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Old 05-03-12, 04:09 PM   #221
Vlad
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Originally Posted by AC_Hacker View Post
Vlad,

I have read all of your radiant floor install report.

Thanks for the information, but I have more questions...

What kind of PEX did you use?
  • PEX-AL-PEX?
  • Oxygen Barrier (coated)?
  • Non-Barrier?
-AC
I used pex with oxybarier. If you look at parts list you can see cast iron pumps, so oxybarier a must be.

Quote:
Originally Posted by AC_Hacker View Post
Did you use any kind of silicone glue or silicone lube between the PEX & the aluminum spreaders?

Do you have any heat-up or cool-down noise?
-AC
No glue, no silicone. Omega shape heat plates is what helped to hold tubes in place. No noise on any stage. The only noise I have is noise from pumps. The main pump variable speed control make it hum more than others.

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Originally Posted by AC_Hacker View Post
You said that your house is three-story high...
  • Is it on slab?
  • Is there a basement?

...if it has basement, is the basement insulated?

How much insulation do you have in the walls of the house?

Are your windows
  • Single-glass?
  • Double-glass?
  • Triple-glass?

How much is your roof/attic insulated?
-AC
1.The house is 3 story building. There is a crawl space 2' high (I hate it GRRRR so low). It is not insulated yet but will be.

2. I have 6" walls with R-22 Roxul insulation

3. Windows are Double with argon and low e coating.

4. Roof has 2 layers or the same Roxul , so R 44

Quote:
Originally Posted by AC_Hacker View Post
  • Did you have any especially cold weather during the winter?
  • What was the temp at that time?
  • Did you measure the water temp coming out of the DWH at that time?
  • Did you measure the water temp returning to the DWH at that time?

Thanks,

-AC
This winter is just regular winter. Not too cold not too warm. We had couple of weeks when at night temperature went down to -8C -10C. During days temperature was cold as well(for our area not for Yukon ).

I didn't make measurements for DHW. I only noticed temperature in underfloor loop. It is easy to see because I have 2 thermometers right on manifold. As I mentioned before on coldest days loop temperature was about 95F in supply manifold.

My DHWT is separated from heating loop by HX. It is illegal to run DHW underfloor because in low underfloor loop you have a chance to grow bacteria (Legeionellosis). For this reason in Canada you have to keep your DHWT at minimum 140F.

Is it Safe To Turn Down Your Water Heater Temperature? : TreeHugger

This is why you can see mechanical mixing valve in parts list.

The HWT you can see on picture is an electric 80 gal HWT. I use it as a storage tank and it shares the same water with underfloor loop. I took one element out and used hole for extra water connection. I kept second element just for emergency but never connected power to it.
I use one of its thermostats to turn on/off SS pump(primary on DHW/HX side) and secondary pump from HX.

I had no idea how much BTU I needed. So I took some extra steps.

1. Raised temperature in DHWT
2. Added extra HWT (storage tank)
3. Kept one electric element in storage tank just in case main DHWT can't keep up.

But now I think I could skip the storage tank and take hot water to loop directly from HX.


Last edited by Vlad; 05-03-12 at 04:26 PM..
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Old 05-03-12, 05:21 PM   #222
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Here is the plumbing diagram and very basic electric diagram. If you have any questions ask them I will post more details.


Last edited by Vlad; 05-07-12 at 02:45 AM..
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Old 05-03-12, 06:01 PM   #223
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Is Webaware still following this thread? Wondering if he has any update on his install with steel decking.
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Old 05-15-12, 09:50 AM   #224
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Radiant floors: All but 3 rooms upstairs and the unfinished basement are done. Let me tell you, it's easy to get spoiled padding around in your bare feet when it's below 20F outside. I didn't realize how much so until I walked across an area that wasn't done yet-BRRR! Staple up can be retrofitted into existing floor by cutting access strips out of the subfloor-easier than removing drywall from below since we are installing tigerwood throughout the entire house including kitchens/bathrooms as each area is completed. After experiencing warm floors, I would never be without it. Realtor surveys of homeowners that have experienced warm floors show that nearly all of them felt it was the best feature of their house by far. By the way, don't listen to naysaying that wood can't be used where humidity is an issue-if it's engineered rather than solid and you use urethane gluedown installation, you are good to go-2 years going and still looking great. The only exception is the first few inches by your shower door-standing water that dribbled out the corners several times every day has caused discoloration. I will cut out wood & install an accent tile strip in it's place to solve this. Staple up works great with 1/2" pex and 12" or less spacing and heat transfer plates, useless without. It can be used with setback strategies and is more responsive during shoulder seasons where a slab type wouldn't put out enough at night but too much during the day. Much easier than structural reinforcement and slab over frame!
MMT (AKA: Mobile Master Tech),

I don't know if you saw what Vlad did on his radiant floors, but I thought you might find it interesting.

There are so many aspects at play in a successful radiant floor, what with balancing heat loss with heat output, that I thought it would be useful to talk about a few of them...

Heating Degree Days...

I went to a Degree Days calculator and calculated what the average heating degree days value would be, assuming that your indoor design temp was 68F, and I got this from the calculator:

Quote:
Description:,"Fahrenheit-based 5-year-average (2007 to 2011) heating degree days for a base temperature of 68F"
Source:,"www.degreedays.net (using temperature data from www.wunderground.com)"
Accuracy:,"Estimates were made to account for missing data: the ""% Estimated"" column shows how much each figure was affected (0% is best, 100% is worst)"
Station:,"ATLANTA DE KALB-PEACHTREE, GA, US (84.30W,33.88N)"
Station ID:,"KPDK"

,HDD,% Estimated
Jan,846,0.1
Feb,661,0.09
Mar,460,0.1
Apr,246,0.2
May,82,0.1
Jun,5,0.2
Jul,3,0.1
Aug,1,0.1
Sep,36,1
Oct,260,0.06
Nov,502,0.1
Dec,731,0.1
Total,3833,0.2
The last line is the one I was looking for, Total = 3833

This would imply that your heating task might be pretty straightforward, especially compared to someone with the very same house who might live in Caribou, ME for instance, where the HDD value would be Total = 9744. So, for someone living in Caribou, 12" PEX spaced staple-up, even with plates might be an up-hill battle.

It would be useful also to know what your house insulation situation is, too. For instance if you have gone to any unusual effort to insure good insulation. Also, what is the situation regarding your windows, both regarding their R-value (single-glass? double-glass?, etc) and also if any thought was given to winter-time solar gain?

Also, since I happen to be a hydronic plate believer, I was wondering abou the details of the plates you chose to use in your plate-enhanced staple-up floors? Were they stamped plated? extruded plated?

I'd also be very interested to know what were the water temps going to the floors and returning from the floors on a typical heating day? I realize that many people wouldn't even think to record this kind of data, but it can be very useful if you did.


You mentioned this:

Quote:
Originally Posted by Mobile Master Tech View Post
Staple up can be retrofitted into existing floor by cutting access strips out of the subfloor-easier than removing drywall from below...
I'm afraid I don't completely understand your method here... could you share some more detail here?

Thanks MMT, this kind of information is very useful to others (such as myself) who are about to embark on a radiant floor.

Best,

-AC_Hacker
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Old 05-16-12, 06:21 PM   #225
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Here goes the first installment of the "RADIANT FLOOR HEATING MANIFESTO"

Our heating degree days are probably a smidge higher-I am actually in Dacula, 30 miles away from Atlanta's heat island, so our lows are usually 2-5F cooler than there. I read some reports from a radiant contractor in Alaska who routinely uses 8-9" spacing with 1/2" pex, both in-slab and staple up. He says it keeps up with the load fine. I can tell you that I originally tried staple up without plates downstairs to save $-it couldn't keep up with a 32F night!! Adding u-groove transfer plates made all the difference in the world, plus they saved the cost of pex-specific staples, since the plates and the joist holes the pex passes through hold up the pex fine. Extruded or Omega plates work better, but I found a great ebay vendor for u-channel plates, Gehman Iron in Knoxville PA, whom I then purchased from directly. They offered 2' and 4' plates at less than $1/ft-the best prices, reasonable shipping and great service. You could also get extra heavy duty aluminum foil on ebay that is 0.0015” or 35 microns thick to do something like what Vlad did(or even make an HRV!) This is 2-4x thicker than standard foils. 24” by 500’ is $112 shipped from pactogo_inc.

I ran a small bead of 100% silicone caulk in the groove before stapling up, which fills the gap around the bottom half of the pex. Silicone is an excellent thermal conductor, so avoiding the tiny air gap makes a huge difference and negates most of the benefits of omega or extruded plates. My house footprint is 42' square minus a cutout for the garage, and the joist bays, which vary from 19.5-24" on-center run the whole length front to back for the first floor. I ran 2 pipes per bay and max 320ft per loop, so they are on 10-12" spacing. I left about 5" between the ends of each 2' plate for expansion, and there is max 6" between the plates. You can feel where the plates are due to the warmer temp but it isn't disconcerting-the cats love to sleep above the first few plates at the hottest end of each loop! I am also stapling up a reflective micro-perfed radiant barrier (again ebay!) just below the loops to direct the radiant heat upward-be sure the barrier doesn’t touch the pipes/plates or it will conduct heat away instead of reflecting it. This evens out the floor temp to where it isn't noticable where the plates are unless you were paying attention to it. Since only some of this is done, the first floor zones are doing double duty keeping the basement warm at 68-70F and the upstairs at a toasty 72-73F. When the basement is finished, the floor will be uninsulated, using the heat stored underneath in the off season (I'll start a new thread for that one) and I will have insulated walls with radiant loops in the bottom 2 feet of wall for any extra heat needed.

Since my system is open loop circulating potable water, I got Bell & Gossett bronze housing E3-6VBTPYZ pumps ($204 ea) manufactured by Laing from Wes at Ihrie Supply (Wilson NC, 252-291-7880). These adjustable speed electronically commutated pumps can flow up to 6 gpm max or 10 ft of head max (3gpm at 8 ft of head) while drawing only 20-27w! I also used E3-4V**** pumps for zones that had only one loop which can flow 1.5gpm at 5 ft of head using 11w! Both types have no seals to leak or cause drag. Since the impeller sits on a single spherical ceramic bearing and is aligned by its own magnetic field, they are jam-proof, as they will just wobble away from any debris that could ordinarily jam the pump (looking at pics on the web makes this easy to understand.) After studying power draw, maintenance issues and noise concerns (I read about some systems where the pumps took 800-1200w just to move the water around and were so noisy they kept the occupants awake), I decided these were the only way to go. They are nearly silent and not much more expensive than other bronze/stainless pumps for potable systems. For non-potable solar/geo circulators, Laing makes non-adjustable more powerful versions called E10 in a composite housing and various nipple/thread types/voltages. It can flow up to 6gpm against 20ft of head using 60w. At 20ft of head and 2gpm, they draw 50W. These are used for spa pumps and can be had for about $130ea on fleabay. Laing also makes 12v circulators of similar design for computers, so these could be used in a battery powered system.

Don’t listen to the naysayers telling tales of woe and safety risks of a potable open-loop system. Any so-called requirements to discourage Legionella or other problems in a radiant system would by definition also need to be applied to any DHW system since they are the same thing with different pipe lengths-when was the last time you heard a requirement to flush & sanitize your entire water heater and plumbing system every week? As long as the system is plumbed so all DHW gets pulled through the loops first to avoid stagnant water in the loops during the summer, an open system meets all national building codes. There are some great schematics for plumbing the system properly on the net. The system is simpler, and you will never have to worry about corrosion problems down the road.

My current heat source is an Eternal GU145S gas condensing hybrid water heater which I bought from Ihrie (by far the best price-$1700 shipped I think.) One of the best on the planet, it runs off a ¾” gas line, vents through 2” PVC, is 98% efficient at normal inlet water temps, and around 88% efficient when return temps are 110F. Incidentally, I will have it for sale once I have the solar/geothermal done, as I won't need any gas service once the kitchen is remodeled! I chose this heater because other tankless models weren't as efficient, had massive pressure drops due to convoluted heat exchangers, or did not have onboard hot water storage, which would cause no heat or "cold water sandwiches" during low flow or stop/start flow conditions. It comes with a built-in flowmeter as well. This unit has a max 145kbtu burner output. I have had all heating zones on, all hot fixtures on, then both together and this heater could keep up. The only disadvantage to this heater is when only 1-2 small zones are calling for heat, since the minimum burner output is 30kbtu. It cycles on for 15-30 seconds, then off again for 30-45 seconds. The manufacturer, Grand Hall, said this application is perfectly fine and won’t affect the efficiency much. They now make a smaller version, the GU100, that can throttle down to 14kbtu and run off a ½” gas line.

I am using a Bell & Gossett Z-6 controller ($208 from Ihrie) to take heating calls (and soon zoned AC calls by operating normally closed duct dampers-another thread!) by switching on 120v power for the pumps. It also exercises the pumps for 10 seconds every 3 days if not used in that amount of time to keep them limbered up. I hooked up my Kill-a-Watt for a whole heating season. The water heater, all circulators and the controller took less than $3/mo of electricity at my $0.06/kwh time of use rate. I used 805 therms of natural gas for the whole year including cooking/DHW. My peak month was Jan-150 therms, and the summer months were 7-15 therms.
I set the heater at 135-140F, steady state return temps are 105-110F while flowing 0.4-0.6gpm/loop. To maximize the heater's condensing efficiency with lower return temps, I have the pumps turned down so the system can just keep up at night. When I switch to geothermal/solar input, I expect to run at full speed with 130F supply and maybe 120F return. That will also even out the floor temps.

My main zone for the entire downstairs is 4 290-320ft loops, the master suite has 2 170-180ft loops, the others have the smaller pumps and one loop each. Doing it again I would have spent the extra $40 per pump to have the larger pump on all zones-when they all are on, the slightly lower head capacity of the smaller pumps means they flow a little less, as the bigger pumps flow proportionally more. It isn't much of an issue, though. I got Sioux 6 zone manifolds that included shutoff valves from Ebay and check valves and various fittings from pexsupply.com. I removed one of the small pex fittings & valves included on the manifolds and sweated on a 1/2NPT ball valves, check valve and fittings for my large downstairs zone which required more flow than the little valves could handle.

Construction & insulation: Builder stock R13 walls/floors, R30 attic, double pane aluminum frame windows with thermal bridging gap/standard air fill/ordinary glass. I am planning to replace these, as they and air leaks are the biggest thermal "holes" in the envelope. Since I am in a mixed climate, I am debating whether I should emphasize u-value or SHGC for my replacement windows, although some e-coated argon filled offerings now let a lot of heat in from solar gain while preventing a lot of heat loss out. We built the house new and were able to make a few improvements when the house went together, such as hot water pipes insulated in the walls, closing off a large chase that was left open to the attic, etc.

AC, you’ll love this “seal & insulate” story-The BR over the garage was the first retrofit staple up room we did. I was lazy and only ran 1 pipe per joist bay, looping each run back and forth between bays 16” on-center with only 26’ of transfer plate in the entire room. This room has ceiling, floor and 3 walls exposed to outside temps, so the floor running all night could not maintain temp. Since fiberglass batts usually aren’t best at conforming to irregularities, I squirted touch n’ foam through access holes in the power, cable & phone boxes on the exterior walls, making sure it sealed up the openings in the boxes and where the edge of the box meets the drywall. Now the floor keeps up even when it is 20F outside! After that lesson, the following easier method is what I would recommend:
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Old 05-16-12, 06:23 PM   #226
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To retrofit an existing floor with staple up, picture the joist bays you want to heat running left/right for their longest direction, in my case 14'. With a circular saw set for 1/8” deeper than your subfloor thickness, cut out 3 strips of subfloor a little over 1 foot wide and as deep as the room about 1 foot away from the left and right walls, plus one at the midpoint of the floor left to right. Now you have access to every joist bay at 3 points-moving from left to right, you have 1' of untouched floor, a 1' opening, 4.5' untouched floor, 1' opening, 4.5' untouched floor, 1' opening, then 1' untouched floor. If your joist bays are longer, add extra openings as needed, spaced so there is not more than 4’ between the deepest you can reach through the openings-the 4’ heat transfer plates will hold the pex to the underside of the subfloor you can’t reach.

Drill 2 holes though each joist via one access opening (let's say the left side). Drill the first ones about 8" away from the leftmost wall, then another set of holes 8" to the right of those. You can now run the supply leg of your pex through the leftmost holes to the far end of the room (presumably the outside wall of the room), then returning back to the near end of the room through the second set of holes. Make U-loops down each joist bay by pulling extra slack down each bay using the middle and rightmost access openings. Keep slack anywhere it loops so you don't kink it, as it's tough to heat and hold still when it's in a joist bay! If you do kink it in a bad place, you can just pull some extra through until it is in an easy place to heat it and remove the kink. Waste the extra you pulled through if needed-you can probably use a short length somewhere.

Once you have pulled all the u-loops through, lay strips of reflective radiant barrier on the bottom of the joist bay or on top of insulation already laying on the bottom of the joist bay. Also make sure your joist bays don’t extend into any areas you don’t want heated and that they are insulated/sealed wherever they terminate. The poly based barrier is much easier to work with than the aluminum woven kind. Have someone help you to guide a 4 ft transfer plate under the pex, lift up against the underside of the subfloor and staple up. You have to have a compact crown stapler that can fit in the joist bay-mine is a Bostich. You can angle the stapler a bit if needed. The plate supports the pex against the part of the subfloor you can't reach between the access openings. Start at the return end of the room and work backwards toward your starting point in case you have to pull some more from the spool or return some to it. Cut 4" sections of foam pipe insulation to place around the pex where it passes through joists to avoid noise as it expands/contracts. If your manifold is far away, you could put a splice in an easier to access place instead of pulling all the return run length through the floor. After pressure testing the loop, screw blocking chunks of 2x4 around the perimeter of your access holes(everywhere you can to avoid future squeaks), lay the removed sections of subfloor back in place, then screw them to the blocking chunks, preferably with a little construction adhesive, then top with your favorite flooring material.

Carpet gets gross underneath even with powerful cleaning, plus it insulates the floor pretty well limiting the amount of heat you can move. I recommend 3/8" to 1/2" thick engineered hardwood of some sort using urethane gluedown methods. We used 5/16" thick 5 ply with real tigerwood for the top veneer because we got a great deal, but you can see slight undulations where the subfloor edges were sanded down from the factory if you look closely. Still, we saved $8k for the whole house compared to anything that was 3/8" thick or better. This is a minor problem and worth the savings. The floor is stunningly beautiful and all our friends and customers ooh and aah everytime they see it! My realtor friend says I have the best looking floor she’s seen and says the warm floors are a “powerhouse” selling feature since extremely few houses have them-mine is the first she has personally encountered.

By the way, don't be afraid to heat pex to repair a kink. Heat it with a heat gun or rapidly moving torch until it starts to turn see-throughish. The kink will magically almost disappear as the molecules try to return to the position they were in when they went through crosslinking. Stabilize until cool enough to hold, and you are done. I was skeptical, so I took a short piece and kinked/twisted/pinched/hammered it WAY beyond anything that can happen accidentally. I then overheated each damaged area until it began to smoke, twisting and kinking it like crazy while hot. It springs back to it's original position like memory metal!!! After it cooled, I clamped tire valve stems in the ends, pressurized it to 120psi, then kinked/twisted/pinched/hammered it while it was under pressure until I was bored, then left it overnight. Even though the outer oxygen barrier layer was demolished, the pipe never gave way or leaked. This pipe will probably outlive all of us. The section you heat and repair will cool to a slightly larger diameter than the rest of the pipe-this is normal.

Blueridgecompany.com has the best pex and best prices I found. They offer many types, but the best is 1000' of USA made Pex-C for $280 shipped. I tried 4 brands of Pex-A, Pex-B and Pex-C from different vendors and theirs was noticably easier to pull and more flexible than the other kinds.
I will take pics and post when we finally do the remaining upstairs rooms, but it will probably be in the fall. We are relocating the manifolds and accoutrements since we made a change to our basement layout. When we do that, I’ll give some detailed pics of the rest of the system.

Craig
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Old 05-16-12, 07:38 PM   #227
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MMT,

Phenomenal report!

I wish everyone reported so much useful detail.

So was there any noise issue? Sounds like you did your best to prevent it.

Also, do you happen to know what the feed temperature range is to your hydronic system? The temp to the floor & the temp from the floor? The reason I ask is that I am in the process of designing my floor and I am going for the lowest possible feed temp... it would be good to know what I should expect.

Thanks again, what you have written will benefit many people.

Best,

-AC
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Old 05-16-12, 08:32 PM   #228
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Concerning Legionella, that is why I am designing for minimum 130F supply temp, preferably 135F. I plan on having a small electric instant water heater at the exit of my 30 meter 1" dia corrugated stainless steel heat exchanger pipe located in the top of my 2000 gal storage tank. The heater will make up the last few degrees just in case the geo/desuperheater/solar can't keep up, and I will put some thin silver rods in the storage tank since silver is bacteriostatic (bacteriocidic if the contact time is long enough). The silver is easy to wipe down should it ever become corroded to maintain efficacy.

130F is hot enough to kill Legionella bacteria. Any hotter, they die faster. That is the reason tank style water heaters can be a serious Legionella risk. If the top of the tank is 130-140F, the bottom of the tank will definitely be below 122F due to stratification-right in their favorite growing temperature sweet spot. The bacteria also need a still place to breed-sediments on the bottom of the tank provide a perfect breeding sponge maintaining that perfect temperature and sheltering the bacteria from being flushed out with the next water draw. Even a gas heater warmed from the bottom by the burner will often retain areas of lower temperature that won't kill off the colony. A tankless system that does not allow any water to stagnate at a warm temp never gives the bugs a foothold. The water is either starting out hot enough or turbulent enough to kill/prevent growth when the system is in use, and quickly cools below their sweet spot once shut off and no longer turbulent. That's why a properly designed "year round flow through" open loop system is important-water can't stick around long enough to get stagnant. How about the water sitting in the DHW plumbing leg that serves the back part of the house you seldom use? An open loop radiant system prevents the water from ever sitting around like that. EVERY time ANY hot water is used ANYWHERE in the house, fresh water is drawn through the radiant loops to replace the water that was used.

It's interesting that Canada requires the 140F water heater setting, but apparently prevents open loop systems that by nature are less risky than unused portions of the DHW system. Open loop systems are ok by our national building codes and most local codes.

I read some reports from the CDC that said improperly maintained chiller equipment is the largest source of legionella infections, followed by tank style water heaters. One of the next largest sources? Windshield washer fluid in vehicles! Since only northern climate washer fluid (the stuff that says "good to -20F") has enough methanol in it to kill the bugs, most people are driving with low or no methanol washer fluid. Add warm summer temperatures, a cozy engine compartment that retains heat, and a way to atomize the bacteria laden fluid (the washer nozzles) into a respirable mist, usually in front of the fresh air inlets at the base of the windshield, it's no surprise. Truckers have a 4x risk of legionella infection compared to the general public since they put on so many miles.

I always recommend putting a capful of chlorine bleach in your reservoir 1-2x per year to prevent this. I see lots of cars with washer nozzles and pumps plugged up with growth in the reservoir. I wonder how many have legionella? I always throw some bleach in there and give them some contact time before removing them to clean them out.

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Old 05-17-12, 11:29 AM   #229
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Any info on noise & temps?

-AC
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Old 05-17-12, 01:38 PM   #230
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The pumps are virtually silent-an average whisper would drown their noise out from a few feet away. I do have a couple of places in our master BR that creak as the pipes expand when coming on from dead cold, but that is almost non-existent except for the first heating call of the day after several hours of dormancy as that is the only time they cool completely off. I chalk these noises up to the way I routed the pex for this room. Since I have two loops in this zone, I had them crisscross back and forth so each loop had one pipe per joist bay. I made a big deal of trying to have the hottest pipes at the perimeter of the room instead of the simplest routing. Because of all the routing issues this caused, plus obstacle clearance,the pipes touch each other, touch obstacles and make lots of passes through joists. I did the simpler "one u-loop per joist bay forming 2 pipe runs per joist bay" on the rest of the system and have not had noises there. The keys to a reasonably quiet floor: not having lots of friction where the pex has to change direction or go over/around obstacles, some sort of isolation surface like foam pipe insulation or cloth at contact points, align the plates in a reasonably straight line, have at least 5" of exposed pex from the end of the previous plate to the start of the next one, and don't constrain the end of each U-loop.

When the water heater is set for 140F, water is roughly 137-138F by the time it hits the first transfer plate and 105-110F by the time it returns from the loop once temps stabilize. It takes a minute or two to make the loop and takes at least 15 min of run time before the return temps stabilize-I don't remember exactly how long. Unless it is super cold or the first heating call of the day, the tstat cycles the zone off shortly after the return temps come up. If I turn up the pumps to full speed, the return is a little over 120F. I imagine with a good building envelope, 9" or tighter spacing, well done transfer plates, 120F water and quick enough circulation so you only have a 10F temp drop across the loop, a staple up system would work well for all but the most extreme climates.

With GSHP and solar for heat sources, both of which lose a lot of efficiency with higher deltaT between source and load, I believe a stratified tank system like I described in the solar tank thread (I have to figure out how to give a link to a particular post) has particular benefit. If you have around 6' depth, you can get around 25F stratification from top to bottom. For GSHP with a counterflow condenser and waterflows balanced well, you could probably return 130-135F water to the tank while the condensing temp the compressor "sees" is closer to the 105-110F you are drawing into the condenser from the bottom of the tank. This way you won't have such a COP penalty on your heat source and the radiant system doesn't have to be a slab type or oversized to get the heat flux you need.

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