 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Solar : Water heater improvement.
Page 1 of 2   |
|||||
| Author | Message | ||||
| George65 Guru  Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Don't seem like there is a proper place to put this but seeing the water heater is solar powered atm and in with the big battery and efficency discussion, this will do. I have a Rheem run of the mill electric 400L heater. It sits on the west side of the house so get sun from about mid day. Has an over flow pipe and a valve and the outlet pipe all conducting heat away along with a couple of plugs on the other side which are also hot and a heat loss. I was going to insulate the pipes with that split foam stuff in case that may make any difference but was also in 2 Minds about extra insulation and direct solar heating. In summer, the outside of the light gray tank is too hot to put your hand on due to baking in the sun. I was thinking of painting the tank Black ( couldn't make it any Uglier) so there is some heat on the outside that may even radiate back through the insulation in to the tank. Not sure but at very least it would stop heat coming out. I was wondering about insulating the back side with some roof bats I have stored away in summer and enclosing the whole thing in winter. As far as I can tell, I'd have to build a complete waterproof inclosure because I can't see the batts getting wet doing anything any good. I am worried about condensation though. At first I thought wrap the batts round and then cover the thing in a big black plastic bag but I'm reluctant to do that for fear of trapping moisture and making everything rust to nothing. Anyone have any info on water heaters and if insulating it more would do any good at all and what the heat loss of these heaters are as standard? I thought I had seen something which concluded they did shed significant heat but can't remember f that was the electrics or the gas ones that weren't so great in efficiency. I have been powering the heater from solar so it's costing me absolutely zero atm so anything I spent ( have the batts doing nothing already and some tin I could enclose it with) would have to be minimal or make a worthwhile difference in the heat loss. Seems like something where they may be some efficiency gains to be made. |
||||
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I would think you would lose more heat over a 24 hour period than you would pick up from the sun on the shell and getting through the insulation to the tank. My HWS is a 320L Rheem solar, I have thought of adding more insulation to it. One thought is to make a small cubical for it from cold room panel to keep the heat in as the factory insulation could be better. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Electric storage heaters are especially good because you can completely insulate the tank. You are quite right about insulation getting wet in winter and rusting out a tank from the outside, that happened to me but with a gas water heater. Gas storage heaters are very different because there obviously must be a flue and heat exchanger somewhere, to get the burner heat into the tank. When the burner is off, the heat exchanger always runs warm and heats the air in the flue which is a giant constant steady heat loss. Not much you can do about that either. Natural gas water heating is still much cheaper than electrical water heating, even though the steady heat losses are much higher. When I was at the Gas and Fuel research labs about thirty years ago, the running cost differential was about 9:1 between using using off peak power and natural gas. I doubt if that has changed very much. Free solar electrical power is a game changer, although its going to struggle in winter. Cheers, Tony. |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Here in Qld that all changes, in winter we have blue skies most of the time, it is in summer when we get most of our rain and struggle sometimes to get enough energy from the sun. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I have a gas storage water heater I removed the gas burner from and fire it up with a waste oil burner. I always thought the flue was like a cooling pipe right through the middle of the thing. What these heaters need is a sensor that activates a flapper on the top of the flue when the burner is firing and closes it when the thing is idle. I believe the pilot lights on those gas storage heaters run all the time which consumes a significan't amount of gas in itself. This is why I will be installing over 20KW of panels when I'm finished. Sounds a lot but when you allow for the winter fall off and I can only orientate about half of it north, the yield drops a lot. I was surprised to find that the panels on the 5o south roof yeild better than the 35o on the west roof. neither as good as the limited north roof however. So far this quarter, with a fortnight to go, I'm still ahead. Have used very little heating although a bit of cooling in the first month. This coming quarter will be the telling one. Lowest solar radiation and accompanying temps. Have to get busy with that last 5Kw on the north roof but not looking forward to putting it up given the 35o pitch of the tin roof which is slippery as hell. Might be better off to just cover the whole heater in insulation and make it's own little enclosure than worry about painting it. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Then there are also heat pumps used to heat water: https://www.energy.gov/energysaver/water-heating/heat-pump-water-heaters Cheers, Tony. |
||||
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes, that would be my choice when the present instant natural gas water heater packs up. Since mine has no pilot light, the burner lights up when the tap is turned on, these things are quiet cheap to run and perfectly adequate for a one person household. So, the excess solar energy available here gets not used at the moment, the plan is to install a split heat pump heating/cooling system. I will have to do some research which ones can be turned on remotely from a full battery relay signal. Klaus |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I was aware of the heat pumps but I did not know how versatile they have made them...if they are available here. Read with interest they can divert the cool air to the house and also can be used for home heating. I also see they are now being fitted with resistance elements. Not always the case and people had problems with the things freezing solid in winter. Saw that happen first hand. A mate of mine who does High end AC just installed a heat pump hot water. Previously he had warned me off the things saying they were hopeless and a complete waste of money. Apparently they were terribly unreliable, parts were exy or impossible to get and they just did not justify their multiple times greater expense than a conventional heater. I asked what changed his mind for him to put one in? He said the company wanted him to be an agent for them so sold him the heater cheap as chips and gave him a control board and compressor unit along with a 5 year full warranty. He said he doesen't really care if it falls over now, in 5 years he will have got his money back and should be able to repair it for another 5 years of operation. He is keen to see how it goes in winter because where we are, minus morning temps are expected if not every day. For me, cheaper to buy more panels to run a conventional heater than a heat pump. |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have heard of lots of bad reports about Heat pumps also, my sister put one in and 2 years later gave up on it as a bad joke. I don't know what brand it was, a plumber who lives around the corner has a heap of them in his scrap pile too. Maybe there are good one but I would be doing plenty of research before buying one. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I've got 2 Rheem's here; both recovered as scrap.  What I've done is recovered the Heat pump unit off the top & converted it to a Spa water heater. There's quite a few points of failure. The Tank Temp sensor, is a strip PCB with resistors & thermistors, that green flexible ribbon type, runs the full height of the tank from top to bottom & measures temp at about 6 locations. It get moisture in it & fails. It's actually got 2 separate circuits; as in a spare, but on the one I stripped out, bonded under the expanded foam, the spare side was almost as corroded as the one is service. Their circulation pump is prone to clogging up & failing, causing the compressor to draw maximum current & eventually blow the Mosfet's on the control board. Basically, the only good part is the compressor/heat exchanger unit. It's quite good. Replace all their control electronics with my home grown stuff & it's an efficient Spa heater in conjunction with the solar water panels. What I'm wondering about doing with the spare water tank though is to put it outside near the inverter cabinet & use excess solar during the day to heat it's 320l of water, then plumb that to the main off peak HWS. In theory it might mean the HWS is fed something warmer than 24°C water in Summer, and better than the usual 10°-12°C it has to heat up in winter. Ideally, it's element could be "Dimmed", to the point where the solar output is kept near it's maximum capacity. Phil. |
||||
| hotwater Senior Member  Joined: 29/08/2017 Location: United StatesPosts: 120 |
I have a NYLE external heat pump added to my electric water heater and made it a hybrid. HPWH only get temps to the low 120's. I power the unused heating elements with solar. This can get an already warm tank higher than that 120F and prevent the heat pump from coming on from typical heat loss. When the heat turns on, I disconnect resistive solar heating and switch a grid tie inverter on. I do not have backfeed into the grid and this is a reltively small system, 30 gallon and 560W of solar. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I was thinking of something similar but in practicality..... not sure it's worth it. Once you heat the 2nd water tank initially you are still going to have the same energy consumption over all barring extra losses from the 2nd tank. What goes into the first tank you save on heating the 2nd so you will still have excess power after the first tank is warmed if you are back feeding now. I was thinking of something more along the lines of thermal storage for inside the house in winter. A drum of water may be problematic as you couldn't seal it and the water would expand and contract as it warmed and cooled and may make the place damp. I was wondering about a drum of sand and heating it with those drum band heaters or putting an old stove element near the bottom ( or maybe in the middle) and running that with a PWM controller to regulate the power. Easy to make automatic with a monitoring relay to sense when the solar is back feeding by the voltage level. Finally starting to get a bit nippy at night here so may be a worthwhile way to get some useful thermal storage happening? |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
A heater element in sand may get too hot as there is no circulation like in a water tank. You could have brine or something else in a tank that holds more energy. If the is a vent with a suitable capture of excess fluid due to expansion you would not need to worry about dampness. I am planning to build with rammed earth one of the big benefits is its thermal mass which results in a temperature variation in a home of only 2-3 degrees over a 24 hour period. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I'm looking at it from the point of view of leaving the existing off-peak controlled HWS in place powered as is; no solar energy to it at all. Just lowering the level of mains it requires. Only certain circuits are on solar here, the rest is on the mains. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I was thinking of a stove element as they can glow red without problem. Pretty sure a water heater element would burn out fast if not immediately. Also thinking one would need silicon wire to run to the element so the high temps didn't burn the insulation off the normal wire. I was looking up thermal masses and density's. Water is impossible to beat in practical applications. Surprisingly, sand is less than 1/4 the energy density of water. You can heat it hotter but that would work out at 400oC to get to the same heat storage and I'm pretty sure I don't want anything that hot sitting in my house. 200L of water @ near 100oC would be about 20 Kwh of heat storage. Going to take 8 hours @2.85 Kw input to get it there plus losses along the way. If you had the thing plugged in to an outlet in the house you could run it at 2KW all day ... or at least when you had excess solar. If you were bleeding the heat out again at Night, You'd probably never get it right up to temp just from the power limitation from the outlet. Another application for a voltage Monitoring relay for controlling the thing with the solar power. Sand would hold about 5Kwh. If we equate that to a cheap fan heater doing 2000w, it's only about 2.5 hrs worth of heat from one of those although would release a lot more slowly.... Which brings it's value into question in my mind. May be OK for a small room like the office I'm sitting in now but you could run a fan heater flat out for hours in every other room here without getting too hot just due to the size of the place. Might be OK to heat a drum to about 40o in the Laundry for the cats to sleep on with some blankets! :0) I also saw something about Cold Storage for AC. 1 Ton of water is good for about 100Kw of energy storage. Apparently some AC systems Freeze water at night at off peak rates then use the stored cold During the day. I saw a 500L chest Freezer recently for sale on Dumbtree cheap. One could fill that with water and put a good length of pipe in it ( may have to be brine filled), Freeze the thing and circulate water through the pipe and to a radiator. That would be a great way to use excess solar to cool a home at night and could be done practically as well. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Makes sense. If one had a limit on the solar they could erect, one could get some used panels and run the First heater off those direct. Would not violate any regulations then if one were Concerned about conforming to idiotic rules. Beauty would be on the cloudy/ overcast days, the main heater would work as normal. I had this idea too at one stage. For a while I was doing it with my oil burner and a gas hot water heater feeding into the main heater. Worked very well but I only had a 125L gas heater and couldn't find a 400 That I wanted that would have lasted a few days. I'm running the normal heater off the solar now with the Voltage relay and the PWM so no need to go to a second heater now although I am keeping my eye out for one just for some solar experimentation. Everything else is pretty much figured out and working well so I need something else to bemuse myself now with the solar caper. Want to get some of those evacuated tubes and learn about them. From what I read those things are so efficient they could be good for home heating. The second pre heat tank is a good idea for a lot of people though and would certainly be hugely more cost effective than those commercial hot water solar controllers. |
||||
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
there is a way to plumb a multi tank system for house heating that is very clever, I will have a dig around for a link. thermal masses behave differently to devices that heat the air inside a house. I have been toying with an idea to smooth the temperature variation with a thermal mass and do some zone heating with far infra red. I haven't found a good supplier for panels that last yet. so still a work in progress. regarding the evac tube, they work best in series with a traditional solar collector for home heating. I'm confused, no wait... maybe I'm not... |
||||
| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Took me a while to find. I needed to credit the guy that perfected the idea. John canivan youtube heat stratification my previous diagram from an old post shows the basic principal. I have done low pressure pvc plumbing with a product called uniseal that are quite good for this sort of thing.  I'm confused, no wait... maybe I'm not... |
||||
| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
it has crossed my mind that pv solar panels shed quite a bit of heat and it could be possible to enclose the back of them to use as a solar collector. Just a thought for the budding experimenter. I'm confused, no wait... maybe I'm not... |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I have had this same thought. There would be a LOT of heat available but putting it into practical application would be another matter. One would have to enclose and mount the panels in such a way there was airflow within the enclosed space, prefrably as even as possible. One then has to get the warmed air into the living space. To do this aesthetically, in a structurally sound manner ( water leaks etc) and also safely ( fire regs) would be another matter. Either a penetration through the roof or the eaves would be needed to bring the air in. This would require either metal or soft ducting. Neither seem ideal. Looking at my own home, this would be difficult to do without detracting from the look of the place and basically de valuing it. It may be possible in the right circumstances to have something seasonal that just sat in the yard on a mobile ground mount type arrangement and ducted the air in via a window with a suitable covering in the open area to attach the ducting to. One of the panels could power a DC blower as heat would be the main objective or the air could be pulled through from the house side. which may be better. I find a lot of things like this. The ideas are workable and efficient in themselves, applying them in a practical method is different. My last house was old and looks werent a big part of the value although the layout and position on the land which although large, was not practical for a lot of things I would have like to have done. Here in a very upmarket area, you really don't want the place looking like the house that Jack built. That said, I am also looking at doing a verandah out of panels on one end of the house. If I keep the ducting in mind at the design stage, it would be far simpler to incorporate the idea than to try and add it to anything existing. I am currently trying to do a deal on 40x 250W panels to use as the roof covering. I could put any leftovers up on the west side of the house roof and sell some of the smaller ones I have presently. Could get my money back on them pretty easily and can't see me needing 30Kw worth of panels. The main idea for this verandah was to create shade in summer along that wall which is a terrible heat soak in summer and result in much lower inside temps if it could be shaded. If heat could be drawn in winter, double bonus along with the extra solar power. I have worked out that used panels at $100 kw would be about double the cost of Colourbond for the same coverage but of course the Colourbond does not give you any savings or return so at the end of a year ( or less) the panels would be cheaper and pay well after the initial 12 months or less. Ducting the heated air in under the eaves would be possible although dampers would need to be installed probably for fire/ insurance reasons and to stop the entry of hot air in summer. If a reversible or 2nd fan was installed, the roof space could also be cooled in summer by taking air out of there. I was thinking of putting a duct with a fan to the peak of the roof with a filter on the end and sucking the warmed air back down into the home from there. Was just goi9ng to make up andother temporary manhole cover for testing and if it worked as I believe it would, then I could just either tap the air into the existing AC ducts or install a seperate AC type outlet. I already bought a double thermostat that would monitor house and roof temp so the thing only kicked in when the roof temp was say 5o warmer than the house temp and if all the warm air got used, it would switch off and wait for it to become warm again. Someone told me they thought this was a less than brilliant idea as they believed the air quality with dust and the vapors given off by insulation materials etc was not good. The suggestion was to install an air to water or air to air heat exchanger. Takes the concept from a No/low cost idea to one that would have to be weighed up carefully on the merits of cost Vs Return. I wonder if there would be a way to measure air quality in a specific roof space to see if the air was ok or best avoided? Perhaps ducting and refreshing the air may be enough with dust filtering for it to be OK? Wonder if there are affordable Charcoal or similar type filters for air like one can get for tap water? Ducting the warm roof space air would certainly be a cheap and easy enough thing to do and I believe would be effective as well. Never been in a cool roof space even in the middle of a downpour at night looking for leaks ! :0) |
||||
| Page 1 of 2 |
|||||
 Print this page |
