Low mass and indirect, outdoor reset?

Constantin

... a low-mass boiler might short-cycle when attached to a low-mass system like yours. There simply isn't a lot of water to go around the system before it gets mighty hot and the boiler has to shut down. This would be particularly evident towards the winter-side of the shoulder seasons, which not only predominate, but which also require less than full-output all the time.

Naturally, a modulating burner would be the shining knight saving your damsel boiler in distress. Trouble is, no modulating oil burner is available (yet) on the US residential oil market, the best we can hope for in the foreseeable future is stepped-output burners and even they are not available yet.

Here is what I would consider doing: Install the system as recommended (i.e. sized to mee the design-day heat loss and no more), then see how it fares.

If you experience a lot of short cycling, you could create a nice primary-secondary system using a buffer tank. Such tanks are not expensive and will allow you to lengthen the burn time, while losing very little in the way of heat during standby times. Simply treat the buffer tank as a giant hydraulic separator in terms of its piping arranagements and you ought to be good to go. Best of all, such tanks do not have to cost a lot of money because corrosion issues should be minimal.

You could also blend the water coming out of the tank on the heating distribution heating side with an outdoor reset controller to reap continuous comfort while also affording the boiler condensation protection.

Dan_15

Low mass and indirect, outdoor reset?

Hello
I'm replacing the boiler in my house and just want to see what people here think.

I had an installer recommend a low mass boiler with a indirect hot water heat.

Right now I have a summer winter hookup and maybe use 750 gal of oil per year, never had a problem running out of hot water. Summer usage of oil is around 100 gal.

He was recommending a zone control with priority for the water heater, made by Taco.
I asked about an outdoor reset and he said he doesn't think one could be hooked up to that.
It looks like Tekmar 260 or 262 could be used instead of the Taco, and it includes an outdoor reset.
For the amount of oil I use, I'm not sure if the outdoor reset would really save much money.
If I'm spending all the money to get the low mass boiler & DHW would it be best I also get the outdoor reset?

I'm thinking about the low mass and indirect since in the long run it should save me money, but figure it will take more than 7 years at the current rate to recoup the extra money spent. If things go as planned, I will be in the house much longer than 7 years.

Oh yes, the house has copper finned baseboard and I'm not far from Allentown, PA, so it does get pretty cold sometimes. I don't think there will ever be more than 3 people in the house.
thank you

Al Letellier_9

low mass boiler

go with the reset. You are right about the 260 in your application, but you may need to use a Taco to control your zones (you didn't mention how many). I have a Weil cast iron boiler in my home with an indirect, a Tekmar 260 and a Taco 6 zone controller with 2 zones of radiant...cut my fuel bill 55% with the same boiler, just went from a tankless to the existing setup...well worth the money.

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Dan_15

another question.

So if I wanted to, It sounds like I should be able to add the Tekmar 260 later on?
I now have 4 zones, I guess the water heater would become the 5th zone. Taco didn't really have too much info on their zone controller. Do you know if the zone controller is what will turn on the zone values? Or do the thermostat wires still go right to the zone valves?

Do low mass systems have short cycle times? It seems to me if there is less water to heat in the system, then the burn times would be shorter. Would that lead to colder flue temps (less burn time means less heat going up the chimney, so it would be colder and lead to condensation? I think I must be missing something here in my thinking since condensation wouldn't be good in the chimney)?

thank you.

Joe Brix

No issues

with my Burnham LE, Riello BF5, Phase III indirect and Tekmar 260.
The Tekmar will fire the boiler to 180 when the indirect calls. I just put the diffrential to fixed 20° rather then the auto differential setting which seemed to always be around 10° to stop short cycling. Just size the boiler correctly for the load, let the indirect priority setting take over the boiler for 10-15 minutes.

Brad White_25

What I love about discussing Low Mass Boilers

is that, sooner or later, somebody recommends adding mass

All excellent points, by the way.

But funny how adding mass (defeating the benefit of low mass boilers) always seems to come up.

Personally this illustrates why I favor parallel-piping my buffer tanks so the mass is "on demand".

This all reminds me how at one time women with curly hair wanted it straightened and those with straight hair opted for perms.

Dan_15

For sizing, I did the Slantfin program, using whole house, not room by room, and came up with a heatloss of 95,000 btu/hr.

My current system's boiler plate says net 129,000 BTU, but not sure what size nozzle is in there(nor what size was used to get 129k)

For the size of a unit, do I want to match that up with the IBR net rating BTU/Hr or the DOE Heating capacity BTU/Hr?
How much can the stated capacities be varied by using a smaller or larger nozzle? I'm sure that depends on the unit, but would it be more like 5000 BTU, 10000 BTU or more variance based on nozzle size? Any drawback to changing the nozzle size?

Brad, with parallel piping so it would be on demand. I know what you mean by parallel piping, but not really sure about the on demand part of it. How exactly does that work?
Thank you, lots of helpful info so far!

Constantin

He he he...

Like I said, if you can get away without adding the buffer tank, great. However, in a land without two-stage burners at the residential oil boiler level, potential issues with short-cycling will persist...

Once oil boilers will benefit from modulation like their gas bretheren, it'll be a whole new ballgame. Then, the need for buffer tanks is likely to be virtually eliminated by the ability of the heating system to exactly match the load. Only scenarios like large "dump" loads would then really justify them, right?

Besides, I don't mind thermal mass as long as it's very well insulated. Pretty much any indirect should beat a boiler in that department, allowing efficient storage of thermal energy, maximizing burn times, and hence having a better crack at attaining the steady-state efficiencies that many boilers can only dream of. Never mind minimizing flue gas condensation potential and other issues that come along with short cycling.

That's why I don't see it as defeating the purpose of a low-mass boiler. It simply adresses the limitations of the burner technology that is out there right now. Plus, the BOP can be a significant source of mass. Our RFH system trumps the high mass boiler by a good margin (54 vs. 31 gallons), for example.

Brad White_25

Parallel On Demand

Barry, Hi

By parallel on demand, that means that the tank is "off-line" and is charged (flow allowed to pass through) when the return water temperature in the main is returning too warm.

(In my case, a condensing boiler, I want the return water to be as cool as possible as well as the supply water, and still heat the house.)

I use a reverse-acting aquastat which turns on a circulator charging the tank (and adding that volume of cooler water to the return heading back to the boiler. When the return water cools below setpoint and the tank drops below setpoint, the circulator stops.

At this point the HWR return temperature is low enough that it bypasses the tank and goes home to the boiler.

Does that make sense? I really should diagram that one of these days...

brucewo1b

I really should diagram that one of these days...

Please do

B.S.

Dan_15

i think it makes sense

I think that makes sense, but a diagram would do wonders. How about a picture of it? It would be alot easier than a diagram if you have a digital camera, but a diagram would be nice.
Sounds like that could be added on later if I do go with the low mass system and have alot of short cycling.

Constantin, what do BOP and RFH stand for?

I did some reading about the Taco Zone controllers, and if I get the one with a power port option, then an outdoor reset appears to be easy to add on (PC700)

Brad White_25

Let's see if this works

I am using my new copy of Siggy's HydroniCAD. Question is, will it post? Finger's crossed...

Brad White_25

Trying as a .bmp

Doing my best here...what format works best for posting diagrams?

Brad White_25

Finally

a PDF...

Constantin

Sorry about that.

BOP = Balance of Plant, i.e. everything besides the boiler
RFH = Radiant Floor Heat

Bruce_15

taco outdoor reset

I think I may have the installer put in a TACO 6 Zone Valve Control /Priority & 2 Power Ports. I should be able to plug in the PC700 outdoor reset into that which isn’t too expensive (relative to the entire cost of the system). I was reading the Taco manual on the PC700 outdoor reset and on the last page, it says portions are copyrighted by Tekmar Controls. Based on that, it seems like Tekmar may be the providers of the Outdoor reset for Taco.

The buffer tank sounds like it would be easy enough to add later on. Do any of you know what the ballpark cost of a buffer tank would be, just wondering if I’d be looking closer $150, $300, $450 or more.

Brad, JPG’s are usually the easiest way to put pictures online. I think only text-based browsers couldn’t handle them, though I THINK many PC’s probably have acrobat on them but JPG still is more universally readable.
Looks like the first file you did with an HCD extension worked(or it asked me to save it), but if people(me) don’t have the HydroniCAD program, they won’t be able to open it.
In your drawing, what is the yellow thing that looks like 2 capital “T”s right next to each other, above the buffer tank. I think if I was in the heating business I would know what that is, but since I’m not, I really don’t know what that is. I’m thinking it might just be 2 T’s in the pipe with a pump/circulator, the buffer tank, and a check valve on the ‘buffer tank’ loop. I looked in Microsoft Visio but couldn’t find those 2 things in any of the templates.

Are two-stage burners something that will be coming to the residential oil burner level in the foreseeable future, and does anyone know if retrofits should be available.

Thanks!

Brad White_9

Barry, your questions:

Barry, Hi-

To your questions:

Buffer tanks might cost you in the range of $450 or more. Depends on your supplier and level of quality. I use a SuperStor Ultra which is for storage only and does not have a heat exchanger. It is all that you should need. I forget what I paid years ago for it, but am guessing in that range.

Thanks for the posting tips. I did a "Save-As" to a .jpg and changed the extention. Tried a bitmap (.bmp) too without result so the Adobe .pdf was the one. I had hoped that the HydroniCAD document would appear as a graphic but obviously did not... I will try the .jpg again just to see.

The two tees you describe are exactly that, "closely spaced tees". They are not a Visio element but a feature of John Siggy Siegenthaler and Co. "HydroniCAD", a recent aquistion for me.

These butted tees are used when I am connecting a secondary load (buffer tank in this case, with a circulator) to a primary circuit (the boiler/radiation loop in this case). The purpose is to decouple the two circuits such that flow in one will not affect flow or pressure in the other. They coexist peacefully.

Reminds me, I should copy Condi Rice on this...memo to self: closely spaced tees can be the key to mid-east peace....

PMyers

> Barry, Hi-

>

> To your questions:

>

> Buffer tanks

> might cost you in the range of $450 or more.

> Depends on your supplier and level of quality. I

> use a SuperStor Ultra which is for storage only

> and does not have a heat exchanger. It is all

> that you should need. I forget what I paid years

> ago for it, but am guessing in that range.

> Thanks for the posting tips. I did a "Save-As" to

> a .jpg and changed the extention. Tried a bitmap

> (.bmp) too without result so the Adobe .pdf was

> the one. I had hoped that the HydroniCAD document

> would appear as a graphic but obviously did

> not... I will try the .jpg again just to see.

> The two tees you describe are exactly that,

> "closely spaced tees". They are not a Visio

> element but a feature of John Siggy Siegenthaler

> and Co. "HydroniCAD", a recent aquistion for

> me.

>

> These butted tees are used when I am

> connecting a secondary load (buffer tank in this

> case, with a circulator) to a primary circuit

> (the boiler/radiation loop in this case). The

> purpose is to decouple the two circuits such that

> flow in one will not affect flow or pressure in

> the other. They coexist peacefully.

>

> Reminds

> me, I should copy Condi Rice on this...memo to

> self: closely spaced tees can be the key to

> mid-east peace....

Ron Schroeder

Brad,

I have been looking at your diagram and I see how you are charging the buffer tank but I can't see how you are using the heat that you are putting into the tank. What am I missing?

Thanks,

Ron

Brad White_9

Missing Information

What is not shown (in order to keep it simple for discussion) is another aquastat at the tank. When the tank is at temperature it keeps the tank charging pump running to deplete it (emptying the piggy-bank).

So the pump runs based on high return temperature (115-120F or so) upstream of the tank to charge the tank. When the return temperature again drops below that setpoint, the contact opens. But if the tank is still warm the pump continues until the water is below 100F or so.

I think of it as a pole-vaulting tank. I admit the setup is crude but the short-cycling had me hopping and I had to do something. In the future I would install an in-line full-port motorized ball valve between two tees to open/close the main upon low temperature.

Hope that helps and thanks for your interest!

Brad

Jed_2

That low mass

boiler won't short cycle on a low mass system with an adjustable(5-30°) operating control. If the HWBB system is designed around a 20° DT, and you have a 30° differential on the boiler, you're going to get long run cycles, and yes, we have them out there running like that with excellent fuel savings. The fixed(limited) cold start control differential would lead to the scenarios you are talking about. You don't run a low mass boiler on an 8 or 15° differential. Run it on 25-30, and you won't need a buffer on a hot water baseboard sytem. Reset, yes. Just protect for flue gas condensation, and make sure the EXISTING installed HWBB is sufficient to cover heat output at the reset temp vs. the heat requirement at the reset temp.

Jed

Keith_8

preheat with the buffer

Brad, How about preheating your domestic water with the buffer tank?

Thanks for the sketch.

Keith

Brad White_36

That is a very good idea, Keith

Thanks for that. I do have an indirect (Monitor companion to the boiler). I suppose if I had enough demand it would work well, hook up a bronze recirculation system, another tank or reverse indirect instead of a buffer.... you are going to get me into trouble here!!

Brad