Difficult Extruded Plate Output--Ideas/Guesses Needed

Mike T., Swampeast MO

I've been able to extrapolate output for some rather bizarre constructions, but this one is really difficult...

Materials used: ½" copper in Thermofin "C".

Panel (under floor-joist bay) construction: 1" cypress; ¾" hard yellow pine; ½" cement board; 3/8" ceramic tile (impervious grade).

Anticipated tube/plate spacing & characteristics:

1) Four plates per joist bay--since they are 4" wide and spacing is a nominal 14½" some trimming of the plates will be involved. The underside of the panel will be essentially solid aluminum excepting the joists.

2) Individual tube runs (½" copper) as measured by feet of plates served about 40'. Why so short? Because I have somewhat similar systems and know from experience that the copper in fin is VERY good at removing heat from the water. Will though consider longer. Runs will be in reverse return and the four passes in each joist bay will come from two different runs with return of run 1 closest to supply of run 2.

3) Supply temp at outside design temp about 135°. System is fully reset with absolutely constant circulation. No thermostat was used (or needed!) in the other radiant floors in this structure and none is desired here. (Although WILL design system such that some form of room air-temperature control can be added easily if needed.)

4) Flow rate: Unknown and variable. Manifold for this floor will come off of constantly circulating mains originally designed for gravity. Non-radiant areas use TRVs.

5) Delta-p: Should be nearly constant regardless of indoor or outdoor conditions. Differential pressure bypass (in system bypass arrangement) adjusted EXTREMELY low so that there is some bypass at all times.

My BIG unknown: What kind of surface temperature can I expect in a space with about 68° air temperature and what I would call "typical" exposure and glass level for a 100-year old balloon-framed house? (Original windows in better than new condition; fiberglass wall insulation; mainly occupied space above; about 1/6th of the space has a roof/ceiling combination with 8" of extruded polystyrene insulation.)

Mike T., Swampeast MO

A bit more info that may or may not be needed...

Heat loss of area at design is about 13,812 btu/hr/sqft as calculated by HVAC-CALC with "typical" infiltration setting but REDUCED by 15% overall.

Area is about 500 sq.ft. for a loss of about 28 btu/hr/sqft. Open (both ends) staircase (to 2nd floor) that runs about 10' along an exposed N wall before turning S into space proper (e.g. staircase has a 90° turn and 2nd leg has no exposure).

Currently 162 sq.ft. EDR of TRVd standing iron in the space. Two rads: one (small, tall) along N staircase wall, but NOT directly at the end of the staircase. Other (big, short) under triple bank of N windows. Possible to add a 3rd iron rad (old panel type) built in to kitchen island much nearer the S end of the space, but am hoping that I won't have to include...

I have another space with both radiant floor and a TRVd iron rad. The two seem to co-exist nicely without over- or under-heating.

hr

You might ask

Dale or Siggy to run this through the FEA software they have??

Here is a couple FEA Siggy sent me comparing pex in slab to Rubber Epdm in slab.

Interestingly Watts calcs predicited a 13.1 tube wall delta t, This FEA model of Siggys predicted 12.5.

Close enough for me.

With pex in slab the wall delta t is 4.8 by Watts calcs, and 5.3 by the FEA model. Again proves the models are close to the long calcs.

For whatever that is worth to you.

Wish I knew how to get a screen shot to this wall post. need a computer guru to walk me through the steps again, as pictures don't show that well

hot rod

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Mike T., Swampeast MO

Screen Dump

Like this? (saved at ¼ size) 1600 x 1200 resolution here so this should be about full-screen for those at 800 x 600.

Press Alt+Print Screen (most keyboards still have the Print Screen key in some form or other).

This copies the current screen image to the clipboard. CORRECTION. Copies the current ACTIVE WINDOW. Print Screen key alone copies the entire screen (including task bar, titles, etc.).

Paste into any image editing software.

Tim Doran_2

Surface temp

The required surface temp to deliver 28 btu/h/sqft with a 68 degree room set point would be 82 degrees.

Tim D.

Mike T., Swampeast MO

Got that part

but any idea on the temperature I would get with that panel and that temperature?

Tim Doran_2

???

Not sure I am understanding you. Give me a call to discuss if you wish. I can probably model the application.

Tim D.