Radiant Heat Warmup - Cold Slab

superchimp

Hi all

We're just starting up a WM Eco Tech 110000 btuh modulating condensing boiler on a radiant floor system in a pole barn. The barn has been cold all winter until now (NE USA) and slab temp is about 32 f.

Slab is insulated. R10 board to 2 ft below top of slab on edge, r7.5 board under entire slab. 12 loops 1/2 inch about 240 ft per loop. Fluid is 20% methanol, 80% water. Building is well insulated and is spray foamed. 

My question is simple... The system is up and running now but we want to avoid thermal shock and cracking on the slab. What is a good starting water temp? Currently I have it set to 60-80 f based on OA reset and plan to increase the temp daily.

Thanks in advance!

Jamie Hall

That should do. If the slab is properly reinforced, I very much doubt that you can put enough heat into it to develop any significant cracking.

hot_rod

no harm in ani harm in a slow warm up. I suspect you could let it run as designed and that size boiler on 2800 sq ft would not be shocked. Curious about the methanol blend? I don’t think any of your components are approved for alcohol blends?  An inhibited hydronic glycol  would be a better option.

superchimp

hot_rod said:

no harm in ani harm in a slow warm up. I suspect you could let it run as designed and that size boiler on 2800 sq ft would not be shocked. Curious about the methanol blend? I don’t think any of your components are approved for alcohol blends?  An inhibited hydronic glycol  would be a better option.

Thanks. I just get a little terrified about cracking slabs given the amount of engineering time that has gone into this structure.

Hmm. I'm not aware of any issues with running methanol, but I have seen some of your past posts on this subject. I've done a lot of work with methanol on the geothermal side. Similar pumps etc. for a pressurized geo system. My understanding was most people use PG because it's safer and easier to find (which I agree with). The problem with PG is significantly degraded system performance.

Any known history of issues with methanol?

EDIT: I think one of the big concerns is boiling point. Boiling point for the methanol-water solution is 190 F+, way more than the future setpoint of the loop. Another concern is whether the solution is corrosive. I haven't heard any evidence of that issue happening either. The other concern is that methanol isn't a safe chemical especially if you connect boiler feed to domestic water (hopefully through a BFP). I am 100% in agreement that that should not be done.

Honestly interested here.

Zman

What is the brand if the methanol product?
I think it is wise to consider the rate of rise. I suspect that the laws of thermodynamics will prevent the slab from being damaged. It will take a good long time for a boiler that size to raise the slab temp.

hot_rod

superchimp said:

hot_rod said:

no harm in ani harm in a slow warm up. I suspect you could let it run as designed and that size boiler on 2800 sq ft would not be shocked. Curious about the methanol blend? I don’t think any of your components are approved for alcohol blends?  An inhibited hydronic glycol  would be a better option.

Thanks. I just get a little terrified about cracking slabs given the amount of engineering time that has gone into this structure.

Hmm. I'm not aware of any issues with running methanol, but I have seen some of your past posts on this subject. I've done a lot of work with methanol on the geothermal side. Similar pumps etc. for a pressurized geo system. My understanding was most people use PG because it's safer and easier to find (which I agree with). The problem with PG is significantly degraded system performance.

Any known history of issues with methanol?

EDIT: I think one of the big concerns is boiling point. Boiling point for the methanol-water solution is 190 F+, way more than the future setpoint of the loop. Another concern is whether the solution is corrosive. I haven't heard any evidence of that issue happening either. The other concern is that methanol isn't a safe chemical especially if you connect boiler feed to domestic water (hopefully through a BFP). I am 100% in agreement that that should not be done.

Honestly interested here.

Just reading the SDS sheet makes me nervous and this is a specific GEO ethanol based fluid. Seems like the product name doesn't match up with the safety data sheet

Is the methanol less dangerous?

One pump manufacturer told me their circulators are not designed or approved for pumping flammable fluids, they consider any alcohol blend any % to be flammable. They were experimenting with resin coated volutes because the alcohol mixes were corroding the cast quickly, maybe inhibited fluids address that?

I wonder how the boiler folks feel? Pretty low flash and boiling point? Wall temperature in a boiler can run 300° +
To me the performance difference between alcohol and PG would not balance the risk.

Jamie Hall

Methanol is toxic. It's a nerve poison, and ingestion leads to blindness and death, depending on how much you get into yourself. Ethanol is the alcohol it liquor -- and is not, strictly speaking, toxic. Both are highly flammable, and both depress the boiling point in water-alcohol mixtures.

Because they do tend to evaporate quickly, they have some advantages when used in applications where a spill could be problematic -- this may be why they are used in the geothermal industry.

All by themselves they are not, strictly, corrosive -- but they do pick up moisture. This is not a problem in uses as an antifreeze, obviously, but in fuel mixtures, such as ethanol added to gasoline, this can be a big problem. They also attack some gasket and o-ring materials.

The major advantage over glycols as antifreeze is that they are cheaper and their heat transfer properties are better.

ewang

Compressor-driven geo systems experience much lower fluid-HX interface temperatures, because its a refrigerant-fluid interface rather than a combustion-fluid interface.

I'd be a bit worried with the flamability of the methanol mix myself