Setpoint met quickly on new Combi boiler

BoilOver2

Just had a Lochinvar Noble installed and noticing that I'm hitting high point really quickly in the evening when the system turns on with one of the smaller zones.

What's surprising to me is that the system fires up at ~50% fire and then modulates down slowly to 15-20%. If it went to min fire faster I'm confident it would stay on for a good long while based on seeing what it does in the mornings. (I've seen a Single zone that will keep calling for heat for several hours without cycling at 10-20% fire rate)

Its piped p/s and I'm noticing that the system supply is 20-30 degrees lower than outlet. I'm curious if it would modulate down faster if it only had boiler outlet temp to go off of?

Anyone else encountered this? Any harm in disconnecting the supply temp the control board to try it out?

Leon82

If that boiler also has ramp delay settings like their other boilers there are some settings that can be adjusted to keep it at low fire for up to 60 minutes. The last slot will set a limit for the output for the entire run time.

If the system flow is lower than the boiler loop flow the Boiler pump is going to be sending freshly heated water back thru the boiler. Is it a milti speed pump on the boiler loop?

BoilOver2

Great suggestion that sounds like it would do exactly what I want, but unfortunately that control option isn't available (the Noble doesn't have/or hides) many of those options. Unless there is a hidden menu some place.....

I'm thinking about using some simple programmable thermostats to do the trick. Set them up to all call for heat simultaneously at say 7 or 8 pm in the evening by putting the desired temp up to 75 (or 73 or whatever) and then at say ten pm ramp back down to the actual desired temp of 70.

The boiler seems to do just fine in the morning/mid day when the number of zones calling for heat goes from 4 to 3 to 2 to 1 but it's too aggressive with it's rate when going from 0 to 1 and causes itself to short cycle until another zone kicks in.

Leon82

If The small zone is smaller than the minimum fire rate it will cycle. No matter what the settings are. So linking a couple zones may be what's needed unless you install a buffer tank

Leon82

If you go to the Lochinvar website under tools I think you can navigate the control from your computer and see what settings are available without actually messing with the boiler.

BoilOver2

For space concerns in the utility area I want to avoid a buffer tank if at all possible. (If we had a bigger area I would have gone with a smaller unit plus an indirect).

I'll double check that the same zone in the morning after the others have shut off would keep the system loaded enough to not cycle, but I believe it is.

I think you are also on to something regarding boiler flow being greater than system flow, but I don't know if the boiler pump in the unit is fixed speed or not.

I wasn't able to track down the tools view you mentioned.

DZoro

Are you using the external supply sensor inside the well? Where do you have it mounted on the system? Do you have the boiler turned down to match your btu load? Odr matched for your system?

Le John

The Lochinvar Noble has setting for Space Heating Max firing rate. You can set that to its lowest setting which is 10% of its input to see if that helps. It will still ramp up after ignition then ramp down to the selected max firing rate. I've had similar issues and this has helped. The opening of other zones as @Leon82 suggests keeps my unit firing at 10% for 25 30 minutes.

Do you have the outdoor sensor installed? Check to see what your outdoor setting parameters are set to. They may be set too low.

hot_rod

https://www.lochinvaru.us/resource/simulator/noble/noblesim.html

Le John

this is very helpful so I'll bookmark this. Thank you @hot rod_7.

BoilOver2

> @DZoro said:
> Are you using the external supply sensor inside the well? Where do you have it mounted on the system? Do you have the boiler turned down to match your btu load? Odr matched for your system?

-- external supply sensor is in the well
-- mounted on supply side of secondary loop close to the closely sourced spaced tees
-- I believe I do, currently set the max rate a little lower than the calculated load would imply while I work to get it dialed in
-- not as sure on the ODR matching but believe I have it in a reasonable spot. 140 at design day which matches the old boiler output temp (radiant floors throughout) , would hit 110 at 70 degrees, but rarely runs when it is more than 55 outsude. Target water temp has been about 125 in the evenings as it's been pretty mild.

BoilOver2

> @Le John said:
> The Lochinvar Noble has setting for Space Heating Max firing rate. You can set that to its lowest setting which is 10% of its input to see if that helps. It will still ramp up after ignition then ramp down to the selected max firing rate. I've had similar issues and this has helped. The opening of other zones as @Leon82 suggests keeps my unit firing at 10% for 25 30 minutes.
>
> Do you have the outdoor sensor installed? Check to see what your outdoor setting parameters are set to. They may be set too low.



1) I could certainly set it to 10% for test purposes, but my understanding is that it wouldn't ramp higher even when it needed to if I did that. Am I missing something?

2) outdoor sensor is installed. 140F at 10 degrees (design day), 110F at 70 degrees on the high end but it rarely runs when temps are above 55.

Thanks!

DZoro

What type of radiant, concrete?

hot_rod

Which DHW mode are you in. " Combi Mode, one mode keeps the boiler warm at all times.

Space Heat Limiting and Anti Cycling should be set also.

Really every window on that setup simulator should be adjusted to your system, ODR included.

BoilOver2

> @DZoro said:
> What type of radiant, concrete?

Essentially, brick floors, tubing is underneath that

BoilOver2

> @hot rod_7 said:
> Which DHW mode are you in. " Combi Mode, one mode keeps the boiler warm at all times.
>
> Space Heat Limiting and Anti Cycling should be set also.
>
> Really every window on that setup simulator should be adjusted to your system, ODR included.

I disabled the pre-heat functionality, but could change it back.

Space heat limiting is set, default anti cycle on these units is 1 minute, I would extend it if I could, but it's not configurable.

Zman

BoilOver2 said:

> @DZoro said:

> What type of radiant, concrete?



Essentially, brick floors, tubing is underneath that

How is the tubing installed? Under floor? Aluminum plates?

DZoro

Don't do any setback with your thermostats. I'd suggest floor sensor thermostats. What size Noble do you have? How many btu's is the smallest zone?

BoilOver2

> @Zman said:
>
> How is the tubing installed? Under floor? Aluminum plates?

It's a brick on sand traditional Adobe home. The copper piping sits right underneath the brick in a layer of finish sand.

BoilOver2

> @DZoro said:
> Don't do any setback with your thermostats. I'd suggest floor sensor thermostats. What size Noble do you have? How many btu's is the smallest zone


It's the 199k to support some pretty heavy domestic demands. I don't have the original build plans for the system, but using the old boiler on/off times and stated efficiencies I calculated it at about 40k for the smallest zone when running water at 140F. Watching the run rates of the new system I think that overstated it, so I'm estimating 30k or so.

DZoro

You have a large mass system. How long ago did you turn on the system?
With that type of a system without a doubt I'd be using floor sensing stats. NO set back.
Your boiler at 10% will be at 19,000 btu, and probably not far from design like you said. I'd set heat max at 15%

BoilOver2

> @DZoro said:
> You have a large mass system. How long ago did you turn on the system?
> With that type of a system without a doubt I'd be using floor sensing stats. NO set back.
> Your boiler at 10% will be at 19,000 btu, and probably not far from design like you said. I'd set heat max at 15%

System was turned on about a week ago. The basic run pattern has been the same. At night, a zone calls for heat starting at about 8pm, within an hour or two at least one of the other zone also calls for heat. System runs all night and when I get up about 6am the fire rate is about 50%, by 10am or so only one zone is calling feet heat and by noon it is satisfied.

DZoro

You have a slow and steady heating system due to the large mass of sand and brick. Which is good, the more constant even temp you can keep, it the better overall comfort and performance you will find. Your water temps maybe a little high also. By lowering your water temps will help with the ups and downs of the brick sand temps, = more efficiency and comfort. Do you have many south facing windows? This too will affect slab and a air only sensing thermostat operation.
Patience with this system is very important.

Zman

Yours is a challenging one. You have high mass, so it will be very slow to respond. Dry sand is not a particularly good conductor of heat making the oversized boiler more of an issue, this is why you are cycling at the lower end. The system just can't transfer the heat quickly enough.

Normally with high mass, you want to run the boiler as cool as possible utilizing outdoor reset. Unfortunately, the lower temps will slow the heat transfer even more and make the short cycling worse.

You can play with the controls and see how much you can mitigate it that way. In the end, you would benefit greatly from a buffer tank.

bob eck

Go to Lochinvar U there is info how to set up the Noble control.

BoilOver2

> @DZoro said:
> Do you have many south facing windows? This too will affect slab and a air only sensing thermostat operation.
Yes, three of the four zones warm up with passive heating during the day when it is sunny

BoilOver2

> @bob eck said:
> Go to Lochinvar U there is info how to set up the Noble control.


Cool info there, thanks for the heads up

BoilOver2

> @Zman said:
> Yours is a challenging one. You have high mass, so it will be very slow to respond. Dry sand is not a particularly good conductor of heat making the oversized boiler more of an issue, this is why you are cycling at the lower end. The system just can't transfer the heat quickly enough.
>
> Normally with high mass, you want to run the boiler as cool as possible utilizing outdoor reset. Unfortunately, the lower temps will slow the heat transfer even more and make the short cycling worse.
>
> You can play with the controls and see how much you can mitigate it that way. In the end, you would benefit greatly from a buffer tank.


One thing that I did not expect is that the heat transfer does not appear to be linear the further I get from a setpoint temp of 140. Closer to 140 I see Delta t's of 10-15 degrees, at 130 it's about 8, but at 120 it's like 3-4. This is all with the inside temp at roughly 70. Would you guys expect this amount of heat transfer drop off? I can observe closer but it's something like that.

Is there a relationship that's used for various types of heat transfer mechanisms (baseboard vs in floor)?

Gordy

Depends on the emitter, and so long as flow rate is unchanged. With your high mass assembly. The narrower delta is simply a function of the room temp, emitter, and fluid being closer matched in temp.

Gordy

This formula defines the relationship. You need to no flow rate.

DZoro

With that large of a mass. The only proper way of even coming close to getting a good delta read would take many weeks at one solid temperature. Your base slab/sand temp is probably close to the 110-115*F mark. That is a wag on those numbers but pretty close I'd say.

BoilOver2

@DZoro

Hmm if I understand correctly, you are thinking that the thing that might be hurting the delta in the morning is that as the water setpoint temp decreases it is going into a really warm environment from the higher night time temps?

Do you have any recommendations? Things are pretty comfy though I am enjoying the tweaking.

Would you advocate turning off ODR?

It's probably worth mentioning that we are in the desert so we have big night/day swings that happen in a hurry at sunset/sunrise

Gordy

Large daily OAT swings with high mass is always trouble some if not controlled correctly. A lot also depends on the envelope.

DZoro

Slab and air sensing thermostat would be your best tweak. Keep the odr on.

BoilOver2

Just as an update before I forget..

I disconnected the system supply sensor and as a result the system modulates on the boiler outlet temp alone.

This removed the short cycling for the last two days when the first zone opens in the evening. The system gets to a steady state at 10-15% fire until other zones open an hour and a half or so later.

DZoro

It would be helpful if you are able to take a picture of the system and piping and post it.

Was the supply sensor mounted in the actual secondary supply loop piping Approx. 12" or more away from your injection piping from the boiler?

Gordy

Good point the system supply sensor should have been monitoring the system loop. Not the primary loop. If that was indeed the case.

Le John

The positioning of the supply sensor is confusing to me. Is this sensor meant to monitor the secondary flow? In the Lochinvar Noble documentation it shows the supply sensor placement in the primary supply before the system pump. What is the difference between the outlet sensor and the supply sensor?

Gordy

There is confusion when talking about primary and secondary. Usually the primary loop is where the expansion tank is place. Some refer to the primary loop as the boiler loop.

I try to refer to them as boiler loop, and system loop. That sensor wants to know what the system is doing.

Gordy

I believe their documentation is referring to primary as the boiler loop, and secondary as the system loop.

The primary is anything on the boiler side of the closely spaced tees. So in the drawing the sensor is on the secondary, or system piping.

Le John

Thank you @Gordy