Adjusting TT Prestige Solo 110 CH Operation

JustinS

Now that it's getting cold again and I turned my heat on for the 1st yesterday, I wanted to get some advice on how I've been adjusting the boiler's CH operation...

According to a ResCheck done by my architect, my house has a UA of 343 BTU/F/hr... since we generally keep the thermostats around 70F and the design temperature for my area (Massachusetts) is ~6F, I'm seeing that I should have ~22K BTU/hr loss on a design day... sound right?

Based on this, I looked at http://comfort-calc.net/pictures/Slantfin baseboard.JPG and that I have ~90ft of radiator fins, it looks like I need ~240 BTU/ft/hr heat transfer... now, recognizing that those numbers are for 65F entering air and mine is around 70, I would need to adjust my water temperature up to maintain the same delta... as such, I set my coldest day setpoint to 140F... I wasn't quite sure how to set the warmest day setpoint so I just set it to 100F...

This morning it was ~38F outside and so the boiler setpoint was 118F...

One thing that I noticed was that the supply and return temperatures fluctuate much more than during a DHW cycle when they are relatively constant; I assume that this is because of the longer piping runs for the CH system?

I also noticed that the return temperatures tend to be no more 8-10 degrees below the supply (sometimes they're equal)... I seem to recall reading that the ideal temperature drop between the two was ~20F...

I'm curious what people's thoughts are... thanks!

Zman

You are heading in the right direction to maximize efficiency.
Here are a few thoughts that may help:
Most baseboard heater output charts have an asterisk next to the lower temps stating that they are calculated ,rather than tested. Don't be surprised if you need to raise that 100 degree number.
The boiler will increase it's on/off differential once it reaches low fire in order to reduce short cycling. It is normal to see 20 degree swings.
A supply/return delta T of 8-10 pretty normal. Many systems are designed for 20 degrees. Not very many run at those numbers.If you are piped primary/ secondary, you should make sure the circ inside the boiler cabinet is set to speed 1. They ship them set to speed 3 which only makes sense if it is piped directly to the emitters.
Carl

SWEI

Minimum firing rate on the 110 is 30k. If your design day heat loss is actually 22k (or even 33k) you might want to consider adding a buffer tank to that system.

JustinS

SWEI said:

Minimum firing rate on the 110 is 30k. If your design day heat loss is actually 22k (or even 33k) you might want to consider adding a buffer tank to that system.

Well, I *think* that it's only 22k - all I have is the ResCheck that has a UA of 343 - from what I have read, this is the heat loss per degree difference... am I correct?

JustinS

Zman said:

You are heading in the right direction to maximize efficiency.
Here are a few thoughts that may help:
Most baseboard heater output charts have an asterisk next to the lower temps stating that they are calculated ,rather than tested. Don't be surprised if you need to raise that 100 degree number.
The boiler will increase it's on/off differential once it reaches low fire in order to reduce short cycling. It is normal to see 20 degree swings.
A supply/return delta T of 8-10 pretty normal. Many systems are designed for 20 degrees. Not very many run at those numbers.If you are piped primary/ secondary, you should make sure the circ inside the boiler cabinet is set to speed 1. They ship them set to speed 3 which only makes sense if it is piped directly to the emitters.
Carl

20 degree swings? In what regard?

What do you mean by "piped primary/secondary"?

How do I adjust the speed of the internal circulator?

Zman

The boiler will allow the operating set point go 10 degrees above the target temp before it turns off and 10 below before it fires again. This is normal, it saves energy by reducing short cycles.

Post a picture if the piping around the boiler or look in the manual to see if you are piped primary /secondary.

The circ inside the boiler cab has switch on the side 1,2,3

Carl

JustinS

Zman said:

The boiler will allow the operating set point go 10 degrees above the target temp before it turns off and 10 below before it fires again. This is normal, it saves energy by reducing short cycles.

Post a picture if the piping around the boiler or look in the manual to see if you are piped primary /secondary.

The circ inside the boiler cab has switch on the side 1,2,3

Carl

I'm not sure if I'm seeing 20 deg swings - I think it fires again when it drops a couple degrees below setpoint, though it doesn't necessarily stop firing immediately above setpoint...

See attached for the boiler set up - does it help?

The internal circulator is set to 2... what is its function since i have a circulator pump on each zone and on the DHW piping? My zone circulators are set to Low...

Paul48

Nice, neat work, but that is not primary / secondary. It either has to be pumped through, or P/S, not both.

JustinS

Paul48 said:

Nice, neat work, but that is not primary / secondary. It either has to be pumped through, or P/S, not both.

So this is the pumped through?

Zman

What you have is circulators in series. You can probably remove the one in the cabinet. It is not right and is a waste of energy.

JustinS

Zman said:

What you have is circulators in series. You can probably remove the one in the cabinet. It is not right and is a waste of energy.

Assuming that I leave it in place, I can probably set it to the lowest speed and let the zone circulators handle the flow...

Is my reading of the ResCheck document correct?

Zman

In reality, you could probably handle the flow with any one of those circulators on the lowest setting. You would have to do the math and see if that maintains the required minimum.
What is troublesome is that the installer obviously does not understand the system he is installing and has left you with a system that is not installed per manufactures instructions. This could leave you hanging down the road.

It looks like you are understanding the rescheck correctly.

Carl

JustinS

Zman said:

In reality, you could probably handle the flow with any one of those circulators on the lowest setting. You would have to do the math and see if that maintains the required minimum.
What is troublesome is that the installer obviously does not understand the system he is installing and has left you with a system that is not installed per manufactures instructions. This could leave you hanging down the road.

It looks like you are understanding the rescheck correctly.

Carl

Well, I would need each of the zone circulators, right? It's the internal circulator that's redundant? Although, I assume that comes with Solo so I'm not sure what can be done about not having it there?

Could you elaborate on how the installer doesn't understand the manufacturer's instructions?

Here's the actual ResCheck, just want to be sure I'm reading it right...

Zman

Triangle tube's preferred piping is primary/ secondary. They have the least problems with this configuration as it always provides adequate flow through the boiler. Your installer seems to prefer zone circs to zone valves so his best choice would have been to pipe it primary secondary.
If he was capable of checking the math on the flow rates, he could have piped it direct with zone valves and only used the provided circ. Another, less pretty option would be to remove the circ in the boiler and replace it with 2 flanges and a pipe.

Your understanding of the recheck looks correct.
Are you wondering why you have a 100k/btu output boiler on a 22k load? You should...

Carl

JustinS

Zman said:

Triangle tube's preferred piping is primary/ secondary. They have the least problems with this configuration as it always provides adequate flow through the boiler. Your installer seems to prefer zone circs to zone valves so his best choice would have been to pipe it primary secondary.
If he was capable of checking the math on the flow rates, he could have piped it direct with zone valves and only used the provided circ. Another, less pretty option would be to remove the circ in the boiler and replace it with 2 flanges and a pipe.

Your understanding of the recheck looks correct.
Are you wondering why you have a 100k/btu output boiler on a 22k load? You should...

Carl

Yeah, I am wondering why the boiler output is so much greater than what I apparently need... that's why I was questioning if my reading of the ResCheck was right...

Of course, there is the DHW tank load but that seems to be small by comparison... there's always future expansion of the house to consider but I'm not going to double its size...

It's beyond frustrating - I wish I had some recourse to have him remedy this but probably not... I wonder how much this is costing me...

JustinS

I just spoke to Triangle Tube technical support and they had an interesting recommendation to help address my oversizing...

He recommended turning my DHW tank essentially into a buffer tank by moving my DHW circulator from the DHW contacts (29/30/31) to the Auxiliary Boiler Pump contacts (26/27/28)...

As a result, with DHW Priority ON - it seems that my boiler would only fire when it was necessary to heat the DHW tank back up to setpoint and not much else...

He also told me that the only time the boiler is not burning fuel is when the status is reading 'Setpoint Reached' - it's not enough for the firing rate to be 0% - if it says 0% and it's still in demand, it's burning the minimum 30K... interesting because the boiler sounds rather different when at 0% than otherwise...

Wondering what you all think?

SWEI

Clever way to make the SMART Indirect act like a buffer tank. Have to think about the control logic a bit, not sure how ODR would interact with the DHW calls, but I suspect it might work better with an ODR-controlled mixing valve between the boiler-buffer-DHW and the distribution system.

JustinS

One thing that I am wondering - I currently have a DHW Post Time configured - this is quite nice since it results in my DHW tank ultimately going up 4 degrees above setpoint (130 vs 126 w/ 146 heater water) after the DHW call is done...

It seems to me that this might no longer function when connected to the Aux Pump contacts? I guess what I am wondering when the Aux Pump runs - is it only during calls OR any time that a connected circulator is called to run (i.e, during post run times too)?

SWEI

The Boiler Aux terminals have power any time the boiler fires.

JustinS

Any thoughts on why my Supply and Return temperatures are so close together?

I was reading another post on this board from several years ago where it was discussed that there was insufficient flow in certain places which was causing backflow so that the Return was being heated by the Supply, I believe...

Paul48

I'm putting some links here.....Please don't be offended....I don't know what you know, or dont know.
http://www.comfort-calc.net/Dont_Oversize_Mod_Con_Boiler.html
http://www.comfort-calc.net/primary-secondary_piping_tutorial.html
http://www.slideshare.net/illinoisashrae/hydronic-basics-primarysecondardy-pumping

JustinS

Paul48 said:

I'm putting some links here.....Please don't be offended....I don't know what you know, or dont know.

Not offended at all, have some basic understanding but still lots to learn... I've looked those over before but will read again, thank you :-) :-)

JustinS

Also, I mentioned what I believe the heat loss (via the ResCheck) to be... I know it has been said that it looks like I am understanding it properly but does it truly make sense for a ~2200 sq ft house (38x28) to have that kind of heat loss?

Paul48

Most people are suprized at the results when they do a heat loss.If they completely screwed yours up, and missed by 75%, you would still be massively over-sized. I'd almost be willing to bet, he sized it according to your domestic hot water usage.

Zman

10 btu/ft is pretty low. I am not seeing an air infiltration factor in the rescheck. That could skew it a bit. Was a blower door test done?
You are still clearly oversized.
You are not going to improve your delta t with you existing piping. It really is not worth chasing it. Put the circs on low and call it good.
I am intrigued at TT's suggestion. I can see it if it was designed from the beginning, just not sure how it will perform after the fact. Keep us posted on how it works.
What was TT's thoughts on your piping?
How are the cycle lengths?
Be sure you have a thermostatic mixing valve on the domestic side.
Carl

JustinS

Ok, I gave those a read through... I think that i better understand P/S piping but since my system is piped in series (for better, or worse), it doesn't seem like excess flow from my boiler (beyond what the zones need) would cause reverse flow, right?

It seems like that the flow would be limited by whatever flow the zone circulators are producing? Or am I misunderstanding things and there could be reverse flow through the boiler itself?

Another thing I am wondering is how to know what the flow rates through my system are... as I understand it, it's based on the pressure drop from A to B but I'm not sure how I can know that?

JustinS

Paul48 said:

Most people are suprized at the results when they do a heat loss.If they completely screwed yours up, and missed by 75%, you would still be massively over-sized. I'd almost be willing to bet, he sized it according to your domestic hot water usage.

The thing is that I only use about 50000 BTU/day for DHW during the summer... that's my average gas usage with a few loads of gas drying in there plus some cooking but the bulk of it is going to be DHW...

JustinS

Zman said:

10 btu/ft is pretty low. I am not seeing an air infiltration factor in the rescheck. That could skew it a bit. Was a blower door test done?
You are still clearly oversized.
You are not going to improve your delta t with you existing piping. It really is not worth chasing it. Put the circs on low and call it good.
I am intrigued at TT's suggestion. I can see it if it was designed from the beginning, just not sure how it will perform after the fact. Keep us posted on how it works.
What was TT's thoughts on your piping?
How are the cycle lengths?
Be sure you have a thermostatic mixing valve on the domestic side.
Carl

A blower test was done after we moved in when I had an energy assessment done... not sure of the units but it was 3824 before they air-sealed the attic and basement and 3643 afterwards...

I didn't have a chance to ask TT about the piping - they were really busy and the guy had to move on to other calls... planning to call back tomorrow... though, I am wondering - if P/S is the way TT wants it piped, why is my setup shown in their installation manual? If it isn't recommended?

I don't know much about the cycle lengths yet as it hasn't been very cold - I am using setback at night and during the day now, last night it dropped 2-3 degrees and took 2-3 hrs to recover... as to how long a cycle will be when it comes to maintaining at setpoint, I'll have to see...

Yes, I do have a thermostatic mixing (anti-scalding) valve on the DHW outlet...

Zman

Your setup is not in the 110 manual http://www.triangletube.com/documents/1/Prestige 110 TriMax Manual 020614.pdf

You do not have reverse flow through the boiler. You have too much flow to get the delta T you are dreaming of.

BTU/HRs = Delta T x 500 x GPM

The BTU's are not going to change much. The only way you to increase the delta t is to reduce the flow.

Measuring the GPM is tricky. In residential systems it is usually just calculated (actually most folks take a wild **** guess). In commercial systems,you measure the pressure on either side of the circ.

If you do short cycle it will be worse on warmer days as the emitters will be unloading less BTU's.

Carl

JustinS

Zman said:

Your setup is not in the 110 manual http://www.triangletube.com/documents/1/Prestige 110 TriMax Manual 020614.pdf

You do not have reverse flow through the boiler. You have too much flow to get the delta T you are dreaming of.

BTU/HRs = Delta T x 500 x GPM

The BTU's are not going to change much. The only way you to increase the delta t is to reduce the flow.

Measuring the GPM is tricky. In residential systems it is usually just calculated (actually most folks take a wild **** guess). In commercial systems,you measure the pressure on either side of the circ.

If you do short cycle it will be worse on warmer days as the emitters will be unloading less BTU's.

Carl

I thought that Figure 9 on pg 21 was pretty close to what I have... granted, it is missing a few things such as the check valve and drain valve on the zone return piping but it looks pretty similar...

In your equation above, is it also used in the http://comfort-calc.net/pictures/Slantfin baseboard.JPG? Is there a more detailed version of it (seems simple without area factor)?

****EDITED****

Actually, I just answered my own question on the equation... it's just the heat absorbed by the water based on mass and delta-T... I guess it was too early ;-) :-)

Did you post that equation to figure out the GPM or merely to show the relationship?

Something else that just occurred to me... if my delta-T is low and as such, I'm only transferring a small amount of heat into the water, I assume that means the rest of produced heat is going out through the flue gas? My flue gas temperature is usually pretty close to my return water temperature... should this be the case? I thought I remember reading something about the flue gas temperature being closer to 100F (at least, according to Wiki) but then National Grid says it's more like 120-140F...

JustinS

BTW, I'm not entirely clear on the definition of short-cycling...

Is it a short cycle if my supply temperature drops below setpoint and the boiler fires for a short time (min or so) to bring it back up?

Or is it the total duration of a heating cycle as the boiler has repeated firings, moving in and out of CH Demand / CH Spt Reached?

Zman

Short cycling is to many on/off cycles. The rated efficiency of an appliance applies to it's steady state condition. When the boiler is constantly turning on and off, the net efficiency suffers. Control parts also tend to wear prematurely. 6 cycles per hour has become the threshold. Less is better.

The hydronic formula I posted is to show the relationship between flow and delta t. If you were to cut your flow rate in half (eliminate a circ) your delta t would double. Same number of BTU's are transferred.

The figure 9 you refer to is primary/secondary piping. Unless you have the tees between the CH and system circs, yours is not primary/secondary. Ironically the configuration in figure 9 would also have very low delta t because there is way too much flow through the unrestricted pipe.

The internet is confusing you. This stuff is hard, but not that hard...

Carl

Paul48

re: "Pretty Close"

The rules that apply for P/S piping, and closely spaced tees don't allow for that.

Many mod/cons have highly restrictive heat exchangers, and require fairly large circulators to pump a minimum amount of water through the HX at all times. To ensure this, they require hydraulic seperation or P/S piping.

The problem that this creates is matching load to boiler gpm. What is not taken away from the boiler and is returning immediately to the boiler. The temperature of that water, added to the return water temperature does not reflect what the sytem actually needs, and that is what the mod/con is basing its firing rate on.

Your boiler and other fire-tube boilers, have much less restrictive HX passages. They still require a minimum flow through the HX, but offer the possibility of pumping through the boiler with a single circulator, to the system. Every ounce of water through the boiler goes out to the system, and returns affected by the conditions that are present. The boiler "sees" the system.

This is a simplistic explanation, and there are more details involved. It is to give you a general idea of part of the problem.

JustinS

Zman said:

Short cycling is to many on/off cycles.
Carl

OK, but what is an on/off cycle? Is the boiler only "on" if it's actively firing and heating the water? Is it "off" if the boiler supply temperature is above setpoint? Wouldn't it always do this as the supply temperature modulates around the setpoint? Or is it supposed to remain at/above setpoint without going high enough to cause the boiler to stop firing completely?

This may be obvious but if there is little to no delta T between supply and return, I would imagine that this means that little to no heat is being emitted via my baseboard heaters?

Something else that I just thought of... if you look at my 1st picture, there are three parallel pipes (top = CH supply, middle = CH/DHW return, bottom = DHW supply)... both top and bottom pipes just terminate to the right near the DHW tank - if I were to link these two pipes, wouldn't that complete the primary loop to be like Figure 9? Or would the fact that I don't have check valves in my return piping cause problems?

Zman

I think you are understanding boiler cycles. Some on and off is OK, too much on and off is not.
If a mod/con boiler is sized appropriately to the load, it can match the load most of the time. A boiler like the TT60 would modulate down to somewhere around 12-15k. Your load would be at or above that most of the time. That means long efficient cycles.

Again, delta t is related BTU's transferred and GPM.

I can't see all off the piping connections under your boiler. A drawing or better picture angle?

JustinS

OK, so here's a sketch of what the system looks like - hopefully, it helps... one thing that I am wondering about - why are my CH and DHW supply lines interconnected, I don't see that on any piping example?

One thing worth mentioning... as I was in the basement looking in greater detail for the sketch, I happened to catch it in a heating operation for CH... the boiler setpoint was 110F, supply was 114F or so, return was 110F or so... the boiler started firing as supply dropped below setpoint and the return temp jumped *before* the supply temperature to about 116-120F or so, followed soon after by the supply which went as high as 132F... this whole process last maybe 30-40 seconds before the boiler stopped firing and returned to 'CH Setpoint Reached'... it then took maybe a minute or so for the supply/return temps to drop back down near setpoint where the above repeated itself... all and all, I saw this happen two or three more times before the thermostat turned off... sounds like a pretty short cycle?

Why does my return temp go up before the supply when it starts firing?

Zman

You are correct, the DHW supply and the CH supply should not be connected. With it piped like that, who knows what kind of ghosting occurs between the two.
You need to get the piping corrected.
Maybe you should send that to TT and get a letter confirming that it is incorrect. Then get the installer to correct it.
Carl

Paul48

I agree with Carl.........We can't even begin to tell you why you're seeing what you're seeing in regards to temps,with it piped like that. It may be just mis-piped, or mis-piped and improperly controlled. Start with the obvious..the piping.

JustinS

I am planning to call TT this afternoon and see what they think...

Thanks

ced48

I think any Modcon that cycles more than once an hour should be considered to "short cycle"-With all the settings and options available, it should be easy to achieve this as a minimum goal. Also, if a boiler is in a heating call, but fires for a breif time period, then shuts down, then refires, these are all considered cycles.

JustinS

I called TT - the guy couldn't say much without looking at the pics so I sent them to him... hopefully, he'll respond tomorrow...

I timed its CH operation tonight - it fired for ~43 seconds, purged for ~30 seconds and then was 'CH Setpoint Reached' for ~52 seconds... at that point, the cycle repeated... this is with the ODR curve at 140/10, 100/70... talk about short cycling...

Interestingly, it doesn't behave at all like this when in DHW... in that mode, the return temperature doesn't go above setpoint and the boiler seems to modulate - I don't think I've ever seen 'DHW Setpoint Reached'... so I don't think it's short cycling when in DHW, it just stays on as it supposed to...