Thanks and TT Prestige Solo 110 questions

masterofnone

First of all, thank you all for taking the time to share your heating knowledge here with the average homeowner. With the knowledge you have been willing to share at heatinghelp, I have been working on a radiant system installed correctly and safely in my central NY home. Dan's Practical Guide and Siegenthaler's Modern Hydronic book (from my sons last Christmas) were helpful. It's taken about two years as funds allowed, and the Prestige 110 has been making our home comfortable (wife's feet are happy) since I fired it up last week, with no major glitches. The system utilizes a Taco SR504 relay, Honeywell T8775A1009 tstats, currently three zones with UPS 15-58 circulators feeding pex manifolds supplying subfloor with extruded plates and FBF. Boiler piped P/S and I plan on installing a domestic tank in the Spring. Outdoor reset not hooked up yet... keeping it simple at this point. Combustion analysis to be completed by a local heating contractor after the New Year. They are overwhelmed with installing systems prior to the energy tax expiration.

I do have a few questions for any that can offer their recommendations:



The TT install manual recommends additional high limit protection, especially with the addition of the domestic tank. What particular model of high limit would be easiest to install for this application?

On the subject of high temp limits: the boiler set point is currently set at 120*, but the burner doesn't shut down until the boiler gauge reaches about 128*; return temp is usually about 122* at burner shutdown. The burner re-fires at about 112* if a tstat is still calling for heat. Is this typical behavior for the Prestige?



The internal circulator was factory set at high-speed, but I changed it to medium with no obvious effect on system performance. Is the internal circulator speed requirement dictated by whether P/S piping is utilized? Primary loop is 1 inch. Previous threads here have mentioned needing 5 gpm minimum through the Prestige.



How critical is the heat cycle rate selection for the tstats for subfloor pex without setbacks? The dip switches are set for three cycles per hour currently.



Thank you in advance for help with these questions.

cattledog

Space Heating On-Off Differentials

Master--



I think that you are seeing the burner cycle on and off based on the space heating on/off differential settings (MCBA parameters 22 and 23 in an older version of the TT110 controller)



Not enough heat is being removed from the primary loop and the outlet water temperature continues to rise even though the boiler has dropped to minimum modulation. The controller is smart enough to shut the burner off at the off differential setting rather than cruising on up to the safety high limit. It comes back on when the temperature drops the on differential below the set point.



First, I would determine if the boiler is indeed dropping to minumum modulation which is about 30k btuh. You should be able to clock the gas meter once the boiler hits your outlet setpoint of 120. If it is, then you will have to figure out why the load loops are not delivering the btus fast enough to keep the boiler from cycling on the differential limits.



The TT110 at minimum fire could be be oversized for the zones, or there may be a zone circulation problem or heat transfer issue.

EricAune

Great suggestions

Cattledog has some good info, but maybe a little over your skill set with the meter clocking (maybe not).



You mention having staple-up with extruded plates.  120*F water is a very low temp, how did you arrive at this number?



I have experienced what I think might be your problem a couple of times and in most cases have had to adjust the differential temperature settings to get the Triangle to run longer. My assumption is your flooring may be rather thick/have a high R-value and transfer rate at that temp are lower than desired.



Try setting the post purge on the boiler to a longer period of time and widen the set-point temperature differential on the boiler.

masterofnone

Tweakin Prestige on a brutally cold day

Thanks for your suggestions.  Most of you are busy this time of year.  I'm fortunate to have a week off to tweak our new Prestige.

Temps with high winds (sometimes out of Canada) today, are placing a decent demand on the boiler.  One zone stat is not being met since I need to better insulate the north/west walls (summer remodel project).  Heat loss on our home is near 70K BTU/H but winter winds need to be taken into account.

I had dropped the setpoint to 120* after seeing the actual boiler supply gage reading closer to 130* before the burner shutdown,  Also leaning toward the conservative end initially with hardwood flooring throughout about half our 1955 ranch.  Floor is a radiant challenge with 3/4" oak over 3/4" subfloor. Best I can tell at this point the floors surface is not approaching 85* so I stepped up the setpoint to around 140* but saw less condensing,  Dropped setpoint to 128* where it's set currently.  Until I finish my pvc/ marble neutralizer tube, a bucket is collecting about 3 or 4 gaI/day of condensate.  The gas meter took 141 seconds to use 1 cu. ft after reaching supply setpoint.  If my math is correct that would definitely be at minimum modulation. Began monitoring return temp (rather than supply temp) and when return gets to 128* or 130* the burner shuts down.  Seems correct for a 128* setpoint. This Prestige must have the newer MCBA controls since the parameters are different than you mention, Cattledog. To make post purge cycle longer (as suggested) I changed parameter 32 "CH Circ. Post Pump Time Period"  from factory setting of 1 minute up in 1 minute increments. I'm not sure it made any impact. Should that extend the time the display shows 6XXX "burner off"? The time frame that the display shows 1XXX "fan prepurge/post purge cycle" is not very long, perhaps 30 seconds, and hasn't changed much with any parameter adjustments.  I assume that to widen CH setpoint differentials I lower parameter 10 "CH Boiler Minimum Setpoint"  to below the factory 86* setting.  My manual shows parameters 38 and 39 effecting DHW on/off differential but no parameters for CH on/off differential. No matter how low I set Parameter 10 for "Minimum Boiler Setpoint" I don't believe I'm seeing any changes in system behavior,  With setpoint at 128* the boiler refires at about 120* but with our frigid temps outside the boiler is running much longer between cycles. At optimum performance, at what approximate temp should the boiler refire given these settings and conditions?  I switched the circulators to high speed on the two zones being called upon much of the day.  Not sure if that would be suggested. The pex manifolds with flowmeters (fully open)  are seeing about a 6 degree delta T. 1/2" pex (two runs per bay) with average loop length at 250'.  I'll be adding more pex/or other emitters if the added insulation doesn't help enough next winter.

The transition from primary to secondary piping takes place just under the boiler with tees perhaps 5" apart.  If the secondary loop began farther away from the boiler or if the tees were further spaced (under 12") would that allow the secondary loops to better draw from the primary loop?  Perhaps dropping the internal circulator to low speed would help but I don't want to threaten the boiler flow.

Thanks again for your time.

cattledog

delivering btu's

Master, here are some new thoughts following your update.



There's good news in your gas usage measurement data in that you now know the boiler is operating properly and moving to minimum fire.



Unfortunately, you're now running a nice modulating/condensing boiler in an on/off mode at minimum fire around the setpoint. At 70Kbtu/h design heat loss, you may have trouble keeping warm. I think you will be seeing higher gas use with the cycling, and reducing the cycling on the boiler for a more steady operation is always easier on the equipment.



I think that you now want to work to minimize and eliminate the time that the control is displaying 6XXX, which is the condition with a call for heat, the burner off after hitting the high differential, the pump running, and the control waiting for the water temperature to drop to the low differential.



The changes you have made to the parameters so far are not really going to address the problem. The extended pump cycle (parameter 32) is more for extracting stranded heat after the burner shuts down with a satisfied call for heat. Your primary pump is already running during the 6XXX period. The boiler minimum setpoint (parameter 10) is only effective with outdoor reset and is not the hysteresis parameter.



I think that Eric was pointing you in the right direction with suggesting a higher operating temperature for the flooring you have. While you see less condensing at 140, and it's disappointing to loose some of the efficiency available with the Prestige, higher water temperatures may be what it takes to bring the rooms to temperature and optimize boiler cycling given your flooring.



I think that keeping the boiler running longer by widening the set point temperature differential (through raising the off differential temperature) is similar to raising the setpoint temperature in that you are getting continued operation at a higher output temperature.



To get your system operating and house warm at lower water temperatures is heading down a different road.



Some additional data which would help you analyse the system is to determine the flow rates in the secondary loops which is associated with the 6F delta T, and the delta T in the loops for different water temperatures.



You may want to post some photos of your system which would help determine if there is a piping problem rather than a floor which is a "radiant challenge".

masterofnone

Pics and comments

Thanks again for the follow up post. Temps outside today are near a balmy 20* with less wind and the Prestige is cycling more often. Only the zone needing more wall insulation and possibly more emitters is calling for heat once in a while. Yesterday most of the stats were often calling for heat and the Prestige was cycling much less often. Overall we were getting enough BTU"s throughout the house to make our home comfortable. As you stated though, there must be room for improvement by either elevating the set point, as Eric suggested, or fixing a glitch in my piping. I'd like to know the boiler and components are working effectively and will last several years. You'll see that under the boiler I deviated from the most common method of transition from the domestic return into the zones return. It seemed like a simpler way to pipe it with the returns to the left and supply to the right. Perhaps this was not a good idea and I can rearrange it. Don't beat me up too bad. As mentioned before, the tees into the secondary are quite close. The primary circulator is still on medium speed. The piping is 1" and 3/4" into and from each zone. The manifold flowmeters will change from about 3/4 gpm to 1 gpm when the circulators are on high. Delta T at the manifolds actually varies (5*-15*) depending on whether other zones are calling. The two manifolds with two loops each are out of sight about 20 feet away. I will add more insulation below the FBF and insulate the copper runs some as funds permit. I left an average gap of about 3" below the 1/2" pex. in extruded Watt's 4' plates covering about 80% of each bay.

Fortunately our old Dunkirk CI boiler is ready as a back up to permit work on the new system. I may flush the old baseboard system this summer and integrate part of it into the new system. That's one reason I installed the wye strainer before the Prestige and began the supply and return for another zone. Our basement is solely heated by a large floor standing cast iron unit with the baseboard system. Fortunately our basement is mostly below grade.

cattledog

more heat in than out

Master--



The basic configuration of the boiler loop and zone piping looks OK.



It looks likely that there are limitations to the heat transfer from the in-floor loops. If I understand your system, there are 7 pex loops in total coming from 3 manifolds. To generalize from the flow and temperature data you provided, if each loop is running 1 gpm and the delta T is 10F then you have a total 35Kbtu/h delivered. This seems consistent with the situation where the boiler at minimum fire is providing more btus than are drawn away, and the boiler is cycling off the setpoint differentials.



You have varied both the boiler and zone pump speeds and it does not look like the situation will be resolved there since it is likely that on both the boiler and floor side the total heat transfer is not highly dependent upon flow rate. The delta t varies with the flow, but not the product of delta t and flow.



I think it best to take additional data at different outlet setpoints and characterize the delta t in the manifolds, the boiler cycling behavior (6xxx time and actual firing run time), and your gas usage. Then you can make some decisions about the most efficient and equipment friendly operating temperature, and decide if you need to add radiation/emitters.

masterofnone

room to add emitters

Thanks for looking at this. I failed to mention that our kitchen currently has no radiant installed. It's a rather small area with about a thousand nails protruding underneath ;-( Avoiding radiant under cabinets, fridge, but still room to add load to the Prestige. More load will be added on the west side of our home this coming year too... and then the full basement heat needs to be addressed. This should create opportunity to better utilize the Prestige output. I felt the next smaller Prestige would have been too small and wanted to stick with the TT given it's great reputation/ exchanger design. Also, wanted to get the boiler running before the tax credit expiration. It seems best to wait until more emitters are added before adding outdoor reset. As stated before, an indirect tank will be added this Spring also.

I'm still wondering whether most here recommend additional high limit protection for the Prestige. The manual recommends it. I'm guessing that with pex it's more of a concern?

Any suggestions on additional high temp protection would be appreciated.