I know patience is a virtue.

Yes they do treat the fluid in outdoor wood boilers most of which are unpressurized but no "open" in the excepted use of the word.

Another example of potentially harmful confusion.

depends on whose commonly excepted definition of "open" you are using, I guess. When we use it, we only mean "open to oxygen diffusion".

Posted By Montysc on 18 Apr 2011 02:46 PM
I expect our design will use a heat exchanger - that seems the safest since we won't need heat the majority of the year, and I don't want a complicated flushing system or anything of that nature.

Based on several of the comments above I want to make sure I understand things correctly. Assuming a heat exchanger is used, and a condensing tank heater (my preference), can we mix radiant in floor and the runtal baseboards upstairs - all zoned separately - and be OK?

I understand that the Runtal is designed for 180 degree water - but would be ok at 120 degrees - we will need to spec larger Runtal radiators to compensate for the lower temp running through them I expect.

We have 2 north facing walls and 1 west facing, all with windows above, that easily can take a 6" or 9" high Runtal in 8ft-9ft lengths - I have a few other locations that might work for the additional heat I may need...

Our calculated hourly heat loss for the entire upstairs is 18,500 - on a liberal design day.

Once you have the thermal mass of the tank to work with, it doens't much matter how many zones you chop it up into, or the thermal mass (or lack thereof) of the radiation in each micro zone- the burner won't short-cycle on zone calls- the zone controllers determine the state of the pumps/valves, not the burner.  In a tank based  heating system the burner is slaved to the tank's temperature controls only, and the minimum burn time is a function of the tank volume, hysteresis of it's temp control, and the heat output of the burner.  When actively heating or DHW is being drawn during burns the length of the burn will be stretched longer than the minimum, but the minimum is always going to be a decent length, independent of the DHW & space heating loads.

Radiation is often SPECIFIED at, 180F, rather than "...designed for 180F..." as a means of comparing apples-to-apples.   At a fixed flow rate the BTU derating curve is fairly (but not exactly) linear, with flow rate further complicating the equation.   Manufacturers often publish a 140F number as well.  

For convecting panel radiators the 140F the output numbers are typically a bit more than 1/2 that of the the 180F rating, and 120F output is going to be a bit over ~1/3 the 180F number.  Some manufacturers supply charts/graphs for designing the correct output for the lower temp numbers with greater precision, but in lieu of manufacturer's data it's conservative to use a 0.35 derating factor on the 180F number as an estimate for the 120F output when designing to a Manual-J type heat loss calc for the room.  You could use 0.30 to pad it out, but it's a given that heat loss calculation itself is already padded, there's no point- it'll keep up even using the 97.5% binned hourly design temp rather than the 99% number for the heat loss calc.   A real hydronic design would also factor in the room-by-room temp drop along the loop for specifying the individual room lengths, etc, but for budgetary estimation purposes assume you'd need something like 2.5-3x the amount of radiator that you would at 180F if you're running the tank at 120F, but only 1.5-2x if you're running 140F.  (The actual factors depend on how much padding there is in the heat loss calc.)

If you're planning on using primarily 9" high units, ~9" tall radiant cast-iron baseboards such Burnham BaseRay or the Weil McLain equivalent have a comfort advantage (due to their higher thermal mass) over lightweight steel radiant baseboards.  They're more "classic" than than "slick modern" looking. and have about the same output numbers of the Runtal UF-2 series (6" tall).

Fernox is one of the major names in water treatment for radiant systems. They have a nice web site.

Open systems are those that are not pressurised, not closed, they have to be topped up to maintain the water level.

I can see that using drinking water might produce a simpler design but I would have thought there would be far too many negatives, especially health issues.

If you're planning on using primarily 9" high units, ~9" tall radiant cast-iron baseboards such Burnham BaseRay or the Weil McLain equivalent have a comfort advantage (due to their higher thermal mass) over lightweight steel radiant baseboards.  They're more "classic" than than "slick modern" looking. and have about the same output numbers of the Runtal UF-2 series (6" tall).

I am leaning towards the Runtal type units due to the fact that they are "slick" and "modern" - fits our home design as we are doing a pretty modern home design.

I did see on Runtal's site that they had a .38 correction factor for 120 degree water - so I will work from that.  I won't do to much yet, as I don't know what the slab temp will be, and I am not the expert.  I will leave the final numbers and sizing to someone who should know a lot more than I do!

I just want to make sure we aren't trying to spec something stupid to begin with!

Thanks!

"If you're planning on using primarily 9" high units, ~9" tall radiant cast-iron baseboards such Burnham BaseRay or the Weil McLain equivalent have a comfort advantage (due to their higher thermal mass) over lightweight steel radiant baseboards. They're more "classic" than than "slick modern" looking. and have about the same output numbers of the Runtal UF-2 series (6" tall)."

I beg to differ. The only comfort advantage would be in if the high mass radiators were used with a bang/bang control on a cast iron boiler, lowering the thermal oscillation - and subsequent AUST between burner cycles.

If I designed a panel radiator system with proper outdoor reset, the only thing more comfortable or efficient would be a radiant floor. Thermal mass is a double edge sword and can't be depended on for anything but resistance to change, both thermal and kinetic.

using drinking water might produce a simpler design but I would have thought there would be far too many negatives,

At some level, everyone runs hot potable water through pipes without problems - the fact that the primary purpose is to deliver hot water to a faucet isn't necessarily relevant. Some homes even recirculate this hot water and some heat inadvertently gets transferred to the floor above. But one needs to look at factors other than what you call it ("radiant heating" or "hot water delivery") to determine if there will be problems.

There is also the option of baseboard radiant (not the finned type)

I have seen it but not tried it, not enough output for my high demand situation but would work well in a reasonably insulated scenario.

Posted By BadgerBoilerMN on 19 Apr 2011 06:54 PM
"If you're planning on using primarily 9" high units, ~9" tall radiant cast-iron baseboards such Burnham BaseRay or the Weil McLain equivalent have a comfort advantage (due to their higher thermal mass) over lightweight steel radiant baseboards. They're more "classic" than than "slick modern" looking. and have about the same output numbers of the Runtal UF-2 series (6" tall)."

I beg to differ. The only comfort advantage would be in if the high mass radiators were used with a bang/bang control on a cast iron boiler, lowering the thermal oscillation - and subsequent AUST between burner cycles.

If I designed a panel radiator system with proper outdoor reset, the only thing more comfortable or efficient would be a radiant floor. Thermal mass is a double edge sword and can't be depended on for anything but resistance to change, both thermal and kinetic.

With that suggestion I was envisioning a K.I.S.S. tank-HW heater based constant-temp 120F water solution here, with bang-bang control on the pump.  The difference in comfort between low-mass & mid-mass baseboard radiators (are there any truly high-mass baseboards?) under bang-bang flow control with 120F water is subtle, but noticeable.

Continuous flow under outdoor reset mixer control (such as the Tekmar 360) is more comfortable, but may not be "worth it" in this low-load app.  It comes at  premium, with a near-zero effect on system efficiency (and not necessarily positive, when pumping power is factored in).   But yes, outdoor reset on the water temp eliminates the issue, maximizing comfort independent of the mass of the radiator.

Como- Runtal UF-2 & UF-3 (and Base-Ray, Snug etc.) ARE radiant baseboard, not fin tube. (And yes, it's definitely nicer to live with than fin tube.)

They look like Radiators to me, just not very tall.

I was thinking of Baseboard that looks like baseboard but also emits heat.

Posted By Como on 20 Apr 2011 09:29 PM
was thinking of Baseboard that looks like baseboard but also emits heat.

This is the best quote ever.

Posted By NRT.Rob on 20 Apr 2011 09:32 PM

Posted By Como on 20 Apr 2011 09:29 PM
was thinking of Baseboard that looks like baseboard but also emits heat.

This is the best quote ever.

Does Runtal UF-2 REALLY look like radiator? 

Or Burnham Base-Ray?

If it's thinner than 3", shorter than 10" and runs along next to the floor it looks mostly like baseboard to me... 

I s'pose there can be "eye of the beholder" issues/definitions applied, but I'm still calling it baseboard, and Como can't stop me!

If you went to your local lumber yard to buy baseboard would you expect it to look like that?

A profile example

Como,

This is an aluminum emitter with very low output even at design temperature (20% of standard fin-tube baseboard) and is of little value in all but the most specific applications.

Dana,

If you operate a conventional water heater at 120°F it will condense to ill effect. I design my small systems (and a new SIP home here in MN) with quiet sealed combustion, condensing tank water heaters "suitable for potable and space heating" with the use of a plate heat exchanger and outdoor reset. Tekmar is certainly acceptable but one of the most expensive ways to gitter dunnnn.

Morgan, which "quiet sealed combustion, condensing tank water heaters "suitable for potable and space heating" " do you recommend?

-Rosalinda

Morgan: I was presuming a condensing tank heater, so in that respect we were already on the same page, but how are you doing outdoor reset control on the heating system water with your condensing tank systems on the cheap? (I don't know of a cost effective way to do it, which is why I was thinking bang-bang flow control only.)

Como: I wouldn't go to a local lumber yard to buy baseboard, since they wouldn't likely carry the stuff I'd use.  The profile of Base-Ray (even the manufacturer refers to it as baseboard) isn't that different from the aluminum profile.  UF-2 may be slightly different in that it's at least POSSIBLE to mount it somewhere other than right at the floor, but it's not all that different. Runtal calls it baseboard too- go figure?

Thermaskirt profiles are substantially narrower than what the goods sold at the box store.   At about 2" UF-2 & BaseRay are both more comparable in overall depth dimensions to fin-tube baseboard (slightly thinner than most.)  Thirmaskirt is also non-convecting (unlike UF-2 or BaseRay or fin-tube), and I'd gather that output per unit length numbers are substantially lower too.

But I'd still call Thermaskirt baseboard before I'd call it a radiator.

I have just installed radiators, which amusingly emit heat through convection as well a radiation. They are designed to heat my considerable heat load (historic building) using relatively low temp water. Even if could have installed underfloor or these they would not have given me enough btu's. Or KW.

I would describe the product I exampled as a good option for those considering radiant floor, same sort of output.

They like radiant floor do not need to emit the same per ft as a radiator, you install it all around the room.

If you are considering radiant for an existing property with access issues for radiant floor, seems to me a worthy option. For new build you have more options. But then new build will have a very low heat demand.

Dana;

Cost effective is another matter. If you want cheap or even ROI you will not be using a condensing water heater.

And yet...

"Tekmar is certainly acceptable but one of the most expensive ways to gitter dunnnn."

...implies there's a less expensive way to get outdoor reset with a HW based heating system???

(There's no ROI to any of it, at Santa Cruz heating loads.)