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Old 01-19-13, 06:14 PM   #1
randen
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Default Under Pressure

Well its happened, The bad luck part. So far the 3.5 ton homemade GSHP was keeping the shop comfortable without any problems. The two details left to tie up was; the loop still needed the propylene glycol. This would prevent the tubes going up the side of the building and in from freezing as well if it ever happened that we reclaimed so much heat from the ground loop as to cause the evaporator HX to freeze up. Also there was a tiny-weeping stubborn leak in a spot I needed to remove the HP to get at it. It was so small the little puddle dried on the heated floor infront of the unit.

I wanted to be professional with professional results. Pulled the unit out tightened the fitting. (it would seem the temperature cycles had loosed the fitting.) Repair made, re-installed no leak all is good. Now the proplyene glycol. Obtained some glycol from my new friend 80 ltrs for a 33% mix and actually drew it in with a vacuum pump no mess not a drop on the floor. Topped off the loop with the addition of water and pressurized the loop. Started the GSHP and purged the air (or so I thought) Ran the system for an hour checking the purge valve. no more air. HMM Somewhere out in the ground loop the un-known air bubble was waiting to cause a world of trouble.

Hind sight.: The system was running fine. I just left the ground loop pump run continuosly during the sub-freezing temps. Not expensive, maybe $20.00 worth of electricity per month. Although the little leak really bothered me I could live with it for a while. The other facet was, if I had a problem, the heat would be off when its cold and we had a big meeting to be held in the office latter that week. In the back of my mind "just leave it alone for now"

But I thought IT WILL BE NO PROBLEM, HA!!

Getting back to the shop, 4 hrs after the repair and purge--The biggest frost ball I have ever seen. The evaporator HX was froze beyond solid. That air-bubble hidding from me out in the ground loop made it in to the circulation pump stopping any flow. As the glycol hadn't had time to mix the water in the evaporator HX froze and burst my HX jacket.

My worst night mare had come true!!! As they say in the movies "now its become personal."

Frustration at 200% tore out the heat-pump again, evacuated the refrigerant and rebuilt the HX. All the while the shop is getting cold.

Remembering BradC talking about a 3 phase compressor coupled to a varible frequency drive VFD. This infinite control can soft start {LOW CURRENT }(no light flicker on start-up) and speed control the compressor for varible out-put. No start capacitor or relay required. Some VFD's have extra I/O for say circulation pumps. And being exposed to this type of VFD control now common in machine tools and the efficiency they have. This is the holy grail.

OK heres the new plan. Don't really have the time, but my bad luck has forced my hand. I have an inexpensive, new 5 ton scroll 208V 3phase compressor on its way to the shop and the original 3.5 ton GSHP still not assembled with the rebuilt HX awaiting the swap-out with a new compressor and VFD. For some reason 3ph motors etc. have a low value when it comes to resale price. I have seen industrial motors, 3ph. sell for $1.00/HP.

Brad C has been experimenting with Electronic Expansion Valves (EEVs). This coupled with the VFD. WOW. Varible compressor speed with varible expansion valve what could be better. Can you imagine a heat pump that will start slowly and quietly and ramp up to full capacity to bring on the heat quickly and slow to a more moderate speed as the heat is starting to flow reducing operating costs, or any desired profiles.

For now I had to install the little 2 Ton that of which was my first attempt at building my own GSHP. It will have its tongue hanging out running 24/7 and its going to be cold here in the next couple weeks. By the time I end up with my final unit all the soldering I've been doing I could have plumbed 3 houses.

The two photos, The 3.5 ton unit awaiting the 3phase swap out. The poor lowely 2 ton trying to keep things from freezing.

The pressure is on to complete and install the inverter drive homemade GSHP before the Canadian freezes

Randen

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Old 01-19-13, 10:03 PM   #2
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A note about the variable speed drives.....there will be a minimum speed needed to get proper oil return, perhaps 30% of max depending on the pot (compressor) AND, as the new one is a 5 ton pot and your HX is sized for 3.5 ton, you will have to keep the max speed down a bit.

I've got more glycol if you need it too
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Old 01-20-13, 10:03 AM   #3
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Quote:
Originally Posted by randen View Post
Well its happened, The bad luck part...
Randen,

Very sorry to hear of the major catastrophe. And at the worst time, too.

But what exactly is this white thing?


... have you invented a hybrid plastic/copper HX? Looks very interesting. Can you say more about the details, for instance, how you got it to not leak? Also, what are the approximate dimensions of it? Length, diameter, etc.

Best,

-AC
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Old 01-20-13, 11:04 AM   #4
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Default Frozen HX

AC-Hacker

The hybrid heat exchanger your looking at is a hose thats typically used in whirlpool/hot tubs. It is 1 5/8 ID It 26 ft long and encompasses 3 pcs 3/8 copper tubes (twisted for turbulance) It has about 11 squre feet of copper surface area for heat exchange.
In heating mode the delta T looks good The refrigerant left the heat exchanger 1-2 degrees lower than the loop temp going in.

In air-condition mode as the air handler would have a delta T of 15 deg C or so the water would enter the HX at 20 deg C and drop to 5 deg C With a large amount fo heat leaving the condenser the evaporator was really cold
-15 deg C. I noticed through the day that one of the three copper tubes began to freeze than another followed by the last. I'm thinking that in air-conditioning mode with no antifreeze given time the icestarts to coat the copper tubes and migrates up the HX as the ice esentually insulates the copper tubes. This is another reason for the inclusion of antifreeze.

Back to the rest of the story. As the ground loop circulation pump cavitated in air the ever-expanding ice in the HX caused the outside plastic shell to split. And it made me grumpy.

To answere your last question. How did you prevent it from leaking double hose clamps and custom stainless ends. See photo of assembly this is the condensor only 2 copper tubes.

My new 5 ton 3 phase compressor awaits me at the border. Guess who's passport just expired.

Randen
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Old 01-22-13, 09:41 AM   #5
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Default Under Pressure poor little 2 Ton

For an emergency stop gap the first homebuilt GSHP has been put in place. The outside temps have been dropping to 0 Deg F. with wind. Burrr. The little thing has been humming away 24 hrs not breaking past 48 Deg F. The office with the infloor heat has not past 65 Deg F. so the air temp is about 55 Deg F.

At-least the in-floor won't freeze that would be disasterous.

Burrr.
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Old 01-22-13, 07:29 PM   #6
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I was wondering if the glycol reduced the performance enough that this might happen. What pump do you have? I bought a rotameter flow gauge which should be here in 10 days or so. I will use them to get some more accurate reading of the heat delivered to the HP and coming from it.
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Old 01-22-13, 07:57 PM   #7
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Mike I pulled a little glycol/water mix out and checked it with my refractometer but the scale only goes to 15% so just a guess because it was off the scale 20-25%. As I had played with it I really couldn't notice any viscosity change. I left some out-side and opps, it became slush at -12 Deg C and became solution at -10 Deg C. Going to need some more Propylene Glycol. I'll just leave the circ. pump run.

My concentration is on the new compressor & of coarse the work thing. The delta T in and out of the HX is only a spread of 1-2 Deg C. I don't think flow is the problem. Just the installer didn't assure all the air was removed.

Still Burrr
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Old 01-22-13, 10:59 PM   #8
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Quote:
Originally Posted by randen View Post
...Guess who's passport just expired...
So, your wife's gonna drive to get it?

-AC
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Old 01-23-13, 06:42 AM   #9
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AC

With My wife's thick Spanish accent and odd looking passport. They may detain her and I won't see either the comp. or her for days.

Randen

Woke up this morning to -18 Deg C (-2 Deg F) But wind is very low.

Really Burr

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Old 01-23-13, 07:30 AM   #10
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-20 here when I woke up, and I have to start to wire in a PV system today . Doax probably thinks we are just whiners given that he could see -30C regularly.

If you can hold on for a week, I might be coming out to your area. I snapped off a wheel stud on the truck (over torqued) and I need to replace all of them before I go on the highway.

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