Radiant heat flow/temp balance

BeefSupreme

Hey everybody. New guy here with some radiant questions. I have installed a new radiant system in and 800sq ft 2 story addition I'm building.

Downstairs is 1/2 pex in slab, with 2 275 loops.
I have no issues with this right now.
Upstairs is 1/2 pex in radiant engineering 4" heat transfer plates. Look exactly the same as uponor joist trak and install the same way. Plates are installed under the floor and pex is installed into the C channel of the plates. 2 loops are 240 or slightly less. Total BTU required for the upstairs zone is 12011. Each floor has its own pump and I'm using uponor flow balancing manifolds. I'm almost to the question, I promise. The bedroom is one loop and the bathroom is on another loop. My issue is that I had to go 12" on center in the bedroom because of joist location. I was able to go 8" on center in most of the bathroom because the joists have more space. I knew the bedroom spacing little farther apart than I wanted and hoped I could use the manifold to balance the flow. The problem is I can only get that side to flow at about .4 GPM max. the other side I can get to flow at .9 GPM max. I'm running a temp of about 135. I used the joist trak table to figure that out. I'm concerned the .4 won't be enough flow on cold days. From what I've read my flow should be more in the range of .6-.7 GPM for that size loop. Any ideas on why it won't flow? I checked for kinks before drywall installation but that's all I can think about right now. Would it even flow .4GPM with a kink? Is it possible my manifold has a problem? Where do I go from here? Thanks in advance for any help.

Gordy

Hmm if both loops have near Same length they both should achieve same gpm regardless of spacing. If anything the higher flow loop which has tighter centers would have a wee bit more headloss.

Could be a kink, fouled flow meter etc.
Shut the bath loop off or near off, and see if bedroom loop gains flow rate. If it does not I would be looking at the above mentioned.

hot_rod

it is possible the construction debris or assembly crud like teflon tape, solder flux, solder balls etc could be caught up in the manifold indicator or adjuster.

It should be fairly easy to remove the flowmeter/ adjuster, and the opposite actuator stem and be sure they are clean and open.

Here is an example of how manifolds assemble.

BeefSupreme

Ok, so if I remove the actuator will I be opening the system? I'm not extremely comfortable with opening the system on my own. I had a hydronic guy install the header and manifolds for me while I helped him. I'm a carpenter by trade and I have some basic knowledge but when he was flushing/turning valves I was lost. I tried turning off individual loops and didnt see any change in the flow rate of the other loop. Changing the pump speed from low to medium and even to high made no difference. It's also slightly possible that I've got the loops confused. I had them labeled but the installer ripped the marking tape off of them before I could double check. I'm going on installation memory from May to remember what is what. The corners were quite tight in the bathroom, to the point that I had 2 kinks develop a few months after installation. I had to put 90's in there to avoid a kink after I covered it up with drywall. If they are opposite of what I think is it possible that there is enough head loss to cause the .4GPM max? If the bathroom is low it won't much matter to me. It has very little exterior wall and only one small window VS three large windows, a door and about 25' of exterior wall in the bedroom. Both rooms are insulated extremely well also. R27.4 walls and R60 attic. I also have R4 reflective foam and R19 fiberglass in between floors the help drive the heat upward. It's not too cold out today (25F) and the upper floor has been at 70F for 2 hrs now without the heat even running on either floor. Maybe it won't matter as much as I think. I just want to make sure I have no problems before I finish my drywall. Thanks for the help, sorry to bomb with so much information, I don't know for sure what info will and won't help.

Gordy

When tight centers are involved it's always wise to spoon the return ends on loops. The 90's you installed are restrictive. Also is it possible some more kinks may have happened after closing up the wall?

An infrared thermometer is always a good investment to help track down issues. Use it to check floor temps, and loop deltas.

BeefSupreme

Well, I understand some of that. Not sure what loop deltas are or what spooning a return end is. Any way to elaborate in a way I might understand? I knew the 90's would restrict, but there was no other way to fix things up. I was concerned that if I reinstalled the pex the same way that it would kink again after closing up. Space was extremely limited in that area so moving my plates was also not an option. I doubt that any more kinks could have formed. I just closed the ceiling up about 2 weeks ago. I didn't notice any kinks while I was insulating it. The tubing has been in since May. The 90's were put in a few months ago after the kinks were noticed. Any opinions on whether my 135 degree at .4GPM might be adequate?

Jamie Hall

Delta T is the difference in temperature between the inlet to the loop and the outlet. You can measure it with an IR thermometer -- use a wrap of electrical tape on the pipes to get a more accurate reading.

The basic hydronic formula is BTU output equals flow in gpm times delta T in Fahrenheit times 500. So -- if you need 12000 BTU, then your flow times delta T has to be equal to 24 (12000 divided by 500).

Gordy

Spooning.

BeefSupreme

Thanks for the explanations. Things are making some sense now. I actually did unknowingly spoon the ends. I pushed them closer to the outside walls before I secured the pex in the C joint to try and get heat close to the bond. The space that got 90's just had no more room to spoon. Probably should have left the plate a little shorter. The bedroom was ran with just 1 plate in between each 12" OC joist so those ends just looped to the next joist bay. Don't think there is any way they could have kinked with that installation method. More and more I'm wondering if my labels are crossed in my head. Would it be a good idea to run the GPM up on the other side to see if it gets better or worse? Is there another way to figure out what loop is what?

I have thermometers on each supply/return on each loop. I'll run the heat a little bit and see what I get for delta T. By my quick estimation there is about 4000 BTU/hr coming from the bedroom. 161 sq feet. Seems a little low for cold nights.

Thanks for the help so far. I'll try to play with it a little bit see what I can get for numbers, and pinpoint the loops.

Jamie Hall

BeefSupreme said:

...quick estimation there is about 4000 BTU/hr coming from the bedroom. 161 sq feet. Seems a little low for cold nights.



Thanks for the help so far. I'll try to play with it a little bit see what I can get for numbers, and pinpoint the loops.

25 BTUh per square foot isn't particularly low for radiant...

Gordy

The most you could get would be 30-35 to limit floor temps for comfort. 25 btus sf is pretty loose construction. Did you really seal up the rim joist area when insulating?

BeefSupreme

Maybe I'm closer to the right range than I think. I'm just mainly concerned because one loop maxes out at .9 and the other at .4 maybe I'm worried over nothing. The delta T was at 30 when the system was warming this morning, and was at 21-22 after the system ran for about an hour. The heat doesn't run too often so it took a while to warm everything back up. With the rooms warm and up to room temperature the 2 rooms did feel pretty much like the same temp.


I sealed up everything well. The loops are just ran up to the exterior wall bond. The bond has R60 fiberglass (11" wall) an 1/2" piece of reflective TUFF-R. I know there are radiant barrier debates, but I figured it couldn't hurt. Ran both floors up to 70F this morning by 10AM, it's now 8PM and it's 69F on each floor. Heat hasn't ran since 10AM. Average temp today was about 32, pretty warm in northern Michigan this time of year. Just want to make sure the system has the BTU to keep up when the -20 nights come. Am I concerned over nothing? I don't have the radiant experience to really know.

A few guys brought up infrared thermometers to check stuff out . We talking the point and shoot kind of like a FLIR camera? If I want to be obsessive and check stuff out how do I check with infrared equipment? What do I do/look for?

Gordy

When you say delta t was it the same for each loop, or different.

Radiant floors shoot for a 10 delta so the floor temp is more even from start to finish of a loop. This would be steady state no setbacks. Radiant works best with out setbacks.

Rich_49

How many total feet is bathroom loop and how many is bedroom loop ? What are their positions on the manifold and what other loops are on that manifold ? Can you post a picture of the manifold ?

What is the design heat loss of each room in question ?

BeefSupreme

I can't find my infrared thermometer, so I only checked the delta T on the entire manifold. Probably should find it so that I can check them individually. I don't plan to run a set back, it was just way too hot for working in after I warmed it up to check the delta T. Thermostat stays at 65 for now during construction. New question, the lower floor slab temp is set at 107F right now. Since the first floor is so well insulated (R42 ICF) should I run a lower temp to keep it from overshooting? How low is too low? Or is it just trial and error for each floor/house?

Rich_49

What do you mean , " the lower floor slab temp is set at 107F right now." ?

Is there a slab sensor , any slab sensors ? Did someone design this for you or is it a DIY ?

Gordy

So slab concrete has a fly wheel effect. You need a slab sensor as Rich mentioned. Is this entire system run off the outdoor reset?

You have an an ICF home. Very well insulated. You need controls on the system to deal with this otherwise overshoot will be a consistent problem.

Rich_49

@Gordy

Sorry Gordy , not what I meant . I do not believe sensors are necessary in every case . I rarely use them on any systems and have no problems with surface temps as a rule . If this is an ICF house ( sorry if I missed that) . I was more questioning whether this an SWT or something else .

Check this one out . Full years usage , ICF home , 14 zone radiant . Ann Arbor area of Michigan .

https://www.facebook.com/RValue/photos/a.340016462575.199306.326447887575/10155571358822576/?type=3&theater

BeefSupreme

The entire house isn't ICF, but the bottom half of my new addition is. Upstairs is R27.4 walls and R60 ceiling with energy heel. The 1st floor loops were ran by a contractor whom was later kicked off the job because he wouldn't show up to work. I ran the upstairs loops and transfer plates myself. Both upstairs loops are 230 feet. I'm not sure about the downstairs loops, I believe about 275, maybe less. I know they aren't above 300 and that they were relatively equal. Each floor has its own uponor 2 loop manifold. I'm not sure how to post pics at the moment. It's a standard uponor flow balancing manifold with 2 loops. My supply water temp is 107 downstairs. Sorry to be ambiguous. I have an old XEB-4 by Dunkirk for my boiler right now. Not sure it could accept a slab sensor or outdoor reset. The problem I run into up here is that everybody just seems to say run equal loops and don't worry about anything else. The guy that set the header up for me even told me it was a waste of money to buy flow balancing manifolds. I bought them anyway. That's why I'm trying to get some fine tuning advice here. He didn't even know what GPM would he adequate. He said either .5 or 2, that he couldn't remember. Pretty big difference in BTU's there from what I now understand. I'm confident the system will work well, I just want to get it fine tuned for efficiency and comfort. People in my small town don't seem to worry about such things.

Rich_49

What small town is that ?

BeefSupreme

Petoskey, 45 mins south of Mackinac bridge.

Jamie Hall

Petoskey? Nice little town. My wife used to go to Bay View in the summers -- many years ago.

Which doesn't solve your problem.

Since you are so heavily insulated on that level, what you really have is a control problem. As I suggested earlier, the idea will be to provide enough heat to the floor to keep it warm enough to deliver enough heat to your space -- without overheating it. There are a number of different approaches to controlling radiant, but they all boil down to providing an inlet temperature which is high enough -- and your 107 may well be too high -- and enough flow so that the delta t is reasonable -- around 10, as has been mentioned.

Outdoor reset is your friend on this, as will be a mixing valve and most likely variable speed pumps. I am not that familiar with ways to control all that, but others are -- and will chime in. Keep in mind, though, that radiant heat responds very slowly -- so don't think about setbacks or fancy indoor thermostats or anything like that.

BeefSupreme

Yep, it's pretty nice up here. Bay View is nice too, as long as you don't have to work on the houses. I just have regular stats and won't be using a set back. Since the system is new I'll probably have to play with it a bit to see what works. I do have variable speed pumps, mixing valves and adjustable GPM manifolds so I'm sure I can dial it in, just looking for a starting point. I've been told 105F for supply by just about everybody but I'm wondering if I can get away with less because of the insulation values. I read on another thread that lower supply temps can help the slab heat more evently. I turned the mixing valve down to almost the minimum. I'll have to wait until Wednesday to see how it does though, the solar gain from the south facing windows was enough to keep it to 68 today.