Interesting project - BUT

Glen

Interesting call the other day - and finally visited the home yesterday. Timber framed/straw bail/adobe construction. HO has poured the slab (4 inch concrete with 4 inches of SM below) with 2 - 200 foot loops of pex in main living area and about 150 - 200 feet in the the entrance. This is not hePex - looks like heatlink potable pex. He is now using the system with copper wrapped around his wood stove flue and a small 15-42 pump - says it doesnt work well. Would like a propane boiler and a simple control system. Would like this to operate on 3 - 500 watts of energy or less. (Solar/batteries/inverter) and he's not ungrading his power source for some time. Every brain cell is telling me to run away - write this HO a nice letter and say - Thanks but no thanks. But - this does have some interesting challenges ... low power consumption, environmental accountablility, etc ..... but that pex in the slab worries me. Advice anyone?

hr

Try

calling Dale at 406-587-3448. They do a lot of remote radiant in NW Montana. They have plenty of experience with PV operated systems.

I tried that exact HX design once. I wrapped a bunch of 3/8" copper around a 55 gallon barrel stove. Wild times More of a steam boiler really!!

hot rod

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Glen

we do that when ..

we're in the bush hunting. 2 coils of copper in the fire pit circulating water to a 5 galllon pail - works great. But back to the HO - would your contact in Montana have an email? (send it privately??) Wouldn't mind bouncing this off someone who has done a few remote installs. Basic mechanics here might be ok with pex in slab etc - it's the low power requirements that are interesting. As technicians we're used to hooking up transformers, tekmars, lots of pumps etc - and don't worry about the watts. This install must be very low consumption.

Duncan

Don't be afraid.

I've done a few remote installs. Used thermostats wired directly to the battery bank (that's right, DC power) by disabling the tstat anticipator and using the tstat to pull in an ultra-low power Potter and Brumfield relays. In the DPST configuration they actually use less power than parallel solid state relays.

One pole of the relay switches the boiler boiler AC (and transformer) into the inverter circuit, the other pole switches either the circ or zone valve. Inverter stays asleep untill the tsat calls for heat. DC wakes it up, relay switches the AC power for gas valve and circ. Simple.

You should have no problem finding a wet rotor circ like a Grudfos 1518 stainless that uses less than 75 watts, and can handle the oxygenated water. Gas valve is another 8 watts, maybe 8 watts for each zone valve, if used. For a small home,I'd keep it one zone. Some small parasitic losses for the transformer, maybe 5 watts, and losses inherent in the inverter.

hr's contact will likely go even more direct, cutting out the inverter and going directly to a DC pump and thermostat with millivolt boiler. Proprietary equipment, the pump, but best option for absolutely lowest power draw. Every design has its tradeoffs.

For applications in my area, if it's not a space station, I prefer to use off-the-shelf components that are easily obtained/replaced, and sacrifice some small parasitic losses for the convenience of parts that are readily available. But your customer may not see it that way, his system may need that extra few watts.

Present the owner with options and let him decide.

Glen

great ideas -

and I'm leaning hard towards a mv boiler, rewinding a couple of Grundfos pumps to 12 vdc - am just checking now with local rewinder re price and consumption. Once full Trace inverter setup (2500 watts) is installed - the power consumption becomes less of an issue. Using a thermostatic (Danfoss)three way - I can get by with two pumps - one zone and this would make the whole install super simple for the HO. He has grid power nearby - and I can't question his lifestyle - but he'd rather pour a little diesel into the generator than pay BC Hydro a dime! Oxygen still a worry and I'll look into the pumps you have recommended.
Cheers from the Canadian Rockies.