Primary/Secondary with Mod-Cons (Part II)

Mike T., Swampeast MO · November 2006

Hypothetical system attached as a .pdf document.

This for a 3,500 sq.ft. home plus full basement (heated) and 1,200 sq.ft. garage (also heated). All radiant floors.

Two-temperature system with seven zones, all using individual circulators. Chose Taco circulators for example. Taco L0205 was closest match for all, but not always ideal.

No flow setters are assumed. I did my best to estimate the actual flow based on the actual tube lengths used. I also computed the required flow based on "Rad Pad" recommendations. Zone delta-t and required supply temperatures based on estimated flow--NOT computed required flow.

Before I start computing what actually happens during operation, is this:

1) A reasonable system? Would you prefer simpler?

2) Are the design paramenters also reasonable?

3) Is the R 1.5 assumption for the floor panel assembly (not counting floor covering) reasonable? If not, please give a suggestion.

Also, please check for obvious errors. Questions welcome.

jp_2 · November 2006

other stuff?

new or existing house?

seems like the floor temps are too high, but maybe if the windows and such are in poor shape you need it?

i find around 76F on bare feet feels nice and warm.(tile & gypcrete, bathroom tile and 1/2 durrock).

edit: what kind of tubing setup? staple up,warmboard, etc....

Mike T., Swampeast MO · November 2006

New or existing doesn't really matter. Given the btu/sq.ft. requirements (22 is the max), I'd say equivalent to new, decent construction.

Double-checked the floor temps on the Rad Pad. All appear to be correct. This is temp required for design load output per square foot with 72° room air temp. Floor temps will of course be lower when not meeting design conditions.

As to type of panel construction, I've given it an equivalent R-value of 1.5. This should be reasonable for decent plates above the floor with sleepers between. Somewhere between below the floor with HEAVY extruded plates and Warmboard.

I'll be HAPPY to change that equivalent R-value for the panel itself (not counting floor covering) if someone wants to provide an actual value for a specific, specified and hopefully fairly common construction.

hr · November 2006

It's rare to see

a garage with 6" spacing. I generally design garages for 55 design temperature. Un;ess you think it may be living space in the future. Sometimes even 15" on center handles a garage.

Not a big fan of 7 circs either. Maybe one for each temperature with ZV's if in fact the load is in that 150K range.

If $$ allow, 2 80K mod cons would be sweet. One for each temperature requirement. Better turn down and no mixing devices required. Put the indirect on the lower load boiler.

hot rod

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Mike T., Swampeast MO · November 2006

Thanks Hot Rod!

I will change the tube spacing in the garage, but here's why I chose 6"...

Assumed that the garage wasn't just for housing cars. "Weekend" workshop (retreat) with normal room temp significantly lower than the house proper but desire for quick (for tube-in-slab) heat-up.

Did you notice the 12" spacing with 3/4" tube for the bulk of the basement? I tried to provide a very broad range of homeowner desire vs. installation cost vs. potential for "striping", vs. efficiency in this hypothetical system.

Nor would I be a fan of 7 secondary circulators! BUT, my original post in this topic had the subject, "AKA zoning with circulators".

hr · November 2006

If speed

is the requirement for the garage warmup a hydronic unit heater would be best.

1200 square feet of slab at 4" is 15 yards, probably more for a thickened edge under the door. So figure 60,000 pounds of concrete to rev up. Do the math, doubtful 6" will make it happen much quicker.

Also garages seldom have a good edge insulation across the overhead door, and edge to driveway detail. That loss will slow down recovery also.

Unit heaters are far from the comfort of slab radiant, but they make it warm within minutes, not hours.

Think I would try a radiant celing on my next custom job, if budget allows. Quicker than a slab and a lot less noise than a unit heater.

hot rod

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Mike T., Swampeast MO · November 2006

You're right. No surprise there;)

And THANK YOU for your time and close attention!

When I made up this hypothetical system off the top of my head, I REALLY wondered about the garage and thought I'd put something odd--perhaps wishful thinking--into the design.

Did I really think this would work? Maybe...

Mike T., Swampeast MO · November 2006

More suggested changes? Please offer! I'm open to anything.

I really want to have a reasonable (if rather high-end) system before I start comparing "design conditions" to reality in a system with fixed flow.

Unknown · November 2006

Mike,

Your flows do not seem to match up. For instance, in the basement you have "Flow Needed" of 1.32 GPM on a 15kBTU load.. which, at a 20 degree dT would be about a 1.5 GPM requirement with rules of thumb, so I'd buy that.. but later in that section, you claim a 9 degree dT and 3.5 GPM. I guess that's from the zoning by pump? If so, I would go with HR's suggestion, use a system pump and zone valves, and assume loop flow meters allowing for proper balancing to something close to a design dT.

Since dT is one of the major issues of contention here in this discussion, you could easily do this in a couple of configurations: a "low flow" system using a 20dT target standard, for instance, vs a "high flow" system using a 10 dT target for radiant areas. Of course, that increases your workload here

Also, ditch the 3/4" at 12" o.c. Maybe, Maybe 5/8" if you want long loops in a high flow situation. but I'd stick to the 300 x 1/2" rule of thumb for a "typical" installation detail.

I don't know where you are getting the R1.5 for a floor R, but with your 8" o.c. spacings I would assume this is "modelling" a joist plate install, in which case I'd say it's close enough, but maybe your modelling is more sophisticated than I am seeing at the moment, can you explain?

Mike T., Swampeast MO · November 2006

"Flow needed" comes from the Rad Pad following their instructions. In my limited experience with RFH, the Rad Pad has proved accurate, versatile and exceptionally easy to use--not to mention extremely inexpensive. (The Rad Pad is available at Heating Help by the way.)

Just because you want x flow doesn't mean you'll get it...

The actual flow estimate is based on the length and number of circuits in each zone with a given circulator. Note that circuit lengths are identical and reverse-return is assumed. The delta-t and required supply temperature are then based on the actual flow estimate, not the required flow from the Rad Pad.

The 12" spaced 3/4" tube was the other rather unconventional choice. Instead of attempted "faster response" as in the garage (the other unconventional choice), here it was based on material economy as I assumed this area of the basement was substantially unfinished "utility", "storage" or "play" space. Like the garage likely kept at a relatively lower space temp, but still able to maintain full room temp if desired and if finished with any reasonable floor covering. Will 1/2" tube @ 12" spacing suffice? Perhaps tightened to 9"? Or is my logic in the original choice mainly "wishful thinking" as with the garage?

Nothing at all sophisticated about how I'm trying to "model" the floor--really nothing more than a semi-educated guess. Rad Pad suggests about R 2.3 for "staple-up with plates" @ 8" spacing. I've used significantly less R-value based on my experience with heavy extruded plates below 3/4" floor or perhaps an above-floor installation with thinner plates. Again, this value does not include the floor covering--it is for the panel itself.

Mike T., Swampeast MO · November 2006

p.s. Hot Rod

For an actual consulting job I AM suggesting a radiant ceiling in the garage for a homeowner who wants relatively quick heat-up in a fairly low-temp system using both recessed and standing iron. (Either that or a lot of standing iron that will take up floor space he wants for other things...)

Unknown · November 2006

Ok, that's what I thought. Absolutely zone valve it, choose an appropriate system pump, and I would really encourage running it in the two scenarios to compare high flow/low dT vs low flow/high dT. I think that cuts to the chase of most of the discussion in the previous discussion.

If material economy is of concern, you don't usually jack the tubing size up. For reference, you can often do a basement with 12" o.c. 1/2" pipe with 400-600 foot loops if a 20 deg dT is ok with you. If not, the 300 ft standard keeps you out of trouble in the typical load-low basement situations. 9"o.c. is usually only needed for output balance in a zone, or for carpeted, walkout areas.

I concur with your R-value guesstimation. Rock on, Mike

Unknown · November 2006

is my memory failing, or have people reported radiant ceiling over bare concrete to be fairly uncomfortable? I've been shying away from it in this situation for specifically that reason, but then again I have not tested it myself.

hot_rod · November 2006

Bake and broil shop and garages

I'd like to try a garage with 15" oc short loops in the slab and radiant ceiling.

Shoulder seasons use the ceiling, before the slab gets "winter' cold.

Then use a tekmar 500 series to run the slab with a not to go below temperature for the slab sensor, limit the air temp to say 50F.

This would keep the floor somewhat warm and dry, but the fast reving ceiling could be brought on if you wanted to work in the shop 1/2 hour from now.

Ice cold cars limit the slab output if you run a heat flux calc on them. but unless you park your cars on the ceiling you have an excellent low temperature wall to wall, gypsum panel radiator type of emitter.

I should have listened to Tesmar years ago!

Great place to try out my peel and stick copper transfer plate and tubes

hot rod

Unknown · November 2006

QUIET HE'LL HEAR YOU!!!!!

Mike T., Swampeast MO · November 2006

Thanks Rob.

Do though indulge me for a moment.

At the very beginning of the original post in this subject, by-lined "zoning with circulators", I asked, "Do you use flow-setters to ensure that secondary (emitter) flow does not exceed primary (boiler) flow by more than 30% or so?"

With no offense meant, I'm certain that I've seen photos of rather similar systems here with banks of circulators--sometimes with flowsetters, sometimes not. I've also seen MANY discussions over the years regarding zoning via "valves or circulators" with no definitive (in my mind) advantage going to either.

My attempt here is to begin with a complex and large (8,250 sq.ft heated in this example) system driven by a mod-con, thoughtfully designed with zoning via circulators and no flow setters. Given the reasonably available circulators at reasonble cost, that little Taco actually seems rather well suited to each of these zones. Even in the tiny master bath zone it should only be moving about 3/4 gpm.

Over the next few weeks, and with thoughtful input and suggestions the system will progress. I'll do my best to demonstrate what happens in reality using nothing more than pen, paper, the Rad Pad, manufacturers' data and my good old books...

Unknown · November 2006

I understand what you are aiming at, all I'm saying is that dT is a primary source of arguement here, and that if you do this in the also-common system pump and zone valve set up, then your ability to check different dT scenarios is much easier, just recalculate for a larger or smaller pump. Personally, I'd really like to see a base 20 dT through the radiant, vs 10 dT, because my suspicion is beyond pumping power this should make almost no difference to the heat source at all, but others are disagreeing

If that's not what you are shooting for, then so be it, just my two cents!

Primary/Secondary with Mod-Cons (Part II)

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