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Old 12-30-14, 11:09 AM   #31
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What type of compression ratio are you discussing and how is it lower or higher depending on the temperature of the gas?

If you fill a cylinder with a gas, close an intake valve, compress it, and release the gas through the exhaust valve and close it again, the displacement when the chamber is at top dead center and at bottom dead center will be different in each position but doesn't change in relation to how much gas(air not gasoline) was allowed to enter in relation to a throttle plate blocking intake or back pressure against the exhaust. The ratio of non-compressed and fully compressed displacement determines the compression ratio of a cylinder when you are talking about engines.

Everything else makes sense to me but does compression ratio mean something different with compressors?

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Old 12-30-14, 05:45 PM   #32
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There are way too many differences between an internal combustion engine and a refrigeration compressor to make sense of anything in this topic, so I'll not even open that box here. But yes, the simple ones of each type do revolve and have constant displacement.

With respect to fridgie compressors, they are generally optimized to work with a single specific refrigerant, within a relatively narrow range of temperatures and pressures. They are also optimized to operate at relatively low rpm's. If you push the conditions out of the design "sweet spot", the compressor usually suffers.

The CR factors in here due to the fact that this is a closed system, with a relatively constant amount of refrigerant in circulation. I say relatively because all phase change systems have some sort of liquid receiver or suction accumulator in them somewhere. Without some space to "stash" extra liquid refrigerant in the system, the compressor would only operate within its design conditions over a very small range. In smaller rigs, this extra space is in the muffler (mini-accumulator) and the crankcase sump. This small buffer space doesn't affect pressures much, so the compressor is at the mercy of the delta pressure between the heat exchangers.

The saturation pressures of each heat exchanger follow the secondary side temperature. Let's talk about r-22 or propane here. In heating mode, at 60 degF outside, the most pressure the evaporator can see is around 100 psig, and normal saturation pressure will be around 80 psig or less. at 75 degrees inside, the least pressure the condenser can see is 132 psig, and normally pressure will be near 200 psig. This is less compression ratio than the compressor is rated to move, so it has a light load and works at high efficiency.

Suddenly, the temperature drops to 40 degrees outside. The evaporator follows this temperature drop and saturation pressure drops to 50 psig. With 2 atmospheres less worth of suction pressure, the compressor can no longer maintain 200 psig worth of discharge pressure, due to its limited displacement. At first, the CR will be high, due to the reduced suction pressure. As the compressor falls behind, discharge pressure will bleed off and the condenser will cool due to the reduced mass flow. The system will balance at a lower condensing pressure and CR, due to the constant volume displacement of the compressor.

This is one thing I had trouble wrapping my head around at first: isn't cooler gas more dense than hotter gas? The answer is yes, at the same pressure. But as far as the compressor is concerned, the pressure swings induced by the heat exchangers are many orders of magnitude higher in terms of gas density. Being 20 degrees cooler will make the same mass of gas 0.005% heavier but it can only exist at 30 less psi in the evaporator. Less intake (suction) pressure, same displacement = less mass flow and lower exhaust (discharge) pressure.

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Old 12-30-14, 09:03 PM   #33
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"Less intake (suction) pressure, same displacement = less mass flow and lower exhaust (discharge) pressure."

I understood the quoted part above already, thanks for explaining the difference. It seems mass flow is the important factor in the recent posts.
It's funny you mention fridges, with my lower winter house temperature, I'm running 20-30 watts less power through the compressor and seeing longer runtimes(30-45 mins depending on temp versus 10 mins in the summer). ..but with the lower ambient temperature the refrigerator is running far less often, I did have to max the freezer air valve diverter since the fridge needs less cooling. Using about 500wh daily with the side-by-side non-energy star fridge in my cold house.
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Old 04-01-15, 02:06 AM   #34
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Has anyone tried fitting a shipping container home with a heat pump- would the process be any different from a regular home?
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Old 04-10-15, 12:25 PM   #35
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Ok ...think i have the basics down... Now tell me this.

Why is there such a difference in SEER values between minisplit systems? What is making the difference (given they all seem to use the same refrigerant)? I look a lot on Ebay at various systems, and i see anywhere from the low teens up into the low 20s...and again...what does this even mean!? If i buy a 15 SEER (say 12K btu) vs a 21 SEER (same btu)...what am i going to see in performance/heat and cooling cost differences? Compressors, electronics, advertising hype?

Thanks...
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Old 07-05-15, 07:13 PM   #36
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I am not positive how deep I will go into hacking a dehumidifier. I'd like to find out what equipment is required for various "levels" I am envisioning.

Level 1
What tools/equipment are needed/recommended for servicing a dehumidifier: checking pressure; topping off refrigerant; and other tasks I probably am not aware of.

Level 2
What tools/equipment are needed for properly removing R22 from my dehumidifier and replacing it with R290? I know R22 has to be properly disposed of, but the "how" and "where" I do not know. How is lubricating oil handled?

Level 3
What tools/equipment are needed for a complete Frankenstein reconstruction: removal of refrigerant; cutting piping; adding new piping; TXV; etc.
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Old 07-06-15, 01:08 PM   #37
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Quote:
Originally Posted by Xzeption View Post
I am not positive how deep I will go into hacking a dehumidifier. I'd like to find out what equipment is required for various "levels" I am envisioning.

Level 1
What tools/equipment are needed/recommended for servicing a dehumidifier: checking pressure; topping off refrigerant; and other tasks I probably am not aware of.

Level 2
What tools/equipment are needed for properly removing R22 from my dehumidifier and replacing it with R290? I know R22 has to be properly disposed of, but the "how" and "where" I do not know. How is lubricating oil handled?

Level 3
What tools/equipment are needed for a complete Frankenstein reconstruction: removal of refrigerant; cutting piping; adding new piping; TXV; etc.
All of these scenarios have been covered in previous EcoRenovator postings.

You have two powerful search tools available to you at the top of each and every EcoRenovator page. One tool searches only EcoRenovator, with a built in search engine. The other does the same thing, but uses Google to do the work. The second one is best.

Sincerely,

-AC_Hacker.
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Old 07-06-15, 05:43 PM   #38
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Quote:
Originally Posted by warmwxrules View Post
Ok ...think i have the basics down... Now tell me this.

Why is there such a difference in SEER values between minisplit systems? What is making the difference (given they all seem to use the same refrigerant)? I look a lot on Ebay at various systems, and i see anywhere from the low teens up into the low 20s...and again...what does this even mean!? If i buy a 15 SEER (say 12K btu) vs a 21 SEER (same btu)...what am i going to see in performance/heat and cooling cost differences? Compressors, electronics, advertising hype?

Thanks...
In the USA, all manufacturers must get their systems certified by an authority before the industry will install or insure them in permanent fashion. The two testing authorities are ashrae and ahri. They both have their own defined testing conditions for different types of systems. Heat pumps get tested different than cooling only units, packaged systems get tested different than split systems.

With cooling units, the performance indicators are seer and eer. Seer is seasonally adjusted eer, which stands for energy efficiency ratio. Eer and seer are expressed as btu per watt. The higher the number, the more efficient the unit ran during the test. A 12k btu unit that scored 12 seer averaged 1kw of energy draw during the test, where a unit that scored 24 seer during the same test only averaged 500 watts.

With heating units, the performance indicators are hspf and COP. Hspf is in the same scale as eer/seer, COP is watts out divided by watts in. The better manufacturers test their heat pumps at a variety of outdoor temperatures, down into sub-freezing territory. The lesser manufacturers test theirs only where they have to in order to get certified. As outdoor temperature drops, so does the performance.

Way back when most units ran a capillary tube and a constant displacement compressor, you could compare units against each other in terms of seer or hspf and get a good idea of which unit performed better than which during the same conditions. Nowadays, there are units that employ advanced metering devices (such as electronic expansion valves and microcomputers) and variable speed compressors that "cheat" on the tests compared to the older systems. The lesser manufacturers design their control schemes so they perform their very best within the tests. The better manufacturers design their systems to work well throughout their design range. At a glance at some charts, it would seem that a certain el cheapo unit beat a more expensive unit by a sizable margin.

It is for this reason, now more than ever, to do some homework before purchasing a new system. Some of the less expensive units perform well when you need them the most, some don't. After a few years time, when service is needed, who will want to touch your unit? How and where will you find replacement parts? These questions are as important as efficiency ratings.

Like AC HACKER said in the previous post, many ecorenovator members have had minisplit systems installed, some have DIY installation. There are a number of users that are very happy with them, and have posted their energy usage and bills to back their data.There are so many systems available, with features and functions that vary so widely, that recommending a system that works for a certain site and purpose requires research.
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Old 12-07-15, 03:56 PM   #39
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https://youtu.be/wJD712DB6S0

everything you ever wanted to know about brazing/soldering
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Old 01-24-18, 01:20 PM   #40
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Continuing, with the heat pumps for dummies theme at what outdoor temperature is it wise to maybe switch to emergency heat option? Last week it was down to minus 15 and it didn't seem that this air to air heat pump was much use. Also what is the thinking behind this nine cycles per hour that the emergency heat was set to.

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