theoretical question

Brad White_9

more important than the supplemental radiation making up the deficit (at least 10K in your equation) is that the distibution of it be continuous and thorough. Distribution takes on much greater importance with all that thinly insulated surface area.

In other words, you would have more success with a continuous application of euro style panel radiators as db suggests, rather than a "big blob of heat" here and there.

I agree that the deficit should be fully compensated for, such that the total at least equals the requirements. Making it more conservative is OK if control is tight.

All of that glass and uninsulated wall points to low mean radiant temperatures (MRT's) and if not checked by a film of warm convective air or appropriate radiant flux, the occupants will feel cold.

The fact that you have radiant floor (or radiant anything for that matter) will cheat the radiational cooling effect so you can run your secondary heating means under tighter control and/or at lower temperatures. I would make sure that the second stage of heat is tightly controlled. It would be easy to over-shoot especially on a sunny day.

My $0.02,
Brad

allenh

theoretical question

I read a couple of Dan's books and have a question.

Lets say there is a room that has loads of windows, little insulation, very high ceilings, and heat load is say 20k btus. And for sake of discussion there is radiant heat that only produces 10 k btus. On cold days this room would be cold. If there is a second stage of heat - running baseboard or rads - would that second stage have to be 10 or 20k btus of heat? I know that if the room had 10 k of rads it would need 10 k more of rads. BUT when radiant is used the ceilings are cooler than with rads.

don_52

It's done almost....

exactly as you describe Allan. I have read this many
times right here.

The problem doesn't seem to be the floor radiant, you or
anybody is actually limited by the amount of square footage
and how much plate, tubing run etc. that can be correctly
installed per that run(s) and it's resultant output.

The issue arises with the "loads of windows" and "high
ceilings" factor, many folks when faced with this issue
will recommend installing the low and long euro-style
panel rads. The fact of "very little insulation" doesn't
help either.

This issue is not uncommon and has been addressed at great
length, try the search function with different key phrases.
I'm positive you'll find your answer.

HTH, Regards, db

S Ebels

As I understand your question................

You're asking whether the second stage has to have a greater output than the 10K indicated by your heatloss because it's of a different "type" than the radiant floor.
Correct assumption? If yes, my answer is no, stick with the 10K. Provided that the secondary is of hydronic nature, like panel rads or baseboard. If it's F/A I probably would "add" a little, maybe 10%.

We try to sell all of our jobs with that type of setup. High mass radiant has such a long "flywheel effect" that close temp regulation can be a challenge in a 100% radiant floor heated space subject to gobs of solar gain/loss. Panel rads are the weapon of choice for us in almost all scenarios.