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Old 05-31-17, 11:40 PM   #11
jeff5may
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So what is the question here? are you planning on building a custom heat pump? I am here to tell you it is entirely possible. The more planning that can be done before anything is built, the better your custom rig will operate. If you are going to try to run the thing directly off the solar panels and a battery bank with an inverter, you definitely want to go with a variable speed compressor. The single speed compressors need a big jolt of power to start, which limits what you can run that won't kill the inverter. Variable-speed compressors can be soft started, eliminating the startup spike. The decrease in peak demand equates to much more useful capacity.

IMHO, battery banks should only be used for emergency power, or if you are going to have a power source that is completely off-grid. The reason being: charging and discharging battery banks is horribly inefficient. On the way in (and out), parasitic losses are typically 10%. You must also oversize the battery bank as to not have large charge/discharge cycles. For regularly used banks, a 25% cycle is typical. So for 10KWH of storage, you need 40KWH worth of storage capacity. To get more depth of discharge, the AGM or lithium battery types are not economical. All of these factors lead to one conclusion: if you can run a grid-tied system, DO IT!

In your situation, I would definitely look into PAHS and include it in the design. The cistern water temperature could be regulated by the ground surrounding it with a small pump. It could also charge the ground for use a few months later. All the heat or cold that accumulates in the cistern could be spread out or drawn back in using your PV power, so basically free.


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Old 06-01-17, 08:42 AM   #12
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I guess the question is what one of the three would be the most effienct way to make this system. Being that I will have a decent size buffer tank does it really make sense to have a variable speed compressor? Obviously with it being coupled to solar it's the best choice in the long run. But will it be worth the extra cost and control setup.? I guess the way I look at it is with the buffer tanks a one speed system will probably do the job just fine. But it wouldn't be nearly as cool as a solar powered three phase system

Planning the system is something I really want to do and do well. I will only have bits and pieces of time this summer between moving and planning a DIY wedding in our new back yard. But once winter time comes around I should have more free time. I suppose if I found a 3 phase water to water unit that was gator built for the right price would be nice. So if anyone runs across a 2-3 ton 3 phase unit let me know
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Old 06-01-17, 11:03 PM   #13
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Good luck on preparing for your wedding. Definitely more important than heating and cooling. In the meantime, keep an eye out on Cincinnati craigslist. Lots of usable units pass through every week. I see 3 of them listed right now for around 200 bucks. Used 3 ton in Hamilton for 200, carrier 2.5 ton ashp in NKY for 200, 2 ton goodman in Erlanger for 300. Probably all single speed single phase units. Some assembly required.
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Old 06-02-17, 06:22 AM   #14
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fordguy,

Be careful of what you wish for. Jeff is a master at taking bits and pieces of this and that, and coupled with his superb fabrication skills can make complex things quickly that have dependability. So is randen.

Doing things yourself can be very rewarding, bur start now on some simple stuff. Like a modest air to water boost for your hot water tank. I don't know your welding/brazing and AC skills (guages, suction machine, etc), but this would get you started.

Understand, I am NOT downplaying your skills - in fact, your planning before doing is exactly the right first step.

I started small on several projects and have not regretted making mistakes on those. It prepared me for doing far bigger projects.

The project you are planning is huge and the worst thing is to get 30-40% into it and realize the "oh crap, what have I gotten myself into". A heating/AC system is essential to daily life and doing it right for dependability is essential.

Hope this does not offend!

Steve
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Old 06-02-17, 08:43 AM   #15
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Steve no offense taken. I've been a member here for a while but I haven't contributed a whole lot.. So little is known about me.. I've just been trying to take it all in. This is by far the best site for phase change information. Anyway.

I'm one of the jack of all trades type. But I'm a master at none. My day job I work at an R&D shop for a very very large company. I'm a machinist welder fabricator designer engineer and so on. They pretty much come to me with a stack of drawings and say make this.. Although I only have a HS diploma so I'm actually not an engineer or anything of the sorts even tho I do the job from time to time lol

Mechanical things are my favorite. Been working on things with motors my entire life. My dad taught me how to weld when I was 9 or 10 and I've been doing it ever since. I'm also pretty good with electrical and plumbing.

Although I won't lie the refrigeration cycle will be a learning curve and I'm sure it will be a big one. I have two 12k btu units I picked up a long time ago. I also have a 2.5 or 3 ton r22 unit from my dads house. It's old but it functioned when pulled. So I'll have lots of units to mess with whenever I get the time.

But I guess to further this project I need to do some real heat load calculations. I think my locat utility does one of those energy audit programs and I'll look into that after I move in. One of the things I'll probably need the most help with is sizing heat exchangers and tuning sizes. I really like the idea of not having the heat pump in the house. I'd rather have it in the barn. But it's easily 150 feet from the house. The pool is right in the middle of that.


I added a photo to my random album. It's an over view of the new property. The blue line is where the fence will go for the dogs. The blue circle is about where the pond will go. I cannot add the picture to my post because I'm on my phone and it crashes when I try to do it

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Old 06-02-17, 11:36 PM   #16
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Heat exchangers are no big deal unless you undersize them. If you are using a water-to-refrigerant method, the heat transfer is different from water-to-water or air. With refrigerant in one circuit of the HX, most of the heat transfer is latent. On the other side, all of the transfer is sensible. What happens is the condensing or evaporating temperature balances with your supply water temperature and flow. Sizing and flow control is all about this approach temperature and maximum leverage. Increased surface contact (either more water pressure or larger HX surface area or both) is a game of diminishing returns.

Brazed HXs are more compact than other types, but they must be fed clean liquids or they will foul and clog up. Other types of HX are more tolerant of contamination, but tend to be larger than plate HXs at the same heat transfer rate. SWEP has a cool app called SSP that helps you calculate whatever you need to. Coolpack is another app that is ultra useful for simulation and armchair tinkering, but is somewhat more difficult to use.

If you can weld and fabricate, building a durable enclosure for the rig will be easy. The plumbing side of the fabrication is the most difficult aspect of the build. Using safety-silv solder is much like soldering copper water pipe, but is not as strong as brazing rod. Brazing with sil-fos rod is more demanding due to the high melting temperature, but is self-fluxing and stronger. After doing some pretty gnarly plumbing on these rigs, I now start out with the sil-fos rod. If things go well, I am done. If not, I add a tiny bit of safety-silv to the ugly joint, and presto, everything wets out nicely.

I'm in the same boat as Steve regarding getting some time under the hood on something small before you put together a big rig. A non-reversing heat pump water heater is a really good test bed to tinker with. Load matching, metering device selection, adjusting refrigerant charge, etc. can all be done without a lot of time or labor involved. Actually operating and observing the unit is very informative and rewarding.

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Old 06-08-17, 07:05 AM   #17
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Yea I was thinking about a small build first. I found out that my soon to be brother in law has a bunch of equipment I can borrow. I knew he had a farm but I never realized he had so much fun equipment! Skid steers and mini backhoes and so on. So I still have the 2 one ton units. Maybe I'll put together something with one of those in the garage this winter. Could borrow the mini backhoe and dig a trench to put a small loop field in. Or maybe I'll just put in a good sized one for later. We will see with time and $$
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Old 06-08-17, 07:51 AM   #18
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If you're going ground source, make sure to plan the whole field out beforehand. Even if you never complete the whole thing, at least you know you didn't put a loop in somewhere it didn't belong. Plan to oversize your field, just in case. That way, if you decide to expand later, you won't be having to make compromising decisions. DIRTFT, because the second time is a lot more difficult.

With the system you cited, a pump-only loop dedicated to evening out the cistern temperature is one of the features that makes the efficiency skyrocket. A little 100 watt circulator pump moving the water through a loop that can realistically transfer thousands of watts of heat is not impossible. It has been done, and the results show up on the electric bill.

Farmers are cool! I recently had to do an engine swap on a car, and had trouble finding an engine hoist. Nobody wanted to loan me one today, now. So I went down the road to a neighbor's farm, and asked him what he had I could borrow for a couple days. I ended up using a hay spear, used to pick up and move those big round hay bales from the field to wherever they end up. He even helped me load it into the bed of my truck! It fit right onto the old Farmall tractor we use to bush hog with.

When I returned the implement, farmer neighbor wouldn't take my money. He said it would have just sat there all weekend anyway. While he wasn't looking, I dumped a can of gas in his truck for payment.
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Old 06-08-17, 07:18 PM   #19
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https://youtu.be/vaCSOu4d1po

Long and kind of boring.. But lots of info based on large systems
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Old 06-08-17, 09:12 PM   #20
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So this ice bank idea is kind of awesome. Although it seems for most cases it pays back faster if you have lower electric rates at night. I don't believe I have that. But I have almost enough solar to run a 12kbtu unit. So my first test rig might be two tanks of water for hot and cold. Hook up the solar and see if a can freeze a tank of water! Sounds easy

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