Joined on January 9, 2009
Last Post on May 23, 2013
@ May 23, 2013 9:00 AM in Don't store a B-tank in your trunk!!When I was a kid, I was in France and saw a guy welding a guard rail on a bridge. He had a gas torch and a tank providing the acetylene. No oxygen, it used atmospheric air and the acetylene came from a very low pressure tank (galvanized sheet metal) with water in it and a basket containing calcium carbide. When he wanted the gas, he operated a lever that put the basket into the water. Primitive. The torch tended to smoke (not enough oxygen, I guess).
@ May 11, 2013 8:53 AM in Primary Secondary ProblemI'll say. This was shown to me decades ago by a woman where I used to work. She was a computer programmer, and I was doing programming at the time too. She allegedly had 12 years of experience, but she was the worst programmer I ever met in my life and she thought she knew everything. Her programs would run 1000x (I am not exaggerating) slower than they should have.
Actually, she did not have 12 years of experience. She had 6 months of experience 24 times and never learned anything from them. Fortunately, she left the company to become a nun. I hope it was a contemplative order and did not have to interact with people.
@ April 27, 2013 8:46 AM in National Plumber Day!Lots of ways of looking at that.
1.) If you eat the whole thing, that is a lot of diet calories (kilo-calories), and you can convert those to BTU.
2.) If you feed a steer all the grains and other additives that they typically get in this agribusiness age, they produce lots of methane. They would not do that if they were fed on grass during the year, and hay in wintertime. But the reality is that most are not so fed. And the methane they produce is the main active ingredient in natural gas (and is something like 10x or 20x worse for the environment than CO2). So there are lots of BTUs in all that methane.
3.) If you keep the steer as a pet, it has a body temperature, perhaps around 100F, so if you kept it indoors, in a well insulated house, it would contribute to the heating. And you could, if you knew the area of the steer, calculate the BTU/hour they produce.
@ April 26, 2013 9:02 PM in National Plumber Day!I have an idea where we would be without qualified plumbers.
I had occasion to live in a house in a town so small, the government rented a room in the next town's borough hall because they could not afford a building of their own. There were two dirt roads in the town at right angles to one another. The roads had no names. The buildings were numbered. There was cold running water from the little stream that ran down the hill: no pumps, just gravity feed. The sandstone sink emptied back into the same stream. The "facilities" for the house I was in was a two-holer outsde. It would have been a 4-family house, but one of the downstairs family quarters were for farm animals; the heat the animals gave off in the winter partially heated the house.. Actually there were no stairs because the hill was steep. So even though it was two stories, all entries were at ground level because the ground came up to meet the upper doors.
I do not miss it at all.
@ April 23, 2013 11:55 PM in What's WrongChris and I disagree about some things.
But here I must applaud his initiative in caring enough about a homeowner whose system is not right to take so much time to make it right. And the homeowner was probably not even one of Chris's customers.
if anyone can explain why the boiler water temp does not correspond to what the manual says it will be
@ April 23, 2013 11:47 PM in Vitodens 100-W temp setting questionIf your boiler is anything like mine, if you disconnect the outdoor reset, the boiler will go up to maximum allowed firing rate, ignoring the outdoor temperature. In other words, it will assume outdoor temperature is as cold as it can possibly get. That will make it put out water as hot as it can.
@ April 21, 2013 10:20 PM in Direct Pump TT Solo 110 with 3 zonesFrom my point of view, you just changed "the whole entire point" again. I continue to assume you are doing all this in good faith, and that your perception is that you have held the same point throughout. We are clearly still not talking about the same things. The longer this goes on, the more you seem to me to be changing the point and it is tough for me to keep up with you.
"You decreased the modulation rate so YOU NO LONGER NEED A BOILER PUMP
MOVING 7.1 GPM. The pump only needs to move the flow require to move out
the btu/hr the boiler created at your new HIGH FIRE...Which is about
3.5gpm. If we could figure out the head of that HX at 3.5gpm you could
install a smaller boiler pump thus removing the flow of boiler supply
and btu/hr running to that boiler return. That's been my whole entire
point. When you did what you did a few years ago you where on the right
track you just didn't finish the job."
I cannot safely reduce the flow of the boiler circulator because I reduced the maximum firing rate (not the modulation rate; to me modulation is changing the firing rate; so modulation rate might mean the rate at which the firing rate can be changed, and in a PID system, this is difficult to specify in a single number, you need at least two numbers, such as gain and damping ratio, for example) from 94% to 55% ONLY when the boiler was heating that little zone. When I run just the slab zone, that takes at least 4x more heat than the baseboard zone, the maximum firing rate is now set at 90%, and when running the indirect, it is still at 94%. I guess the indirect is a red herring since when that is running, the boiler pump is off, and the indirect's 007-IFC is on.
If I concede that when running the small zone, that a slower boiler pump might suffice, I still do not see why it would make any difference other than lowering my electric bill slightly. In other words, pumping 3.5 gpm from the boiler and leaving the heat of the other 3.6 gpm in the boiler is different from pumping 7.1 gpm from the boiler and returning 3.6 gpm to the boiler is different how? If it does not change the heat rejected by the system, how does any of that matter? You say the returned water will be cooler, and I do not see that. But even if it is as it mixes through the return T, it immediately mixes with that extra hot water in the boiler, so it is all the same as far as condensing is concerned.
@ April 21, 2013 9:23 PM in Direct Pump TT Solo 110 with 3 zonesMy position on this changes as my understanding of what Chris is talking about changes. If I accept the one where it was said that all he was trying to tell me that my boiler was oversized, and some things I could do about it, my positions are as follows:
1.) I agree that it is oversized.
2.) Since I cannot lower the firing rate below 16,000 BTU/hour without cycling, and since I did not want it cycling 12 cycles per hour, or whatever it was, I made several changes.
i.) I raised the minimum supply temperature from 85F (or whatever it was) to 110F. This increased the amount of heat rejected from the system into that heating zone when it was running, slightly decreasing the cycling rate.
ii.) I increased the boiler differential from 10F (default) to 15F, and that reduced the cycling rate some more.
iii.) I reduced the maximum firing rate when the boiler was driving this zone from 94% to 55%. By itself, this would not matter much, but at start up it helped a lot because the delay through the feedback loop was so long. Before I did that, the boiler would initially fire at 50% (I cannot change that), and it would then run up to maximum firing and rush to the upper limit before the control could lower the firing rate. By limiting maximum firing rate to 55%, boiler temperature went up slowly enough that the feedback of the controller could catch up and lower the firing rate to minimum. This further lowered the cycling rate. It is now between 5 and 6 cycles per hour (depending on outdoor temperature) that I decided was good enough.
I had done all this by a couple of years ago.
2.) We then spent a lot of time confusing one another about what Chris was talking about. Was he trying to help me get more heat out of the emitters by increasing the delta T? I though he was even though doing that would reduce the heat out of the emitters.
3.) We then confused ourselves about getting better heat transfer through the boiler, also by increasing the delta T there, which would also actually reduce the transfer rate and efficiency.
4.) Now we are just trying to reduce the return water temperature by lowering the flow through the boiler, and I do not think that is correct either. All the heat that is produced in the boiler either
i.) stays in the boiler if the boiler pump runs too slowly - \
ii.) Goes out of the boiler to the hydraulic separator and back to the boiler right away, or goes to the emitters. The heat that does not go to the emitters returns directly through the separator to the boiler. This is equivalent to 1.
iii.) The heat to the emitters is either delivered to the zone or returned to the hydraulic separator, added to the water going staight from the boiler, and sent back to the boiler, so this, too, is equivalent to 1.
iv.) Therefore the cycling rate is going to be determined exclusively by the amount of heat rejected by the emitters.
v.) Therefore, the only way left to decrease the cycling rate is to increase the heat rejected by the emitters. How is this to be done? One way it is not to be done is to reduce the flow to the emitters in order to increase the delta T up there, because that will reduce the heat rejected, not increase it, because the average temperature of the emitter will be lowered.
I think this in what my position is, now that I think I understand Crhis's position. But I am not all that sure I do understand his position.
@ April 21, 2013 8:00 PM in Direct Pump TT Solo 110 with 3 zones"The bottom line is your boiler is to big for the heat loss, and
connected load. No matter what technological bandaid (circulator) you
think may fix it. It is still a boiler to big for the load. I think Hot
Rod was kinda leaning in that direction many posts ago. Chris has been
trying to point that out."
I have known that since about a year after I got that boiler; i.e., by the end of its first winter. I have even posted (not this thread) some things I have done to reduce the cycling rate to an acceptable rate, at a slight loss of efficiency.
So it that is all Chris was trying to point out, he could have done it in one sentence, without all this stuff about delta-T circulators, etc. I spent a week or more trying to understand what he was saying and whether it was about lowering return water temperatures, whether I understood hydraulic separation, and so on and so forth. I even spent some time trying to see what mental blocks I might be suffering from, calculated things from first principles. Now you tell me this was all wasted because all he was trying to tell me is that my boiler is too big, which I new years before this topic even came up?
@ April 21, 2013 7:09 PM in Direct Pump TT Solo 110 with 3 zones"No matter how you cut it....everything is predicated on the emitters
ability to disperse btus. If only half the btus go out to the secondary
the return mix is that much cooler."
But is it that much cooler? And even if it were, it is still the BTUs, not the temperature, that matters. If only half the BTUs go to the emitters than are going currently, does the return from the emitters drop enough? Clearly not, since less heat is leaving the system than before. The heat that did not go up to the emitters did not disappear. It went "backwards" through the twin Ts and were mixed together and fed into the boiler. So actually more heat was going back into the boiler rather than less.
Now if I reduce the flow through the boiler circulator, the mixing takes place in the boiler instead of the return T, but that does not make any difference.
As you said, "everything is predicated on the emitters
ability to disperse btus." and that says it all.
@ April 21, 2013 6:42 PM in Direct Pump TT Solo 110 with 3 zones"Paul I was trying to get JD not to change his secondary side pump but
his primary pump to shrink that primary flow rate down from 7.1gpm.
Would help in his short cycles and he would still stay in condensing
mode all the time even with a small need to increase his max supply
water temp. .."
Right. And Chris will not get me to change that pump until he can explain that pumping less heat out of the boiler will reduce the cycling rate, if that is what he was talking about all this time*. Because if I slow down the boiler pump, the heat will stay in the boiler, where if I leave it alone it will go up to the twin Ts and go right back into the boiler. How will that change the cycling rate?
The cycling rate is high because the firing rate is too high because the boiler is too big for the heating zone in question, so the heat into the system is greater than the heat rejected by the system into the load. So the only ways to lower the cycling rate are to lower the heat into the boiler by lowering the firing rate, or to increase the heat removed from the boiler by increasing the output into the zone. Lowering the heat into the system can not be done by reducing the firing rate by modulation, since it is already at minimum when rapid cycling is taking place. It can be reduced only by turning it on and off. And the most diddling the pumps can do is lower the heat removal from the system, not increase it.
*It seems to me he was continually changing the subject of what he was talking about. First, he wanted me to put a deltaT pump in the system loop to increase the delta-T in the baseboards to get a lower return temperature in the system loop and, presumably to get a lower temperature in the boiler loop as well. Later he seems to have switched to puting such a pump in the boiler loop, where it seems it would make even less difference in getting more heat from the boiler into the load. All his suggestions on how to do that will reduce (sometimes only slightly) the heat removed from the system, and that will not reducing the cycling rate, only increase it..
@ April 21, 2013 5:02 PM in Direct Pump TT Solo 110 with 3 zonesRight, and I doubt I get anywhere near 15 gpm out of those 007 circulators in my system. ;-)
@ April 21, 2013 5:00 PM in Direct Pump TT Solo 110 with 3 zones"If you agree with every quote I posted then why do I have to move the
same flow on the primary side as you do on the secondary side. My only
job is to move btu/hr to the secondary side."
You don't. I never said you do, and I do not believe it either. I think it would be unusual for the flow in the primary and the secondary loops to be the same. It could happen.
"Whether I can move your boilers full 71,000 btu/hr with 7.1gpm or 4gpm
to the secondary side what does that mean anything to the secondary
If I grant that you can, it would mean nothing to the secondary side.
"You can still move what ever gpm at what ever flow rate you want on the secondary side."
Not exactly. If I understand what you are trying to say, I have a fixed size radiant slab and piping, or a fixed size set of baseboard. In either case, I cannot reject the amount of heat I desire unless the flow rate is high enough that the heat emitted by the emitter is high enough, and there are only two ways of doing this, and one is not acceptable. The first way is to use a high enough flow rate so that the delta T is low, and the other is to raise the supply temperature so that it puts out enough heat in spite of the delta T loss from using a lower flow rate. And in the interest of efficiency, I do not want to raise the supply temperature.
"I just want to move out the btu/hr to the distribution system and get it
away from b-lining right back into my boiler return at the closely
spaced tee's thus keeping my boiler return from seeing an elevated water
Well, the way to get the most heat (not temperature) out of the boiler is to ensure that the heat exchanger is running at the lowest possible temperature. And to do that, you have to run a flow rate high enough that the delta-T through it is as low as reasonably practical. Now what prevents it all from coming back to the boiler is how much of that heat (not temperature) is picked up by the secondary loop and rejected into the load in the secondary loop. And, as I have said before, whatever the temperature being delivered by the secondary loop at the output from the supply-side of the closely spaced Ts (or the hydraulic separator) is going control the maximum amount of heat that will be rejected by the emitters. Lowering the flow in the secondary can reduce this, but cannot increase it. So when you are all done, the way to get low temperatures is to get the heat out of the boiler as fast as you can into the secondary, where you get the emitters to reject the heat into the load as fast as you can. And mainly, in most of the heating season, the only reasonable way to ensure low return temperatures is to reduce the firing rate so end up with as low as possible temperatures are delivered to the secondary loop as you can get, consistent with providing enough heat. The W-M Ultra does this by controlling the temperature with a sensor at the output of the closely spaced Ts.
"The problem is the majority of installers wouldn't know how to do the
math and there are 4 boilers that I know of that offer a supply side
sensor, Loch, Viessmann, Burnham Alpine and Triangle. One, Viessmann
makes it so you have to use it the others list it as an option."
I do not know most installers; only two, and one does not understand mod-cons. Unfortunately, I picked them to design, supply, and install my system. My current contractor is much better than the first, though not ideal either. What math do you need them to do? They should be able to do the heat loss (that my installer did not do), but they can get computers to do that if they do not know which end of a pencil to press against the paper. It is only 6th grade arithmetic after all: tedious, but easy.
"There are some that are fixed that the elevated 5-6 degree boiler supply temp
cuts down on efficiency. The math shows while I would have an elevated
boiler supply temp I would be condensing while they would not."
It is not clear to me what you are talking about here. What elevated temperature? If you make a boiler run at a higher supply temperature, your efficiency is lower than if it runs at a lower temperature because the heat not absorbed by the heat exchanger goes up the stack instead of into the water.
What math and what does it show?
"That 160 to 140 degree supply water temp in the majority of baseboard
applications is the heart of the season and in most cases with large
boiler flow rates and small system side flow rates condensing boilers
struggle to get into condensing mode."
I do not understand what you are saying.
How does slowing the boiler pump help this at all? I see no difference between a high speed pump in the boiler loop pumping water up to the closely-spaced Ts and having most of it go right back down to the boiler on the one hand, and a low speed pump in the boiler loop leaving the heat in the boiler. There is actually a small benefit in the former case: the increased flow in the heat exchanger will reduce the possibility of local hot spots that could damage the heat exchanger before the control system could lower the firing rate, or cut off the burner entirely.
If you use such high supply temperatures, I am not surprised that it is difficult to get much condensing. But lowering the flow rate in the secondary will not help. Doing that will cause the secondary to reject less heat, so the return heat will be more: just what you do not want. In such a situation, the best solution is to increase the size of the baseboard or add more radiant panel so the same amount of heat can be delivered at a lower temperature. That, for example, is why I took out the two three-foot baseboard units and had two 14-foot baseboard units put in. Just so I could get the heat I needed at a lower temperature.
"You case is different in the aspect that you don't need higher then 130
degree supply water temp so this really doesn't effect you. The majority
of installations out there though it does. Even in your case you don't
need a 007 as a boiler pump. "
I need the 007 boiler pump because W-M are so convinced that I need it that they supply it just so my contractor will not put something smaller in there. And if I change it, good bye warranty. I secretly believe that W-M know what they are doing. Also my calculations show that that size circulator will get the heat out of the boiler faster than a smaller one would.
"You don't need flow from the primary side
you need btu/hr. How I get that btu/hr doesn't make a difference. You
said yourself you don't need the full output of the boiler. Why can't
you limit the modulation rate and size your pump accordingly?"
I need the flow W-M specify because if the flow is too low, I am afraid the pins on the fire side of the aluminum heat exchanger would melt off, or burn off. I need the flow so that the amount of condensing is maximum. To get that I want the average temperature of the heat exchanger to be as low as possible, and that is with the maximum flow.
I can limit the maximum firing rate (not the modulation rate), and have done so because I cannot adjust the damping ratio of the feedback control system on the U-control board of the boiler; but that is not relevant here. I cannot lower the firing rate below 20% and that is far too high if my baseboard zone only wants 1500 BTU/hour, or whatever it is, on a fairly warm day.
As long as that pump is big enough, and not so big as to cause noise, erosion of the pipes and fittings, and use way too much electricity, there is no point in changing it.
"The only reason boiler manufactures give the pumps they do is because
they are afraid of who is installing the product and the pump they give
is based off the same math and pump they give with a cast iron boiler.
That's what installers are use to working with, the standard 20 Degree
Delta-t. Takes the thought process out of it."
I do not believe it. I think the reason is that they do not want damage done to their heat exchangers and supply the pumps they do so they do not overheat.
@ April 21, 2013 2:32 PM in Direct Pump TT Solo 110 with 3 zonesAre you paying attention? I believe neither Tony nor I are stuck on the system side.
I am paying attention to both subsystems: the boiler and the emitters. The considerations are the same. In both cases, you want as great a flow as possible to get maximum heat transfer at the lowest possible temperature. And this requires the lowest delta T.
If we consider the boiler subsystem separately, the easiest way to increase the efficiency is to turn it off: no heat wasted at all. But this is silly. That is why we must study both subsystems. But the considerations are the same.
@ April 21, 2013 1:16 PM in Direct Pump TT Solo 110 with 3 zonesExcellent idea! I hope he has the patience to deal with it.
@ April 21, 2013 1:09 PM in Direct Pump TT Solo 110 with 3 zonesAbsolutely right!
In this discussion, I am ignoring that because, while true, it does not affect the issue.
In a practical application, of course it must be considered.
I happen to run with very low delta-Ts in my system. It just happened, not by design, but because the installing contractor probably had a lot of Taco 007-IFC circulators on hand and used them everywhere. I observed the low delta-Ts and wondered if I should close the isolation valves down somewhat in order to raise the delta T. I did not do this because I did not wish to harm the circulators. It may be that it would not harm them, but I did not want to risk it.
So then I wondered if I should replace them with smaller circulators, 3-speed circulators, or what. I did calculate the flow rates as best I could, but do not have great confidence in my calculations, because all the piping in my slab is in the slab, so I do not know how much tubing is in there, what elbows and Ts are in there, and so on. All I know is that five 1/2 inch copper tubes enter the slab and one 1 inch copper tube comes out. Similarly in the baseboard zone, I know for sure there is 64 feet of half-inch tubing, 24 feet of 3/4 inch tubing, 28 feet of 3/4 inch baseboard, lots of 90 degree elbows (I do not know how many, but lots more than 10, and some more 3/4 inch and 1/2 inch stuff. I did the best I could with that zone and came up with, I think, 2.8 gpm. I should be able to run that through 1/2 inch tubing and stay under 4 ft/sec.
In any case there is no noise from either zone except when there is air in the baseboard zone, and that has disappeared a few months ago now.
@ April 21, 2013 12:51 PM in Direct Pump TT Solo 110 with 3 zones"The water within the system is neither the source of the heat nor its
destination; only its "conveyor belt". Thermal energy is absorbed by the
water at a heat source, conveyed by the water through the distribution
system piping, and finally released into a heated space by a emitter."
"The overall hydronic system consists of four inter-related subsystems.
The Heat Source, Distribution System, Heat Emitters and Control System."
Sure, if it helps your understanding of this issue, divide the heating system into as many subsystems as you like. I thought two subsystems were enough, but if you need more to understand it, fine. I could say there are five, the kind of insulation the boiler jacket has, or the color paint of the cabinet. I just do not see that they matter.
"For example, if you observed the operation of a hydronic heating system
for an hour and found no change in the temperature of the water leaving
the boiler, although it was firing continuously, what could you
conclude? Answer. Since there is no change in the water's temperature,
it did not undergo any net gain or loss of heat. The rate the boiler
injected heat into the water was the same as the rate the heat emitters
extracted heat from the water."
"It has been stated the every circulator in a primary/secondary system
operates as if it were installed in an isolated circuit. The primary
circulator (boiler circ) does not assist in moving flow through any of
of the secondary circuits, or vice versa. The function of the primary
loop is simply to convey the output of the heat source to the secondary
circuit, "pick up" points, while operating at or close to a selected
Contrary to myths that exist in the industry, the primary circulator
does not necessarily have to be the largest circulator in the system. It
may even be the smallest circulator in some systems. The primary
circulator also does not need to operate a flow rate equal to or greater
than the total flow rate of all the secondary circuits that can operate
simultaneously. The flow rate necessary to deliver the full output of
the heat source using a specified temperature drop can be found using
Required Flow Rate = Qhs (btu/hr) / (Delta-T x 500)."
" John Siegenthaler, Modern Hydronic Heating 2nd Addition." The 3rd is in my office and didn't have it handy to use.
Sure to all that. That changes nothing in this discussion.
I gave away my 2nd Edition, so I cannot check it, but since it is the same as Equation 4.7 in the 3rd edition, I do not dispute it except for two points.
1.) He does not say this is the Required Flow Rate. He is giving this as the Sensible Heat Rate Equation.
2.) He says IF you have a flow rate of f and if you get a specific Delta-T, then the heat transfer rate is be Q, He does not say you can get that. Furthermore, he does not say (at least not here) on what basis you should pick one temperature drop instead of another.
In my system, for example, the water temperatures I need to supply to make up the heat loss are such that if the outdoor temperature is 50F or above, I put 76F into the slab, so unless I heat that zone to less than 66F, I cannot possibly get a delta-T of 10 no matter what flow rate I use. So although his equation is correct, it does not apply in this case.
It is rather similar in my baseboard zone, although the differences are not so striking. On 50F outdoor days, I put 110F into the baseboard and get 108 to 110 F back. So delta-T is between 0 and 2. I calculate the flow rate to be a little under 3 gpm. It is not clear what flow rate I would have to use to get a delta-T of 10, for example, but if I used that, since the baseboards are in series and that cannot be changed without ripping out the floor of the two rooms, one will run with an average temperature of 107.5 and the other with an average temperature of 102.5. Since the heat loads of the two rooms are the same, one could be much warmer than the other and that would be unacceptable. Recall that the comfort is the real goal here, not mere boiler or system efficiency. And it might be even worse than that. If the flow rate to actually get a 10F delta T is so low that all the heat came out in the first room and none in the second, because as the temperature to a baseboard is reduced, its output drops faster than the temperature inside is reduced. So to get a delta-T of 10F, perhaps I would be getting 9F in the first room and 1F in the second. But whether this happens or not, if I reduce the average temperature in the emitters, the heat output is less than if the emitter runs at the same temperature from end to end. And increasing the delta-T necessarily reduces the average temperature of the water in the emitter, so the output from the emitter is reduced.
"I know some think I've been beating a dead horse but my whole point is
to give the best advice on how to make THE BOILER operate more
efficiently while still maintaining the comfort the customer needs and
I agree pretty much that that is the goal. I just do not think that that is the way to achieve it. With a mod-con, and probably all boilers, to get the efficiency of the boiler to go up, you need to have the water temperature of the water in the boiler heat exchanger to be as low as possible, and if you increase the delta-T of the water in the boiler's heat exchanger, then the average temperature of that water is higher than it would be with a lower delta-T and that will reduce the efficiency of the heat transfer. Similarly, if you look at the condensing in a condensing boiler, you want the average temperature of the fire side of the heat exchanger to be low enough to condense, you need as small a delta-T as you can get to keep the average temperature down, and that, too requires a higher flow rate.
@ April 20, 2013 3:50 PM in Direct Pump TT Solo 110 with 3 zonesWe sure are after btu/hr!
I assert that whether you use direct or primary-secondary, there are two (sub) systems in a heating system: the boiler and the emitters. I further assert that the heat produced by one subsystem is equal to the heat consumed by the other under steady state conditions.
Heat enters the system by the combustion in the boiler.
Heat leaves the system by radiation and convection from the emitters.
Heat is measured in BTU and heat flow is measured in BTU/hour, not by temperature difference between supply and return (there is a relation between temperature difference and water flow on the one hand and heat flow on the other, but that is not relevant to the present discussion).
By the high-school laws of physics, if the heat entering the system is the same as the heat leaving the system, the system temperature will remain the same. If the heat entering the system exceeds the heat leaving the system, the system temperature will increase without limit. If the heat leaving the system exceeds the heat entering the system, the system temperature will drop without limit.
Of course, there are limits. If the temperature goes up too far, an aquastat will stop the fire, or the water will boil and the pressure relief valve will work. If the temperature goes below the room temperature of the emitters (actually impossible) the emitters would absorb heat from the zone and return it to the system.
Therefore, in normal operation, the heat added to the system is equal to the heat removed from the system and the system temperature remains the same if the environment remains the same.
So we do not really care about temperature drop through these systems. What flow rate gets the most heat out of an emitter with a given input temperature? The maximum flow rate it makes sense to use, because any lower will cause a fixed size emitter to emit less heat. This flow rate will, in fact, have the lowest delta T.
Now consider the boiler. Here we want the boiler to absorb the most heat from the fire. Similarly to the case of the emitters, what flow rate is required to do this? To get the most transfer between the fire and the water, we want the maximum temperature difference possible between the fire side and the water side of the heat exchanger. And how is this obtained? It is obtained by using the maximum reasonable flow rate, because if you use less, the temperature at the exit of the heat exchanger will be hotter than if you used a higher flow rate, and less of the heat would go into the water and the rest would go out the venting system. This flow rate will also have the lowest delta T.
Notice what is going on.
With high flow through the boiler, the gradient between the fire and the water will be highest, resulting in maximum absorbtion of heat (and minimum temperature rise).
With high flow through the emitters, the gradient between the water and the air will be highest, resulting in maximum emission of heat to the load.
Now if the load is taking the maximum heat, there will be less heat returned to the boiler. Its temperature will be higher than with lower flow, but the heat will be less due to the greater flow. We are returning less heat to the boiler.
If the boiler is taking in its water from the emitters at a higher temperature, but at a greater flow rate, such that the actual heat is less that at lower flow rates, the actual cooling of the boiler will be greater than otherwise. So the entire system delivers the heat at a lower temperature. That helps everything in a system such as these.
@ April 19, 2013 3:24 PM in Strange CO problemI share your concerns. Someone here (probably Tim McElwain) suggested one of these, that I now have. I have two big-box store CO detectors as well, but this one is right in my bedroom: Mine is a slightly older model.
Here is an interesting video. People here already know it, but it is interesting anyway.
@ April 18, 2013 3:20 PM in I hope I am not beating a dead horse.One of my 007-IFCs is oversized. Not so large as to cause noise, however. I have to look at the thermostat to see if there is a call for heat unless I put my ear right on the baseboard where the supply pipe enters the house. Or I could touch it.
@ April 18, 2013 9:36 AM in I hope I am not beating a dead horse.It may be an extra 100 bucks to install a bee if you are putting in a new system, but if I have a perfectly good 007-IFC removed to put one in, it is whatever the retail cost plus the labor to have the bee installed. And for that I would like the hope of a payback greater than the amount of the electricity saved.
@ April 17, 2013 10:30 PM in I hope I am not beating a dead horse.Actually, I disagree with that.
I am after understanding, not patronizing.
We are back to that other thread where it is clear we disagree, but I am unclear where the disagreement is. So we can go nowhere.