New radiant floor heat system/shop questions.. opinions please
Last Post 01 Mar 2015 11:30 PM by bob light. 56 Replies.
Printer Friendly
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Page 3 of 3 << < 123
Author Messages
nightlightUser is Offline
New Member
New Member
Send Private Message
Posts:14

--
26 Dec 2014 06:56 PM
placing more pex say 6" on center with shorter loop runs will yield faster results and lower head tuss running the pump on level 1 (12-30) watts


take a 10x12 room and place one baseboard under the window than take same room and place the baseboard all around the perimeter of the room - which will heat up faster ??????


I dont see any driveways(snow melt) , warehouse building with less than 5/8 its ether that or 3/4 - 1/2 is a joke specially for a 3000sqf area - perhaps if you had a small 10x12 utility room or something maybe u could do 1/2 pex else 5/8 or 3/4



ICFHybridUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:3039

--
26 Dec 2014 09:47 PM
50btu/h
What is this value?


NRT.RobUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:1741

--
29 Dec 2014 09:37 AM
Nightlight is way out of the park on this one.

I would leave your bypass valve as is (open, as intended)... though I can't find the pressure drop through that boiler, and this is a single zone system so it might be fine either way, but your report would seem to indicate low flow in the boiler circuit so leaving that "Full closed" might really drop the flow rates through the shop. It's certainly not great practice to have two pumps pumping through each other.

Your temperature report would seem to indicate you have less flow in the boiler circuit than the radiant circuit, which is odd. same return temp in both cases, diluted hot water in the radiant, means the radiant is circulating faster than the boiler. so the "flow issue" resulting in the super high Dt is the boiler pump which can't be pushing more than a couple GPM here. Apparently it works enough to heat the building but it's not a flow I would normally expect in such a short circuit. Does the boiler pump have a speed control? You could raise that one and see if you find the system to be a bit more responsive.

that said you shouldn't need more than 100 degrees in the slab, and the 58 degree situation being only 2 degrees off of setpoint could very easily just be thermostat swing. This system may be operating just fine and all of this may just be interesting but not really a problem.


Rockport Mechanical<br>RockportMechanical.com
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
29 Dec 2014 10:26 AM
Agreed, Nightlight’s advice is less than good.

Agreed, hydraulic separation between the pumps should be provided so each pump’s flow rate is independent of the other pump. The degree to which the pumps will adversely interact with one another depends on the head loss in the piping path that they share (i.e., the common piping). Successful hydraulic separation is achieved by keeping this common piping and associated head loss very small.

Agreed, I also think this system should work fine. My only remaining concern is that we still don't know if the heat source is adequately sized for the building...which can only be determined by doing a proper heat loss analysis of the building. However, given that this building isn't considered living space, this may not be a real problem either...but one still should always do a heat loss analysis BEFORE designing/installing any HR system...


Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Limited87User is Offline
New Member
New Member
Send Private Message
Posts:16

--
29 Dec 2014 10:51 AM
Thanks Rob for your input. I think your on to something here. Yes both pumps have 3 speed settings.

I did more messing with it this weekend. I completely agree with you on the bypass valve by what its showing me. I have all 10 circuits set at 0.5 The flow rate drops to the slab to 0.1 to 0.2 if I do this with the valve (fully close it). It also increases the pressure several psi on the return going into the boiler and also will DEcrease the temp of the output of the boiler several degrees. If I just cut it back to 3/4 or a little more it will increase the input heat to the floor much closer to the boilers output temp but still try's to do what it does when the valve is fully closed just not quite as bad. Is this because I'm sending all the 68 degree water to the boiler instantly now instead of letting it blend with the input going with the slab water?

When the valve is open as its intended and the boiler is set to 125 degrees and sending 125 degree water to the panel by the time it hits the floor lines its maybe 100 degrees after going past the valve. The return is 68 degrees max after running for a long time. I don't see how its ever going to heat the slab up hotter than this at this rate. Seems like I def need hotter water coming out of the boiler or somehow get the 125 degree water to the floor the boiler is actually putting out. The boiler is supposed to be able to put out 140 degree water but the only way I can get it to climb to 140 degrees is to slow both pump speeds down to level 1.. then it will put it almost instantly to that.. BUT then my flow rates are back to almost nothing and I cant increase them more than the 0.2 gpm no matter how much I try to increase them manually.

The temp was in the mid/low 20's last night. The system was running non stop but holding the 60 degree thermostat setting. I went and bought and infared point and shoot thermometer. I shot the floor pretty much everywhere and I have some floor areas as high as 65 and some are as low as 58. Most areas were in the middle of that range. I wont count the areas where all the lines come together to the manifolds at 68. I have to figure out how to make the inlet water temp get way more inline with the boiler outlet temp if I'm ever going to get alot of heat out of the floor. Yes I could let it run for days on end and MAYBE with sending 100 degree water to it it will eventually heat up but I will go broke before that happens paying a thousand dollar elect bill a month, or propane, gas, etc whatever I was using.


sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
29 Dec 2014 11:15 AM
As we stated previously, you should not need more than 100F supply to the circuits UNLESS your building heat loss is HUGE. A 85F circuit supply temp to your efficient concrete HR emitter would keep a well-insulated, well-sealed building cozy at 72F when the outdoor temp is 20F.

The reason you are seeing that large floor surface temp differential is because of your large 32F circuit temp drop differential (i.e., the delta T difference between supply/return temp). For residential buildings, we normally design for 15F or less delta T. Only shorter circuits or more flow rate will reduce this delta T and the associated floor surface temp differential. Again, for this building, I would not worry about this large differential floor surface temp as we previously discussed. However, I would worry that your average floor surface temp may need to be a much higher temp in order to keep your building adequately heated and that your current heat source may not be able to accomplish this. Again, this is why a building heat loss analysis is so important.


Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Limited87User is Offline
New Member
New Member
Send Private Message
Posts:16

--
29 Dec 2014 11:44 AM
Ok.. this whole thing is puzzling. Lets take the building out of the equation to a point. Someone stated that the temp of the building will only be as warm as the slab. If the temp of the concrete will only get to 65 (infared thermometer point on concrete) at 100 degree inlet temp for whatever reason.. is it safe to say that the building will never go over this temp?


NRT.RobUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:1741

--
29 Dec 2014 12:19 PM
No, because it's currently thermostatically controlled and is maintaining setpoint. So it's not actually running constantly and the floor temp is being cycled around the current thermostat setting's requirements.

Limited, I think you're obsessing a little here. You do not need or want more than 100 degree water going to the slab unless you have some floor coverings here like wood or something. Don't worry about the temp drop or the run time: this is a modulating boiler. The only things we care about are:

1. are you able to maintain the temp setpoint you are trying to maintain
and
2. are you able to do it in a reasonable (for a 6" slab) amount of time.

at a 25-30 degree drop at your loop flow rates you are putting out something like 65-75kBTUs/hr into the slab. If you up the speed of the boiler pump or raise its temperature, you could raise that to the true max output of the boiler (5 x DT x 500 is the formula) and then you're done: you'd be putting as much heat into the slab as you could possibly do with that heat source. And you're already pretty close, so that's that, it would be a incremental increase in either case.

Then the only question is whether you'd have overshoots of room temp and if so then you need to lower the water temp and raise your flow rates to try to compensate, or change your thermostat to something better for high mass radiant.

It's pretty unlikely that your design load is higher than your heat source output here and I think you just caught the system in a temporary undershoot once. High mass can be hard to control. That said, if your "R30" wall is because of shiny shiny foil or something instead of real insulation... maybe that's not true.

Absent something like that jacking up your load way beyond where I think it would be, I would say this system is either working as best as it can or is very close to that point.


Rockport Mechanical<br>RockportMechanical.com
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
29 Dec 2014 12:51 PM
I fully agree with Rob.

To specifically answer your question: “If the temp of the concrete will only get to 65 (infrared thermometer point on concrete) at 100 degree inlet temp for whatever reason.. is it safe to say that the building will never go over this temp?”

A HR emitter can NOT heat a building to a higher temp than the emitter surface temp. So YES, if you never get the slab surface temp to exceed 65F, the building indoor temp will never exceed 65F. However, you need to also keep in mind that the floor surface temp is also affected by the downward heat transfer into the ground and the upward heat transfer into the building. For example, if you were to increase the building indoor temp to say 85F by heating the building some other way, this would heat the slab to a temp higher than 65F. So it isn’t solely the supply temp to the slab that determines the slab surface temp.

Perhaps better questions... What happens when you set your thermostat to 70F? Does the heat source maintain this higher set point or is your heat source unable to keep up with this increased building heat loss? How high an indoor temp do you really need to keep this building? Does the building need to be at this temp all the time? If not all the time, there are likely better ways to accomplish this than by using a high mass HR emitter.


Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Limited87User is Offline
New Member
New Member
Send Private Message
Posts:16

--
29 Dec 2014 12:57 PM
Ok I see.. The lowest temp the boiler will ever modulate is at 86 degrees. The lowest setting of hot water heat. Id have to get my temp from the floor to that at a minimum for that to ever happen.

I just want to make sure this system is operating as efficiently as possible. My electric bill is gonna be insane this first month working the bugs out and that 2 days of non stop running to get concrete up to temp from 30 degrees.

The R30 is 9.5 inch thick pink Owens Corning roll insulation. Its def what its supposed to be.

Let me ask you this.. does speeding up the flow increase heat to the tubes/floor or slow it down? Does more or less gpm through the tubes increase heat flow?





NRT.RobUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:1741

--
29 Dec 2014 01:01 PM
Increasing flow always increases heat transfer until you hit the max output of the boiler.

Nothing we have talked about in this thread has anything to do with your thermal efficiency except the tube placement (an incremental issue) and pump speeds (higher uses a bit more energy). At the end of the day concrete takes a certain number of BTUs to heat up and you have a certain heat load and heat from the boiler is going to one of those two things OR back to the boiler OR raises the room temp.

If your room temp is not rising, and the boiler doesn't have to modulate down because of higher return water temps, then the energy being produced is needed and being used and that's that. Pump speeds, glycol, or water temp rises won't change that.



Rockport Mechanical<br>RockportMechanical.com
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
29 Dec 2014 01:13 PM
Neglecting downward/upward heat transfer (or assuming this total is the same as the actual supplied BTUs/hour...which is a reasonable assumption), the change in slab temp per hour will be the actual supplied BTU/hour to the slab divided by the quantity of 27 times the slab thickness (in feet) times the slab area (in square feet). Say 70,000 BTU/hour / (27 x 0.5' x 3072 SF) = 1.7F/hour.


Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
ICFHybridUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:3039

--
29 Dec 2014 09:51 PM
When you are running at a comfortable steady state have you taken the temperature up by the ceiling? Fourteen foot ceilings are huge. You may need some circulation.

Also, is the slab exposed at the doors or did you put in appropriate thermal breaks?


TCM75User is Offline
New Member
New Member
Send Private Message
Posts:2

--
29 Dec 2014 10:33 PM
I am not an expert but have been through a radiant project of my own 3 years ago. I will provide some information in hopes that it may help you or someone else, but if you want the condensed version I will make two recommendations: 1) make sure there is no air in the system, and 2) make sure there is no debris in the system. I am in Northern NJ, so the climate is a bit more mild than your location but it can still get down to the teens for an extended period (weeks, not days like last winter for us). In winter of 2011 I had a 48' x 96' Butler building built for additional workshop/storage space at my Company. For years I had wanted to build something with radiant floors and I finally had my chance. We put an 8' thick slab with Insultarp insulation below and (I think) 3/4" Pex lines in three zones throughout the slab. Block walls were built to 8' high and then a rigid panel with R-14 on the remainder of wall height (6 more feet) and rolled insulation on the inside of the standing seam roof...in retrospect more insulation would have been better. The heat source is a Buderus GB142/60 condensing boiler which can put out ~190,000 BTU. The building was finished in the spring/summer of 2012 and besides a short test of the heating system (it was warm within one day) we had to wait a few months to test it out "for real". Fall and then winter came around and I was happy that the building stayed very comfortable. The first zone was is a maintenance workshop and we leave it at 58 degrees. Warm feet make a big difference...the older building next door needs to be at least 65 degrees to feel just as comfortable. I do want to add that the building had no trouble achieving 68 degrees in the cold of winter...that almost seemed too warm and I never tried to adjust the thermostat higher. The second heating season (last winter) was a different story altogether. The system struggled to keep all three zones at 55 degrees. Numerous calls to the installer led to a lot of finger-pointing ("well, we contract out the system design...") and another quote that suggested I install new pumps to increase the flow. The system was bled the following summer, serviced, and we still could not get the flows I had seen in the first year. I was sure something had gone wrong with the pumps. Unfortunately the design of the system lacked isolation valves and an effective way to get air out of the system. I received another quote from a second plumber who worked on "some" radiant systems and he suggested about 5 thousand dollars in labor and material to make the system work "better with no guarantee". He also added that the boiler was undersized. FInally I found a third plumber who only works on radiant heat projects. The bottom line after he spent a couple hours looking at my system was that we needed more flow. The original system had a 1" header coming from the boiler which then split into three zones and circulator pumps, also which had a 1" pipe. He explained that it probably worked under ideal conditions because there was more than enough heat output and flow, but it was marginal at best. His recommendation was to increase the header to 1.5 inches. Interestingly enough, this person said that the boiler was too big! I decided to follow #3's recommendations based on his logical and technical explanations (I am an engineer and don't appreciate when people gloss over the important things) and we spent a few days changing the plumbing around. At the same time I purchased the next size up of Grundfoss 3-speed circulator pumps (unnecessary in retrospect). He also recommended to remove the mixing valves the original installer included before the circulator pump. Adding isolation valves and threaded hose fittings meant that we could "power purge" each zone with city water pressure of around 50 psi, bypassing the boiler's ~17psi relief valve. I am attaching an image of what we believe to be the main culprit in restricting the flow. No idea how this junk got in there besides sloppy construction practice. The good news is that the system works great, we are seeing a 20 degree differential between supply and return, and no more short cycling (didn't mention this before, but this is what increasing the header to 1.5" solved). Not sure if this helps, but I'm happy to answer any other questions about this. I love radiant heated floors - nothing is as comfortable and quiet...just need to make sure you have the right people!

Attachment: IMG_3554.jpg

sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
30 Dec 2014 10:00 PM
TCM75, sounds like you and Gurunno should get together for coffee sometime, LOL!

HR Contractor Issues in NJ

I really would have expected better HR contractors in the NJ area.


Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
nightlightUser is Offline
New Member
New Member
Send Private Message
Posts:14

--
04 Jan 2015 10:33 PM

12" on center BTU output 13btu at 100 deg and 24btu at 120deg


9" on center BTU OUTPUT 16btu at 100 deg and 29btu at 120deg


6" on center BTU OUTPUT 18btu at 100deg and 35btu at 120deg



hmmmmmmmmmmmmmmmmmm ohhh my what does that mean ??? less spacing faster results more BTU less head === $$$ SAVINGS duhhhhhhhh not rocket science


12" on center 90 degree water outputs 7 BTU you have 3000 sqf area anything below 80 produces 0 BTU to fix your problem PUMP MORE GPM which will increase head loss which will require a higher pump at higher wattage usage



bob lightUser is Offline
New Member
New Member
Send Private Message
Posts:11

--
01 Mar 2015 11:30 PM
This is "lighthouse" with a totally different question. Why can't you add the pex on top of the concrete slab with some thickness of foam in between. This would decrease the heat loss in my thinking. Yes I am just getting started in this. I will be building a new home 2500 sq each level with radiant heat on each level. I will staple the pex to the main OSB floor up with the 1 1/2 concrete backfill followed by tile. Can I add OSB to the basement floor over the suggested foam barrier. Appreciate your thoughts and wisdom.


You are not authorized to post a reply.
Page 3 of 3 << < 123


Active Forums 4.1
Membership Membership: Latest New User Latest: hudson2000 New Today New Today: 0 New Yesterday New Yesterday: 2 User Count Overall: 34707
People Online People Online: Visitors Visitors: 179 Members Members: 0 Total Total: 179
Copyright 2011 by BuildCentral, Inc.   Terms Of Use  Privacy Statement