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Old 07-12-15, 05:07 PM   #1
stevehull
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Default Hacking a 12K BTU water source heat pump

Recently I posted on a problem I am having in my guest house. It is tight as a drum, well insulated, but getting moisture out is a problem. When not occupied by guests/friends (most of the time) , I set the thermostat to about 83F (in summer). Running a 600 watt dehumidifier does remove moisture, but it adds heat. Against my Yankee heritage . . . .

The existing two ton geothermal heat pump in the unit barely runs enough to remove water vapor at that air temp set point. I am in Oklahoma and the average daytime high temp here is about 95 or so. At night, (relative humidity of 100%) it dips to 75 F, but the air is also at the same dew-point. I bet that is where the moisture comes from.

What to do . . . . My wife and kids were gone to cousins this week, so I had the place to myself. Time on my hands . . .

This past Friday, I went to my friends at the local AC shop (are dealers for both WaterFurnace and Climate Master) and told them my problem. At low cost, I have done a lot of consulting for them over the years and they told me to go search the "junk trailer".

So, I scavenged though their trailer and got run out by wasps. Two cans later of "knock down spray" and I got lots of old and disused junk. My "find" was an old two ton R22 unit (circa 1988) with a bad compressor, blown out electronics, a bad blower motor, etc. Got this for scrap price ($2). The cabinet was most value!

Then, they found an old, old 120 VAC reciprocating compressor "about the right size" and gave that to me for $10. No literature, but looks unused. Found out later, it is a lot smaller than the old one in the unit, but the price was right. It came with capillary tubes, and Schrader like valves, but looks like it was made in the '70's. The shop boys are calling my vision - Hull's Frankenstein. The damn wasp spray was almost more than the cost of parts.

Borrowed a tank of dry nitrogen and they said compressor should have oil in it (it does slosh a bit when inverted).

Friday, I troubleshooted and have replaced the burned out relay (fried contacts), fixed up the motor blower bearings, soldered in a new wire to the 1/12 HP AC blower motor, replaced the shorted starting capacitor, rewired the electrics and have sweated in the "new" compressor. Also found out the low voltage AC transformer was shot (primary to secondary short), but found one of those in the parts bin here.

I have wired it up so the reversing valve can work (it does mechanically "sound like" it works) and will use the capillary tubing from the new compressor.

The evaporator condensate pan was rusted and had a few holes. The "new" condensate pan is now a used (but cleaned of paint) plastic roller pan with a hole drilled in it and a silicon sealed tube. One attraction is that these paint pans are tilted so there is now better drainage towards the drain tube.

So far, the blower spins (no bearing squeal), the transformer energizes the relay and I have 120 VAC into it. Gonna get free R22 as they thought the BBQ gas was a joke (it wasn't and it isn't!). But it is all the right price. Yes it is kludged up, but this will give me a small unit that you simply can't buy.

This AM, tested the water lines and they hold pressure with no leaks. Put a gate valve on the water inlet side and adjusted valve for a water flow of about 2 GPM. Re insulated all the evaporator lines with wrap on foam tape. All old insulation was just "crunchy" and turned to black dust when you removed it.

My calculations indicate a current draw of about 9-10 amps. Very hard to read the old paper label on the compressor. Given the size of the compressor and evaporator coil, I expect about a 30 F delta t across it and some 200-400 CFM from the blower, I hope to get about 14,000 BTU (1+ ton) out of it. Not a great EER if my current calculations are correct . . . .

Have done a LOT of soldering and welding before, but never brazing. This copper brazing was really quite easy. Started on some scrap copper. Used dry nitrogen as a flow through purge to prevent interior scaling. As AC has suggested, "cherry red" is the color you want, then the rod just flows . . . .

Purged, then filled compressor and lines with nitrogen; hope pressure will be there tomorrow. So far, at four hours and no drop in pressure.

Tomorrow, the boys are coming out in the AM with a tank of R22, a super vacuum pump and drier. I hope and pray that this works or I will be the butt of many of their jokes!

But it has been fun!


Steve

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Old 07-12-15, 09:09 PM   #2
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Awesome, after 4 hours and no pressure loss, I would say the circuit is not leaking. Good luck in the morning.
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Old 07-13-15, 07:49 AM   #3
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Sounds like quite the contraption. Looking forward to hearing results.
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Old 07-13-15, 10:59 AM   #4
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Well it works! The shop boys state that my "Frankenstein" lives.

It is in the shop and cooling. Been running for about two hours. So far here are the stats.

Input water temp 65F, output water temp 80F (delta t of 15 F)

return air 75F supply air temp 45F (delta t across coil of 30F)

return air rel humidity 50% supply air rel humidity 95% (almost saturated, so the low fan speed looks good

water flow ~ 1.5 GPM (6 L/min) I may adjust this to 2 GPM to see if BTU output goes up.

condensate volume output 0.6 oz per min (20 ml/min)

at 115 V ac, it draws about 9 amps ~ 1 kW.

I will try to find an air flow meter tomorrow to measure the blower output in cfm. With that info, I should be able to calculate the effective BTU/hr output.

Or do I have enough info right now?


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Old 07-13-15, 04:42 PM   #5
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Well, I have to replace the blower motor. It froze up and died a squealing death. The bearing "fix" did not take. Right now, I have a box fan on it and that keeps the evaporator coil from frosting up.

But it is sucking water out of the shop like crazy.

Question for the group. Now thinking of replacing the reciprocating compressor with a scroll type. The EER of this unit isn't great (12 or so). Am thinking of getting a better coil in coil heat exchanger also. Saw a few of those in the wasp den . . . .

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Old 07-14-15, 04:17 AM   #6
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Grab another blower motor from the boneyard, raise your flow rate, and see how it fares. If it works, button it up and show the men who helped. At first glance, what you have built from recycled junk may seem trivial, but it is in fact the opposite. People just don't do much of this any more. Take lots of pics. Show us.

When you visit the boneyard, find some new guts along with your new used motor. For an r22 based system, compressors abound in units on the second hand market. Just pick a capacity and start looking on bookoo or Craig list. I found a few12kbtu window units for 20 bucks last summer. A carrier and a Haier came home with me.
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Old 07-14-15, 10:47 AM   #7
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SH,

Congratulations on your successful hack, can't wait to see the pics.

* * *

In your original post, you spoke of the RH being extremely high...

Quote:
I am in Oklahoma and the average daytime high temp here is about 95 or so. At night, (relative humidity of 100%) it dips to 75 F, but the air is also at the same dew-point. I bet that is where the moisture comes from.
I have precision RH measuring instruments, and living in Western Oregon, I have plenty of experience with rain. I have measured the RH while it is raining, and my RH readings are about 93% to 95% or so.

RH of 100% means that you are well past the point of the air's ability to hold water vapor, and liquid water is well into the process of precipitating liquid from the air, in other words, it is raining. With that as a starting condition, any drop in temperature would continue the raining condition, it will not accelerate it, because the precipitation is already at maximum rate. This is very extreme, to say the least. If this is the steady state case in your area, it would indicate that you are living in a tropical paradise.

I never really thought of Oklahoma as a tropical paradise...


Above is a screen grab of yesterday's Arcadia weather. The RH is not approaching 100%. In fact, it's only getting to about the 70% level at night.

All of which indicates that you have somehow created a tropical terrarium, and you are referring to it as a 'Guest House'. Lucky guests, if they happen to be ferns!

You stated in the first sentence, regarding the guest house, "It is tight as a drum". This could be part of the problem...

But if the above weather chart is typical for your location, then there is some condition that is continually forcing water into your guest house, and there is no way for the water-soaked air to get out.

Continuous mechanical ventilation would be an obvious solution, but it still does not address the root of the problem, which is the forcing of water into the enclosed space.

Is the Guest House on slab? Is there a water barrier between the wet earth and your slab? If there is not a completely effective water barrier, then this would be continuously pumping water in, and the floors will be continuously wet.

If ambient conditions actually are as severe as you describe, nightly roof condensation run-off could be finding it's way into the interior of the GH. Check the roofing and rain drain system for failures.

From what I see, it looks to me like mechanical moisture removal is a patch, while the real cause goes unaddressed.

-AC
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Old 07-14-15, 10:59 AM   #8
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Are you going to be using this contraption as a heater, cooler, dehumidifier, or all of the above? If your existing gshp is providing too much cooling, you could run into the same problem with this. Of course, you could run a desuperheater on the condensing side of whatever you build. This could give you domestic hot water or rewarm the dehumidified air stream. The possibilities are endless at this point, while the rig is still on the build process block.

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Old 07-15-15, 07:37 AM   #9
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This year, humidity is a problem here in Oklahoma this year (lots of rain). Our yearly rainfall is ~ 35 inches and we have already had that with almost 15 inches in the last month.

I misspoke about the 100% humidity . . . , it is very high and unusually so for this geography. In the early AM, the pasture grass is wet, wet and walking through it will soak your boots and pants. Unusually damp. This is more like Mississippi/Alabama weather!

Just looked at the weather data at 6 AM and the temp (75F) is just above the dewpoint (68F) with a relative humidity of 79%. Last night, before midnight, the dewpoint was 76F. This is very humid! In the daytime, the air temp goes to mid 90's F and the dewpoint may drop a bit, but it is still quite oppressive.

The guest home is built up on piers, the dirt floor is completely covered with plastic and "skirting" surrounds the periphery. Moisture is not coming in there and the skirting allows ventilation without snakes. No roof leaks either. The only sources of water in the house are the drains, toilets, sinks, etc. When not in use, I turn off the water valve to all those so there is not an inadvertent flood from a blown out valve or something. This house can go for weeks with little use. Accordingly, not much need for AC or heat. No mold, no inside condensation, but if no AC at all, then a slow gradual buildup of relative humidity up to the 62-64% range. And at that level, you will get mold.

Therefore the need to run the AC to remove moisture and therefore the conundrum of the AC capacity being too large. The existing geo heatpump, running at stage 1 (~16,000 BTU) kept the house at 75 F in the coldest of winter nights (0-5F) running almost 100%. This delta T (70F) with an 16 KBTU input shows a remarkable amount of insulation. I mention this as a summer delta t of only 10F (inside to outside) means the AC geothermal unit hardly runs at all and consequently does not remove sufficient moisture.

Normally, our July midday dewpoint is in the high 50's to low 60'sF. With a breeze, this is certainly tolerable. And at night, we don't normally have the oppressive high dewpoints with wet grass in the AM.

This 12 K BTU hack may even be too big for the guest house to remove moisture. It is in the SIP shop now and doing a GREAT job of removing moisture and lowering the air temp. The volume of that space, 36K CF, cools to about 25F off the daytime high with Frankenstein running. The condensate continues to pull out moisture (8 oz every 18 minutes). This floor of the SIP shop is made of concrete pavers on dirt and that subsurface dirt is drying out rapidly.

I have a broken dehumidifier (broken fan motor) and the compressor is an R22 unit with a 6 KBTU capacity that draws about 250 watts (according to plate). That may be about right just to dehumidify the guest house when not in use. I can use the evaporator in that unit, coupled to a coaxial heat exchanger, to serve as a small AC open loop unit.

The local dealer's boneyard has a lot of old geo units and I bet I can scrounge up a coax exchanger for the cost of killing wasps. If I am correct (please check), I can use a coax unit that is larger in capacity. I can use the existing dehumidifier box, the scroll compressor, electronics and evaporator in place.

I know, . . . there are new variable speed geothermal compressor units out there that can modulate between 5 and 110% compressor speed. They do a simply outstanding job of removing moisture at very low cost, but the purchase price is astounding.

Today's job is repairing the blower motor with bad bearings. They are sealed in, the shaft wobbles and, when turned on, they squeal and then the shaft binds up. I oiled them before and got the shaft to spin, but the bearings are shot. Hard to find a 3 inch diameter 1/12 HP AC motor . . . The large squirrel cage blower, from an old 3 ton ac unit, is simply too large. I have to restrict the air output to allow a lower air flow across condenser. That just loads blower and is not a solution.

Will see if I can resurrect a small DC motor (more efficient than split capacitor AC motor), but then I have to build a high amp DC power supply. But wait, I think I do have one of those that used to power a 6 meter ham radio rig!


Steve

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