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Old 05-16-11, 06:09 PM   #1
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Default Hello from Milwaukee, WI

Found this site because I've been lurking over at eco-modder. Great Site here! I've been tweaking my hydronic heating system for years now, but an oil-fired boiler is hell to clean. I'm interested in ground source heat pump systems and have been following AC Hacker's posts.
I took an AC motor from an old washing machine and bolted it into place on a walk behind mower where you'd expect to see an ICE, and enjoyed a season of lawn mowing that was so quiet I could hear the birds chirping while I mowed.
I do have trees, so had to be a bit strategic about how to mow without wrapping up the very heavy duty extension cord, but it was no big deal.
Here's to reading many more interesting posts at this site...

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Old 05-17-11, 09:05 AM   #2
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Welcome to the site Weed Dog.

We'd love to hear more about your home made electric mower. Perhaps you could start a thread on it?
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Old 05-17-11, 09:51 AM   #3
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Default The AC powered Walk-Behind Mower

Alas, the AC motor met a smoky death. Before I appreciated the need to use a properly-gauged extension cord, i.e., 12 gauge, I mowed the back forty using two 14 or 16 gauge cords and burned out the motor.
Wiser now, I'm on the prowl for another AC motor at "curbside" pricing. Anyone getting rid of an old washing machine?
I got the engine-less mower deck and handle for nothing, the motor was free after I helped move the washing machine out of a basement, and a handful of nuts and bolts, a bit of angle iron and wiring, brought it to life.
Lawnmower blades typically rotate at 1800 to 3600rpm, and this motor topped out at 1750rpm, a fairly common speed for its' intended application. Still, the mower worked well with the homemade blade I put on it. I made a blade because the motor shaft spun in the opposite direction from the shaft on the ICE, and while it was possible to reverse the motor, I'd read that doing so might sacrifice a few rpm, possibly even some torque(?).
The "deadman" or kill switch on the original mower became the on-off switch for the motor, hence the switch was used for much the same purpose as originally intended. One upgrade I'm researching would be a disc brake on the motor shaft to stop the blade more quickly, and devising some way to have it engage automatically should the kill-switch open. Maybe a relay connected into the switch circuit...
I'm also toying with connecting the motor shaft to a blade shaft via belt or chain-driven pulleys that are sized to increase the blade rpm, to see the effect on grass-cutting effectiveness. The motor does take a few seconds to spool up to speed. A crude strain relief on the handle keeps the cord up and away from the mower deck.
Fun, fun, fun, and quiet. No earplugs needed. And maintenance? Clean and sharpen the blade as needed. No spark plug to clean or change, no carb to clean or adjust, no fuel to drain or replace, no filters to replace. I'm using already-generated electricity. (Help! my carbon-feet are shrinking!) Mowing around trees becomes a mental game...where will the cord be if I...
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Old 05-17-11, 03:31 PM   #4
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Welcome to the forum. It's good to see another Wisconsinite here.
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Old 05-17-11, 07:28 PM   #5
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Quote:
Originally Posted by Weed Dog View Post
Found this site because I've been lurking over at eco-modder. Great Site here! I've been tweaking my hydronic heating system for years now, but an oil-fired boiler is hell to clean. I'm interested in ground source heat pump systems and have been following AC Hacker's posts.
AC_Hacker here...

The GSHP and Hydronic floor is a match made in heaven... but the key word is "match".

I'm guessing that your radiant floor is already installed... and that it was designed for an oil-fired boiler.

With this combo, the boiler can output 140 to 160 degree water easily. To match this, floors are usually designed with loop spacings every 9 to 12 inches (usually 12 inches. Or the floor uses tubing underneath a suspended floor. This will all work out if you have a high feed-temperature system.

GSHP run well at lower temps, so some GSHP can hit 120F, but at reduced efficiency. They are much happier (and cheaper to run) at temps between 90F and 110F. So to get the heat into the room, you'll need to space your tubing closer... like maybe 6 inches. This is less than the bending radius of 1/2" PEX will allow, but if you run staggered rows, it is possible..


...here's a photo of what I mean... Only this is an underfloor setup, it should be possible to do something like this inside a slab or on the surface of the floor.

Under floor hydronic heating is not so good for GSHP...

-AC_Hacker
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Old 05-19-11, 03:48 PM   #6
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Default Under Floor PEX Efficiency

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Originally Posted by AC_Hacker View Post
AC_Hacker here...

The GSHP and Hydronic floor is a match made in heaven... but the key word is "match".

With this combo, the boiler can output 140 to 160 degree water easily. To match this, floors are usually designed with loop spacings every 9 to 12 inches (usually 12 inches. Or the floor uses tubing underneath a suspended floor. This will all work out if you have a high feed-temperature system.

GSHP run well at lower temps, so some GSHP can hit 120F, but at reduced efficiency. They are much happier (and cheaper to run) at temps between 90F and 110F. So to get the heat into the room, you'll need to space your tubing closer... like maybe 6 inches. This is less than the bending radius of 1/2" PEX will allow, but if you run staggered rows, it is possible..

...here's a photo of what I mean... Only this is an underfloor setup, it should be possible to do something like this inside a slab or on the surface of the floor.

Under floor hydronic heating is not so good for GSHP...

-AC_Hacker
Above you find AC Hacker's commentary. I'm reading up on GSHP and doing some preliminary measurements and calculations, and may attempt a small-scale, proof-of-concept installation and measure the performance of same. My home has finned-tube baseboard radiators, most installed on perimeter walls, a set-up that would not lend itself to connection to a GSHP, given that the water from my oil-fired boiler is heated to 160 degrees and a GSHP would heat water to about 90 to 110 degrees, optimally.

The home is a two-story, balloon-framed farmhouse, built in 1903, though I've done extensive remodeling to reduce air infiltration and between-the-studs air migration, sealed the exterior walls and foundation, and thickened the insulation. I also moved the stairs, moved the first-floor bathroom and kitchen, resized and reshaped the first floor rooms, moved, resized, added and replaced windows, finished off the second floor (it had been a huge, cathedral-ceilinged, knee-walled and uninsulated attic of sorts since 1903) and have lived in this on-going experiment for some 23 years.

The unfinished basement ceiling gives me access to the underside of the first floor, where I could run loops of PEX, as illustrated in AC Hacker's photo. While my finned-tube baseboards heat primarily by natural convection, and I suspect to a lesser extent by thermal radiation, the underfloor-PEX installation heats by conduction. I note the PEX is secured by metal (possibly aluminum) heat transfer plates which aid in transferring heat to the floor. I suspect a bit of thermal radiation may be in play here, too.

I've seen and read about underfloor PEX installations which were rendered less effective due to the casual and untutored manner of the installation. Some installers simply stapled the PEX directly to the subfloor. Only a small arc of the exterior face of the tube actually contacts the subfloor surface, reducing the efficiency of heat conduction. And, you can imagine, some sections of the PEX may not actually touch the underside of the subfloor. Heat transfer in these locations occurs primarily by convection, which will not be very efficient if the water in the PEX is only 90 to 110 degrees. The use of heat transfer plates is vital because they have a “U-shaped” cross section. The PEX is pushed into this groove, allowing much more of the exterior face of the tube to contact the plate, increasing the efficiency of heat conduction. I've also seen projects in which the space between the floor joists, after PEX installation, was left open, i.e., completely uninsulated. Insulate that space, effectively enclosing the PEX in a sealed cavity, and less of the heat is lost downward to convection and radiation.

Were I to build a home from scratch, I'd install a thin-slab radiant floor. But until that ship comes in (and I just received an iceberg advisory), I'm going to tinker with an underfloor PEX-style install, optimized to any reasonable degree possible.

AC Hacker's shows two PEX runs between joists. But you could squeeze in three runs between joists. Many of the commercially-available heat transfer plates are five inches wide, the space between 16” O.C. joists is 14.5”, so some trimming of plates, or a 90 degree bend on the outside edge of each outside plate, and voila, three PEX runs between joists. Or you could make your own plates...

Still to be considered are the responsiveness of such a system, (GSHP, remember) to a call for heat (I suspect that in such systems “overshooting” the called-for temperature is not common), and...?

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