Question about Setpoint/Supply and Pumps on an old house setup..

Javelin

Dear Heating Pros,
Over the past couple years you guys have been great in getting me educated enough to put in a new boiler. I've put up diagrams in the past and all is working, but I'm not quite seeing the efficiency I was expecting.

Namely, I'm wondering if my main zone pumps (Taco Bumblebees - http://www.supplyhouse.com/Taco-HEC-2-Bumble-Bee-Circulator-w-Integral-Flow-Check-1-20-HP) are getting the heated water "out" of the boiler fast enough. My boiler generally gets the supply temp up to the stepping them pretty quickly, but then cycles off with a "CH Setpoint Met" type message.. Only after a timeout, does it then continue to heat up the water a bit more, until the RETURN water actually heats up.

I guess what I'm asking is given that it's a 250k BTU boiler on a, 5,800 sq. ft. or so house with one zone covering MOST of the house, is this Bumblebee's GPM enough? The original pump that was old/corroded, etc. was a B&G 100 model which looks like it pumped out 33 GPM compared to the Bumblebee's 15 GPM max.

I was thinking of replacing the one zone's bumblebee with a higher GPM model so that it can get the heated water "away" from the boiler faster, eliminating the cycling.

Then again, I'm a web designer and am still learning all of this, so really have no idea. Anyone have any thoughts?

I've attached a mockup of the system as well as a few photos of it firing if it sheds any light.

THANK YOU ALL IN ADVANCE!

Jay

SWEI

Are you running the pumps in ΔT mode?

Javelin

SWEI, I started with deltaT, but because of my fear, changed to contact speed at the highest level (4 I believe). In terms of radiation - the house has all old cast-iron radiators.

The system DOES work and has been working for the last two winters, but the first was filled with a LOT of firings (before I changed to constant speed pump setting and timeout delay), last winter was ok, but as I said, not as efficient/economic as I had hoped.

I realize it's a big old house and that might just be the nature of the beast, but wanted to be sure at least the boiler settings are correct.

Zman

What is the lowest boiler firing rate you see?
How much does it overshoot and undershoot the target temp when it is cycling.
Normally the boiler will drop to it's lowest firing rate and cycle on and off with a 20 degree differential when it is at the lower end of it's firing modulation.

Gordy

Having a 30 degree delta is not bad for cast iron radiation. You are a little more than that. The bee is probably a bit under sized.

Question is are you comfortable?
Maybe the VT 2218 will get your delta a little narrower. But is it worth the switch? Will it fix the short cycling probably not.

Those are nice return temps for a mod/con so cycling is the issue.

I'm with Zman maybe a boiler parameter issue.

Javelin

Thanks guys,.. Zman, I've seen firing as low as 4% the panel says, and when it overshoots the target temp, it usually only does so by about 4-6 degrees. But what is the "supply" reservoir? I mean, what is it heating to 120deg? The internal water in the boiler? if that's the case, isn't that just a few gallons, then cold water comes in and it fires again? Is that the way it's supposed to work? It seems to me that it should be firing for more than the 5 minutes or whatever it takes to hit the setpoint.. no?

Gordy, That VT 2218 you mention looks like it only has a few more GPM than my bumblebees. The reason I asked about the B&H model was that it moved a LOT more water through.. isn't that what I'm after here? to "clear" out the hot water from the boiler and get it up to the radiators more quickly?

Gordy

Was the original a 100 or a 100 hv? The difference in curves are a lot . The hv having a steeper curve.

Quercus

How far into the heat call are you taking those pictures? With a big CI system there is lot of mass to warm up and it will take a while for the return temps to come up. If you are running all the time and those are equilibrium temps, then you may have an issue with setup parameters. Are you using ODR?

How many therms do you go through in a year and where are you located? If you are connecting to large pipes with parallel piping you shouldn't have huge pressure loss through the pipes.

Harvey Ramer

Put bigger pumps in please. Your house will heat more uniformly and the boiler will be happy.

Never personally seen or heard of a TT that liked excessive delta-t's.

Those old high mass gravity systems like you have; I like to see them run on a dialed in ODR curve at about an 8°- 15° delta-t range (high end to low end of curve) That's when every nook and cranny in the house becomes snookam, as weezbo would say. I think it's Alaskan lingo. It really works well on constant circulation with indoor feedback. I may be mistaken, but I believe that is a feature of the trimax control on your boiler.

SWEI

Be aware that 4% doesn't actually mean 4% -- the boiler can only turn down to a 65k firing rate.

We have a job with a pair of cascaded PTS250's using HEC-2's as primary pumps which are working just fine on speed 4, though we had all manner of weirdness trying to run them in ΔT. To be fair, there is nearly zero resistance in the loops (less than 15 equivalent feet of 1-1/4" steel pipe there.)

We are running ΔT (30˚F IIRC) on the DHW loop and have not seen issues with that.

Javelin

Gordy, Quercus, Harvey and SWEI, - thanks again for your continued help trying to get me right... A couple more points for your consideration/recommendation if you don't mind:

1) The system does have an ODR and the boiler is set to Switch and Outdoor reset.

2) The boiler seems to meet the setpoint fairly quickly (in about 5 minutes), but as stated, I think it's meeting it this quickly, because the hot water it heated isn't getting "away" from the boiler fast enough (due to the lower GPM of the pump maybe). 90% of the old house is on one zone, and I don't think there is much resistance as it's all old gravity fed iron pipes - 2-3" in diameter.

3) Getting a new pump.. is there a brand/model that you'd recommend? My Indirect tank has a Taco 007 which seems nice, but at 23 max GPM might not be a big upgrade. What do you recommend, and the flange distances should be pretty standard right? so I can just fit it in fairly easily?

Thank you all!

Jay

SWEI

15 GPM will pull everything that boiler can deliver at full fire without tripping an alarm. As the RWT goes up, the boiler will ramp down its firing rate until it gets to minimum. At that point, the only thing it can do to try and maintain SWT is to stop firing.

Oversized boilers are a bummer.

Javelin

Thanks SWEI, I don't think it's oversized. Back a few years ago, JStar came out to the house and did a whole Manual J or whatever it was. It's a large old house with little to no wall insulation, and while we're continually upgrading where we can, heating loss will continue to be an issue in the future. So you say that 15 GPM is enough (which the bumblebee moves right?), But Harvey Ramer says that I should put in a bigger pump.

Thoughts?

SWEI

The HEC-2 can move enough water as long as it has very low head. I'm guessing your distribution piping may be slowing it down a bit. Any way to measure pressure on both sides of the pump? The displays don't show measured flow, just an estimate. I'm not sure how good the Taco algorithm is -- I hope it's better than some of the others.

Eastman

Javelin,

You are saying the boiler shuts down with 80 degree return temperatures? Can you confirm that it is 80 degrees? --that is cooler than body temperature.

Gordy

Is the Boiler piped direct, or P/S?

I'm a little confused with the low return temps, and system is meeting setpoint. Copious amounts of radiation?

Steam heads paper on sizing circs for converted gravity systems may be worth a look, but it deals with CI boilers.

Eastman

I calculate about 6.6 gpm based on the 38 degree delta T and 51% firing rate. (Assuming 51% equates to 125k btus per hour)

Eastman

In the original post there is an included photo of a bumble bee pump running with an indicated flow of 13.4 gpm. The included diagram indicates this pump supplies only the family room. Are the issues you described related only to the family room zone? Are the boiler operation photos taken during a family room zone call for heat?

Gordy

It seems the concern is efficiency of the boiler operation.

Javelin

Eastman, I have two zones... one is the family room, and one is the rest of the house (about 90% of the house). The BIG zone (served by one of the bumblebees is my concern). I'm going to fire it up and make notes of specific times/temperatures tomorrow so I can share them with everyone here.. Maybe even put up a time lapse video or something.

Thanks,

Jay

Eastman

That's great. But were the photos in the original post all taken at the same time for what I assume is a call for heat from the family room zone?

Harvey Ramer

I'm trying not to hit this to hard but, I would be putting a bigger pump in. A Taco 0010 might be about right.

Gordy

https://heatinghelp.com/systems-help-center/sizing-circulators-for-old-gravity-hot-water-systems

Harvey Ramer

That chart Gordy posted, produces very desirable results. Especially when coupled with ODR control. I have used it again and again. Every time, after you see the drastic difference in comfort, you get that nailed it feeling.

Gordy

Gravity flow is more ferocious than some people realize in its natural state. Think of it like this. If convective flow can happen with in a single small diameter pipe with hot and cold water flowing in opposite directions. Just think about it in large diameter piping

Javelin

Hey Guys, Would you believe that I haven't replaced my pump yet, but as heating season approaches I'm thinking I'm going to tackle it this year. On the chart Gordy referenced above, it looks like my system (250k btu Triangle Tube Prestige boiler) would be looking at 35-40 GPM on a gravity conversion system... With 3 1/2 feet of head to account for boiler/near boiler system, it seems that a TACO 0010 at 30 GPM might not even been enough? Think I should try a 0012? (Quite a bit more $)?

I'm guessing either would be a bit boost over the Bumblebees that on the system now, just want to be sure I do it correctly (finally).

Gordy

The 0010 should do it if your head is correct. However the 0012 3 speed would give some latitude.

Javelin

How do I know what my head is? I was going just from that chart posted before.. All the pipes ARE big old iron, gravity fed conversion.. only new copper is around the boiler.

That being said, I'd RATHER user a 0010 if it's close as the flange distance is the same as my bumblebees - so no re-sweating, however, it's much more important for me to do it right...

Are TACOs the best?

On my system I have two zones (controlled just by the pumps). Zone 1 is most of the house, zone 2 is an enclosed family room that is close to the boiler, but where heat loss is probably more.

Maybe I should get one 0010 for now for the BIG HOUSE ZONE, see if it helps out a lot, and if so, leave well enough alone - or maybe get another 0010 for the second family room zone.

If the 0010 doesn't cut it for the main house, then I can upgrade to a 0012 for the main house later, then use that 0010 for the family room zone?

Do I want/need the IFCs on these pumps? I see that it reduces overall flow...

THANK YOU! AGAIN!

Javelin

So I think I'm overthinking all of this. In looking at my near pump setup, there isn't a lot of room to easily expand the flange distance, so I think I'm just going to order 2 0010's that will swap in easier and call it a day. Their GPM is literally twice what the bumblebees are now, so it's got to help right? Any real reason not to? Worst case I figure it won't be enough for the main house in which case I'll have to really re-configure things for the bigger 0012 down the road.