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Old 09-14-09, 01:15 PM   #111
AC_Hacker
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Default Vacuum Requirements for HVAC work...

dremd,

> WOW man
> MAD props!

Thanks, it was a ton of work (actually 8 tons of work)!

Quote:
Originally Posted by dremd View Post
WOW man
If you are going for cheap - Harbor Freight Tools - Quality Tools at the Lowest Prices is impossible to beat; you will need a big air compressor to run it; but if you are doing this , once per year you could borrow one . . . mine pegs my automotive HVAC A/C gauge every time.
The manifold gauges get non-linear near the end of their scale which is very unfortunate, because we really need to know what is happening at that end to be successful.

I found a very useful link to vacuum equivalents here:


...probably a good idea to bookmark AND print it out and tape it to the inside of your HVAC tool box (I have one in mine).


The venturi-type vacuum pump you linkled to (HF #96677) is able to hit 28.3" of mercury at sea level. So this would be 'Inches Mercury Gauge' on the chart. Notice that this is around 94.8% vacuum. For HVAC work, we need to pull down to at least 80 microns (99.995% vacuum) and hold it there for a while to let all the moisture that may be in the system turn into vapor and get sucked out by the vacuum pump. It's true that the venturi-type vacuum pump may peg your manifold gauge, but the extra vacuum is where the de-moisturization magic happens.

The micron gauges use the principle that heat dissapates very poorly in a total vacuum. The gauge has a tiny heater and a tiny thermocouple together in the space that is getting vacuumed. While there is air, etc in that space, the heat dissipates well. As a vacuum is approached, the heat dissipates progressively less well, and the temperature rises. The thermocouple measures this heat rise and turns that data into vacuum readings.

The other pump you linked to (HF #66466), the Two Stage 3 CFM Air Vacuum Pump would work just fine.


Might want to keep your eye peeled for a good micron gauge to show up on ebay. I bit the bullet and bought one new.


Best Regards,

-AC_Hacker

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Old 09-14-09, 01:32 PM   #112
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Default Next is Trenching...

Quote:
Originally Posted by Daox View Post
Alright! Congrats on getting all the holes done!

Next is trenching?
Thanks for the congats, yes, next is trenching. I'm trying to co-ordinate the trencher with a friend who is replacing water main pipe at his place... save us both some money.

I'm also re-testing for leaks on all the U-tubes.


And I will repeat the thermal transfer test I did previously, this time with HDPE pipe I'm actually using and hole depths I'm actually using.


Regards,

-AC_Hacker

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Old 09-14-09, 03:42 PM   #113
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Default Reply to NiHaoMike...

NiHaoMike,

Quote:
Originally Posted by NiHaoMike View Post
Sam's Laser FAQ - Vacuum Technology for Home-Built Gas Lasers
I don't have a gauge that can precisely measure the vacuum level, but it pulls as low as the gauge set will measure. I estimate 1 Torr or so since it is a rotary compressor.
Thanks for the link to the laser/vacuum page. Lots of very good info there.

However, in the section on using refrigeration compressors, it stated:
Quote:
Almost any real vacuum pump (including refrigeration service types) - even one that has been neglected and abused - will pull a better vacuum than most refrigeration compressors
So, in my opinion, for the purposes of experimentation, a refrig/freezer/de-humidifier compressor would be just fine to test out the technology.

But the purpose of this thread is enable you to build your own highly reliable, very economical Ground Source Heat Pump for your home. A properly built heat pump should last decades. And since refrigeration reliability is very much dependant on purging your system of any water, for the final version of your heat pump, you might want to get pretty serious about the vacuum thing (known good vacuum pump, known good micrometer vacuum gauge, strict adherence to proper procedure, no short-cuts).

As I have gone through this saga of learning all I can about GSHP technology and coming to grips with all the sub-technologies associated with it, my standard of comparison is a $35,000 GSHP system with a COP of 3.5. If I can approach that performance for a tiny fraction of the cost (I'm still shooting for a final cost of under $1000), then I have completely succeeded.

Regards,

-AC_Hacker

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Old 09-14-09, 07:03 PM   #114
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Default

Quote:
Originally Posted by AC_Hacker View Post
dremd,

The venturi-type vacuum pump you linkled to (HF #96677) is able to hit 28.3" of mercury at sea level. So this would be 'Inches Mercury Gauge' on the chart. Notice that this is around 94.8% vacuum. For HVAC work, we need to pull down to at least 80 microns (99.995% vacuum) and hold it there for a while to let all the moisture that may be in the system turn into vapor and get sucked out by the vacuum pump. It's true that the venturi-type vacuum pump may peg your manifold gauge, but the extra vacuum is where the de-moisturization magic happens.
I make no claims to the accuracy of my test equipment, nor the performance of my vac pumps; but.

Harbor freight venturi vac pump
http://gallery.me.com/dremd/100071/V...12529717130001

Harbor freight 2 stage vac pump
http://gallery.me.com/dremd/100071/I...12529728370001

Not trying to make any point here; but that's my quasi scientific test results.
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Old 09-15-09, 08:32 PM   #115
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Default

Quote:
Originally Posted by dremd View Post
Not trying to make any point here; but that's my quasi scientific test results.
dremde, I'm not at all trying to disrespect your gauges. I'm sure your equipment is just fine.

The problem is that the gauges like the kind in your photos (Bourdon type) generally have their maximum sensitivity and accuracy at mid-scale readings and are the least sensitive and accurate at the extremes. In HVAC work, some very important stuff happens at the deeper levels of vacuum. This is why the micron gauge was invented.

The specs for the Harbor Freight venturi-type gauge suggests maximum vacuum it can pull to be around a 98.4% vacuum, and for the rotary vacuum pump it is 99.995% vacuum.


Bourdon Gauge

The Bourdon type gauge is just not physically able to distinguish between 98.4% vacuum and 99.995% vacuum. But it is at the 99.99% end that the water flashes to vapor and is pumped out.

The issue here is the inherent limitation in the design of the Bourdon Gauge.

Here are some links regarding the micron gauge and deep vacuum in HVAC:

pulling a vacuum - HVAC-Talk: Heating, Air & Refrigeration Discussion

Pulling A Good Vacuum Equals $$$ For The Contractor - How To - Air Conditioning, Heating & Refrigeration NEWS

why use a micron gauge - Google Search

Best Regards,

-AC_HAcker
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Old 09-18-09, 07:32 PM   #116
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Default

I actually used an incandescent lamp to warm various parts of the plumbing during the second and third vacuum pull. I actually have a sight glass with moisture indicator, which indicated that it was dry on the first vacuum pull, without using the lamp. Therefore, the pump I used was sufficient for my application, but then again, it is not particularly demanding since I can use a lamp to help remove the last traces of moisture. Setting up a heat pump on a cold day, on the other hand, would demand a very good pump system. That's where an ion pump or diffusion pump comes into play.

Has anyone thought about building a precision vacuum gauge? Take two pieces of glass tubing, fill one with vacuum pump oil, and cap off the end so there's no trapped air. Then take a piece of vacuum hose, connect one end to the glass tube filled with oil, fill it with oil as well, and connect the other end to the other glass tube. Mount it on a stand in a U configuration and connect the remaining open end to the vacuum pump. If the density of the oil is known, the vacuum level can be calculated by measuring the difference in level in the tubes and translating it into pressure.
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Old 09-19-09, 07:57 PM   #117
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Default Trenches are all dug...


With a favorable weather forecast, I decided to work like a demon while time and weather are on my side.

I went in with my friend Bruce-the-Pirate to rent a trenching machine. We visited the local power tool rental establishment to see what they had.


We selected a Ditch Witch which was probably second choice, but it did have the advantage of being 'maneuverable'. It turns out that this type of machine has no real steering, it just goes backwards in a generally straight line and digs as it goes. Changing direction is not easy and consists of grabbing this horribly heavy machine and using all of your strength and moving it a few degrees, then repeat until properly positioned.

But once positioned, the controls are all hydrolic and the engine is fairly powerful and it sure beats digging by hand.


Here's William_Hackerson at the controls. He'd had a bad day at his regular job but grudgingly admitted that running the trencher made him forget his bad day at work. Maybe not so different from being at war makes a country forget the serious social and economic issues it faces.

So the trenches went in and great care was used to not damage any of the polyethylene loop pipes.

The pic at the top shows how the trencher was run up close, but not touching the pipe...


...the pic on the bottom shows digging the trench next to the loop pipe.

By the way, I asked the man who ran the tool rental store what they had in the way of hole diggers. He asked how deep, I said maybe 20 feet, he asked how many and I said maybe twenty or so, he threw up his hands and said no, there was nothing like that, and went on describing how it could not be done.

I told him that I had already dug sixteen holes that were each seventeen feet deep, with a shop vac!

I didn't have my camera, but this was the look on his face:


Best Regards,

-AC_Hacker

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Old 09-22-09, 06:33 PM   #118
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Default

Vacuum on the Cheap - Refrigeration Compressors
Quote:
A compressor such as this will evacuate a small chamber to about the 1 Torr range. While it is theoretically possible to obtain a better vacuum with two compressors connected in series, I have only had limited success with this. Lee was able to achieve pressures to 10 mTorr with two series-connected 1950s vintage Frigidaire Meter-Miser compressors and you should feel free to experiment.
So it looks like it is possible to build a good vacuum pump from refrigeration compressors. Just get two and not just one. The modern high efficiency ones should work even better since they have tighter tolerances for higher efficiencies.
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Old 09-23-09, 10:01 AM   #119
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Default

Quote:
Originally Posted by NiHaoMike View Post
Vacuum on the Cheap - Refrigeration Compressors

So it looks like it is possible to build a good vacuum pump from refrigeration compressors. Just get two and not just one. The modern high efficiency ones should work even better since they have tighter tolerances for higher efficiencies.
NiHaoMike, good info here.

And just in case anyone might miss it, your link also contained this link to a PDF with detailed but dated instructions to build your own vacuum pump:

http://www.belljar.net/fbleeconversion.pdf

And here is a link to HVAC vacuum pumps on ebay:

vacuum pump, great deals on on eBay!

Additionally, here is a link to vacuum pumps at Harbor Freight:

Harbor Freight Tools

Harbor Freight used to carry a 1.5 cfm pump which was cheaper than any in the above link, and would work fine, though more slowly.

And here's a discussion from an HVAC blog about how you can't/can/can't/can
build a vacuum pump from a refrig compressor:

Compressor ID for DIY vacuum pump - Refrigeration-Engineer.com forums

One of the posts (#14) is worth re-quoting:
Quote:
Did you ever measured that reached vacuum, with that compressor, is some decent amount below boiling point of water at that temperature?
Boiling point of water at 68F is 0,3394 PSI.
You need a lot lower pressure to boil that moisture and suck that out of system.
You can not measure that vacuum with [Bourdon] gauges!
What is the point in vacuum drying if you cannot lower system pressure to boil water and then suck that evaporated moisture out?
Compressor is not designed to pull decent vacuum. You need rotary vane vacuum pump
Rotary vane pump - Wikipedia, the free encyclopedia
(preferably double stage capable of pulling to 50 microns => 0,05 torr => 0,000967 PSIa)
and electronic micron vacuum gauge to measure reached vacuum, and if water still boils.
So, for HVAC work, it looks like 1 Torr is not quite low enough.

If you're going to build your own vacuum pump (or buy used), it would be advisable to get your hands on a micron gauge so you know for sure what kind of vacuum you are actually pulling.

Best Regards,

-AC_HAcker

P.S.:


The loop-field is 50% in and tested. Working like a demon to try to beat the rain.

After this project, I don't care if I never see a shovel again!

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Old 09-23-09, 11:32 AM   #120
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Default Welding vs. Barbs...

Earlier in the blog ("mini-hack") I showed how to make heat fusion (AKA: plastic welding) tools.

So far while installing the loop field, I've had some situations where I thought I'd have to resort to barb connections rather than welded pipe. I got some brass barbs and installed them up and tested them.

I can now report that when comparing welded connections to barbed connections,

Welding is cheaper
Welding is easier
Welding is more durable
Welding is faster
Welding is more likely to yield a leak-free connection

The choice is pretty clear.

Regards,

-AC_Hacker

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