Advantages of outdoor reset sensor?

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Old 01-02-17, 06:35 AM
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Advantages of outdoor reset sensor?

I've installed a Weil-Mclain CGA-3 (natural gas) and it has an option to install and Outdoor Reset sensor.

I do understand the purpose of it but wonder if the $26 for the sensor will really lower fuel consumption.

What do you think?
 
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Old 01-02-17, 01:53 PM
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according to this site: energy-savings
5% to 30% reduction in fuel burn for the average boiler, though this company is in it to sell these things.

i haven't been able to tell if using the ODR really does me any good on my modulating low-mass boiler, but the CGA-3 is a cast iron on-off boiler, i'm sure there will be savings, more than enough to cover the $26 in the first year, just make sure that if you use the boiler for domestic hot water that the control is wired properly so that when the dhw is calling for heat it overrides the ODR.
 
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Old 01-02-17, 03:30 PM
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Vilord,

Thanks for the reply and insight and link.

It wasn't that costly so any savings would probably be gained over the life of the boiler. Hopefully it'll work out well.

Craig
 
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Old 01-02-17, 05:14 PM
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There have been numerous discussions here on that topic. Search for them.

Trying to establish with reasonable certainty the fuel savings, if any, is difficult. One way, not simple, is to run a test while outside temperatures and wind are very constant over several hours and indoor temperature is maintained constant. Clock the gas meter with and without the ODR turned on. It is very possible that some ODR systems will actually increase fuel usage during cold ambient conditions.

Comparing one year's fuel usage to another is not very accurate - unless actual heating-degree days, indoor temperature settings, and other factors are carefully cranked into the analysis.
 
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Old 01-03-17, 06:31 AM
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Especially for a cost of $26 using ODR is a no brainer. Even for $160, the Tekmar 256, it is well worth it. With typical homes often paying $1,000's a year for heating, payback over the years is well worth the cost.

With ODR's the circulator deltaT is kept remarkably even on warm or cold days. The main variable in building heat load is outdoor temperature and that is what the ODR adjusts for.

Most boiler manufacturer's offer the option because it is widely appreciated.

While it is largely subjective ODR makes a home more comfortable. My wife who is hyper sensitive about room temperate is very happy with the system.
 
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Old 01-03-17, 03:55 PM
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It is very possible that some ODR systems will actually increase fuel usage during cold ambient conditions.
Gilmorrie offers no supporting data, but does plant the seed of doubt.

Comparing one year's fuel usage to another is not very accurate - unless actual heating-degree days, indoor temperature settings, and other factors are carefully cranked into the analysis.
Gilmorrie again raises doubts about a very good way to compare year to year system performance. Using oil consumption alone is simplistic.

Also dividing degree-days by gallons used provides degree-days per gallon, very meaningful and useful info.

Using actual building data is far more accurate than heat load calculations. For better focus use shorter periods i.e. days, weeks, months.

Clocking burner run time hours data can provide actual nozzle firing rate. Stamped nozzle ratings are at 100 psi +/- 10%. At 150 psi are ~ 20% higher. This way provides more accurate nozzle GPH and can be used to calculate boiler actual output.

I keep a running log for the season. Periodically check the results for a period. Found in very cold weather the degree days/gallon rises as the amount of heating going for domestic hot water is the same. Also ODR's help to flatten circulator deltaT over the season eliminating the need for an ECM type.

The accuracy of this data may not satisfy all, but it does help to understand what is happening and see the value of changes made.
 

Last edited by doughess; 01-03-17 at 06:30 PM.
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Old 01-03-17, 04:21 PM
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Gilmorrie offers no supporting data, but does plant the seed of doubt.
Most, if not all ODRs increase boiler water temp with lower outdoor ambient. The Tekmar 256, which you highly recommend, does this. (Refer to the Tekmar website.) That control scheme works if the home is under radiated - and the water temp needs to be raised to heat the house during cold weather. Otherwise, if there is more than enough radiation, it is counter productive to raise the water temp and incur lower boiler efficiency.
 
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Old 01-04-17, 09:04 AM
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Outdoor Sensor

I think the advantage of the outdoor sensor is more even heat on the shoulder seasons. The idea is to have a suitably hot boiler temp in the cold winter, and a lower boiler temp as temperatures warm such that you have more even heat, less spikes of overradiation followed by no heat as the temperature resettles. So may not be a fuel savings but more of a comfort improvement.

Seems to me these outdoor sensors on boilers designed for them are good ideas, the sensor is low cost, and you just need to understand the "temperature curves" that the sensors control in the boiler to make sure the set up is optimized for the actual climate conditions you experience. The wrong curves will not do any favours in energy, rads could be too hot for safety and/or condensing boiler optimal temps, etc.

At the least, seems very low risk to experiment a bit, and you will in the end understanding your system much better.
 
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Old 01-04-17, 07:46 PM
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The basic idea of ODR is to adjust boiler water temp to what is need at a given outdoor temp. That avoids waste from heating water above temp actually needed. It goes without saying the water temp will kept between 133F to avoid condensation and below 180F to avoid scaling.

Because of variation in hydronic/radiation systems that effect BTU's delivered ODR's have settings used to optimize it for a given building. Some of the system are not linear and create issues. On mine a minimum of 140F water is OK to ~40F outside, when it goes below 40F minimum has to be raised to 155F for better response time.

The ODR curves are to bring water temp from 140F at various design day temps of +20F, 0F or -20F to max of 180F water. Put another way on design days the water temp should be 180F max.

Because the ODR controlled water temp is being adjusted to outdoor temp/heat load, room temperature is more comfortable and even, as reflected in the relative flat circulator deltaT.
 
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Old 01-05-17, 09:08 AM
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On mine a minimum of 140F water is OK to ~40F outside, when it goes below 40F minimum has to be raised to 155F for better response time.
Are you saying that you have to monitor the outdoor temperature and manually intervene and reset the minimum? How is that then automation? Maybe I misunderstand.
 
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Old 01-05-17, 11:34 AM
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Curves

The climate curves programmed into the unit I use, being a Baxi Duo-Tec, does require you to select a curve, one of 10 choices, so it is not completely automated. Once the curve is set, it is. You have to determine the curve that most fits the range of temperatures in your specific area, as well as the amount of heat needed for your specific home, really you are selecting for the desired outdoor temp at which the max or highest desired heat/boiler temp will occur. Since most boilers are oversized for most homes, the outdoor sensor really is an indirect way to right size the unit output to the specific home and environment, although the unit modulating is trying to do this as well so a bit of belt and suspenders I think. But as I mentioned, it is also mostly a way to maintain the desired set home temperature to as small a range as possible by optimizing boiler temp for that purpose.

With all that, it is hard to imagine the sensor would ever increase fuel usage, and I suppose if you had massive climate variation from season to season you might end up needing to revisit the curve selection to optimize. But for my unit, the difference between about 7 of the 10 curves are pretty subtle, and the remaining 3 are quite different, clearly designed for homes in very mild conditions and/or that the boilers are so oversized that they can provide necessary heat at much lower than max boiler settings. So you probably can't really be too wrong in selecting a curve that might not be perfect for a given season, but would still be better than no sensor at all.

So to confirm, it is not fully automated. That would require some sort of sensor that could measure the actual temperature experiences in and out, iterate that with the specific heat load of the home under such conditions, and in effect develop some sort of real time boiler temp curve to optimize the trade between heat, efficiency and variability from the set point, and alter that proactively with some predictive algorithm. I suspect some commercial systems are around that try to do just that, as the economics of heating large buildings makes the expense of such control system potentially worth while.

For $26, the current outdoor sensor looks pretty good! Even cheaper is for a boiler enthusiast to alter the boiler temp manually through the season, a human sensor is still pretty accurate!
 
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Old 01-05-17, 01:22 PM
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Since most boilers are oversized for most homes, the outdoor sensor really is an indirect way to right size the unit output to the specific home and environment, although the unit modulating is trying to do this as well so a bit of belt and suspenders I think .
While they are related, linking ODR, over sized boilers and modulating burners leads to mushy thinking. Each has their own attributes, values, pro /cons and should be considered separately.

Oversized boiler/burners can easily be made more efficient by reducing the the firing rate with a smaller $10 nozzle.

Modulating nozzle firing rate in steps according to out door temp really optimizes it. On a day when outside temp requires only 20% of boiler BTU capacity it fires at 20%. Since boiler efficiency goes up as firing rate goes down there is direct increase in efficiency.

ODR's at $160 have other benefits.

Boiler manufacturers offer options for both modulating burners and ODR because each separately add valve, but at big $$$$ that typically does not justify the cost of replacing an existing boiler and burner system.

For an existing systems the simple, easy way is a $10 nozzle and $160 ODR. Even without a detailed efficiency/ cost benefit analysis, pay back should be obvious for $170 on the average annual heating bill .
 

Last edited by doughess; 01-05-17 at 02:27 PM.
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Old 01-05-17, 02:43 PM
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I understand that a curve must be selected and that the selection is not automated, but it sounds like doughess is saying in post #9 that in his case manual monitoring and intervention is required while operating on a given curve.

It seems to me that cannot be viewed as automation in the sense that these ODR’s are advertised as. At least that’s the way it seems to me.
 
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Old 01-05-17, 02:51 PM
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Yes, agreed my explanation was mushy and too simple.

Indeed, I referenced "oversized boiler" when I meant oversized system with larger radiators/radiant loops than necessary, which would allow for lower boiler temperatures to provide the necessary heating. An old home with original radiators, but with modern windows and upgraded insulation, might be a good example of such a system.

My comment on oversized boilers relates to my understanding that combi units which have high flow domestic hot water capability by design end up having more home heating capacity than many homes need. Not sure you could deal with a combi unit inherent oversizing by changing the nozzle as you noted? Isn't this why the units tend to modulate to a very low level, to handle the competing design requirements?
 
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Old 01-05-17, 05:40 PM
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Something to keep in mind with regard to using ODR w/conventional cast iron boilers is the danger of flue gas condensation when system return temperatures fall below a certain level....I think it's 140* or so for gas-fired units. Operating at such lower return temps over sustained periods, the corrosive condensation can be a real threat to heat exchangers and exhaust vent pipes (and this would be in addition to any other condensation that is formed when firing the boiler from a "cold start").

So right off the bat it seems that you probably can't take full advantage of all of ODR's attributes without running the risk of damage to the system. You will have to set a minimum boiler temp that will assure your boiler return temps won't fall below 140* for extended periods.
 
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Old 01-05-17, 06:05 PM
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...I think it's 140* or so for gas-fired units.
Make that 130 degrees.
 
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Old 01-06-17, 10:04 AM
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Make that 130 degrees.
Burnham ES-2 units on natural gas can run as low as 110 degrees without condensing.
 
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Old 01-06-17, 05:38 PM
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Burnham ES-2 units on natural gas can run as low as 110 degrees without condensing.
Are you suggesting that the OP should scrap his new Weil-Mclain CGA-3 and replace it with an ES-2?

Just kidding.

Seriously, I was not aware of the ES-2 and its new approach to cast-iron boiler design. Interesting stuff. I did a little research on the subject and came up with this:

The ES2 has the ability to operate at low return water temps because of the casting design. There are no extra controls, software, valves, piping, or pumps required for the boiler operate with constant 110F return water temps as long as the supply water temp is 130F or greater. ES2 castings incorporate a sophisticated baffle design that evenly distributes return water throughout the each casting. This prevents the return water from collecting in one area of the casting, and creating a cool spot that could condense. The baffling acts like a sparge tube – by evenly distributing water throughout the casting rather than dumping it all in the same spot.

In addition, the inside surfaces of the water jackets have a special texture which creates turbulence and causes the water to constantly tumble – mixing and blending water temperatures throughout the casting. As water tumbles through the casting, cooler water makes contact with the hotter flue surfaces, enhancing heat transfer, and blending water temps. (Remember - heat transfer is increases when there is a greater temperature differential.)

The ES2 extracts more heat from the combustion process, which allows the boiler to achieve a higher efficiency (85% AFUE), but this also results in lower flue temperatures than boilers with lower efficiency ratings. The chimney liner requirement is there to protect the homeowner and the installer from chimney or draft problems. NFPA requires chimney liners in many atmospheric boiler installations, so the liner requirement is not exclusive the ES2 in many instances. Hope this helps.

Nate Warren

Product Manager

U.S. Boiler Co / Burnham
Source: Burnham ES2 - Heating Help: The Wall
 
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Old 01-07-17, 08:11 AM
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Because of that design I am able to run my high-mass system (large diameter piping and cast iron radiators) at 150* with a 30* differential, bypass closed. Even at cold start the boiler temp is up to 110* in less than a minute. The system was installed in 2013 and I have had no condensation issues.

I do have a separate zone for a greenhouse (200+ orchids) that has copper fin tube. That zone is connected to an ODR because it needs higher supply temps especially at lower outside temps. The curve for that is set for 150* minimum and rises to 180 at -10 degrees outside. Occasionally when the greenhouse and main house zones are calling for heat simultaneously, the house system gets the higher temp supply water as well. However the zones are controlled by programmable thermostats and the timing is offset enough that they seldom require heat at the same time. When they do run together it is usually at the lowest outside temperatures (below 20*) and the higher supply temperature does not cause overheating in the main zone.

Just thought I would add that to the ODR discussion.

Details are here: http://www.doityourself.com/forum/bo...s2-boiler.html
 
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