Circulator location

Discussion in 'Boiler Forum' started by JohnCT, Jul 14, 2020.

  1. JohnCT

    JohnCT Member

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    May 16, 2018
    Location:
    Northeast
    Now that the weather's warm, I'm going to install the new boiler I bought three years ago..

    My original boiler is a Thermodynamics that has two circulators and are on the low or return side. The Slant/Fin manual shows a drawing of the TR-30 boiler as having the circulator on top or the feed side.

    I am replacing all the piping anyway, but since I have to have two circulators, the return side would make a neater installation IMO.

    If there's no difference, I'll put them on the low side. If there is a reason to put them on the high side, I'll do that. This boiler is in the basement of a two story colonial with a heat exchanger in the attic, so it's a bit more than two stories I guess.

    John

    EDIT: since I am adding a thermostatic mixing valve to my hot water system, will this eliminate the need for a flow regulating valve that Slant recommends to keep from overdrawing the tankless coil, or should I use both?
     
    Last edited: Jul 14, 2020
  2. fitter30

    fitter30 Active Member

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    It doesn't matter what side the circulators are on. Where is the expansion tank pjped? Mixing valve whera is going to be piped boiler or dhw and what problems were you having with old system.
     
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  4. Sylvan

    Sylvan Still learning

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    Decades ago most circulators were installed on the return (which I still do) Then B&G had a heating expert that published several books

    One of his suggestions was "pumping away" meaning having a pump on the supply rather then on the return

    The reasons I like to place the circulator on the return are

    1- Cooler water is heavier then hot water so it is like natural circulation as they had prior to pumps / circulators

    This is why on old systems they oversized the supply as as ther hot water rises th cooler water would circulate naturally

    2- Cooler water will help the circulator last longer (less thermo stress)

    3- looks a lot neater

    4- If a circulator leaks I rather have it closer to the floor not on top of a hot cast iron / steel boiler
     
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  5. Sylvan

    Sylvan Still learning

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    A flow control valve is to prevent stratification of hot water rising (see above remarks) when the boiler is firing to maintain temperature

    A circulator adds just enought force (pressure) to allow the weight to lift allowing for HW to pass
     
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  6. Sylvan

    Sylvan Still learning

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    "thermostatic mixing valve " is usually used to temper but it is not considered an anti scald device


    You may want to consider (if you have a 2 pipe system) non electric thermostatic valves on each rad or fin tube so you can save a fortune and fine tune the system such as a Honeywell V110E Radiator Valve

    or the ones I like

    Non-Electric Zone Valve Operator - Danfoss Operator W/Remote 6' Cap - Danfoss 013G8252
     
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  7. Sylvan

    Sylvan Still learning

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  8. Dana

    Dana In the trades

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    What boiler model are you installing?

    With many higher-head water tube modulating condensing boilers it's actually BETTER to be pumping toward the boiler to raise it's pressure relative to the rest of the system. If pumping away from the boiler it's pressure would be lower than the rest of the system, making it more susceptible to flash-boil/kettling type issues (or even cavitation on the pumps, if the expansion tank is on the return side of the boiler), requiring a higher system pressure overall to suppress them.

    Whether pumping away from the boiler or toward the boiler the expansion tank it's better for the tank to be on the intake side of the pumps to help suppress cavitation. If pumping toward the boiler (return side) with two pumps the expansion tank can only protect one pump, since the return sides have to be separated. But if pumping away from the boiler the expansion tank will protect both, since the supply from the boiler is a single pipe (or manifold) on the intake sides of the pumps.

    With a low head cast iron boiler the expansion tank can be on either side of the boiler, but it's still preferable to NOT be pumping toward the expansion tank, putting the pumping head of the radiation between the expansion tank and the intake side of the pump:

    [​IMG]
     
  9. JohnCT

    JohnCT Member

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    Location:
    Northeast
    The expansion tank is currently on the outlet side and the circs on the return side.

    The original boiler had a catastrophic failure of the combustion chamber. A backfire broke up one side of the chamber. I discovered this when checking my oil level in the tank and noticed the right side of the boiler literally glowing red hot. I put the chamber pieces back together with refractory cement and it's been running cool ever since, but the original boiler is approaching 30 years, so I thought I'd just replace it rather than trying to replace the chamber which requires (I think) total disconnection of the boiler and turning it over.

    John
     
  10. JohnCT

    JohnCT Member

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    Let me add some more info: my system is what is generally called a "hydro-air". I have two air handlers: one in the basement that services the first floor and the other in the attic that takes care of the second floor. Each has a hot water core and each is serviced by its own circulator, but I have no radiators in the traditional sense even though this is a hot water system.

    The flow regulating valve I was referring to was what SlantFin recommends to be used to limit the cold water input to the tankless coil so as to not overdraw the hot water through the coil. I thought that since the "thermostatic mixing valve" will be adding cold water to the DHW line to reduce temp, it would also reduce flow through the tankless coil. So I was wondering if the mixing valve would reduce flow through the tankless coil to eliminate the need for the flow regulating valve. I hope that makes sense?

    The mixing valve I was referring to is just for the DHW and is what I believe you mean by tempering valve. If any of my definitions are incorrect, I apologize for that.

    Right now on my original system, the output of the tankless coil goes directly to the DHW line, so we've been surprised several times with 160F or more water at the kitchen sink. Ouch. Over the years, I've seen your posts on scalding from improper installations and even though mine was code when the builder installed it, it's not code any longer I'm sure.

    Our two shower valves are Symmons Temptrols circa 1993. I don't know if these are anti-scald valves but they are the pressure equalizing type, so a toilet flush doesn't surprise anyone with a sudden temp increase at least.

    Regarding anti-scalding, what additional equipment do I need beyond a tempering valve? If the tempering valve is enough, is 140F the correct setting to allow heat loss to the fixtures, or something lower?

    John
     
    Last edited: Jul 15, 2020
  11. JohnCT

    JohnCT Member

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    The boiler I will be using is a Slant/Fin Intrepid TR-30 firing at 1.10 GPH. It is equipped with a tankless coil but is otherwise unremarkable. The boiler I'm replacing is very similar: Thermodynamics S-Series with the tankless coil. It is currently plumbed like your third example (the "AVOID" example) with the two circs on the low side and the expansion tank on the output.

    John
     
  12. Dana

    Dana In the trades

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    The Intrepid series are low-head cast iron. Pumping away from the expansion tank & boiler would be preferable given there are two separate zone pumps. With a single pump on the return and zone valves on the boiler supply it would be nicer to the pump. Going with a single "smart" pump and a pair of zone valves the electricity use would drop about an order of magnitude too, but the pumping power is tiny compared to the hydro air blowers, so it's not necessarily "worth it" to go that route in your system.

    What is the model numbers &/or BTU/hr ratings of the hydro-air handler zone?

    With 1.1 gph nozzle the TR-30 puts out 130BTU/hr, which is 2.5-3x (or more) the space heating load of a typical house in CT. It takes about 250 of typical fin-tube baseboard (or the equivalent hydro-air handler) to emit heat at that rate. Without a large fraction of that amount of heat emitter on each zone it's relying on the thermal mass of the boiler, zone radiation & distribution plumbing to keep it from short cycling.

    There isn't much water mass in a hydro-air handler. If each air handler is capable of 100 BTU/hr it's going to be sending too-cool return water back to the boiler when both zones are running, but that can be dealt with using system-bypass plumbing. If only capable of 50,000 BTU/hr the burner is going to be doing a lot of cycling when only one is calling for heat.

    So now is the time to do the analysis on what you have, and design or re-design any protection necessary to keep sub-140F water from entering the boiler.
     
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  13. JohnCT

    JohnCT Member

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    I'll post that info when I get home tonight.

    My house is about 2800 sq ft. All walls 2X6 construction w/fiberglass insulation. Using an on-line calculator, a zone 5 home at 2800sqft needs a boiler with about 150,000 BTUH, which is what the original boiler was and what the TR-30 does at 1.10gph.

    I appreciate all the help from all the learned folk on this forum. My plan was to simply replicate the original system as it worked well and continues to do so (other than the boiler chamber issue). But certainly, if there's something egregious in the layout I'd rather take care of this now even if it means selling the new boiler I have and choosing one more suitable for what I need. What I can't really do is change the layout of the air handlers without extraordinary efforts.

    John
     
    Last edited: Jul 15, 2020
  14. fitter30

    fitter30 Active Member

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    Did your boiler cycle at 0* and what water temp were you running? Your expansion tank was on the supply.of the old boiler and what problems with water pressure did you have?
     
  15. JohnCT

    JohnCT Member

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    Not sure of your question. If you're asking if the boiler will run constantly or cycle on and off when the outside temp is zero degrees F, then the answer to that is that it would cycle, but would run at 70 percent of the time during a real cold day or night. But to be honest, I didn't pay that much attention to it.

    As for the boiler temp, I'm pretty sure it maintains 190F.

    Yes, the expansion tank is on the supply/high side of the boiler and the two circs low on the return side. I don't have any pressure problems (still running original boiler), at least none that I am aware of. I'm replacing the boiler due to age and due to a badly damaged chamber that I cobbled back together with refractory cement. But otherwise, it's running normally. In fact, I've had the new SlantFin in my basement for like 3 years now. Just been procrastinating. I don't want to go through another winter with the cobbled fire chamber.

    I've never had any significant problem with this system in almost 30 years besides the broken chamber- just the occasional circulator failure, having to resolder the relays back on the boards in the Honeywell controllers, and typical Beckett AFG maintenance.

    Thanks.

    John
     
    Last edited: Jul 16, 2020
  16. JohnCT

    JohnCT Member

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    They are First Co. air handlers (builder spec I'm sure), and the printed ratings are 34,000 max BTU @140F for each one. Model number is 24MAX-3HW.

    Thanks.

    John
     
  17. Dana

    Dana In the trades

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    Coils that deliver 34KBTU/hr with an entering water temp (EWT ) of 140F should deliver about 54-55K at a EWT of 180F, maybe pushing 60KBTU/hr at an EWT of 190F. That's still less than half the DOE output of the boiler- it's definitely going to cycle on/off quite doing a bit at a about a 45% dutyc cycle when only a single zone is calling for heat- the question is how short and frequent the burn cycles end up being. It'll do just fine when both zones are calling for heat, but the odds of calls for heat overlapping are probably pretty low, given that the 60K output of just one of the air handlers is probably enough to heat your whole house when it's -40F outside. Even at design condition the higher load zone (probably the upstairs, especially if the ducts in the attic are above the attic insulation, adding a parasitic load) will probably be running less than a 30% duty cycle on the air handler. (This week isn't a good week for testing that, eh? :) )

    There isn't enough combined air handler heat deliver capacity to result in sub-140F return water with the high-limit on the boiler set to anything over 155F, so it's not going to need a system bypass or boiler bypass for protection. The short cycling potential is going to be the bigger issue to watch out for.

    If you have a few of last winter's oil fill-up slips and dates it's possible to get a good handle on the design condition heat load of the house using these methods. If on a regular fill-up service that stamps a "K-factor" on the billing slips, a few wintertime K-factors is good enough. (The "K-factor" is in units of base-65F heating degree-days per gallon- it's straightforward arithmetic to convert that to BTUs per degree-hour.) From there one can figure out the total heating season burn time & seasonal average duty cycle of the burner, as well as the duty cycle at the 99% design condition. As long as average burn cycle is longer than 5 minutes the large oversizing factor isn't going to be a big efficiency hit. I haven't studied the boiler controls on the Intrepid, but there are ways to maximize burn times and minimize cycling by how it's set up. A retrofit heat purging economizer should be able to tame the worst of it if the cycling can't be brought to reasonable levels by the standard controls.

    If the basement walls are insulated to CT's code-min R15 continuous insulation most of the standby and plumbing distribution losses (which are substantial, at the low duty cycle) won't be truly lost, but would be helping to heat the first floor.

    If the basement walls are NOT insulated, air sealing and insulating the foundation walls & band joist will take a double-digit percentage off the wintertime oil use. If taking on that project (either DIY or contracted out) there are good/better/best (as well as brown/green/greener, and expensive/cheap/cheaper) ways to go about it that won't turn your basement into a mold farming operation, topics I've addressed several times in other forums on this site.
     
  18. JohnCT

    JohnCT Member

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    I haven't been able to calculate my home's heat loss yet, but in the meantime, I had emailed Slant/Fin about downfiring the TR-30 because the instructions that came with it show four nozzles for the Beckett with the same burner and same burner head: a .85, 1.00, 1.10, and 1.25. It came with the 1.10 installed and they also shipped a 1.25 in the accessory box.

    Slant only said it could be indeed be run with the .85, but was hoping they would give more info as to real world fuel usage or efficiency. Also, I read that the boiler should be matched to the air handlers, correct?

    Is downfiring the boiler good practice as long as it's setup for that nozzle size?

    John
     
    Last edited: Jul 17, 2020
  19. fitter30

    fitter30 Active Member

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    Change the nozzle to .85 thats 119k btu's @ 140k per gallon before taking into the efficiency. What water temp are u running?
     
  20. JohnCT

    JohnCT Member

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    I haven't installed the new boiler yet (waiting for some new ball valves and DHW mixing valve to arrive). The old Thermodynamics S has a Honeywell aquastat/controller and is preset to 190F I believe. If it's adjustable, I never played with it. The system has always worked perfectly and if it wasn't for age and a broken up combustion chamber, I wouldn't be replacing the Thermodynamic boiler.

    The Slant was shipped with a Hydrostat 3250-Plus already installed and wired. I believe that is (nearly) infinitely adjustable, although I don't know how this will work with a tankless coil. I'll figure out if there are any adjustment tweaks later I guess . o_O

    Thanks.

    John
     
  21. fitter30

    fitter30 Active Member

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    Existing boiler did you ever have the fin tube warm up in summer using the tankless coil? If so a flo control valve would be needed to stop the gravity flow.
     
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