09-14-09, 01:15 PM | #111 | |
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Vacuum Requirements for HVAC work...
dremd,
> WOW man > MAD props! Thanks, it was a ton of work (actually 8 tons of work)! Quote:
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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09-14-09, 01:32 PM | #112 | |
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Next is Trenching...
Quote:
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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09-14-09, 03:42 PM | #113 | ||
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Reply to NiHaoMike...
NiHaoMike,
Quote:
However, in the section on using refrigeration compressors, it stated: Quote:
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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09-14-09, 07:03 PM | #114 | |
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Quote:
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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09-15-09, 08:32 PM | #115 | |
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Quote:
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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09-18-09, 07:32 PM | #116 |
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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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09-19-09, 07:57 PM | #117 |
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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 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Last edited by AC_Hacker; 09-19-09 at 09:01 PM.. |
09-22-09, 06:33 PM | #118 | |
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Vacuum on the Cheap - Refrigeration Compressors
Quote:
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09-23-09, 10:01 AM | #119 | ||
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Quote:
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:
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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09-23-09, 11:32 AM | #120 |
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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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air conditioner, diy, gshp, heat pump, homemade |
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