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Joined on December 23, 2003

Last Post on May 1, 2011

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good point brad

@ May 1, 2011 11:52 AM in water thermal expansion & pressure

"... Anyone that makes too much of a deal about that should take up knitting,..."

you're right, technical trivia is only going to confuse bubba the plummer/heeting pro. little extra knowledge is for the birds.....

lets keep it simple, R10 works anytime and all the time for slabs, short cycling a fact of life no way around it, 2 boilers work better than 1.........  gotta keep things at old school for sure....


need more info

@ April 30, 2011 4:28 PM in water thermal expansion & pressure

first off, i do agree water is not that compressible, but it can compress and that's good information to know, used or not.

as far as the steamer, I would ask:

what was the temperature change?  

what was the volume change?

what was the change in volume ? percent wise?

was the change transient or stable? 

seems a lots going to happen going from 250psi to 25 psi.


if you go here you can see that volume expansion is also dependent  on temperature, as temp increase water will expand even more and more, its not linear, or proportional.  look down on at the chart for water.

life outside the boiler box.....

@ April 30, 2011 12:12 PM in water thermal expansion & pressure

ME, the wall thickness of the pipes  were a couple of times the ID.  somewhere i have a piece of it laying around.

life does exist outside your pex world, sometimes it comes in handy knowing all the facts, you're not so likely to go off course somewhere.   graph comes from btw.

JDB, high school physics is a great start, but a lot of times you first learn simple approximations then later learn why those approximations aren't totally valid.

but you seems to agree water is compressible away.......  it either is or isn't.

if you change the density of a sample of water, its volume will change.  we all know water expands(ice) why is it so hard to believe it doesn't contract?

standard practice

@ April 27, 2011 10:23 AM in oversizing mod/cons YES!!!!

NRT i didn't know it was standard practice to use an indoor tstat with ODR?

if you increase the Tstat from 68F to 74F how does the boiler know to increase the supply temp?

as your post suggests, short cycling should not exist then.

I am confused NRT?

@ April 26, 2011 1:54 PM in oversizing mod/cons YES!!!!

I thought  if you hooked up an outdoor sensor to a modcon ,  the circ would run anytime you were below a certain outdoor temp?

  I'm not sure what you mean by "'firing differentials"?

what do you call a short cycle heating wise?

if your ODR calls the boiler to run and the outdoor start up is 60F and its 59F outside how will the boiler act?

I don;t agree boilers need to modulate down to 5 btu's to solve short cycling heating problems.  that becomes inefficient in itself.

maybe the other way around?

@ April 26, 2011 12:33 PM in Baxi Luna 24fi motherboard issues?

sounds like its the sensor that 'sees' the pressure that's bad.  so you could say the system losses pressure in a backward way, when really the board stops seeing pressure.


@ April 26, 2011 10:54 AM in oversizing mod/cons YES!!!!

I thought the idea behind ODR was constant circulation and constant firing? so if the boiler can't modulate down any further in mild weather it starts short cycling?

as I said in another post, micro zoning is a bad practice, unless you pull heat from other zones instead of firing a boiler when the zone is only 10% of minimum fire; or you use a buffer tank.

can tekmar also monitor indoor temps a long with outdoor?  can they let the homeowner make small adjustments to room temp,  I understand most  ODR can't do this?

volume change vs pressure

@ April 26, 2011 10:45 AM in water thermal expansion & pressure

I don't know the answer either, but I do know at 55,000psi you can compress water by 10%.   another words, compress 10 gallons of water down to 9 gallons of water.

yes & no NRT

@ April 25, 2011 5:30 PM in oversizing mod/cons YES!!!!

you are right, the boiler can modulate down to ambient temp.   but the ODR is forcing it to modulate down without giving it room for longer burn cycles with time in between.

this means allowing a larger dT.  remember I'm talking about the shoulder season,  my guess is wider dT at this time of year would go unnoticed.

 the time you want to worry most about efficiency is when you are burning the most fuel per day, around here that would be dec,jan,feb.   in the shoulder season, according to viesmann, you'll be at the top of efficiency away.  

but this is all talk, you only have a couple different size boiler out there to choose  from.

STILL, the ODR should be modified to go off of constant circ  firing mode when under say, 30-40% min modulation.  you could do this in the ODR or the boiler control.  so then it starts acting more like FHA or older style boiler w/tstat.

the BIG saving comes from lower boiler supply temps, the saving don't really come from  running constant circ. though its part of it.  so you widen the dT and you save more fuel.

ADDED:  this now ties the 2 posts together, short cycling and oversizing.

good point nrt

@ April 25, 2011 10:38 AM in oversizing mod/cons YES!!!!

my main idea was looking at the period of greatest usage and sizing for highest efficiency.   around here, that would be dec,jan,feb. 

did you read my post on short cycling?  that would clear up inefficiencies in that department.  ODR falls apart under minimum fire.

by the way, I think your math is a little rusty, .04% of the year is a little under 4 hours?

can't you

@ April 23, 2011 6:11 PM in Indirect hot water heater with gas steam boiler?

force a steam boiler only to make hot water in the summer?   seems this would be possible?   would save money if you can run the steamer at 170F during summer for making DHW.

apples and oranges, nah...

@ April 22, 2011 6:16 PM in short cycling in shoulder season, fact/fiction/improper design ?

""""""The attempt to compare forced error system to a multi zoned hydronic
system is no where near fair. Can your forced error system handle micro
loads? Does your forced error system have a 5 to 1 turn down ratio? Does
your forced error system have thermostats that are located in different
loss zones, or is it one stat centrally located in the core of the
home? See, no comparison... Apples to Oranges.""""

ME, i gotta disagree a bit here.  just because you can make a micro load,  doesn't make it a good idea, and the bucking modcon lets you know.  most boiler operated systems I have seen only have 1-2 tstats.

 how well does an iron boiler take these loads? my guess it acts similar to the FHA or its hiitting its high limit, which in turn is no good either.

 still doesn't make sense that the FHA runs once an hour and the modcon bucks and kicks trying to run constantly- a fault of ODR in mild weather..

i see no reason why not allowing it to cycle once every 1/2 hr (for example) and give it a 1/2 hr break would be a bad idea?  as you say on/off/on/off just sends heat out the vent and overshoots its set point, so you're loosing your constant circ modcon efficient then.

boiler size- water temp

@ April 22, 2011 2:40 PM in oversizing mod/cons YES!!!!

boiler size,  water temp no connection.

as per the graph, boiler load is inversely proportional to efficiency.   harder you drive the boiler, the lower the gas mileage. 

eliminating short cycles, modifing ODR

@ April 22, 2011 12:14 PM in short cycling in shoulder season, fact/fiction/improper design ?

ME I agree, you can't do much about DWH cycling, with recircs and the mini smart things get worst.   but machine cycles are the facts of life, you need to design them in, its really not that hard.  think of a punch press that cycles all its life.  or your poor truck that has to run from -25F to 100F with 170,000 miles on it.  think of the poor electronics that work in those conditions and then worst, think of an airliner flying from fairbanks to hawaii , thats a thermal cycle.

micro zones are the fault of the design, why in the world would you hook up a 500btu load to a 100,000 btu boiler?  a better design would be to try to move water from higher mass loads to the micro load between cycles, similar to your idea of moving water from south face rooms to north facing.  I understand if a customer wants a tstat for every radiant panel thats what you do, but thats not what this discussion is about.

to me, the fault in ODR/constant circulation is in the shoulder season, when loads are say 25-35% below minimum fire, system should switch over to a modified indoor tstat bang bang operation.  this will fluctuate indoor temps more, but in the shoulder season it should be hardly perceptible.  this also assumes your sizing is closer to actual.

I no longer think outdoor temp sensing only is the way to go, adding an indoor sensor and compensating  ain't rocket science

trying to keep the boiler running constantly in the shoulder season is a poor design when the FHA system stays off for hours at a time.  which would you call efficient? isn't a system thats off 100% efficient!!!

thanks tim

@ April 21, 2011 5:15 PM in readings that point to efficiency

I'll comment more later, I guess what I'm really curious about is the hit efficiency takes when short cycling, its talked about a lot here, but there seems to be no hard numbers. 

it seems short cycling itself has no hard definition either, so that makes it more of a fuzzy subject.

so, thats why I'm asking about the combustion side, I think that's where the answer lies in the short cycle debate. also  combustion stability/instability should be able to define short cycle, certainly any time before things get stable can be considered short.

slight correction

@ April 21, 2011 5:04 PM in short cycling in shoulder season, fact/fiction/improper design ?

I 've thought about this some more, the programming modification should be made at the boiler, or in the boiler control programming and not the ODR controller as in the tekmar.

I wouldn't really call it faulty programming, just an improvement that could be made.

this problem/complaint  of operation has come from the pro's here, I just thought I might have a solution.   more later...........

readings that point to efficiency

@ April 21, 2011 11:20 AM in readings that point to efficiency

Tim, what numbers can tell you the most about the efficiency of the equipment you are testing?

if you didn't know, what numbers tell you the equipment is still cold and not up to a stable operating condition?  how much do they change?

I'm mainly wondering about inefficiences due to the equipment on cold start up?  as in short cycling?  what are your thoughts?

short cycling in shoulder season, fact/fiction/improper design ?

@ April 21, 2011 11:09 AM in short cycling in shoulder season, fact/fiction/improper design ?

in houses with FHA heating, I never see this as a problem.  early fall, late spring, furnace will run in morning, be off most of the day and run in evening, but they do not short cycle. short cycling- series of on/off on/off's in relatively short time periods. 

  so why do boilers apparently have this problem? improper design? improper set-up?

flaw in outdoor reset control strategy?

oversizing mod/cons YES!!!!

@ April 21, 2011 11:01 AM in oversizing mod/cons YES!!!!

with some modifications, this is the better approach for staying in the higher efficiency areas of the graph.  see graph below.    the graph clearly shows in worst case 160F supply temp, oversizing by 30% would be beneficial.  of course if the system can be ran at supply temps below 130F this wouldn't applied.

the error lies in the control design of these boilers and the famous tekmar's.   they are designed with inherent flaws that force you to use smaller boilers that need to be driven harder and less efficient.


@ April 21, 2011 10:36 AM in question about zoning hot water system

I well understand ME's comments, I 'm only asking for some verification that 2 boilers will be well worth the cost when 1 boiler is possible?

I know ME likes big complicated systems,  I agree, they are fun to design, fun to go through start up, but I am tending toward the masses where simple systems can be far more practical..  but lets see some numbers here.

use the graph below as an example.    I could see maybe saving 10% on and around design day.

if house requires 100K btu do you suggest two  50k's or two 100k btu?  boiler makers only seem to offer 2-3 different sizes for typical home sizes.  Seems ME is suggesting two 100K here?

Ok charlie

@ April 20, 2011 3:30 PM in question about zoning hot water system

forget I said oversized,  lets get back to the 90% of the other comments I made.

lets quantify  "that Depends".  I made my arguments......

cost of short cycles

@ April 20, 2011 1:04 PM in question about zoning hot water system

I agree on paper that 2 boilers run more efficient.....  but at what cost?

how many years will it take to break even on the 2nd boiler?   How much waste is really going up the chimney in the fall and spring when loads are small to begin with?

you would be much further ahead to use the cost of a 2nd boiler insulating the house.

DO we really care about short cycling when its 48F outside?    where the real problem can be the wrong control for the boiler or if the boiler is way over sized.

LETS SEE some real numbers on this subject, not just idealisms.    if you loose 15% eff on a day that needs only 10% heat, is it cost effective?
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