Author Topic: Water heater economy  (Read 1240 times)

0 Members and 1 Guest are viewing this topic.

george65

  • Sr. Member
  • ****
  • Posts: 426
  • Country: au
Water heater economy
« on: November 12, 2017, 02:29:17 AM »

The hot water coming from my water heater does not seem all that hot. I can keep my hand in the water for short periods which means it's around 50o.
I cannot see any tempering devise on the tank or anywhere else so I assume ( haven't checked yet) it's what the tank is set at.

Normally I like the hot water system dialed right up because it gives you more hot water basically when you use less.
I was going to check and see what the thermostat is set at but then I got to thinking.  There are only 3 of us here and my wife and I take pretty quick showers and my daughter does not shower every day.  The system is 250L so we have heaps even when my daughter does take 7 showers in one and is in there till she looks like a prune.

I was wondering what is the most economical setting to have a water heater?
Turn the thing right up so you use much less mixing it with cold water, use more cooler water or it does not matter?
I have some thoughts but I won't divulge them to influence responses, i'd just like to hear if here are and tests/ studies/ facts on this prefrably and then opinion and what that is based on.  Generally we shower at night and the heater is offpeak so generally we are showering 18hrs after the off peak has finished and the water has been sitting there.

The tank is right behind the main bathroom, 1 room away from the en suite and we don't hot/ warm wash except for the very odd occasion in winter when the water is cold and my clothes are greasy. Water heater is also right behind laundry.
The tank cops the full sun from at least midday on and it feel almost hot in the afternoons even though it is a mid density colour. I'm thinking of painting the thing black to attract as much warmth as possible. I don't much like the look of the thing or where it is so the other idea was to enclose it and wrap the whole thing in home insulation bats to help with reducing heat loss....if it would make any difference.

I don't want to get into one of these chasing every watt/ Kj of heat scenarios but if a bit of extra insulation would make a difference, not much work of any significance to do it.

Main thing ATM is  if using more cooler water is more economical, use less hotter water or it's 6 of one and half dozen of the other?

frackers

  • Sr. Member
  • ****
  • Posts: 396
  • Country: nz
  • Is it finished yet?
Re: Water heater economy
« Reply #1 on: November 12, 2017, 04:18:23 AM »
Legionnaires disease bacteria thrive from 20-45c but are killed by over 60c. My DHW system (overkill with 30 tubes) has a mains topup so that if the temperature does not go over 60c for 10 days it will crank it up from the grid.

At this time of year its venting (I have it set at a very low 80c) a couple of times a day.
Robin Down Under (Or Are You Up Over)

george65

  • Sr. Member
  • ****
  • Posts: 426
  • Country: au
Re: Water heater economy
« Reply #2 on: November 12, 2017, 06:26:35 AM »
Pretty sure you can't set it under 60, probably for that reason.
I was thinking more the lowest or highest setting which I think is 80 C

dnix71

  • SuperHero Member
  • ******
  • Posts: 2268
Re: Water heater economy
« Reply #3 on: November 12, 2017, 09:14:36 AM »
You can set it as hot as you like, but there is supposed to be a fast clamp at the shower and faucets so if it comes out above about 117F it gets shut off.
You would not use this on a dishwasher.

http://www.cashacme.com/product/tafr/ Direct thread on, no power needed.

If you can't be sure no one would be hurt by direct contact with the hot water if the cold/hot mix failed, the auto shutoff could literally save your skin or life.

Otherwise letting warm water sit in a tank will grow bacteria. There is no completely automated simple way to balance the 2 risks - scalding vs. legionaires.
https://canadasafetycouncil.org/home-safety/heated-debate-about-hot-water

OperaHouse

  • Hero Member
  • *****
  • Posts: 1077
  • Country: us
Re: Water heater economy
« Reply #4 on: November 12, 2017, 11:15:57 AM »
There are tempering valves that go on the tank between the cold and hot side that blend water to the desired temperature. Often called tank boosters because they can make a 40 gal tank perform like a 70 gal tank.  We are exposed to Legionares bacteria and that sort every day of our lives.  It is only a problem in massive quantities and those of compromised health.  The water is chlorinated, fairly free of nutrients and changes quite often.  And what about all the stuff growing in pipes that is turned into a mist when first turned on.  Lower temp is not really an issue.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2268
Re: Water heater economy
« Reply #5 on: November 12, 2017, 01:44:43 PM »
Disneyland and American Airlines have had issues with Legionaries disease recently. It's a lot more common than people realize.
http://www.newsweek.com/disneyland-shuts-cooling-towers-legionnaires-disease-outbreak-708915

george65

  • Sr. Member
  • ****
  • Posts: 426
  • Country: au
Re: Water heater economy
« Reply #6 on: November 12, 2017, 03:52:02 PM »

Not worried about legionnaire's or scalding. ....

What I am asking is it more economical to have the heater set to where it is now, maybe 60C or turn it up high as it will go which I think is 80?
 Way I see it is I'll use more water from the tank when I dilute it less with cold water and the heater has a greater volume to heat back up.

If I turn it up, the element will have to heat less water but to a higher  temp.
Is there a difference in ELECTRICAL consumption or other trade offs that make the lower ( Still bacteria safe ) temp  a lower energy consumption proposition or is having the temp set higher going to use less power over all?

dnix71

  • SuperHero Member
  • ******
  • Posts: 2268
Re: Water heater economy
« Reply #7 on: November 12, 2017, 04:01:00 PM »
That's an easy thermodynamic question. The hotter the water the greater the difference between the water and the environment. That means greater wasted heat, as losses from the tank back into the environment, unless you increase the insulation on the tank. If you are not running out of hot water at a lower temp and don't have a better use for the electricity, then you don't need to go higher. If you are running out of hot water, then go higher, add insulation and dilute as needed.

The most efficient method is to have a point of use heater (spot heater) near the point of use. But you can't time-shift electrical use with that. Your current setup allows you to heat water during peak production and "bank it" for later use.

Bruce S

  • Super Hero Member Plus
  • *******
  • Posts: 4586
  • Country: us
  • USA
Re: Water heater economy
« Reply #8 on: November 13, 2017, 09:22:52 AM »
Here's what I do.
I turned the hot water temp to what the "normal setting was. Then turned it down until someone complained about it being too cool. I turned it back up til the complaining stopped. I've done this at each house, through different water tanks and 6 people in the house at one time.
We've not yet been sick from the water and I don't have to worry about mixing with cold water.

Hope this helps
Bruce S
A kind word often goes unsaid BUT never goes unheard

ontfarmer

  • Full Member
  • ***
  • Posts: 124
  • Country: ca
Re: Water heater economy
« Reply #9 on: November 13, 2017, 12:57:16 PM »
Several ideas here all good.  My son told me one time that he wished he had of put in a larger hot water heater.   When he wants to take a shower after the family have the water is cold.  I told him he should of put in two small ones.  When the first one turns cold they would wake up and get out then he could turn the tap for the second tank and have his shower.

OperaHouse

  • Hero Member
  • *****
  • Posts: 1077
  • Country: us
Re: Water heater economy
« Reply #10 on: November 13, 2017, 03:40:13 PM »
I was given a water heater that didn't supply a lot of water.  In cleaning the internals, I found about a 5 gal bucket worth of scale in the bottom.  f you don't use high density heaters, scale never forms.  It is the result of boiling on the element.  Water turns to a gas and calcium is left behind.  But, I also found plastic pieces.  They use a plastic tube to send cold water to the bottom from the top port.  Cold water immediately mixed with the hot.  Tests with my heater indicated that it requires about 65W continuous to maintain temperature loss.  Smaller surface area of a small tank is better.  To bad two tanks cost much more than a large one.

george65

  • Sr. Member
  • ****
  • Posts: 426
  • Country: au
Re: Water heater economy
« Reply #11 on: November 13, 2017, 04:24:13 PM »
The hotter the water the greater the difference between the water and the environment. That means greater wasted heat, as losses from the tank back into the environment, unless you increase the insulation on the tank.

Exactly what I thought.
The more powerful the hot, the stronger the urge to find cold.
But I thought I would confirm that.  :0)

We don't run out of hot water so I'll leave it on the factory setting it is now. certainly more than hot enough for showering, just I like the hot water to be really hot for other things.

I just did our power bill calculation.  Meter is due to be read tomorrow and I have worked out we used about $73 worth of hot water. 663 KWH @.11c  or about 81C a day.  I'll see how my solar setup goes with the other power and when I get a gauge on that I might look at some diversion.
At that rate, not a lot to be saved. The " Supply" charges combined are over $1 a day.
That said, the 190W panel array I have of 1.6Kw only cost me $200 so I'd probably make my money back on them in a year.

OperaHouse

  • Hero Member
  • *****
  • Posts: 1077
  • Country: us
Re: Water heater economy
« Reply #12 on: November 14, 2017, 03:14:11 PM »
That is in line with my numbers.  I'm getting back into heating water again and just started running a test to get my baseline.  In a 24 hour period I used 3.3KW/day or 41 cents with my heat pump.  Given a COP of about two that would be 6.6KWH/day or 82 cents.

I just ordered two Suniva 280W panels today and they will be delivered Thanksgiving day. That gets me enough time to get a good average usage.  Even with a good price for panels it will be hard to pay them off at 25 cents a day.  But I needed them for the development work going on.  Just got in 500 big electrolytics and thinking of ordering another 600.  It is good to live in the land of plenty.  I'll have to do grid tie to make this pay off.

george65

  • Sr. Member
  • ****
  • Posts: 426
  • Country: au
Re: Water heater economy
« Reply #13 on: November 14, 2017, 03:51:31 PM »

I want to get 10 Kw worth of panels on the roof excluding the 190 set which are at odds to the 22 250's I have.  I'm winding the meter back atm but only because the weather has been mild and we haven't been using the AC. I thought summer was what I would have to cater for the most.

I was looking over the numbers I downloaded off the PV watts website yesterday  with regards to panel angles which I thought I would go for summer.
Turns out the summer angle provides the most overall power for the year. I miscalculated that before  and thought I'd take a slight loss which was fine but the correct Summer angle give more power overall  than the " correct" latitude angle.

Thing I missed though is the winter dropoff. That's going to give me half the generation in the coldest part of the year as it will the hottest. I will want the AC for warmth  even if not quite as much as I will for Cooling.
Might be running the Lister or one of the other diesels  over winter, see how I go. If I have to lay a new conduit for heavier cable to the garage, I might put in some water pipe as well so I can run some hot water back to the house for a co-gen or even just a veg fired heater water setup.
Might just see how I go the first season. Not trying to eliminate all useage and create suspicion just get it down low enough to be passable .

Seems most people around here spend more time away on holidays than they do at home so I doubt a low bill will cause any suspicion at all. I'll bet the variances in the area are huge anyway. Some people light their places up at night like monuments every night and a lot run home businesses while others as I said, never seem to be home.

petect

  • Jr. Member
  • **
  • Posts: 53
Re: Water heater economy
« Reply #14 on: November 14, 2017, 04:26:41 PM »
Hi George
Insulate the hell out of it. I set my water heater on 4 inches of hi-R foam with a piece of plywood over the foam. Wrapped it with some R19 fiberglas, and some poly. It's not pretty, but when I cut through the fiberglas to get at the thermostat a LOT of heat came out.

You might want to try solar preheat. I'm sure you could put something together pretty easily, and cheaply. You can probably find an example or 2 here that you can copy.  https://www.builditsolar.com/
It might even turn into an Arduino project.
Pete

Bruce S

  • Super Hero Member Plus
  • *******
  • Posts: 4586
  • Country: us
  • USA
Re: Water heater economy
« Reply #15 on: November 15, 2017, 12:39:14 PM »
Gary at builditsolar is a long time poster here.
He'll answer just about any question you ask, if you send them thru his website
His website and long detailed posts are pretty awesome.
A kind word often goes unsaid BUT never goes unheard

frackers

  • Sr. Member
  • ****
  • Posts: 396
  • Country: nz
  • Is it finished yet?
Re: Water heater economy
« Reply #16 on: November 15, 2017, 04:02:55 PM »
I was looking over the numbers I downloaded off the PV watts website yesterday  with regards to panel angles which I thought I would go for summer.
Turns out the summer angle provides the most overall power for the year. I miscalculated that before  and thought I'd take a slight loss which was fine but the correct Summer angle give more power overall  than the " correct" latitude angle.
Never seen that site before - it seems to be coming up with pretty good numbers (70% of what I've measured over the last 3 years). The panel angle is a bit hit & miss though, I prefer http://www.solarpaneltilt.com/ which allows for all sorts of adjustments during the year.
Robin Down Under (Or Are You Up Over)

MattM

  • Sr. Member
  • ****
  • Posts: 425
Re: Water heater economy
« Reply #17 on: November 18, 2017, 06:41:19 PM »
If gains are 30% for tracking configurations versus stationary ones, it sounds more worthwhile for off grid types than grid tie types.  Off grid types are dependent on the energy and 30% in gains makes it worthwhile, especially the part of the year where output is severely limited.  But grid tie users would simply want to be focused for best performance at the peak usage hours and not muck with the array.

If someone opts for vacuum tube solar water heating, does it need to be tracked to get maximum output most of the time?  PV technology isn't real practical to boost with mirrors, but vacuum tubes should love them.  It would seem one could simply maximize output by mounting them at optimal pitch, yaw, and roll angles for wintertime, and supplementation via mirrors.
« Last Edit: November 18, 2017, 06:51:39 PM by MattM »

OperaHouse

  • Hero Member
  • *****
  • Posts: 1077
  • Country: us
Re: Water heater economy
« Reply #18 on: November 18, 2017, 11:42:48 PM »
There is theoretical and practical. Far more are constrained by the site.  My solar panels are not even on my property and by necessity lie almost flat although I am at mid 40's latitude. Unless you are the unibomber living out in the middle of nowhere, site presentation will be an overriding factor. Aside from being slightly larger and everyone being scared as hell of electronics, PV water heating beats evacuated tubes anywhere there is freezing potential at  prices today.

frackers

  • Sr. Member
  • ****
  • Posts: 396
  • Country: nz
  • Is it finished yet?
Re: Water heater economy
« Reply #19 on: November 19, 2017, 02:38:44 AM »
PV water heating beats evacuated tubes anywhere there is freezing potential at  prices today.
I'd agree with that - I put my tubes in 8 years ago, just before PV prices got affordable here.  If I was doing it again, I'd use all PV and avoid the overheating, the frost protection and the new tank that cost way too much.
Robin Down Under (Or Are You Up Over)