Operating cost comparison......hot water

[teddy bear]

An indirect water heater will give you almost infinite hot water. An electric water heater will give you hot water for about 30 to 45 minutes and take about 2 hours to recover.
.

This is misleading. Better to state: An indirect water will give you a small flow of infinite hot water. An example is 1 kw of electric heat supplies 5 gals. of 80^F rise per hour. A 10 KW indirect heater supplies 50 gals per hour or less than 1 gal. per min. This is hardly enough to keep a good shower going. God forbid someone less in the home opens a hot water valve.
An 80 gal electric with a 4.5 KW element takes 4 hours to heat up. It is capable of suppling 10 gal. per minute for 8 minutes. This enough to fill a tube in a couple minutes. The difference in efficiency is 10% for the standby losses.
The complexity of the indirect is significant when compared to the tank heater. Liming is a serious problem in the indirect and difficult to fix. But be my guest. Regards TB

[beenthere]

Liming of any tank can be a problem.

[teddy bear]

Liming of any tank can be a problem.

Liming in astorage tanks is a minor problem compared to small heat exchanger. Regards TB

[Frostie]

It really depends on the recovery rate needed by the users. Electric hot water is the most limited as far as quick recovery, but here it is much cheaper and efficient than any other option if you have predicatable use patterns. We pay 5.9 cents per kW hour for the first 175 kWhrs and 5.7 cents for every kWhr after that. The rates are very stable and can only go up if approved by the utilites board.

[jeremy-lvhm]

One should install a heat pump
(and time-of-day use electric rates, if appropriate )
to heat the hot water to save > 60% ( $150 / year) of the energy.

http://www.nyletherm.com/waterheating.htm

The relay will save ~ $10 per year.
... seems like the pay-back periods might be 2 to 6 years.

40 --- Gallons / day
30 --- days /month
---
1200 --- Gallons / month
8.3 --- lbs / gallon
9960 --- lbs / month
---
115 --- HW Temp
50 --- Water In
65 --- dT
---
647400 --- BTUs/ Month
3412 --- BTUs/ kW
189.7 --- kW / month
---
0.11 --- $/kW
$20.87 --- $ to heat hot water / month
$250.46 --- $ to heat hot water / month
60% ---
$150.28 --- Savings/ year with heat pump
---
4.0% --- Savings for use of relay during daytime
$0.83 --- $ Savings / month
$10.02 --- $ Savings / year

Wow that was really hard to read. You guys and all your crazy calculations. Are you that bored? LOL. Ive thought about the heat pump water heater. But you tell me how the installation cost of something like that would justify everything. AND don't those little guys have condensers on the top? The ones I seen years ago did. This would be alight in the summer because it would give me a little cool air inside but what bout the winter? Cold when I want warm. I honestly didn't think they made one anymore. I should have looked. And how do you figure the relay would only save 4%? I would think 8-10 hours of not having to keep a tank warm would save a bit more than that. Hell I can even time it to stay off all night too with a timer.

I just checked out that site. Nice looking little thing. Might have to check that out. Right now I am too poor to spend that kind of money but it definitely looks interesting. I thought you were talking about the old heat pump on top of the tank complete setups. I've only seen about 2 of them myself. That little thing though looks pretty neat though. My Only question is how easy is it to clean out the calcium buildup? Have you had any experience with them? It would be okay if it was like the rinnai and easy to flush out the buildup. Thats pretty cool that it offers a duct to get rid of the cool air when you dont want it too. Guess that answers my cooling in the winter comment. I admit the savings on my dehumidifier would be nice too.

[beenthere]

Form Spread Sheets make all those calcs quick and easy.
Onc the formulas are entered, you just enter the area rates, conditions, what ever, and the calcs are done before you can blink.

[dan sw fl]

And how do you figure the relay would only save 4%? I would think 8-10 hours of not having to keep a tank warm would save a bit more than that. Hell I can even time it to stay off all night too with a timer.

That little thing though looks pretty neat though.

Savings might be up to 1/2 of the inefficiency
( 100% - 92% = 8%) / 2 = 4% ... and 4% might be on the Generou$ side ..

HWTs are rated in the mid 90% range.
State Premier electric = 95%
State Select 40-Gallon = 92%

http://www.statewaterheaters.com/lit...c.html#premier

How do You determine that a relay would save > 4%?

The relay would effectively only operate the unit
Longer with Fewer periods.

[beenthere]

Without a discount rate for off peak usage, the timer only saves because of the lower standby heat lost from the lower water temp.

[dan sw fl]

Wow that was really hard to read. You guys and all your crazy calculations. Are you that bored?

How simple can one state it ...
heat the hot water to save > 60% ( $150 / year) of the energy

I guess some people actually like or have to sleep .. seems boring to me.
Whats' 3-minutes in a 20 hour day (1/4%)?

No significant sized building is developed without many hours/days/weeks devoted to load analysis and energy calculations as required by state building and mechanical codes.

[jeremy-lvhm]

Without a discount rate for off peak usage, the timer only saves because of the lower standby heat lost from the lower water temp.

Exactly. So instead of heating your water back up first thing after all the showers then having it cycle how many times in a day to stay warm you offset your recovery until later on when you use it again. I Would think this would do pretty well. Not to mention shutting the damn thing off when you leave for the weekend or longer. At least if I have a switch at the top of the stairs it would make it easier to play with. My boiler cycles at least 5-6 times a say when I'm not using hot water. Plus when I do its even more. I could get by with a luke warm tank all day to wash my hands. I guess I'll have to get actual runtime numbers each way to see how it works. And if its only 4% then so be it. What does it cost me to take a used contactor off my truck and some tstat wire? And I'll put a disconnect in bypass with the wiring in case my contactor goes bad and I need it to run fast. Or I can just leave a properly sized screwdriver in the contactor. LOL.


Maybe I'll just switch to solar.

[jeremy-lvhm]

How simple can one state it ...
heat the hot water to save > 60% ( $150 / year) of the energy

I guess some people actually like or have to sleep .. seems boring to me.
Whats' 3-minutes in a 20 hour day (1/4%)?

No significant sized building is developed without many hours/days/weeks devoted to load analysis and energy calculations as required by state building and mechanical codes.

Everything seems like a good idea until its proven otherwise. I've seen plenty of calculations go wrong and if you say you haven't your a darn liar. LOL. Anyway if my savings from the heat pump was 150 a year thats one hell of a long payback period no? I'm not ditching the idea. But how long do these things last? They obviously get alot of runtime. So if it takes me about 7 years to pay for itself and it only lasts ten its not really marketable to others. After markup to the homeowner, etc. And there has to be some maintenance to these just like a tank less coil. Something that the average homeowner wouldn't be able to do himself. And as these things start to get all crapped up inside I am sure they wont run as efficient. I'm not ditching it. But once again its not a fix all. Have you had any experience with them? I'm curious.

Oh god. I just realized your an engineer. LOL Forget it. I know this will be an argument not worth fighting. If it can't be put on paper most of you guys dont believe it. I'll just concede that Im a lowly technician and you know more than me. Don't get me wrong but I have dealt with many an engineer when I worked industrial. And I have gotten tired of the arguments. Im just throwing up the white flag before it gets nasty. lol