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Piping a Wallhung Modcom for concrete radiant. (24 Posts)
Piping a Wallhung Modcom for concrete radiant.OK, here’s what I have, I built this house in 95’when in-floor heat was all the rage in this area (Colorado Mountains). The system was thrown together with the basic conventional wisdom of so and so has this set up on his house and it works like a champ…. I know that’s bad. This setup has actually worked fairly well for 19 years but probably not very efficient. The dwelling is 3765sf total including 765sf attached garage. 2 story, slab on grade 1765sf (1000sf living, 765sf attached garage) lower walkout with IFC foundation walls, 2” rigid foam under 4” slab, 2 zones , 1 living, 7 loops@200Ft, 1 garage,5 loops@200ft and a 150 loop in the entryway manually controlled. All tubing ½” wirsbo on 8”IC. The upper main level, 2000sf, 2 zones, main living area,1000 sf, 7 loops@200ft 8”OC and Master Suite 1000sf, 5 loops@200ft wider OC than main living, all tubing on the upper level is in 1.5” lightweight concrete. The house has Corbond sprayed insulation giving it R20+walls and R50+ ceilings. I have completed many heat loss calculations using various programs and keep coming with around 108mbtu requirement using -20 for ODT. The current boiler is a Larrs Mini -therm II, running NG, rated at 186k btu/h (161.7k net I=B=R),(before altitude de-rating, 6700ft). That would make it way oversized than required which appears to happen a lot from what I can tell. 1 circulator (Grundfos 26-79F) I think that’s way too much pump) and 5 Honeywell zone valves (including DHW), There is a 80 Gal Amtrol WH-10 indirect water heater. I run programmable stats that basically fire the boiler from 1.5 to 2.5 hours in the early AM and the concrete and house stays warm without the boiler firing again until the next AM for say all but maybe 30 to 40 days in the winter or a DHW call. Piping was set up with a single circuit with a bypass per the Larrs IO manual. I experimented with the bypass early on and it seemed to get the best results with the bypass about ½ open. No matter where I adjusted the bypass I always ended up with a boiler DT of 11 degrees f no matter if 161 out and 150 in or 131 out and 120 back. It has been running 131 out and 120 in since installed. The Larrs ended up in bad spot the garage in order to provide for the vent which goes straight up through a upstairs closet and out the roof, I am recovering that space by going direct vent out the back wall with the wall hung modcon. I looked at the TT and there seems to be quite a few out there and the Lochinvar which seems to have more robust controls, liked them both. The Local supply house loves the NTI firetubes and claims they have the least amount of trouble with them(I’m sure their margins have nothing to do with their opinion) and doing a guts to guts comparison there was not a lot of stand out differences . I determined that a NTI TFT110 would be good even though my calculations indicate I could need as much as 108BTU, this TFT110 nets out at 99 (86 IBR). The NIT IO manual advises to De rate 12% at my elevation. The next size up puts me way over what’s needed and from what I can tell by reading on this site, I would be better off on the small side than the big side for efficiency’s sake. I felt that none of the heat loss calculators I used took into full account of my insulation Corbond + Fiberglass batt so the calculated 108mbtu requirement I think is on the high side . We have 300+ days of sunshine per year and I get good passive solar and have a Gas fireplace for the rare 1 time every 5 years it gets -20 a couple of days in a row. This house has always been warm due to the flywheel effect of the heated concrete, we have to open a door a lot even in the winter. I am convinced that I will be better off to stabilize the slab and house temps with a modcon maintaining 68 to 70 instead of bombing the heat and letting it cool off.
Here is the question, since I have already Hung and vented this NTI TFT110 on the back wall, the boiler is 10 pipe feet (7 ft horizontal and 3 ft up away from my manifolds and zone valves, I’m thinking I can create a primary loop from the new boiler to the existing piping and pump it with UPS 15-58, leave the zone valves where they are and pump the secondary with an Alpha 15-55 which in theory would increase flow if multiple zones call. I would run all the heating calls on low temp (130 max) and use another 15-58 pump for DHW at higher temp for my 80 Gal Amtrol and set it as priory. I anticipate there will be a need to tune the controls and maybe the piping, I’m just trying to assemble a starting set up. I have been keeping in mind Chris’s Universal hydronic formula of GPM=btu/hr / (delta T x 500) but I’m completely sure how to apply it to my situation.
I was an auto technician by trade, similar to HVAC, i.e we have to know mechanical, electrical and plumbing in our work. I built this house in 1995 and been remodeling and upgrading ever since. I considered letting a HVAC pro do this upgrade, but after getting a few quotes and listening to the wide range of opinions as to what boiler to use and how to set it up I could not find anybody that I was comfortable with. I am semi retired and have the time to mess with this and really enjoy the challenge. The professionals that contribute here are really appreciated and thank you in advance for any input.
You're headed in the right directionWithout getting into the details of the heat loss, it appears that you installed enough tubing in the right places (which is pretty much the one thing you really can't change.)
Sounds like you have a snowmelt loop in the driveway -- did I reed that correctly? If so, that loop should have glycol and a heat exchanger along with some extra controls.
Can you post some photos of the boiler and manifolds, along with a drawing if you have one? If I'm understanding your layout correctly, you may not even need a primary loop given the low restriction of a fire-tube HX.
Nice...Looks like you are off to a great start.
Your existing boiler is approx 80% efficient and because it is atmospheric should be derated 4% per 1000 above sea level. 186 x. 80 x .73 = 108.6k/btu output.
The new boiler is about 90% efficient and only derates 2% per thousand. 110 x .9 x .865 = 85.6k/btu. Unless your old boiler ran 24/7, I think you "dun good"
The tubing spacing and lengths are great. The slab and building insulation are also great.
The recommended drawings in manual seem like a perfect fit for your house.
Alpha pumps work really well in radiant systems. Without checking the math, it looks like a fit. You would not need the bipass with the alpha.
15-58 for the other circs will work well.
You will want to use the outdoor reset feature in order to reduce overshoot and increase efficiency. I think you will be blown away at how low you can turn down the water temps.
If the amtrol is original, I would toss it sooner than later. The heat exchangers in those units are not very robust and they have a habit of springing leaks.
Does your garage have a drain for condensate?
Do you pics of the existing manifold?
The tubing is Hepex not aquapex? Folks had trouble with that for a while.
CarlThis post was edited by an admin on March 18, 2014 5:32 PM.
SWEII do have additional loops in the driveway zone over and above what is stated above. I do not intent to heat the drive and was never able to get it to work very well with the Larrs. I have story's of people up here having to deal with what happened to the melted snow after it ran off their property and on the to neighbors and caused an iceberg. We average about 300" of snow here a years. I have determined the best way to take care of that is with a Skid steer kept in the heated garage! I intend to abandon the driveway system for now. The whole system has Cryo-Tek 100 glycol in it. I will leave it the driveway tubes and remove it from the rest of the system. I will post some pics in a little while, Thanks for the response
Abandoning the snowmelt loopsAre the snowmelt loops on a separate manifold? If so, I would consider separating them from the space heating system and (after checking the glycol pH as Carl suggested) leaving them isolated. Then refill the house system with straight water plus an inhibitor. If not now, then perhaps when the glycol does need changing.
Pics of current setupI have 13" ceilings in my garage to accommodate my automotive lift. The Amtrol tank was just to the right of the zone valves, I built this deck and moved it up where it is now, the piping to it now is temporary to the old boiler. when I disconnected it was very clean inside, once its up to 120F it will sit and hold it for a long time. My tubing is Wirsbo-hePex. the water in the system is still running clear (red with the Glycol)
Good stuffI would check the PH of the glycol before connecting the boiler. The newer indirects are going to have higher flow rates. I would run 1" for the future.
Proposed pipe set upI am thinking of sticking with the drawing on page 46 of the I/O manual attached below. except would I would come out the bottom of the boiler add a Temp & pressure gauge, Isolation valve, and union, go straight down through my deck across under the stairs, I am assuming the Expan. tank, air scoop, bleeder & fill need to be in the secondary, true or false? How close should pump B be to the boiler inlet?
PipingThat drawing will work well.
Be sure that the closely spaced tee are just as drawn in a straight piece of pipe.
There is no hard fast rule about the expansion tank and air separator location.
That boiler will do a nice job of purging any air that runs though it. I has a design that slows the water that passes though. It also has an air vent on top.
I would put the a micro bubble separator on the secondary as drawn. It is important that the circulators are "pumping away" from the expansion tank. In the drawing all of them are. I like that the expansion tank is closest to the circulator that is doing the most work and generating the greatest pressure differential.
The exact location of pump B is not critical. It is better to have a straight pipe on the intake side.
CarlThis post was edited by an admin on March 18, 2014 11:02 PM.
VentingThat dip in the vent where it passes under a beam is problematic. Condensate will pool in it and (partially) block the vent. If the dark (insulated?) pipe going down from the dip is a condensate drain, it needs to be trapped or combustion gases could escape that way. Either way, the manual probably has language in it about exhaust pitch etc. that this would not conform to.
Can you mount the boiler a couple of inches lower, so the exhaust clears the beam without dipping?This post was edited by an admin on March 25, 2014 7:57 AM.
Optical Illusion?Hi Gordan -
I think it is an optical illusion that makes it look like there is a dip in that section.
Ah...Yeah, I can see how it could be. I was wondering about that since it looked like it should have cleared anyway. Thanks, Mark!
Thanks for lookingI made sure that there is the minimum of 1/4" per foot of slope back to the boiler, including the elbows. the picture was taken from the floor, the ceiling is 13' high. I thank everybody for their input, I will update as the project progresses,
UpdateUpdate: it is been up and running since 4/7. All instructions in the IO manual were followed. A permit was pulled, so it is going to be inspected so if there are any obvious problems hopefully someone will point them out. We have had a few nights of 10f and it is seems to be operating properly and keeping the home comfortable. The firing rate for this NTI 110 model is 1625 to 7000. Upon a call for CH it fire up to 7000 with the at the boiler maxing out around 16Dt, as it runs, the will come down to around 10Dt on the primary and the boiler will modulate down to 3000 to 4000 with 1 of 4 zones calling. As additional zones call it will crank back up to 7000. The gauges I placed in the secondary indicate a ranging from 23Dt at first fire down about to 15Dt as the loops warm up. The CH setpoint I'm using for high mass in concrete is 135f
DHW: Zman’s observation that the heat exchangers are not very robust is verified as true. On a DHW call, max at the boiler is about 13®and quickly narrows to around 5® forcing the boiler to modulate down to around 2500. I have the aquastat set to 115 and when calls for DHW it only runs for about 15 minutes. (set point 150f) Temps taken directly at the Amtrol inlet& outlet indicate a 16Dt . The up side of this is with 80 gallons of 115f water it can handle everything this dwelling can throw at it with 3 adults using 2 kitchens, 3 baths & 2 laundry’s. Since it is stainless, it can’t rust and start leaking (can it?), it must have been assembled other than on a Friday afternoon. It will hold temp very well as it doesn’t seem to call unless there is usage demand. I installed a recirculation loop (at great pain) controlled by a motion sensor and timer (Insteon ® home automation stuff) that is working like a champ. I will plan on replacing the indirect as soon knock off a few other things on the to do list.
So, the question at this point is: Do these operating temps seem normal? Does anybody see anything that is going to cause the Pro I get to come over and verify combustion numbers be to freak out? Any suggestions for improvement? Thanks again for taking a look and any input.
Nice workI do see one big issue.The T&P valve must be installed on the boiler per manufactures instructions. The boiler could explode if someone closes the isolation valves with the T&P installed there.
I assume the exterior vent terminations are per manufacture spec?
Double check the instructions on the vent pipe support at the boiler. I know this has been a hot topic with inspectors since the Lofgren accident. The vent can sometimes blow off the top of the boiler if the boiler is having ignition issues.
Your delta t numbers seem normal enough.
You mention a setpoint temp of 135. It is unlikely you need temps that high. Your high mass system will probably run best with a design day water temp in the 110 to 120 range.On a warmer day 80 degrees would work. Have you set up the outdoor reset? High mass systems have a tendency to overshoot and undershoot your target room temps. Outdoor reset and low temps will make for a more comfortable home.
Also the lower the return water temps, the more efficient the boiler .
Overall a nice install. The T&P issue will make the inspector and the Pro "freak out"
Zman, I see that nowI got fooled by the fig 10-1(a) where it shows it mounted underneath, I see now that the valve is inside of the isolation valves. I will move up top. Question: can I tee together T&P for the indirect then run then down?.
Also fig 4-5(a) regarding exterior termination, why would the horizontal be 4-12" or greater than 36", does that mean it could not be, say 20" ? mine looks exactly like fig 4-5(a) with my horizontal right at 36" (see attached PDF of pages 20 & 38 of manual)
also, I will move my set point down and see what happens, thanks again for your help. Kirk
P.S. I am using the outdoor resetand it seems that the warmer it is outside, the lower the firing rate, I think that might be as designed.
Gas CockI can't tell from the photos but the gas cock should be within reach of the appliance. You should come out of the top of the boiler with a nipple, then to a union and then install the gas cock. You can then transition to the CSST. You may have to install bonding clamps on the CSST as well. Inspectors can get finicky about the bonding requirements nowadays. Personally, I would just pipe it in iron and be done with it. I only use flex connectors on movable appliances anymore.
Gas lineRobG, I was going to pipe it direct but the book recommends a flex line to eliminate strain on the boiler gas components(see attached PDF). I guess I'll find out if it is acceptable.......at inspection. Thanks for looking and commenting.
The t&p lines need to stay independent.
If they blowoff, there can be no restrictions.
The way I understand the directions 20" would not be OK. I have not seen that before. Perhaps they think the plum from the exhaust is asymmetrically shaped? Mod con boilers sucking in there own exhaust is a serious problem.
Is that a dryer vent or a fart fan?
As the boiler supply temp goes lower, the heat transfer rate at the floors will also decrease. It is normal for the modulation rate to lower as well.
OK, I will move the boiler T&P valveto the boiler outlet and pipe it down separate from the Amtrol.
Venting: That other vent is a dryer vent. Please take a look at attached pages, Pg 22, #7. how can the top elbow be in compliance if what I have is just like the picture in on page 20,fig 4-5(a) and page 25, fig 5-2, i.e "elbow no more that 1/2" away from the wall? Thanks Zman and everyone else for the help. Kirk
I think from a code/inspection point of view, you are in good shape.Some jurisdictions require a pressure test on the vent some do not .You make have cap and test the pipe. Not a big deal.
I think the 1/2" they refer to is from the wall to the hub of the 90. It is important to not have horizontal vent pipe out side the heating envelope as the condensate can freeze and build up in the pipe.What you have is unavoidable.
It looks like the air intake is about 36" from the dryer vent. I would be nervous about lint being sucked into the boiler. I don't think it is a code problem, It will plug up the boiler if it occurs.
Thanks ZmanI will make suggested corrections and report back after inspection. Regarding the intake possibility sucking dryer lint, I will check it out, we don't use the dryer very much, we usually hang our clothes on a line in the laundry room, for 3 reasons: provides humidity in the house, we have a very low average humidity in this climate, we like how the clothes come out, i.e. stiff without starch, (some of my wife's stuff get the dryer treatment) and we are cheapskates... maybe thrifty would be a better word ..Thanks again, Kirk