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Old 09-21-12, 02:09 PM   #1321
charlesfl
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Free heat
http://www.mcquay.com/mcquaybiz/lite...011_120407.pdf

This is a site that deals with piping

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Old 09-21-12, 09:06 PM   #1322
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To run 2 separate coils on the same pump could be a bit challenging as far as keeping things balanced. You'd never be able to properly set subcooling (as a condenser) to optimum numbers as the condensers will almost certainly be of different capacity and size. You would almost be better off running the condensers in series. You could run 2 evaporators together in parallel, or selectively, if you had properly set up properly rated TXVs as they could compensate for the load change if one branch is shut down (single valving to avoid trapping unknown amounts of charge in one coil). Fixed orifice metering would be out of the picture as there would be no way to properly set the charge. You may be able to have selective condenser usage with txvs and a suitably sized receiver. Is this going to be a reversible heatpump or a straight heat/cool system? It could become quite complex requiring 4txv, multiple valving, and a nightmare trying to set superheat/subcooling, all while still achieving a suitable oil return to the compressor. The simplest approach would be to run your coils in series if possible, and have selective use of the fan on the air over coil (such as pressure/temperature).

To your question of piping, Oil return on long runs can usually be assisted by using traps and inclining the return line in favor of the compressor. The pipe size is directly related to both pumping capacity and length of run. Ill have a look around and see if I can find a suitable loss chart that can help select the correct size for your installation. There is a (small) efficiency hit due to frictional losses in the pipe, but unless its a very long run, you'll never see it.
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Old 09-23-12, 10:23 PM   #1323
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Default Another angle to consider...

Quote:
Originally Posted by RB855 View Post
To your question of piping, Oil return on long runs can usually be assisted by using traps and inclining the return line in favor of the compressor. The pipe size is directly related to both pumping capacity and length of run. Ill have a look around and see if I can find a suitable loss chart that can help select the correct size for your installation. There is a (small) efficiency hit due to frictional losses in the pipe, but unless its a very long run, you'll never see it.
Another angle to consider is that there seems to be a critical inside diameter for the refrigerant tubing. The tubing needs to be sized so that the velocity of the refrigerant/oil is high enough to sustain turbulence and to keep the lubricant circulating along with the refrigerant... too large a diameter (lower velocity) and the lubricant may be left behind... too small (higher velocity) and friction of circulation takes its toll.

There are probably enough key terms there for you to find more authoritative information on the principle.

BTW, nice copper craft!


Best,

-AC
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Old 09-26-12, 10:33 PM   #1324
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Everything you could possibly want to know, and more about sizing ref piping.
PDF Link, large - 70pages
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Old 10-02-12, 01:47 PM   #1325
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Some surplus Coax coils FYI: Surplus City Liquidators
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Old 10-03-12, 09:03 AM   #1326
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Quote:
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Some surplus Coax coils FYI: Surplus City Liquidators
What is the meaning, defining conditions of the TONage rating of these HXs?
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Old 10-03-12, 02:10 PM   #1327
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What is the meaning, defining conditions of the TONage rating of these HXs?
Great question...

In refrigeration in the USA, the 'refrigerating power' (my term) of a system is referred to in Tons, BTU/hr, Kilo-Watts/hr and Horsepower.

Most frequently, it is referred to in Tons, and the definition of Ton is historical. A Ton is defined as the refrigerating power of one ton of ice over a twenty four hour period. In more modern terms, 1 Ton equals 12,000 BTU/hr. or about 3.822 kilo-Watts/hr. The horsepower rating of refrigeration equipment can be kind of 'squishy' and is not used quite as often. Even though the Ton measure originated with cooling, it is also used as a measure of heat pump output (heating).

So, in the practice of hacking your own system, various factors will dictate the overall size of your system... in particular, how much heat output will be required from your system to supply heat to your house at the same rate that heat is being lost on the coldest winter day. As an example, let's just say that your house required 24,000 BTU/hr on that coldest day... this would equate to 2 Tons.

So, in hacking together your system (or systems), you would choose a compressor that had this capacity, so you would choose a compressor rated at 2 Tons of output. Note that in refrigeration, bigger is not necessarily better. In fact, slightly smaller is best, and be prepared to use some axillary heating to fill in the gap on those extreme days.

Next in your homemade hack-a-thon is the selection of a heat exchanger (often referred to as HX). If you choose a HX that is smaller in capacity than your compressor, your compressor will not be able to realize its full output. If you choose a HX that is equal to your compressor, it will be able to reach full capacity. If you choose a HX that is larger, it can improve efficiency to a certain degree, but you will face the law of diminishing returns, in that a small increase in size will give you some increase in efficiency, but subsequent increases will give you progressively less increases in efficiency.

There have been spirited exchanges in various threads here at EcoRenovator, about whether increases in efficiency will actually occur, and if they do, how much. So far there has been much hot air circulating about this issue, but no rigorous testing that I know of.

It is my opinion that any real increase in efficiency should be vigorously pursued, as I think that the price of energy will be relentlessly climbing.

Another consideration regarding HX selection is where will your heat come from and where is it going to? For instance, I put in a very small hand-dug ground source loop field in my back yard, and I have tested it to be functioning with a very small compressor. Building a bigger system with a bigger compressor and properly sized HXs will not necessarily equate to more heat output, as my loop field is the limiting factor. This leaves me only one solution, which is to reduce my rate of heat loss... AKA: rigorous infiltration remediation, and insulation improvement... I can also reduce the amount of my house that I choose to heat.

Randen built a fairly large loop field to begin with and had enough excess capacity that when he increased his compressor & HXs by 75% (from 2 Ton to 3.5 Ton), he was able to realize that extra output. Last I heard, he is also embarking on adding solar heating to the mix, and additionally improving insulation, as these will reduce the run-time of his heat pump.

I hope this is the information you need...

Best,

-AC
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Old 10-03-12, 03:14 PM   #1328
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Thanks Hack, for the well stated reply.
I understand that 1 Ton of heat transfer equals 12,000 BTU/hr.

My Q is more specific regarding this rating as a measure of HX performance, i.e. the specific “standard conditions“ if any, of this rating.
1. Heat source side Delta T, Flow rate, Fluid thermal and change of state parameters.
2. Sink side, same conditions.
3. Delta T across the exchange surfaces, ect.

Last edited by berniebenz; 10-03-12 at 03:17 PM.. Reason: calrification
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Old 10-03-12, 03:53 PM   #1329
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Quote:
Originally Posted by berniebenz View Post
My Q is more specific regarding this rating as a measure of HX performance, i.e. the specific “standard conditions“ if any, of this rating.
1. Heat source side Delta T, Flow rate, Fluid thermal and change of state parameters.
2. Sink side, same conditions.
3. Delta T across the exchange surfaces, ect.
Well berniebenz, you have correctly identified nearly all the factors that would affect heat transfer across a HX.

The capacity value (Tons) that is associated with each HX is a simplified number that assumes typical working conditions that would be encountered in the HVAC trade. There are variations from refrigerant to refrigerant, but these variations are pretty modest.

If you wanted to use a refrigeration HX for water-to-water, the differences would be large enough that you would need to re-evaluate the capacity. Conversely, if you found water-to-water HXs that you wanted to re-purpose for refrigeration, the differences would be large and, again you'd need to re-evaluate.

To be able to delve into heat exchangers in the depth and detail you seem to be seeking, you should pick up some books on HX design and dive into the real nitty-gritty... for this, you will certainly need to brush up on your calculus skills, as this is how the design criteria are discussed and developed.

If, along the way you discover anything that could be of value to this humble thread, please feel free to share.

Best,

-AC
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Old 10-24-12, 07:19 AM   #1330
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Been off the forum a while-busy with funerals and weddings! While researching energy storage methods for surplus off-grid PV electricity, I thought of using a commercial icemaker drawing "patented 32degF phase change material" from an insulated storage tank to fill the tank with ice, then use a heat exchanger coil in the bottom to obtain chilled fluid for air conditioning as needed.

It turns out this isn't an efficient idea, as even the best Energy Star rated commercial machines take around 4kwh to make 100lb of ice! However, I learned that some machines are water cooled (sending potable water down the drain to dispose of the waste heat-what a waste!). These contain excellent counterflow cupro-nickel tube-within-a-tube heat exchangers, as well as the refrigeration components needed for a GSHP. Icemakers come as complete units or modular icemaker heads to fit on a separate bin.

If anyone can score a good deal on a used one from a restaurant equipment supply pulled out of service because of the water waste, it would be interesting to see one hacked. Plus, you would still have a perfectly good motorized auger for who-knows-what! Anyone have any experience with these units?

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