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First high efficiency boiler on my own...short cycling! Help! (16 Posts)
First high efficiency boiler on my own...short cycling! Help!I have piped a lot of boilers for companies I hjave worked for and feel confident in doing so. I recently last year went out on my own, at first things were slow but momentum is finally moving my way! Im scheduling work a week out and it feels great to earn.
I understand the concepts of a mod con boiler, outdoor sensor, primary secondary loops etc. I have heard several times in my career that the greatest plumbers are lousy heatguys and vice versa, but I am determined to be great at both. The onset of the heating season has brought in a lot of boiler inquireies/estimates and the first estimate i gave wanted me for there boiler...(Most likely because I priced it to cheap...)
So I know that Burnham Alpines are very popular with plumbers in my area so I thought that would be a good choice. The boiler there was...odd. It was a steam boiler converted to hot water (never saw that before) and it was. their hot water heater was in rough shape so I suggested adding on some tees for a future indirect and I inquired with the one of the sales guys at the supply house about the sizing. He said that the sq ft and baseboard of the condo only called for 60-70k BTUS and that it was customary to add 100k for the indirect....ummm ok that sounded a little ridiculous.
I figured I would put in the alpine 105 and leave an extra 30 or so for the indirect. So fast forward...all done with the boiler. (pic attached) So I had a friend of mine who is also a licensed plumber help me. Honestly he is not so confident with high efficiency systems but he has more experience than me. First off, I installed a programmable thermostat that was sent to the homeowner from the state as part of their rebate. My friend and I went through all the settings. Adjusting anything we knew for sure needed to be changed, outdoor reset:on indirect:off priority:off etc. And the ones we were unsure of we left alone like the set points. I went up and turned the thermostat up to kick the burner on, which it did. When I turned it up, i turned it all the way up to 90's which might have confused the boiler a bit since the temp outdoors was in the 70's. The boiler short cycled a few times up to 140...off...down to 120 or 130, back on up to 140...It was late and not cold out so I left the boiler off and took the book home to read up. So went back today and tried turning up the thermostat a little above the room temp
and the same thing...short cycles. Called burnham, first off I was scolded for oversizing the boiler. the tech said you never add anything for a indirect set on priority...he asked me if my tees on the primary loop were spaced appropriately and yes they were. He suggested jumping out the TStat on the boiler to eliminate that as the problem. I jumped it out, fired it up and it actually went up to 130 as limited by the outdoor sensor and then I heard it "Modulate down and maintain the temp" just like the burnham guy told me...it stayed there for about two minutes before shutting off and then started short cycling again....I am extremely frustrated. I will be calling the burnham guy again tomorrow but was hoping some of you heat experts could give me any tips. Thank you in advance!This post was edited by an admin on September 26, 2013 12:34 PM.
What is going on with the temperature of the pipes?
It sounds like the boiler is running fine but the water is not getting to the zones. Are you getting hot water to the radiators? What kind of radiators?
Which circulator do you have on the primary?
You are missing the boat on the outdoor reset. That is a different subject
alpineThanks Carl, I think I meant outdoor sensor, as in if its 70 out its not gonna fire up to 180. The return is coming back hot, although I did not go upstairs to feel the baseboard but I will check that tomorrow. Another thing I thought of, probably a long shot, but the primary pump speed? I think when it initially started short cycling my friend tried flipping it up to high...Although I dont see how that would make a difference. I thought the primary loop was to feed the boiler with prewarmed boiler water instead of cold baseboard water. On the primary I have the Taco 3 spd that came packaged with the boiler and on the zone i have a 007. Thanks Carl.
alpineshould I have a flo-chek in there somewhere? The piping diagram showed one but the diagram had more than one zone...my system only has one zone...Im thinking maybe there should be one in there because of the primary sortof acting as a second zone...
Sqare feet and baseboardNever size your boiler to the radiation installed , NEVER . Square feet within the building is not accurate either . All buildings are different and depending on construction , insulation , windows can vary drastically . Find an online heat loss calculator and perform a room by room heat loss . Never listen to a supply house guy that makes his living by what he sells you determine your equipment sizing , there is just a conflict of interest there . The first guy that plumbed this house could have been using a rule of thumb like the famous old one that states " North of the Mass pike you use 35 BTU per ft and South of the pike you use 25 . Sounds pretty stupid huh . If you have inherited a home that this guy sized the radiation for you will be lucky because you should be able to lower the SWTs quite a bit and get some of the rated efficiency of that boiler out of it . Operating as it is you are quite probably getting no more % than a quality mid efficiency cast iron boiler . The lower the water returning to it the better .
Definitely do the heat loss , measure square foot of each room , exterior walls , R value (insulation) window sizes and types , doors (same) , and enter the numbers . You may well find out that you only need to provide 15 - 20 BTU per square foot which will let you dial that boiler down drastically . Besides that you may want to manage the Delta T of the secondary loop with a variable speed pump so it slows the water down through that loop and returns water a bit cooler to the boiler . If baseboard use a 20* Delta t and if radiators you may want to go between 30 and 40* The Burnham tech can tell you what speed to set the primary circ at , setting it at a higher speed increases your short cycling issue by putting more hot return water through the boiler .
If you can make the time I would look into a 2 day trip to Cranston RI for Tacos course called Advanced soup to variable speed nuts , there is a class scheduled in October . This course is by far the very best learning opportunity available at present for up and coming hydronic guys . No , I don't work for Taco .
You didn't get what you didn't pay for and it will never be what you thought it wouldThis post was edited by an admin on September 25, 2013 8:22 AM.
CorrectRich is absolutely correct. Applying random "rules of thumb" and listening to the counter guy is a bad plan.
Now that you are stuck with this thing, the length of your cycles are determined by the amount of radiation compared to the minimum output of the boiler. As Rich said you should never size a system based on available radiation, but now that you are trouble shooting, it is important to know whether this is a boiler problem or a local one
How much radiation is attached to this system?
The speed of the primary circ can be important in a modulating boiler. If the speed is off it can trick the controller into doing strange things.
Just wanted....to bring up a comment on the picture... if you move that shut off for the expansion tank between the tee and air scoup, you will isolate the water feed too, and if it ever has to be replaced will be a piece of cake.
Let that shut off take care off both. ;)
thanks guys.Thanks Guys...Im headed back tomorrow and will let you know how it goes.
Rich that class sounds great, I am definitely going to look into it and hopefully attend.
Ok, first thing tomorrow I will check to see if changing pump speed helps at all.
I will find try to find a heat loss calculator and crunch the numbers.
Once I do, how would I go about dialing it down?
Eric...good idea, wish i thought of that.
Thank you all for your help
Heat loss calculation will tell you a lotthe number you want to watch is the ratio of the design day heat loss to the _minimum_ firing rate of the Alpine (21 MBH in the case of the 105.) The higher that ratio, the less short-cycling you will have.
Boiler PumpSince you over sized the boiler your unable to move the flow rate being produced by the primary/boiler pump out into the secondary side. The boiler pump supplied with the Alpine 105 is moving 7.7gpm on the primary side every time the pump runs no matter if its 60 out or zero out. You can never change that because it's a fixed speed pump. Your not pulling that 7.7gpm out of the primary into the secondary side. That's why your short cycling. What's not being pulled out to the primary is making its way back up the boiler return.
If you measure the temp between the boiler out and boiler in what's the delta-t? 5,4? The fix, a buffer tank. Lick your wounds and fight another day.."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."This post was edited by an admin on September 27, 2013 3:05 PM.
Opinion on a Delta T SolutionZman, Chris, Rich and Eric, what's your opinion of using a Delta T circ as a solution for this short cycling issue?
I would think if we slow the BTU train down (thanks Dan - use this a lot) increasing the delta T would help the boiler to stay on longer.
SteveThank you for your help in the past on many discussions about the Delta T - P debate . As always I am a firm believer in Delta T pumps , ECM or other (vdt) . This is from my previous comment here ". Besides that you may want to manage the Delta T of the secondary loop with a variable speed pump so it slows the water down through that loop and returns water a bit cooler to the boiler . If baseboard use a 20* Delta t and if radiators you may want to go between 30 and 40* " . This is always a good idea . I do believe this system is gonna require a bit more help also however .You didn't get what you didn't pay for and it will never be what you thought it wouldThis post was edited by an admin on September 29, 2013 2:11 PM.
Boiler PumpI don't think a delta-t pump on the secondary side is going to help. Actually it
will increase his problems. The fixed speed boiler pump is flowing more then
he needs. By lowering the secondary flow rate your just predicating more
of the nice hot water of the primary flow rate back to the boiler return increasing
the short cycling even more.
The ideal here is that the boiler through it's control logic could control
a variable speed pump matching the pumps flow rate to the modulation
rate of the burner. In this case here there are two fixes. The first a buffet tank,
the second, cap off the high end of the modulation rate and size a pump to
deliver the flow rate needed at your new top end. I'd also use a LLH instead
of pri/sec."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
Short cyclingAt some point our industry will learn to do heat loss' for every job. Nothing works better or saves more fuel than properly sized or slightly smaller due to multiple zone boilers.
The Alpine can be de-rated both for heat and DHW, also can slow down or speed up the modulation rate, differential above and even the light-off rate to reduce input in the first 10 seconds.
One stat and cast iron radiation should be able to work this out. I would not add anything for the indirect unless big hot water demand.
Another SolutionThere is one more solution although it certainly won't help your boiler efficiency. Do away with the outdoor reset, set the water temp at 180° and your boiler differential at 50°
Read this artical and your problems may be solved.
(credit given to Chris as original poster)