Buffer tank ,Mod Con, how to?

furnacefigher15

It's not shutting

off on the high limit, but the reset limit.



Yes, raising the supply water will ultimately raise the return temp.



Energy flows from High to low, and the higher the spread the faster. I don't care what kind of energy it is. In this case it is heat energy.



If the room temperature is 70 and the supply water is 80, that's a 10 degree difference.



If the room temp is 70 and the supply water is 90, that's a 20 degree difference.



The greater the difference between water temp and room temp, the more heat emission there will be from the boiler water to the room ultimately causing a greater difference from the water leaving the boiler to the water returning to the boiler.



The boiler has a minimum output of 25600 btu, and in order to get the boiler to run continuously on a call for heat, the heat emission from the baseboard has to match that #. In order for that to happen, the difference between the supply water, and the room temperature has to have a certain spread.



The spread can be achieved by either arising the supply temperature, or lowering the room temperature, or a combination of the two.

Ronbo

confused?

sorry for any cunfusion but my space does get heat. in my test above i gave all the outcomes. it took only 45 min to raise all the zones 2 degress.

with that said i did the test to see how many btus my furnace was using per hr with all zones calling and trying to determine if those btus where being used by the baseboard.

my thought was if not being used then there could be a flow problem or a radiant release problem with the baseboards.

The test for me at least shows there is some type of problem along those lines because im not using 33% of the btus.

The boiler puts out 120,000 btu.

it ran at 32% the whole time.

i have 61,410 worth of baseboard output.

32% of 128,000 is 40960......where is the other 20 450 btu going? Well back in the boiler raising the bottom temp and pushing the top....thats where i think its going.....question is why? im thinking flow because even with dust bunnies i aint losing no 33% but who knows? now the boiler pump is stronger than the system pump so i guess its sucking it all in by design then?

Ronbo

yupper

yes thats what im talking about....slant fins test rating are based though on my test senerio 70 degree indoor temp ......supply water at 140! So i still want to know about that 32% and i want my jets to win and 3 other teams to lose! lol

PeterNH

lost and found

Hello,

32% of 128,000 is 40960......where is the other 20 450 btu going?32% of 128,000 is 40960......where is the other 20 450 btu going?



The boiler only produced 40960  btu's

There is no missing, 20450 btu's.

The 20,450 is' not "going" anywhere, because is was never produced.



Peter

Paul48

Actually

Because of significant restriction in the boiler itself, the 0014 is pumping at around 12.1 GPM, and the 008 running at max is around 15.Which means it's taking just under 3gals of return water back. 25%

CMadatMe

Don't Think So

The 008 at 0' of head may move 15 but not on a zone call. I've read the Ultra manuals and cannot find one missing piece of info. Why you cannot run a 40 delta across the boiler. Reducing the flow rate on the boiler side will enable you to pull out the btus on the secondary side running on a 20. The secondary side is just pulling btus made on the primary side it doesn't care how they are made. Still think the LLH is the way to go with a smaller boiler pump moving 7gpm out to the LLH. Seems to me 7gpm takes care of your needs. The colder boiler return water temps will be an asset.

Ronbo

?

it ran at 32%(40960) the whole time.......and had to reduce /increase a couple times but ran 95 % of the time at 35% and that extra is going somewhere and i think i just found out. 1 1/2 header/manifold /other parts like seperator /pumps/exchanger/parts/etc...... 10% up thu flu (depending)) all release heat and also the dusty/painted baseboard all lending a hand was not accounted for in my findings. time to clean some base board/add some baseboard which i planned to do anyway for lower temps plus a buffer should do the trick.

Ronbo

maybe but

maybe your right but i and most of you guys who install would/should be worried to not follow manual. it says that the 0014 supplied with the boiler must be used in a primary / secondary install .......page 10 NOTICE and page 10 uder notice it specs the pump to be used for each model in the circulators notes.

PeterNH

new math

"and that extra"



Do we  agree there was only 40, 960 but produced?

Yes or no?



Do we agree that you have radiation that can remove up to 62,000 btu's hr +/-

Yes or no?



If only 40,960 btu's were produced, and all of it radiated, how can there be

20,000 btu's missing?

Sorry, i'm missing something, as i didn't learn "New" math, so i need to take this one step at a time.





Peter

CMadatMe

Manual Also

Gives you boiler head loss at different flow rates and I'm not pri/sec piping using a LLH. The 0014 is given to move the needed gpm using a 20 degree delta which is just about all you'll see using pri/sec. At that gpm the 0014 is required to overcome the boiler head. Slow down the flow rate you reduce boiler head. Not a Weil user or fan but a good question for the tech dept. Still feel LLH, larger boiler delta is the way to go.



Wouldn't installing a buffer tank also defy the manuals stance for primary/secondary?

Ronbo

better

Hey Pete check my last post at 451pm.....it explains what I missed.  I run much lower temps today and stay stable after some tweaks to the delta pump and new testing.....had 132 target going today mod @ 25% with no problems (I had high @165 and low at 110)but that's with the house as one zone.....will shoot for lower temps tommorrow. Is there a way I can wire my thermostats to come on when called upon by only one locations thermostat  but shut off when each of the others hit there desired marks at their individual locations?

meaning all come on when location 3 calls for 70 but if 3 is not yet there

 1,2,4 will still all shut off when they each hit 70

this will start them off as a team but end each on there own

PeterNH

ouch

Tekmar has network thermostats that "talk" to each other and will hold off some zones from starting to enable more than one zone to start at the same time.

Only one problem.

Ouch $$$$

There is likely a way to do it with relays, but it would be quite a project.



Peter

Jean-David Beyer

Only one problem.

Only one problem.

Ouch $$$$



I guess so, but how much more fun it will be with a really interesting control system! My guess, since we do not discuss pricing explicitly here, is that it would be less than a good model railroad setup, and some people willingly pay for those.

Ronbo

one more thought

By running all the zones as one am i risking damage to my 008 with more head?

also one more thought on a buffer idea. If I ran all the 3/4 returns to a tank then ran 1 1/2  from tank to the 1 1/2 return on boiler that would keep only my last used return temp in tank(more than likely close to the same temp for next usage) and ready to roll and add mass. this would let me use a cheaper tank and retro fit fittings. Would this also add more head? LOL that's my last crazy idea of the day...i promise. PS dang jets stink! Ty again my brain really hurts from all this.

furnacefigher15

Be more specific

Do you mean all zones in series, or just running all the zones at the same time?



If all in series, you would need to recalculate the head requirement of the pump.



If just running all the zones at one time, the head is the longest zone.



Forget about the buffer tank.



Focus on settings, and adding and cleaning baseboard.



PS add the baseboard in series with base board that already exists, not in parallel.

Ronbo

I'm a high maintenance poster eh?

i just installed jumpers across the zone valves 1,3,4 and removed the existing wires to the zone valves 1and 4 , so when zone 3 thermostat calls it opens the  1,3,4 zone valves at the same time then the pump kicks on.

Ran everything for one hour at target of 130 mod @23% avg and held on tight to a 7 degree delta the last 45min......is it the low return temp (south of 130)or the higher delta that condensates more? If temps in the home are OK in each zone, I think this could work but i want to replace the tricked out (rigged)008 with a standard 008 or 007 and sell the delta 008 I have the return sensor installed on a cold water line to keep it at peak flow ,lol. The longest run is a 3/4 pex 191 ft run which includes 46 of baseboard to my addition, figure 14 elbows.....what size pump do you think?

If I have not said it enough, thank you all for your continued help with a newbie.....you all made me laugh.....cry.....wallow in self pity and rejoice,lol

PeterNH

MRR

Yes Jean,

Far, far, far, far, less. Trust me, i know all to well.

One could have one of every Tekmar device, in the catalog, and still miss it by a mile or two.



Peter

PeterNH

condensing

, is all about low return temps, less than 130.

That's why, furnacefigher15 and others suggest adding more and arranging existing baseboard in series.





Peter

Ronbo

?

arrange existing in series? what do you both mean by in series.....one long loop/zone as opposed to three side by side loops? 

Jean-David Beyer

condensing is all about low return temps, less than 130

This is true. And while condensing starts as you get below 130F, you get only a little at that temperature. In other words, at 140F, your mod-con may run at an efficiency of 86%. At 130F, 87%. At 120F, 90%. At 100F, 94%. At 80F, 97%. At 60F, 98%. At 40F, 99%. These numbers assume you are running at maximum firing rate. Since this is unlikely, your efficiencies may be a little higher than this at lower firing rates.

Ronbo

delta vs 130

So high deltas are more about achieving lower return temps to get under the magic number 130. Not the fact that the return temp is a greater distance apart from the supply temp?

Also in my case, even if I can achieve a 20 degree drop from 132 to 112 return temps I am only looking at 3-5% savings max? they may not be worth the buffer trouble then. Ill add more baseboard as needed and find my curve/refine things a bit. I went from a boiler that was a 100,000 btuh all the time at 73% eff burning oil to a boiler thats 87 %and up modding at 40,000 btu that was a big jump.....my mistakes cost me 4% or so.....live /learn i guess. 

Jean-David Beyer

It depends. Things are not that simple.

"even if I can achieve a 20 degree drop from 132 to 112 return temps I am only looking at 3-5% savings max?"



Those savings are the ones resulting from condensing. But it seems to me that the modulation function gets you even greater savings, and an increase in comfort besides. Even though the gas probably burns at about the same temperature whether you are firing high or low, the transfer from the fire side to the water side of the heat exchanger increases as the temperature of the water decreases. So more of that heat goes into the water and less up the chimney That is why mod-con boilers need a blower to assist air flow through the burner; the exhaust is just not hot enough to get sufficient flow up the stack.



The comfort results from delivering just the right amount of heat to the house instead of delivering design day heat most of the time when it is not needed. The temperature swings are much less when you have outdoor reset controlling the boiler temperature. This is even more important if you have a radiant slab zone where my swings were sometimes close to +|- 4F that I found really unpleasant.

NRT_Rob

I disagree with scott on this

the purpose of a buffer is to reduce cycling.



if the mod/con doesn't cycle when it sees the return water, then you don't need a buffer. this will occur with any system with a heat load over the min-modulation of the mod/con boiler.



But it only happens when you are over that load. the buffer tank is there for the 50%+ of the time that many systems are under the min-mods of the boilers on the system. If your min mod is more than 50% of your peak load, then you're in cycle-town for more than 80% of your heating hours.. close to 90%!



I agree that zone sync is a great alternative as well. but an oversize boiler will NEVER be more efficient than a right sized boiler. A right sized boiler is under 50% max fire for nearly all of the heating hours already, and you don't pick up that much going lower... whatever you gain would be lost with the problems of an oversized boiler.



the only difference is that with mod/con boilers you should be sizing by MINIMUM modulation as well as maximum. if your boiler has 4x the max output over another, but the same minimum (not that those exist, but still...)... then it's not "oversized".

NRT_Rob

method 3

is on the outlet of the boiler, which is the method I prefer.



then you can't satisfy your load until after the tank is heated.



heat in the bottom, out of the top as well... but that requires a sensor watching the outgoing water temps... then you don't initiate a demand until the tank is depleted. That typically requires external controls but some mod/cons have external sensing capabilities.

NRT_Rob

primary secondary

DELETED. double post.

NRT_Rob

primary secondary

is primary secondary. how much heat is extracted is about flow rates and temperatures, not how many different sets of closely spaced tees you are using. The best way to avoid hot water return is not to use primary/secondary... but then you better manage those flow rates well.

NRT_Rob

why would you replace the pump

wider firing differential would help... twice the difference is twice the firing length. but trying to achieve this with a slower pump just makes a short cycle worse. you have to get all the water in the circuit through the boiler fast enough to move the BTUs out.



slowing down the boiler circuit will not help achieve that. increasing flow in the secondary circuit would, if we do have a situation where we are heating the boiler, but not the rest of the circuit, too fast.



You don't get to cheat unless that boiler circuit has a... wait for it... buffer tank on it and the problem is already too little flow. but just changing the speed of water around a ring of pipe, without actually extracting those BTUs at a different rate, isn't going to change anything.

CMadatMe

Rob

Don't know much about the Ultra itself but since the boiler is oversized wouldn't it make sense to get the boiler side delta out to 40 reducing the flow rate out to a LLH. From there he can run his 20 with the VDT. If His heatloss is only 60K wouldn't getting 7gpm out of the boiler be better for him then the 13gpm? The boiler return would be seeing substaintially colder return water temps.

scott markle_2

control

Rob,



Low firing rates produce more condensation (higher efficiency) than do high firing rates,

IE. a big boiler modulated down and making 60k will burn less fuel than a small boiler in high fire making the same 60k. Do we agree here?



I have demonstrated (years ago) in my own house that an oversized boiler can be "forced" to operate highly efficiently and without excessive cycling. I don't use a buffer, just the mass of a slab, a fixed min firing rate, and an interval based reset control. I could see how an oversized boiler in a low mass situation could be paired with a buffer to accomplish the same thing. I'm certainly not recommending intentional over-sizing, but with some out of the box thinking an oversized unit can be wrangled to run efficiently, even potentially exceeding the efficiency of a smaller boiler that spends much more of it's time in a higher firing rate.



Most boiler firing rate logic is determined by the "perceived" load, not necessarily the actual load. If ample amounts of cool return water are provided the boiler will generally ramp up to maintain target.. thus adding mass to an oversized boiler can have the unintended consequence of unnecessarily ramping up the firing rate. Agreed?



I have noticed some real improvement in the logic used to govern the firing rate and burn periods on the newer generation Viessmans. They are much less eager to reach target in a hurry, and more willing to allow an over-shoot in the interest of prolonging the burn.



To the other poster that complained about the expense of Tekmar. I say look again, the new wiring centers and house controls are fairly reasonable. If all you want is zone sync. you can skip the house control and do this with a wiring center and Tn2 stats alone.

NRT_Rob

have to be clear

heat output = GPM x 500 x DT



If you cut flow in half and double the DT you haven't increased apparent heat output. To increase the DT without cutting the flow, you have to increase the load (pull the heat out faster). That means higher flow on the load circuit, not the boiler circuit, unless you are already under-pumped on the boiler circuit which is nearly impossible in most cases.



Increasing the FIRING DIFFERENTIAL, or Hysteresis setting on a boiler, will increase the firing time linearly. If it's set to fire to a 20 degree rise, changing that to a 40, with a 10 degree increase in supply water temp to make the average temp work out, would double your run times over what you are seeing now. That is helpful. In fact the advanced boiler controls with 'variable' boiler differentials will do that automatically in low load conditions to reduce boiler cycling.



but you can't increase output or reduce cycling by slowing down flow. Ever. In any circumstance. The only thing reducing flow can do is increase temperature rise which might be of value in some circumstances, but not this one.





If you have an oversized boiler, simply your options are only:



1. Zone Syncronization controls

2. Buffer Tank

3. Wider firing differentials (NOT loop Delta-T's)

4. Less, larger zones with higher flow rates and hopefully some mass like radiators or slab floors.





Wider Loop Delta-Ts might be better from a condensation standpoint and thus for efficiency: that's true, though I don't think most boiler manufacturers will allow you to run a 40 degree rise across their heat exchangers, most want you to stop at 30. But that will not help an oversize boiler with cycling control, it will only help with condensing efficiency. And Frankly, I am not even convinced it will help with that as I believe outgoing exhaust temps are related to the supply, not the return temps, but I am not a boiler engineer and I'm not sure which is most important for efficiency, return or supply temp.

NRT_Rob

Agree

but with the same boiler firing logic determining when to fire, the apparent load on a boiler should not be any different with a buffer on the supply, or the return.



I don't believe you will ever get better efficiency out of an oversized boiler than a right sized boiler. By what I see with bin data (and I'm going to contradict the other post I made last night with the 50%-80% stuff, as I stopped looking at heating HOURS and starting looking at heating BTUs with my bin data):



1. Right sized boiler will be at under 20% modulation (min mod) for about 10-15% of heating BTUs per year.

2. Same boiler will be in the 20% to 50% range for about another 45% of heating BTUs.

3. and will be over 50% mod (where oversizing could help) for about 40% of heating BTUs.



If you double the boiler output, you are now:

1. in Cycletown (under 20%) for 45% of heating BTUS

2. at 50% or under for 55% of heating BTUS.



So you've only increased the percent of BTUs in the "sweet spot" by about 10% of total. But you've increased the percentage of your load that is cycling by about 30-35% of total.



That can't be great for the lifespan of the boiler, or for its efficiency, though post purge controls could help. and I dont' think going with a 50% oversize or anything like that yeilds much different results... your cycle period is going to increase faster than your "sweet spot" increase because cycle period BTUs occur at lower, more frequent loads and your sweet spot is extending into colder, less frequent hours.

Ronbo

Idea

I havea problem with my toe kick in the kitchen not coming on with low temps ,the built in aquastate comes on at 140 and off at 110. Can it be fixed by 

1. installing a relay to the end switch of the zone valve.(the heater is 100 and the valves are 24v)

2. removing the toe kick and adding element (8' long in every other bay of the joist bays below the kitchen) this I was told is much like radiant heat and would also help with adding element to my zones. There is a drop ceiling below this area so it would be easy(but would too much heat go downward also through the drop ceiling?)

CMadatMe

On the Right Track

So in the end, getting the delta wider on the boiler side (pri), ie 40, while still maintaining the 20 on the system side (sec) is a logical approach. In Viessmanns world 40 is the way to go for boiler delta and flue temp is generally 20 degrees higher then return water temp.

NRT_Rob

kind of

not for cycling control.



You'll pick up a little condensing efficiency that way, but you are doing nothing to control cycling. If you don't care about that, so be it... the thread is about buffer tanks, so I am assuming that was still the main focus.



good to know about the viessman DT spec though. If anyone was going to 'break the rules' I'd expect it was them

furnacefigher15

I wouldn't

I wouldn't replace the pump. I was trying to make the case to not lower the flow through the boiler.

furnacefigher15

I could not agree more.

Well said.

Ronbo

almost there

Ok so now  I have four zones running at the same time running off one therm, which  is 4 -3/4 copper returns/supplies and running 5 degree delta at 120 degree /modding at 21%. In my mind thats as low as I can go without throwing money away ( lower than 20% is fruitless yes?) 

So if I run it all in series(one pipe) to get lower temps on return and greater delta will it make sense? Does condinsate refer to the supply or return temp being lower?

1st off- 4 pipes at 4 gpm=16gpm  vs 1 pipe = 4gpm seems odd to me but I guess if  4 gpm is 20 degrees cooler vs 16gpm 5 degrees cooler

So the savings(btuh) i reap (condisatinting )goes directly toward current water heating yes? wont it just be applied to my already low of 20%? meaning to take advantage i would have to run hotter temp?

furnacefigher15

It's not that easy.

Sounds like you have it tweaked well enough.



Leave it alone.

Ronbo

Found a problem?

I think I found a problem. My expansion tank and auto fill is located on the flow side, not the suction side of the 008 pump. Does this not slow thee pressure/flow greatly!

mage182

still short cycling.

I am in the same boat. My modcon is chort cycling pretty much all the time. Here are some tweaks I've done to improve it.



-Turned down max fan speed for heating from 5500rpm (default) to 2000 rpm (min is 1300rpm)



-Set high/low diff to -7/+5



-Remove IHW tank priority. The tank is piped like a zone, so if the zones want to come on while I'm making hot water, let them, it just increases the load.



I'm still short cycling, but it's been a little better. My plan for the spring once heating season is over is to combined the two small zones on the first floor of my house to create one larger zone, and to replace all the multipak 80 baseboard I put in with cast iron baseboard which will provide more load. Just have to figure out how to join the sections together and hope I can find some end caps that fit.



I'm hoping the increased load of those rads will increase cycle times and provide more even heat to the rooms.



Great post.