Troubleshooting My Propane Fired Radiant Heating System

[Raspy]

You're looking at the whole problem in the opposite way I am and am making some assumptions that have not been shown with a schematic.

As I understand it, HillStreet said the delivery temp was controlled by the tempering valves at 110 degrees. That means they are mixing return water from the floor loops with hot boiler water to deliver a temp lower than the boiler setpoint. And it means the mixing valves do have an affect. We just haven't seen how they are actually piped in.

Arguing that the return temp determines condensation misses the point. If the boiler is cycling, and we know it is, and if it's set at a higher temp, which we know it is, then the inlet and outlet are close to the same unless there is a severely incorrect flow rate. So close that the boiler has to cycle. They can easily both be above the condensing point or both below it. If the outlet is below it we know the inlet temp is to, but not the other way around. This is especially true with the underfloor delivery system as compared to an in-slab system. With in-floor systems the boiler can be overloaded for some time and have a large differential. Since this is a condensing boiler, we want it to condense as much as possible. But we still don't know how the DHW system is tied in, so we can't necessarily just turn it down. If we can adjust the CH different than the DHW we can turn it down. Just too many unknowns here to make a lot of assumptions.

He has already said that the house heats with 110 degree water, so that is close to the minimum it should run at. 130 or 140 would be a more practical temp, possibly, but apparently the mixing valves are only allowing 110. Since we don't know exactly how his delivery is arranged, or his lifestyle, we can't say that slow even heat is the best either. Often, it's not.

If you have a slow even heating system, one that circulates constantly, or almost constantly, then the outdoor reset begins to make more sense. But if you have a tempering valve controlled delivery, the outdoor reset is somewhat defeated. When heating rooms that are not constantly used, such as spare bedrooms, or even the master bedroom in most cases, slow even heating is a disadvantage. It's better suited to living rooms where retired folks might spend the majority of their time and want a constant temp all the time. Faster recovery works better where you want to sleep in a cool room but get up to a warm floor. That's where the setback thermostat gives better control than delivery temp.

Too bad we can't see a schematic or know more about what is actually going on.

 

[dadster4]

"As I understand it, HillStreet said the delivery temp was controlled by the tempering valves at 110 degrees. That means they are mixing return water from the floor loops with hot boiler water to deliver a temp lower than the boiler setpoint." The mixing valves have 180 degree supply and 160 degree return to mix- there is no way 110 degree water is supplied to the loops.
"But we still don't know how the DHW system is tied in, so we can't necessarily just turn it down. If we can adjust the CH different than the DHW we can turn it down." The DHW is a separate loop off the primary supply loop with it's own circulator pump, the boiler will ramp up to 180 degrees to heat the DHW on a call for heat from the DHW aquastat, and when satisfied, will revert back to the supply temp chosen for the radiant heat.

 

[HillStreet]

Cooler return water is still the best method to provide condensing conditions in the heat exchanger (that's why it is so bad for a standard boiler to have low return temps), the supply temp will be whatever the boiler is set for.
The outdoor reset control will adjust the boiler supply temp downward from the setpoint but not increase it above the setpoint. It will not affect boiler temp below 0 degrees outdoor temp, and only modulate it down slightly with large increases in outdoor temps.
Water temp in his system was never lower than 160 degrees, so the mixing valves had no effect when set to 110 degrees. The goal is to have a supply temp just high enough to provide proper heating of the space (140ish), a return temp low enough so that the mixing valves have cooler water to mix with the supply (120ish), and a mixed supply temp at the manifold to provide a slow even heat to the loops (130ish).
I wanted Hillstreet to try these changes first to get closer to a good running condition, I still think the boiler control settings should be changed to lower the output of the burner, but making these changes will familiarize him with how to operate the controller...Let's see how it goes today!

Well, I just made the changes to the boiler controller. No problem at all, pretty easy to follow the menus, you get the knack quickly.

Central heat = 140, DHW = 170, outdoor sensor is DISABLED, and the mixing valves are set to approximately 140. (I say approximately because range is 70 to 180). Should the mixing valves be lower?

The house today is 80 with the sun and coal stove adjusted to minimum. The boiler I would expect will come on sometime Saturday night. I will watch it closely and let you know. I have to say thanks to everyone who chimed in, this has been a good learning experience for me. I know I could not put up with all of the run hours and cycles, it was really bugging me. I think we are getting to the bottom of it now.

 

[dadster4]

Try the mixing valves at 130, you want them set lower than the supply temp. The real test is to see what return temp you get back to the boiler, less than 130 would be good- lower even better. Good Luck :thumbsup:

 

[teejk]

Try the mixing valves at 130, you want them set lower than the supply temp. The real test is to see what return temp you get back to the boiler, less than 130 would be good- lower even better. Good Luck :thumbsup:

Glad I don't have mixing valves! I do have a few manifolds (Rehau) though, all with their own supply/return temp gauges and flow control valves for each loop. The computer on the Weil McLain would say 160F supply for under-floor radiant. Return is up to me I think so it amounts to goofing with the manifolds to maintain what my installer says should be a 15F "T Delta" (his son says it should be 20F and I think that is probably closer to the truth with modern boilers but probably not a big deal either way).

 

[HillStreet]

Try the mixing valves at 130, you want them set lower than the supply temp. The real test is to see what return temp you get back to the boiler, less than 130 would be good- lower even better. Good Luck :thumbsup:

When the system starts up again I will read the mixing valve temps at the manifolds and adjust more accurately.

Now, assuming for the sake of argument that all loops are equal in length. I think that I have each manifold loop flowing at maximum rate. It is a Uponor manifold, and I have the adjusters screwed out to where the sight glass has the least amount of stem showing.

 

[Rustyiron]

FWIW, the design temp of my radiant system is 112*, tempered down from the boiler (mixing valve) with return water & then supplied to the manifold(s).

 

[Raspy]

"As I understand it, HillStreet said the delivery temp was controlled by the tempering valves at 110 degrees. That means they are mixing return water from the floor loops with hot boiler water to deliver a temp lower than the boiler setpoint." The mixing valves have 180 degree supply and 160 degree return to mix- there is no way 110 degree water is supplied to the loops.
"But we still don't know how the DHW system is tied in, so we can't necessarily just turn it down. If we can adjust the CH different than the DHW we can turn it down." The DHW is a separate loop off the primary supply loop with it's own circulator pump, the boiler will ramp up to 180 degrees to heat the DHW on a call for heat from the DHW aquastat, and when satisfied, will revert back to the supply temp chosen for the radiant heat.

We still don't know how the mixing valves are plumbed. So they could very well be delivering 110 to the system by recirculating the floor loop and only adding a little boiler water as needed. I've done this many times with a lower delivery temp than the boiler high limit or boiler return temp. We don't have the schematic so we can't say for sure what is going on.

We also don't know the DHW storage or HX plan, so again, can't really come to any solid conclusions. There is more than one way to do this. You're right on your explanation about the boiler in a general sense, but I wasn't wondering about how the boiler works. I'm wondering how the storage works to determine if the boiler should be programmed in a normal DHW/CW heating mode with priority or if we can make it better. There are a number of ways to manage DHW.

It's better to have experience and be curious, than it is to be absolute with limited knowledge or argue about something we don't know.

 

[sailfast]

dadster4,

I will certainly reference the manual. I'm retired and it's winter, what the heck, need something to do. I will keep excellent notes so I'll not get lost.

The supply and return pipes are connected at the end where supply turns into return. There is a quick turn valve in the end, set at about 1/2 open. The supply loop and return loop tees off to the mixing valve, then the mix goes to the circulator, that goes to the manifold.

I will lower the heating setting in the boiler to 150 degrees, and I will set the mixing valve to 140 degrees. The "controller" you refer to I assume is integrated into the boiler. I have a Taco 4 position electrical box where the t-stats, outdoor sensor, DHW sensor, and circulators all connect but that is just electrical connections. I will read the boiler manual.

The regulator was checked by the propane company. One guy here several hours while the plumber adjusted the vent stacks (some harmonic imbalance that had to be corrected. Plumber did offer that it "was not my fault".

I do appreciate all the effort from you guys, it is a big help to me. I am able to comprehend these things but do need input from you folks. I really don't know what the run time should be but know if it runs 80% of the hours when the sun is down it is way too much.

Seems to me you are in way over your head. I recommend that you contact a local HVAC professional experienced and licensed in radiant heat. Otherwise you will likely never get this truly done right. That is what I would do.

 

[sailfast]

Thank you Raspy. I am going to read the manual for resetting these parameters. I guess I will make the changes while the coal stove is running so in case I screw it up I will have