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Should I direct pump this boiler...radiant floor with one zone.
nickh1
Posts: 16Member
I have a 7000 sq ft shop built in the mid 80's with radiant floor heat. It was heated with 2 40 gallon water heaters until this fall. I just put in a HTP UFT-80W boiler and it is humming along great. It was suggested by the boiler supplier and many things I read that it should be piped primary/secondary. The supplier spec'd out Grundfos 15-58 pumps.
There are 9 loops of 3/4" pex, but I honestly don't know how long they are. What I do know, is the pipe is only in the center 3500 sq ft. My assumption and by feeling the floor as it warmed up is they are on 2' centers, which would make them 200'ish loops. With the secondary pump on the lowest speed, I am getting about 10-15 degree's delta T. I currently have the boiler set at 115 and the return water is around 100. Both Primary and secondary pumps are one the low speed.
I'm content how it is operating, my question is if I'm wasting power with the 2 pumps and I would get the same results with one. It would not be a big deal to take out the extra pump/tee's and I have a need for a pump on another project so it would save me some cash to do so.
There are 9 loops of 3/4" pex, but I honestly don't know how long they are. What I do know, is the pipe is only in the center 3500 sq ft. My assumption and by feeling the floor as it warmed up is they are on 2' centers, which would make them 200'ish loops. With the secondary pump on the lowest speed, I am getting about 10-15 degree's delta T. I currently have the boiler set at 115 and the return water is around 100. Both Primary and secondary pumps are one the low speed.
I'm content how it is operating, my question is if I'm wasting power with the 2 pumps and I would get the same results with one. It would not be a big deal to take out the extra pump/tee's and I have a need for a pump on another project so it would save me some cash to do so.
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Comments
The parasitic cost of operation of these pumps are minimal, and it ensures peak performance from the heat source. If the heat source has it's own circulator, then it knows what it is supposed to be doing, and can "see" the influence of the connected loads and respond accordingly.
Will it work with just one pump? Probably, but not as thermally efficient as it would with two separate pumps.
I'm certain others will express different opinions, but based on personal experience, these are mine.
ME
Can you post that info with the circ at the 3 different speeds?
I agree with Mark that if you don't know, you should play it safe.
Albert Einstein
I debated about replacing the old manifold with a newer one that would allow balancing. In my brief search, I didn't find any that had adapters to 3/4 pex. I also figured that I would have to buy two for sizing and to deal with where the pipe comes out of the floor. The original setup had a fairly large pump on each water heater that each ran half the loops. The current manifold has I believe 1" female straight pipe thread on the pex adapter with a washer. Would there be any modern manifolds that use 1" npt vs bsp?
I was going to fill the loops with water and blow it into a bucket to measure the volume of each loop, but figured in the end I can't change the outcome so I didn't' take the time. But if they were unbalanced, it would make a case for a new manifold.
I personally would be surprised if they are much over 200'. This shop was built in the middle of the 80's farm crisis years and my family has a genetic history of being minimalists. 7000 sq ft is small by today's standards, but I'm very thankful to have it, even more when the floor is warm.
By controlling the flow across the heat exchanger, you can achieve efficiency gains. Lowering the return water temp by controlling these flow rates will increase efficiency. Not really sure if this is considered "thermal efficiency".
In the system in question, I would be a bit surprised if these efficiency improvements would be worth the additional operating and installation costs associated with the additional circ. In reality, it would take a pretty thorough study to figure it out and it probably doesn't matter much.
In the end these debates usually end up being an exercise in hair splitting.
Albert Einstein
Taylor
Low was 20/18.5, medium was 20.5/19 and high was 21/19.
I have a 12 psi pressure reducing valve on the makeup water and filler/flushed it with cold water. Is 20ish psi in the ballpark?
If loop lengths are identical divide values by 9 for individual loop flow rates. Rough guess at best.
Measuring loop deltas is most accurate when done correctly.
Based on the info provided, you could eliminate the primary secondary and leave the remaining circ on low. You would maintain minimum flow rates, increase delta t and save electricity.
Albert Einstein
However as zman said accurate gauges 0-30 psi, and accuracy between the two gauges can change the readings a lot.
I checked the return lines with my flir camera and as I suspected, some were around 94, others were 97-98. Would I be able to radiate more heat if I slowed flow down? Or would it just even out the floor temp more. My assumption is if I increase delta t at the expense of gpm btu's stay the same.
I also looked at the floor and the pipe is 24-36" on center. The floor temps range from 60 between and 75 on top of the line. Not ideal, by today's standards, but we aren't wearing t shirts either. The sides of the building without pipe had a floor temp of 55.
Thanks for the thoughts guys.
There is a backup modine heater in the building, so it wasn't completely cold in here, but the floor definitely wasn't warm.
Taylor
Supplies are on the left and returns are on the right , top and bottom . RTFM !
Langans Plumbing & Heating LLC 732-751-1560
Serving most of New Jersey , Eastern Pa .
Consultation , Design & Installation
Rich McGrath 732-581-3833
I wondered if it was barrier pex. I guess time will tell.
That diagrahm showed the pump on the supply line, but it is P/S it should be on the return?
The spirovent instructions said to place it after the boiler, and I was told to pump away from the tank, so that is what I did.
The manual for the UFT shows a definitive approach of indirect bottom set, and ch top set. Or vice versa. Not sure if using top and bottom s/r in this case is okay.
Rich has a deep understanding of this boiler.
Seems cycling is non existent.
To make what you have correct , you must remove tees and lower circ , replace tees with 90*s . That would then be direct piped .
If you want P/S you must move the air eliminator , make up water and expansion tank to the system piping , move the boiler circ to the return .
Instructions are tricky things . We all must determine which instructions are most important , in your case choosing the instructions that come with the most costly and dangerous piece of equipment would have been prudent .
Langans Plumbing & Heating LLC 732-751-1560
Serving most of New Jersey , Eastern Pa .
Consultation , Design & Installation
Rich McGrath 732-581-3833
Fernox, Sentinel and Rohmar are reputable products.
The grey PB tubing generally does not have an O2 barrier. It is less of an issue when embedded in concrete.Running low temps will also help. If the 15-58 does not hold up, switch to stainless.
Albert Einstein
Sometimes pictures only paint part of the story.
As to why I plumbed it like I did, I dont have a good reason, other than I came out the top thinking having the air vent and blead valve high would help get rid of the air. I returned on the bottom just because I didnt think there was a real need to return to the top. The top and bottom fittings are connected by a copper tube inside that is teed in the middle to the heat exchanger.
Usually the boiler manufactures want the circ pumping into the hx so the circs pressure differential is raising the psi in the hx preventing the possibility of the water in the hx flashing to steam.
Pumping away from the hx the circs differential would lower the pressure in the hx. This was more of an issue with higher head loss hx designs.
In a closed system, the expansion tank is the PONPC.
Albert Einstein
Our Op does not need the second circ and I recommend , due to circulator selection that he make the modest changes to go direct piped . The circ probably be more than sufficient on Medium speed also , possibly even Low .
Did you also turn the cartridge on the system circ Nick ?
Langans Plumbing & Heating LLC 732-751-1560
Serving most of New Jersey , Eastern Pa .
Consultation , Design & Installation
Rich McGrath 732-581-3833
Just for curiosity. If I left it P/S is there a better sized circulator I should have used.
The flow through the boiler could be so low, and the delta so high, that it will continually bounce off of its ODR high limits. Having the boiler set up as P/S allows the boiler to "see" what the load looks like (a variable), because it knows what its flow rate (a constant) is, and can determine the best burner operation based on the true connected load. It will still cycle due to output exceeding connected load, but not as drastically as it would if piped P/S.
Also, you stated that 24 to 36 inch centers was a problem. How can you determine that? The rules of 12" OC maximum for residential space heating do not apply to commercial/industrial applications. If we did our heat losses and heat gains on a per square foot basis of the building, being nearer to the outside walls, the loads increase significantly. Just as they drop significantly near the interior.
With the conductive heat loss formula being A/R*delta T, with an R 30 ceiling, and a 70 degree differential, 1/30* 70 = 2.3 BTUs/square foot per hour. Infiltration would need to be aded to the conductive losses.
I am not 100% sure, but based on what I've read, this is either a storage barn or a possibly an equipment storage shed on a farm with heat only being delivered to the center core. People are not walking around in their bare feet doing the ooh ahh dance on warm/cold spots. They are conditioning this floor and the connected space. Also, from an overall perspective, the physical plant is only able to deliver around 20 btu's /sq foot per hour (72,000 divided by 3,500 sq. ft. conditioned space). Radiant floors, with constant human contact, are limited to 30 btu's/sq ft/hr (85 degree F surface temperature).
As it pertains to thermal efficiency, across the boiler, a large delta is not conducive to good net thermal efficiency. The lower the delta across the heat source within reason, the lower the average log temperature between the fire and the fluid, the better the thermal performance of the heat exchanger/burner assembly, which equates to less stack loss.
People have a tendency to get hung up on the CON of a MOD CON appliance, when in reality, much of its efficiency comes from the MODulation capabilities of the appliance to match its capacity to the load, eliminating excess air in the process, which is second only to short cycling for killing the thermal output of a given appliance. Large heat exchangers and small flames, combined with low entering water temperatures provide good thermal efficiency. I've witnessed this through the use of a combustion analyzer with the equipment under fire, intentionally varying flow rates through the appliance. Higher delta T equals more stack loss.
To the original poster, unless my eyes are playing tricks on me, I count 10 supplies and 9 returns. Am I missing something or did they split one of the loops out in the field?
Mechanically speaking, you do have the system set up for good and optimal pump/boiler/PONPC operation. If it were me, I'd cut a ball valve in between the P/S tweener tees. Close the valve, disable the load pump and you're in direct series mode. Open the valve and you're in P/S mode. See which appears to be the most efficient and run it that way. Might even need to partially close it.
Also, not being familiar with this particular product, you'd said there was an internal bypass? What controls it? You usually only have one P/S bypass unless you are trying to intentionally control the return water temperatures to keep an appliance (non condensing) return water temperature from being too low.
To @gordy, I find it hard to believe that the pump is experiencing nearly the same delta P on all three speeds. I guess anything is possible.
Try generating a "system performance curve" and plot it on the manufacturers pump performance curves and see where the chips fall. Take the known flow and its associated pressure differential, and double the flow rate. Plot a 3.3 times head increase at that point on the chart. Now halve the load (GPM wise) and plot the head pressure at 1/3 of the original.
Now using a French curve, draw the system performance curves for all three speeds.
Hope this helps all concerned...
ME
Those tridictator gauges are less than desirable for accuracy in performing a delta p circ test.
This boiler is not cycling, and modulation is mid %. I also see the primitive condensate drain. Might want to tend to that. How much condensate is the boiler producing?