Sizing Circulators

I am not super-familiar with

the B&G line, but do have access to the NRF-22 curve. It runs from 15 feet at no flow ("dead-head" flow) out to 22 GPM with no resistance. Mid-point is roughly 10 GPM at 8 feet of head.

For your "Baby Zone" (Jeesh why bother, just open the door! , Might the NRF-9F/LW low wattage circulator be a much better choice? Even if you use a full 1.0 GPM (oooh!) you can deliver that against 7 feet of head. Assuming a 20 degree delta-T this is reasonable.

By comparison, a Grundfos UPS 15-42 (if they still make it?) is good for 1.0 GPM at about 11.0 feet of head even on speed 1. This may be more than you need and draws 45 Watts. The B&G draws 40, not much difference though. Your call, but only when you know the resistance.


Sight unseen and with average conditions, this does not seem out of line especially if secondary pumping is going on here.

Your prime heating zone at maybe 4.0 GPM could be met by the NRF-22 against 12 feet of head. That seems like a lot but again I have no particulars of lengths and fittings. My own house pumps 7.5 GMP against 7.5 feet more or less, but this is secondary to my boiler circulator. My distribution splits from 1.25" copper to 1" most of the way and is piped reverse-return. Round trip is about 110 LF plus fittings as a point of reference only.

I would use the smallest circulator that does the job, David, we agree. The Grundfos line is excellent but regardless of the adjustability, the selection still has to come close. I think of the 3-speed feature as being like getting three different pump models firstly, and adjustment to load secondarily.


Save the big flow for the indirect and bathe that sucker in hot water. But heating is forgiving of flow variation as you recall. If it drops by 50 percent, you will likely get 90 percent of your capacity. We all need slack in life but I hope you get more than just good flow.



Brad

Thanks Brad--that's a shot of fresh air

I gather we'll have to measure the length of main supply run and then lengths of 3/4" supply and returns to and from rads, and elbows and tees. Some of this might be hard to see. I guess from the monotee off the main below the 3/4" will have at least one elbow going into the convector and one out. (Though sometimes due to conditions I've seen multi-elbow combinations near the element.)

So then the head and gpm can be calculated knowing the length of run plus branches, elbows, tees, pipe diameters and heat loss. I think this measuring (estimating) shouldn't take more than 45 minutes or so.

I have been reading Dan's pumping away--but in small doses since it makes my brain hurt. Interesting you say that a drop of 50% of flow will only lose 10% capacity. But overly fast flow as I understand it--especially through baseboard--can prevent emitter from discharging the btus.

thanks,

David

When I run into one of these

I generally look to see if the main house zone can be split. Sometimes it can be- this is great if you can put bedrooms on one zone, main living areas on another. Having the capability to run lower temperatures in areas that are not occupied will save fuel.

Monoflo systems can be tricky since the flow splits so many times. The special tees that make the system work, add a noticeable amount of resistance ("head") that the circ must deal with. The more Monoflo tees, the more resistance.

Try this: Get an infrared thermometer. Start up your system with all radiation turned on. When the return line gets warm, compare the supply line temp leaving the boiler with the return temp. You're looking for a difference of 20 degrees or so, if this is what you get the circ size is OK. If the difference is noticeably less, the circ is too big (most are). If there is too great a difference, the circ is too small.

Note that many infrared thermometers need a black surface from which to take a reading. If you have copper pipes, wrap some black electrical tape around them before taking readings.

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Valves are short money

When I want to take a shower, I go to the tub. Valves rule.

I-R Thermometers

are the best invention since Data Loggers... IMHO. Plus with the laser feature you can endlessly harrass the cats.

As Steamhead says, a spot of black (paint or tape) will yield the results.

Absent an I-R thermometer, a good multi-meter might have a thermistor feature (very accurate) and can measure surface temperatures precisely.

Your measurements at the surface will be off by a degree or so from what is in the pipe, but it is the Delta you seek. All other things being equal, surface measurement is just fine. Besides with a MonoFlow system, your temperature will decay along the lenght. Each runout set to emitters should read about 20 degrees differential and the S-R differential at the boilers likewise shouls also.

Many systems work perfectly fine without any fancy balancing because flow to output can be so forgiving. But how well they do is good to know, to have a base-line. Key to the exercise is to cut down your parasitic transport losses (circulator amperage) to their minimum.