Mod/Con, outdoor reset and fin tube

Brad White_128

and do favor radiant (don't we all?) over straight convective. Yes, the reset curve should get a little more flat at the base, perhaps levelling off, but comfort is what ultimately dictates.

Time was I was more strident about the "fintube with reset" stratagem, but after seeing the Dr.Butcher study at Brookhaven National Labs, I came away with a more supportive view. I would not personally call it a "mis-match", but rather, "not as ideal".

As you well note, reset curves have to be set up for the type of emitters. We all hope that the radiation is oversized relative to conventional application and proportionately oversized across the board.

Phil Yarbrough_2

Hello everyone, I have a relativly new modulating/condensing boiler with fin tube baseboard. I added a tekmar 256 for outdoor reset control. Watching this thing operate for the last year, I have some doubts as to if the tekmar is a good idea with this boiler.
What seems to be happening is that during mild weather the water temp. is so low that one of the small zones doesn't seem to satisfy.
So my question to you is, is the reset a good idea with this boiler? Since the tekmar shuts off the boiler before it has a chance to modulate down.
If you think tekmar is ok what temperature should be set as the minimum on the Tekmar?
Next, At what point does the baseboard become a problem, output wise? (Lower temp less output).
PS I should mention that this is a combination boiler, Heat/DHW on demand.
Thx for any input.
Phil
Premier Heating
Ludington, MI>

tim smith

mod/con & reset

Phil, what kind of mod/con is it. Reset is good with any type of radiant but may have to tweak a bit.

Phil Yarbrough_2

Thx for the reply. It is a quietside QVM90. One of it's drawbacks is maximum water temp. It only has the capacity of 176f. which gives me an average water temp of about 160f. I tried setting the minimum to 120f but I'm concerned about short cycling.

tim smith

QVM boiler

Does it not have built in reset on the boiler.

Phil Yarbrough_2

I don't mean to be rude...But why would I add a 256 if it already had outdoor reset.?

Unknown

I'm not sure. Why would you put an on/off boiler control on a modulating boiler?

tim smith

response

No response to that!!!!!!!

Phil Yarbrough_2

256 on a mod boiler

That is the question to begin with. Is outdoor reset a good idea on a modulating boiler?
I appologize if I rubbed any of you the wrong way.
I just wanted some input on this system. Please feel free to ask questions if you need more information.

tim smith

reset and mod/con

Yes reset is a good idea imho, but if it is keeping the unit from modulating down I wonder if maybe it is oversized for the application. Just a thought. If it had built in reset then hopefully it would modulate down as it approached set point rather than be based upon just delta T. Other possibility is what if the pump was to large and maybe the delta T too low, causing the unit to try for high fire too much. ???????? Just misc. thoughts. Tim

Unknown

Outdoor reset is definitely a good idea, but you're using the wrong controller. Quietside *should* have one for this boiler. If they don't.. I don't see it on the tekmar list of compatible boilers, but I might be out of date.. talk to tekmar.

Basically you need to be able to get a variable strength signal to the boiler for modulating reset. The controller you're using is just on/off. Not what you want, IMO.

Brad White_118

All your question tells me

is that the deficient zone has less radiation compared to heat loss as your other zones.

OD Reset with modcons and Fin Tube are indeed compatible. The means and methods discussion notwithstanding it can and should be done.

Personally, I would enhance (add to) the radiation in the deficient zone so that it does not dictate a higher temperature than the rest of the house needs.

My $0.02

Brad

GMcD

Getting closer

I think that the combination of the fin-tube and mod-con is also a bit of a mis-match if the control curves aren't set up properly- the output of the fin tube falls off rapidly at lower average water temperatures because it loses the convective heating part of it's capacity. Fin-tube elements are designed to heat via convective heat as well as a little bit of radiation from the cover, and at higher average hot water temperatures they are mainly a convective heating element. The heating output curve of the fin-tube needs to be factored into the HWS temperature reset curve.

GMcD

The \"system\" vs the techno-solution

I hear you Brad, it's just that people are too easily sold the "techno-solution" without a complete whole system approach to make sure that they are getting the right bang for their bucks.

Perry_2

A simple explaination

Phil:

As another homeowner I think I can provide a simple explaination.

1) Is a modulating boiler with outside reset something good to do. YES. This maximizes boiler efficiency - and properly done will produce amazing results.

2) Can you do it with your boiler and system. Almost certainly to some extent. The question is how well can you implement this. The key factors are correct boiler sizing and getting the right setback curve for your system.

3) Will it work with your current controls and the way you have described how you set up your boiler. No.

4) What should you do? Most likely a change to the right control system - and the selection of the proger setback curve will do wonders. So, you should first learn about the issues (what setback curves are, why some controllers have a range of selections - and other controllers only have 1 curve, etc). Then either you should call your heating contractor who installed this and request that it be setup right; or if you installed this yourself - figure out which controls will allow you to run your boiler most efficiently.

However, first I'd do a heat loss on the house and ensure that your boiler is sized right. If all you need most of the year is 40,000 Btu/hr then your boiler is well oversized and you will not get any real advantage to a setback controller as the minimum firing rate is more than your normal heat load. The boiler will always cycle on and off. Good rule of thumb on modulating boilers - their minimum firing rate should be 1/3 or less of your required heat load for the worst day of the year.

Perry

Read his other posts

perry

Perry:

Number one, he is not a home owner

Number 2 - you are not an expert. you came here shopping for a new boiler for your house and are all excited because you found a closet to run some pvc through.....

Number 3 - I read your inaccurate, misinfomed posts on the energy industry. Please don't post if you have no clue what you are talking about. And at least take the time to read his entire post.

Maybe you are an expert metallugist(I don't have enough infomration to judge your comments on hydrogen induced stress cracking in stainless alloys) - for all I know that could be bull droppings as well - but I know for certain
that oil companies make more than 1/10 of a cent per gallon or whatever you claimed, and diesel and gas differ in price for reasons other than shipping dealysfrom the port or whatever....please don't just whip off info you don't know.........

S Ebels

On the Wall

We try to remain civil and polite in our dialogue with each other regardless of their position, skill level or title. (Even engineers and architects get treated decently) If you have a beef with someone you can easily get their e-mail address by looking for it when you click "reply", then taking it to them privately. Most folks here do not hide their address because they are civil enough to carry on a public conversation without embarassing themselves.

mtfallsmikey

Now, back to the subject at hand

This is interesting because in the not too distant future I want to install a mod-con,OD reset, with baseboard in my wife's house, and I want to make sure I buy the right control system, so what is the best way to go? Sorry, no radiant..it's a 110 yr. old house.

Tony_23

Wow...

You're so secure in your knowledge that you don't dare use your real address or name

I didn't see much of Perry's post that was that wrong or offensive. You resent someone who's educated themselves about your business, and probably understands it. Intelligence in others scare you ? It usually does to small minded people.

If you're going to take personal shots at least have the gonads to post your name...

S Ebels

It depends.......:)

> This is interesting because in the not too

> distant future I want to install a mod-con,OD

> reset, with baseboard in my wife's house, and I

> want to make sure I buy the right control system,

> so what is the best way to go? Sorry, no

> radiant..it's a 110 yr. old house.

S Ebels

It depends.....

A lot of the success when using a mod con boiler with fin tube depends on the amount of "extra" fin tube you have. If the amount of fin is barely adequate to heat the place, you're going to be forced to run high temps (170*+) a lot of the time. This gets your flue gases out of the condensing range so the M/C boiler's capabilities are limited to shoulder seasons of the year. Still a benefit for you but not as much as it could be.
The place to start is a good heat loss calc to find out what the actual load of your building is. Then measure up the lineal feet of active fin and see if you have any "extra" heating capacity. Figure an average of 500 btu's per lineal foot at 180* water temp for your fin if it's of a standard type.
When you have those numbers put together you can make an easy decision as to whether or not an M/C boiler will be a good investment.

As to the brand, more and more manufacturers are incorporating an integrated control package built right onboard the boiler or available as an additional piece.
Viessmann leads the way with the package on the Vitodens although there are many others that will do very nicely for your application. I'm familiar with the Lochinvar Knight boiler and the Munchkin from Heat Transfer Products and both of them have basic reset capability which would be all you need. I'm sure other guys will chime in here with other brands and models that will also work well for you.

PS: Let me explain the "extra" fin thing..........

Let's say your heat loss shows a load of 8,000 btu's for a given room. In that room you have 20 feet of active fin. This would give an output of 10,000 btu's using the 500 btu per ft figure. From this you can see that lowering the water temp and thereby the output of the fin tube will still heat the room. There are more factors at play here than just that one but that's by far the most critical one to consider.

Rob_35

getting extra fin

And remember that you can effectively gain fin by reducing the room/building heat loss. I knocked a good 1000 BTU/hr off one room by replacing a cheapo slider (being used as a "picture window") with a proper high-performance low-E window, sealing, insulating, etc.

Granted that approach cost more than sticking another couple feet of element on the loop, but wow did it improve the comfort and looks of the space.