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Da Rolling Eye
November 5th, 2007, 03:12 PM
So we have a solar water heater, but didn't have enough sun the past couple of days to get the water up to the "normal" 140+. Water heater kicked in and got the "recommended" 120. :rolleyes:

Wuz wondering. Anyone try those tankless heaters? Are they more economical than trying to heat 80 gallons of water? Your thoughts or experiences. Mahalo...:)

joshuatree
November 5th, 2007, 05:55 PM
So we have a solar water heater, but didn't have enough sun the past couple of days to get the water up to the "normal" 140+. Water heater kicked in and got the "recommended" 120. :rolleyes:

Wuz wondering. Anyone try those tankless heaters? Are they more economical than trying to heat 80 gallons of water? Your thoughts or experiences. Mahalo...:)

Got to try one as a guest in a house so can't give you numbers but my experience/opinion is that tankless heaters are more economical if you don't use a lot of hot water. Figure you don't have to waste all that energy heating up huge amounts of water and keeping it hot. Since you are supplementing a solar water heater, maybe it would work out for your scenario.

68-eldo
November 5th, 2007, 07:20 PM
I think the only advantage of a tankless heater is it can be placed close to the point where the hot water is used. The advantage is it does not use so much water to get the hot water to the faucet and it leaves less hot water in the pipes.

If you have a fairly new water heater it probably does not lose heat very fast. Some one told me he had a timer on his water heater that only allowed the heater to work for a couple of hours a day. He assumed he was saving money. The timer went out and had to be bypassed. He reported there was no change in his electric bill.

I have a gas water heater and I can hear the burner running on it. The only time I hear it is during or right after someone has used hot water. So that tells me the water heater has very little heat loss between uses.

I donít know how a tankless heater works but if it has a sensor that would shut off the heater if the water was already hot then it might be of some value. If it heats the water anytime the water is running then it would be a big waste of energy with your solar heater.

craigwatanabe
November 5th, 2007, 08:39 PM
Yes there is a sensor that will tell the On Demand Water heater to light the burners.

One of the problems with gas on demand water heaters is that they require a 3/4" NPT pipe fitting to allow for a greater flow of gas as opposed to a standard gas water heater that can utilize the 1/2" gas piping.

As for electric on demand water heaters, when that sucker kicks in watch your electric meter spin like a dickens. You simply cannot disconnect an electric water heater and use that same 220-vac two phase connnections to run your electric on demand heater. A typical electric water heater uses two 30-amp circuits for a combined load of 60-amps of usage every time that heater is running. An electric on demand water heater requires two 40-amp service circuits or 80-amps per hour of electrical requirements.

Back OT on your solar water heater there is typically a 120-gallon booster tank that has heater elements built in for those overcast days.

lavagal
November 5th, 2007, 08:49 PM
Same thing here. The water tank isn't on any kind of trigger to kick in should the sun not shine for a few days. So we take cold showers until one of us gets industrious, removes the obstacles between us and the water heater closet, and flips the switch.

MixedPlateBroker
November 5th, 2007, 10:02 PM
I know tankless water heaters are popular in Germany. There it's more efficient to heat water at the point of use rather than pumping hot water through pipes which get very cold during the winter. I'd personally prefer a heat pump though. My aunt has one and it helps to cool a portion of her downstairs living area while simultaneously satisfying her hot water needs.

Nords
November 6th, 2007, 07:11 AM
Wuz wondering. Anyone try those tankless heaters? Are they more economical than trying to heat 80 gallons of water? Your thoughts or experiences. Mahalo...:)
It's a tossup. The tankless heaters are so much more expensive (especially with Hawaii's added shipping/installation costs) that the payback can take the life of the heater. Of course 21 cents/KWHr here speeds up the cost recovery, but only using it for a few weeks a year (and using the solar water heater the rest of the time) really slows down the cost recovery.

Some tankless water heaters use over 100 amps of AC current when they're running, which puts a very heavy load on your house wiring.

Then there's the issues of reliability, minerals clogging the pipes, special wiring to the kitchen/bathrooms or special gas piping...

I'd say that having a reasonably modern water heater, indoors, perhaps with an insulating blanket, never seeing the weather dip below the high fifties, is at least as energy-efficient as a tankless heater. Last year during the 40-days-and-nights-of-rain we flipped the electricity on our solar water heater only a half-dozen times.

68-eldo
November 6th, 2007, 08:34 AM
Yes there is a sensor that will tell the On Demand Water heater to light the burners.



I know there is a sensor to turn the heater in the tankless heater on, but is it a flow sensor which turns the heater on whenever the water is flowing or is it a temperature sensor that will turn on the heater only if the flowing water is cold? The point being that if the solar heater is working you would not want the tankless heater burning energy to heat already hot water.

joshuatree
November 6th, 2007, 01:28 PM
I know there is a sensor to turn the heater in the tankless heater on, but is it a flow sensor which turns the heater on whenever the water is flowing or is it a temperature sensor that will turn on the heater only if the flowing water is cold? The point being that if the solar heater is working you would not want the tankless heater burning energy to heat already hot water.

Good question and I tried looking on the net but didn't get a clear answer. It appears a flow sensor on some models. If it's a temp sensor, I think that would be a great supplement to a solar water heating system where on days, the water is not at the ideal hot temp, the tankless merely has to heat the already warm water to the ideal hot temp.

Da Rolling Eye
November 6th, 2007, 03:11 PM
Guess I'll just stick it out with my present system. Was just running some thoughts and wanted some input. Mahalo plenty.

At present, I have a 2 panel solar system with an 80 gal. heater/collector with a timer for those cloudy days.

With the higher fuel surcharges, our bill is up to almost $200 pre month with some day and nighttime A/C usage. The same usage, pre solar, used to run us $100 per month and dropped to $60 per month, post solar. So much for our savings and making up the cost of the damned unit, ah? :o

Zovo
November 21st, 2007, 11:52 AM
Good question and I tried looking on the net but didn't get a clear answer. It appears a flow sensor on some models. If it's a temp sensor, I think that would be a great supplement to a solar water heating system where on days, the water is not at the ideal hot temp, the tankless merely has to heat the already warm water to the ideal hot temp.


Most tankless water heaters are equiped with flow sensors as opposed to temperature sensors. This is why tankless is not often used in conjunction with solar, because yes, they waste energy by heating hot water.

As for your solar timers; the timer box (most often a "Little Grey Box") has inside of it a set of switches which you can customize to your usage, so you can set your electrical back-up to come on at times when you might not have ideal sunlight (ie: late at night, or very early morning). As for days of inclement weather; most solar systems are installed with temperture sensors on the roof and temperature sensors on the tank. If the temperature in the tank begins to drop and the temperature on the roof is not hot enough it's supposed to kick on the electrical element in the tank. If this is not happening, contact your installer and have them service the controller box.

Additionally, if a sensor goes bad, your pump may be cycling cold water into your hot tank cooling your water. This can most easily be diagnosed by checking to see if your pump is running during the night time (your pump should never come on at night, ever).

In my experience, solar hot water works very well once the system in correctly configured. it's that configuration which most often causes problems.

Oh yeah, and try the reset button on your tank if your electrical back-up isn't coming on. If you have frequent poer outages, that reset button is often the issue.

Nords
November 22nd, 2007, 03:30 AM
Additionally, if a sensor goes bad, your pump may be cycling cold water into your hot tank cooling your water. This can most easily be diagnosed by checking to see if your pump is running during the night time (your pump should never come on at night, ever).
That might depend on the piping. Our solar water system works fine (consistently between 130-150 degrees) but the pump cycles 2-3 times/night for about 20-30 seconds.

I've always thought it's the hot water in the insulated pipes (not the tank) and the collector making its way back up to the top of the collector (where the sensor is) and triggering it. A timer could avoid that behavior but it hasn't seemed worth the bother for a 100-watt pump.

When we first put the system together it used to cycle every 20-30 minutes, but a thermal loop by the tank and a check valve have brought that down to the current numbers. At this point the only other change I could make would be to move the hot-water return (from the collector to the tank) to the side of the tank instead of bringing it in the top. Not sure why the original plumber used the top of the tank instead of the side-- one less connection?-- but the side's been capped off.

How else do you tell if the thermocouples have gone bad-- resistance checks and a pot of hot water?

Zovo
November 22nd, 2007, 07:51 AM
The reason you pump shouldn't run at night is because (unless your system is plumbed strangely) the pumps purpose is manly to aid gavity in brining water down from the panels. At night, the water in the panels will be colder so if it's running at night then it's pumping cold water into your hot water tanks.

If you're getting so much back flow that you think it's filling enough to trip the sensor on the roof, then you may want to have the check valve replaced (the whole purpose of the check valve is to prevent that) or turn down the temperature on the element on the tank. If your electric element (which should be running at night) is making so much hot water that it's back flowing then thee is something wrong in that department.

As for your sensors; First, make sure the connections are good, inspect the wires to make sure they haven't been UV damaged, aren't to dry and brittle, and make sure the thermocouple is laying flat against the pipe at both the rof AND tank side. If you're getting a low reading at the tank in the evening, this could cause your system to pump water from the roof simply because it believes it to be hotter than what's in the tank.

Second, do you have a digital read out on your controller box? If so, you could use it to see what temperatures the sesnor are reading at any given time. Keep an eye on the pump, when it kicks on (at night) take a quick temperature reading of the sensor on the roof and see what it thinks it is; if it's reading 120+ at midnight, I'd be wiling to bet the poblem lies either n the sensor, or the controller.

If you don't have a digital display and you want one, you might want to look into the new digital controllers. They're pretty sweet. They've got a really simple push button system, and instead of a little red light showing you whether or not your pump is on, it's actually got a digital animation.

Nords
November 23rd, 2007, 04:42 AM
... unless your system is plumbed strangely
That's probably the main reason (a five-year-old used water heater). We added the check valve (which works OK) and the anti-backflow loop because it seemed a better way to go than trying to break the cap off the heater's side connection. If this tank ever goes bad then version 2.0 will be plumbed with hot-water return on the side, not the top.

As I talked it over with my spouse, we also realized that it could be the system resetting after it cools below 150 degrees. The controller shuts off the pump when the tank thermocouple heats up to 150 degrees, so the rest of the system (the panels and the piping) probably heats up to 170-180 until sundown. If hot water is used from the tank and it cools below 150 again, then the rest of the system gets pumped down. I've insulated all the piping so there's not much heat loss, and the pump only seems to come on a couple times a night. I haven't bothered to track it all night, I just hear it once in a while.


... or turn down the temperature on the element on the tank. If your electric element (which should be running at night) is making so much hot water that it's back flowing then thee is something wrong in that department.
We've had the elements turned off since spring 2006 (when the sun started shining again after the 40-days-of-rain weather system). We only have three people in the house so 80 gallons at 150 degrees is more than enough to get us through that night and the next morning.


As for your sensors; First, make sure the connections are good, inspect the wires to make sure they haven't been UV damaged, aren't to dry and brittle, and make sure the thermocouple is laying flat against the pipe at both the rof AND tank side. If you're getting a low reading at the tank in the evening, this could cause your system to pump water from the roof simply because it believes it to be hotter than what's in the tank.
That's all good. In addition to the controller we have a separate old-fashioned analog temperature dial sticking up out of the top of the tank so the controller seems to be behaving OK. I was hoping to learn that modern thermocouples have an easier method of troubleshooting but not much seems to have changed in the last 25 years.


If you don't have a digital display and you want one, you might want to look into the new digital controllers. They're pretty sweet. They've got a really simple push button system, and instead of a little red light showing you whether or not your pump is on, it's actually got a digital animation.
Thanks, I'll have to take a look at those. What would really cut through the troubleshooting is a controller with a timer circuit that can be programmed to shut everything off between, say, 8 PM and 6 AM. Otherwise I'll have to add another Little Gray Box...

jkpescador
November 23rd, 2007, 08:47 AM
What do you think of this:
http://www.hot2o.com/
Skylights of Hawaii has a link to it. Skylights installed our solar fans which we like.

I don't think I would install it myself.

The discussion in this thread indicates you folks are quite knowlegeable about solar water heating.

Zovo
November 23rd, 2007, 09:12 AM
Looks like a standard hot-water system to me. Looks to me like they simply designed a lighter-weight panel; which looks suspciously like the solar panles currently used to heat swimming pools.

I'm wondering if the polymer panels can reach the same temperatures as the copper; or if they heat the water part of the way and the electric tank does the rest?



The discussion in this thread indicates you folks are quite knowlegeable about solar water heating.


Have to be; it's my job. :)

Nords
November 24th, 2007, 04:27 AM
Skylights of Hawaii has a link to it. Skylights installed our solar fans which we like.
Longtime owner Ron York was getting ready to sell the company (cardiac health). If Skylights installed your solar fans before 2005 then before you buy again you might want to check to see if he's still running the show.

We installed our solar water system from scratch-- used tank, used panels, about $700 of new piping & valves, our free labor. It's (over)built like a brick outhouse and we have more hot water than we can use. For around $2100 FAFCO says they'll give you the materials to make about half of the hot water you need, and I'd be a bit concerned about hurricanes. Meanwhile you can have a local HECO-approved contractor put in a system for about $2000-$3000 after HECO's $1000 rebate. (And then you take the federal & state tax credits on top of that for a total cost under $2000.) The contractor's new materials are probably worth at least $1500 retail.

You might want to contact a half-dozen of the contractors on HECO's list (http://www.heco.com/portal/site/heco/menuitem.508576f78baa14340b4c0610c510b1ca/?vgnextoid=15895e658e0fc010VgnVCM1000008119fea9RCR D&vgnextfmt=default) to see how their systems & prices compare to FAFCO.


The discussion in this thread indicates you folks are quite knowlegeable about solar water heating.
Thanks, it's a hobby...

GeckoGeek
December 10th, 2007, 10:05 PM
Just to tack on a few things....

Tank heaters are not that inefficient. Contrary to "common sense" it doesn't take any power at all to keep hot water hot. It takes power to make up for heat lost though imperfect insulation. Improve the insulation, and that big tank of water is no longer a problem. You can do a lot with just $20 with of stuff to insulate the pipes near the heater.

Now, is the goal to save energy or save $$$$? The answers may not be the same. HECO is giving a $3/month credit to allow them to put a box so they can cut off your heater when they need to react to peak demand. Can't do that with tankless.

Also, HECO is getting ready to switch to a rate structure that charges different prices at different times of the day. A tank heater can heat up at night on cheap power. With a tankless you're stuck with whatever the rates are when you take your shower.

Nords
December 11th, 2007, 05:31 AM
Also, HECO is getting ready to switch to a rate structure that charges different prices at different times of the day.
Although HECO gave us a digital meter last year to implement time-of-day metering, they've been teasing us with that feature for years.

Has anyone seen anything even remotely resembling an implementation date for time-of-day metering? We're ready to shift to a "dishwashers & clothes dryers only after sundown" routine...

MixedPlateBroker
April 8th, 2008, 08:36 PM
Wuz wondering. Anyone try those tankless heaters? Are they more economical than trying to heat 80 gallons of water? Your thoughts or experiences. Mahalo...:)
Tankless water heating bad:
Home destroyed by electrical fire
(http://starbulletin.com/2008/04/01/news/briefs.html)
A malfunction in a tankless electric water heater caused a fire Thursday that destroyed a Niu Valley home, firefighters have determined.Heat pump water heating (http://www.toolbase.org/Technology-Inventory/Plumbing/heat-pump-water-heaters) good!

Heat pumps have traditionally been used for space conditioning, but are now also being used for electric water heating. They are usually three times more efficient than electric resistance water heaters ...
Because HPWH take heat from the surrounding room air, they cool and dehumidify a space ...
System cost is from $600 to over $2000. Installation cost may be between $300 and $700. Estimated payback is 2 - 5 years ...
Try visiting the Pakalana condominium on Piikoi if you're curious to see a heat pump, albeit a giant one, in action. The underground parking there feels as is it's air conditioned. Very nice if you're spending a Sunday afternoon waxing your ride.

Oh, btw, visit one of the open houses as an excuse as the parking is gated.:p