System Design Help


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Old 04-17-10, 12:55 PM
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System Design Help

Hey All,
I'm in the early planning stages of completely redoing my house, basically knocking it down and dropping a modular on the existing foundation. The new house would be ~2300sqf and the manual J heat loss estimate is 34MBtu. I'm looking at the Burnham MPO84 as the boiler and would like to do full ODR if that is really the most efficient method. I've cobbled together a basic schematic from stuff I've read here and other sources. I'd like your opinions and suggestions about the plumbing aspects and the control electronics. I'm not sure what Tekmar control would allow full ODR (P/S w variable speed injection) and also control a buffer tank to prevent short cycling of the boiler. Am I on track here or am I over complicating this... My fall back option is to go with a system 2k. Thanks in advance

Keefe_sys.jpg picture by gak427 - Photobucket
 
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Old 04-17-10, 01:04 PM
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I should add that the radiation is fin tube baseboard. Builder does not do radiant heating, I could go with ultra-fin type radiant after the fact but I haven't heard too much about it. thanks
 
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Old 04-17-10, 02:58 PM
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I don't see any point in using the pumped buffer tank when you can use a passive one:

Boiler Buddy

This would take the place of the first pair of CST's ... the supply and return from the boiler into one pair of ports, the injection loop out of the other.

The CST's on the injection loop are backwards. The 'run' of the tees goes on the system loop, and the 'bull' goes to the loop.
 
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Old 04-17-10, 03:17 PM
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Something like this...



I think the control you would use would be the Tekmar 361...

Also, if you don't use a Delta P pump for the SYSTEM loop, there should be a differential valve out there (meant to draw that in, but forgot)
 

Last edited by NJT; 04-18-10 at 05:11 PM.
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Old 04-17-10, 08:40 PM
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Thanks Troop for the super fast replies and great suggestions. Using the Tekmar 361, would the buffer tank be at the the boiler temp seting or the mix temp setting?
Thanks again
 
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Old 04-18-10, 05:00 AM
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How can I reduce the stand-by losses of this system? When I look at the System 2000, I think the real reason its so efficient is because the stand by losses are much lower, is there any way to reduce them in this system? Is an automatic flue damper the best option or is some sort of post boiler purge better? If you had a 2nd IHW run as a second loop to preheat the DHW entering the main IHW tank, the temp would be much lower then you could really get all the heat out of the boiler? Thanks
 
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Old 04-18-10, 06:35 AM
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The MPO has very low standby loss due to increased insulation values. Add that to cold start and being pressure fired operating with a zero draft.
The MPO will soon have the Burnham IQ control which is presently on the ES2 which will incorporate post purge circulator option along with a plug in ODR card.
 
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Old 04-18-10, 07:28 AM
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The MPO has very low standby loss due to increased insulation values. Add that to cold start and being pressure fired operating with a zero draft.
I think I used the wrong terminology when I said flue damper, what I really meant was vent damper. Does the MPO have some sort of vent damper incorporated into it that closes when the boler is not firing? Also isn't the insulation loss not as important as the draft loss because its still heating the house?

The MPO will soon have the Burnham IQ control which is presently on the ES2 which will incorporate post purge circulator option along with a plug in ODR card.
Would this work with the Tekmar 361 or is this a totally separate approach?
Thanks
 

Last edited by NJT; 04-18-10 at 08:07 AM. Reason: added quotes
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Old 04-18-10, 08:21 AM
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Using the Tekmar 361, would the buffer tank be at the the boiler temp seting or the mix temp setting?
The buffer would be at boiler temp, mix temp would be controlled by the amount of hot water pulled out of the buffer and injected into the system loop under variable speed control from the 361.

There has been some debate over whether the boiler sensor should be in the well of the buffer tank, or directly on the supply line out of the boiler... I don't think there's been a definitive answer on that yet.

I believe the 361 has some limited post-purge features.

I think I used the wrong terminology when I said flue damper, what I really meant was vent damper.
Same thing in my book... the Field OVD can be used. Supposedly savings of up to 5% ... I think that's optimistic, just my opinion, but even 3% makes it worthwhile.

If you had a 2nd IHW run as a second loop to preheat the DHW entering the main IHW tank, the temp would be much lower then you could really get all the heat out of the boiler?
Not sure what yer drivin' at here? TWO indirects? Please explain a bit more...

I'll let rbeck comment on the IQ vs. 361 controls as I'm not too hip on the IQ... but in the meantime, you might get more info on that from the ES2 manual.
 
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Old 04-18-10, 09:25 AM
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Hey Trooper,
What I was trying to do was have a 2nd IWH is series with the main tank but all its job would be to able to draw out all the heat of the boiler after it has shut off... It would preheat the cold (50F) water before it gets to the main IHW tank. My thought is that it would be at a much lower temperature ~ <100F and could extract more heat out of the boiler... Maybe its a long way to go for a little gain..
Thanks
 
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Old 04-18-10, 10:18 AM
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I think I'm followin' now...

"Little" or, maybe no gain... probably simply purging the heat into the single indirect after a heat call would do the same thing... I believe that's what S2K does.

Still, with the well insulated boiler, and buffer tank, there would be little standby loss anyway, so why not just store the heated water where it sits? Yer gonna eventually use the BTUs anyway, right?
 
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Old 04-18-10, 03:38 PM
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If you are lowering the water temp in the boiler with outdoor reset and have a circulator post purge your standby losses are reduced. Cooler boiler water temperature lower standby losses. You may be getting into an area of diminished returns with the extra tank idea. I would keep it simple. Do a buffer tank, MPO w/IQ control, ODR and variable speed pump for the system. If you are not using radiant you will be fine. I might even forget the variable speed pump unless you are using zone valves.
The MPO does not come with a vent damper but can be added after market. The newer burners have less natural air flow through them than the older style burners and the boilers are cold start as compared to many hot boilers yesteryear did so the savings will be less than the older boilers would have been using vent dampers.
 
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Old 04-18-10, 04:56 PM
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I scribbled a bit on Tekmar's drawings... and came up with this:



I'm not 100% sure it's correct, so check and double check, and if anyone has suggestions, let's hear 'em!

I didn't put an indirect in to keep it clean, there would be another relay needed to run that.

Then, my brainiac wondered about something more complicated... and of course, more expensive, and whether there would be any advantage to using the 361 to control the mix temp... and ALSO resetting the boiler with a 256. If running an indirect, the 260 would be used in place of the 256. This may be completely unecessary, so I'm just throwing it out here for discussion:



Pros ? Cons ? anyone ?

By the way, on your original drawing that I marked up, I did some more changes, so scroll back and take a look. If you use the buffer tank, you don't need the Spirovent because the tank has an air vent on it. Also, the cold water fill can move to that location.
 
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Old 04-18-10, 05:28 PM
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Let's talk about the first diagram...

Tekmar wants the boiler pump to run whenever there is a call for heat, and that's why the system pump and the boiler pump are shown in parallel.

However, the REASON they want this is to insure flow past the boiler sensor so it reads the proper temperature. This is something to think about.

If the sensor is in the well on the buffer tank, the flow issue is sorta moot. That sensor will be reading the temp in the tank, flow or no flow. It's not like it's on a pipe that is subject to cooling off.

For this reason, I think that leaving the boiler circ wired to the boiler aquastat would be OK. The advantage to this would be that the boiler pump would not need to run whenever the system pump is running, and save a wee bit of 'tricity. It would only run when the 361 sensed that it couldn't make the mix temp and fired the boiler.

There IS a rub though. In the case of an indirect WH, when the indirect called for heat, it would mean that the boiler pump would also run. It would be a pretty easy matter to wire up another relay to shut the boiler pump down during an indirect call. Another relay would be needed anyway, so making it a triple pole instead of a double would do the trick.
 
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Old 04-18-10, 06:04 PM
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Hey Trooper, wow your good, lots to think about here... I don't think I understand how you would shut off the boiler pump during an indirect WH call, is this a normaly closed relay in series that would be opened when the indirect calls for heat? Also the Tekmar drawings with the 256 to do boiler reset, would the minimum temperature be ~140F to prevent flue gas condensation?
Also, Back to the original drawing, the vent in the buffer tank would be able to remove dissolved O2 as well as the spirovent???? Can I put in an air scoope in on top of the expansion tank, they are cheap....
Thanks again and again.....

RBeck,
When will the MPO w/IQ control be available?
 

Last edited by MrWanderLust; 04-18-10 at 06:34 PM.
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Old 04-18-10, 07:16 PM
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I don't think I understand how you would shut off the boiler pump during an indirect WH call, is this a normaly closed relay in series that would be opened when the indirect calls for heat?
Yes, that's what I was thinking... but I think I've come up with a way to do that with a two pole relay, as in the 361 application brochure, but with a twist... I'm gonna try and draw that up, cuz I can't explain it.

Here's the application PDF in case you haven't seen it:

http://www.tekmarcontrols.com/litera...robat/a361.pdf

You will notice the extreme similarities between their drawings and mine...

Also the Tekmar drawings with the 256 to do boiler reset, would the minimum temperature be ~140F to prevent flue gas condensation?
Yes, exactly, but the MPO can take a bit cooler temps on the return due to the design of the boiler... so you might be able to go down to as low as ohhhhh, maybe a hundred on the return... rbeck please correct me on this if it's bad info...

But, I really don't think you will need the second control with the buffer tank. You actually might benefit from charging the buffer to a higher temp... letting the 361 fire the boiler as it sees fit... I dunno, it's just a concept at this point that needs to be totally thought through. I'm pretty sure the benefit, if any, won't outweigh the added expense.

the vent in the buffer tank would be able to remove dissolved O2 as well as the spirovent????
As well as, perhaps even better. When the water and air go into the tank, because of the volume of the tank the water will slow WAY down... allowing the air to bubble up to the top.

Can I put in an air scoope in on top of the expansion tank
Sure, if ya want...

When you do the final design, one thing to consider will be where to place valves and such, so as to make it possible to fill the system, and purge the air ahead of the water. Like track switches on a railroad... you want to be able to direct the water where it needs to go, and have a way to get the air out as the pipes fill.
 

Last edited by NJT; 04-18-10 at 08:27 PM.
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Old 04-18-10, 08:18 PM
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Here's a possible electrical...



The DHW and BOILER circs would both be powered from the boiler aquastat.

When the DHW is idle, the boiler circ is connected to the aquastat via the Normally Closed contact on the relay, so that if there is a heat call, the boiler circ will run.

When DHW calls, the relay flips, fires the boiler (up to high limit if necessary to heat the indirect), the DHW pump in now connected to the aquastat via the Normally Open contacts.

Another advantage to this is that it will provide DHW Priority, because if there is a heat call and DHW call at same time, boiler pump won't run, but DHW pump will. Heat call will have to wait until DHW is done. In the meantime, heat call will use what's stored in the buffer tank.
 
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Old 04-19-10, 07:47 AM
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Trooper I always admire your thought process and diagrams. What you show will work fine, took a little thinking what the relay was doing. Slow on my end today, vicodin on the brain.
My only question is in this not way overkill?
The IQ control with ODR card will give us the option of priority for IWH, pump purge to buffer tank, boost feature if needed, priority protection which means if priority is chosen and the pump fails for the indirect it will time out and go back to heating and still try to heat the tank, may use EnvirCom stat, adjustable high limit differential along with buffer tank differential is an aquastat is on the tank, trouble shooting codes, error code history, able to read flame signal from cell without meter or green stick etc.
He really does not have to do injection on this system as all heating zones are the same temperature.
Yes, the MPO can receive 100 return water temperature so you can send out as low as 110 due to reduced delta-T at lower water temps of course depending what the differential is on the buffer tank.
The down side is this control will not be out until maybe June. Same control as the ES2 but changed to work with oil primary control. The IQ is actually programed into the electronic aquastat and than add the OCP (Optional Control Panel) which also makes it easy to add the LWCO required by most states.
 
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Old 04-19-10, 08:55 AM
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Thanks for the kudos...

These are some of the questions we had actually... whether or not the 361 setup would even be needed with the MPO plus IQ control.

I'm following MrWanderLusts lead of what he was looking at doing... I've carefully avoided saying whether or not it's a good idea... I would love to have a system such as that which I could fool around with and adjust stuff... but the reality is, as you suggest, that it may be overcomplicating things with little or no return on the extra expense...

If the MPO can in fact go down that low in temperature, then the whole injection mixing thing is probably not worth the trouble.
 
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Old 04-19-10, 07:23 PM
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Trooper,
I'll second rbeck's admiration for your thoughtful replies and the thoroughness of your solutions. Your dedication to this forum is amazing, I already owe you big time! Thanks
So after reading rbeck reply it seems that the IQ electronics will do everything I was trying to do with the original design. It even sounds like it will do boiler reset and still be able to recharge the IHW tank @~160F and then do a post boiler purge in to the buffer tankwhich could be as low as 100F..is that true?

rbeck,
Do you think the IQ electronics will be upgradable to a MPO84 purchased now??
 
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Old 04-20-10, 03:31 PM
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I read up on the IQ control in the ES2 last night. The outdoor reset comes from a 'plug-in' module that is added to the system. Very neat setup... seems to have most of the 'bells and whistles' that the Tekmar controls do.

The choices really come down to 'payback'... how long will it take to pay off the extra expense for the more complicated system? How much extra expense to maintain the extra equipment? etc...
 
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Old 04-20-10, 05:21 PM
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The MPO will do 100f return without a problem.
Unfortunately it will not be an upgradeable control to the now purchased MPO as it includes a jacket change to accommodate the OCP control. It will resemble the ES2 design.
It is only April so we have plenty of time before winter to your installation completed.
 
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Old 04-20-10, 06:52 PM
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rbeck,
I know that you know what your talking about but how can the MPO Supply 110F and return 100F without having flue gas condensation? Does it some how keep the internal cast iron surfaces above 130-140F... Also do you have a rough guess as to how much the IQ electronics will add to the cost?

Trooper,
Have you read the report: Performance of integrated hydronic systems by Thomas Butcher at Brookhaven National Labratories(2007). It does a efficiency comparision of 12 hydronic different systems, condensing, tankless, and so on. It doesn't name names of the systems but you can guess fom the descriptions, the system that I believe is the EK system-2K is the most efficient of all, even better than the condensing systems. The big difference is the stand-by losses. Just curious if you read it and what you thought?
 
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Old 04-20-10, 07:37 PM
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I hope rbeck doesn't mind if I answer his question... I wondered about it a while back myself and did a little research, and may have even asked the same question myself.

If you notice where the return tapping enters the MPO you will see that it doesn't feed into the bottom of the boiler. Rather, it feeds in almost at the TOP! Also, the return fitting is actually an 'injector jet' that shoots the water into the middle of the boiler, ABOVE the combustion chamber. The result is that the return water is 'mixed' with the heated water before it travels down and around the combustion chamber. So, it is pretty much as you suggest, that the fireside surfaces of the boiler are not cooled by the return water, and are for the most part maintained above the dew point.

Yes, I did read that report, but it's been a while, and my memory isn't entirely clear on the results. I do remember making a sort of 'game' out of trying to ID the different boilers by the clues that were given. I am certain that one was the S2K... somewhere around here I've got a sheet that I printed out and wrote what I thought they were... but if you could see my office, you would know that I don't have a prayer of finding it again! If you've got the URL handy, why not post it up, and I'll read the report again.

Some thoughts on why the S2K might have scored highest, or at least higher than the mod/cons... A mod/con is at it's 'best' during the shoulder seasons, when the home doesn't need the extra hot water. As soon as the cold weather rolls around, and the home needs hotter water, they lose their 'edge' over conventional boilers. Once the weather is cold enough for them to stop condensing, they are in the same boat as the conventionals. One thing that would help mod/cons score higher would be if they were connected to a very 'over-radiated' system. If there were enough heat emitters installed such that one could heat their home in the dead of winter with 120-130 degree water, they would score much higher on the seasonal efficiency testing.

Conventional boilers are at their best when it's really cold out, but suffer badly during the shoulders.

If all is to be believed about the S2K (and there's actually plenty of evidence from owners that they DO save a lot of fuel), the savings are probably achieved by the CONSISTENT nature of what they do... they just chug along, sucking all the BTUs out of the oil they burn, shoulder seasons, or dead of winter... and the OVERALL, SEASONAL efficiency scores highest.
 
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Old 04-20-10, 08:40 PM
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Troop,
Thanks for the MPO explaination and Mod/Con stuff, Is there a reason why mod/cons aren't always over-radiated..... the cost differential can't be that much... I just seems a shame that we don't do a better job as a whole with more efficient system designs, the know how is out there but most installers I talk to don't care about it at all.... thanks again for the tutorials, really enjoying going to school here!

Here's a link I found to the paper:

http://www.bnl.gov/est/files/pdf/ButcherAachenPaper.pdf

funny tho its not quite the same as the version I have, this one only has 10 systems while the one I have has 12.... and the descriptions are not as informative, if you want I can e-mail you my version
 
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Old 04-21-10, 04:09 PM
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On a retro-fit job it's highly unlikely that the homeowner would want to spend the money to add extra radiation... on a NEW install, I can only think that if the system were not designed with this in mind that somebody needs to check the installers brain.

Thanks for the link, I'll take a look again.
 
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Old 04-21-10, 05:53 PM
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Panel radiators (Myson, Buderus, whatever) would be easy to oversize (i.e., design to be big) to run at lower temps. Also simple to install in a modular structure. Simple 1/2" Pex-al-pex homeruns from a manifold.

2300 sf building with 34k manual j is probably really about 24-27k. Even with baseboard, you could run a lot with <100F return water. More if you design for low water temps.

Might be worth looking hard at full ODR using the tekmar 361. You could also go with something like a Taco iSeries setup on the space heating instead of the tekmar. Let the boiler push the buffer, and the iSeries draw off as needed based on ODR curve of choice.

Nice thing about the 361, however, would be indoor feedback, which runs the system based on the actual heating load. That approach rocks.
 
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Old 04-22-10, 01:44 PM
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Does anyone have any opinions about the Ultra-fin radiant heating system:

Radiant Floor Heating Systems - Radiant Heat Installation| Ultra-Fin

Low mass radiant system intalled between the joists..

Also, they house plans has a kick heater in the kitchen, basically a radiator with a fan attached to it, fan automatically comes on when it sense a water temp >130-140F. I'm guess this would not be a good heat source if you are doing ODR and the temp is below that.... I was thinking about the Ultra-Fin as an alternative to that, is it a good Idea to mix the High Temp Ultra-Fin and baseboard on the same heating zone?
 
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Old 04-22-10, 03:43 PM
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The problem with 'mixing' different types of radiation within a zone is that the response times differ... and cause imbalances in the heating. I don't think there would be any problem if each room in the zone had the same PROPORTION of baseboard to in-floor though. Example: room by room heat loss is done, and the infloor is selected to provide say 80% of that heat, and fin tube providing the other 20%... in EACH ROOM. As opposed to say, in-floor in the kitchen, and fin-tube in the dining room, each sized for 100% of the heat loss in their respective rooms.

For the kickspace heater, the manufacturers have low temp thermostat options available, I think down to like 120 degrees... if you do install the low temp t'stat, you would have to look at the BTU output curve of the kicker to see that it would satisfy the heat load of the room at the lower temp. And again, be careful of the 'balancing' issue. I think it's generally recommended that kickspace heaters be piped as 'home runs' though... check the manufacturers recommendations. I believe you can also wire up the fan to run under control of the boiler controls, but as with any 'fan coil' device, you can't run the water too cool, or the air comes out feeling cold... it will still contain heat, but if it's blowing on the feet, it will feel like a draft.

I can't really comment on the Ultra-Fin, but looking at the product, it seems fine from what I've read.
 
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Old 04-22-10, 05:20 PM
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Originally Posted by NJ Trooper View Post
For the kickspace heater, the manufacturers have low temp thermostat options available, I think down to like 120 degrees...
Beacon Morris, and maybe other kickspace heater manufacturers, will send you a free low-temp aquastat if you call them. For me, the stock (hi-temp) aquastat took too long to come on.

In the winter, at the breakfast table, I really like the kickspace heater blowing on my feet. If your feet are warm, you're in good shape!
 
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Old 04-24-10, 04:15 AM
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Thanks for the info on the kick space heater and the panel raiators. All this talk about "over radiating" has gotten me thinking, almost constantly(????), about heating systems..... and efficiency.
I've been wondering why ODR/constant circulation systems are more efficient than on/off systems. First pass you would think the cost of electricity to run the circulator would make the system less efficient but the reason I believe they are more efficient is because they lower the overall system temperature. Higher temps mean higher losses, dosen't matter Mod/Con or not, so that being said, and if its true....Shouldn't the system design goal be heat the house with the lowest possible temperature water... To do that shouldn't all systems, radiant or baseboard, be overradiated to the lowest possible temperature to satisfy the design load and then modulate the circulator when less BTU's are needed? Is my thinking flawed on this? I know I'm regurgitating a lot of other peoples words here but I'm trying to get it all straight in my head..Thanks
 
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Old 04-24-10, 08:48 AM
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Yes, the lower the water temperature you can use, the better. It simply costs less to heat water to a lower temperature.

An automotive analogy: Sit at a red light, turns green, FLOOR IT! Stay on the gas until the last possible moment, and jam on the brakes at the next red light...

OR:

Accelerate gently, use yer brainiac to process the speed you need to get to the next red light just as it's turning green... this means that you would get off the gas early, and coast up without using the brakes, and as you arrive the light changes and you continue on your way... easing up to the guy in the next lane who floored it and jammed on the brakes. You both got to the same place at the same time, but slow and easy wins the race, because you won't have to make as many stops at the gas station, or the brake repair shop. Turtle.........turtle........turtle.....

This is very basically the difference between a mod/con with constant circulation, and a 'bang-bang' cold start system.

shouldn't all systems, radiant or baseboard, be overradiated to the lowest possible temperature to satisfy the design load and then modulate the circulator when less BTU's are needed?
Yes, and no... only if the boiler and distribution system is designed as a whole to handle the lower temperature water would this be possible. Ruining a conventional boiler by condensing the flue gases 90% of the time just ain't a good thing.

Modulating the circulator speed isn't an efficient way of modulating heat distribution either... plain and simple, it causes more problems... with system BALANCE. If you pump water through a heating loop very slowly, by the time the water gets to the end of the loop, it's too cold to heat the rooms. The first rooms on the loop get warm, the last ones are cool. You want to keep the flow through the system at the design, so that all rooms have adequate heat energy in the water to keep the system balanced.

If you've read about variable speed circs (and I know you have) you know there are different types... Delta T and Delta P... these modulate the speed based on DESIGN criteria, and as long as the design is proper, don't have the above problems. In other words, the difference in flow is accounted for in the design of the system.

In the VS injection setup you are/were looking at... that variable speed pump is used for transporting the correct amount of heat 'across the bridge' between the two loops. The FLOW in the distribution is always at design. (as it is in the boiler loop also). The water TEMPERATURE is what is being modulated in that type of system, which is a MUCH more feasible way of controlling the amount of BTUs available.

In a properly designed constant circ system, the tradeoff between the very slight extra electricity useage of the pump running is far offset by the fuel savings.
 
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Old 04-24-10, 09:29 AM
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Don't know if you've seen this essay or not? Worthwhile reading...

http://www.tekmarcontrols.com/litera...robat/e021.pdf
 
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Old 04-24-10, 10:45 AM
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Trooper thanks for picking up my slack. I have been in and out lately through recovery. I tor my bicep muscle from the tendon and the tendon from the bone. Had to get muscle reattached and the tendon drilled and screwed to the bone.

MrWanderLust your link is forced draft or negative draft equipment. It does not include a unit like the MPO which is pressure fired, "0" draft. This reduces the chimney losses and more thermal transfer into the water along with the three pass design. The MPO also has increased insulation for less standby losses. BTW Troopers response about flue gas condensation was right on.....Thanks Trooper.
 
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Old 04-24-10, 05:16 PM
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no problem rbeck, I knew when I saw that reference to the pain killers that something got hurt... and I'm hurtin' right now, but nothing a tall glass of Crown Royal Purple Sack won't cure... just got done spreading 3 dumps of top soil, leveling, seeding, rolling, and my butt is whupped...

Mend well my friend!
 
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Old 04-24-10, 05:49 PM
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Trooper, I do realize that you have to always stay above the condensation temperature in a cast iron boiler, my point was that even when you are doing full ODR with variable speed injection, you should also be doing boiler reset with the minimum temperature being just above the condensation point. If you just had the boiler going to the high limit, ~190F, the system efficiency is no better than if you didn't have the variable injection. Is this true, I think it is but I would like your opinion about that....I know I keep going back to the theory that stand by losses are the biggest loss factor in a system like that mentioned above...and by stand by I mean losses up the flue pipe, not through the jacket because that is useful losses as compared to going up the chimney....
That brings up my next question, should you direct vent these boilers for better efficiency, you won't get the hot gas rising and cool gas falling into the boiler. Thanks Rbeck for pointing out the drafting difference in those boilers, I didn't realize the difference. Does that mean the stand by losses of the MPO would be better than the systems in that test?
 
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Old 04-24-10, 09:15 PM
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I looked at that report again... and I think system #3 is the S2K. You are right also that the report you linked is not the final result. I remember the one that I read had more than 4 system tests completed. This one seems a bit dated. It's a curiousity that the high and mighty Brookhaven lab would not have the latest report on-line. I'm not sure that I completely agree with their test methods... definitely not 'real world', but I suppose that what they are doing is designed to treat all the systems exactly the same.

I need to say that all my thoughts on this setup are completely theoretical, as I've never fooled with anything like this. So all this is only what I THINK is the way it would run, based on considerable time studying it. Myself and a few of the others here (Xiphias was instrumental) helped a member design and build one a while ago, and he's very happy with it... maybe John will come by and see this thread? He used the buffer tank, and the 361, but not the 256/260.

I believe I had proposed the second control at that time also, but it was decided that the extra cost and complexity wouldn't really be worth it.

And it wouldn't have been fair to use a member as a 'guinea pig' to test a theory... BUT, the almost identical setup IS shown in the Tekmar literature... so it must be a bit more than theoretical and good for something!

when you are doing full ODR with variable speed injection, you should also be doing boiler reset with the minimum temperature being just above the condensation point.
Let's say that you COULD also be doing boiler reset, because it's not an absolute necessity. This is why I posted that schematic with both the 361 and the 256/260 controls. I'm not sure that there would be much advantage to the dual control setup when using the buffer tank though. If you think of the buffer as a battery it would appear that the most efficient use of it would be to 'charge' it full, and then draw it down, charge again, etc... the injection pump only drawing off the BTUs it required to satisfy the heat load. In this case, you might actually find it's more efficient to let the boiler and tank hit high limit, and then just sit there, waiting for the 361 to decide to fire the boiler or not.

If I were building one for myself, I might even be tempted to run the buffer tank as a sort of 'warm start' system, using an aquastat on the buffer tank with a WIDE fixed differential, so that the boiler would only fire say... when the buffer tank went down to ohhhh, 130 or so, then the boiler would recharge to high limit... a nice long efficient burn, and then a long time off. I THINK you can do this with the 361 by setting a wide FIXED differential on the boiler limits.

I'm not sure I would even attempt to do VS injection without a buffer tank... I think the system would be plagued by a short cycling boiler.

should you direct vent these boilers for better efficiency,
The MPO is, as you know, available as DV, but I don't think it affects the overall efficiency much, if at all... rbeck? you feeling up to answering this? If not, I'm sure the specs are in the manual.

Thing is though, if it's stack loss up the chimney you are concerned about, the vent damper would take care of that.

I think the bottom line here is that a conventional boiler is physically capable of a maximum of around 87% combustion efficiency. That's physics, and even the O'bama administration can't change those laws. BTUs are BTUs, and to heat the home you are going to need them, now or later. The only real difference here is how and when those BTUs are generated, stored, and transported into the home.
 
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Old 04-24-10, 09:25 PM
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Nice thing about the 361, however, would be indoor feedback, which runs the system based on the actual heating load. That approach rocks.
Xiphias, thanks for mentioning this... I meant to myself, but kept getting side tracked...
 
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Old 04-28-10, 04:24 AM
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Hey Trooper and everyone else, Thanks again for all your help! I've decided to got with your original design with the BB-30 tank and a Tekmar 361 control. I really like the indoor reset option, like eveybody else! I can add the 260 later if I want, and do a direct comparision in fuel efficiency. It looks like I can use Taco 007 for all the pumps even the vs injection. I'm also going to add the webstone purge tee as the CST in the mixing ckt, just for easier purging. As soon as I get a chance I'm going to draw it all up, flanges, pumps et all, in as much detail as possible for future reference. BTW, what are you using for all your drawings?
Also, I finally RTFW for the MPO and on page 30 it does say that the MPO can handle 100F return water as far as thermal shock but that sustained operation below 135F with result in boiler damage due to condensation.... Just wanted to mention that because it always seems to be a topic of concern. Thanks again for all the help and I'll post the final desing ASAP
 
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Old 04-28-10, 04:51 PM
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I'm going to draw it all up, flanges, pumps et all, in as much detail as possible for future reference.
Be sure to post up the final design with all the bells and whistles for us to look over before you commence to building.

what are you using for all your drawings?
I have been using PaintShopPro 7 for a while now... basically a photo editing program, but I find that it works great for me for doing schematics etc... Mostly I start with a drawing I 'swipe' from someplace else and modify. If I'm starting from scratch, I use a 'library' of component drawings that I 'swiped' from yet another place... copy and paste... connect the dots.

the MPO can handle 100F return water as far as thermal shock but that sustained operation below 135F with result in boiler damage due to condensation
Yeah, that's the "CMA" clause. I think basically what they are saying is that the boiler is much more tolerant of occasional low temp return water, as in cold start on high volume systems, but you wouldn't want to design a system around that ability and expect a long life. With fin-tube baseboard and the like, it's not really a problem because the system comes up to temp quickly. If you were to use ODR on this boiler with a standard piping scheme, you would still want to set your BOIL MIN at around 140 or so.

We didn't get any feedback about my question of whether the boiler sensor should be on the supply out of the boiler, or if the buffer tank well was the proper location. So be prepared to experiment with that a bit. I'm don't know how to get in touch with the fella who built this exact system... but I'm sure he would have some good input. Hopefully he will read this and 'come on down!' ... last I heard he was planning on trying the sensor in the buffer tank, so his input/experience would be helpful here.

When you get it up and running, I think you will find that the best settings on the 361 are going to be a FIXED differential, and fairly wide... you want that tank to charge and then discharge to some degree to take advantage of the longer cycles that will provide. I think if left on AUTO DIFF the 361 will attempt to 'optimize' based on what it knows... and it won't know there's a buffer tank out there, no way to tell it so. That's one thing that I was hoping Tekmar would somehow add to the firmware... settings for a buffer tank.
 
 

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