How efficient is this Boiler setup
I moved into a 15 year old home last year. Attached is a picture of the boiler room setup.
I have never dealt with boilers before, so this is all new to me, but this doesn't seem very efficient. With the continous loop under the 2 boilers, one boiler is potentially reheating the heated glycol from the other boiler. I would expect the return and supply to never be joined together except in the boilers or in the individual heating coils (radient flooring, hot water tank, not sure if I am using the correct term here). If I am going to talk to a local plumber, I would like to be at least somewhat educated in this.
Thanks for any advice.
Comments
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what’s the thinking behind the 2 boilers? Just redundancy?
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A common series primary loop. Think of that loop as a conveyor belt.
One or both boilers can add heat to the loop, the 3 way mix valve and circ on the bottom pulls heat from the primary loop, as does the air handler and indirect tank.
It's possible the controls in those boilers have them staged. It runs on one boiler until the load is too large, then the other kicks in to help. They could be alternated also to get equal run time.
Looks like a high temperature secondary for the forced air coil, and one for the indirect tank.
The close spaced tees are a bit wide, I would have used a close nipple between them, but workable.
I don't see an air purger?
How many loops on the 3 way mix valve?
Could be a 3.7 Cv Honeywell, so 8 gpm would be about the max flow, 10.8' head at 8 gpm through that valve.
A Y strainer before the mix valve should be cleaned occasionally, put a cup under it and blow down any debris.
I think the upstairs forced air loop keeps you from running the boilers at a more efficient radiant temperature, and eliminating the mix valve.
A B+ from the Utah judge 😌
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
This would be a better piping design
The Return intake of each boiler and the Supply output of each boiler does not add to the temperature of the main Primary loop. Both boilers get the same intake temperature and can add heat as needed to the system.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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There are many modular design systems that use 2 or more smaller boilers to offer a larger size output. For the most part these systems can be less expensive that having one large commercial boiler that does a million BTU need. one boiler goes out and you have nothing at all. if you have 5 199,000 BTU boilers and one goes out, you can get by without until the failure can be repaired.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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With two boilers you have 20-1 or more turn down, which can be a nice feature.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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what are you hoping to achieve by calling a plumber? Are you using a lot of gas? How much?
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thanks for looking at my post.
I had 2 100,000 btu Veissmann boilers pre installed, they both crapped out 2 weeks ago. I had them replaced by these 2 110,000 btu IBC boilers, we were quoted for 1 200,000 btu boiler, or 2 110,000 boilers. We went with the 2 boilers for redundancy, as this is our 2nd winter in Northern Alberta and had boiler issues both winters, last year it was when it was in the -40s, then we just lost one boiler, this year it was in the -20Cs, so we liked the idea of 2.
Getting to know the system better, the loop just looks inefficient as apposed to not having a loop. Or how Ed has drawn it, looks better than it is, Sorry Hot Rod, most of what you wrote is well above my plumbing knowledge, I will have to do some research into all this.
Right now It is not cold outside -10C tonight, but Thursday -30C, so now I am running only one boiler, which is running around 50,000 btu.
I am just trying to make the whole system more efficient, and natural gas prices in Alberta are not that expensive, but the delivery charges are. But last January we used 37 Gj of gas, but our dryer and stove are also gas. And it was damn cold. I don’t know how that compares to others in cold climates and I have nothing to compare it to as I moved from Vancouver Island where it seldom got below freezing.0 -
The building is what dictates the fuel cost.
Hopefully it is well insulated, all air leaks sealed up. An energy audit that includes a blower door test and infrared scan may be worth the money? Sometimes utility companies offer that service.
A different piping will not change fuel consumption much, if it mainly runs on one boiler. Only a heat load calculation would tell you how often both are needed.
I would run the boiler supply temperatures as low as the air handler can use and still keep the upstairs warm enough
most boilers have data logging in their control it would tell you the run time, maybe even how many hours at what firing rate. It may show you how often they cycle.
You may be able to access that info online if the boilers are able to be connected.
I would ask if the outdoor reset function is being used, that can help a bit on efficiency.
Turn down or off the indirect if the home is empty for extended periods.Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Thanks HotRod
I am recently retired, so now living off my pension, so if I can spend a bit to save a bit more, that is what I will do. I believe the house we have is well insulated, but large.
I did start the boilers at the default temp of 130*, but that didn't seem hot enough for the forced air, so bumped it up to 140, and now 150.
If one boler can accomplish what we need I will continue to use one and see if it keeps up. and I will switch from one boiler to the other just so they get used an equal amount. I believe one will do the job, now that everything is at the temperature we want it to be.
Thanks for your wisdom, I will no longer be wondering if I should be changing the plumbing for this system.
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This video explains the primary / secondary design your system is using.
https://www.youtube.com/watch?v=0sA-b2vLU78&t=5
I know this is about manifolding the emitters (radiators) but the same concept is true in reverse when you pipe the boilers the way yours are piped as opposed to manifolding them like my diagram.
Hope this helps you to grasp the reason for Primary / Secondary
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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just from what I can see your two loads, the radiant and air handler are piped with 3/4” So probably you are not movering more than 8 gpm when both are calling. Your 110,00 boiler at. 87% is 95,000 btu/ hr output. I don’t see a time where both boilers would need to run at the same time. DHW is probably a priority zone as it needs 180f. So what you have, piping wise works fine.
The second boiler will be a bit less efficient as it may see return around 140 if the first is running 150, which blends down when it hits the primary from return from the operating zones. Certainly not worth a repipe for what little efficiency gain you might get. And if one boiler is always off, it’s a moot point.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Thanks Ed, That video just quadrupled everything I know about hydronic heating systems. Based on that, If you don't mind looking at the 6 pumps (1 is out of the picture to the left going to the indirect hot water tank) I have, they all have 3 speed settings. What should they be at? I think they are all set a speed setting of 2, perhaps they shoiuld be set differently. The only one I had anything to do with was for the forced air heat exchange, I sped it up to 2 from 1 as I felt the heat loss was just too great, based on the different pipe temperature going in vice coming out.
Thanks
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With a modcon efficiency is all about return water temperature, supply temperature doesn't matter. You want the return back from any heat emitter to be at least 20F less, 30F even better. You want a big difference between supply and return.
Adjust the pump down until the fan coil unit can no longer keep up with house heat. This is best done on a cold day.
Same for the loop pump, lowest speed that about heats the house.
Delta T is your friend, it is free fuel saving for pretty much zero cost.
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The trade offs go like this.
If you want more output from an air coil you have a few options. Speeding up the pump as you did, will give you some increase in heat output. You basically increased the AWT average water temperature in the coil. Notice the manufacturers specs show a few flow rate options, 3,4,5 & 6 gpm in this coil example. However you also increase the return temperature, lowered the delta T to the boiler and lose some efficiency.
Or you can raise the SWT, supply water temperature, the vertical columns in the spec sheet.. This can get bigger output gains, but you will also lose some boiler efficiency with higher supply, and higher return temperature.
In a perfect world that coil could have been sized to work at lower temperatures by adding more rows to the coil. It would be nice if the radiant and fan coil could operate at one low temperature, 120F perhaps. As is you will need a high and low temperature provided by the boiler.
With what you have it will be a bit of a juggle to maximize air coil output and also keep the boiler efficiency up. Comfort vs efficiency?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Thanks for your replies. This makes total sense, for the pumps that are supplying the individual coils. What about the pumps that are pumping to the boilers and the main loop that everything feeds off. Or does one setting dictate how the next one gets set. For example slow down the pump to the air handler means slowing down all the pumps in the system?
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The series primary loop you have is a bit old school in my mind.
#1 IF in fact both boilers run together that primary loop pump needs to move 20 gpm, 10 gpm from each boiler. It would be 1-1/2" copper and a large 20 gpm primary pump.
Looking at the bottlenecked primary loop and the small diameter secondaries I don't think it was ever designed to run both boilers together?. You don't have enough connected load to support both boilers. Maybe 4-5 gpm to the radiant, 4 gpm to the AH. We would need to see a system design to know for sure the intent. . At best you can move 8-9 gpm maybe 90,000 btu/hr. It sounds like the boilers are operated manually anyways?
.
With a horeshoe primary loop you get rid of that odd duck primary pump, run the system with only 5 circulators. Loads are parallel, boilers are parallel as @ed mentioned so all loads get the same SWT, both boilers the same RWT.
At this point all the suggestions will help maximize what you have, I doubt it is worth a $$ repipe.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
With a horeshoe primary loop you get rid of that odd duck primary pump, run the system with only 5 circulators. Loads are parallel, boilers are parallel as @ed mentioned so all loads get the same SWT, both boilers the same RWT.
At this point all the suggestions will help maximize what you have, I doubt it is worth a $$ repipe.
In thinking about this further, the "odd duck primary pump" actually serves to raise the return temperatures to the boiler. That loop is effectively at the same temperature due to the constant flow by the "primary pump". It is a mix of SWT and RWT. The RWT from the zones will be raised considerably by the flow from this pump and the efficiency of the boiler will decline because of it.
Furthermore, the output of the boiler is restricted due to the elevated RWT to the boiler. For example, if the RWT to the boiler is 150°F and the SWT in the boiler is set to 160°F, the boiler is going to instantly modulate down due to the narrow DT. The zones might have an RWT of 135°F but the "odd duck primary pump" is mixing the SWT and the RWT to result in a higher return water temperature to the boiler.
This is NOT a proper P/S setup and it is impossible to to have the RWT to the boiler match the RWT from the zones.
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Yes, we are all speculating without some actual data. All we know is the boiler(s) have been turned up to 150? Pumps are on speed 2?
I think the continuous loop pump may be a 15-58, so it cannot move the 20 gpm I suggested. If so it cannot move the output of those two boilers at maybe 95,000 btu/hr (9.5 gpm at 20∆) each. Looking at the 15-58 curve, attached, and assuming that is a 1-1/4" copper loop with a few fittings there is not much flow resistance, pressure drop, IF it is a 15-58 maybe that loop pump is moving 10 gpm? Maybe less on speed 2 :) Run out on that pump is 14 gpm
With some pump flow info and temperatures you could model the temperature in that loop, using the mixed temperature formula. If the boilers are flowing 10 gpm, and the primary loop is flowing 10 gpm, then the first set of tees should be getting close to 150F that the boiler runs up to
Primary Secondary Pumping Made Easy , by Dan Holohan takes you through a number of examples of mixing, flow rates, flow reversal in the closely spaced tees, in a loop like shown.
By odd duck pump I mean a pump to move 20 gpm with just a couple feet of head isn't a common pump. So that pump is typically running way off it's curve.
Yet another unknown… where is the expansion tank connected? Is it out of the picture in the loop to the indirect? Then that is the primary loop, just to keep the terminology straight.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Since you don't need both boilers to run, you can improve the setup a bit without a major replumb.
You can put a ball valve between the closed space Ts of each boiler and remove the loop circ and replace it with a length of pipe.
To run the first boiler, closer the ball valve bellow it and open the ball valve under the 2nd one. Now the loop is directly connected to the boiler and avoids any of the mixing mentioned earlier. It also saves the running cost of an extra pump which does add up over a heating season.
The nice part of this setup is you can still use the 2nd boiler in staged config if you ever need more BTUs without any changes.
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Agreed with the exception of the capability to use the second boiler in a staged configuration. You can't move enough water (with typical pumps) to keep the DT reasonable. Running both boilers simultaneously would likely result in both running at 50% or so.
The piping is setup to deliver approx. 100K at typical flow rates. Each boiler has about the same output.
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Thanks for all the info. To answer a few questions asked. The expansion tank is out of the picture at the top right. You are correct that the pumps are 15-58.
I turned up the supply temp to 160* as the forced air heat wasn't warm enough and it took forever to heat up the house.
This morning when the heat came on to raise the temp from 17 to 19C the one boiler being used was running at full output. I now have both boilers on as we are expected to get into the -30s C over the next week. With both boilers on so that they are doing close to same amount of work I have the first boiler set to 150* and the second set to 160*. The first one being the one on the right. If they are set to the same temp, the first one does all the work. And they both run around 50% or a little less in this situation. I have ordered a secondary loop sensor from the company that installed my boilers so that the boilers can work out for themselves how they will match up.
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can we ballpark how much gas is being consumed? Before touching anything :)
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No, I was just looking for the simplest way to make it more efficient, only if it was going to be simple and cost effective.
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I am doubtful that you will ever get them run more than………….say………….60%…………….because they cannot get a sufficient flow rate and you probably don't have the capability to deliver more than 110KBTU with the emitters that you have.
Of course, it you do a cold start with a huge DT, then they probably can go higher…………….but under steady state conditions…………….not possible.
When you perform a recovery at those low temperatures, you certainly must use a setpoint close to maximum (typically 180F). Be interesting to see if they both modulate down under these conditions (-30C).
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That is the issue with series primary loop. Unless you add some exact gpm numbers to this drawing you cannot predict what the blended temperatures are. The AH cannot get 160 SWT as it is being blended with the return, which could be 20- 30 ° degrees cooler than the SWT it is actually getting. So you are running a much hotter boiler temperature than you need. A thermometer on the supply to the AH would shed some light on the questions we have.
The AH may in fact have enough BTU output at 145- 150, but it is taking you a hotter less efficient boiler operating condition to get there.
Are the pipes to the AH 3/4" or 1" copper? If they are 3/4 I don't see a second boiler adding any additional btus?
4 maybe 5 gpm in 3/4 copper is all the 15-58 may be shoving up there.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
The pipes to the Air Handler are 3/4"
I tried an infared thermometer on the supply to the Air handler, but it was only reading 100*, but it is much hotter than that, I cannot touch it for more that a second without fear of burning myself. The return is considerably cooler, but sttill too hot to hold
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Do you have a probe type meat thermometer? tape it against the copper. Wrap a wash cloth around it for some insulation.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Put a piece of black electrical tape around the supply on the Air Handler. Then shoot the black tape with the the infrared gun. The infrared gun will read much too low when it gets a response from the copper. No bright surface will ever provide accurate results.
I've shot my balancing bearings after being in a 300F oven for 30 minutes. The typical reading is about 175F. Worthless.
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That was an excellent suggestion
The supply was at 144* the return was 129*
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If the piping up to the AH is not insulated you are dropping more temperature before it gets to the coil.
Maybe more like 140 at the coil supply, 134 at the coil on the return. A 16∆ with 4 gpm, gives you around 32,000 btu/hr
But your boiler is running at 160°?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Yes, that is showing as the supply temp.
I have the pump running to the Air Handler at the lowest speed
If insulating these pipes in this room would make any difference, I can certainly do that
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30,000 @ a measured DT of of 15°F.
Raise the boiler SWT and see if you can increase the DT. You can't get any more output with additional flow.
If the readings are accurate, you're losing 14°F during the trip (if the boiler is at 160°F…………….why?
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I have the pump running to the Air Handler at the lowest speed
If I had to make a bet, this is sufficient. But, as a test, raise the pump to the medium speed and take the measurements again…………..AFTER THE SYSTEM IS IN EQUILIBRIUM…………….boiler output temperature steady……………modulation steady…………running for at least 15 minutes. We'll see if the flow rate has any significant difference (I doubt it).
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increasing the pump speed will increase the output a small amount. It closes the delta across the coil which increases the average temperature across the coil, which increases the btu output
Decreasing the flow rate, all things being equal, will reduce output, regardless of the type of heat emitter.
It’s called a hockey stick shape on a graph. Big change up to a certain flow, then additional flow gets you not so much. The 3/4 tube is the limitation. Although the coil size is part of it also.
Increasing the blower speed will get you more output also, increases the forced convection.
3/4 fin tube example attached
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Well said. I doubt that he'll get much of any benefit from additional pump speed. Additionally, with a narrowing DT, it is easy to conclude that LESS BTU are being delivered when the opposite is the situation (due to the higher average coil temp). The dangers of strictly relying on DT as a measure of heat transfer. 😉
We've had this discussion before……………..
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are the radiant zones running when you take those temperatures? In not, they will cool down that primary loop, and the SWT to the ah, as their return temperature blends in
EDIT I was looking at the primary loop flowing clockwise, the radiant being the first load. When it looks like the loop flow direction is CCW. So the AH should get close to the boiler output temperature.
If the ah pulls 5 gpm at 160° with a 20∆, then 140 RWT blends with the primary loop 160, so the radiant mix valve sees 150°. Which is fine since it blends down to ??, maybe 110°?
Also a graphic showing two loops, both being supplied with 160° The low flow rate, .2 gpm, high ∆ shows the fin tube temperature dropping along the loop, the last couple fin tube seeing a low SWT, little if any heat output.
Th higher flow, bottom graphic, 1 gpm, providing a 14∆ has the fin tube at the higher AWT, higher output.
The upper example at a very small .2 gpm is what you may see in a ghost flow condition, a zone valve that has some debris holding it open a small amount, perhaps. Warm fin tube even with the thermostat off, for example.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
This is why I find primary/secondary piping is not the optimal solution for modcons and heat pumps.
Unless you have active means of matching flow rates between the different loops (ie delta T circ on both), you are either mixing the supply down at the device from the return or you are mixing up the the return water at the boiler with supply water. Neither is optimal as the boiler needs to supply hotter water than what the device sees and the return to the boiler is hotter.
Not something the will work with the OP's setup, but direct to load is the better way to go for new installs. It is also much easier to mess up, so not for everybody.
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Unless you have active means of matching flow rates between the different loops (ie delta T circ on both)
^^^
This
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If only the small radiant zone was calling would the boiler get enough flow for a direct piping method? I think the fire tube boilers are more forgiving for direct piping. Are these fire or water tube boilers?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
This all depends on the boiler. I have installed some that will accept 2GPM as a minimum flow rate. Most won't.
Be nice to know who the manufacturer is for them………………………and the model number!!
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