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Old 07-20-17, 11:35 AM   #1
gtojohn
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Default A/C repair dropped my power usage by 45%!

Folks, its been a long time since I've been here. My time is so limited I don't spend much time on the web anymore. This fortunate accident seems big enough I should share with like minded people.

My 2 ton Ruud r-22 unit locked its compressor after the 4th of July. Its 12 yrs old, a little early to fail and I'd rather not deal with complete replacement until the Fall. I installed a slightly used compressor, from 14 seer Ruud installed for a month before the coils were stolen. It was sealed and has sat for a couple of years. Both copeland compressors were rated for 21btu the only difference was the newer one designed for Puron 410a...It was a bit of a gamble but the family was out of town. I recharged the system with NU22B, it looks to be compatible with poe and mineral oil residual.

It runs a bit weird. High side at 160psi, Low side 78psi about 48f. I get a 14f differential at 100f outdoor ambient. High pressure line cool to touch, 84f. Checked it last night after dark and it was sweating...a bit like a minisplit. My previous wattage was around 1800 watts, current power usage is 1000w!!! Dropped about 45%! Very unexpected! And yes its still cools the house!

I've been tracking our power usage and its gone down about 5kw a day. The wife hasn't complained about it not cooling as well either. My guess is the savings coming from the new compressor being designed to pump to 400psi against a more restrictive metering device, less head pressure less power.

I will put together part numbers and pics for those interested.

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Old 07-20-17, 02:01 PM   #2
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So the ratings for r22 and r410 are very different. Not sure of the exact numbers but I believe a 3 ton r410 might only be a 2 ton r22 or something along that line. So you effectively have a smaller unit.
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Old 07-20-17, 11:52 PM   #3
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What FordGuy said. TANSTAAFL. Hopefully your system will do a halfway decent job of pulling moisture out of the air. If not, just run a little dehumidifier. I imagine your insulation and radiant barrier has a lot to do with why your system is of adequate capacity to cool the house.

Please elaborate on the system. What SEER rating was the unit before it was modded? What kind of metering device(s) is in it? How did you determine how much refrigerant to charge the system with? The system pressures are rather close to each other for your unit. I would definitely watch the pressures after the really hot weather goes away.
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Old 07-21-17, 10:54 AM   #4
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Its was a 14 seer ruud rectangle unit. Indoor is adp coil with txv. Furnace ruud 50k with standard psc blower. I was afraid the tonnage might go down considerably but it seems to cool as well as before. I'm cooling 1200sqft with about 800sqft of attic, in the hottest part of the year (100F). I don't think I could pull it off with 18kbtu or less. Its dehumidifying quite well. Running amps were 4.3-4.8 which is below what I usually see on 1.5 ton. I usually expect 3.5 amps per ton when I check modern a/cs. I used to know where to look up the btu efficiency of refrigerants but google didn't help this morning. Seems like I remember r22 being very efficient with propane having slightly more btu, and 410a having less. That would mean needing to pump more refrigerant for the same amount of cooling. Its getting a good test this month we'll see if it lives. I'll see about getting more info out this weekend.
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Old 07-21-17, 02:01 PM   #5
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sounds undercharged to me. How can ambient be 100 degF and liquid line at 84 degF? At 160 psig, the bubble point is 86 degF, so 2 degF of subcooling. I haven't looked for specs on your unit, due to lack of info, but the install manual will spec subcooling value for TXV metered boxes. Since you are moving less gaseous refrigerant, the subcooling value may not reach spec, but there should definitely be more than 2 degF when it's hot out. I smell something foul or amazing, I can't tell yet....
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Old 07-24-17, 11:14 AM   #6
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Here's what I have:
Ruud Uapc-024jaz built 9/2005, came with copeland scroll zr21ka pfv-130, matched with 2 ton adp txv coil. Replaced compressor with 2008 copeland zp21ke pfv-130. Original run cap 35mf new one requires 40mf.

I tried tweaking it this weekend trying to get more temperature differential out the vents, as the high side pressure went much above 160 the amps did go way up to get 16f of cooling diff. Probably the txv closing and liguid backing up. 150-160 seems to be the sweet spot with 14f cooling. Also amps seems to go up considerably more with the ambient temp compared to what I normally see. 6-6.5 with 100f ambient, unloads to 5 amps at 95f. I do have a 2 ton 15 seer american standard right next to it for comparison, it pulls 7.2 amps and unloads to about 6.8 when its 85f. I'm using infrared for my line temps which I don't always trust. I will try to dig up some probes for better results.

Being a mismatch of compressor and refrigerant I don't have a manual for such, and when I finished welding in the compressor at midnight I didn't bother weighing in the refrigerant. I just charged it until I got the superheat down. Understand it was a gamble to begin with and I didn't think it would work. I've probably lost some cooling, nu22 already cools about 6% less than r22. It does seem I should be getting some economy from getting a good suction pressure temp with only 160psi head on a compressor designed to operate at 400psi.
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Old 08-08-17, 04:20 PM   #7
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Interesting project. Reminds me of the days when 134a was new and everyone was trying to run it in r12 systems. They didn't cool well because the condensers were too small and inefficient but mainly due to 134a needing a good bit higher cfm pump.

With yours it's an odd mismatch however if it's not using as much electricity and it's keeping the house cool and not overheating the compressor then just run it.

Your old one dying at 12 years is about the norm. Here we expect 10 years then anything past that it's on borrowed time. Due to our cooling loads and how much abuse compressors get in the summer is why I'm not the biggest fan of heat pumps. I don't like running a compressor any more than I have to.

What's the humidity in the house now. Preferably 50% or less. Ours is usually around 45% to 48%. Also what is your supply and return temps after its stabilized for 10 minutes or so.
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Old 08-08-17, 09:27 PM   #8
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I intentionally had a project that used a R410 compressor running R134 due to special circumstances. If I am recalling correctly, a 12kbtu compressor downrated to about 8500btu using the other gas. Using fuzzy logic (its late and i haven't looked at a T&P chart in some time) You are probably operating in the 16-18kbtu range with your new 24kbtu compressor. Also, using a IR therm for critical temperature measurement is shooting in the dark. You need a real contact thermo that is calibrated before making any claims of superheat/subcool. Also, its not possible to have a 85* liquid temp with 100* ambient unless I misread something or you have a restriction in the system. That compressor should chug along just fine on r22, just at a lower system capacity and possibly slightly reduced actual efficiency since the compressor motor is slightly oversized. You may have discovered your 2t is oversized for the house if you have made any significant improvements to the envelope since the house was rated for 2t (or in my case, I have a large tree shading and my ac is oversized now...)
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Old 08-09-17, 11:25 AM   #9
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I picked up a new set of contact probes, will check this weekend when time permits. I will do more tests. Last months utility bill was 2 year low for that period. 13 days left for this period. Unit is still chugging along, cooling the house well. Though I don't yet know exact liquid line temp I guarantee you it sweats as the ambient drops.Both compressors had a 21kbtu label rating. I never felt it was oversized before. Previously when we had summer company it struggled. 134a runs at about half the pressure as r-22 which is why it was popular in automotive, less likely to leak, less drag on the compressor.
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Old 08-09-17, 12:45 PM   #10
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I was simply using 134 as a example on retrofitting 410 compressors. Pressures aside, mass flow rates of 134 and 22 should be somewhere in the same neighborhood, unlike 410a. There's no possible way your liquid line could sweat short of a restriction. Liquid line temperature is often 3-10*f Higher than ambient outdoor temperature. If your liquid line is sweating, you have a significant restriction that needs addressed, and may explain your issues with setting subcool. Only exception to this rule are Minisplits, because the metering device is in the outdoor section. The suction/vapor line absolutely will sweat. On other notes, you may see an actual efficiency increase since your condenser is rejecting less heat and is operating more efficiently.

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