Energy efficient electric water heaters
shawncal
| Posted in Energy, Heating & Insulation on
We are searching for the best (energy efficient, and durable) water heater to install in an all-electric vacation home. The big box store carries this Whirlpool Energy Smart model: http://www.whirlpoolwaterheaters.com/products/electric/ which has variable heating programs to minimize standby losses. It sounds like a great idea, and the price is reasonable- wondering if anyone has experience with them? Or other recommendations for electric water heaters?
Shawn
Replies
Which leads to the question of how tight an insulated box can be added to save on heat tranfer thru the walls of the tank?
Check this one out. http://www.marathonheaters.com/
They can't get your Goat if you don't tell them where it is hidden.
Yeah, that insulated tank is the cats meow...
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Rust Free to boot.
They can't get your Goat if you don't tell them where it is hidden.
This is the one that I have. It works very well. I have yet to run out of hot water for my shower. I went from a 20 gallon electric standard water heater to the H.H20 and electric bill remained the same.
http://howardharrisbuilders.com/
Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
Not sure I understand- Aren't you heating the same amount of water (based on useage) as you would with a conventional tanked heater? Do the savings come from reduced standby losses?
And how much did it cost?
Thanks!Shawn
A typical hot water heater has cold water coming into the tank and diluting the hot water that is in there. That is one peeve on mine, knowing that this is happening. Even as one draws water from the tank, not only is the hot water being used but the makeup water that is replacing the hot water is cold, thus an extra process going on that shortens the usuable time of the standard water heater.With the H.H20, there is no mixing of cold and hot water as the shower is run or the tub drawn. Instead, the cold water runs through a coiled, finned copper tube immersed in hot water. Now the hot water no longer fighting an influx of cold water but instead doing what it is supposed to do, heat water for consumption only. I don't know if this makes sense or not. As for standby loss the tank is very thick foam. I placed an additional circle of foam on top of my tank to make it even more efficient. All sides feel cool to the touch to me.My price was $225 from a local plumbing supply store about three years ago. The owner since retired and sold his business so a call to H.H20 should get a current price. This is not a very well known product at all but I recommend it just fine.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
You are right ... use of hot water costs X to heat ... period. NOTHING will change that. Inefficiencies of heating can change your bill. Inefficiencies of storage, ditto. If you take a shower with a certain shower head, at a certain temp and length of time, it will cost you the same regardless of the source (i.e. tankless vs. tank).
The guy w/ the H.H2O system said ... no savings [in heating water].
It is an interesting concept ... biggest benefit ... no pressurized tank (implying lower cost??). Assuming the heat exchanger works really well ... which it seems to claim (and needs to do), it will give you the same hot water ... and at the same price.
I have contacted the H.H2O company and they provided the following information:
A conventional water heater may pull 10-14 kilowatts every time it turns on.
*The H.H20 only pulls 5.5 kilowatts when it turns on and only looses 1/2 of a degree an hour.
A conventional water heater which has a metal tank will radiate the heat out of the tank.
*The H.H20 has a double plastic wall tank and hold the heat in.
When a water heater is running....
A conventional water heater... you are adding cold water straight to the heated water itself.
*The H.H20's holding tank never sees any additional water. The cold water that goes into the H.H20 which needs to be heated goes thru the copper coil and is heated by heat transfer.
I'm still trying to get my hands around the benefits of this heater- it looks to me like the reduction in standby losses (because you can get by with a smaller sized tank) is all you gain. And the plastic tank for longevity is a plus, of course. The H.H2O until sells for $350, plus around $100 to have it delivered since there are no dealers in my state. So $450 is pretty steep! That said, I think I would agree with the recommendations to super-insulate a standard hot water heater....Shawn
I called them too and was disappointed in the cost. I think the main advantage of the system is the flywheel effect, and the separation of the flywheel (the water tank) and the delivery system (a hx instead of stratification). Water is an extremely good heat storage medium, second only to Ammonia in its specific heat capacity, so not constantly lowering the temperature of your flywheel with cold water mixing makes sense to me. And because there is no stratification in the tank, the hot water delivery should be more consistent across a set gal/time than a typical tank.The system, being non-pressurized, makes it ideal for modding. You could easily make an AirTap like device out of an old A/C unit without having to worry about your fittings leaking. Or a simple solar system with an ARTTEC differential controller (you'd have to make sure that the 30 gal reservoir would large enough for your system), with a HX made of soft copper pipe. Plus it's already got a builtin electric "backup" for when you've got no sun. A Marathon is way expensive, and a cheapo 40gal from HomeyD is $300+, so perhaps this isn't too bad a deal after all.Would you still need heat traps on a system like this?Z
I called them as well and apparently I bought my unit before the price of copper went up. So that is how I got mine for $225. Those are interesting thoughts about using the unit as part of a solar system. And yes, the flywheel effect is eliminated with these.The unit itself is very light, maybe 40 pounds? It is a simple design. Perhaps if it is freighted to a local freight yard the shipping would be lower?
The major drawback of the H.H20 is the lack of a drain plug at the bottom of the unit but that might not be a drawback after all because the integrity of the plastic tank is not compromised and after all it is nothing that a siphon cannot do.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
Need heat traps? ... Absolutely. Hot water in the tank heating water in the HX ... it will thermosyphon ... only it's only on one pipe, I think (the other comes in the bottom, right?
Pretty sure heat traps are code here.
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
Dan-
What are heat traps- some sort of valving? Please explain, thanks!Shawn
Yeah, a special sort of valve, one for hot and one for cold. (You gotta use the hot one on the hot pipe and vice-versa, plus get them pointing in the right direction.) They prevent hot water from drifting up into the pipes when water is not flowing.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
I think you are pretty much right on. My personal opinion about what the company said ... so? They are providing sbiased information to sell you a system. Smaller tank, smaller heater ... means longer recovery if you have a large demand. It is simple energy science ... for a given demand, you will use a certain amount of energy ... regardless of the size of the tank or heaters in the tank.
Smaller tank, smaller heat loss ... but that difference is small ... assuming your metal tank is well insulated. Plastic heat loss is smaller, but if you insulate both tanks to say R-15, there is no other heat loss difference (other than tank size).
If you have a smaller tank and a large load, you may have to turn the tank temp up. That is, you can use a smaller tank for a large load ... but it means you have to turn the temp up to ensure you don't run out of hot water. Higher temp means higher heat loss. Pay your money take your choice.
The H.H2O will give you the capacity of a conventional tank of the same gallons (theoretically). If it is 30 gallons, that is how much hot water you get. If 30 gallons isn't enough for you now ... it won't be w/ the H.H2O system ... and you will need to increase water temp.
In defense of the H.H20 it is actually a little different than other water heaters. The reason it can perform better despite its 30 gallon holding tank capacity is the lack of the flywheel effect that mackzully referred to in post #20. The end result is longer hot water times out of the same 30 gallons than the convential hot water heater can provide since no new cold water is being introduced into the mix. I just wanted to clarify that and as a user of the system I can attest that my showers no longer end with lukewarm water but stay hot since all the element in the tank needs to do is to keep the stationary 30 gallons in the tank hot as the heat exchanger piping circulates the shower water through it. You may be right that the same amount of energy is going to be expended regardless of what system is used in order to derive hot water but I put forth the H.H20 as a more efficient system in the regard that it is a heat exchanger type and thus less likely to run out of hot water than a similar 30 gallon water heater.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
Actually it's more efficient because of the "flywheel" effect of having 30 gallons of very efficient heat storage. Once you get that flywheel up to temperature, the high specific heat of water means it's able to store a lot of energy and it will take quite a bit to cool it down. A regular tank has this too, but to a far lesser extent, and works far differently, as you're actively removing 'mass' in a sense from the flywheel when you extract the hot water. That coupled with stratification and turbulence, as well as where and how large the elements are, make a regular tank unit a far more complex system than the HH20. Z
Thanks for the clarification. Now I understand what you say when you refer to the flywheel effect. At first it is a lot to wrap one's head around but it gets easier after a while.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
There's no difference in efficiency other than what can be accounted for by insulation differences and total surface area.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Perhaps there isn't any difference. But you could have a regular tank unit that is the same efficiency, but its delivery of hot water by vol/time could be less. Just as a tankless unit is less efficient from a total energy input perspective (i.e. it takes a LOT of energy to raise the temperature of water quickly), it provides "endless" hot water, so effectively beats out a regular tank unit that is more efficient in the vol/time measurement. And in the end, who cares how efficient the unit is if your shower gets cold half way through? I think that is probably the advantage of a tankless or hybrid unit like the HH20. The recovery rates are either zero (for a true tankless) or far quicker for the HH20, as it'll take a loooong time to drop the temperature of the water in the tank reservoir to that of the water in the hx. It'll certainly take more than 30 gallons through the hx to reach equilibrium. Say you disconnect the power/gas from a regular tank unit once it's reached its operating temperature, then fill a tub with 30 gallons of hot water from it. What is the temperature of tank now? Probably the same as the incoming water. And the temperature of the 30 gallons of water that you got from the tank was slowly decreasing the more you drained, as the tank refilled with colder water. The final temperature of your bath (assume no loss through the pipes) is far less than the starting temperature of the tank. Z
> Say you disconnect the power/gas from a regular tank unit once it's reached its operating temperature, then fill a tub with 30 gallons of hot water from it. What is the temperature of tank now?Assuming a 40 gallon tank, 50 degree water in, and 120 degree water out, the average water (ie, after stirring) internal temp at the end would be about 70/4 + 50, or 67.5. For the H.H20 it would be about the same (after adjusting for relative volume), assuming they take advantage of stratification the same way a regular water heater does. If they don't take advantage of stratification (though I'd assume they do) then the water in the tank would be warmer, but the water out would be cooler towards the end. (Even when taking advantage of stratification there's a good chance that the H.H20 will exhibit an output temperature decline curve initially more rapid than the tank unit.)At most the H.H20 has an advantage in that there's less turbulent mixing in the storage tank, so stratification is better maintained. This would indeed probably allow a 30-odd gallon tank to do the job of a 40 gallon regular tank, but there's no magic involved, and no increased efficiency.TANSTAAFL
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Generally, I'll have to disagree to an extent ... and tend to agree w/ DanH. The flywheel of each system is about the same (given an equal quantity of water). If you consume x amount of hot water from the system, the 30 gallons will be at the same temperature either way ... and you will consume the same amount of energy.
The big difference from conventional is the difference in the stratification of the hot water in the tank as a conventional is designed to maintain that stratification ... offering warmer temps off the top. The H2O may have a tendency not to stratify ... giving you somewhat lower (?) storage temp (and therefore supply temp as you consume hot water. This would be due to the better efficiency of the H.H2O heat exchange to the supply hot water ... which will take heat more evenly out of the tank. This isn't entirely true, but a close approximation.
The H.H2O system seems to act much like an oversized instantaneous ... yet it has a small element ... leaving me with a bit of confusion as to its capability.
If you have two 30 gallon water heaters ... one being the H.H2O ... then you will likely see nearly identical conditions ... You take your shower and end up with about the same temp of water in the tank. Just because you heat that supply water a little differently doesn't really matter. As you consume water and remove heat from the surrounding water should really make no difference. The water in the tank will end up about the same [average] temp.
If your showers are giving you hotter water to the end ... I'm thinking there is another variable that you haven't accounted for ... e.g. storage temp of your water heater and/or a different shower head flow rate or different mixing valve on your shower. Maybe your old water heater cold inlet pipe rusted and broke off ruining your stratification (which would definately affect your available hot water).
Benefit of the H.H2O system as I can see it is good insulation and a smaller tank. Both of these will affect a normal hot water heating bill in a very tiny way.
The best way I can explain it is to consider the incandescant light bulb and the fluorescent lightbulb. Put 100 watts into an incandescant bulb and it will give off so many lumens. But put 26 watts into the fluorescent lightbulb and it will give off the same amount of lumens as the 100 watt incandescant bulb. It is just a more efficient way of giving off light. Granted, there are many things wrong with this analogy since most of the energy going into the incandescant buld is wasted as heat. A fluorescent is cooler to the touch as not wasting as much electricity in the form of heat. If a standard water heater is the incandescent bulb and the H.H20 is the fluorescent bulb, what the H.H20 is doing is delivering the same amount of hot water (light) while using less electricity as the less efficient standard water heater giving off a comparable amount of heat. They (the H.H20 and the standard water heater) are two different mechanisms of delivery. Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
I can't even count the ways your analogy is wrong.A standard electric water heater is essentially 100% efficient. You can't get any more efficient than that unless you use some sort of a heat pump.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
I admitted it is wrong. But we are not talking about a standard water heater here. We are talking about a heat exchanger (the H.H2o) and how much more efficient it is than the standard water heater. In some ways my analogy is right.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
No, your analogy is wrong. The well-insulated heater is a closed system, for most intents and purposes -- no heat goes in or out, so long as there's no water running. A watt-hour "consumed" inside such a closed system produces so many calories of heat, and that production is always precisely the same and always 100% efficient.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
My analogy is wrong in that respect. Then I must use a different analogy. The standard water heater outputs 120 degree water at first and ten minutes later it is outputting 110 degree water.The H.H20 outputs 120 degree water at first and ten minutes later is is outputting at 115 degrees. Both water heaters use the same amount of electricity. But the H.H20 is not mixing cold water in the tank like the standard water heater. It is using the more efficient heat exchanger to draw its heat from the thermal mass. In this way the H.H20 is more efficient than the standard water heater.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
I'm sorry, there's no way for the heat exchanger to be "more efficient" -- thermodynamics is very stubborn that way. And IMO it's more likely that the output temp of the H.H20 unit will drop more rapidly at the start (but that depends on a number of messy details).
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Draw 15 gallons from a standard 30 gallon water heater set at 120 degrees. It will take 20 minutes to recover.Draw 15 gallons from the H.H20 set at 120 degrees. It will take ten minutes to recover. Both use the same amount of electricity to recover. Again, the H.H20 is not fighting the dilution of thermal mass like the standard water heater is. They are outputting end results in different manners. The H.H20 is doing it in a more efficient manner. I wish I could draw a .gif file that displays what is happening. If I could visuate (my word I made up based on visualize) the process it might become clear. But who knows. I could be dead wrong. I am open to being right too. Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
Sorry, but Bullfeathers!! If you draw out 15 gallons at a certain temperature you've removed a certain number of calories (or BTUs or joules or whatever quantity you want to use) of heat. It will then take a corresponding number of watt-hours of electric energy (1.163 watt-hours per 1000 calories) to reheat the remaining water in the heater back to where it was.The H.H20 unit IS fighting the "dilution" of the thermal mass. Instead of diluting it with cold water, however, the heat is being extracted from the static water via the heat exchanger.TANSTAAFL
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
For the H.H2O system to recover in less time, it will take a larger element to do so. You said yourself the electricity consumed will be the same ... to do the same job (recover 15 gallons of use at a certain temp).
If your conventional water heater recovers the 15 gallons using two 4500 watt elements, it will recover a lot faster than the H.H2O w/ the 5500 watt element (or whatever size it is).
Your thermal mass ... theory/dillution thing doesn't make any sense at all. There is something about the way that you are thinking that is screwy here. I know you are struggling with a thought about how you think it might work. But it is fairly simple energy thermodynamics ... and like the other guy said (shawncal), the manufacturer admits no savings in energy to heat water used. Just because you are using a little different method of transferring energy into the water you use will not improve the temperature outlook or energy used.
I contend that if you take 15 gallons out of the H.H2O system, your tank temp will be lower than say a conventional 40 or 50 gallon tank AND ... you have a smaller element to put that energy back in ... so recovery will be longer.
If your conventional tank 2nd element doesn't kick in (that is, you don't use enough hot water to kick in the 2nd element ... the H.H2O system will win the reheat race with its slightly larger element (e.g. 5500 W vs. 4500).
I also contend that the H.H2O system at the same temp will have a lower load capacity (well duh (thinking to myself), than a larger volume conventional. If you do run out of hot water because of large loads (e.g. teenage daughters from hell in the shower) ... you would need to increase your storage tank temp to compensate ... just as you need to do in a conventional system.
You have a disconnect and I'm not sure if I or DanH has been able to get you reconnected. Maybe you will have some other discussions or find the answer in some other written form ... this is certainly fairly awkward way to communicate sometimes ... especially where the two sides cannot connect for whatever reason.
Edited 11/1/2008 12:36 am ET by Clewless1
I contend that the H.H20 is more efficient. Why? Because of the factor that I keep restating, that has failed to be plugged into your equation. I will restate it. The standard hot water heater has cold water coming into the tank, diluting it. At the same time it is outputting hot water. Therefore it is reheating water twice. The H.H20 has no cold water diluting it. Therefore it only has to output hot water. It does not have to fight the influx of cold water. It is not reheating water twice, just once. I googled "H.H20 water heater" and came across a number of sites other than the manufacturers that grasp this concept. I can see that some of us are seeing things from the "since it is an electric element it is 100% efficient" perspective. This is true as far as we know. But plug in the factor I am stating above and the H.H20 is more efficient. Anyways, I know some of you are thinking I am being dense and that is ok, I am not trying to agitate anyone. If you need some sites from my google research to back up what I am saying I will be glad to provide them.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
It is CAN NOT more efficient.
It takes the same amount of electricity to raise the same amount of water the same temperature.
A standard electric water heater may be more efficient in that the elements are in direct contact with the water. There is a loss associated with any heat exchanger.
Simple physics.
In fact, the cold water entering the H.H2O is cooling the tank. Turn off the power and run cold water through it for an hour and then check the tank temp. Betcha 100 bucks it is the same temp as the incoming water.
It does heat the water twice. Once upon initial startup and then during use.
For normal usage, it will probably have a better recovery rate due to the stored energy combined with the elements.
But the real test is the first hour delivery. Fill both heaters with cold water, turn the power on to the heaters and open a hot water tap. Assuming both have the same size elements, both have to consume the same amount of power.
Having said all that, if the plastic tank holds up over time, it may actually be a better electric water heater.
Run 35 (for good measure) gallons of water through a 30 gallon standard water heater that has the electricity turned off. Ok, now the temp in the tank is the same as the cold water entering it.Run 35 gallons of water through the H.H20 that has the electricity turned off. Ok, now the water has only dropped 15 degrees and is still outputting substantially hotter water than the input.See my point?Overall, month to month, I am getting 10 to 15 percent more efficiency out of my H.H20 than if I was using a standard hot water heater.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
Yeah, but you had to turn on the H.H20 BEFORE you can heat water. You heated the heater before you can heat the water.
Fill both heaters with cold water and turn them on. If they both hold 30 gallons, and they have the same heating elements, they will use the same amount of energy.
It takes 1 btu to raise 1 lb of water 1 degree.
You can't get away from that simple formula.
"Fill both heaters with cold water and turn them on. If they both hold 30 gallons, and they have the same heating elements, they will use the same amount of energy."Yes. I agree.Now let us use some of that energy. And see what happens. Again, for arguments sake, let us turn the heaters off after they reach 120 degrees. Let us say that the input is 55 degree water. Again, we will run 35 gallons of water through each of the heaters. Ok, after running 55 degree water through the standard 30 gallon water heater for 35 gallons the temperature in the tank is now 55 degrees. Agreed? Now let us run 55 degree water through the H.H20 for 35 gallons. Now the temperature in the H.H20's tank is 105.Now we will flip the power back on to both heaters and raise the temperature to 120 degrees again for each tank. The standard water heater has to heat the water from 55 degrees to 120 degrees. But the H.H20 has to raise the water from 105 degrees to 120 degrees. This is where the H.H20 beauty shines. It is more efficient than the standard water heater in real world operation.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
No, the H.H2O has to raise the tank temp from 105 to 120 and then it has to raise the incoming water from 50 to 120.
The problem is we have two different ideas of efficiency. You want to know if you will run out of hot water. Fair enough.
Depends on how long and how many gpm the shower uses.
I want to know how much energy it uses. Apples to oranges.
I've worked on a direct contact water heater. It uses the combustion gases to directly heat the water. It is rated at over 90% efficient. I guarantee you could shower for 24 hours a day and not run out.
Actually, you could hook up about 1000 showers to it and not run out.
But I don't think you would want to pay for the gas that gets burnt at 25,000,000 btu's per hour. LOL.
Edited 11/1/2008 4:32 am ET by rich1
Just curious. Do you know for sure that the temp will only be 105?
It has a first hour rating of 40 gallons. Running 40 gallons should take it a lot lower than 105. A lot depends on the size of the heat exchanger and the flow rate.
The amount of energy to recover the tank from 105 to 120 is less than the amount to recover it from 55 to 120. By the dint of a standard water heater's operation it would be less efficient than the H.H20. And I don't know if it will be at 105 degrees after 35 gallons have run through it. I can run a hot bath tomorrow and estimate when 35 gallons has gone through and take an infrared reading of the H.H20's tank through its fill valve, with it shut off just prior to running the bath. It will be more than the temperature of the incoming water. From the link http://www.newhopeconstruction.org/nov07.htm "For instance, we recently discovered a new water heater that uses thermal conductive methods to heat the water as needed rather than heating an entire tank of water only to keep it heated until used. The H.H20 is an electric water heater that only heats water as it is used and Georgia Power gives it a 98% efficiency rating. H.H20 has been tested by Georgia Power and the results were very favorable. The tests show the H.H20 water heater has quick recovery and reheat time which is particularly important when hot water is being used by multiple appliances or several people showering one after another. According to Georgia Power, "One of the main set-backs to most standard electric water heaters is that it takes a long time to recover temperature, or the unit seems to run out of hot water." The H.H20 water heater will recover in half the time of a standard water heater with the same first hour rating. And because of the type of plastic used in creating the tank, it will be recyclable at the end of its use."Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
"The H.H20 is an electric water heater that only heats water as it is used and Georgia Power gives it a 98% efficiency rating. "BS, plan and simple.Turn the breaker off UNTIL you want hot water.Then turn it on and immediately start drawing "hot" water.How hot is it.Now to the claim that this heater is MORE EFFICIENT than a regular heater.EFFICIENCY has a specific meaning. It is the USEFUL energy out ( in this case heated water) divided by the energy in (in this case electric).Any energy that In that does not end up as Energy Out has to go someplace.Unless you know of someplace else the only place for losses to go it through the insulation into the ambient air. Both this and the conventional heater will have about the same standby losses.This WH "might" be more EFFECTIVE, not efficient in that it might give more first hour output. Don't know. And if might recover quicker. But it has has a larger heating element and thus uses more power whenever the element is on.Part of this effectiveness might be cause of the fact that the heated water is isolated from the heated mass and there might be an improvement in useful output because the income cold water does not mix with out going hot water. Don't know how much affect this has.
> Now let us run 55 degree water through the H.H20 for 35 gallons. Now the temperature in the H.H20's tank is 105.Only true if the water coming out of the H.H2O unit was cooler (which it probably was). When you take heat out of the tank, in the form of hot water, you lower the average temperature of the water in the tank by a quantity corresponding to that amount of heat. There's no way to avoid this.Think about it this way. We have an H.H2O setup with a 35 gallon storage tank, heated to 100 degrees. We also have a second insulated tank that contains 35 gallons of cold (50 degree) water. With power off we run a pump to circulate water from the second tank through the H.H2O. We do this for several hours, until the water in the second tank can get no warmer.Ignoring the heat gained from friction (power input to the pump), the temperature in both tanks will be 75 degrees.Repeat the experiment with a conventional tank instead of the H.H2O and the temperature will still end up as 75 degrees.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
No , your exchanger water starts at 55 deg as well. Add the tank water and then measure the energy use.
They can't get your Goat if you don't tell them where it is hidden.
For clarification, I have done some thinking and I get the fact that no matter how I end up getting hot water, I am simply converting electricity into useable BTU's i.e. my bubble bath (not that I actually take bubble baths lol). To make a claim of increased energy efficiency (although the H.H20 does have low standby losses and even less since I have placed a disc of 1 1/2" thick foam on the top of the unit) I would say that the efficiency is due to incremental gains. Running a standard water heater side by side with the H.H20 and making them perform a series of identical tasks in say, a six hour time frame... I am inclined to think that the H.H20 will consume less electricity. I did test my H.H20 today, popping the fill cover and measuring the temp before shutting the breaker to and then running an approximately 35 gallon bath. I have it on the highest setting since I live alone and there are no children in house. The temperature read was 145 degrees. After filling the bath (Roman tub faucet, roughly 2.5 gpm, and 20 inch deep soaker tub) I measured a temperature of 120 degrees in the H.H20's tank. I measured a bathtub water temperature of 100 degrees, just perfect. BTW I did not use the cold water (alas I forgot to measure the incoming temp) at all, just straight hot water tap. Then I turned the breaker back on, hopped in the tub for a soak and read the WSJ. Twenty five minutes later I tired of the bath and hopped into the shower for a rinse off. The water was hot, with no indication that a tub had been drawn in the past hour. So the recovery time is good. To prove my inclination to believe that the H.H20 will consume less electricity over a set period of time requires more resources than I currently have. If I was the owner of the company I would want to put together a video or an example of side by side testing with easy to see numbers (i.e. gallons used, watts used, time used) and see bar graphs or the like illustrating it all. As a breaktimer I feel I have to now leave that burden of proving actual claims to be beyond my purview and to instead simply be a happy user of the product. Its strengths are good.This is a good and very valid discussion that this thread has generated. I trust that the OP is no less bewildered now than he was at the time he first posted. I am interested in seeing how the H.H20 continues to perform for me presently and in the foreseeable future. Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK
The true test is the 1st hour rating. here are the ratings for BradfordWhite.
http://www.bradfordwhite.com/energyfactor_electric.asp
And here are the ratings for Marathon.
http://www.marathonheaters.com/cons_specs.html
For a 40 gallon heater, BradfordWhite beats Marathon.
The energy factor reflects the standby "efficiency" of the water heater, and in that regard the Marathon is typically 1% better than the Bradford White. (A negligible amount.) The BW has better 1st hour ratings, though, probably because the Marathon typically uses smaller elementsYour standard better quality electric tank is so efficient that there's not much improvement to be had with exotic schemes. The Marathon's main advantage is the plastic tank, though it has a corresponding disadvantage of being larger physically for a given capacity.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Sorry, but you're wrong. The H.H2O may contain warmer water at the end of your 35 gallon experiment, but only because the "hot" water coming out was cooler. TANSTAAFL
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
I'll admit that I was no Rhodes scholar, but I didn't sleep through THAT many thermodynamics classes. You're deluding yourself. It's a common sort of delusion (as you can see from the multiple web sites) but still it's just plain wrong -- bad physics.There's no "reheating the water twice" -- the heat content of the water is a function of its temperature, period, and whether you "remove" the heat by dilution with cold water or by extracting the heat through a heat exchanger, the temperature will drop the same for a given amount of hot water (at a fixed temperature) removed, and it will then take the same amount of heat to raise the water back to the original temperature.The H.H20 unit has several things to recommend it, but efficiency (beyond better insulation) is not one of them.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
The cold water dumping into a conventional tank ... is only somewhat dilluting the tank temp ... the tank is designed to have stratified water. There is no more dillution in a conventional tank than the H.H20 system. You run cold water through the HX and your tank temp drops (dilluting the temperature, and therefore making less hot water/energy available ... just like a conventional tank.
I calc'd heat loss of a conventional 40 gal vs. the 35 gal H.H20 .... At $0.08/kwh, the conventional tank will cost you a whopping $0.96 annually over the other tank. This assumed insulation type was identical. If you assume the conventional tank only has 2 inches instead of 2.5 inches ... you over triple the savings to $3.50 a YEAR. This assumes the 120 degF tank setpoint and 70 deg cold water inlet (which IMO is 15 Fdeg too high for northern climates).
The sales pitch in the website has some issues: They don't seem to know the difference between LOAD KW ... kilowatts and energy consumed KWH. They treat them the same. This tends to lower my confidence that what I am reading is presented by people who don't know how to talk basic science.
The manuf. touts benefits to be: #1 tank life (it's plastic) #2 Quick recovery - 5500 watts has 22% more recovery capability than 4,500 watts ... and #3 demand management benefits ... you can heat it at night and use water during the day ... which is really no different than a conventional storage tank water heater. This "tool" is no more perfect than the conventiona storage tank water heater as indicated in the sales pitch.
Their tests, and test results and testimonials from engineers don't really document energy savings or anything ... they just say who did some tests ... and some results ... which don't counterdict anything I or DanH have said. It did state an "energy factor" of 0.0923 ... without even providing units or explanation of what that value even means. There test didn't even compare the exact same conditions w/ a conventional water heater ... so the energy consumption, recovery, etc. become meaningless values ... designed to make the reader 'read' 'higher efficiency' or 'better' ... when they say it really isn't.
If you remove 3 gpm from both water heater to do a job (the rate they claim the H.H20 is designed for) ... let's say to take a shower for maybe 5 minutes at 110 degF ... the H.H2O system tank temp will be dilluted fairly evenly due to the efficiency of the heat exchanger that affects the entire tank ... maybe the element won't come on, now, but you've still consumed the energy and at some point when the element does kick in, it will replace that energy used.
The conventional tank dumps cold water in the the bottom of the tank to replace the 15 gallons consumed. You still have very close to the 120 degF water at the tank outlet w/ the cold water dumps in the bottom ... kicking on the element to recover.
While the two elements of this comparison are not kicking on at the same time or for the same period, over a period of time and multiple uses, they will both consume virtually identical KWH (that's kilowatthours) of energy to provide identical water consumption.
Claims of big savings by users are likely accompanied by other 'big changes' in the household ... raised energy awareness may have motivated them to change shower heads, take shorter showers, and/or get better appliances (dishwasher/clothes washer). Maybe they replaced an old [uninsulated] water heater w/ a new one or one that had the dip tube broken. Or one w/out heat traps in it.
To claim big savings is like log home proponents touting the thermal mass [energy] benefits of a log house and how their electric or gas heating bills are so small while burning 5 chords of wood ... but that didn't cost anything (i.e. energy ... said sarcastically).
Not sure if I added anything to the discussion that I haven't really already said. If not, my apologies. You'll run into something that will trigger the right perspective. I feel I've missed maybe part of your point ... but also feel I've got it at the same time, ya know?
Energy Factor, if properly used has a specific meaning.It is from a standard test that measures the energy used over a period of time based on a certain schedule of hot water usage over a 24 hr period.That is the number that is listed on the federal label on the tank.For electric WH's it is basically a measure of standby losses.Gas WH's, because of combustions losses in cold starts when firing the details of the water usage schedule can make a big difference.A while back I found some research that compared the EF for a gas tankless and tank as installed in a house and the typical usage patterns of hot water was much different that what is used in the standard.Here is the offical list electric WH's and their energy factors.http://tinyurl.com/6ggsrxI could not find this company in it.And you will find a number of units with .91 and .92 EF and .93 and 94 are not unknown.And a couple of .95 units.This heater has a rating of 0.0923.http://howardharrisbuilders.com/testsperformed.htmlBut I hope that was a typo and should be .923.Which is good, but only average compared to other models.
It should be pointed out that, in a standard electric tank, the two (typical) 4500W elements never both run at the same time. This is to limit current demand so that a single 30A circuit can handle the load. Two elements are used so that quick recovery of a small volume of water can be achieved with the upper element. When the top of the tank is hot the upper element is switched off and the bottom element is switched on. If the H.H2O has a single 5500W element (does it?) it will recover faster -- simply because of more heat input.If you want really fast recovery it's possible to rig a standard tank so both elements can operate simultaneously, each on its own circuit.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
OK ... interesting. I have to admit, I never knew that both elements would not kick on ... but based on the amp CB rating ... I suppose that makes sense. I just assumed if you emptied the tank, they'd both be on.
If you emptied the tank they'd both be burned out.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Dan ... I meant emptied it of hot water ... used all the hot water filling it totally w/ cold water. But you knew what I meant didn't you?
I can read 2-3 meanings into just about every post made here.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
With all due respect, that is incorrect. Your analogy doesn't hold water (no pun intended).
You have to remember that all watts in a light bulb result in heat energy. ALL of them, all of the time. You get more lumens from the fluorescent, but all the watts end up as heat, non the less. This is a common misunderstanding about light bulbs. The fluorescent is cooler ... because there are less watts. Yes it lights much more efficiently, but a 40W fluorescent gives off just as much heat as a 40W incandescent.
You cannot heat water more efficiently (significantly) with the H.H2O system because of it's basic configuration/method of heating the water. It is effectively no different as they are both electric elements immersed in water. Each element gives off X amount of heat. If you require a certain amount of hot water to do any particular job (shower, dishes, clothes washing), the same amount of energy will need to be put into both hot water heaters. If you use a smaller element, it will take longer. If you have a very large tank, it will still take that element just as long to put that heat back into that tank as it will a smaller tank (ignoring the greater surface heat loss of the larger tank).
The H.H2O system may have some small differences in the way heat is transferred to the water ... it really won't impact (substantially) the heating of the water required to do the job you want (i.e. the energy you need to heat that water). You cannot heat water to a certain temp with less energy ... period.
In a combustion type heater you can use less energy to heat the same water to the same temperature ... but that is only because you've improved combustion efficiency ... it still takes the same amount of energy to heat the water for the same task ... you simply throw less energy away in the combustion process.
The benefits of the H.H20 system is tank size and the fact that it is not a pressure vessel (which requires a much more stringent standard of manufacturing) ... and maybe it is insulated better than the average tank. If you calc the heat loss on two tanks ... conventional and this alternative ... you will find that over a year the difference in heat loss will be very small (energy/cost wise) particularly compared to the typical hot water loads in a residential application.
After pondering this for awhile, I talked with the HH20 company today. From what I was told (and this makes sense to me), the energy savings really just come from the fact that you can get by with a smaller tank size. This reduces the amount of water that must be maintained at high temp, thus minimizing standby losses. The well insulated tank (2.5 inches of foam) obviously helps, too. They don't make any claims that it is more efficient in the way the water is heated.
That said, I STILL haven't got my arms wrapped around the thermodynamics of the hx arrangement and how this allows for faster recovery....Shawn
Standby losses are a function of square inches of surface area and the R value of the insulation. The quantity of water kept warm has no effect other than a smaller amount of water requires fewer square inches of surface area.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
So, then, are you agreeing with me? Smaller volume of water=less surface area=reduced standby losses, right?Shawn
Potentially. But the differences are apt to be miniscule.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
We have never disagreed w/ that statement, but that has virtually nothing to do with the arguments you've been talking about. If you estimate the heat loss from the two tanks, it will show you that your H.H2O is superior. By exactly how much? Maybe it is 50% better (I doubt it), but 50% better of a very small number is still a very small number (relative to hot water energy consumed for e.g. showers, etc.).
If you take 35 gallons of water PROVIDING THE SAME TEMPERATURE (i.e. doing the same task at the same temperature) out of both tanks, the temp difference between the tanks will be negligible (i.e. w/ non energized tanks). NO. You will not end up w/ 55 deg water in one and 105 in the other. You take X amount of water at X temp out of both 120 deg tanks, you will end up w/ the same temp in both tanks.
You can not consume the same temp and volume water out of both tanks and have the temp difference you are theorizing.
Somehow you are mixing up one concept with the other and then thinking somehow it is more efficient. But you yourself even said in a previous post ... that both elements will consume the same electricity.
If the conventional heater put the cold water back into the tank right at the top of the tank ... it would tend to short circuit a bit and go right out the hot water supply ... shortening the capacity of your shower water temp. But they are not designed to work like that and generally, they don't. Does someone who knows water heaters well know if the cold water inlet will ever get a hole in it or 'break off'?
As the H.H2O cools down due to hot water consumption, its average temperature will be no different than the conventional.
Somehow you are still missing a disconnect in your train of thought, here. I'm going to cogitate (my word for think hard) about this for a day or two, maybe I can think of the right words or diagram or equation to explain ... till then.
> Does someone who knows water heaters well know if the cold water inlet will ever get a hole in it or 'break off'?There was a rash of broken dip tubes some years back. Manufacturers changed to using a plastic dip tube, and the plastic they used turned out to become brittle when subjected to prolonged high temps.When the dip tube breaks it does "short circuit" the tank as you suggest, resulting in cold water very quickly coming out of the hot tap, or, at best, the water temp switching between hot and cold rapidly.Normally the dip tube introduces cold water into the bottom of the tank and does so with minimal mixing with the upper part of the tank. Since warm water rises, this results in a "stratification" in the tank, where there is slowly-rising boundary between cold and hot water as hot water is removed from the tank and not replaced. When the boundary nears the top of the tank you fairly suddenly "run out of hot water".
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
But the upside was a tank with a broken diptube was cheaper to run.
Which was probably offset by the cost of flushing all that plastic out of the system.
Yeah, it definitely makes you take shorter showers.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
"So, then, are you agreeing with me? Smaller volume of water=less surface area=reduced standby losses, right?"Yes, for the same type and thickness of insulation.
You are correct ... and the manuf. has not lead you astray. You are thinking straight ... now get Pebble to understand. You won't necessarily make a wrong decision to use it. I wonder about loads that stress the limit of the element in this system, though. If your current load stresses e.g. a 50 gallon tank at 120 degF, the H.H2O will struggle for sure ... unless you turn up the temp of the tank. That is OK ... increases standby losses a bit ... but again, standby losses are [relatively] small.
To look at our current heating costs, I ran some numbers myself. I think this might shed some light on the subject for everyone.
First I should say that I agree with Clewless and Dan, in that the heating of the water should be no more efficient with the HH20 unit than with a conventional water heater.
In my house, it is just my wife and I using about 30 gallons/day of hot water each (probably a bit less, but I'll use this number for example). Our elec. cost is about $.08/KW and our incoming water is in the low 50s. That said, I calculated the cost to heat our total hot water for the month to be about $23.
Using our existing very old 50 gallon conventional heater, I calculated the standby losses (based on 1 degree temp drop per hour) to cost us an additional $7 monthly. So, the standby losses, correct me if I calculated this wrong, are accounting for about 25% of our total DHW costs!
Now, if I buy the HH20 31.5 gallon heater, which has a listed standby loss of 0.5 degrees per hour, the monthy cost of standby losses alone would drop by about $5 to around $2.25/month. This would reduce our monthly total DHW costs by 5/30 or 17%...
Since Pebble (who has the HH20 unit) claims to have gotten a 10-15% reduction in his utility bill, that would follow with what I calculated, right? AND, it would support the notion that the savings come from better insulation of the tank (ie. reduction in standby losses), not from the Hx method of water heating...
Discuss?Shawn
I believe that your analysis is roughly correct. There's probably about a 2x difference in standby losses between the best-of-the-line units and the cheapest ones, even more for older units.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
You have some incomplete information. The temp of the 30 gallons of hot water used. Based on your results, I estimate your hot water use temp to be 115 degF. This gives you the $23/month. This will be for either tank. FYI ... 60 gallons per day hot water is generally a LOT of hot water for the various average uses (showers, lav, dishwasher, laundry). Don't know your lifestyle, but that is a lot of hot water (maybe, though you take a bath every day rather than a shower). I'm betting I don't use more than 15 gallons a day on average for all my uses ... but I haven't set down and estimated it recently (I have done it, however). You might be right. My hot water bill averages $8 a month (gas heat old style). (don't take this out of context, though since gas energy is a different animal (cost/efficiency) than electric).
I calc'd standby loss for the H.H2O based on the manuf. dimensions and the assumed 2.5 inches of insulation. The one degree drop per hour means very little if at the end of the day, the element comes on and replaces that lost energy. While there is a fluctuation in heat loss due to fluctuations in temp, it is small. Assuming a constant tank temp, I calc'd the loss on the H.H2O to be $9.31 per YEAR using your 8 cents/kwh, NOT your $2.25/month. (and I assumed the constant temp and a space temp of 70 degF).
If you have an OLD uninsulated tank, you might see a loss that is quite high, but assuming you are replacing even a minimally insulated tank I calc'd a annual cost to compensate at just over $33 per year ... savings over real old tank is $24 per year. For a well insulated modern hot water heater (what you should compare this to), as I indicated earlier ... Just under $1 savings per year is all you get. This is not a 10-15% reduction in your (admitedly high) hot water bill ... it is about 0.36% (less than 1/2 of one percent). Assuming you grossly overestimated your hot water consumption by double (just for arguments sake), now standby losses maybe approach 0.75% of your monthly bill.
You cannot say ... I replaced a piece of junk w/ the H.H2O system and got huge savings ... therefore they are efficient. Not apples to apples comparison.
Hmmm. This is a good argument for installing a home energy monitor, so I can document actual useage rather than theorizing about all this. Hasn't Somebody out there documented standby losses/heating costs by now?
I consider myself conservative with water use, so am surprised that you think my estimate is high. I installed a 2gpm shower head and we never use the bath. I do take two showers a day (at least), as I am an athlete and a hard worker, always getting dirty and sweaty...so two five minute showers alone would be 20 gallons per day, not counting other uses of hot water (kitchen and laundry). My wife likes long showers- her "one" luxury while living up here at the North Pole, so she probably consumes more than I do even if she only showers once per day.
Is 30 gallons/day really considered high use? Maybe I need to work on this.
As for standby losses, I am using the information given to me by HH20 themselves- they measured this to be 1/2 degree per hour...so number of $2.25 per month should be accurate. I appreciate your attempt at calculating this, but in this case I'd go with the manufacturers numbers, wouldn't you?
Your math in the final paragraph doesn't add up to me. You said that you calculated standby losses to be $9.31 per year. So if I go with YOUR number, then based on MY estimate of $23 per month (or $276 anually) DHW heating cost, that'd be 3.3%...I think your decimal point is off a couple places, isn't it? Furthermore, if my hot water usage is estimated high (double, as you suggested), than the actual percentage cost of standby losses could be doubled to about 7%, right? And if the HH20 data is accurate, then your cost estimates are quite low, so my previous statement of 10-15% standby loss cost is not unreasonable.
I'm certainly not trying to be argumentative, just want to understand the issue, and decide what is the best purchase to make. Why are the well-insulated Marathon water heaters, at close to $1000 a crack, so popular if standby losses are asinsignificant as you suggest? This doesn't make sense to me.
My current thinking for our guesthouse is to buy the HH20 unit for its well insulated durable tank design (since it costs only a little more than a new conventional design), then retrofit it with an Airtap heat pump to efficiently heat the water. The exhaust from the Airtap can be captured for summer air conditioning as well. I can do this for about $900 total cost, around double or triple the cost of a conventional water heater. But even with conservative estimates, I should save over $100 anually, so the payback looks good. Shawn
If your water usage is doubled then your % standby loss is halved.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Shawn. I don't think you are trying to be argumentative at all. Just getting the facts straight and this mode of communication can be awkward ... and message intensive.
I got you thinking about your water consumption which is the reality of what we need to do sometimes. Is your shower head 2 gpm or 2.5? Most modern shower heads are 2.5 ... the max. allowed. I recently installed some Jet Stream shower heads where I work ... at 1.5 gpm AND the users love them (I had a couple of 'teenage daughteres from hell' not want to give them up when allowed to just test them). Pricey, but easily worth it according to my estimates.
So ... maybe you do approach 30 gallons a day per person. Laundry frequency and dishswashing frequency will tell the rest of that story. If you have an efficient dishwasher that you use once every other day and it uses (guessing here) 3-4 gallons per use divide by two 2 gallons per day per person if you use it daily. Laundry once a week at ... (WAG again) 8-10 gallons per load for the two people.
Your showers may easily be your biggest hot water user. 2 - 5 minute showers fits what you do ... but if I ever take a second shower, it is usually very short ... maybe 2 minutes. A 5 minute shower (which I think I take, too), is a luxury shower (IMO); I brush my teeth in the shower ... my luxury and that is half the shower time.
Standy loss - They are telling you 1/2 deg per hour ... not sure why other than ... your hot water will last long. My calc is rock solid and did make a couple of minor assumptions, but not significant. I would bet you would actually measure standby loss to be very close to my calculation ... actual will be somewhat lower due to the reduced loss as the tank loses heat and the element doesn't kick in (not sure how much it has to drop for the element to kick on).
No ... my decimal is not off. I was referring to the DIFFERENCE in standby loss between the two water heaters. The difference was roughly $ 1 a year and that amounts to a fraction of 1% of your 30 gal/day/person or even my 15 gal/day/person.
It was the SAVINGS that we are talking about here ... how much savings in standby loss is a fraction of a percent of the projected energy for hot water. Standby loss is about 3.3% of YOUR water bill ... double if it is mine. Higher than I anticipated, but I often deal w/ a full family of 4 in my calcs.
As you conserve hot water, the standby component becomes larger and potentially a bigger focus of energy related efforts.
So savings from the H.H2O is tiny ... relative to a modern COMPARABLE water heater and that savings comes from standby loss ... due to the smaller tank. You serve only two people ... my guess is it would serve you well ... for only occasional guests, it is again a reasonable choice (although occasional use, as I said earlier, a good application for a on demand type system ... given reliable energy source). You aren't gaining a whole lot, but you aren't spending much, either.
Just making sure that your choice is informed and not skewed by hype of excessive savings that simply aren't there. The H.H2O system is an OK system ... has its benefits. If someone theoretically saved a bundle after installing one, I assure you ... there is a missing element (or 2 or 3) to the equation ... I think one poster claimed big savings ... but we are missing lots of information I suspect and as I indicated in a previous comment.
"My current thinking for our guesthouse is to buy the HH20 unit for its well insulated durable tank design (since it costs only a little more than a new conventional design), then retrofit it with an Airtap heat pump to efficiently heat the water. The exhaust from the Airtap can be captured for summer air conditioning as well. I can do this for about $900 total cost, around double or triple the cost of a conventional water heater. But even with conservative estimates, I should save over $100 anually, so the payback looks good.
Shawn
"And I think this is in the end, and as I said before, one of the benefits of the hx unpressurized style HW hearter. It's dead nuts simple to modify for even a mild boost, no need to worry about pressurized fittings, etc, you could just run a coolant loop straight down from your solar panels and right into the tank. Drill a couple of holes, and a little silicone later, you've got an affordable SHW/electric HW system for a small fraction of the price that you'd pay for a separate HX, a storage tank, a separate electrical unit for backup/primary etc.As for the Airtap, their pricing just skyrocketed to $799. Time to find a good A/C technician and just make one out of an old window unit. Nothing really needed than to lengthen the piping before the condensor and add a thermistor to control its cycling. Run the coolant loop into the tank, and you're done.Z
Now THAT may be a great idea ... i.e. using the H.H2O concept for a solar water heater heat exchange preheat tank ... Always seems the solar water heater heat exchangers are expensive ... maybe there is an issue that it isn't double walled, though? Food for thought ... got my creative juices flowing.
Double walled? Since it's not pressurized I'm not sure why you would be required to have a doubled wall tank. Just run a coil of pex around inside the tank. Get a differential temperature pump controller, so that you aren't pumping cooler water through the loop and you should be good to go. The most expensive part, outside of the WH, would be the ethylene glycol for the loop I'd bet. There is a company that makes collapsible SHW storage tanks, but they're several orders larger: http://www.stsscoinc.com/Products_SolarAndDHW.aspx and they have a similar system with an electric backup.Z
Double walled heat exchanger. Sometimes required depending on the configuration of the system and if the medium has e.g. glycol or other non potable material in it. ... but I confused myself ... while using the copper coil in the H.H2O is easy ... I've done nothing w/ it ... so, like you said, put another coil in the tank ... 'cept pex isn't so good ... need a copper coil ... preferrably w/ fins like the one already in the tank.
Back to the drawing board. Maybe just get a second coil and put it in the tank. w/ the two coils separated, that might be considered 'double wall' ... more thought is required. Got a start maybe. Whaddya think?
On minor point about the H.H2O -- If the storage tank is kept at an elevated temp to compensate for the temperature drop across the heat exchanger then that could lead to higher standby losses, since loss is proportional to delta T.
Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous
Marathon is the Rolls-Royce of water heaters. I wouldn't install any other kind of electric heater.
Another opinion:
buy the cheapest WH you can find, build a plywood box around it with 8" of insulation.
Good or better than anything you can buy for overall value over the years.
Even had a timer on mine, but found that with 8" of insulation, the timer was better put to use elsewhere.
The other best ways to save are to take shorter showers, and tell the kids to find someplace else to do their laundry
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
shawn.... i'd get cheap 40 gal... and build a foam insulated box around it
do you really want to leave a vacation home in standby ?
we always drained ours down when it was not being used in winter
Edited 10/28/2008 8:38 pm ET by MikeSmith
In terms of pure efficiency, Marathon brand is the way to go, if money is no object. But any top-of-the line unit will be very efficient. You're nattering over the difference between, say, 99.2% and 99.5%.
The one you linked, though, may be a good idea for a vacation home, since it has a built-in switch for "vacation" (unoccupied) mode.
Occasional used water heaters may be the best application for tankless water heaters. I'm not a big fan of them, but if any application is right for it, it is the occasional used vacation house. Other alternatives are to turn it down or off when gone ... not sure if that is kosher (turning off) (except the H.H2O might be a good candidate for that). Does the house freeze when unoccupied?
The other part of tank style heat loss is the convective loss from thermal cycling up the pipes out of the top of the unit. Install pipe 'loops' to minimize this or you can buy the handy thermo one way valves that eliminate/minimize the thermal cycling (available at the big box stores, I thiink).
A well insulated tank has small loss, but a vacation home ... that could be your biggest user of hot water heating (hence my tankless comment above).
I shouldn't have used the term 'vacation home', as this is actually a 'guesthouse' that we are building on our property. Since it will not be occupied all the time, I was looking for options to deal with the standby losses. What I have always done in our house, when we leave for the weekend or longer, is to simply shut off the breaker to the hot water heater and let it cool down (I've also found that after being 'off' for a weekend, we can still return home and take a couple of hot showers, so the standby losses are not as great as I once thought).
From what I understand the efficiency of gas-fired 'on-demand' water heaters is very poor, so you lose energy here. The electric on-demand heaters require too much power for what we have available. So a tanked system is our only option.
My thought at this time is to put in a conventional electric water heater and retrofit it with a heat pump (http://www.airgenerate.com) to boost the efficiency. Also, box it in with addition EPS insulation.
Now to address the convective losses...Shawn
"From what I understand the efficiency of gas-fired 'on-demand' water heaters is very poor"Hunh????
Closed combustion furnaces run 95%. Closed combustion tankless heaters are pretty close, I think...I suppose I should look it up, but I'm lazy.
In any case, there are various pros & cons to tankless heaters, but in general I've never seen efficiency compared to tank heaters be the deciding factor.....
Most tankless gas water heaters are not condensing, according to my understanding, and therefore would have max efficiencies in the 80s. I believe there are a very few tank-type gas water heaters that get into the 90s, however.
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
I believe you are correct. There are some sealed combustion tank-type heaters......probably in the 90s
I thought all major manufacturers made a 90+ efficnient water heater.
Have to agree a little w/ 'jr'. The new combustion efficiency on a gas unit is liikely quite good ... relative to old fashioned conventional gas. FYI ... You can also get high efficiency gas tank style. The benefit of on demand is you heat the water and only the water you need when you need it. Down side is the size of the equipment to do it ... as you noted on the electric side.
I have one of the Marathon electric HWHs and it's great. I had to special order it through Home Cheapo. You have to tell them it is available through (if I remember correctly) the Ruud catalog/distributor, then say a little prayer that the particular "associate" who is helping you gets it right.
Conventional storage water heater is one of the best water heater to use at home. It is very convenient to use and also heat the water quickly. It also consumes the electricity even in the standby mode.