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Direct Pump TT Solo 110 with 3 zones (67 Posts)
Direct Pump TT Solo 110 with 3 zonesI have 3 zones with the following flow requirements:
Zone 1: 4.6 GPM at 30 degree delta-t.
Zone 2: 1.8 GPM at 30 degree delta-t.
zone 3: 1.0 GPM at 30 degree delta-t.
Oversized, cast iron radiators in all three zones.
I've been watching the ongoing discussions on circulators ....
If I were to direct pump the TT Solo 110, what circulators would you suggest I take a look at? My question primarily centers around maintaining the required flow through the heat exchanger. - there would be times each zone would be the only zone calling for heat.This post was edited by an admin on April 18, 2013 11:34 AM.
Based OnTriangle wants a min of 5.5gpm across the HX at High Fire. Hence, when everything is calling. You need a pump that will move 7.4gpm based on your posted flow rates and delta. Which by the way exceeds the btu/hr out put of the boiler. 7.4 x (30 x 500) = 111,000 Btu/hr. Your head loss across the boiler is 5' now add the head loss of that longest zone and you need a pump that will move 7.4gpm @ X Ft of Head."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
I'd rather be slightly undersizedWe plan on installing two 20,000 btu gas fireplace inserts at some point, so on design days we'd use them if needed, or sweaters. Third floor won't have installed radiation for a few years yet and will be used sparingly.
I'm mainly wondering about outcomes when all the below are promoted.
1. Zoning, with some some zones having fairly small GPM requirements.
2. Avoiding over-pumping.
3. Large delta-t's, which I would assume regularly mean zones with very low flow requirements.
4. Direct-pumping.This post was edited by an admin on April 18, 2013 2:44 PM.
Bumble beesmay work, are you doing 3 separate circulators or zone valves...
if you balance the system correctlyand tune the ODR curve well, those zones should run almost continuously.
If the following were assumed- Zone valves.
- Well-balanced to match heat loss of each room.
- Minimum flow through boiler.
Can I really take advantage of a more sophisticated circulator such as the Grundfos Alpha, or shoudl I just get something that meets GPM and X ft. of head.
Why is direct-pumped better than primary-secondary?
A couple of reasons1. With a single ECM pump running 24/7 it is a bit cheaper than running 2 pumps.
2.Your supply sensor is in the proper spot sending exactly what your ODR is calling for.
3. Because the boiler is heating the water to exactly what is being called for the boiler will run at a lower temperature than if it was heating the water hotter then mixing it downstream.
Why is Direct BetterIt isn't in America. Why? Because we need to make our boilers cheap and affordable so we can sell them. Our boilers don't offer the control logic to control the speed of the pump for the most part. Lochinvar at least offers the ability to limited control but nobody else does.
Viessmann tried it here with the WB2A but the boler was so expensive compared to the competition they ditched it here in North America. Across the pond it's standard practice for the boiler to control it's pump.
Stay tuned for the Vitodens 222F in the next few months. It will sport a 30 gal indirect below a Vitodens 200 in a single cabinet, floor standing all pre piped and ready to go. No more Power Pump Module, 120 Volt Ready and a Control set up for North America out of the box.
Triangle, Burnham and Lochinvar all offer supply sensors to midigate the mix stream temp. Nobody uses them for the most part. Viessmann forces you to use them which along with also wanting boiler pumps sized for a 40 Rise reduces the elevated return temps seen in the majority of condensing boiler applications."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
Your return tempsare already determined by your existing radiators and your heating curve. It doesn't matter how you heat your water or mix it, in order for your system to match the heating curve, the temperature of the water entering the radiator and leaving the radiator is pre determined by your heat loss and the size of your radiator. Heating some of the return water hotter and then mixing it downstream to the temp required by the ODR only serves to increase your vent temperature and lower efficiency
There is nothing more efficient than a boiler replacing exactly what was used at the lowest possible temp Your TT boiler can do that because it has a low pressure drop exchanger because of modern computer controlled robotic welding. Casting, bending and stamping just cant accomplish this nomatter how you try to twist the math.
Not TrueYour return temps are influenced by the gpm that fixed speed boiler pump is moving. In a Pri/Sec piping arrangement it kills you because the system side can rarely take the gpm made by the boiler pump out into the system side. What goes into a tee must leave a tee.
In a direct pipe system it is also dictated by the operation point on the curve of the given circulator. In a multiple zone application your zone flow rates are never the same so at some point your are over pumping.
The boiler btu/hr out put is dictated by the boiler rise period. You must maintain the minimum flow rate required to move the min boiler btu/hr output. Those stupid charts mean that is the flow rate needed to get the full btu/hr output of the boiler at that given rise.
Boiler rise is a moving target and never stationary with a fixed speed boiler pump. Too many guys are hung on water temp. Btu/hr doesn't care about water temp and flow is just the conveyor belt that moves btu/hr. Water temp is what the emitter requires and has nothing to do btu/hr deliver by the boiler. The temp difference between a given supply temp and return temp does.
You cannot get around no matter how hard you try, gpm = btu/hr / (delta-t x 500) when a system is running on 100 percent water. Add glycol and we change the 500 number."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."This post was edited by an admin on April 19, 2013 10:17 PM.
@ChrisHow will your advice change when (if) variable speed pumps become standard?
Chris, I believeThat you believe what you say is true......so good luck with that theory.
Good Luck?Let's look at the Triangle PT 110 which has an output of 87,000 Btu/hr.
Flip that manual open to page 82. Here are the listed flow rates at different Delta-ts.
20 Delta - 8.7gpm so 8.7 x (20 x 500) = 87,000 Btu/hr
30 Delta - 5.8gpm so 5.8 x (30 x 500) = 87,000 Btu/hr
40 Delta - 4.3gpm so 4.3 x (40 x 500) = 86,000 Btu/hr
The min flow rate at high fire is 5gpm so we know we cannot run a 40 Delta. So if that is a fixed speed pump flowing a fixed flow rate every time it comes on and your not moving 8.7gpm or 5.8gpm on your system depending on what delta-t you are using where does the rest of the gpm left over go?
Because your a top notch installer you are using a pressure differential by pass on every installation that is direct piped as show in every diagram in the Triangle Application Guide right? If not your beating up that boiler pump which will eventually fail but it will be the pumps fault right?
So now that we know at operating points in the system we are not taking that full flow given by the boiler circulator we can never keep our BOILER return at the 20 degree or 20 degree temp difference between boiler supply and boiler return unless the system is taking the full flow rate and all zones are operating on the same delta-t. That happens ONCE if EVER and that is when your system needs 87,000 btu/hr.
Eastman my theory wouldn't change with a variable speed pump being controlled by the boilers logic. The boiler is doing the math for me, telling the pump what gpm to move across it's HX at that given time. The boiler is going to fire the burner to the btu/hr required based off what the system wants, ie the difference between boiler supply temp and boiler return temp.This post was edited by an admin on April 20, 2013 9:15 AM.
Ok Chris lets keep this simpleWe go into a single room home to replace the boiler, we measure the house the glass ect and do a heat load calc. The calc says that this home needs 2080 btus on a 9 degree day to maintain 70 degrees inside. OK
On the wall we see 4 feet of Burnham 9a baseboard. Its already there, we are not adding to it, subtracting from it. It is our job to figure out how we can make that board heat the house on a 9 degree day. So we go to our little baseboard fact sheet( ill include a link) and we find that if we heat that board to 170 degrees we get 520 btus per foot.
So what I would do is send 180 to the board then adjust my flow so 160 is leaving. This would be an average of 170 across the board with a flow of .20 gpm.
Forget about outdoor reset, forget about the fact that the closer the water temp gets to ambient the slower the transmission of heat. Today it is 9 degrees and thats all we care about. Now tell me what temp and flow you would use to heat that house?
And Where DidThat other 6.7gpm that boiler pump flowed across the HX go? It's a fixed speed pump and you can't change the 8.7gpm it is flowing.
Now back to your question. I agree with you. The basis of the entire post has to do with the effect the fixed speed boiler pump has on the boiler delta-t (Temp Rise) not the systems. In the scenario you posted that boiler would be short cycling to death.
Is it not also the installers responsibility to make sure the entire heating system is operating efficiently and not getting beat up, or is it just about one facet of the heating system?
Would it not be nice if your boiler pump only flowed the 2gpm you needed in your scenario instead of 8.7gpm and then when the next zone called and you needed 4gpm the pump ramped up to meet the demand all done through the boiler controls logic to match the burner btu/hr out put?
I used a flow valve to regulatemy gpm. Thats how you adjust flow through different circuits. Forget about short cycling the boiler, we will pretend we have a mini modular that fits inside our mini house that modulates to 0.
The point is Chris, in order to heat this house we must deliver a certain temp water in order for the radiation to do its job. Therefore no mater what boiler or piping strategy we use, the return water temp from our radiation will be the same, in this case 160.
Now if we take that 160 at .20 gpm and just add enough btus to bring it back up to 180 or we could do it like you say, take our 160 return and pull .10gpm through the boiler and heat it to 200 and let the other .10 gpm go through the t's and mix them downstream to regain our 180, which one is more efficient?
Your boiler is operating at 200 and mine is 180, you have two pumps and I have one.
Also, as our outside temp goes up and we get closer to our condensing temps on the boiler. We both will be pulling the same temp return water in, but I will be pulling in twice as much causing my boiler to condense more...making it even more efficient.
Sorry, not a flow valve a balancing valve!I meant a balancing valve.
No You Will Not Condense MoreYour leaving out the fact that the boiler pump is fixed to move an X amount of flow across the HX. If your using flow meters then you are using a pressure differential. You have to or the boiler will continually go off on high limit (short cycle) because you cannot pull out the btu/hr it is making. Pipe pri/sec and it;s the same.
You cannot just disregard the boiler pumps flow rate in your math. Yes your zone will be running on a 20 but your boiler will not.
You still haven't answered the question as to where the left over gpm the zone isn't taking goes to?
Take the attached as an example. This could be your two closely spaced tee a low loss header of even what happens with a pressure differential by-pass. You have to account for the boiler pump flow in your math for the boilers not the systems return temp.
In this example my boiler supply water temp may be 6 degrees higher then yours but I'm condensing and your not. So what's more important boiler supply water temp or boiler return as it pertains to efficiency?
When you pipe the Prestige direct your suppose to be using a pressure differential by-pass at a minimum in multi zone applications. Why? Because you'll kill the boiler pump and force short cycling of the boiler. That on board pump is moving 8.7gpm across the HX always even on low fire.
It seems to me that a lot of installers think that the system side return temp is always going to match the boiler return temp and that is just not the case.
The second attachment shows where the boiler operates in btu/hr output at different BOILER Temp Rises or it's delta-t.
How can you say running a boiler not the system on a 20 is better then running it at a 30 or 35. I'd say the sweet spot for the Prestige is running a 30 on the boiler side, pipe pri-sec and run the system side on a 20.
The 3rd attachment is all 3 rises running a 145 Supply flowing 5gpm on the system side. System side flowrate based on a 20 degree delta in all 3 examples.This post was edited by an admin on April 20, 2013 1:09 PM.
There is no leftover GPMI have throttled my flow rate down to obtain my 160 return through the board!
Now if we both have a return coming back at 160...ahhh forget it, I have to go weed wack my driveway!
How Did You ThrottleDown the boiler flow rate? It's a fixed speed pump moving 8.7gpm at all times. You do have a pressure differential by pass when direct piped correct? CH Blocking is just a fancy name for post purge. They put in in there because of exactly what I'm trying to get across.
They know and understand that the on board boiler pump flows more then the typical system is able to pull out. We like zoning here in America. If you had ACV's Pretisge from across the pond that pump would be controlled by the boilers control logic. Like everyone else over there does. The boiler pumps flow is matched to the boilers btu/hr output via variable speed. Less btu/hr pump slows down, more btu/hr pump speeds up.This post was edited by an admin on April 20, 2013 1:52 PM.
You should notDirect pump that boiler with that piping design. You must primary secondary.
What Boiler???Your missing the point. This was a hypothetical question using real easy numbers, it wasnt about any boiler just temps needed to serve a space.
But I know what your going to say and I dont agree with that.
Lets say I actually was talking about putting a 110 prestige on that 4 feet of board(Which I wasnt) Our ultimate goal is to have the boiler fire at a rate equivalent to what the house is losing, So how is pri sec going to change that? If the boiler cant modulate low enough for the demand it is going to short cycle just as rapidly on pri-sec that it does straight through....to the second.
This is why the tt110 has selective blocking times and a larger...3-1/2 gallon exchanger
Here is my concern Chris:I think a lot of people are reading your posts and coming to the conclusion that the best course of action would be to get a couple of dT pumps and enforce various combinations of different primary and secondary temperature deltas. But clearly there is no point to this, since that would ensure the primary and secondary flow rates are never in synchronization.
Who SaysThey have to be Eastman? In essence when piped pri/sec or LLH you have three different systems or segments to the complete heating system. System 1 being the boiler system moving a fixed gpm of x amount of btu/hr at a certain water temp to System 2 the secondary or distribution side takes it's x amount of btu/hr at a certain water temp to System 3 the emitter which delivers it's btu/hr out to the space. How much btu/hr system 3 takes from system 2 dictates the delta-t. System 2's only job is to move the btu/hr. Well I made it in system 1, gave it to system 2 so now it's up to system 3's to take what it needs.
Flow rate is nothing more then a conveyor belt moving btu/hr around the system and since we are hydraulically separated system 1's flow rate has no influence over system 2's. System 2's does though have an effect on system 1's return water temp. We are after btu/hr are we not?This post was edited by an admin on April 20, 2013 1:34 PM.
We are after btu/hr are we not?We 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.
I Quote"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."
"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 temperature drop."
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 the Equation:
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.
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 wants.
It's here nowI didn't know the argument was continued in this thread.
On reflection, I don't feel that either method is necessarily wrong, just different. The btus per hour will be used either way, and I can see applications for both methodologies. J-D's approach would work well with emitters in series, and Chris's approach would work better with emitters in parallel.
The only caviat I would add to J-D's approach, is, that you must stay within pipe sizing guidelines to avoid velocity noise.This post was edited by an admin on April 21, 2013 10:45 AM.
you must stay within pipe sizing guidelines to avoid velocity noise.Absolutely 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.
Quotes from John Seigenthaler."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.
You are of course correct.
This thread is a great example of why the manufactures have not taken this technology across the ocean.
American heating contractors are just not ready to embrace (or understand) something this advanced.
IncorrectChris is dead wrong!
I am going to email John Seigenthalerand see if he would put an end to this nonsense.
NOOOOOOThese are the best threads.
I am going to email John SeigenthalerExcellent idea! I hope he has the patience to deal with it.
Tony and JeanAre stuck on the system side. Everything I'm trying to get across is on the BOILER SIDE or primary. Even the Triangle piped direct with a pressure differential by-pass is going to elevate the boiler return temp. And, yes, your are suppose to use a pressure differential by-pass.This post was edited by an admin on April 21, 2013 2:12 PM.
Tony and Jean Are stuck on the system side.Are 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.
Ok ThenIf 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.
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 side? You can still move what ever gpm at what ever flow rate you want on the secondary side. 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 temp.
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. 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. 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.
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. 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?
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.
ChrisIf the target temp is 130* and he wants to pump 15 gpm primary and secondary......What's the difference? Again, I am not arguing right or wrong,it's just a different approach. The boiler is producing what it should(based on ODR). The emitters will use what they need.
I might argue this approach with cast-iron radiators. We all know they suffer when over-pumped. But, for his baseboards in series, it's six of one, half-a-dozen of the other.
What's the difference?Right, and I doubt I get anywhere near 15 gpm out of those 007 circulators in my system. ;-)
My English must be worse than I thought."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.
Poor IvanatorLost interest after his third post.
The poor horse hide is tanned, and stretched ready for making gloves.
I think we need a delta t section on the wall......seems to be a lot of this discussion this season for some reason say delta t circs? Trying to right boiler sizing wrongs.
GordyStop It! Or we'll have an argument about the color of the horse hide.
I Was TryingTo answer Ivans post because it fit right in. His question was direct pipe or pri/sec and he wanted to run a 30.
I think we got off kilter and I apologize to Ivan. Still sticking to my guns though. I think the 30 on a TT is the sweet spot. It's that on board pump that might not allow it. Did you guys know TT offers the PT110 in Canada without a on board pump? Found that interesting.
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. ..
ChrisNo 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. Again, I understand what you are saying, and your reasoning, but I believe there's an application for both strategies.Both could be right, or wrong if mis-applied.
the return mix is that much cooler"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.
OKThat's enough! No matter what I say, you find a way to argue it.You're like a GD pitbull. Give it a rest!
If I HaveA boiler pump flowing 7 GPM to the closely spaced tees and if anything less then 7gpm is being taken by the secondary the left over goes to the boiler return tee. So my return temp is warmer not cooler.
I am moving 7gpm of 130 Degree Water out to the secondary. The Secondary takes 2 around the distribution system. The 5 left over had to go some where?
(Boiler Flow - System Flow) * Boiler Temp + (Rtn Flow)* Rtn Temp / Boiler Flow = Boiler Return Temp
(7-2)*130 + (2)*125/7 = 129 Degree Boiler Return Temp
I used 125 based on what JD see's on his system side. So he has a 1 Degree Temp Difference between his boilers supply and return. Thus why he short cycles so often. So the boiler is almost in thermal equilibrium.. Basically almost no net gain or loss of heat.
Not an argument Paul for JD..This post was edited by an admin on April 21, 2013 7:41 PM.
ChrisAll that "calcumulating".......The return temp has to equal the change created by the emitters.
The BOILER RETURNDoes not. You moved 7gpm across the primary side you only took 2 out to the distribution system. The other 5 left over has to go some where and it goes the opposite way, the return tee headed for the boiler. So you sending 5gpm of 130 degree water into the return mixing with 2gpm of system return water temp. I used 125 return because JD says it's common.
This is what I think most are missing. Just because the system return is X temp it doesn't mean that is what the boiler is seeing unless you remove the entire flow rate from the primary side into and around the system side. This is why I keep saying size boiler pumps for smaller flow rate. Your still moving the same amount of btu/hr from the primary to the secondary. You are not moving any more btu/hr with a higher flow at a smaller rise then I am with a lower flow with a higher rise. The formula of
gpm = btu/hr / delta-t x 500 tells us that.
JD case is not the norm. He is in condensing all the time because of the radiant house and that little heat loss on his 2nd floor. But look at a baseboard system that the majority of mod/cons are going in and it applies to most applications. Send me an email and I'd like to send you the excel spreadsheet. Play with it, using different flow rates and water temps for both the system side and the boiler side. You may find it very interesting.
I'm just trying to educate. I could really care less what JD does, it's his house. I like JD and think he gives good advice to the fellow home owners that come here.
ChrisUsing your calc, and dropping the boiler flow to 4 gpm, I get a return temp of 127.5*?
YupIn this case. JD system is not typical. I wouldn't be running a 5 delta-t nor would I be moving 2gpm. His system fix is a little more then just the boiler pump. How about capping off the high end modulation rate to 50% which is 35K btu/hr. Now I need a pump moving 3.5gpm. His total heat loss is, I think 32K. Run the radiant which I think he said is 25K at design. 25,000/ (10 x 500) = 5gpm. Oh no..Too much flow on the secondary side. We have a formula for that to. He would need 140 degree supply water temp at design but his boiler return would still be 130 and he still would be condensing.
Supply Temp = (Sys Rtn Flow - Boiler Flow) * Sys Rtn Temp + (Boiler Flow) * Boiler Temp / Rtn Flow
I also think the wear and tear of the short cycling in the end will cost more then the minimal fuel saved for the 1% of the season he needs these water temps. Same goes for that baseboard loop.
shrink that primary flow rate down from 7.1gpm"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..
Haven't lost interestI was up at 4:00 A.M this morning drinking my coffee and reading the wall until 9:00 A.M.
I spent most of the day down in the basement running new copper for our domestic water supply. I have a Triangle Tube Solo 110 down in the basement sitting on a temporary wall. I wanted to get it down there and run gas and water in order to fire it up and run it for a bit. It had a cracked heat exchanger. I bought it used and replaced the heat exchanger. I wanted to make sure everything works, and it does. It was a gamble, but it worked out.
I have a way over-sized Slant-Fin (210,000 input) installed with a Unico hot water coil that was undersized (putting out about 60,000 btu). This was installed by a contractor who I now know was a forced air guy, and not a hydronics guy.
The Triangle Tube will eventually take the place of the Slant Fin, and the hot water coil will go away as well, replaced with cast iron radiators. I put in radiators for the first floor last October. I have radiators for the second floor sitting on the front porch. I have extensive structural repairs to make in the basement before I put the Triangle Tube in place for good. In fact, I'm going to pull the Triangle Tube out of the basement before I start repairs. I'm rehabbing an 1888 house and there is fire damage in the basement that previous homeowners did not address, so I need to run new joists and pour footings and put in new posts and beams, then I'll put the boiler in for good.
I piped the near-boiler piping primary-secondary, but keep thinking about things. And wanted to see if there is some way I can make use of the Grundfos Alpha as the boiler pump. I was wondering about some things Chris has touched on in more than one post.
I think I'll be running constant circulation with ODR. My design temp is 130 degrees. I have the third floor that will not be used very often so I would still like to consider zoning in the future.
The cracked heat exchanger is in front. See the slight bulge?
IvanWould be interested in that crack HX. Any ideas as to the cause. I'd like to apologize for high jacking your thread. Tried to answer your question and then got a little side tracked although it does pertain to what you were originally asking about.
JDBThe 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.
With all the new tools coming out for the tool box you still have to know when, and where to use it, and whether, or not its justified.
Edit: sorry HotRods post was in another delta t thread.This post was edited by an admin on April 21, 2013 7:38 PM.
your boiler is to big for the heat loss"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?
No JDI agreed from the beginning your boiler was over sized. Was trying to give you a tool in helping minimize the short cycling. Your stuck that you need that Taco 007 as a boiler pump and you don't. Call Weil. Then again, they might not give you the right answer because you are a homeowner.
If you limit the high end modulation rate and convert that rate to btu/hr then you only need a pump to flow the gpm needed to get your new max btu/hr at a particular boiler temp rise. Problem with Weil is it's top secret stuff finding out the pressure drop in the HX. We had to go to the indirect chart in the manual to figure out the pressure drop and flow rate that the Taco 007 was doing.
The minimum flow rate should be defined better. They should list both the high and low flow rate. So the charts in the manuals should read as an example.
20 Degree Temp Rise (GPM = Btuh/hr / (Delta-T x 500)
Min Flow Rate Low Fire 1.7GPM ( 1.7 x 20 x 500 = 17,000 Btu/hr)
Min Flow Rate High Fire 7.1GPM ( 7.1 x 20 x 500 = 71,000 Btu/hr)
*If system flow rate exceeds 1.7gpm boiler must be piped in a primary secondary piping arrangement.
What if I don't need 71,000 Btu/hr and I want to cap it at 50%. If 0 is off then 17K is 24% modulation so 35,500 btu/hr would be 50%. Why can't I have a boiler pump that only moves 3.5gpm. That flow rate would meet both my min and my new max. This would def help you with that radiant zone if you could limit the high end of the modulation rate.
Just giving you some advice that you should take in and look at. Heck you have all summer to think about it and gather more information in making any decision if you even want to make one.
You system is unique and not one that most installers are coming up against in the majority of applications. Most mod/cons are being installed in baseboard systems and having a smaller boiler flow rate does make a difference in the boilers return water temp.This post was edited by an admin on April 21, 2013 8:51 PM.
How can I get in on this?I'm not sure what to argue against. Can we summarize our positions at some point?This post was edited by an admin on April 21, 2013 8:55 PM.
Sure EastmanThis has nothing to do with JD's system.
My position is that when a mod/con is piped in a primary/secondary piping arrangement or a differential by-pass is used the primary flow rate should be sized to minimize and/or eliminate elevated boiler return water temperatures.
I imagine everyone is sick of this by now. By last week, probably.My 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.
JDYou 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.
Once you reduce that flow you will need to boost that water temp up to probably 140 and widen you system delta-t to 10 at design but you still will be condensing. The wear and tear of the short cycling in the end will cost you more then the pea of fuel savings if any by running a 140 supply instead of a 130 at design.This post was edited by an admin on April 21, 2013 9:51 PM.
That's been my whole entire point.From 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.
I enjoy these discussions.I like the idea of synchronizing the hydraulics. If I could get a delta 0 pump I'd put the sensors across primary output and secondary input, with the pump itself working in perhaps the secondary loop.
You've Come OverTo the dark side? Took you long enough. :) I like the term synchronizing because that is exactly what I'm trying to do. Sync the secondary flow to pull all the primary flow leaving as little or nothing of the primary flow to head right to that boiler return. Nice word use Eastman.
What the..not sure to sayThis post was edited by an admin on April 21, 2013 10:00 PM.
That's actually a very interesting idea!It had me thinking for a while - I don't think I've heard anyone mention running the sensors for the delta on boiler and system loops, and it's certainly not in their installation manual as an application. There are a couple of issues with it, though - firstly, if you really want balanced flow, the best way to get there is to get rid of hydraulic separation. Even for imbalanced flow with a fixed degree of imbalance, a fixed bypass with a balancing valve would be the way. It seems like you're trying to use complicated controls to do something very simple. The whole point of hydraulic separation is to NOT couple boiler flow to system flow.
Secondly, there's an issue with system feedback. You want the circ to respond to greater system demand by increasing the flow. What will actually happen is that, as zones open, you will get cooler return and more flow in the system loop at the same circulator duty point. Assuming that the boiler is good at maintaining its supply setpoint, this will now result in the boiler supply being mixed down some with system return, which your control algorithm would interpret as excess system flow and turn down its duty point until system supply is once again equal to boiler supply - but now at a lower flow. So the response would seem to be the opposite of what's required.