boiler bypass / flow rate

Timco

With my volume being soo large, I am installing a boiler bypass with circ and auto flow meter to get my delta t down. My boiler gets to 150 on supply, and stays at room temp on the return of the longest loop for about 15 minutes, then climbs. With the boiler bypass protecting the boiler, should I increase my flow with a 00-10 to get that return up faster? Currently using a Grund 15-58 on speed 3 to circ aprox 200' of 3/4 loop feeding 1 large, 2 med and one small rad. Largest rad gets full temp before last rad heats.

Thanks,

Tim

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Timco

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Bob Sweet

Timco

are you using a deep set back on your t-stat? Not sure of your piping set up or boiler, are you setting your bypass up pri/sec. that would be my choice. With 200' of pex figuring 4' hd per 100' add 50% for fittings you've got 12' hd, the 15-58 and 0010 are about the same performance @ this point in the curve. After that the 15-58 performs at a higher head than the 0010. The 0010 has a flatter curve, more gpm less head.

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Timco

t-stat is standard honeywell round. Boiler is Crown Auruba, 162k btu. Am comming off supply manifold with 1" bypass to return, controled by small circ & flow control...4-5gpm, 150*.. No fittings besides at rads on runs. Local rep says 0010 would get the return temp up faster, which was my concern. Units warm well, but last rads on the loop do not quite make full temp when t-stat is satisfied. As I mentioned, it takes about 15 min from cold to get the return temp to rise. Would you suggest a superbrute to speed up the flow? thanks for the advise...Tim

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Bob Sweet

Timco

It seems the boiler is oversized if the t-stat is satisfying in 15 min. Doesnt seem as though it's a lack of gpm pump. If you were to pipe it in pri/ sec it would allow you to use 2 smaller pumps and de-couple the pressure loss between the boiler side and the system side giving the boiler protection, and the system proper flow. I'd use a 15-58 on the system side lower the supply temps and try and get a longer run time out of the boiler, possibly slowing the flow to get a more even heat distribution on speed 1 or 2.



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Timco

When I say 15 min, that's to get the return rising. Takes about 35 min or so to satisfy a 3* rise in temp on a bright sunny day in one unit with no others running. 4-plex. Almost 3000sq' total, all single pane, wood floor, avg.insulation, double brick...I will try 150* water today after the bypass is installed. Seems if the front of the loop is not getting soo hot, the back should catch up and I should get a longer run time.

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Empire_2

I don't mean to interupt, but

Am I reading this correctly:,,, 3000sq/ft with 3 rad's? I am surprised that it heats the house. Even with the 162btu, boiler. Also, is your 200 ft out and back? is the rad's in series or on separate supply and return?

Just another note @ 3/4" pipe @ 200' with fudge factor, looks like 12-14 ft head required. The only problem is that you really do not have the volume due to pipe size to convey the 160M/BTU/Hr to your set up. At minimum you can work with (Ideally)1 1/4" pipe, but 1" would work if you increase you delT. 160M @ 20* Del T requires 17 gpm flow thru boiler, but since your 3/4" pipe is so small you delta t is gonna be very hi, and I'll bet that puppy is screaming. Your velocity is currently very hi. Almost out of range. In other words,....Change your supply piping. I just cannot understand the # of rads though..;-)

Mike T.

Timco

Units 1&2 have the same rads...1 very large, 1 large, 1 med, one small. Unit 3 has 1 very large, and one large rad. Unit 4 is all slantfin 3/4 BB. I installed my bypasas today, 1" off 11/4" manifold with 15-58 circulating through a watts flow regulator. Return & suppy are 10-15* difference now, but largest rads still heat first, and cook the front room before the rads at the end of the loop heat. Tomorrow I am changing the two largest zones to parallel pipe design, as the loop was too uneven with the EDR of the largest rads. I believe the 15-58 will work well in that design without moving up to the 2600 series. All should heat even and have pleanty of flow at 3/4" runs entirely. Reduced water temp to 150 as well.

Thanks for the advise. All is appreciated. I have serviced and swapped boilers, but the entire system is a bit new to me.

Tim

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Mike T., Swampeast MO

These are cast iron radiators? Connected in series?

If so, just increasing flow rate is very unlikely to help much with the imbalance problems. The first rads will STILL hog the heat...

You either need to set up a two-pipe system or one-pipe system with diverter tees. If using diverter tees please study the system VERY carefully before you start changing the piping...

Timco

All CI rads, except #4. (BB) I think it is easiest and best with the loop in place (rads currently in series) to just run them 2-pipe. Would I find diverter t's these days that would work on a 3/4" hpex loop? Maybe that would be easaier afterall....The supply is across the hall from where most rads are to get to the farthest rad (largest) and the rest of the rads would have fairly long arms to get to the supply pipe.

T

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hr

A bypass without a brain

may not be of much use. You really need a control that can sense the return temperature at the boiler and adjust or respond accordingly.

A delta t pump, like the Grundfos Miximiser may be a better choice, or add a tekmar vs control to your pump, vary speed based on temperature.

A Paxton 3 way thermostatic wold be another simple way that has some brain power to react to temperature.

Sounds like you need some repiping to split the loop to get good supply temperature to the distant emitters?


hot rod

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Timco

I re-piped today...all is perfect. Went to a two-pipe system, and left two rads in series from a tap to get some resistance. All warms perfectly even. As for the bypass, I set it for a 10* delta t and walked away. The 15-58 circs it well, and throughout warm-up, even when a cold zone starts to circulate, I maintain a 10-15* DT. Seems to be mixing well. I have a large, single zone converted gravity system boiler swap comming up and will use a bypass with a brain on that one....I do believe this boiler, however, is happier now than yesterday.

Thanks for the advise!

Tim

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