Outdoor-Reset Opinions

Rich L.

ODR is basicly cruise control for your home heating system. Simply put it tries to balance the heat loss of the structure with the heat added to it. You don't need near the heat added to your home on a 40 degree day that you need on a -10 degree day. ODR compensates for this by lowering the water temps on the warmer days and raising it as the outside temps drop, as much as your boiler and piping system allow. I really don't understand why anyone would not want it unless they're doing deep setbacks as Brad mentioned above when you would have potentially much longer recovery times. That's ODR in a nutshell! I'd highly recommend it. I'm a contractor and I have it on my home system.

Good luck, Rich L

mjj_2

Outdoor Reset & Temp Control

Our contractor is planning to install the Biasi B4, (oil-fired) in our hot water, CI rad. heating system. Our heat loss is at ~98,000 BTU's. Should I add out-door reset or pass on it? Several contractors (although not our current one) have discouraged us from installing the reset, saying that homeowhers don't adapt to it, ask to have it disconnected.

If we install the reset, will it cause our small-mass boiler to run more often? Will it over-ride the T-Stat temp control? Will running supply water at lower temps affect the rest of the equipment (heat exchanger)in any way? I realize that these are simple questions, but I'd like to learn more about the control. Thanks.

Brad White

Some thoughts

Using outdoor reset (ODR) is a proven energy-saver, more so than night setback for example. Even in colder climates (which require hotter water longer), the shoulder seasons (either side of the bell curve peak) have enough hours to justify it.

Where ODR can fall flat is when people set back their temperatures too deeply over night or when away for the day. The system runs to make setpoint but the ODR control slows the process by limiting the available water temperature.

The occupants can perceive a delayed gratification of their desired temperature. The deactivate the ODR and get rapid recovery but never see the savings potential.

The real solution is to get an ODR control with a "boost" feature to ignore the ODR setpoint until the house is at the desired temperature. Then the ODR takes over to maintain the desired temperature. Constant water circulation is essential to even comfort too.

Properly applied ODR will impose a widening differential on the boiler. In other words, say your normal operation right now has a setpoint of 180 degrees F. and a fixed differential of five degrees on either side of that. The boiler will start to fire when the boiler temperature drops to 175 and will shut off when it gets to 185. (The temperatures may coast above and below this as a function of thermal momentum but you have to start somewhere...)

BTW: I am just making up these numbers for discussion purposes- actual operation can vary.

With ODR and a variable differential, this can widen to ten or more degrees and also be balance with minimum boiler on-times. Say it is 30 degrees F. outside and you need, oh, 141 degree water. Your differential might be eight degrees so will fire when it drops to 133 F. and shut off when it gets to 149 F. This will allow some "coasting" between firings to lessen short-cycling. If the system has a minimum 2-minute run-time, this may overshoot a bit but not so much as to cause a problem.

What I mention above is just for the boiler. Oil-fired boilers or any non-condensing boiler for that matter, have limits as to how far down you can set their operating temperatures.

ODR on the SYSTEM side (Radiation-side) of things can go all the way down to near room temperature for the mildest days and take what the boiler can give on the coldest days. That is where the better part of the savings can be realized.

Picture your boiler firing to maintain it's appropriate range of temperature. The secondary side might well be 20 degrees cooler (and still able to heat the house). The secondary side will "sip" hot water, using less of the hotter water to get you the temperature you need. You can see the savings right there.

Much more to it than this, but I suggest you see the Tekmar or Taco web sites for essays on the principles I mentioned.


My $0.02

Brad

Mark_46

Hi mj,

Brad is always on the money and is far more knowledgeable than I about HVAC subjects. However, if I may, allow me to offer a homeowner explanation of ODR and a view of your situation from what I can gather?

First, some of the contractors saying ‘homeowners don't adapt to it, ask to have it disconnected’ is more or less non-sense in my opinion. How so you say? I had a contractor tell me the same thing! Comments like that are probably driven primarily by lack of understanding of the technology, unwillingness to learn, set in their ways in terms of equipment they like to install, etc.

Secondly, a key concept to understand regarding ODR is that your room thermostats still dictate room temperature set points. So no, it will not over-ride the T-stat. ODR dictates how the system/boiler should achieve the room thermostat set point based on outdoor temperatures with efficiency as the objective. In other words, ODR has little to do with room temp.

With ODR, the savings is yours.

Brad White

I like that analogy...

Cruise control. Thanks, Rich.

Rich L.

You're welcome!

I'd love to claim it as my own Brad, but a journeyman described it to me that way back when I was just a cub in this trade. I love analogies, they stick with me!

Regards, Rich L

radioconnection_2

ODR

I'm a homeowner with a Biasi B4 and a Tekmar 260 with an indirect for DHW with priority. So far the system is running to expectations. If anything my burner cycle time is too short, since I think the B4 is a bit large for my heatloss.

I went as far as using P/S piping on the heating loop, with a Danfoss TV valve to protect the boiler return temp. That also gives me constant circulation on the secondary side (heating loop) to delay freeze-ups in case the burner fails; and it allows setting my supply temp as low as as practical in the shoulder seasons.

Pete

Unknown

depends on your maximum temperature requirement.

If those CI rads can run at condensing temperatures, you can't run the boiler any lower than that... you could set the temp lower and forget the reset.

If you need 180 in the rads... well, make the rads bigger! Or, use reset.

Robert O'Brien

With

fuel prices,it would be crazy not to have it.A very short payback!

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st heat

OUTDOOR RESET

A biasi b4 is not exactly a light weight. There is good evidence of savings using odr. for every 3 degrees faren.that you can lower your water temp you will save 1%. oversizing rads are not a bad idea in order to reduce your design temp but comes at a price.I would prioritize better insulating technique.

Unknown

The difference in price would rarely pay for a significant insulation upgrade.

Most radiators are oversized anyway, because no one sized them appropriately to begin with. I still haven't run into a baseboard system already installed that actually needed 180 SWT to operate, ever, and likewise for radiators.

st heat

odr

you are right on with that . most boilers that are recent installs look too large to me . sometimes 50 % . sometimes 60k baseboard and a 135k boiler. WHAT DO YOU CALL THAT. its unbeleivable and a shame.

radioconnection_2

98K BTU heatloss and B4

For the heatloss he mentioned, wouldn't the B4's net BTU rating be a bit on the light side? Pete

st heat

ODR

HEAT LOSS...... gotta see it to believe it.

Timco

Look into the Tekmar 460 reset, Tekmar 336 zone controller with Tekmar 542 stats. (tN4 system) Besides reset, the stats sense how fast you are coming up on setpoint and pulse the circs until you just reach temp. Each zone resets separate, using just what supply temp is needed and has extended away features as well as warm weather shut down. After each call, the system learns what it could have done better. I have yet to overshoot the set temp and the house is very cozy with the coolest water needed. The stat shows outside temp, min & max outdoor temps, boiler temp and of course room & set temps. The stats are programmable for 4 events as well. VERY smart & versatile system. Very cool...Works well with CI boiler or mod / con and the stats are programmable for CI rads or any convector to gain best possible efficiency.

Tim

Mitch_4

What do I call that?

around here? The norm...

Sad but true

Saggs

I have a 4 sect buderus g-115 oil, w/ a smart 40 and a tekmar 260 I put in. I have one zone of radiant and the rest is standard B.B. Question is: w/out P/S circulation, how low can I safely put my supply temp w/out causing condensation or damage to my boiler? I think I have it set at 140 for the lowest setpoint. Would a buffer tank work better than a P/S loop and a mixing valve to keep the return temp up? Pete mentioned the mixing valve earlier.

radioconnection_2

You can use a TV valve with one circulator and without P/S piping for boiler protection. But, you will not have flow in the heating loops until the return temp reaches 140 degrees, permitting water flow in the system side of the return. Pete

mjj_2

ODR & Sizing ?

Thanks to Brad W. & Rich L. for explaining the basics of ODR, and Mark C. & Pete for the homeowner perspective. We already have large CI rads, so I'll try lowering the water temp., but I'll definately add the ODR. The Taco and Tekmar sound like excellent modulating devices but my contractor is recommending the Becket Heat Manager which has been discussed in other threads. Thanks for everyone on the boiler protection warning, I'll have to look into this.

Boiler Sizing Note - I had 2 professional heat losses done - one at 77,000 and the other at 98,000 BTU's. Did 2 myself, one was close to the lower estimate, the other, more comprehensive software yielded a # close to the higher one. I chose the next largest boiler size over 98,000 BTU's based on DOE Heating Capacity. Should I look at the IBR Net (our rads are Hot H20) instead and go one size higher to the Biasi B5(Heating Capacity = 124,000, IBR Net = 108,000)? Pete if you don't mind my asking, what is your heat loss, do you heat w/ water or steam?

Brad White

Boiler Sizing

I would stick to the gross output number, not the de-rated I=B=R number. (Yes, I know this sounds confusing but the DOE or AGA gross output is higher and it gets you a smaller boiler...) The I=B=R rating reduces it by about 15% for piping and pick-up but with ODR you are already cruising...

Of those heat losses you had calculated and what you did yourself- I tend to find that the infiltration assumptions (air leakage) are the most variable and subjective. Educated guesses if you would, unless at least a blower door test is done. With a blower door test, at least you have an inkling of how tight the house is.

Find out what the infiltration rates were assumed to be in each. See if you cannot reconcile the differences.

So may SF of wall, glass, roof, etc. at certain constructions and insulation qualities tend to be more "stable" hence more quantifiable numbers than infiltration.

I would take these "transmission" or "conductance" loss sub-totals from each of your calculations and see how they compare. Say that they all fall within 10 percent of one-another. Maybe a range of 55-60,000 as a guess. Reasonably close.

The remainder is infiltration. Of that portion, was it based on linear feet of crack (=door and window sealing surfaces)? So many air changes per hour? So many CFM per SF of floor area? -See how "guesstimable" these numbers can be?

Point being, find a core transmission loss (or an average of them if close) then if you can, average the infiltration numbers and add them in to get a total heat loss that you can live with.

Try that and let me know what you come up with. Then we can better size a boiler for you.

Here is another thought: Are there any meaningful opportunities in your house to improve the envelope? Can you seal or foam the rim joists? Seal plumbing penetrations through basement ceilings and attic floors? Seal obvious cracks? Add insulation anywhere? Weatherstrip doors? Thinking anything to tighten up your heat bucket. What do you think?

GW

yo MJ



There are simply too many ways to answer your questions. But, if you have cast iron radiators, it is simply stupid not to go with outdoor reset, preferably with an indoor sensor and constant circulation. If you're one of these home owners who loves to dance the thermostat up and down, forget about it. A modest setback at night will be best, unless you have jumbo radiators you might want to set back a bit deeper (if your reset control lets you, when Buderus came out with the outdoor reset control on the GB142, I got myself in trouble; no nighttime set back)

Many people will have a reset job installed, yet still use their good old American thermostats. I have never been a fan of using outdoor reset without true constant circulation, but I realize there are opposing opinions on this.

I always have to smile when it come time to talk about heat loss... do you know what the air change per hour is on your home? I'm guessing not. You need a guy with a blower door to know this. In our society, it simply blows my mind how many conversations center around insulation, yet infiltration is never discussed; truly amazing. For example, if you have a one story home with so-so infiltration, not the end of the world. But, if you have a 2 1/2 story with marginal air tightness, that factor can really jump of the page because of the (there are several terms) stack effect/chimney effect/stratification.

I get my thrills in life when I dramatically lower the BTU input on a new system install. I think my record is a 3 family home: it had 3 boilers, (obviously grossly oversized) and 3 gas water heaters, grand total of input BTU was 427,000. We put in a 106,000 boiler with 60 gallon indirect.

If your home is tall and you've got holes in the top and/or bottom, go big, you'll need it. If it's short, go small, you'll do well with the smaller unit running longer burn cycles.

Gary

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GW

cuisin'


I've used that phrase for years; people know what a cruise control is. I give my hearers a visual affect as well, as I'm describing the concept of cruise control, I put my straightened hand in the air at about 45 degrees (yes, like the commercial), and I explain when the cruise control senses a hill, it depresses the gas pedal (I lower the angle of my hand like a gas pedal), and explain that's just what happens when the reset control sees colder temps outdoors.

Good stuff; and I can't remember where I first heard of cruise control. The hand thing is all mine though.


Gary

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fatty

good point about infiltration -
i like to tell people about wattle and daub houses, which have been around since Neolithic times. Plenty of wattle and daub houses are more thermally efficient than 'modern homes' due to the near zero air infiltration. its a real thinker for some.

mj_4

1 blower dr. test; 2 bypass

A government energy audit rep. came up with the 98,000 BTU heat loss. Among other things, he did a blower door test which yielded: 10.8 ACH (Air Changes per Hour?)@ 50 Pascals and 348 inches sq.ELA (Equivalent Air Leakage?). Sounds extremely leaky (the house is a 2-storey). This test was done on a "room temp. day" in Oct. if it makes a difference.

Twenty percent of my larger heat loss was due to infiltration, but I'm still working on the infiltration of my smaller heat loss.

Because of old wiring and a fieldstone foundation which retains moisture we can't put in insulation of the highest R-value throughout the house, but may be able to add some more to the attic.

The T-Stat? we "set it and forget it", so it looks like I'll be adding the ODR. My contractor plans to put in a bypass valve which will temper the return water to 130 deg.

Brad White

Blower Door Tests- Some Comparisons

Having one blower door test result (which is great to have) does not give you a degree of "good or bad" without some comparison.

Here attached are a set of tests I did for my own house and that of my sister Kim's house. Both are in the same neighborhood (neighbourhood to you!), are of comparable size (two-storey frame construction) and style. OK, Kim's house has better housekeeping.

You are correct that ACH is air changes per hour and the ELA is equivalent leakage area by the way.

My house has an ACH50 of 8.98, Kim's is 13.98 versus your 10.8.

My house has an ELA (Canadian EqLA at 10 Pa) of 242.6 Sq. inches. Kim's has 495.1 at the same standard, versus your 348 square inches.

It seems you are right in the middle of both of us.

My winter ACH for infiltration is 0.94 ACH, Kim's is 2.04 ACH.

[Kim is not a very happy person right now, so I bought her some foam cans for an early Christmas present ]

You did not mention your factor but if your rater used a Minneapolis Blower Door, that might well be on the report. All things being equal, you may be right in the middle as for the other numbers given.

In any event, it sounds like you can improve this number somewhat. Find a few good leaks (even with a window fan blowing out as a means of detection) and see what you can do.

Hope this helps!

Brad

Tim_41

Install ODR

I installed an ODR as a early x-mas present for my parents in September. They would not let me replace the oversized boiler however. They have cast iron baseboard in their house and reg baseboard in the rental. Mom complained "I don't feel any heat." I said are you cold she said no. Classic stuff. Also, their window is no longer open while the heat is on.

Rich L.

Classic!

Isn't that the truth Tim! I'm sure they'll appreciate the cooler radiators after some real winter heating bills start rolling in

mjj_2

Thanks

Thanks Brad, for the leakage test results, you've put the infiltration into perspective! I was just wondering, what is CFM? Could this be the factor that you mention?

As far as detecting leakage, I can almost do that without the window fan now, as its getting cooler and breezier every day. I should get to work on this as the First Day of Winter is just around the bend.

Tim, Classic indeed! My parents are the reverse of your mom, they agreed to boiler replacement, but now I have convince them that ODR is the way to go. With all of the suggestions from Wall Contributors, I should be able to do that!

Thanks Everyone!

Brad White

CFM

Hi MJ-

CFM stands for "Cubic Feet per Minute", a measure of airflow. As a factor I mentioned, the last one was "ACH50", but my point was that if your test was done using a Minneapolis Blower Door (The Energy Conservatory in MN) and their Tectite software, you would get a similar report. The units and terms however are fairly consistent in the industry, so see where your report aligns in the other categories.

It is rather interesting and odd that "CFM50" is one of the most standard terms, mixing Imperial with Metric units. Sort of like expressing velocity in "Furlongs per Fortnight"

Glad you found the blower door test data helpful. It is very satisfying to seal while under the influence of a blower door. Foam up a crack and watch the blower door gauge CFM go down yet keep pressure or ramp down to maintain pressure. Ahhhh!


Grab some cans of that foam and let us know how you do.

JBW_2

ODR frustrations

Going back to the earlier part of this thread...
I think that one of the largest problems regarding ODR is that I see it being sold to clients as the END-ALL solution to their heating problems. Most commonly in apartment blocks, where there is no control in the actual living spaces. The individual apartment heat losses vary so widely, that without individual control (i.e. thermostatic/pneumatic valves) one guy's boiling while his neighbour is freezing.

Regards,

Josh W

GW

not so sure

The whole topic can be explained until the large lady sings and people are blue in the face, but still the average home owner simply can not digest all the factors, the pros and cons. The science of it and the overlapping factors (lesser flow vs. lesser temps, and what controls handle those two items, so on and so forth) can not be understood by most home owners (let alone some heating contractors).

I have a guy who had us install a new panel rad system this summer who told me last week he wasn't happy with his system we installed. You see, the home inspector gave his new (old house) house the 'thumbs up'; nothing mentioned about thermal envelope issues. So, when his heat bill was high (it was) this past billing period, it MUST he the systems fault. Originally, I explained in the contract I was sizing the new panel rad system for 'average' conditions, and that if the house was actually lesser than average, we could give him a price for a larger capacity system, or better yet, he could spend that extra money on improving the thermal performance of the house. He, of course, forgot that I wrote that in the contract. Within minutes I found some pretty significant infiltration issues, but even when I pointed these issues out, the HO still believed it must be the heating system. I went back a few days later and noticed that they followed some of my directives (there was a third floor room, it has a small swinging door that accesses the attic of the main house, it was extremely leaky), taped around the door as a temporary fix.

One might ask, "Gary, you seem to know about building performance, why wouldn't you tell them the house has issues before you start a job". My answer is because no one wants to "pay" for that time. Hence the wording in the contract. It's OK for doctors and lawyers to charge for advice, but our culture isn't quite ready to pay the heating guy (some people are/do). Now, don't get me wrong, like the next guy I'm using a manual J and plugging in all the factors, and addressing issues that are simply obvious. I just use "average" for infiltration in manual J, like the rest of you (or loose or tight, or whatever dart is being thrown at the wall, at least I'm TELLING the customer what i'm calculating at... if there's a concern I stop the process, quote the fee to get the real infiltration rating, and start again).

I probably blabbed a bit too much there, but those of us selling this stuff must be on their toes, I find that no matter how hard I try, there are still occasions where I forgot to add one more bit of communication, and now I'm in the hot seat.

As far as the example about apartment buildings, I don't understand the point. If the heat loss is at least close, and the emitter system is at least close, and the apartments are all over the map, I fail to see how it's the heating systems fault. Either there's a lifestyle issue, a building thermal issue, a mechanical issue (heating guy's problem), or a combination of all of the above.

I tell you all, if I didn't do some training with thermal performance related topics like blower door and infrared, I would have had my rear end handed to me many many times. For those of you selling this stuff and you "think" you know infiltration, I hereby recommend getting some training, because you're day will come when you'll badly need it. If you can not explain "where" that heating energy is going and why the bills are high, you're on the hook.

These modern panel rad systems with ODR and TRV with home runs can really suck some fuel. You see, the previous system had OK efficiency, and the distribution system was just OK to maybe poor. Now comes the Euro-system.... now you're pumping heat where heat has never been pumped before, and the HO says, wow, what comfort! This is great! I can finally be warm! No more sweaters! Then the first bill comes in and WHOOAAA... You see, heating energy costs money, if you're sending heat to rooms that never had it before, don't be stupid and think that isn't coming out of the HO's pocket.

If you "increase comfort" (lets call this "add heat"), don't expect the bills to be lower, this makes no sense. Someone out there want to disagree? You can't add heat and have that energy some from nowhere. Many old systems that Euro contractors are selling increase comfort and increase heating distribution.

Now, if anyone is Still reading this, if everything is like for like, and all the rooms are heating the same way (sensible heat, you know what I mean), then of course the new system will be more efficient



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Rollie Peck

Outdoor reset

Hi MJ

One other benefit of outdoor reset that I have not seen mentioned so far is the more even heating it provides.
In mild weather, using the 180 degree water in your radiators needed for -20 degree outdoor temperatures, the room temperature quickly rises and shuts the thermostat off.
Then the radiators cool off and no longer heat floor level air and circulate it. This is more of a problem with low mass finned tube baseboard than with high mass cast iron radiators, however.
Outdoor reset varies the temperature of the water in the radiators so that there is warm water in them nearly all of the time, causing nearly constant circulation of air in the room and reducing the probem of cold air at floor level.

Rollie Peck

Homeowner