Replies

1. Expert Member
   Peter Engle | Jan 04, 2019 07:42am | #1

   You might find a few here who can answer your question, but most of us are not hydronic gurus. Find your way over to heatinghelp.com. They do tolerate questions from homeowners, and the guys there know everything about hydronic heating.

   That said, hydraulic separators and closely spaced tees both do a similar job of balancing the flows. The claimed advantage of a HS is that you get air and dirt removal in one piece and also that the HS doesn't have the same requirements for straight runs on both sides of the Tees. This all saves some space and labor and might offset the higher cost of the HS. Either one will probably work, if set up properly.

1. 
   Krohner | Jan 04, 2019 11:30am | #4

   Thanks, I will check heatinghelp.com.

2. Expert Member
   Dana Dorsett | Jan 04, 2019 09:09am | #2

   Closely spaced tees IS a hydraulic separator, just not a fancy specialized component.

   Putting the electric boiler on closely spaced tees AFTER the cast iron beastie works just fine, but needs it's own pump to drive it's primary loop. The CG doesn't usually need hydraulic separation, (literally almost never) but when used with a higher flow system hydraulic separation is a good idea for the electric boiler, and for water tube modulating condensing boilers. Can you post some pics of the near-boiler plumbing?

   Having it in series is a pretty bad mistake, the high pumping head lowers the flow rate, increasing the delta-T across the cast iron boiler, possibly inducing short cycling.

   Putting he electric boiler on the entering water side of the CG raises the incoming water temperature, lowering it's raw combustion efficiency a bit, and forcing it to run at a higher operating temperature, increasing distribution losses and jacket losses. Putting it in on the output side of the CG raises the overall system temp without the hit in combustion efficiency, and the jacket losses of an electric boiler are small relative to those of a cast iron boiler.

   Odds are pretty good the electric boiler isn't even necessary (or perhaps is it a backup, in case the propane runs out?) Even the smallest in the series (CG25) has enough output to heat my house down to about -5F or so. Which model CG do you have? Even if you keep the electric boiler, leave it off until/unless you need it, unless electricity is dramatically cheaper than propane in your local market.

   With 5 zones it's likely that there isn't enough thermal mass to keep the boiler from short cycling a bit on zone calls. Ideally the minimum burn times on the CG would be 10 minutes or longer (time them with only the smallest zone calling for heat), but 5 minutes wouldn't be a huge hit- maybe 1% to 1.5% hit in as-used AFUE. Those cycling losses increase rapidly as burn times go ever shorter. Depending on how the system behaves it may be worth installing a retrofit heat purging economizer control to better utilize the available thermal mass, reduce the average boiler temperature (reducing jacket losses), lowing the number of ignition cycles (which waste fuel on every start up.) If you want to analyze this, list the amount of radiation & type, zone by zone.

1. 
   Krohner | Jan 04, 2019 01:03pm | #5

   Thanks for the feedback,

   There are several issues with our current header system. The more I dig the more I find. Some of those other issues lead me to believe a failure and replacement of one or both of the boilers is probably in our future. I am trying to take it in bite size pieces to get my head around it. So my apologies if didn't give enough info, I will try to get some pictures posted once I get home tonight. The electric boiler is on the other side of the room from the CG connected the 1 1/4" copper pipe that run up over the ceiling and back down to where the electric boiler is mounted on the wall, so about 30 feet of pipe. Each of the supplies to the different zones are 3/4" and header loops are 1 1/4". Starting from the circulator and "primary" loop currently goes:
   1) Circulator
   2) CG Boiler
   3) Expansion Tank And makeup water (needs to be moved to suction side of circulators)
   4) Supply to 3 way mixer valve to infloor zones (garage and entry way)
   5) High heat zone 1 valve supply
   6) High heat zone 2 valve supply
   7) Indirect Water heater circulator supply
   8) Manual bypass valve
   9) Supply to 3 way mixer valve for infloor heat (basement - non oxygen barrier pex )
   https://www.greenbuildingadvisor.com/question/non-oxygen-barrier-pex-in-existing-slab-infloor-heat

   10) Return from 3 way mixer valve for infloor heat (basement)
   11) Return Manual bypass valve
   12) Return from High heat zone 2
   13) Return from High heat zone 3
   14) Return from infloor zones (garage and entry way)
   15) Supply to Electric boiler
   16) Return from Electric boiler
   17) Return from Indirect water heater
   18) Back to the circulator
   I hope that helps with a better picture of our system, until I get pictures later.

   I forgot about the difference in cost structures around the country. The Duel fuel program through our utility gives us a reduced electrical rate for the ability to interrupt our electric boiler for upto 12 hours during high loads. So both boilers are sized that they should be able to handle the heating load of the house. The controls are setup so that the electric fires up first, then the CG fires if the electric can't keepup or the interrupt is sent from the power company. So there is plenty of potential for short cycling.

   Also we have a PV system installed and would like to get our heating and electrical loads down to be supplied by that over the next couple years. But one step at a time, first step understanding our header system.

   Here is our cost structure:
   Net Metering Rate is $0.0996
   Our cost to produce is about $0.045 averaged over the warranty of our PV system and free after that
   Duel Fuel on our Coop is $0.065 per kWh
   Propane over the last 5 years in our area $1.24 - over $4 per gallon given the best cast performance of the CG at is about $0.065 to over $0.212 per kWh equivalence if I am doing the math right.

   Thanks again for the feedback.

1. 
   joshdurston | Jan 04, 2019 01:29pm | #7

   I assume you meant move the makeup and expansion tank to the suction side of the pump where it belongs.

1. 
   Krohner | Jan 05, 2019 10:47pm | #13

   Yes exactly, sorry I was typing it up quickly while on lunch at work. It should be fixed now.

3. 
   joshdurston | Jan 04, 2019 09:29am | #3

   Also note, a buffer tank can function as a hydronic separator and conveniently adds a bunch of thermal mass to reduce cycling. It doesn't necessarily have to be huge to be helpful.
   I second the heating help website, they have pro's from all walks, from single pipe steam to modern systems.
   Since you have an older non-condensing boiler, be mindful to proactively avoid flue gas condensation in the boiler, this may become more of a problem as you tighten up a building (reduce runtime and operating temperature), and add control (manage flowrates and temperature throughout the system).
   The suggestion of closely space'd Tee's (and then generously sized headers for the zone supply and return), for each boiler with the propane boiler first sounds like a good method. Each boiler will need a primary pump, and I would include a thermostatic bypass between the tees and pump boiler to allow the primary (boiler) loop to recirc until it comes up to temperature to protect your boiler.
   Here is a diagram.
   https://www.pmengineer.com/ext/resources/PME/2016/August-2016/4-pme0816Siggy_Figure4.jpg

   Are you zones controlled with valves or individual pumps?
   The coffee with caleffi video series and the associated idronics journals, offer a wealth of information. Just be aware that the videos are produced by a hydronic component manufacturer, so it features a lot of Caleffi products. But they do a pretty good job of keeping things balanced.

   https://www.youtube.com/playlist?list=PLmsj2FE7SN2-CDqMqTGBi0DSzFNVZrPgL
   Idronics if you want to geek out a bit more: https://www.caleffi.com/usa/en-us/technical-magazine
   The hydronic separator can be a space and time saver, it will probably add component cost but may save a bit on labor especially if you going to add dirt and air separation anyways.

1. 
   Krohner | Jan 04, 2019 01:08pm | #6

   Thanks for the feedback I'll dig into those resources once I get home tonight.

4. Expert Member
   Dana Dorsett | Jan 04, 2019 04:12pm | #8

   So the electric boiler is there solely to burn up excess PV output and take advantage of the interruptible big load rate structure?

   The Thermolec B18 puts out 61,400 BTU/hr, enough to keep my house warm at -40F outdoors, 70F indoors. Does this mean you're running the CG-4 (or is it the CG-3)? How big is the house, and what's your 99% outside design temp? (I've gotten pretty used to dealing with heat loads half that size or less.)

   Since this is always a either/or and never both situation, setting them up in parallel and controlling which one is in use with high flow zone valves would seem pretty straightforward and reliable. You'd probably still want to run the electric boiler on closely spaced tees with it's own separate pump to keep the heating system flow rates high without over-pumping the B18. What's the delta-T you're seeing across the B18, typically?

   If there isn't already an automatic flue damper on the CG, it's worth installing one. With no flue damper on an atmospheric drafted boiler you would still be losing a lot of heat up the flue even when no heating water is flowing through the boiler.

5. 
   krom | Jan 04, 2019 07:34pm | #9

   It may take more pumps, but why can't you do a primary loop with a pump, and hook both boilers to it with closely spaced tees, and their own pumps??

6. Expert Member
   Peter Engle | Jan 05, 2019 07:56am | #10

   You've got a ton of heat loss from that piping system, and with all of those zones having different friction losses, balancing is just about impossible. If you want guaranteed supply to each zone when it's calling for heat, you need separate pumps for each boiler, the primary loop, and each secondary (zone) loop. That's a lot of pipes and pumps, a lot of heat loss and a lot of pumping losses.

   A single condensing gas boiler would bump up your efficiency by ~20%, and that would offset most of your different in gas/electric cost. It would also simplify the system, and might (?) let you simplify the piping considerably.

   Alternately, since you are considering revamping the system, keep an eye on air/water heat pumps. That would let you go all-electric with a single very efficient system.

   Just seems like a lot of wasted effort to take advantage of a synthetic electric pricing system. If you want to game that system, you could look at the air/water heat pump with a large thermal storage tank. Heat it up when electricity is cheap, and draw from it when it's not. With proper controls, you could heat it up using primarily excess instantaneous PV capacity, if you have that in wintertime. How often does your program actually shut you down, and for how long?

1. Expert Member
   Dana Dorsett | Jan 05, 2019 09:26am | #12

   >"A single condensing gas boiler would bump up your efficiency by ~20%, and that would offset most of your different in gas/electric cost. "

   With electricity being between 4.5 cents (PV) and 6.5 cents (the dual fuel rate being charged), there is no reason to use the fossil burner for any thing but backup.

   At 82% efficiency the existing cast iron boiler delivers best-case about (91600 x 0.82=) ~75,000 BTU/gallon, or (75,000/3412=) 22kwh worth of heat into the house. A mod-con would deliver about 25-26 kwh/gallon not more, and that's not counting the additional maintenance cost or power used by the boiler. At any price more than 25 x $0.065= $1.63 /gallon the electric boiler will be cheaper to run on marginal cost (fuel only). With the additional maintenance and boiler power factored in the break-even point on operating cost is realistically more like $1.50 gallon.

   At the 5 year average price of propane even a condensing boiler would not offset ANY of the cost, it would be a significant loser, not even breaking even on operating cost, let alone pay off the very substantial up-front cost. Keep the cast iron pig and run it as little as possible, put a flue damper on it (if it doesn't already have one.)

   In fact, if the system is capable of heating the place as-is (no changes), it may not be worthwhile doing anything to it.

   The future price of electricity will likely continue it's decades long price deflation in inflation-adjusted dollars, while the price of fossil fuels will continue to be volatile. Betting on a cheap-propane future is a much risker bet than a cheap electricity future. Even without subsidy the cost of utility scale PV and wind are still on a double-digit percentage learning curve, and have already beaten all comers (even at record low natural gas contract pricing to combined cycle gas plants), and is continuing to decline, as is the cost of utility scale storage. Closing fossil burning generators is already proving to be a net savings to the ratepayers, but that will be even more true within the lifecycle of a boiler.

   The 60K capacity might be significantly oversized, and more careful analysis would be needed before digging into hydronic heat pump solutions.

2. 
   Krohner | Jan 05, 2019 11:04pm | #14

   I totally agree with you and moving to something more efficient is the end goal. We are in heating Climate zone 7 in Northern Minnesota. So I was thinking we might want a boiler as a backup for the -40 Degree Days and the 1 week we usually get where it doesn't get above 0 Degrees. I figure if I get the headers figured out, then it will make upgrading easier as the next step or we can do them both at the same time.

   I am still teaching myself this stuff but based on our utility bills vs heating Degree days and my attempt to do a Manual J on our house at -20 Degree both suggest we would need about 50,000 BTU/hr to keep our house at 70 Degrees. So yes the combination of the 2 boilers in series seems way over sized.

   Our utility only shuts us off 1 to 4 nights a year typically from 5 pm to 9 pm.

7. 
   Jon_R | Jan 05, 2019 09:25am | #11

   +1 on reviewing if thermal storage makes sense. As I see it, non-pressurized can cost < $.01/kWh.

   Reading below, it's hard to deny increasing adoption of air->water heat pumps and thermal storage.

   https://www.cleanegroup.org/hawaii-tou-solar-storage/

1. 
   Krohner | Jan 06, 2019 12:14am | #15

   Thanks I will look at that.