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Forum Index : Solar : adding solar hot water plate collectors
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| rgormley Senior Member  Joined: 22/02/2006 Location: AustraliaPosts: 245 |
Couple of questions / ideas needed... Years ago i built a solar hot water plate collector from copper tube and left over glass panels from work, stuck the think on mums roof and connected it to the existing gas storage HWs it worked like a charm for 7 or so years, until one "cold" morning it froze and split a pipe in the collector, i replaced the pipe and was good for another 2 weeks then another pipe split, i took it down after that. basically this home built unit i made saved 50-70% on gas bills to heat the water. Now the questions: I have another "home built" unit that i want to connect to our own gas hot water storage unit. the HWS unit is a Dux 135 LTR gas starage like this one http://www.agl.com.au/home/EnergyShops/HotWater/Pages/DuxPro flo%C2%AE170.aspx the incoming and out (house) hot connections are on the left side plus gas connections. What i have noticed is there is also additional "inlet" and "outlet" connections on the right side. (plugged of with a cap and plumbers tape) SO are these connections plumbed in parallel internally to the main water tank with the inlet and outlet connection on the left side??? If so could i connect my plate collector to the right side connection (thermo siphon mode or small pump mode) to aid in the heating of the water?? Thanks... |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Think of it this way ... its a cylinder inside with a left and right inlet at the bottom and a left and right outlet at the top or should i say 2 holes in the cylinder at the bottom and 2 at the top...thats it with the water in between. What you are asking will make no difference which inlet/outlet you tap into as they are really each one of the same. What i have seen from the guys using this system in cold climates, they run a 2 stage heat exchanger that the solar collector heats a container of water that then heats the incoming water to the heater. This way the solar collector can run antifreeze or radiator coolant or imploy a drain back system for during night to prevent freezing and pipe ruptures. In Oz you can buy water heaters that have inbuilt exchanger coils for use with slow combustion wood stoves and they run coolant (anti boil/freeze) in that system. Pete. Sometimes it just works |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
so this idea should work! 
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Hmmm, if the collector is setup as drawn than the cold water needs to come into the bottom of the collector and not the top as shown. Hot water rises remember. What is the collector coils made out of as you will need to support them so any water hammer effect from washing machine solonides etc dont rattle them to bits with time. If its plastic pipe than this wont matter...copper will. You might want to include a check valve on the return path so you dont get reverse effect during the cold nights or it might cost you more than you save. Im not sure on how well it will work because the collector will need to get to a temp hotter than the water heater before you will get any thermo siphon. I still think the 2 heat exchanger coils is a better system as this raises the temp of the incoming water before it gets to the heater, weather its a 1% or a 100% increase it is always a gain where your system might sit doing nothing most of the time. Or worst still, actually cool the water if designed wrong. The more i think about this the less i like it because it is really designed ass about. If the heater was on the roof and the collector was on the ground then it would work as the hot water will rise but you want the hot water to go down and the cold to go up and something tells me this might not work. Ever wondered why a solar heater has the tank above the solar collector??? ...tip... it aint for looks. I have been wrong before. Pete. Sometimes it just works |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Close coupled systems have the tank above the panels. What Richard needs is a small circulating pump, as is used on many commercial units with a ground mounted tank. The pump circulates water based on temp differences, and can be automatically turned on intermittently, to prevent panel freezing. Gordon. become more energy aware |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
another picaxe project for pete to turn the pump on and off. hot water pumps are about $90 on ebay, my system did it like that, also even though an evacuated tube system circulated hot water through the manifold if temp dropped to 1deg thus no anti freeze and no freezing problem even in the snow. Luck favours the well prepared |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
[quote]another picaxe project for pete to turn the pump on and off. [/quote] Gizmo has already done that on the front page. Pete. Sometimes it just works |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
this looks like what i will try. complete kit apart from misc copper pipes,lagging,tees etc (can get from Reece or bunnings) (I have a 240V GPO nearby) http://sunhot.com.au/products/evactubeproducts/rfk.html |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
I'm jumping in a little late here, but I'll toss in my 2-cents' worth anyway. I'm a plumbing contractor in the USA and have been one all my adult life (and then some!). I have already done nearly exactly what you have pictured above, with a few exceptions: Since the collector is above the storage unit, a closed-circuit recirculation pump is necessary. Heat rises, but unfortunately here, the "heat" is already at the top of your system. I configured my collector(s) so at the top of the system (away up on the roof) there was a "burp" valve. This is merely a little valve that lets the air out of the system. On that same line, I installed a copper tee with a solenoid-operated valve on it. I had a sensor that compared the temperature of the stored water in the tank with that of the surface up at the collector. When there was a 15-degree temperature difference, the little pump (magnetically-coupled by the way) kicked in and circulated water between the panel(s) on the roof and the tank below up to a pre-set maximum. It's important to realize that you can BOIL the water in the panels and you certainly don't need the water THAT hot ever. In this country, a "Tempering Valve" is sold with solar applications and it mixes cold water against the water coming from the solar storage tank (or panels -- depending on how the system is configured) to prevent "scalding". The valve is graduated by temperature and all you do is select the range and the valve (when it works correctly!) takes care of the rest. When the temperature sensor on the roof went below 40 degrees, it sent a signal to the solenoid-operated valve on the roof and also one to a motor-driven "Ortega" valve (three-way ball valve) outside near ground level. When the temps fell too low (approaching freezing), the panel separated itself from the storage system and drained. That little "burp" valve let air into the top of the system when the pressure drops. This way, even if it gets below zero, there's no water in the panels to freeze and they are freeze-protected. I no longer have the system or I would gladly pass along pictures. I still have the pump and will take a picture of it and come back later to throw it in using the "edit" feature. Whatever you do, do yourself a favor and build a 3-valve "H" pattern isolation valve setup so you can isolate things and leave the water on in your house. I had a system for the panels and another one for the tank, so I could fiddle with just about anything and not entertain complaints from the peanut gallery (wife). If you wind up using a Grundfos (brand name) pump as is pictured in the link you posted, be aware that this pump is designed to be mounted in the horizontal position. Mounting it any other way will ruin the thrust bearings in a year or less. One last thing. DO NOT use the bottom inlet nipple to draw cool water from the tank. Instead, install a check valve at the top of the cold side so cold water cannot be drawn through the house through the hot water system and put a "tee" at the top inlet. Doing this will take the water from the "dip tube" (a plastic or metal tube that carries cold water to 5% above the bottom of the storage tank). This will prevent the pump and the rest of the system from "fouling" due to sediment uptake. Very important! Also, by putting the water in at the top both from the make-up supply as well as the solar application, when it's time to replace the water heater, it's just a change-out and not an all-day re-piping affair! Hope that helps you out some. I'll be back later with the pump picture. Here ya go: 
This is the 110 VAC pump. I have "hose" ends threaded on now. I cannibalized it to be able to hook it to a hot loop I built on my water heater. I allows me to use the heated water in my garage water heater to pass through a fan-forced fin-and-tube core and heat my workspace when I take the time to hook it up (seldom-just lazy!). 
This is an end-view. The center is the inlet and the other one is the pumped side. Get this backwards and it's just a paperweight!  Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Just a note regarding Mac's warning about connections. Here in Aust. most heaters are made with universal in/outs so one left and right so they will replace either previous brand. The extra connections you ask about using is not the same plugged fittings that Mac was talking about so should be fine to use. Even with a pump i would still use a check valve to stop the hot tank water rising up into the collector. Pete. Sometimes it just works |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
hhhmmmm efficiency question... if i hook a collector to my exsisting gas storage unit, sure the sun will heat the water during the day (none or less gas usage) great!! BUT we shower at 10-11pm at night, so once we have showered, the tank will be refilling with cold water and the gas will kick in to raise a full tank of water and cycle all night long maintaing temp, using lots of gas. ...bad 1: Turn the gas tap of /risk cold showers during winter? 2: Lower the temp of the thermostat over night?? hhmmmm.... |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
You could add a pre storage tank for the solar heated water and the water in that replaces the used water from the heater. Any increase in the water temp prior to reaching the heater = reduced gas requirements. Pete. Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Hi; me again. I have successfully used oil as a solar-collection working fluid too. Oil (temperature) will go much higher than water and if you were to keep a (buried!) receiver full of solar-super-heated oil, then you could merely divert the water flow from your existing gas-fired water heater through a heat exchanger inside the hot oil and you'd achieve the same thing without all the bother and worry about freezing. Just an idea. If you're interested, PM me and I'll run you through what I did. By the way, this "can" be really dangerous if you don't take some precautions. I've done it before and been down that road, so I'll try to steer you a straight pathway, if you're interested. I am reticent to post all the details taking a precautionary stance just in case someone wants to go it alone. If you're not very careful, you can create "flash steam" and blow things all over the place, causing both property damage and perhaps near-fatal injury. LIke I said, it's a bit on the dangerous side when the oil temperature rises above 212 degrees F and believe me, it goes way above that! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
hot oil, burried tanks over 212D nope!! not for me i`l just stick some evacuated tubes on the roof, and pump the water around with a controller in/out of my HWS tank i`ll go the simple safer way... |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
rgormley If you're squeamish at 212D, you're wise to bow out. This kind of thing gets easily twice that hot with only a flat-plate collector (no concentrating). I have been planning on making a very small, portable unit using oil as a working fluid to use when I go "camping" in my RV. My RV has a propane-fired water heater, but I consider that "cheating". When I get around to doing this, I'll post pictures on this 4m. The whole thing will be no bigger than about 2-foot square, double-glazed and I'll manufacture it so it will thermo-siphon (receiver above the collector), deleting the need for a pump. The receiver will be no more than about 2 gallons, sealed in a 2-inch jacket of beach sand for insulation. I'll be using it for air as well as water heating. I may even incorporate it into a "solar oven". . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
ok guys why the bends (dropped loops) on the inlet and outlet to the HWS ??? item 2 and 8 
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Loomberah Regular Member  Joined: 11/06/2008 Location: AustraliaPosts: 43 |
To accommodate expansion and contraction! As the pipe heats up and increases in length, its going to put a lot of stress on the connection to the HWS, a U-bend eliminates much of that stress, as the U opens and closes instead. Loomberah weather +solar&UV, astronomy, photography, organic farm |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Whenever you plumb with rigid pipe there should be a minimum of 3 changes in direction between any 2 fixings, to allow for movement in each of the 3 dimensions that occurs with changes in the differing thermal expansions that occur with cyclic temperature transients. If you don't then the pipes will fatigue crack over time. This is achieved with the combination of the 2 elbows, and the U. Basic plumbing 101. Gordon. become more energy aware |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
thats what i thought also.... Also interesting i found this in the dux install guide 
Care needs to be taken when running flow and return lines through the eaves. Flow and return lines should be neatly installed. return line must run horizontally to the tank (as pictured) NOT directly vertical to the solar return socket. • This prevents reverse thermo-siphoning. I.e. hot water loss where hot water moves from the storage tank to the collectors and storage tank heated water can cool[IMG]uploads/rgormley |
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