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JC77

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Reply with quote  #1 
Hello, I've been cruising around here for a while but have limited time for research so I thought I'd throw it out here and see what I can find out. I'm planning a solar water heater build this spring. I'm going to construct a 27x8 or 27x10 hizer style panel that will be located roughly 125 feet from the house. I'm planning on heat storage of 2 gallons per sq ft of collector area and doing the system pretty much as described on the BIS site. I plan on installing radiant floor heating and also baseboard heat to assist my geothermal heating system in the winter and also preheat my incoming well water before it enters my tankless water heater. My basement isn't finished so I have lots of options open on how to configure things in the house.
My biggest dilemma at this point is that my house is a tri-level which means my basement floor is about 4 feet below grade. Which is giving me fits figuring out slope for drainback. I've read that 1/8th inch per foot slope is acceptable.. my supply and and return lines to the collector will be one inch piping but I'm thinking over a 125 foot run, it's going to be impossible to keep dips out of the lines so maybe 1/4 inch per foot of slope would be better but that puts the lines coming thru the basement wall less than 16 inches off the floor.. so I'd have to build a small drainback tank inside the basement next to the storage tank to hold the volume of all the piping outside the house. Not impossible. 1/8th inch per foot gives me about 30 inches of height off the basement floor.
I live in central Illinois. None of my trench will be below the frost line which adds frost heave into the equation. I'm kind of resigning myself to a closed loop system. The trench won't be straight either. It will have to come out of the west side of the house and make a 90 degree turn to the south, go south for about 90 feet and make another 90 degree turn back to the east to reach the collector. I'm just wondering if anyone has any good advice or experience with slope and drainage on something like this. I could use one inch pex and eliminate the 90 degree turns but I'd have to hire the trench digging because I'm not good enough to get that precise. The other option is to go closed loop and make the entire trench below the frost line so I'd only have to insulate against the 57 degree constant ground temp. Any help or references is greatly appreciated.
I already have a small 4x8 collector on my roof and a 55 gallon plastic drum for storage tank that I've been using for two years. It's a drainback setup that's worked ok. I'm ready to scale up my solar but I'm kind of at a crossroads on system design. My current thinking is to construct the system with drainback in mind and do all my experimenting this summer to see how well it drains. If it doesn't work, then I'll put solar grade glycol in it and call it good. One thought I had was trying my best to achieve drainback but still have a closed loop system. I'm almost certain I could get it to drain well enough that the collector would be empty once the pump shut down but I highly doubt I could get all the water to drain out of the trench lines. So maybe have a lazy drainback/closed loop setup with glycol so the collector and lines are protected in the event the pump stops on a hot day but I'm not sure how well it would empty out if there were a small dip in the return line that might restrict air from getting to the collector.
I don't have much experience in drainage and what you can and can't get away with. My neighbor has a mini excavator that he can about give back rubs with. He has a laser transit level and is a highly skilled operator. A precise slope is definitely a possibility but it comes at a cost. I have a tractor with a spade attachment so I could do a closed loop trench myself and spend the money elsewhere. With a 1/4 inch per foot slope, I'll have to build a small drainback tank inside the house because the storage tank will be to tall for the return line to be above the water level. I'd like the storage tank to be at least four or five feet tall to accommodate heat exchangers. I'm currently thinking a closed loop system makes more sense because that allows the collector to be bigger.
My current plan is a vertical collector mounted flush to the south wall of my garage. I'm limited to 8 feet of vertical height by the soffit on my garage but the ground slopes away from the garage wall where the collector will be located so I could gain a couple more feet in height by going with a tilted collector instead of vertical. Tilting the collector to a 70 degree angle means I could build it a full ten feet tall for just a small amount of digging but that puts the bottom of the collector too low for drainback.
So I could build a 27x8 (216 sq ft) and possibly have drainback or build it 27x10 (270 sq ft) and commit to a closed loop. It's another 54 sq ft so it's definitely worth going after. But there are efficiency losses with glycol plus the efficiency loss of having another heat exchanger that wouldn't be needed on a drainback. But I'm thinking drainback is questionable at best so maybe I'm ahead to just plan on closed loop. Which is what brought me here. Once it's built, it won't be cheap or easy to change it. One added plus of a closed loop for me is it opens up the possibility of routing the supply and return lines thru the attic of the house/garage and eliminating the trench all together but that still needs further research. Also, a 70 degree tilt will be helpful for winter collection.

SolarInterested

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Reply with quote  #2 
You sound like you've researched this quite a bit. If you haven't already you might want to have a look at Scott's project:
http://www.n3fjp.com/solar/BigProject/BigProject.htm

and Jamie's:
http://simplysolar.supporttopics.com/post?id=7175299

They both went with closed systems with fairly long pipe runs to their panels.

A few words about your post. Breaking it up into paragraphs might help the readability rather than having a 'wall of words'[smile]

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JC77

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Posts: 15
Reply with quote  #3 
Sorry. I'm on my mobile. I'll try to make it look better if editing is possible. I've looked at Scott and Jamie's projects front to back seeing how they did theirs. I also didn't clarify very well in my first post. If I can go with an 1/8th inch per foot slope, it puts the return line coming thru the basement wall about 30 inches off the floor so I could build a storage tank low enough to allow drainback. 1/4 inch per foot slope puts the lines coming thru the wall around 16 inches off the floor and I'd probably be ahead to go with a closed loop as I'd already have to build it that way anyway. I basically need to know if an 1/8th inch per foot slope is doable in a one inch pipe run that's 125 feet long. It sounds risky to me but I'm not very knowledgeable in this area.
sundug

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Reply with quote  #4 
With the distance and slope difficulties you have, consider another approach-                                              
MAILBOX: PV-Direct Water Heating Vs. Solar Thermal | Home Power Magazine
In Mailbox HP179, Hugh Piggott cited some advantages that make PV-powered water heating preferable to solar thermal technology. Here are a few more:

Reliability—There’s no heat-transfer fluid that can leak or deteriorate; and no circulating pump means no moving parts that can fail.
Simplicity—The systems are easier to install, test, and commission. A tank water heater having one ordinary and one solar immersion element is no big deal, compared to a special “solar tank” with its necessary heat exchanger.
Autonomy—Many solar thermal systems need grid electricity for the pump controller and the circulation pump. PV systems can be entirely self-powered—ideal for those in developing countries, as well as “off-gridders.”
Layout flexibility—It’s easier and cheaper to run cables than plumbing. There are no airlock worries, either.
Guaranteed energy harvest—Lower solar input in early spring, late autumn, and winter, can compromise a solar thermal system—will the collectors achieve the necessary temperature to input heat to the tank? With PV, if there’s any energy available, it’ll be harvested. Plus, PV modules are more efficient in cold weather.
High-temperature capability—Even if the available PV power is low, it can directly heat the hot water supply tank; there’s no need for a preheat tank.
Instant delivery—By using a Willis-type external immersion heater arrangement (popular in Northern Ireland, but universally applicable), hot water can be drawn almost as soon as your PV array starts generating a surplus.
Greater end-use flexibility—With a PV-heat arrangement, you aren’t just restricted to heating water. With a little creativity and electrical know-how, you can use conventional switches and relays to readily swap between water heating, background space heating (very useful in spring and autumn), or greenhouse soil heating. You can also cook with PV power—think of the deforestation, the fuel-collecting time, and the smoke-related illnesses this could prevent. Meanwhile, even Scots, Alaskans, or Canadians can—using a conventional AC hot plate fed from a dedicated “PV surplus” socket, on sunny days—be bulk-bottling fruit or juice, jam-making, or brewing beer in large batches, and enjoying full tanks of hot water!
https://www.homepower.com/articles/solar-water-heating/domestic-hot-water/mailbox-pv-direct-water-heating-vs-solar-thermal

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JC77

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Reply with quote  #5 
I started looking at PV panels before I got into water heating panels... from what I've read, PV panels are roughly 20% efficient meaning they're only capable of capturing 20% of the available energy from the sun compared to DIY water heating panels that are roughly 50% efficient. And I'd still need to build a storage tank to be able to store hot water. I just put in a takagi tankless water heater because I'm tired of replacing tanks every five to ten years plus I need more hot water than an 80 gallon tank can deliver in one hour. Feel free to correct me if my figures are wrong on PV's comparison to DHW solar panels. I think air heating panels are probably the most efficient of the solar collection methods but I can use hot water year round which tips the scales towards a DHW system for me. A DHW system lets me store heat easily and also put the heat directly where it's needed. I have room for PV but it just doesn't look like the best bang for the buck right now. I would think the EPDM liner in a DIY solar storage tank could last upwards of 20 to 30 years. I don't know of any conventional water heater tank other than one of those plastic Marathons that have that kind of longevity and even those aren't big enough.  
    I looked at solar air heating options but I need the ability to store heat for overnight use. I have more space for solar than I have wallet depth so I plan to make expansions to my system as time and funds become available. I have four kids aged 17 to 11 and use a LOT of hot water. From what I've researched, solar water heating makes the most sense for my situation. I shouldn't have any trouble using all of the heat captured. My home is about 3300 sq ft with about a third of it insulated with icynene. I put in a geothermal system about ten years ago and I'm happy with it but it really likes it's electricity. I think if I went the PV route, I'd probably just go with a grid tied array to help offset my entire homes electric use but those systems are still very expensive. My friend put one in two years ago and I think he spent around $28,000 after incentives.  He said he's looking at a 30 year payback... Anyway, my long term plans are to build a large water heating panel this year. Then build solar air heating panels for the places on my house that aren't conducive for water heating. All told, I'll end up with 270 sq ft of water heating and about 130 sq ft of air heating. 
     One thought I had was passing the geothermal loop fluid through the solar storage tank or even the collector if possible to add some BTU's directly to my already installed HVAC system and forgo the radiant floor and baseboard heaters but I haven't heard back from the geothermal manufacturer (Climatemaster) to get tech specs on my unit. Another thought I had was installing a second set of geothermal loops. I'd use one set for heating and one set for cooling. In the summer, when I'm cooling the house, the heating loops would be out of service. The fluid in the heating loop could be heated with a solar collector all summer basically making a large section of earth warm to be ready for winter. Then during the winter, the cooling loops would be out of service and I could run those through some kind of water to air heat exchanger and use the entire winter season to freeze a large chunk of earth to help with cooling during the summer. But thats a little far fetched at this point. I'm guessing if it were that simple, all geothermal systems would work like that. I doubt the heat would remain in the ground long enough to be very useful and likewise for the cold.  It's been my experience with my system that the heat extracted out of the house during the summer is mostly dissipated by the time the heating season begins and likewise for cooling. But maybe passing the geothermal fluid thru the solar storage tank right before it goes to the unit might be helpful for heating.  I'm definitely game for combining solar and geothermal but for an average DIY guy with a limited budget, a DHW system will provide the best return.
JC77

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Posts: 15
Reply with quote  #6 
I'm giving up on drainback. My trench will have to pass under my gravel driveway on the shallow end near the collector. Frost heave plus the driveway are more risk than I want to mess with. I'll have to put the lines inside schedule 40 pvc at a minimum for protection and deeper is better at the driveway.

I have some questions regarding a closed loop system. First is about expansion. I saw how Scott and Jamie did theirs with jars and buckets but I also saw someone post the idea of using a tee fitting that allows for a reservoir to be created above the line to remove air and also allow the fluid to expand. That is probably how I'll do mine. Is there any certain volume the reservoir should have? The collector loop will have roughly 15 to 20 gallons total in it with about 8 or so being in the collector at all times. If the collector stagnated, I'm guessing there would me significant expansion. I'll probably put my expansion reservoir near my sump pit so I could plumb an overflow to the sump but wondered if there was a certain volume I should have. Or should I just put in a regular expansion tank and call it good?

My other question was about zone valves. Since I'm going with a closed loop, the other two places on my house that I was going to put solar air heaters could now be hydronic heaters. I'd put a single pump dedicated to the main collector but I have two smaller areas that could each get collectors. One is 64 sq ft and the other is 90 sq ft. These would be future builds but I'd make accommodations for them now. Could the two smaller collectors be served by a single pump so long as the pump was sized to handle the flow? I'm thinking I could throttle flow to each collector with a ball valve to set the proper flow and use a differential controller to open a zone valve to allow flow to a collector when it got hot enough. Both collectors would receive full, unobstructed sun all year but I'm not sure having controls just in one collector is the right way to go. The smaller collector will be tilted to about 70 degrees while the bigger one would be vertical. And how would I start the pump if the differential controller was wired to open zone valves?
I'm not very educated in controls and relays abs solenoids and such. I could just put a separate pump and controller on each collector but I'm trying to reduce the amount of pumps I have to run.
sundug

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Reply with quote  #7 
How about PV pumped closed loops for the two smaller systems?

http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm

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JC77

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Reply with quote  #8 
No reason why that wouldn't work. Looks like I've got more research to do on solar powered pumps. Thanks for the suggestion. My big panel is going to be about 270 sq ft and require around 11 gpm. I figured I'd keep that one AC powered with a differential controller but I'll see what's out there.  Looks like sizing the pump and PV panel are absolutely critical.
JC77

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Reply with quote  #9 
Work has been busy tonight but I did a little looking around and found a few PV pumps at Backwoods Solar that are around $250-$300 plus I'd need at least two 30 watt PV panels. The 90 sq ft panel needs 3.6 gpm (90sq ft x .04 gpm per sq ft). I can buy an AC powered pump from menards and a differential controller for under $200. I'm going to keep looking at PV powered pumps. I'm reading that the wide fluctuations in voltage from a PV panel can cause problems. I'd definitely want some kind of temperature indication from inside the collector regardless of how I set it up so maybe the AC powered pump/differential controller would be the way to go. From my perspective right now, even if I had 3 AC powered pumps on 3 separate collectors and one pump pushing fluid through radiant heating zones in the house, I doubt their combined use would exceed 3 or 4 kw/hrs a day. I think my geothermal unit uses around 15-30 depending on the outside temp. Not that my solar setup would eliminate that entirely but it looks like I could get a reduction in the 30 to 40% range during the heating season. And that's not counting the LP gas saved on domestic water heating. I might go with AC pumps and bank the savings for a while and spring for PV pumps later on once I have everything built and running and have a good feel for how it operates.
     My geothermal makes for an awesome air conditioner but it really gets a workout heating the house. It has never needed the backup electric heat to maintain temp but it runs quite a bit. It can only put out about 88 degree air at the registers and it gets closer to 85 towards the end of the heating season (I keep the thermostat set at 66, any lower would be cause for all out mutiny at my house) What it lacks in temperature output, it makes up for in air volume. It has to move a lot of air. Anyway, I figure anything I can do to keep the geothermal compressor from running is a savings. If I knew more about thermostats and relays and such, I thought about putting a large air to water heat exchanger right in the main duct coming off the geothermal unit and figure out how to make the fan that's already there run. Then I could use solar heated water similar to how you'd tie in a woodburner to an existing gas furnace. Not sure what way is more a more efficient use of the solar heat. Radiant and baseboard heaters or installing a heat exchanger right in my existing ductwork. Putting a HEX right in the ductwork would definitely be an easier install...        
sundug

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Reply with quote  #10 
$60- 
https://shop.heliatos.com/Heliatos-HS-17-Solar-DC-Circulation-Pump-0130021.htm

$45 with shipping- 
https://www.amazon.com/dp/B00XOITM90/ref=asc_df_B00XOITM905401998/?tag=hyprod-20&creative=394997&creativeASIN=B00XOITM90&linkCode=df0&hvadid=167157220945&hvpos=1o3&hvnetw=g&hvrand=3398631182216731067&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9024019&hvtargid=pla-310749797160

Pv pumps can take varying voltage, that acts as a controller

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