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Author Topic: inslab radiant heat question  (Read 7919 times)

sceptre74

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inslab radiant heat question
« on: November 05, 2014, 03:35:21 PM »

I'm about ready to hookup my in slab radiant heat in my shop for the first time. I have 6 loops of approximately 250 ft. I'm using a 50 plate off the bl 2840 and that will be hooked up to this manifold. http://www.ebay.com/itm/360791092709? Since this unit has adjustable flow rates built in, what should I be setting each loop at? I'll be installing a mixing valve so what should my supply and return temps be at the manifold? Sorry for all the questions. Not the least bit familiar with this kind of system. Thanks
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coolidge

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Re: inslab radiant heat question
« Reply #1 on: November 05, 2014, 04:24:50 PM »

I would think you would want more heat by your doors. I am running mine at 80 in and have 75 coming back. Expect a lot lower return temps when you start. Takes my 28 x 40 shop 2 days to come to temp, that's when it's 40 outside. I have one ft on center in front of my doors and 18" in the middle.
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sceptre74

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Re: inslab radiant heat question
« Reply #2 on: November 05, 2014, 04:47:15 PM »

So the loop by the doors should be on a higher gpm than the others? I went with 12 inches on center for all the loops. Can the supply be warmer than 80? I was planning on setting it at 110. Like I said, totally clueless with this stuff so expect many more questions.
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slimjim

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Re: inslab radiant heat question
« Reply #3 on: November 05, 2014, 04:53:45 PM »

If they are all evenly spaced and you have flow meters on each loop and can increase the flow at the doors then by all means do so, the lower the supply the better as long as you can satisfy the demand, 80 is low but no more than 130 F
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sceptre74

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Re: inslab radiant heat question
« Reply #4 on: November 05, 2014, 04:58:15 PM »

I at least have somewhere to start now. Thanks guys
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hen house hansen

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Re: inslab radiant heat question
« Reply #5 on: November 05, 2014, 05:59:47 PM »

I Have my shop slab set at 120 on the supply line. and tubing spaced about 12" apart. This will work just fine for you also....
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mlappin

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Re: inslab radiant heat question
« Reply #6 on: November 05, 2014, 09:23:07 PM »

I have my sidewalk set at 125F and it works just fine, indoor linesets can probably run a little lower.
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LittleJohn

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Re: inslab radiant heat question
« Reply #7 on: November 06, 2014, 07:31:13 AM »

In the past when I installed (in-slab) the perimeter would get 6" OC spacing for the first couple feet or passes, then switch to 9" or 12" depending on size of slab.  FUTURE RREFERENCE

OK, I will assume a few things and hopefully point out some pros & cons, along the way
1) Supply water temp of 80f (probably a bit low); in-slab can easily be run with 120f water going into floor (looking for a delta T across supply vs return, to reduce stirping and maintain an even heat across all of the slab)
  *Use of a thermostatic mixing valve (purely MECHANICAL and only allows you to control the inlet temperature)
  *Use of a powered or actuating mixing valve (may allows for out door reset, control of delta T & max temperatures) -> CAN GET COMPLICATED AND REQUIRE ADDITION ELECTRONICS TO CONTROL
2) You say all loops are approximately the same length, GREAT start
    Now about the balancing, I would start off with all loops having the same flow (wide open as possible) and allow the system a few days to get up to temperature and see how the shop feels. Big question is do you know which loops feed which areas because it greatly affects the next step.  If there are any noticably cold areas, what you can do is slow down some of the other loops that do NOT go to the cold area.  Again give a few days between adjustments, as slabs have SLOW reaction times


***My shop is 48'x80' with an office off one end (4k sf), if I start heating early enough building comes up to temperature within a day.  However the first year of heating that building we had a fwe hiccups in the system and did not get started until after it had been 40f outside for a week.  Took 2 solid days of runing the OWB wide open to get that slab up to temp; but once it gets there, it stays there  :thumbup: (other than some afternoon solar gains)
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sceptre74

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Re: inslab radiant heat question
« Reply #8 on: November 06, 2014, 08:49:21 AM »

All runs are with in 20 to 30 feet of each other in length and no more than 250. We ran them starting on the outside and worked our way in as we went. Looked around for plans on laying them out and never really found anything to go by. I will be using a mechanical mixing valve and running it around 110 to 120. Hope to have it up and running by the end of next week
« Last Edit: November 17, 2014, 07:39:45 PM by sceptre74 »
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LittleJohn

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Re: inslab radiant heat question
« Reply #9 on: November 06, 2014, 10:14:40 AM »

All runs are with in 20 to 30 feet of each other in length and no more than 150. We ran them starting on the outside and worked our way in as we went. Looked around for plans on laying them out and never really found anything to go by. I will be using a mechanical mixing valve and running it around 110 to 120. Hope to have it up and running by the end of next week
You get a star, for running loops from Outside of building to Inside (putting hottest water near largest expected heat loss)
You get a 2nd star for keeping loops so close in length (since you are in slab, probably would not even need to balance, but since you have the manifold its nice to use the flow valves as a good gauge of if system is working or not)
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Sprinter

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Re: inslab radiant heat question
« Reply #10 on: November 12, 2014, 11:31:29 AM »

Set all your flow meters to 75% then balance from there. Make your mix V easy to adjust. I was just servicing a greenhouse yesterday and they run 180 in and 150 out till it comes up to temp , then 150-155 supply.

Their MV was way too small so I put ball valves in instead.( homemade mixing valve) and will handle all the flow the pump can do at a quarter of the price of a MV that can handle the required flow. Now it only take 4-5 hours to come up to temp from a cold start instead of a week. They have 5/8" viega pex @ 9" centers. It's 15 years old and not a crack in it. Not sure if it's better Crete or standard 3000psi stuff. Anyways they now can run much lower temps and get fast response. Their pex is on chairs in the pictures so not at the bottom of the concrete and foam except for the ends of the greenhouse. They have some lag time. Double of the rest of the GH. The FLIR is handy for balancing
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sceptre74

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Re: inslab radiant heat question
« Reply #11 on: November 17, 2014, 07:46:33 PM »

Got things hooked up and running this morning. The temp inside and out was 40. I have a 26 99 on the boiler side and a 15 58 on the slab side of the hx. Speeds are set on high on both.  The supply temp is set at 120 and the return is coming back at 80 right now. Flow is 3 gpm on each loop. Does all this sound about right?
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LittleJohn

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Re: inslab radiant heat question
« Reply #12 on: November 18, 2014, 06:31:01 AM »

A delta of 40F is a bit high, but not unrealistic since from what you describe as a "COLD" slab to start with.

Question, you say you are getting 3gpm per loop??
  That mean your floor is sucking up something like 360k Btu/Hr -> (3gpm x 6 loops) x 40f x 500
  Combine that with what sounds like a 1500 sf building, 6 loop x 250' @ 12OC
  (360000BTU/hr)/(1500sf) = 240BTU/sf  :o- That is Snowmelt type numbers

**I am not saying any of your numbers are wrong, but they do seem HIGH!  How has your OWB been reacting, has it been gobbling (could not hold back, so close to Thanksgiving  ;D) up the wood!

There is nothing wrong with running with your the delta T that high, but a few draw backs are as follows;
1) May feel warm and cool spots in floor, or may notice heat striping
2) Your OWB my not be able to maintain its setpoint with water coming back so cold
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sceptre74

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Re: inslab radiant heat question
« Reply #13 on: November 18, 2014, 09:01:24 AM »

That's what I'm fearing. Is there anything I can do to improve my delta T?
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LittleJohn

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Re: inslab radiant heat question
« Reply #14 on: November 18, 2014, 09:45:38 AM »

Generally you just increase GPM, but if you are at 3 gpm, you may not be able to go any faster.

How has you OWB been reacting, does it seem like it is struggling to keep up or has it been puttering along??
After a while does the return temperature start to come up or does it stay way down at 80f?? 
*If slab is "cold", it may take a while to before you start getting decent return temps; but once you get it there, it will only take small amounts of heat to keep a constant temperature
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