Any tips for elec water heaters?

[Walker]

Time to replace my 25 year old elec water heater.... no leaks at present but it's bound to fail soon. Expect to install a 5kw grid-tied system this year. What would the optimal setup be to run an elec water heater.... I'm figuring put it on a timer to heat during the day. What kind of on/off cycle time can I expect.... If it's on for , say 8 hrs a day, will it retain reasonable heat for the other 16 hrs? Or cycle it on/off 4 times a day?
I don't use a lot of water, just me in the house, so figure one daily shower (early afternoon) and the usual kitchen use. I've been using about 180 kwh/month for the water heater.... it's a big one, 80 gal, sized for the garden bath tub I rarely use. Will likely downsize to a 40 gal unit unless there are advantages to a larger one.
Natural gas isn't avail nearby, Propane is much higher cost than elec for water, so I'll stick with elec.
What type of setup (size, timers) works well in combination with solar? Thanks.

[Mike90250]

If you are going to use a timer, get the larger tank, only the top half of the tank has the really hot water in it.

Make sure the timer can handle the voltage and wattage of the heater, Sun (solar) is strongest 10am -2pm or so, depending where in your time zone you are, so set the heater to run then,

Also, the "heat pump" style of water heater, is more efficient, but has lots of moving parts, valves, compressed gas and stuff to go wrong,

[PNPmacnab]

I have a NYLE heat pump attached to mine. These are an add on unit that can be attached to any tank. This saves throwing out a system every 10 years. Doesn't sound like a problem in your area. Heat pumps typically have a COP of about 2 making electricity costs half of resistive heating. Typically these units are about 600W and slow recovery compared to a 4500W heater.. We are low usage and haven't had a problem with recovery. Our tank failed years ago and I quickly installed a 30 gallon tank I had around. That was plugged into a 120V outlet resulting in a 700W element. We managed to live with that for a while with no issue, we only live in the house half the year. The new NYLE became available left over from a . utility HOT SHOT test program for $370 shipped. It was a no brainer compared to the $1600 stand alone units. Wife loves it as it also dehumidifies the basement.. Our costs were 46 cents a day. At my other house I heat with excess PV energy. I wanted to have a combo solar/heat pump setup, but the numbers just aren't there.

Heat pumps are a light load for even a modest inverter, but they can not get tank temperatures much above 120F. For a timed system, you need to get tank temps up to almost 150F and use a tempering valve which mixes in cold to bring temps down to 120F. Every big box store has these. Those who use hot water as a dump load often have two or more tanks in series. These operate to temper the water so cold is not mixing with hot and recovery is faster.

[DanS26]

I also use the Nyle heat pump water heater. But as usual I have it set up a little different than normal.

I have it plumbed to a powered LP 40 gal standard water heater. These powered WH's use a small fan to draw the heat up through the unit. Usually vented through the side of the house using PVC pipe. I have both the power WH and the Nyle set up on timers. From 10pm to 5am everything is shut down.....not so much to save energy but to keep noise down in the house during sleep-time.

In late fall, winter and early spring the Nyle is shut down since it outputs cool air to the house. I do not need to heat the air in my house twice.

In late spring, summer and early fall the Nyle is set up to run only when the sun shines...from 9am to 5pm and the LP is shut down at those times.. It does a good job heating my water, cooling my house (its rated as a one ton AC) and dehumidifying the basement. I have the cool air output connected directly to the return air duct work of the HVAC system. So basically the Nyle only runs on solar PV power.

I also received a rebate from my POCO, but the irony is that it uses very little POCO power. After all the rebates and tax credits my net cost for the system was $429. Of course, I installed it myself......my first experience with "shark bites". Turned out fine...see pic.......

Nyle.JPG

[Walker]

Thanks guys,
The Nyle heat pump sounds like a nice piece of equipment. Unfortunately a new unit is over $900 shipped, and it's Energy Factor rating is just below what is needed to qualify for my POCO (Peco) $350 rebate. But I'll be keeping an eye open for a used unit..... you got a great deal on yours.
I'm presently sorting through TONS of info on the waterheatertimer(dot)org site. Some great ideas for timer options ranging from basic mech to wireless control. As usual, I'm probably overthinking this, but I like an engineering challenge.
I'll likely pick up the basic 50 gal unit now on sale for $344 and then look for a timer/control system.

[bcroe]

Lots of interesting ideas there. I suppose the Nyle is quite an efficient way to air condition the
house, using the cool ground water? I currently have a high efficiency propane WH, but they are
quite expensive and there is a problem with house heat going out the vent 24/7 in winter. If the
PV energy collection process here gets optimized, I might go back to electric. The WHs here
seem to have a problem with minerals and developing leaks, so a cheap electric with no vent
might be a good choice. Bruce Roe

[J.P.M.]

You're in SE PA ?

1.) SWAG about 1/3 of your DHW load is attributable to system losses. Some from piping, most from standby losses from the tank. It sounds unnecessary, but whatever size of the new tank (if that's how you go), add more insulation to it. You'll get your money back in very short order.

2.) Insulating the piping will also save some $$ , but not entirely for reasons you may think. If you're conscientious and thoughtful about water use, and in this case hot water use, insulating the piping will save some in the way of energy if hot water draw is frequent - but much less if the hot H2O draw is less frequent. The math is well developed but boring. As a practical matter, after a few hours the water in the pipe will cool off at least half way or more and probably pretty close to the surrounding ambient temp., pretty much irrespective of how well the pipe is insulated. Insulate long runs if it's a DIY and lines are easy to get to , but don't break your butt over it.

3.) A HPWH can produce savings with the additional benefit of some AC load reduction during cooling season (but perhaps some addition to heating loads during heating season if HP discharge not vented outside). Some adjustment to the C.O.P. of the heat pump will also be necessary for outside air temp., depending on climate.

HPWH are more complicated and thus prone to requiring more maint. Something to consider. How much time do you spend on you current tank ?

4.) If you reduce your standby losses by, say 20%, and your resulting DHW load goes to ~~ (180 * 12)* (1- (.33*.2)) =~ 2017 kWh/yr. A HPWH with a seasonal C.O.P. of, say, 2.5 for talking purposes, will result in a usage for HW of ~ 2017/2.5 = 807 kWh/yr., or a reduction of electrical usage of maybe 2017-806 ~ = 1,200 kWh/yr.

Depending on how much such an annual reduction spread over a year might reduce your electrical bill, the difference in price between a HPWH and a conventional tank H2O heater a HPWR may be cost effective.

[Mike90250]

Here's what the water tempering valve looks like

http://www.caleffi.com/usa/en-us/catalogue/valves-domestic-water-and-hydronic-systems

20160811_100719.jpg

[bcroe]

If you have long lines and need to run a circulator to keep water hot at the ends, the insulation on the
pipes will be more important. The insulation at big box stores is very poor; J. P. M. might refer you to
some that really works. Oh and the cheap stuff starts curling up and separating before too long, at
which point its worthless. Noting that, this place got new pipe insulation wrapped with duct tape to keep
it in place longer. But this cheap stuff is warm to the touch. Next time... Bruce Roe

[J.P.M.]

If you have long lines and need to run a circulator to keep water hot at the ends, the insulation on the
pipes will be more important. The insulation at big box stores is very poor; J. P. M. might refer you to
some that really works. Oh and the cheap stuff starts curling up and separating before too long, at
which point its worthless. Noting that, this place got new pipe insulation wrapped with duct tape to keep
it in place longer. But this cheap stuff is warm to the touch. Next time... Bruce Roe

FWIW, having a circulator type system to avoid less than instantaneous hot water at the ends of moderate to long piping runs is one of the most wasteful and conservationally inappropriate, counterproductive and cost ineffective things that can be done. I know, I know, energy is less expensive than water in some places. So, - PUT UP WITH SOME COLD WATER FOR 30 OR SO SECONDS AND WASTE NONE OF IT. Or get a spot heater and a small point of use tank. Another trick: keep the water lines out of cold(er) areas and away from building perimeters in colder climates.

Suit yourself - not my money/house/life/whatever, but even when insulated, and even when on timers, circulators waste electrical energy for pumping, and, more importantly from an energy use (waste) standpoint, are a gross waste of heat - often contributing to an A/C load, or often offsetting some of a heating load, but in less than ideally controllable ways and/or heating otherwise unheated areas. Besides, circulator systems increase the length of a hot water piping system by about 2X, effectively doubling the heat loss, not to mention system cost.They are a waste designed to make plumbers rich. Great and necessary for large systems like hotels, hospitals etc., but in a small dwelling - dumb, or hubristically inspired.

If the choice is to insulate the piping, the residential and practical gold standard is closed cell foam. Not a plug, but a product called Armaflex seems to last forever and is easy to use - but it ain't cheap, and may take some economic gyrations to make it cost effective from an energy saving standpoint - @ least for residential hot water service lines. If used, just remember to compress it lengthwise about 3% or so for shrinkage, It's waterproof, has a high service temp. and does not outgas. But - DO NOT expose it to sunlight . If used outside, wrap in aluminum (NOT duct) tape. I've got 1/2" Armaflex on all service hot H2O lines in the house and 1" on all the solar H2O heater lines. 9 years and no cracks/breakage/water damage. Get the 1/2" thick @ big box (I think it's ~ $1.00/lin. ft. in 6 ft. lengths), and resist the urge to cheap out on the Frost King product - that's simply inferior IMO and not worth it. The insulating value of the crap stuff drops off after a yr. or 2 even if it doesn't spall off. A waste of $$.

For the most part however, piping loss is a relatively small part of the overall system loss in a well designed, or even a not so well designed system. Reason: the volume of water contained in a residential piping run is relatively small. Example: The amount of water in 100' of 1/2" piping is less than 1 gal. The heat saved by R3 vs. R1 bare pipe will save about 100 or so Watt-hr. of energy even if the water cools 60 F degrees or so. Better tactic/answer: Run less hot water. Overall, while it may be a bit wasteful of energy, insulating piping may one of those tasks not real high on the priority list. The inconvenience of "waiting" for hot water is usually the more visible flag that frustrates people and raises visibility, but it isn't really that costly to leave piping runs bear, at least if other measures to conserve H2O are taken - think about it - less water used = less water to heat and less heat loss to insulate against.

Take what you want of the above. Scrap the rest.

[bcroe]

So there you have all the evils of a hot water circulator system, and the right way to insulate it. Of course the other
occupant of this house has reaffirmed that the circulator WILL be kept in good running order, so my hands are tied
(at least that's my excuse). She told me what "hubristically" means.

As bad as my pipe insulation is, adding it still did made quite a difference to the circulator constants. The circulator
has the other advantage that considerable partially heated water doesn't go unused down the drain. Being a 100%
DIY project, there were no plumbers collecting fees. Anyway the 4 decade old house started as "all electric", and
there were some strange things left over after the subsequent propane upgrades. The original water heater was
about 60' from the master bedroom shower. Now its set up my way, subject to more changes.

Since I have a couple temp sensors for the water heater and the end of the line, the pump can be controlled to only
run as needed. The temps or differential can be selected for display. I was able to reduce the on/off hysteresis
(temp variation) with the pipe insulation

My 12V wimp pump was purchased from a "green" source who claimed it only used 3W; it runs with no head. I
measure more like 4W, so with intermittent operation it might use 25KWH per year, out of the 27,000KWH my PV
array generates. Fully half the year the lost heat just helps keep the house from being too cold, unlike the situation
in the SW desert. The other times the heat forces my PV powered heat pump to run a little longer.

Some of the circulators I looked at in stores seemed to be designed to be cheap and very easy to install; probably
a lot more costly and less efficient than mine. Bruce Roe

[J.P.M.]

So there you have all the evils of a hot water circulator system, and the right way to insulate it. Of course the other
occupant of this house has reaffirmed that the circulator WILL be kept in good running order, so my hands are tied
(at least that's my excuse). She told me what "hubristically" means.

As bad as my pipe insulation is, adding it still did made quite a difference to the circulator constants. The circulator
has the other advantage that considerable partially heated water doesn't go unused down the drain. Being a 100%
DIY project, there were no plumbers collecting fees. Anyway the 4 decade old house started as "all electric", and
there were some strange things left over after the subsequent propane upgrades. The original water heater was
about 60' from the master bedroom shower. Now its set up my way, subject to more changes.

Since I have a couple temp sensors for the water heater and the end of the line, the pump can be controlled to only
run as needed. The temps or differential can be selected for display. I was able to reduce the on/off hysteresis
(temp variation) with the pipe insulation

My 12V wimp pump was purchased from a "green" source who claimed it only used 3W; it runs with no head. I
measure more like 4W, so with intermittent operation it might use 25KWH per year, out of the 27,000KWH my PV
array generates. Fully half the year the lost heat just helps keep the house from being too cold, unlike the situation
in the SW desert. The other times the heat forces my PV powered heat pump to run a little longer.

Some of the circulators I looked at in stores seemed to be designed to be cheap and very easy to install; probably
a lot more costly and less efficient than mine. Bruce Roe

Bruce: With all possible respect, it's all the same to me how/what you do, and I do appreciate your predicament. Like I wrote, not my house/money life/etc. But, and IMO, and I believe it's a reasonably educated and experienced opinion in these matters, residential hot water circulators require a lot of extra material and energy (with probably about the same energy waste regardless of who builds the system BTW) to construct and function as designed for what I see as the relatively small advantage of having a bit more rapid access to hot water. The cost/benefit ratio is way too high for me.

I also believe if more people knew the true costs of such a system, or how to calculate those costs, there would be a lot fewer of them. That so many exist says a lot to me about lack of knowledge and the hangover of profligate energy use from the days of cheap energy. They're like having a distributed radiator system in your home, with at least some of the heat transfer surface(s) running through what were designed as unheated spaces, and/or putting heat into a dwelling in what's mostly an uncontrolled manner.

Respectfully,

[inetdog]

More complex than a circulating system are the loop pumping systems with temperature sensors at each end of the hot water pipe.
Less than a minute before you need hot water, you flip the switch and it pumps water from the hot water line at the outlet into the cold water line until it starts getting hot water.
You then use as much water as you want. When you are done, flip the switch the other way and it pumps cold water back into the hot water line until it sees the cold water slug reach the heater. It then shuts off and waits for the next use.
No heat loss in pipes except while you are actually using hot water. Needless to say it does not work with a tankless system.

[bcroe]

More complex than a circulating system are the loop pumping systems with temperature sensors at each end of the hot water pipe.
Less than a minute before you need hot water, you flip the switch and it pumps water from the hot water line at the outlet into the cold water line until it starts getting hot water.
You then use as much water as you want. When you are done, flip the switch the other way and it pumps cold water back into the hot water line until it sees the cold water slug reach the heater. It then shuts off and waits for the next use.
No heat loss in pipes except while you are actually using hot water. Needless to say it does not work with a tankless system.

I guess that could be done with 2 different pumps. I'd be inclined to have a momentary push button that
lights when in the hot water mode; it would change back automatically in 20 minutes. Or change back when
a big temp differential developed between the source and use point; those would stay nearly the same in use.
Bruce Roe

[J.P.M.]

More complex than a circulating system are the loop pumping systems with temperature sensors at each end of the hot water pipe.
Less than a minute before you need hot water, you flip the switch and it pumps water from the hot water line at the outlet into the cold water line until it starts getting hot water.
You then use as much water as you want. When you are done, flip the switch the other way and it pumps cold water back into the hot water line until it sees the cold water slug reach the heater. It then shuts off and waits for the next use.
No heat loss in pipes except while you are actually using hot water. Needless to say it does not work with a tankless system.

Opinions vary, but that seems to me like a lot more hassle, cost and maint. than it's worth for the small savings which might well be achieved more easily and for less effort by simply not using hot water as often.

But, I've been shaving in cold H2O for 50+ years, and trying to uncomplicated my life in such ways for most of it. Different strokes I suppose.

I seem to remember a rather long, printed, eventually R-rated, and abysmally politically incorrect office humor type joke that went around about automatic toilets that do everything and the complications that can arise.