Follow-Up: Experiment With Low Speed for 3-Speed Circulator

I just saw a presentation by the well respected HVAC professional John Siegenthaler, and in his dissertation he stated that we really need to get away from thinking that 20 degrees of Delta-T (temperature drop) across a zone is the ideal. He mentions that there are cases where designing for 30 to 40 degrees of Delta-T make better sense.

http://www.slideshare.net/cooppower/siegenthaler- ... tion-small
(see slide # 110)

This has me re-thinking the Taco Bumblebee vs. the Grundfos Alpha circulator. The Bumblebee can be set to maintain any desired Delta-T from 10 degrees to 50 degrees (though it comes from the factory pre-set at 20 degrees).

If the Taco Bumblebee will deliver 6.8 GPM into 8.4 feet of head (as indicated by its pump curve for speed 4), and I have 4 roughly equivalent zones, then:

6.8 GPM / 4 approximately similar zones = approximately 1.7 GPM of flow per each zone. Nothing wrong here since it is between 1 and 4 GPM.

Allowing Delta-T to expand from the previously assumed 20 degree ideal, and assuming that my boiler can crank out up to about 91,000 output BTUH's at 70% efficiency, what actual Delta-T would I dial into the Bumblebee?

91,000 BTUH = 6.8 GPM x Delta-T x 500
Delta-T = 91,000 / (6.8 x 500)
Delta-T ~= 27

If I set the Bumblebee at a Delta-T of 27 degrees it should meet my needs and deliver the full output of my boiler. At a set Delta-T of 27 degrees it should have the capability of "nominally" delivering 1.7 x 27 x 500 = 22, 950 BTUH into each of my 4 zones.

Taco's literature has me convinced that since the Grundfos Alpha is a Delta-P speed varying pump, and since "Delta-P" is not found in the heat equation (BTUH = GPM X Delta-T x 500) it is flying blind and leaving you guessing as to its actual BTUH delivery into each zone.

Of course, to deliver a true 1.7 GPM into each zone when all 4 zone valves are open would require some valve throttling and flow monitoring to equalize the flow through each zone at 1.7 GPM, but once this throttling has been accomplished the Delta-T solution seems to make better sense.

Pretty sure Delta-P can convert/calculate to give GPM.

McGiever wrote:Pretty sure Delta-P can convert/calculate to give GPM.

Well, you've got me (and Taco) there!

I'm aware that feet of water column (I,E., Head loss) divided by 2.31 = PSI (pressure drop, as Delta-P)

And I'm also aware of this formula:
H = K * C * L * (F^1.75)

Where:
H = head loss in feet
K = a constant for the given pipe or tubing internal diameter
C = a correction factor for the fluid type and its nominal temperature
L = the equivalent length of piping for a zone including all the valves, fittings, zone valves, boiler etc... (converted to Equivalent length of pipe).
F ^1.75 = the flow rate through pipe in GPM raised to the power of 1.75

This formula could be rewritten as:

PSI * 2.31 = K * C * L * (F^1.75)
F^1.75 = (PSI *2.31) / (K * C * L)
GPM = F = [(PSI *2.31) / (K * C * L)]^(1/1.75)

Hope I did that correctly.

So yes, technically GPM can be (and is) equated to PSI (pressure drop). But it would still be a neat trick to equate it to BTUH's without monitoring and controlling the Delta-T (though I surmise that even this can be accomplished via pressure drop alone if you set the right equations equal to each other and solve for Delta-T).

As in doing something like this perhaps:

Delta-T = BTUH/(GPM * 500)
GPM = [(PSI *2.31) / (K * C * L)]^(1/1.75)
Delta-T = BTUH/([(PSI *2.31) / (K * C * L)]^(1/1.75) * 500)

Pressure drop, for example, across a water coil (with a know head) can be equated to a known flow (gpm) through that coil.

Fluids and gases moving through pipelines are measured or metered by reading the pressure drop from before and after a given or known orfice plate restriction size installed in the line.

Well, well! Taco has a new Delta-T variable speed circulator with a super efficient ECM permanent magnet motor. It's called the "Viridian VT2218". It has greater output (as well as a broader range of speed variation) than the Bumblebee and a perhaps tad more output (GPM's) for a given friction head loss than the Alpha. So far I can't find anyone who is selling it, but I presume that before long it will be available. Perhaps I'll have to give Taco a call. If it has solved the noise issue that plagues the Bumblebee and they can price it competitively it should easily be a winner. It has the look of quality. The digital display goes well beyond the Bumblebee or the Alpha, and the variable speed operating range is impressive.

http://www.emersonswan.com/ckfinder/userfiles/fil ... 00-114.pdf

I've had the circulator on low speed for roughly a week now and it is working fine with up to 3 zone valves open simultaneously. I don't know how well it will handle the flow with 4 zones open yet, but I suspect that all will be well. The circulator is quieter on low speed, and that's a plus.

Lower speed = lower water flow = lower BTU's delivered to fin tube = lower BTU's captured before hot gases exit going up the stack too.

No Free Lunch Here.

McGiever wrote:Lower speed = lower water flow = lower BTU's delivered to fin tube = lower BTU's captured before hot gases exit going up the stack too.

No Free Lunch Here.

I'll have to see if I notice a spike in the pounds of coal consumed per HDD after I have given it more time on slow speed. I already perceive that I'm seeing my zone valves remaining open for longer spans of time, and I'm also seeing more likelihood for multiple zone valves to be open at the same time, and due to all of this the circulator appears to be running a lot more. If the circulator is drawing lower Watts but running noticeably longer, then perhaps there is no net electrical energy gain, and it may even turn out to be a net loss on the electrical current front.

So far for January I'm at 1.426 lbs. burned per HDD, and for December I was at 1.417 lbs. burned per HDD. Less than 1% difference, so it is statistically too close to call, even though for much of January I've had the circulator on slow speed. So far it doesn't seem to matter much which speed I'm running it at. My observed month to month variations for past months and seasons while running the circulator exclusively on medium speed have been similar to greater, so the minor variation I'm seeing now is not at all indicative of any consumption change that can be solely attributed to the circulator speed.

As to the potential for less flow (BTU carrying GPM's) going through the emitters when on low speed, it could rather be that with the circulator on low speed my spring operated DPBV is merely not being forced to open as wide (I.E., it is seeing less circulator pressure) and that consequently less flow is being bypassed through it (and returned unused to the boiler) while similar flow (vs. medium speed) is being permitted to travel through the emitters. By this logic I may actually be seeing a greater percentage of the flow passing through the emitters on low speed than I did for medium speed (as long as only 1 to 3 zone valves are open simultaneously). But as I always say, logic and/or intuition often make for bad science.

Where I may see delivered heat drop off for low speed is when all 4 zone valves are open, but the garage zone (which is one half of our basement) hardly ever calls for heat unless we drop below zero, and even then it is very rare to see all 4 zones calling at once. I saw this last season when we hit minus 17 degrees though....

Mikeeg02 wrote:When is the last time that zone called for heat? The longer it sits, the cooler it gets, the more heat it dissipates returning to radiant temperature. Hense why I believe what I took from Sting, the closer to continuous circulation the better. (Although I think he likes continuous, my take on it is the closer to continuous the better. ). Less temperature swings both in the room and at the boiler.

Our garage zone can go weeks to perhaps months without calling for heat. Much of the garage is underground. All of the baseboard footage is below ground level. Why waste energy circulating heat through it continuously?

just a plumber not an engineer, pole barn is about 150' from boiler shed and about 15' in height difference, feeding a indirect water heater to feed radiant floor[24x48]. loop runs constant through 3-way zone valve feeding water heater, grundfoss is on low speed, pole barn holds 60f with out a prob, point is use the lowest speed possible,easier on motor/bearings/light bill. ps I am hooked on grundfoss pump they just plain kick ass. don't want to brag they put one in at the plant about 6-7 years ago, for boiler feed pump its pushing 220 degree water at 160 psi 24-7, lost one motor bearing

plumberman wrote:just a plumber not an engineer, pole barn is about 150' from boiler shed and about 15' in height difference, feeding a indirect water heater to feed radiant floor[24x48]. loop runs constant through 3-way zone valve feeding water heater, grundfoss is on low speed, pole barn holds 60f with out a prob, point is use the lowest speed possible,easier on motor/bearings/light bill. ps I am hooked on grundfoss pump they just plain kick ass. don't want to brag they put one in at the plant about 6-7 years ago, for boiler feed pump its pushing 220 degree water at 160 psi 24-7, lost one motor bearing

Good to hear! Grundfos makes top shelf circulators, that's for sure. The height difference is irrelevant as in a closed circulator loop system there is no "height differential" induced head, only "friction" induced head. If you are merely pumping from point 'A' to point 'B', and point 'B' is 15 feet above point 'A', there are 15 feet of "height" head (in addition to friction head), but if the water that goes up hill also comes down hill all "height" head gained in the climb against gravity is effectively erased (negated) by the down hill return.

how aout when it was connected to my old outdoor wood boiler with maybe 2psi on it

plumberman wrote:how aout when it was connected to my old outdoor wood boiler with maybe 2psi on it

If it is considered a "closed system", there is no "height" head to overcome. This old Bell & Gossett dissertation will help you understand.

http://websupport.completewatersystems.com/entrie ... oves-Water

good point, thanks