VIESSMAN 100-W not Heating house

Rabbit02

I have a VITODENS 100-W B1KA 35KW COMBI propane gas boiler installed January 5, 2018 with a low loss header that is not heating the house on cold days, lets say 10 degrees F and below. The old unit that this one replaced was a Peerless Pinnacle PI-80LP which was installed October 4, 2004. The Pinnacle was piped incorrectly per manufactures instructions. It was series piped, no primary secondary. The Pinnacle despite being installed incorrectly heated the home perfectly fine for 13 years and 2 months. The new Veissman cannot keep up. The outdoor sensor is installed. The temperatures are as follows: 170F supply out of boiler into low loss header, 165 return back to the boiler from the low loss header. 158 F out of low loss header on secondary side and 150 F returning to the low loss header on secondary side. 2 zones with Grundfus UPS15-58FC circulator pumps on speed 3, fast as they go. Internal Circulator on highest speed also. On last visit to job, it was discovered that the flow to the low loss header is not piped in the direction that is specified in the manual. The manual shows cross flowing it, it is not. Going to job to fix, switch the piping around to get the direction right next week. I have my doubts this will fix the problem. Is the flow direction that critical? I know about measuring the baseboard to get the connected radiation and of course the heat loss, but old boiler heated it.... Any Thoughts?

Alan (California Radiant) Forbes

I'd slow down the pumps because your Delta T is so close together. An 8 degree Delta T on your system side is way too small; should be at least 20 degrees.
Put your boiler pump on speed 2 and your system pump on speed 1.

Jamie Hall

Ah... unless I'm reading the specs wrong, the new boiler is roughly twice the rating of the old one? If the old one could keep up, and the new one can't -- something is seriously wrong.

Brewbeer

Fin tube baseboard that needs to be cleaned?

woodrow

what kind of heat emiters did you adjust gas pressure and do a combustion test and i second turning the pumps down

GW

I’ve been down this road. Sometimes 170 does not cut it.

HVACNUT

What's the boiler say outdoor temperature is? Is the ODR set for X boiler temp to Y design day outdoor temp?
Not sure but I believe if you raise the thermostat all the way it overrides the ODR as theres no way to actually remove it.

sunlight33

how often does your boiler cycle on/off in one hour?

GW

> @Alan (California Radiant) Forbes said:
> I'd slow down the pumps because your Delta T is so close together. An 8 degree Delta T on your system side is way too small; should be at least 20 degrees.
> Put your boiler pump on speed 2 and your system pump on speed 1.

Alan the zone is hot, hot means convection, how is 20 going to help? Seems like more temp is needed

DZoro

Correct the flow and I think you will be fine. Your numbers look like the flow is backwards.
D

GW

I read way too quickly, yes the boiler side and the system side should be much closer in temp, swap the header piping like you indicated

Rabbit02

We're gonna swap the piping on the low loss header and see what happens. Thank you all for your suggestions, I do appreciate it. But I must say that the faster the water goes, the more gallon per minute equals more btu's. I've had this discussion with service techs, install techs, comfort consultants and there is a myth that the gpm can be too great. The facts are that the more gpm the more btu's to the radiation. The only down side to fast water delivery is noise and energy consumption. People think if the water is moving too fast that a btu doesnt want to "jump off" the train because its too dangerous, but that is simply not the case. A 10 degree temperature difference is better than a 20 degree temperature drop. A 20 degrees temperature drop is for 1 GPM for each 10,000 btu. So a 100,000 btu boiler needs 10 GPM to have a 20 degree temperature drop. One has to look no further than a manufacture's fin tube baseboard literature to prove this. I know this will start a frenzy of a conversation, it always does. lol I respectfully disagree with slowing the pumps down. See attachment. I'm hoping the swapping of pipes fixes it.

Rabbit02

The boiler is cycling, it heats up to limit and shuts off, just can't seem to get the heat out to the baseboard.

Canucker

> @Rabbit02 said:
> We're gonna swap the piping on the low loss header and see what happens. Thank you all for your suggestions, I do appreciate it. But I must say that the faster the water goes, the more gallon per minute equals more btu's. I've had this discussion with service techs, install techs, comfort consultants and there is a myth that the gpm can be too great. The facts are that the more gpm the more btu's to the radiation. The only down side to fast water delivery is noise and energy consumption. People think if the water is moving too fast that a btu doesnt want to "jump off" the train because its too dangerous, but that is simply not the case. A 10 degree temperature difference is better than a 20 degree temperature drop. A 20 degrees temperature drop is for 1 GPM for each 10,000 btu. So a 100,000 btu boiler needs 10 GPM to have a 20 degree temperature drop. One has to look no further than a manufacture's fin tube baseboard literature to prove this. I know this will start a frenzy of a conversation, it always does. lol I respectfully disagree with slowing the pumps down. See attachment. I'm hoping the swapping of pipes fixes it.

That's what the calculations are for, finding the sweet spot. Exponentially larger pumps with the associated higher power draw and fitting erosion, for minimally more BTU delivered are bad.

Gordy

Would you agree that you can get 100k out of that boiler at different flow rates, and wider deltas?




I’ll agree higher awt across an emitter increases output, but with diminishing returns.

Gordy

What you gain with a lower gpm, and wider delta at the boiler loop is condensing efficiency more often when Loads allow.
I believe a 35 delta is allowed with that boi
System side flow should always be more than boiler side.

The math is very important.

Alan (California Radiant) Forbes

Agree with everyone. I wanted to see if a reduced flow would result in better LLH mixing. If you're correcting the piping, it should all fall into place. Let us know how it goes.

GW

Viessmann has some unique math if you really want the “full” output from their boilers (if you follow the max flow tables). Thankfully most of the installs are a bit oversized (we inherently overshoot the boiler size). The normal boiler changeout will never see 30 degree drops. Temp needed to heat the home when it’s super cold has little to do with what temp drop (delta t) you “expect”.

We “could” slow the flow to actually achieve a 30 drop but that will likely mean a cold room or two at the end of the loop. More so, didn’t we send fewer BTUs to the home is this scenario?

Gordy

The system side doesn't care how it's getting it's say 100k from the boiler side does it? Whether it's 13.33 gpm at a delta of 15, 10 gpm at 20 delta, or 6.67 gpm at a 30 delta. The boiler cares as it could possibly condense, and be more efficient.

The system side should always flow more gpm than the boiler side. For efficiency.

In this scenario If the sep was piped right, the primary is seeing 165 return to the boiler, and the secondary is seeing 158 out to the system from the hydraulic separator , and 150 back to the sep. then the system is not using all the btus the boiler is making. Those btus go back to the boiler. Wasteful.

Hopefully the repipe of the sep. changes things.

Rabbit02

thanks guys for the replies, good stuff here. I will let you know the end result. We wont quit working on it til its resolved.

Rabbit02

Nope, it did not fix it. Still not keeping up. Thinking about removing the low loss header entirely and series piping it straight thru the boiler. That way the boiler has to fire. Right now it is in low fire because of the temperature difference is small. Series pipe it in and let the thing fire up.

GW

please excuse the quick-slung wiring----when it's cold out we are not waiting for the wire boys

RPK

What were the temperatures after the piping changes? Were you getting the full 170 out to the zones? If you are, I think you’re probably bumping up against the max output of your emitters at 170 degrees.

GW

we did two boiler jobs recently- one oil boiler and one Bosch Greenstar. Both mentioned 'it's not warm enough in here". The oil--we had that at 180 high with a 20 degree diff. So we go back and made it 190 with a 10 deg diff. The Greenstar---we went back, jacked the setting to the point where the outdoor reset is virtually useless, and maxed out the high limit and reference temps to 186. I would have had huge problems with a Vitodens 100. Wonderful unit (I have one at my own home), but the max temp is a little scary

Alan (California Radiant) Forbes

What kind of heat emitters do you have? Are you sure you've purged the system properly?

TAG

GW -- that's an interesting T you made up. Do you typically not use the LL header? From your last post --- are you indicating that in retrofit situation the need for 180 water is often the case ? And the 100 or 200 is not able to provide (Viessmann is around 170 max correct?). Just trying to understand you and the OP's situation as I think I'm going to use a 200 in my next project. My plan was the LLH as well.

Gordy

You have to be careful when using the V unit with existing radiation. Making sure there is more than enough to properly function with that 170 max temp out of the unit.

DZoro

What are your numbers after the re-pipe? Do you have baseboard radiators, if so how many feet of fins?
D

TAG

Gordy: That was my thought when I went looking ... even with design .. I was wondering how the 170 was for factoring DHW production. Have about a 52k load and the smallest Viessmann is 67K in .. I think around 62K out ... so at 170 ..what's my DHW production. 2 showers no tubs .. Even with 52gallons what the recovery. Has me thinking ....

Gordy

My thinking was more along the lines of the existing radiation. Can it meet the 52k with what water temp? If it is only enough for 170* awt for a design day one is screwed with this passed polar vortex.

In GW’s scenario he was able to bump the water temp up to get a little more output with the boilers he used.

Gordy

My point is when using the unit you have to think about the max supply temp, and make sure the emitters can meet the load with the AWT of the system. If emitters are short for it you need to add more, or go to a boiler that can give you a higher AWT.

Gordy

As far as domestic you raise tank temp, or the indirect size. Adapt to the recovery. Usually it’s not a big deal unless there are huge gpm usages.

GW

Hey TAG i have a small rebel steak (Good God that was supposed to be Streak) within my soul and I am not totally swayed that the LLH is necessary, at all. If there's junk in the system then i made provisions for that. I've used llh's in the past but not often. The t set up-- it's an Alberta Tee and I buy them in 6 foot lengths and cut them in sets of two. It looks fab in my opinion. It's not cheap, but it is less than a LLH.

http://www.profit-products.net/images/companies/alberta/72in.pdf

I know Viessmann says it's necessary for proper math, but my math doesn't seem to understand their math. That's a different thread I guess

100 and 200 boilers----unless you have lots of time on your hands to analyze existing heating systems (determine if 170 will cut it or not, and, by the way, the home owner will be the judge and not you), it's a little scary.

I've installed 89 100s and 39 200s a and b series over the years (just visited my spreadsheet). I've been called to the carpet a few times and it's NOT FUN. Thankfully I was able to slither away and the homeowners agreed that tightening up the home was a good idea, but if i had hard-case people to deal with that would have been a real pain.

Gordy

With a combi it is what it is. That’s why they have such high inputs to meet that domestic load. Not sure what the V was thinking on making that unit a combi with the input it has. Other than probably European hot water habits verses North American.

GW

Yes, it's the temp of the water, how much emitter and the Heat loss of the home that dictates how fast the gas meter will spin. The boiler is just one cog in the wheel

Gordy

As you can see it’s kinda weak on DHW. 77 degree rise at 3.5 gpm.

TAG

Sorry to jog the OP's thread -- but I was trying to understand the LLH in the mix and if it can indeed cause lower output vs close T's. I get the OP's idea of piping direct (if possible) that's going to eliminate any possibility of not getting all the BTU's. I see that with the LLH you are not going to get above 160 out to the house. So the LLH is eating 10 degrees of the 170 max .. ouch if you need 180 to a radiator.

Have used high mass boilers in the past -- my new project is Warmboard and slabs. Have to use a small physical boiler (small mechanical) -- only propane. This will be my first with wall type boiler. I'm using an indirect HW

Gordy

There is plenty of formulas, and literature reading see Caleffi

It’s all about the system side flow, and boiler side flow to get the mixed temp desired out to the system. With a mod/con you want the best balance of low return temps to the boiler also. System side greater flow than boiler side.

Really closely spaced ts do the same mixing.

DZoro

@Rabbit02 Could you post some pictures of the system. Something just seems amiss.
D

SuperJ

If the boiler is bouncing off the high temp limit and the system temp isn’t up to set point then the boiler flow should be increased.

Is there a chance the hydro sep is undersized for the flow and creating some odd unpredictable turbulent mixing inside from the high velocity? The temps don’t really make sense. You should see a blended boiler return and blended building supply at the same time, only one or another.

Alan (California Radiant) Forbes

".......i have a small rebel steak...."

Is that an Eastern cut? We have rib eye, filet, skirt, flatiron......

|:~)