ODR with conventional on off boiler

Kirkhj

I don't understand how this could work. At least not in my case. As an example I tried lowering my high limit in small increments as temps outside rose. It seemed that below a certain point at almost any outdoor temp, all the boiler did was cycle on and of every 5 minutes. Yes I realize the ODR would control it better than what I was doing, but from what I saw leaving my limit above 155 was the only way to satisfy the therm without a lot of cycling. Maybe if there was a delta t circulator?
Just curious...

Leon82

You still get a little savings from running the water at 180.

And the equipment needs proper sizing too so you may be fighting that as well

Kirkhj

This old boiler is too big. Thanks that's what I was kind of thinking too!

Leon82

You will want to make sure your return water doesn't go below the condensation point. So 155 may be your lowest safe starting temperature number anyway.

The delta t circ may help also, and some can run boiler protection mode

Kirkhj

Thanks! I'm actually quite surprised this old CI boilers still alive. When I moved in here it was cycling like crazy. They had the high limit set at around 145. No wonder that chimney liner fell apart!

Jamie Hall

Just sort of a general point -- if the boiler cannot modulate it's combustion rate... the only way it can accommodate varying loads is to modulate by turning on and off.. Cycling. And the only way to change the length of that cycling is to change the spread between on and off -- greater spread will give you longer on times and, correspondingly, longer off times. Which is better? For efficiency? For longevity? too many variables, will not compute...

Kirkhj

Haha Jamie well said. Does not compute. ODR won't work without modulation as I've seen. This talk of ODR with conventional might work in some situations but certainly not mine!

STEVEusaPA

One way ODR may work in your case is with a buffer tank, and a 3way valve to protect from condensation

mikeg2015

You could use a wider temperature differential. So use 30f instead of 10, 25 or 20 to increase cycle times. So might only vary from 160’nto 180 but would dip to 130 to 150.

Kirkhj

This old boiler is coming out soon. For many reasons I'm not sure as yet what's going in but if it stays conventional, 3 way ESBE is the way I would go. Buffer tank likely not. All the black and CI rads holds around 80 gallons. I'm also adding indirect to replace an electric.

JohnNY

We've been doing outdoor reset with conventional boilers for far longer than we've been using mod-cons.
With a bypass at the boiler to maintain temperature and a maximized flow rate through the system it all works fine. Yes, a mod-con invariably makes it work better, but sometimes it's hard to justify the costs. Either way, nearly all hydronic heating plants should be set up as primary-secondary systems anyway and once that's done, you're halfway there to ODR.

Kirkhj

Thanks Johnny. Good to know.
This old system has NO bypass and the only boiler protection is an aquastat controlled 15-58, which is also the only circulator on the whole system.
I am in the process of having this boiler changed out and will be going p/s.

Zman

Outdoor reset does reduce the emitters ability to discharge heat. This does make short cycling worse with non modulating boilers.

Kirkhj

Ok all lets assume these parameters.
Comments please!

Present system.
Standing pilot 150 btu in weil. Test just showed an actual input of 144.
104 IBR
6" flue, no damper, no fresh air in.
Cold start with one 15-58 on the return side
Approx 80 gallon black pipe/ column rads
Heat loss is 88k
High limit at 170 (scared to go higher. Lol)

New system
Weil cgi 119 in 87 IBR
Power vent. Chimney closed. Fresh air opening. Primary secondary with 2 circulated zones. Or

GV 90+ 105 in 84 IBR same p/s with 2 delta t variable pump circuits.

Realistic expected savings 10-15 ish % with the CGI and maybe 20% with the GV?

Tried and true is really sounding like a better option here!

Keith M

In my old house I had a 20 year old gas-fired, I added a Tekmar ODR control and saved around 20% on my gas bill while improving my comfort. It helped eliminate short cycling while supplying hot water to my baseboard at a temperature where the baseboard output almost matched the actual house's heat loss. The Tekmar control came from a friend who is a Tekmar rep...Don Rathe of Rathe Associates.
Keith Muhlmeister

Kirkhj

Hmmm. Sounds like ODR. Can really make a difference. I think in my case what will likely happen, mostly due to my curiosity and wanting to be able to have documented proof just for myself, that I will likely get this old thing changed out and run it that way for one winter, then add ODR. The chance of me getting an actual modcon is pretty slim so it will be an add on anyhow.

Keith M

In 2012 a federal law went in effect requiring boiler manufacturers improve the controls on new boilers. ODR would satisfy the requirements. Slant/Fin uses the Hydrolevel Hydrostat controls and these controls change target water temperatures based on frequency and duration of calls for heat, I call this "indoor reset" and consider it more desirable than ODR. These controls also have a "boost" feature that improves compatibility with night set-back thermostats. These controls can also be made into ODR controls by adding an optional outdoor sensor with the ODR retaining the "boost" function. This is the standard control on all gas and oil fired case iron water boilers Slant/Fin manufactures. It is not a control for modcon or steam boilers.
Some other manufacturers use the same controls.
Keith Muhlmeister
Slant/Fin Corporation