Prestige Triangle Tube Solo 110, delta T and pump speed


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Old 11-21-09, 12:32 PM
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Prestige Triangle Tube Solo 110, delta T and pump speed

Hello Members,
After the installation of the Triangle Tube Solo 110 (piped direct, 1 zone, no DHW) my contractor and I did a high fire test with the circulator on medium speed to determine delta T and flow (gpm). We were amazed at the low delta T (approx. 8-10 degrees) we were getting and as the boiler temp got higher the delta T spreads became smaller. Now this test was performed when the temperature outside was in the low 60's.

When I did a system head analysis, I came out with approx. 4.4 feet on a flow rate of 10 gpm, 140 degree water. I used the figures from copper tubing and fittings to determine my head loss (this was the only guidline available).
http://www.taco-hvac.com/uploads/Fil...irculators.pdf
According to the chart (p.72 of the installation manual) I should be getting a flow of approx 9 gpm on medium speed.

Of course I don't have copper tubing, I have cast iron radiators and large diameter black pipe feed and returns. Is it possible the reason(s) for a low delta t is, #1. There is not a sufficient load on the system (colder outside temperatures), eg. the heat loss from the pipes are not as great as they would be if there are colder temperatures, and #2. because the large diameter black pipe is retaining more heat because they have more mass than copper pipe?

The formula to determine flow is F=Q/(490*delta T)
Hydronics Piping Checks Can Be A Breeze
F= flow rate (gpm)
Q= DOE output (99,000 btu/hr for the Solo 110)
490 (constant for regular water)
Delta T = temperature drop

The technician at prestige told me to "maintain at least 5 gpm. At 5 gpm, you will have a delta T of between 35-40 degrees. A delta T of 30 is best, so the gpm should be between 5-10."

Now its interesting if you solve for Q using the information they provide on p.72 of the installation manual, they're Q is closer to the IBR rating for the Solo 110 (86,000 btu/hr). To be exact.
For a delta t of 20 and 8.7 gpm, Q=85,260
For a delta t of 30 and 5.8 gpm, Q=85,260
For a delta t of 40 and 4.3 gpm, Q=84,280
I'm sure they are using those published figures to stay within the "safety envelope".

I now have my circulator speed on low and I'm getting an initial delta T of 22 degrees (that is when the outside temps are in the middle 30's). Of course the delta T will probably become greater when the real cold temps come roaring in (December, January and February) eg. The load on the system becomes greater.
So if I use they're figures I should get:
F=Q/(490*delta T)
F= 85,260/(490*22)
F=7.9 gpm (and this is the circulator on low speed)

If you plug in a delta T of 30 degrees you get F=5.8 gpm
So if I stay with a delta T of 30 degrees or lower the boiler is in the margin of safety.
I appreciate any comments, agreements or disagreements.
 

Last edited by Beezee; 11-21-09 at 01:20 PM. Reason: correction
  #2  
Old 11-21-09, 05:06 PM
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#1. There is not a sufficient load on the system
I don't think the load on the system is going to make quite as much difference in the DT as you might logically think. Since the piping and rads are pretty much in conditioned space, and the temperature in that space is regulated, the 'driving force' stays more or less the same. It's the difference in temp between the hot water inside, and the air outside that establishes how fast the heat is lost... now, if the pipes and rads were outdoors! of course you would see a bigger difference.

One thing to keep in mind is that since you have a high mass system with the black pipe, and the CI rads, it will take some time for that mass to heat up. When you bring it up cold, you can expect a higher DT at first because that mass is being heated. Then, once it IS heated, yes, it will tend to retain that heat longer.
 
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Old 11-21-09, 05:16 PM
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I assume you are only measuring delta-T in the boiler. Most mod/cons want to see a 20 - 35f delta t. The faster water movement will move the same amount of btu's but at a lower water temperature. You will not see much modulation. I know what the I&O manual says but this is why I like to pipe them p/s with a valve on the supply side of the boiler so you can control the delta T.
I am glad someone read my article.
 
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Old 11-22-09, 05:44 AM
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5-10 gpm is a factor of two. Don't sweat it; lots of room here to play around (which if I'm reading rbeck correctly is one of his concerns about piping direct in some situations). Watch how the system behaves as we get into colder temps.

For now, concentrate on making some observations of outdoor temps, supply temps, and how long it takes to satisfy the thermostat. Dial in the reset curve to get the lowest supply temps possible for a given outdoor temperature. The more you keep the return temps in the condensing range, the better.
 
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Old 11-22-09, 03:25 PM
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I've got the same boiler, and I've never seen a DT of more than 10 degrees. And even that 10 degrees is right when the burner first fires and then it quickly vanishes. This is with fin tube baseboard and water temps in the 100 to 110 range.
 
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Old 11-22-09, 09:40 PM
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I'm not sure what the problem is, if any.

As the speed of the circulating water (with a fixed supply temperature) goes up by a factor of 2, the delta-T (which measures the amount of heat lost from the water) should decrease by a factor of 2, almost exactly if you disregard the effect of turbulence in the water. This makes sense from a number of different perspectives: the water spends half as much time in contact with the emitters, so the heat lost is half; the total heat loss (gpm x deltaT) should remain roughly constant, but since gpm increases, deltaT descrease, etc.

As the temperature of the water goes up, the delta T should go up as well, as the amount of heat transferred from the water to the emitter should also increase as the temperature difference between the water and the emitter increases. The amount of heat transferred goes up as the temperature outside decreases (if you are using outdoor reset), but it's because the floor is warmer in order to maintain the heat inside the building, not because the temperature outside has decreased. In order to maintain the higher temperature in the floor, you need warmer water, which - as the temperature differential between the water and the floor increases - will result in a higher delta T.

Both of your observations - high pump speed and lower temperature water - will lead to smaller delta T's. I'd expect to see the large, "design" delta T only at the design temperature, unless you are using a fancy delta-T pump...

Jeff
 
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Old 11-23-09, 05:32 AM
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I might challenge one of your thoughts.

Since the water temp adjusts with ODR, so does the heat output of the emitters.
Since they become less effective at heating the space at a given lower water temp, they therefore extract less heat from the water.
This combined with ODR should keep delta T across them fairly constant. At least in theory.

I have not had the chance to set up a test condition with ODR and a precisely fixed delta T and follow it throughout a winter to see how it behaves. One day soon maybe
 
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Old 11-23-09, 12:02 PM
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Originally Posted by TOHeating View Post
Since the water temp adjusts with ODR, so does the heat output of the emitters.
Since they become less effective at heating the space at a given lower water temp, they therefore extract less heat from the water.
This combined with ODR should keep delta T across them fairly constant. At least in theory.
Equating "less effective at heating the space" and "extracting less heat from the water" is not correct. Consider 100 degree water that maintains a floor at 75 degrees. It is that 25 degree temperature differential that governs the amount of heat that is extracted from the water, not the temperature outside.

The temperature outside only governs the amount of heat that the room loses to the outside. So, if it's 70 degrees outside, the room may lose no heat, and the 75 degree floor may cause the room temperature to rise, but if it's 40 degrees outside, the room may lose 15 BTU's / square foot, and the temperature in the room may decrease.

Floors that are spec'ed at 15 degrees delta-T under design do not perform that way - with outsoor reset - when the outdoor temperature is not that low. Think of it thus: When the amount of heat required to keep the room "at temperature" is lessened because it is warmer outside, the amount of heat extracted from the water - the Delta T - is necessarily lower, unless the pump changes speed. The lower water temperature and the lower floor (or other emitter) temperature combine to make this happen.

Jeff
 
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Old 11-23-09, 01:26 PM
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I don't know if this link will help but it can't hurt.
Look at the second and last choices. As flow increases heat output changes. Increase flow and increase heat output providing you don't exceed 4 ft per second.

Technical Menu

Also look at radiation charts which show the higher the flow the greater the heat output at any given water temp. see this link and compare to others. It does not change the idea of increasing flow and increasing output.
http://www.comfort-calc.net/pictures...rd%20Chart.JPG
 
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Old 11-23-09, 02:06 PM
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Originally Posted by jbaron View Post
Equating "less effective at heating the space" and "extracting less heat from the water" is not correct. Consider 100 degree water that maintains a floor at 75 degrees. It is that 25 degree temperature differential that governs the amount of heat that is extracted from the water, not the temperature outside.

The temperature outside only governs the amount of heat that the room loses to the outside. So, if it's 70 degrees outside, the room may lose no heat, and the 75 degree floor may cause the room temperature to rise, but if it's 40 degrees outside, the room may lose 15 BTU's / square foot, and the temperature in the room may decrease.

Floors that are spec'ed at 15 degrees delta-T under design do not perform that way - with outsoor reset - when the outdoor temperature is not that low. Think of it thus: When the amount of heat required to keep the room "at temperature" is lessened because it is warmer outside, the amount of heat extracted from the water - the Delta T - is necessarily lower, unless the pump changes speed. The lower water temperature and the lower floor (or other emitter) temperature combine to make this happen.

Jeff
Jeff,

The OP said nothing about infloor heating.
He talked about copper and cast iron.
If I put 80 degree water in a cast iron rad, I will not get 90 BTU per sqft out of it now will I.
If I put 140 F water in it I will get that.
Hence, with ODR the reset curve drops water temp, which makes the emitters less efficient at emitting heat, which reduces the output, this in turn increases the on time to heat the building.

We could get into a lot of math and look at btu's and flow rates etc, but I really am not into it right now.

I can agree that at the low end of the water temps, an in floor slab will reduce it's delta T simply because the return water is at or near the room temperature.

Now,
"Think of it thus: When the amount of heat required to keep the room "at temperature" is lessened because it is warmer outside, the amount of heat extracted from the water - the Delta T - is necessarily lower, unless the pump changes speed." or you drop the water temperature and keep the flow rate the same
 
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Old 11-23-09, 04:49 PM
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The greater the difference in temperature, the greater the rate of heat exchange will be. As the temperatures come closer together, the rate of heat exchange slows down.

A 180F radiator will exchange heat with 70F air faster than a 120F radiator will.
 
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Old 11-24-09, 02:41 PM
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Circulator Speed

Hello Members,
Thanks for the spirited input!

Today for an example:
Outside Temperature=47 degrees
My thermostat is set at 64 degrees
From a cold start:
On low circulator speed (spd. 1) my delta T is 20 degrees and is condensing nicely (25 minutes high fire) until it modulates down to a boiler water temp of approx. 104 degrees (modulates for another 45 minutes until the Tstat is satisfied). When it modulates it gives me a delta t of 8 degrees.

I just got concerned running it on low speed because if I'm reading the Plot Graph correctly (p.72 of the i&o), if you plot my gpm against my head loss:
Lets say my system head is 5 feet (I added 1/2 foot because of the extra 1" pipe added to install the boiler).
My flow rate f=Q/(490*delta T)
f=85,260/(490*20)
f=8.7 gpm
From p.72 of the installation manual:
http://www.triangletube.com/document...0%20Manual.pdf
If you plot my gpm against my head loss to the Solo 110 curve it runs between spd 1 (low) curve and spd 2 (med) curve. Unless I'm not doing this properly.
I am just concerned that spd 1 (low), is not a fast enough flow for my system although my math contradicts that.

What is the reason for the statement from Prestige "At 5 gpm, you will have a delta t between 35-40 degrees which is the max the boiler should operate at. A delta T of 30 is best, so the gpm should be between 5-10 gpm"?
I'm assuming that Prestige doesn't want a very large delta t because it will cause boiler shock.

If you can address the three points (1. The plot of my gpm against my head loss, p.72 (i&o manual), 2. Running the circulator on spd. 1 (low), 3.The Statement from Prestige.
Thanks!
 

Last edited by Beezee; 11-24-09 at 02:43 PM. Reason: correction
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Old 11-24-09, 06:50 PM
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1) Speed 1 cannot flow 8.7 GPM thru the boiler.
2) At 5 GPM speed one has about 3' of head available to be used
3) The MCBA will reduce the firing rate of the solo at 45 degrees F.

Does that help at all ?
If you have only 3' of system head then by all means run on speed 1. If not run on speed 2, doubt you would ever see any cost differences between speed 1 and 2.

You can place the solo in high fire and watch the delta T on the boiler after 5 or so minutes of run time. I think high fire times out at 10 minutes. If the boiler delta T starts to hit 45 F then the burner will modulate and you will not get rated output when you need it. Therefore use speed 2, if it's still starts to modulate go to speed 3. From memory it will not look at the CH setpoint.
 
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Old 11-25-09, 02:39 PM
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You are putting waaaay too much emphasis on boiler delta-t. Delta -T has way too many variables to try to lock it into a single number. As I stated earlier it has to do with flow, resistance and water temperature which all change continuously throughout the cycle.
If you want to keep a steady delta-T buy a variable speed pump and set and forget it. Otherwise it is what it is. You could also include flow meters if you want to know what the flow is any any moment.
 
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Old 02-07-11, 11:34 PM
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I would guess that the purpose of measuring Delta T at full fire and a known flow is to make sure the unit is performing as designed for high output scenarios like when you have an indirect DHW tank attached to the PS110.

For maximum efficiency, I'm shooting for maximum condensation at a minimum firing rate constantly all day. I have a primary secondary loop and want the secondary loop pump to run all day. Since I have a primary loop I assume the head on the pump is essentially zero. So my pump is set at the minimum speed. I would think that would lead to the highest Delta T, allowing the hottest output temps with the coolest input temps, hopefully leading to maximum condensation. I think my Delta T seems to settle in between 6-12 degrees. It's going to fluctuate as the burner turns on and off (because even minimum firing is probably too much in 40+F weather).

Coolest possible temps --> Max condensation = max efficiency. (Probably very far from max fire rate.)

Delta T seems like it should only be measured to assure you can get the max BTUs out of the system. Right?
 
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Old 02-08-11, 08:34 AM
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Primary / secondary piping is not necessarily condusive to lowest possible return water temps.
A better approach is to inject the boiler into a system loop, that way you can usually predict where the mix point is.
It does it also in primary / secondary pipework, but you really have to control the primary loop flow.
 
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Old 02-08-11, 11:07 AM
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Originally Posted by TOHeating View Post
Primary / secondary piping is not necessarily condusive to lowest possible return water temps.
A better approach is to inject the boiler into a system loop, that way you can usually predict where the mix point is.
It does it also in primary / secondary pipework, but you really have to control the primary loop flow.
I think that's what TT means by primary/secondary piping - a boiler "loop" injected into the system "loop".
 
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Old 02-08-11, 03:10 PM
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I think what TO is talking about is where the boiler is a primary loop, and the system is a primary loop, and the two loops are connected via an 'injection bridge' with a VS pump. I might of course be wrong presuming that though... I don't see how such a setup will promote cooler return temps and condensing.

There's an essay at the Tekmar site that explains this and has design details... E021 maybe?

Isn't the easiest way to promote condensing installing as much radiation as possible in the home? i.e. OVER radiating?
 

Last edited by NJT; 02-08-11 at 03:28 PM.
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Old 02-09-11, 03:20 PM
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No i was referring to who TT instructs people to pipe the boiler.
True PS piping has the boiler in a small primary loop, each load comes off that loop using close spaced tee's.
With some careful planning one could have a nice 40 degree delta tee on the boiler loop if you had multiple loads at varying temps. The original concept for P/S piping was of course for boiler protection and helping deal with multiple temps.

If there is one load, then I like to inject the boiler water into the system loop as shown in the TT diagrams.
As for promoting condensing, over radiating sure does that. And what controls over radiating ... ? (the pocket book ;-) )
 
 

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