New Boiler Circ on my Lochinvar KHN199 - looking for input on which of the 3 speeds to use.

acruxksa

Hi All,
It's been a while since I last posted, mostly because my KHN199 has been quietly chugging along without issue. I recently had the boiler circ pump fail (left over Taco 0011-F4 from previous intallation so 12yrs old). Anyway, I had the heating tech install the circulator that Lochinvar apparently ships with their KHN199s for new installations. Grundfos UPS26-99FC. Boiler is back up and running, but now I'm wondering what speed to set the pump to? I'm going to attached two video's to show what I've got and whats going on. Probably easier than typing it all out, but I'll give the basics.

I'm guessing the Taco0011-F4 was over pumping because I never saw a delta-t higher than 5f, usually closer to 2f or 3f.

Boiler circulator loop is 12ft of 1.25" copper tubing with 5 90deg elbows (assuming 2 T's count as 90s), 2 45deg elbows and 2 ball valves.

With the Grundfos UPS26-99FC set to low speed and all 8 zones calling for heat, I'm seeing 18f of Delta T.
With largest zone and 2 farthest zones calling for heat, I get 5f-6f of Delta-T at the low speed setting.

ODR is set for -20f design day and 125f SHW on the low side and 80f SHW on 60f days (could probably tweak it a little more, but it seems to work pretty well)

With outdoor reset and 37f outside temps, all this testing was done with the system calling for 93f to 96f water.

https://youtu.be/hGo_nH7SWVI - all zones

https://youtu.be/XlEwwH6eldw - 3 zones

Is my thinking way off base? I really don't understand the Delta-T discussions on here and don't know enough about hydronics, or rather probably know just enough to make myself dangerous. Any input would be appreciated. Since I didn't build the house, I have no idea on loop spacing, length etc, but I would guess that it's reasonably well designed given the portions of the installation I can see and the fact that we've had no issues heating the house.

Ironman

I'd leave it where you got the highest delta T and everything still heats fine.

acruxksa

Thanks for the input.

That was my thinking, but I just wanted to get opinions from people who know more than me. I find that my primary source of confusion stems from the fact that after the pump was installed, it was left on high by the tech. Granted, he isn't very familiar with my system, but does maintain Lochinvar boilers.

I spent a bit of time looking at the Lochinvar installation manual but couldn't make sense of the pump graphs and tables.

I did find this "Flow rates are based on 20 feet of piping,
4 - 90° elbows, and 2 - fully ported ball valves. " Which seems close to my 12' and 6 elbows.

Just guess on the low speed since the same circulator is used for two larger boilers. Assumed the 399 was set to high and the 285 to medium. Quite a stretch really......... and totally not scientific......just a WAG. Will know better later in the week when temps are supposed to drop back down into the single digits.

EBEBRATT-Ed

You want as much delta as you can get so the boiler will condense. 18 deg on low speed is fine I would leave it as is

acruxksa

That is what I've always read on here. Even on slow speed, It would seem I may have more tweaking to do because the 18 deg delta was with every zone calling for heat and that never happens. More typical is the 3 zone situation which is only 5-6 deg delta t.

Guessing the boiler is oversized to accomodate the heated sidewalk and/or -18f design day, which is becoming increasingly rare. (used to happen regularly when I was a kid, but now it's probably happened once in the past 5yrs)

A buffer tank has been mentioned on here as a partial solution, but for some reason the boiler techs up here that I've talked to almost immediately discount the idea........

Zman

Techs generally know very little about design. They also ALWAYS leave the pump on speed 3. More is better, right?

I would suggest logging your run times and cycles to determine how badly you are short cycling. Most controllers keep track of this, so you should be able to go through your manual and find total run time and total cycles.

Gordy

You are piped primary secondary. To get best possible performance at the condensing boiler system flow should always be greater than boiler flow.

Leon82

Turning the knob will get you to a screen with cycles and run hours. This will give you an idea of cycle times

SuperJ

You want to make sure you have a system sensor installed after the boiler water mixes with the system water. That way it can compensate if the boiler flow is lower than the system flow.
You can also limit the high fire so the Delta doesn't get to high .

acruxksa

I do have the cycles and run time. It isn't good, but is getting better. We lived in the house for 3 months before I installed ODR. up to that point, the boiler was set to 125 deg SWT and would cycle several times per hour. After ODR, it got better, but still does cycle more than necessary. I've currently got it limited to 85% with extended ramp up times (takes 20 mins to go through the ramp before it gets to %85) to keep it running a bit longer, but unless it's 0f or below out, it rarely makes it that high before modulating back down.

I'm guessing they installed the 199K btu boiler because of the heated sidewalk (heat exchanger is something like 50K or 60K btu rated). However, I turn the heated sidewalks off when temps are below 10f anyway (as do most people around here), so I feel like it really shouldn't have been figured into the boiler sizing equation. In fairness to my current service company who installed the lochinvar, they simply replaced an unserviceable 199K btu munchkin boiler with a 199K btu lochinvar boiler at the direction of the previous homeowner (required in the sale of the house).


I took this picture this morning. Boiler has now been running for approx. 15 months.


System sensor is zip tied to manifold just to the left of the air trap. a bit over 1ft. from the boiler loop.

neilc

shouldn't that sensor be under insulation?
isn't it reading ~1/2 room temperature?
try wrapping a bath towel around it

SuperJ

Location looks fine, but some thermal conductive paste and insulation will make it better.

Personally, I would probably throttle the boiler ball valves a bit until the max delta is closer to 25-30F (or whatever the higher end of the range the manual allows for) with all your heating zones calling, and boiler at max fire/85%limit. That way your return will stay lower under part loads, since you won't be diluting it with hot recirc'd supply as much.

Is the boiler cycling during a heating call (boiler btu > than the zone) or are the cycles just when the heating call ends? If it is cycling during a heating call, you call usually tune the offset where the boiler starts (degree below setpoint), and offset where it stops (degrees above setpoint), and maybe even a min off time.

You should put a ball valve with a drain on your expansion tank so you can set the bladder pressure properly (without draining you system).

acruxksa

Thanks guys.

I'll get some thermal paste and insulation on the system temp sensor.

I believe the boiler primarily cycles at the end of heating calls, but I have seen it got to "setpoint met" and stop while one of the zones was still calling for heat. It's tough to troubleshoot at the moment because our temps are in the mid 30's right now (common for us during an El Niño year). I will be able to dial things in better later in the week when temps drop back down to a more normal range. (high single digits to low double digits).

When throttling the ball valves on each side of the boiler pump, is one side better than the other or both at the same time?

SuperJ

It's better for a pump to push into a restriction than pull thru one. So I would restrict the supply ball valve. Note that this won't improve the cycling since the BTU output is the same, but it will help part load efficiency.

acruxksa

OK,
I've got the system sensor insulated and partially throttled the ball valve on the output side of the boiler circ. Throttled about 30deg on a 90deg valve. Haven't really noticed much difference in Delta-T though, maybe a degree or two. Going to leave it there for a couple days to see how it's working.

Boiler is modulating between %10 and %35 depending on what zones and/or how many zones it's supplying. Typically 1-2 zones but occasionally 3 zones. I haven't noticed it in standby or set point met since this morning, but I really haven't been paying attention. I'll let it run a few days and then compare cycles/run time with the picture above.

Gordy

With a ball valve it takes quite a bit to throttle. 50% flow reduction is not 1/2 the stroke of the handle travel.

acruxksa

@Gordy
Thanks for that. I knew it wasn't linear, just wasn't sure how far to go. I'll slowly throttle it down over the next few days and see what happens. Guessing no matter what, it'll still be better than what was happening when the old pump failed.