Too much cycling

Discussion in 'Boiler Forum' started by Handymaner, Sep 30, 2012.

  1. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Tweaking Delta T's

    OK, I’m back. Work has been crazy; I’ve been forced to be away from home literally since the end of December. The boiler has been working GREAT, the reset curve seems to be really close as it just barely keeps up-which is the goal I guess? The usage has continued to be around 50-70% of last year, so I’m really happy with that.

    The only trouble I’ve had is one of the baseboard radiators started leaking. I came home from work at about 2AM. I’ve been very in tune with what the boiler is doing since the install and after parking in the garage I instantly realized something was up, as the boiler sounded like it was at 100%-which it never is except for DHW and a 2AM that seemed odd. I went over and looked at the screen, and sure enough it was at 100%, the set point was calling for 130*, but the system temp was only at 80* and I realized I could hear make up water flowing! In the hazed thinking of panic (worried about a flood in the house) I noticed that only the upstairs loop was on. You can imagine the sleeping wife’s surprise as I ran the perimeter of the house turning on all the lights checking the baseboards looking for the flowing water! The upstairs was dry-so to the basement I went, thinking it may be from a portion of piping within the walls. No sign of leakage there either. Only then did it hit me that all the loops are pressurized through the return even if the zone valve is closed. So my dash continued through the sunroom and finally I found the leak in a semi-heated storage area off the sunroom. Thankfully I had the foresight to plumb in ball valves on both the return and supply side of the loops, so I could isolate the loop easily (without completely shutting down the boiler) for later repair. My wife said that she had heard water running prior to going to bed, so I know it had been leaking for 2 or 3 hours. I was later able to just bypass the bad baseboard.

    I still need to tweak the delta t. I discovered that squeezing down the radiation loops actually lowered the delta t spread as read on the diagnostic screen. I guess that the pump on the primary loop must be recirculating more heated fluid when the radiation loops are slowed. I did squeeze down the valve in the primary loop as per Dana’s suggestion, and that method is able to raise the delta t considerably. With me being away I did not want to risk it being unmonitored, so I opened it back up.

    Now that I will be home for a time I want to start tweaking again. I did have a chance to do some experiments but I haven’t found a reliable way to measure the temp of the pipes to find the delta t’s of my radiation loops. My IR gun is all over the map. I tried the tape suggestion, but it didn’t seem to help. I then grabbed my little desktop digital thermometer, the kind with the 5’wire with a probe on the end that you stick out the window to get indoor/outdoor temps. I tried to place the probe inside the pipe insulation but still can’t seem to get consistent results. My next attempt will be with the wife’s candy thermometer stuck inside the foam insulation. Any suggestions for an easy reliable way to measure the pipe temps?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    A curved surface is tuff to get a consistent reading of, especially if it doesn't have an accurately aligned laser pointer.
  3. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Hold on. I can't watch anymore.

    First, the Alpine boiler will suffer a 40° delta T (not for beginners) so slow the pump down as Dana suggests.
    Second, by limiting the max operating temperature you are also limiting the potential output of the boiler and the radiation connected thereto. Raise it to 180°F.
    Finally, setback thermostats are all the rage and perfectly acceptable for forced-air furnaces and the people who own them, as they don't know real comfort anyway. As Dana suggests, a ModCon boiler such as the Alpine will modulate supply water temperature based on a properly programmed--built-in--outdoor reset. No special radiant thermostat needed. Many of our retrofit condensing boilers are still "controlled" by a Honeywell mercury switch (I know, I am going to burn) providing perfect comfort while regularly cutting fuel bill in half.

    The Alpine, and many other ModCons, may also let you set back the design water temperature while asleep or away. This will save fuel without sacrificing comfort.
  4. Dana

    Dana In the trades

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    Thank you Morgan!

    BTW: One mercury-loaded Honeywell contains as much mercury as 1000 compact fluorescent light bulbs that some folks get all tweaked about- maybe you really WILL burn for leaving any of those in place! :)
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    Much better than throwing it in the trash (which is illegal!).
  6. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    OK Badger....evidently I'm not making myself clear enough. I'm not using any set back on the thermostat. My issue with the thermostat was that it was only calling for heat for a couple of minutes and then off. I found no way to adjust the hysteresis (even calling Honeywell tech), it must only allow a half a degree or some very small amount. I would rather it had a larger spread (maybe 1.75 deg) to promote longer cycles. Does anyone know of an electronic thermostat that allows this adjustment, or is that relegated to the older dial type units?

    I've got the design temp (-6 deg) system temp on the outdoor reset curve at 160, but that doesn't limit the max operating temp if it gets colder.

    My problem with the delta t is that I need a consistent way to measure the individual radiation loops. I discovered that the readout on the (Lochinvar Knight) screen gives you the delta t between the system temp and the return water. The trouble is that the return water has (potentially) already been mixed with the heated supply water via the primary boiler loop. I think this is what is limiting my delta t now, as when I slow the flow in the radiation loops, the delta t on the display screen is reduced NOT increased. My theory is that there is not enough return water flow causing the primary loop to make up the difference by drawing hot water from the supply along with the return water coming from the radiation loops, thereby preheating the return water. Obviously if the goal is lower return water temp to increase condensing efficiency of the boiler, this is to be avoided. But to confirm this I need a way to measure the return water via the copper pipe. The pump on the primary loop came with the boiler with instructions to run it on medium-I've already got it set on low. Before I start further restricting it with a ball valve, I want to get reliable measurements of the delta t from the radiation loops. Perhaps I even need a larger pump for the loops, anything is possible but I won't know until I find a consistent way to measure the temp of the copper tube on the supply and return ends of the radiation loops. Any suggestions for that?

    With my (Quite possibly inaccurate) understanding of the outdoor reset you want the system temp as low as possible while still keeping up with the heat load. If it is set like that then you could not set back the design water temp while asleep or away or it wouldn't keep up and the house would get cold, right?

    Thanks for your insight.
  7. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Stretching the differential (Dana likes 'hysteresis') will effect comfort more than system efficiency. We don't do it. Many of the ModCon boiler manufacturers, in their mania to sell boilers to anyone, anywhere, have not only encouraged, but often mandated the seldom needed and always costly P/S pumping system. It took me a year to get rid of the UP2699s that Lochinvar was sending with a 3gpm 50mBtuh boilers--most went to snow/ice melting duty. We don't use P/S unless it makes sense and yours is a prime example of our argument against the practice. If you can't widen the delta T at the boiler, your secondary pump is too big. If you had one pump, and it wasn't over-sized, it would be a simple matter of slowing it down--choking ball valves is not recommended.

    By the way, the nice folks at Burnham will let a professional use one pump if he can do the math. I appreciate that and don't ever have to disqualify them for some of our simple, one-zone gravity conversions.

    It is a complicated matter and best done on paper, leaving field adjustments to the installer.

    When does fishing start?
    Last edited: Mar 14, 2013
  8. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    It's still pretty frozen over. Just went through a 2 day blizzard last week. But since we've sprung forward it's not dark until 9PM!

    Maybe in this case it's not optimum to follow manufacturer's instructions and dealer's guidance regarding P/S-but that's all I had to go with. I'd sure like to optimize what I got. Slowing the secondary loop reduces delta t at the boiler so a smaller pump won't help in this case unless something is changed in the primary loop. Secondary pump is a Grundfos UPS 15-42 F. It's flowing through two 75' main loops of baseboard and a third of about 50', with I'm sure many elbows in each. My dealer thought it was too small for my system, but it's what was there so I thought I'd try it. Is it lower flow than the primary pump that Lochinvar sends out? If so could that mismatch be contributing to my issue? Because it seems to me the primary pump is flowing more than the secondary causing recirculation, although I'm far from a hydronics expert. If that does turn out to be the case then that's probably why the manufacturer wants P/S. There must be a Grundfos flow chart I can find somewhere.

    I still need a reliable way to measure pipe temps so I know what the delta t of the radiation loops are and go from there.
    Last edited: Mar 14, 2013
  9. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    In a residential, single boiler hydronic heating system, the circulator serving the boiler is consider "primary" and the circulator or circulators serving the distribution system "terminals" are considered "secondary" or tertiary.

    Yet another reason to hire a professional designer before you start. But hey, keep plugging away.
  10. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Yes I am totally aware of that. Absolutely no confusion there on my part. I'm calling the primary pump the one that came with the boiler that's in the primary loop. The secondary pump listed above (Grundfos UPS 15-42 F) is the one that's always been serving the baseboard loops, and if I SLOW that one my delta t as read on the boiler screen DECREASES. That's how I came to my hypotheses that the secondary pump flows too little causing the primary loop to back feed a portion of the heated water coming from the boiler directly back into the boiler without going through the radiation loops, thus lowering delta t.

    To avoid this happening, the secondary (radiation) loops would have to flow at least as much as the primary loop, correct??
    Last edited: Mar 14, 2013
  11. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    We prefer more flow to the system. If the boiler, or the pump serving same, is grossly over-sized, the net results are hard to correct.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    Too low of a flow would do several things: not heat the room unless the inlet temp was higher, or produce less even heating. There are a lot of tradeoffs between, efficiency, comfort, and a long-lasting, trouble-free install. It's hard to overcome a too big boiler's part in this balancing act.
  13. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Thanks to this forum (mainly Dana's advice), the boiler is not over sized. Here's a link to the sizing thread: http://www.terrylove.com/forums/show...load-calc-help

    Everyone locally recommended 120 or 150k boilers, I went with 85k-despite dire predictions of freezing this winter which has not turned out to be the case. The boiler often often cruises at 20% (min fire) on milder days in the 30's when only one zone is open. Even with 4 out of 5 zones open (the most I've seen at once) it runs at 70-80%. So I'm glad I didn't listen to the local installers.

    The pump serving the boiler came packaged with it, so I would hope it is correctly sized.
    Last edited: Mar 17, 2013
  14. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Well, I've found a way to measure delta t that's accurate enough. I have 2 of those digital thermometers that have a lead to place out through the window (for outside temp). By putting the lead under the pipe insulation in the area I want to measure, it's consistent enough. It's not a true representation of the actual temp inside the pipe, but for for delta t should work.

    I have proved my theory that I'm getting significant recirculation in the primary loop. I've got one sensor on the return line just prior to the closely spaced tees, and one just a few inches up the return side of the primary loop. With just one zone open, I get 7-9 degrees difference (hotter in the primary loop than the return water). The difference decreases as more zones open, with 3 open there is 3-4 degrees of difference. I'm assuming with more than one loop open there is less head pressure and therefor more flow in the radiation loops thus recirculating less of the already heated water back to the boiler.

    I think this will significantly effect my efficiency. At times it keeps me completely out of the condensing range, and it always reduces efficiency. I'm not sure the best way to fix it. The boiler (Lochinvar Knight) has a readout of primary pump percentage. Last I looked at it, it was at 35%. Does anyone know if it actually controls the speed of the primary loop pump? It's the pump supplied with the boiler, Grundfos UPS 12-28 with 3 selectable speeds (a slip of paper in the box with the pump said to use speed 2 for my boiler size, but I've got it on 1). I tried Dana's suggestion of throttling the ball valve in the primary loop and I could increase the delta t but the inlet water temp did not decrease, the output temp of the boiler increased-which does not meet my goal of increasing efficiency.

    I think the ultimate would be a var speed pump for the radiation loops (they are all on one pump) with a simple controller that measures the temp of the return water and the output temp of the boiler, and adjusts the pump speed to maximize the difference between the two. No matter how many (or how few) zones were open the flow would be adjusted to optimum, finding the best combination of lowest return water temp and least recirculation in the primary loop. But I am not familiar with the var speed pumps, what controls them, cost, etc.

    Any ideas? Dana, is this similar to the fix you hinted at a few posts back?

    By the way, I finally had the city inspector come out for my inspection (I did pull a permit). He was pleasantly surprised, said that hardly any of the homeowner installs pass on the first try! So I was really happy about that. He only had a couple small suggestions for me, easily taken care of. And as to the original subject of this thread, cycles-I'm VERY happy with that. My average burn time since first firing up the boiler (including the short shoulder season cycles) is at 43 minutes!
  15. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    First, the Knight condensing boiler is too "big" for the load. It is, like so many, bumping off the bottom.

    You may slow down the system pump, but if the boiler pump runs faster your problem may not go away.

    The Knight is a fire-tube condensing boiler and as such, will suffer a 40°F delta T across the heat exchanger (Many water-tube and aluminum condensing boiler will also). The higher the better, from an efficiency standpoint. If the boiler flashes-to-steam, a.k.a kettles, you can turn the pump up. Fin-tube baseboard is not the perfect emitter for any hydronic system but it has a predictable heat curve and may be properly sized and balanced to any boiler...as long as you have enough to heat the space at design temperatures. We prefer European style panel radiators.

    For the next guy:
    How to fix this problem on the Knight or any other condensing boiler?...ACCA Manual 'J' heat load analysis and review of the hydronic system as a whole, to include radiation and zone loads, by an experienced hydronic designer. (No, I don't care how long your installer has been throwing in boilers.) Getting a bigger boiler is not the answer, nor is getting a bigger pump. Getting a bigger brain is the thing.

    Reading, understanding and following the installation manual is the thing.

    Primary/secondary pumping was designed to keep boilers hot! It is not required for most Mod/Con installations (even though Buderus, WeilMclain and others still insist on it). It is, by definition a waste of energy. We have installed many Lochinvar Knights here in Minneapolis and repaired/re-piped many more, with perfect results. We do not use primary/secondary piping for any boiler unless it can't be avoided (My own driveway snow/ice melting system is driven by an condensing boiler and a single pump). We always consider the highest load zones and the radiation therein when designing hydronic control systems. We always pump into low-mass boilers, this includes all copper and electric boilers.

    Or you can, I guess, get a boiler that is too big for the space/load and install a buffer tank to lengthen the burn cycle.

    Proper ACCA Manual 'J' heat load $500.00
    Buffer tank with labor design help $1500.00.
    New, properly sized boiler installed. $8800.00.
  16. Dana

    Dana In the trades

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    "Getting a bigger brain is the thing."

    I gawdda git me wunna doze sumday, eh? :)

    But seriously, there seems to be a dearth of boiler installers with a grasp of the fundamentals. How tough is it to pick up the book, really? It's not rocket science, but it takes more than napkin-math to dial in the last 5%, even if the napkin model can easily find the (all too common) gross errors.
  17. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Do you honestly think it's oversized? On what do you base that decision? With 43 minute avg burns and only "bumping off the bottom" with mild temps and a single zone open that seems pretty good to me. Am I to understand that a boiler properly sized for -6 deg design temp would never run at min fire on a mild day with just one zone open? That seems to be a tall order. I don't believe the next size down would cut it on design day, let alone colder. I'm just ecstatic I didn't (thanks to this forum) accept the multiple recommendations I got from local installers for 110 or 150K boilers, and went with the 85K instead.

    I've come to the conclusion that I need to speed up the system pump, not slow it. That's what I was hoping to get insight on, before I proceed with changing out the system pump. My goal now is to optimize the system I have and get the return temps down as low as possible. Perhaps I can find out from Lochinvar if I can use a smaller pump on the primary loop to help my re-circulation problems. That's the only way I imagine a smaller boiler would help my situation, if it came with a smaller primary pump.

    I also would prefer different emitters, I hope some day for warm board or similar. Thanks again for all insights!
  18. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    You don't need Warmboard for a retrofit like yours. I would look for a good deal on European style wall-hung panel radiator properly sized to low temperature applications and controlled for optimum comfort and efficiency.

    PS Yes, the pump that came with the boiler is over-sized, and no, the boiler does not control the pump "speed"...yet.

    Glad you and Dana got it all worked out.

    Attached Files:

    Last edited: Apr 3, 2013
  19. Handymaner

    Handymaner New Member

    Messages:
    41
    Location:
    Alaska
    Hey Thanks Badger. I'll look into a smaller pump and check out those panel radiators. If I could come up with some of the old cast iron base boards I would use them, but I've never seen any up here. Shipping too high for that kind of weight probably.
  20. Dana

    Dana In the trades

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    Location:
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    You can buy panel radiators online if you know exactly what your going for. PexSupply and others even have free shipping on them to US addresses. I'd assume they would honor an AK order, but the shipping might be slow.

    They're a fraction of the dry-weight of cast iron, but the can be even higher in thermal-mass. Steel & iron have about 1/9 the specific heat of water, so every 100lbs of iron is the same thermal mass as about 11lbs of water, or about 1-1/3 gallons- it doesn't take a lot of water volume in a panel radiator to have the same thermal mass of 20' of cast iron baseboard.
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