Heating elements in hot water heater on/off?

Discussion in 'General Discussions' started by hardchines, Jan 22, 2009.

  1. hardchines

    hardchines Member Forum Leader

    I noticed in a post by Engineer that he has his upper element "OFF", I have seen some post about turning down or disconnecting the lower element. Engineer can you explain your methodology, any other opinions on best way to heat water when adding preheated water. I am preheating my water with Geo. and supply the 80 gallon electric water heater with 85 to 105 degree water,I have the lower element set to 100 and the upper to 125, am I backasswards?:cool:
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Upper element is off because I'm cheap and lazy

    First, bear with me for brief lecture on how dual element water heaters function - apologies in advance to those who already know this stuff.

    Upper element on tanks 20 gallons or greater seems to me to be installed only as an aid to rapid recovery of some hot water to a tank full of cold water. Tanks are wired so that at no time can both elements fire simultaneously. If upper element comes on, tank has almost no hot water left and upper element (relatively) quickly reheats a few gallons of water at top of tank.

    Only when upper element is satisfied is lower element allowed to fire. Most of the time only part of tank's water is used (1 shower or load of wash, etc). Lower element stat senses replacement cold water and fires until that is heated - upper element never comes on.

    So what does that have to do with my being a cheap and lazy engineer?

    We moved into new house last May and I sought to instrument the geo system and water heater and gather electricity consumption data to support my various hypotheses. On older house I had two 50 gallon tanks and mechanical hourmeters on both elements of the main tank. The meter wiring was crude and not especially safe. I did learn from that setup, among other things, that the upper element rarely fires.

    I found Redington model hourmeters that run on any voltage from 20-277. That's very handy as it spans from as low as HVAC control voltage up to 240 line voltage.

    New house has dual 80 gallon tanks, plenty of capacity, so to avoid buying and installing an additional Redington, as well as having to read it and do extra math, I disabled the upper element and metered only the lower element.

    Builder recently asked for hot water cost data - in 8 months it has been right at $100 for 4.5 occupants (stepson here half the time) That includes element run time, desuperheater circ pump run time, and a 10% allowance for desuper diversion during heating season.

    Finally, I should describe an experiment underway for a month now: Electric co installed new digital meter on new house. It displays peak demand as well as total kwh. We are not billed for demand, but minimizing demand is a 'green' thing to do as well as making it easier for standby generator (and possible future PV array) to carry the house load. Additional data for geek to collect and chew on -

    I rewired the main water tank from 240 to 120 volts. That quartered its consumption from 5500 watts to 1375 watts. It also quartered element watt density, which I expect will eliminate hard water sediment. Of course, run time increased by 4 times, and recovery of a completely empty tank would take 7 hours, but it hasn't been a problem owing to spare capacity.

    Tank stat setpoints:

    Without a preheat tank, shutting off lower element and running desuper water into main tank is an alternate implementation. It is weak since it drastically reduces volume of available hot water during times of little or no heating and cooling.

    With a preheat tank, there is little need to vary main tank upper + lower element stat setpoints. Doing so does offer possible advantages of spreading load more evenly between elements and slightly reducing tank standby loss. A possible disadvantage is a shower user experiencing temperature fluctuation as plug of hot water at tank's top runs out and is replaced with cooler water immediately below.

    I advocate setting domestic hot water as 'cool' as possible - in our case 115 only because wife demands very hot shower. I set at what she needs + 5 degrees to accommodate stat on / off gap. I used to get by at 110. In my opinion, any hotter than necessary for comfortable showering is a waste of energy and exposes small children to scald hazard.
  3. Kdeclercq

    Kdeclercq New Member

    I use a Whole House Tankless Hot Water Heater

    I use a Marathon Hot Water Tank (98 Gals) with no power to the unit. So it's used only as an insulated storage tank (It is wired so I could power it up if my tankless goes down). My DSW heats the Marathon Tank hot enough (98 Gallons at about 120f)that the Tankless hardly has to work. I noticed that with the DSW off it still heats water to about 80F in the tank(Just from heat flow I assume).
  4. mx125

    mx125 Member

    Can I ask . . I'm sure it's been covered elsewhere . ..but as you've come up with an efficient solution:

    How should I have the installer plumb my domestic:

    -Cold water in the top or bottom of storage?
    - Desuperheater "out" into bottom or top of storage?
    - DSH into top or bottom of storage (and do I need a separate circulator or will DSH do that?)
    -Storage out to top or bottom of electric water tank?
    And finally I assume I feed house hot water from top of electric?

    Many thanks.
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Plumb storage as though it is a regular water heater. supply into CW inlet, HW outlet to main tank. Desuper in and out both go to bottom of preheat tank - can tee into CW and boiler drain or use the fancy coaxial fitting - direction not important as long as desuper in and out both connect to bottom of preheat tank

    CW inlet has a dip tube taking it all the way to bottom of preheat tank - leave it intact.

    House water feeds from top of electric - HW outlet
  6. hardchines

    hardchines Member Forum Leader

    Engineer; Thanks excellent answer as usual!;)
  7. mx125

    mx125 Member

    Yes! I second that. Very clear. I will print this off and take it to my installer verbatim. Thanks again!!
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Better to have a picture

    Both Waterfurnace and Climate Master show differing but IMO equally effective arrangements on installation docs available on their websites.

    I strongly suggest you download and print one or the other for installer
  9. mx125

    mx125 Member

    I will. Thanks. They currently have the infloor and domestic connected to a 60 gallon heat exchangeer style tank. Documentation recomends 80-120 gallon for the infloor alone. . . .so I'm guessing that is an issue aside from the plumbing. My furnace is a geosmart Q series.
  10. mx125

    mx125 Member

    And another question(s) if I could.

    The temp sensor for infloor is taped to iron pipe at the top (output) of the storage tank. When the temp drops below the threshhold it calls for the compressor to turn on.
    - Where is the best location for the DSH/Domestic temp sensor?
    - Will that call for the unit to turn on? If so, is it the same coil as the infloor water?
    - If above is yes, how can I isolate the domestic storage from the infloor so that I dont heat both tanks in summer. Perhaps the DSH only makes heat passively when I'm running the AC? Note: There is a "hot water on/off" switch. Installer said I can turn that off in Summer . . but will that impact DSH. There does not seem to be anything in the manual.

    With all of the above, although installer should know, I have the feeling I need to have a general idea and understanding of wha I want and how it works.

    Thanks again.
  11. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I hope you are not mixing domestic and in-floor water

    Jury is still out on danger from Legionella from doing that.

    DSH as a parasitic rather than primary function - it is available only when the system is running for heating or cooling calls. It csnnot run the system based on a domestic water call alone.

    There are systems out there that can run solely on domestic water calls, but that brand isn't popular here or at GBT. There are other systems that can do both air and infloor, but the single wall heat exchanger for infloor is not suitable for potable water.
  12. mx125

    mx125 Member

    I'm not mixing infloor and potable. The DHW is feeding only the infloor supply. The potable cold is input into the coil that surrounds the infloor storage tank. In theory, I guess, it leeches heat from the infloor supply. But given is is a 60gal total capacity I can't imagine there is really much potable water "storage".

    Should I confirm that the DSH feeds (when I utilize them) do send my potable water through a separate coil? Or is that the purpose of those separate DSH outputs?

    I see your point on the lack of separate water heating duties. So should I keep my infloor sensor at 110F (currently at 95F) and when when there is a water call it will also heat my potable storage tank? In summer should I close a plumbing valve on the infloor input and move the temp sensor to the potable supply? Or just let the DSH leach heat passively when cooling cycle runs?
  13. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm confused

    Please take it from the top and describe what heat pump(s) tank(s) and heating methods you are installing

    So far I think you have a geo heat pump, one or more infloor zones, a main hot water tank and some kind of preheat tank that somehow is to do double duty. I'm stuck on that.
  14. mx125

    mx125 Member

    No problem.
    I have a 6ton geosmart Q heat pump and 4 zone infloor (basement only). We also have an electric domestic hot water heater.

    The heat pump (other that forced air) has two pairs of water feeds. They are both labels DHW but according to the manual the two unused are for domestic DSH option which is installed but not connected.

    The part that confused me as well was the dual purpose storage tank. It has a core in out to which the infloor feeds are connected. There is a separate coil (which i assume spirals the core coil) which has potable cold in from my well tank and an out to my electric domestic water heater. It is a 60 gallon total but I don't know the split. The temp guage which triggers the heat pump is connected to the iron pipe which feeds my 4 infloor zone pumps.

    I plan to (if it's the correct solution) have them replace this dual unit with a dedicated infloor tank and add a separate domestic storage tank connected to the DSH heat pump feeds.
  15. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Looks a bit like a Waterfunace Synergy and may even be one private labeled. I don't have experience with that. I did note that it heats water or air but not both at same time.

    I'm not comfortable suggesting you ask your installer to swap one tank for another, etc. I defer in this case to 'boots on the ground'

    Presumably there are installation docs with a piping diagram - if the Geosmart site doesn't have them but the unit is a private labeled major brand, look at the major brand's site.
  16. mx125

    mx125 Member

    Will do. Thanks. I did more research on the water tank. It's an Amtrol and appears to be in indirect fired water heater. So there is not dual stoarage but is designed to heat storage water with an external boiler runnning through coil. So it appears my infloor zones are heated directly from my heat pump (no storage tank). That coil setup will not heat my domestic properly in my opinion. The manual says specifically that a storage shank should be used for infloor, so I'll have questions for my installer.
  17. hardchines

    hardchines Member Forum Leader

    I have the Amtrol storage tank, I was told it would not work well and I am sure it is not as efficient as a no loop tank. That said I have hard water and felt clogging the heat exchanger in the Geo. unit would be imminent, and I wanted to keep my oil system in tact so I could switch back to oil need be with the closing of a couple of valves and the flip of a switch. I hooked up my HWG to the tank coil and am amazed how well it works, I monitor output water temp every day in the AM, normal temp out is 106F going to electric HWH, main Geo unit is 3 ton running 56% of the day with outside temp average of 16 F. Proof is in the numbers!
  18. rw1995

    rw1995 Member

    Thank you for the Waterfurnace note, I was getting confused with the coaxial fittings, both desuperheater connections entering the bottom on the storage tank.

    I pull my desuperheater from the cold entering the storage tank, run it thru the desuperheater and back to the bottom on the storage tank. This is the Waterfurnace described method with storage tank.

    I'm using a NG waterheater. All the internet calculators I've used have the NG being more efficient for heating water. Would you agree, or should I be looking at converting to electric.

    Thank you.
  19. mx125

    mx125 Member

    Wow . .that's very interesting. Could you explain exactly how your Amtol is routed again? My apologies for dumb questions. What is HWG? Do you have your heat pump heating the main tank in the Amtrol and looping back and using the internal coil to heat your domestic hot water? I assume then, you have the domestic cold water "in" feeding into the coil bottom. Is the domestic able to heat that quickly . .passing straght through the coil and out? I could be way off base . . .so feel free to correct me!
  20. hardchines

    hardchines Member Forum Leader

    HWG =hot water generator/superdeheater.

    OK lets try this, I have used my Amtrol for 20 years for hot water, it is on its own zone on my oil boiler, I did not want to loose the ability to make hot water from boiler if needed, so I Tee'ed into the existing lines going to Amtrol from boiler. I had isolation valves on boiler for that circuit, I plumbed the lines from the HWG on the geo unit to the tee's , I installed a small expansion tank and pressure gauge then purged the entire system with boiler water and shut the valves on the boiler, and connected the HWG pump built in the geo. unit. Now when the geo runs the water circulates through the coil in the Amtrol, no domestic water goes throgh the HWG in the geo unit, it is a closed loop. I then deverted the hot water out line on top of the Amtrol to the cold water in port on top of a 80 gallon electric water heater, and the hot water out line from electric heater to the house. I then did something I have not done in 20 years " I SHUT OFF MY OIL BOILER ", I monitor the electric usage everday since I turned on geo. units three weeks ago and see NO increase in electric usage since turning on electric water heater and shutting down the oil one week ago. I have three females taking hour showers and all of them say no problem!

    hope this helps

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