Zurn Thermal Track basement walls

GroundUp

I've got a customer who is finishing a small 700 sq ft basement with low headroom and we decided on radiant walls. I like the Zurn Thermal Track but have never used it before, and I'm unable to find a submittal for it anywhere. It's one big open zone and the plan is to do the bottom 4 ft of each side wall in two 250 ft loops. Manual J shows a loss of 5600 BTU at design, and I'm having difficulty figuring out what SWT to use. We will use the existing WM boiler to serve it, which previously served 85 ft of 3/4" BB on the bare block. Yes, 85ft. The basement will now have R10 EPS against the block with a 2x4 stud wall inside, stuffed with R13 glass. The interior finished wall will be 1/2" lightweight sheetrock over the Thermal Track. 20* DT at .3 GPM per loop makes 6000 BTU right? How does that vary with temperature? Maybe that 20* Delta is at 120* SWT. Suppose the SWT is raised to 180* and flow rate remains the same, is there a way to determine what the DT would be? 30* in correlation with the SWT rise?

Jamie Hall

The BTU output varies with flow and delta T. But that's a little misleading. The BTU output of the emitters varies with their average temperature -- and is much greater at 180 than it would be at 120. There is a table for that somewhere... but as a very rough first pass it's more or less linear from zero at a 70 degree surface temperature to 240 BTUh per square foot at 212. So you are going to deliver about twice the BTUh from the panels with a SWT of 180 as you would at 120. Correspondingly, the delta T will almost double if you keep the flow constant (actually it won't go up quite that much, as it is the average water temperature in the emitter which governs output, not the SWT alone).

GroundUp

240 btu/sq ft at 212* (AWT?) with the 8" spacing of these particular panels? Where do those numbers come from? AWT would of course rely on DT to determine, so that's what I'm trying to find out a formula or chart for. I feel like I've seen it somewhere or perhaps Zman mentioned it somewhere but I cannot for the life of me find it now. Say 110* AWT with a 20* DT puts out 3k BTU per loop. In theory, a 180* SWT would bring maybe a 35* DT therefore a 162.5* AWT and put out 5,250 per loop? Rough numbers of course, but am I on the same page? A chart for this would be awesome if it exists... I know Wirsbo says not to exceed 120* SWT under gyp, but I'm skeptical of that being enough in a low mass system like this

hot_rod

When finished, this radiant wall panel is indistinguishable from a standard interior wall. Its low thermal mass allows it to respond quickly to changing internal load conditions or zone setback schedules. The rate of heat emission to the room is approximately 0.8 Btu/hr/ft2 for each degree Fahrenheit the average water temperature in the tubing exceeds room air temperature. Thus, if the wall operates with an average water temperature of 110oF in a room with 70oF air temperature, each square foot of wall would release about 0.8 x (110 - 70) = 32 Btu/hr/ft2. This performance makes it well-suited for use with low-temperature hydronic heat sources.

hot_rod

One thing to consider with wall or ceiling is the allowable temperature up against the Sheetrock or wall covering. Some suggest limiting to 120 temperature, so a 115 to 120 max supply. Above is the multiplier to estimate wall output.

You mentioned a 5600 btu load, what is the floor space dimension? determine required btu/ sq ft. Then use ambient room temperature desired in the formula.

As you can see radiant walls and ceilings have a higher output due to higher surface temperatures, so you should have plenty of output at temperatures below 120 SWT

Radiant floors might design around a tighter delta 10-20 for consistent floor surface temperature. Not to worry about that with walls and ceilings, unless you plan on walking the walis

Zman

This model should be pretty close. It works out to 114 degree water and an 11 degree delta.

GroundUp

Very good information, that's just what I was looking for. Thanks gentlemen! @Zman what program is that?

Zman

It is Siggy's Hydronic Design Studio.
It lacks specs for many of the newer circulators. It does give you the pressure drop so you can always use those numbers to plot the curve yourself.
I think the still do a free trial.
https://www.hydronicpros.com/software/index.php?id=20

Gordy

One thing to keep in mind is furniture placement along walls which can block output, and decrease response time.

Depending on what the room will be used for this could be a point of interest in the design.