When would you not use ODR?

TAG · September 2022

Over the years there have been discussions where people are unhappy with system performance and the discussion of ODR comes up.

I don't understand why you would not use ODR if the boiler can do it ? Am I missing something ? Are there situations when retrofitting into an older house where the use of ODR does not work?

Have used ODR on every house I have done since the early 90's --- from old school cast radiators -- to retrofit panels and houses were I have installed all new radiant ..... combinations of all three ? There is always going to be a main part of the structure that will use/ need the hottest water and you peg the ORD to that. Adjust the others based on what is possible. Panels are easy with thermo heads -- as are radiators if you can retrofit.

I don't understand this combination that people try and do with a thermostat controlling the boiler in an on an off fashion and still having some ORD curve .... unless it's on constant circulation the curve has to be higher temp output to recover.

ChrisJ · September 2022

I probably shouldn't even comment on this because I'm just taking a guess.

ODR requires thought and tuning.
People don't like that. Slap a thermostat on the wall and done.

Then there's the people (customers?) who feel hotter is better so if the radiators aren't super hot and the system is slow to respond that must be bad.

I've met several people who swore that oil heat was hotter and their new natural gas heat isn't as hot so it's not as good. They said the thermostat was shutting it off, but they didn't care, it wasn't as hot. No idea what they were thinking, but ok

EdTheHeaterMan · September 2022

When would you not use ODR?. If I own the building but the tenant pays the utility bill. There is no cost/savings benefit for me. Just an economic answer. The harsh reality of capitalism.

In a perfect world, there is no reason not to.

Edit: there was this old lady with a new boiler that was uncomfortable with the lower home temperature. I'll look up the thread.

hot_rod · September 2022

If the load on the building changes quickly the ODR can slow recovery, by allowing only the SWT calculated by outdoor temperature.

The very best is outdoor and indoor reset, or feedback. So if the room temperature is dropping, boiler SWT could bump up to recover a falling behind condition.

The changing outdoor ambient does not always mean the load on the building is changing the same amount. The early tekmar designers really promoted the "system" with both indoor and outdoor feedbacks.

Commercial or public buildings with large and sudden occupancy loads are one example. The building opens at 8:00 AM and doors are swinging or staying open for an hour or so. Occupants leave their coat on for the first hour until the heat catches up.

Churches are another example where a quick large influx of people, all 400 BTU/hr. radiators, could cause an over temperature condition. Not an ideal building use for radiant floors

I worked on a radiant floor system in a small church near me. They tried setback thermostats to lower the inside temperature an hour or so before Sunday mass, trying to get ahead of that upcoming over-heat condition.

The control logic is really building and use specific. And how much time and knowledge you have to tinker and get it exact

bburd · September 2022

There is not much point in using ODR on hydro-air systems that usually need SWT of 180° F or so to prevent the occupants from feeling a cool draft.

pedmec · September 2022

Application and implementation is why ODR doesn't work, not ODR in itself. it needs to be set up properly to work. That means trial and error until you find what works. But that cost time and money. Who's going to pay for that? Not the contractor with the lowest bid or the homeowner who thinks that they got a great deal. Nobody's happy and they blame ODR. Same thing happened when mod/cons where introduced. Installers were piping them like cast iron boilers only to find out it can't be done that way. But what happened? Everybody was blaming the equipment and not the installation. Hopefully we stop blaming the ODR and start learning about setting up ODR properly.

TAG · September 2022

hot_rod said:
If the load on the building changes quickly the ODR can slow recovery, by allowing only the SWT calculated by outdoor temperature.

The very best is outdoor and indoor reset, or feedback. So if the room temperature is dropping, boiler SWT could bump up to recover a falling behind condition.

The changing outdoor ambient does not always mean the load on the building is changing the same amount. The early tekmar designers really promoted the "system" with both indoor and outdoor feedbacks.

Commercial or public buildings with large and sudden occupancy loads are one example. The building opens at 8:00 AM and doors are swinging or staying open for an hour or so. Occupants leave their coat on for the first hour until the heat catches up.

Churches are another example where a quick large influx of people, all 400 BTU/hr. radiators, could cause an over temperature condition. Not an ideal building use for radiant floors

I worked on a radiant floor system in a small church near me. They tried setback thermostats to lower the inside temperature an hour or so before Sunday mass, trying to get ahead of that upcoming over-heat condition.

The control logic is really building and use specific. And how much time and knowledge you have to tinker and get it exact

My first full rehab project was turning a 5500+sf brick and frame extend/ expanded cape into my home and office. Built on a slope --- looks like a long two story house from the front -- but, it has a full walk out basement to the back yard. 1950's construction -- first floor being brick and plaster with little insulation -- second floor typical frame and fiberglass. The twin 750g oil tanks should have given me an idea. Huge garage. It was forced air and the second the heater went off it was cold and drafty -- especially the main part of the brick floor. Anyway -- boiler, floor plates, panels and slab radiant went back. I did order the inside Buderus room controls for the boiler -- back then it was Eccomatic and BFM's. For the most part it worked w/o the inside room controls --- after playing with it for a while. They were somewhat needed in the shoulder season ... but that went away about 7 years ago when the heatpumps replaced the straight AC. The panel radiators saved the day. Guy in Chester PA gave me so much help --- did a room by room calculation -- matched the panels to design and water temp throughout the house. Only needed the Danfoss heads on the couple rooms I wanted cooler or would not be using all the time. Still own the house -- my sister lives there and one of my offices. It runs all winter on ODR. That place was a great learning experience.

I can see how in a commercial situation with odd loads coming into play there would be need for additional controls ..... Not so in a house. I have yet to install the Viessmann inside control on the 200 boiler . Each project I try and make it less complex ... I still chicken out and run wires for room thermostats just in case I'm off on calculations and they run hot

pecmsg · September 2022

My home ODR does a good job but night set back gets canceled when single digits and windy.

I also move the couch away from the wall rads and the cover from the stair well radiator.

When would you not use ODR?

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