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Old 10-24-12, 12:58 PM   #1331
AC_Hacker
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Originally Posted by Mobile Master Tech View Post
...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...
I think your idea is a good one. Actually, using ice as a PCM has been used for quite a while in office buildings. The idea is to take advantage of lower off-peak power rates, by storing cheaper coolness at night and calling on it during the day when power rates are higher. You are also quite right about the wasted energy.

What is the capacity of your AC system right now? 4 Tons, 6 Tons?

-AC

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Old 10-25-12, 09:47 PM   #1332
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Originally Posted by AC_Hacker View Post
It was me thinking thoughts like that, that started me on this very interesting journey.
  • I had never brazed before...
  • I had never opened a refrigerant line before...
  • I had never bought any kind of pump before...
  • I had never welded before...
  • I had never built a power machine before...
  • I had never dig a hole deeper than two and a half feet before...
  • I had never dug a trench before...
  • I had never built a plastic welding tool before...
  • I had never welded plastic before...
  • I had never blogged before...

It's time for you to start doing research and making drawings.

You could get very old waiting for "them" to do it.

-AC_Hacker

Good advice !

I want to build a off grid eco-house with a multitude of systems tied to each other, including a 120v day time use ground source heat pump, powered directly by solar panels, for reliable heating. The less battery storage i can design into the house the better.

Research has begun, next drawings ! then, sell this house and buy my off grid acreage and begin

Some good info here for the beginner:

How Do They Work?

Remember, a geothermal heat pump doesn't create heat by burning fuel, like a furnace does. Instead, in winter it collects the Earth's natural heat through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond or lake. Fluid circulates through the loop and carries the heat to the house. There, an electrically driven compressor and a heat exchanger concentrate the Earth's energy and release it inside the home at a higher temperature. Ductwork distributes the heat to different rooms.

In summer, the process is reversed. The underground loop draws excess heat from the house and allows it to be absorbed by the Earth. The system cools your home in the same way that a refrigerator keeps your food cool - by drawing heat from the interior, not by blowing in cold air.

The geothermal loop that is buried underground is typically made of high-density polyethylene, a tough plastic that is extraordinarily durable but which allows heat to pass through efficiently. When installers connect sections of pipe, they heat fuse the joints, making the connections stronger than the pipe itself. The fluid in the loop is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system.

Another type of geothermal system uses a loop of copper piping placed underground. When refrigerant is pumped through the loop, heat is transferred directly through the copper to the earth.
http://www.consumerenergycenter.org/...eothermal.html

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Old 10-27-12, 09:13 PM   #1333
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One thing is for certain, you will need more batteries than you want to use IF you want to use a heat pump and solar only. The compressor needs a regulated voltage and it must stay within that voltage and , they are almost all AC that can heat a house anyway so an inverter is necessary. The compressor has to be able to get the current it needs whenever it needs to operate and panels by themselves cannot guarantee the supply of current, moment by moment.

If you can get the house heat loss down to 2-3kw, you might just be able to make it work (with batteries and inverter), and you use solar hot water too.
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Old 10-27-12, 09:21 PM   #1334
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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
In the trade, we use the term "ton" in a very loose way. Usually only to denote a package product size such as a "3 ton split system". When talking about heat transfer or more specific ideas it is always a watt, kw, btu, or a mass flow rate. A ton is a term most people in the scientific or engineering side, that I know, really don't like to use.
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Old 10-27-12, 10:22 PM   #1335
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One thing is for certain, you will need more batteries than you want to use IF you want to use a heat pump and solar only. The compressor needs a regulated voltage and it must stay within that voltage and , they are almost all AC that can heat a house anyway so an inverter is necessary. The compressor has to be able to get the current it needs whenever it needs to operate and panels by themselves cannot guarantee the supply of current, moment by moment.

If you can get the house heat loss down to 2-3kw, you might just be able to make it work (with batteries and inverter), and you use solar hot water too.
Ahh yes, i should of know that.
My main idea is not to store the electricity but use what i can while its daytime. A small battery pack, 500 amp hours would suffice for the main house lighting and the various electronics that would be needed or wanted. And a separate small battery pack specifically for the heat pumps.
I do not want to babysit a large bank of batteries for the rest of life, so i'll keep a simple and small battery bank.

I understand about the unnessasary clutter, if like delete my off the topic posts, for the greater good!! ?

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Old 10-28-12, 01:08 AM   #1336
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Default Solar & Battery Powered Heat Pump...

I think your solar/electrical discussion is a pretty good one, and deserves it's own thread.

It seems to be departing from the subject of this thread, which is modifying vapor-compression machines for the purpose of extracting heat from the ground.

Best,

-AC
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Old 10-28-12, 09:35 AM   #1337
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I really like were this topic is going. Solar powered geo thermal heated/cooled home!! I had seen in a Home Power mag. a few years back a husband wife team had done just that. Built a new home in the countryside away from any grid connection and heated/cooled with solar PV powered geo-thermal. They had also installed a 10kw Bergly wind turbine as the winter wind blows harder and the sun shows up less in the winter. They had a sizable battery bank but all new deep cycle batteries made for solar power back-up.

Xringer proved the concept out with his heating water utilizing the A7 airsource hot-water heater and solar PV and battery back up. I think he had it running a couple weeks.

It seams so amazing that its possible now to build a stand alone home that can power itself and keep its occupants warm and well lit for years without any connections to outside fuel sources. And to imagine this can be done cost effectively and not be one of those show-case projects that are only done by groups with deep pockets.

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Old 10-29-12, 12:20 PM   #1338
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What is the capacity of your AC system right now? 4 Tons, 6 Tons?

-AC
"1.75 tons." Originally equipped with 2.5 ton downstairs and 2 ton upstairs units. We have the downstairs unit disabled for basement renovations/relocating and operated our 5BR/3.5BA house solely with the upstairs unit and a little help from a 8000btu portable unit from time to time. The upstairs unit has one of the four cap tubes soldered off (yes-soldered, not brazed!) due to formicary corrosion, plus it is in the attic. This cuts down its capacity to at most 1.75 tons. The energy star rated roof we put on last year really helped. The upstairs unit ran almost 24/7 and maintained 74-80 on all but the hottest/most humid days. Then the temp sometimes got to 83-85 in the house but was still comfortable using ceiling fans because the nonstop running kept the humidity under control.

I am replacing both units with a zoned 23 SEER Nordyne(Tappan brand) inverter drive system, variable between 1.75-3.5 ton output, which will be up and running for next season. Combined with a 7.1kw water cooled off-grid capable PV system preheating the field for a hacked GSHP with a large buffer tank, I am pretty sure I will be energy bill free, similar to what Randen speaks of. My electrical co-op only pays 2.5cents/kwh for surplus production, so I may leave it off grid-I have to sell over 900kwh/mo back to the utility just to offset the monthly fees.

I thought about the ice storage for surplus solar production, but the most efficient icemakers will take somewhere around 80kwh to make a ton of ice. It would work, but I'd rather put the money into an extra 48v string of golf cart batteries. Thought a watercooled icemaker would make a great donor for GSHP parts, though.
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Old 10-29-12, 12:29 PM   #1339
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By the way, I bought my A/C components from Surplus City Liquidators. If you buy an air handler and outdoor unit, they will give 10% off their already low prices on everything on that order-ductwork, wyes, etc. Since the A/C units lower the "class" of freight, it adds almost nothing to ship high-damage-risk items like sheetmetal which would be cost prohibitive to ship by themselves. They have nearly everything you would need to hack build a GSHP.
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Old 11-17-12, 08:25 PM   #1340
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Hello all,
Have been enjoying all the information here. I am currently building a drilling rig to bore some holes in my backyard. Very interested in what is going on here. I have only read up to page 66 and need to post to see images and links.
Keep the information coming.

thanks

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