Problems Unresolved, Seeking Input {Looking for References, Chicago Area -- Mod Con Boiler}

4xlt

Thanks Stephen and Rich.

Stephen -- "Is the flue vent and combustion air piped to the outdoors in the same pressure zone?" I don't know how to determine this but the 3" PVC intake is through a side wall of the house, about 12-14' from the boiler. The exhaust is sent out the opposite side of the house with probably 35' of 3" PVC with I think three 90s to get there. ???

Rich -- "Please tell us what rooms are on what zones." If the heat loss calc worksheet and the floor plan pages I posted a little earlier today shows for everyone, the rooms on which zones are shown there. Only the 15 x 25 family room and the 8 x 12 breakfast room are on the small zone, which is zone 2, which is the baseboard zone and the one with both 1/2" and 3/4" copper. Every other room in the house is on zone 1 and they all have good old upright iron sectioned radiators. I've attached another version of the floor plan to this post.

Rich -- also, "As for me suggesting a Grundfos , you have the wrong guy , never did it." correct, -- sorry, someone else named the grundfos pump, but other than the pump reference I got wrong I'm still not clear on what you said there.

Thanks to all for this help!

4xlt

is this the air separator?

What I don't think I have is a downstream temp sensor. Of course I don't know if it's a must but the I & O manual says the manufacturer supplies them and says it "is to be installed."

Tinman

No, that's an air vent. You should have an air separator that's scrubs smaller air bubbles from the water.

Tinman

I like the placement of that vent but it's not enough.

bmwpowere36m3

They come with a supply temp sensor (thermistor), but it doesn't "have" to be installed. If its not installed, the control logic uses the boiler outlet temperature instead. I imagine its to better regulate the supply temp and firing rate/modulation when its piped P/S.

Gordy

The near boiler piping is a mess granted, and needs to be changed. But that problem zone needs repiped in 3/4 period. There is plenty of baseboard to get the btus out if you can get them there with out a screaming flow rate to keep a decent average water temp. You need 334 btus a foot thats doable.

Gordy

Thats a shame to install that grossly oversized boiler, and a heat loss was done. The WHN line has way closer sizes to pick from. Its an added cost but you really need that buffer tank or your boilers components are going to see excessive wear from all that cycling.

furnacefigher15

To get the boiler to stop alarming in the middle of the night, you need to limit the available heat capacity to the addition. The only way that can be done is to reprogram that zone as DHW and set the DHW fan speed limit to 30 or 40 percent and remove domestic priority. I'm in Chicago by the way, but I doubt my shop will do work at your house unless you happen to also own a high rise or other commercial operation. Send me a private message to furnacefighter15@yahoo.com reference this post and I can point you to a company that can get you squared away.

Gordy

furnacefigher15 said:

To get the boiler to stop alarming in the middle of the night, you need to limit the available heat capacity to the addition. The only way that can be done is to reprogram that zone as DHW and set the DHW fan speed limit to 30 or 40 percent and remove domestic priority. I'm in Chicago by the way, but I doubt my shop will do work at your house unless you happen to also own a high rise or other commercial operation. Send me a private message to furnacefighter15@yahoo.com reference this post and I can point you to a company that can get you squared away.

Is that your solution??

furnacefigher15

Gordy,
I didnt read through the entire post, so not entirely no. But ultimately the OP asked for a referal, so if the sends me an email, I will refer her to a local company that has the talent and knowledge to thoroughly address all the issues at hand ie not enough baseboard in the addition, incorrect piping etc...

But, in the past I have resolved similar issues on other boilers with simple reprogramming and it has worked in those situations.

You have to realize this person has spent a small fortune on this boiler system already, so if there is a simple low cost stradegy that can be applied and have the system work, then its worth a shot.

So im not sure what your getting at, and I don't care for the tone you have taken with me.

Rich_49

Would you add a buffer tank and leave the DHW priority alone ? How about changing the 1/2" to 3/4" where necessary ? If this would be your low cost solution how would you possibly refer someone capable ? So , would you also change the SWT in the logic to be lower than when producing DHW ? How would DHW be produced then after these changes ?
By the way , we realize exactly what this individual is going through . What you must realize is that by your comment and advice , you have proven that you are not as smart as we think you are . In fact this would just be taking more of their dollars with NO real solution .

Gordy

furnacefigher15 said:

Gordy,
I didnt read through the entire post, so not entirely no. But ultimately the OP asked for a referal, so if the sends me an email, I will refer her to a local company that has the talent and knowledge to thoroughly address all the issues at hand ie not enough baseboard in the addition, incorrect piping etc...

But, in the past I have resolved similar issues on other boilers with simple reprogramming and it has worked in those situations.

You have to realize this person has spent a small fortune on this boiler system already, so if there is a simple low cost stradegy that can be applied and have the system work, then its worth a shot.

So im not sure what your getting at, and I don't care for the tone you have taken with me.

I guess my tone is read the entire thread, and or threads linking the OP's issues. What you suggest is a band aid for the moment not a solution to the entire list of issues.

These are story problems that have information to put into prospective. The beauty of most of these story problems is you can ask more questions to get more information to draw a more vivid conclusion to the host of issues to be resolved.

So jumping in the middle with part of a solution to a whole list of problems is not conducive to helping with the definitive answer. You offer help IF this person is affiliated with a commercial building! Or high rise operation. The OP is a home owner. All though anything is possible.

So sorry for the tone.

Gordy

Rich said:

Would you add a buffer tank and leave the DHW priority alone ? How about changing the 1/2" to 3/4" where necessary ? If this would be your low cost solution how would you possibly refer someone capable ? So , would you also change the SWT in the logic to be lower than when producing DHW ? How would DHW be produced then after these changes ?

And what @Rich said

furnacefigher15

Gordy,
Point taken. Sorry to cause a stir. I did not mean to infer anything wierd with the highrise comment. That is just the reality for the company I work for. Its a large commercial industrial shop, and the only single family type residential work we do is for owners/higher ups connected to the commercial or industrial customers we work for.

furnacefigher15

All,
Disregard my previous "solution" Like I said, I didnt read the entire post. I didn't mean to offend anyone, so I am sorry. Ive been working alot of hours lately with the cold here in chicago and was just trying to wind down for the day. I read the post where the customer was having middle of the night fault outs and was reminded of another situation I ran into where the boiler was oversized for DHW usage, but the space heating load was very little. 30 ft of baseboard on a 200,000 btu boiler. All good in dhw production, but in space heating mode it would short cycle heavily and fault out for all manner of reasons. That boiler happened to be a weil mclein that had a way to limit the available btu output to each zone. I looked in the manual for the lochinvar and it only has that function for limiting the dhw.

So take that for what its worth.
Again sorry for butting in. Honestly apologies all around.
And take care.

4xlt

Thanks again to all.

Is it correct to say:

1) that a buffer tank would be necessary due to the small zone (even if the entire loop had always been piped 3/4"), but

2) the large 199k size of the boiler means the buffer tank needs to be larger? For example, presuming a buffer tank is basically necessary, if the boiler were a 155 or a 110, would the proper buffer tank be smaller?

Tinman

1. Yes
2. On the 155, you would need a smaller tank - 40 gallons. On the 110, you shouldn't need a tank based on the numbers provided.

Rich_49

I respectfully disagree Stephen . By not installing the buffer you still allow the boiler to short cycle during the very many low load hours which the boiler will be operating in . Remember we are sizing the tank to design conditions , at above design conditions the requirement for a buffer becomes greater . Granted , the streams will flow right across supply and return ports at design and we could do w/o the tank it is still needed possibly 50% or more of the between October and April .

Tinman

Thanks Rich. I appreciate your input. In your estimation, at what point do you suggest no tank? In the above scenario we seem like we'd be very close. A 110 with a 5:1 turndown and the smallest load/zone being 24k or so?

blee597

I don't know if this has been resolved, but here goes. Sorry for the long dissertation, but not sure what your knowledge base is (apologies to all the docents). You can scroll to the end for the summary.
The piping in the addition is connected to finned tube baseboard which is a cost effective way to blanket the heat loss where it happens (at the outside walls). The problem is that the capacity of the finned tube drops off drastically at low MWT or AWT (depending on who taught you heating). The rule of thumb is that you want the temperature above 140. This is where the system starts convection and the heating output goes up dramatically. That being said, your finned tube zone will require much higher temperatures than your radiators (which were sized on gravity flow and have a very small convective rating). This means the water temperature leaving the boiler has to be above 140 (assuming that your loss based on OA is above the 30 BTU/LF that the ¾” copper can handle. Not only does the supply temperature have to be above 140, but the return water has to also be above 140 because all of the finned tube length needs to be adding its convective heat which requires 140 degrees. Also, be careful not to raise the water temperature too high as the drafts from the excessive convection will make the occupants cold due to the increased air moving across the body. The usual design for a finned tube circuit is 1 GPM for every 10K of heat loss at 20 degree ∆T. If your loss is 30K then you will need 3 GPM circulating through the circuit. The typical design for 3 GPM is ¾”. This keeps the velocity high enough so that there is a little turbulence in the piping which aids in the heat transfer. Can you move 3 GPM through ½” tubing? Yes you can, but the cost is bigger pumps, higher electric, and lots of noise. You have several options, but here are the two that I would use. Re-pipe the circuit with ¾” on the supply and returns, or (better) run a ¾” supply or return to the middle of the circuit back to the boiler. This will cut your MWT in half at the same circulation rate.
I am a huge fan of P/S systems. I am also a fan of large water volumes and properly sized boilers. A buffer tank in the system assumes that the water leaving the buffer will be at sufficient temperature to carry the load of the finned tube. Since the finned tube in the addition needs waters above 140, the buffer tank will need to have water temperatures above 140 to carry the load in the off cycle. Let’s assume that the boiler is looking for a design water temperature of 155. Let’s also assume that we have a boiler that will turn off when the return reaches 155 and the dead band is 10 degrees (the water will have to get to 145 before the boiler will fire). If our P/S circulator is sized for the output of the boiler the rate of circulation will be between 10-20 GPM; depending on who you talk to, but based on your piping I would assume that it was 10 GPM. When your boiler fires it will try to maintain 155 degrees output. If the return is 145 and the supply is 155 with 10 GPM, the boiler is adding 50K of heat to the system. If your load is 30K then the net result is a tank gain of 20K (this is per hour). In simple math you would need a tank that is roughly 240 gallons (20,000/(8.33*10)). As the system temperature increases, so does the return water temperature (as we are exceeding the heat loss). Eventually the boiler starts backing off and starts moving towards matching the load. This would be fine if we were at the design day conditions all year long and we can find room for a 240 gallon tank. The fact is that we are usually at a fraction of the design load most of the time and a 240 gallon tank is pretty substantial (expensive, heavy, and needs to be insulated). In addition to that the boiler output will fall off as the return water temperature increases (and it will because all of the load is not used). Eventually, on the few near design days, the boiler output will match the load. If we use a load of approximately 50% or 15K, we would need a tank of 60 gallons. If we say we can allow some cycling, we could use a 30 gallon tank. We can install a smaller tank if we can allow the water temperature to drop in the off cycle to another 5 degrees. Again, the boiler output at startup will be at 50K at 145 degree return temperature. At 140 degrees the boiler will be at 75K. Our best bet for this is to adjust the ramp speed of the boiler (how fast it tries to achieve supply temperature) to limit the output. If we can slow the ramp speed the sooner we will get to the desired output for the given outdoor temperatures and the longer the boiler will run. So to summarize, you should get a buffer of at least 30 gallons and up to 60 gallons. You can insulate this or not depending on where you locate this and whether you can take the additional heat in the room that it is installed in. You will also need to slow the ramp rate of the boiler control.
Air elimination is also a key to the correct operation of the system. Micro bubble elimination is efficient at elimination of all air as the more air you remove from a given volume of water the more that volume can grab from the rest of the system. The air in the system will attempt to seek equilibrium so the better you scrub the water of air, the better the removal of air in the entire system.
A note on the sizing of your boiler. The suppliers for these systems usually make the mistake of sizing the boiler based on the instantaneous domestic load. That is an 80 degree rise with a 5 GPM domestic water flow. At the same time, they sell you a storage tank that should mitigate the peak load that the domestic puts on the system which is selling at both ends of the load. The truth is, in an average sized home, you would have to be running a full shower, with multiple body sprays, washing dishes, washing clothes, and filling a bath for the kids to ever see these flow rates. If you had a boiler that was sized for the connected heating load, plus say 5%-10%, you would never be short of heating or domestic hot water.
On your flue and intake. It is always better to have them on the same side of the building. If that is not possible then you should avoid the east and west sides because the prevailing winds are always from the west. This would cause a pressure difference between the sides and might cause burner failures. Also, just an FYI; your flue is PVC which is not rated for the temperatures you are running your system (155 operating means about 165 flue temp). Does it work? Yes, is it correct? No.
Solutions:
1. Install new piping to split the finned tube into 2 circuits on the same zone or eliminate the ½” piping.
2. Install a de-coupler (bridge, low loss header, etc) and make a primary circuit. The domestic can parallel this and should if you require higher temperatures to make the domestic. This should also contain air elimination as well.
3. Install a 30-60 gallon buffer tank (thermal mass) if you are unable to get the volume satisfied by the de-coupler. Remember, the more water the better.
4. If you still have issues, you will have to do something with the flue.
If you have any other questions, please email me at blee597@gmail.com.

CarradineArchitects

Looking only at the system board layout and your floor plan comments, notice what is different between the working and non-working zones? Yes, the non-working pipe size is reduced to 1/2", but more importantly, the pump is also reduced. The smaller pump may be working just fine by itself if the other larger pumps and zones are shut down. If so, with all pumps on, the larger pumps are back-feeding the loop with the small pump. The reverse pressure is too high for the small circuit to function at all -- zero! The solution is to match the small pump to the same PSI, or just replace it with another pump matching the existing pumps. Installing a back-flow valve in each circuit will not help, the PSI must be the same in the system. Send you comments please to silverfox-at-cxv.net