrying about flue gas condensation when I shouldn't? Any suggestions are welcome!

Rich_49

It can certainly allow you to come as close to design Delta for the longest period of a heating season , as long as you have done your math .
Programmable Delta from 5 - 50* . So long as you offer the minimum resistance and keep the head above the performance curve it should be able to maintain your design Delta through all parts of the system .

Here is an early VDT example , keep in mind this circ was not an ECM but the principle is the same . Again , you have to do your job in the math .

http://jbblog.flopro.taco-hvac.com/anthonys-voice/

SeymourCates

@SuperTech

You already have the best possible device built into the L7224U. It holds the pump out until the temp reaches 140F. If you use the VT in the boiler protection mode and "pump slower", you've spent $200. to achieve less than what you already have.

If you use the VT in the traditional mode, it will pump like mad at a very wide DT (cold start) trying to get the DT down. That's exactly what you don't want.

Of course you can use the VT in the traditional mode in combination with the L7224U protection if you want to maintain a specific DT throughout the operating range. There are a multitude of opinions on the benefits (or lack thereof) for this on a CI system. It's invaluable on a mod-con.

hot_rod

Unless it has been changed, the VT2218 will only modulate down to 30% in boiler protection mode.

It could be "tricked" into working with a properly adjusted ∆P bypass valve.

Some of the non ECM type VS circulators still out there could work, they tend to be fairly $$.

You would want to pipe a P/S not direct, in either case.

Zman

This seems to me to be a pretty clunky way to go about it. As Hot Rod mentioned, unless you go primary/secondary, it won't work. You will get your supply temps up but the return temps will be low. The radiators are still going to want the energy, by lowering the flow, you will just raise the delta T.

Paul48

Well beyond my rudimentary math skills to try and figure out what an ever-changing flow rate would do in a monoflo system.

SuperTech

I guess I'm just determined to over complicate my system. It makes sense that it's not ideal for my boiler. I suppose the best idea is to utilize a thermostatic boiler protection valve so flue gas condensation won't be an issue.

I saw the boiler protection feature of the VT2218 and just immediately thought "that looks cool! I need one!"

Paul48

If your boiler control has the ability to hold out your circ based on boiler temp, why bother? I've seen a DT circ used in a simple supply to return configuration, for boiler protection. But in your situation, I doubt there would be any net gain from doing that.

hot_rod

I had a 140 temperature control on my wood fired boiler. It does bang/ bang the circulator a bunch of times as it hits 140 and a slug of cold water comes back, not the most elegant way, but cheap and easy.

IF you really need the protection the thermostatic valves slowly allow flow as the boiler temperature ramps up, it's a proportional flow instead on on/off/ on with a single speed circulator and temperature control.

Only if your boiler operates below 130F return for extended periods, over 10 minutes after start up, would you need return protection. It's rare that low or medium mass systems need additional protection. Fin tube, cast baseboard, air handlers, Ultrafin, etc. are usually fine without additional protection.

Observe your system on a cold day, first start, to see how it behaves.

SeymourCates

@hot rod

Ever see a four section oil fired boiler in a 1500 square foot house?

"Bang-bang" doesn't begin to describe the experience.

There are millions of them.

SuperTech

I was just at a house that fits that description. The worst thing about it was that the homeowner wanted me to modify the boiler so it would short cycle.
He literally asked me to do the following things, install a much bigger nozzle then specified by the manufacturer, remove the barometric damper (because it's noisy) replace the 007 circulator pump with a 0011 and he wanted me to turn the high limit up to 200 from 180.
Any time I tried to explain to him that his request would negatively impact efficiency he just insisted that shorter burner cycles make for the highest attainable efficiency.
It made me wonder why he called my company, since he's obviously an expert.

hot_rod

SeymourCates said:

@hot rod

Ever see a four section oil fired boiler in a 1500 square foot house?

"Bang-bang" doesn't begin to describe the experience.

There are millions of them.

Oh I know they are out there.

We have the technology now to almost completely eliminate cycling. modulating burners, VS circulators, buffer tanks, proportional zone valves.

i would not purposely build a bang/ bang control logic