Series Piped Water Heaters - Opportunity Load and Propane

Anawa

Erik, my previous post about simultaneous HVAC operation and water heating is for a comparison of a DC set-up to an AC set-up.
Anawa

SolarMusher

Photowhit wrote: »

Eirk, I'm not following you, why can't he just use his existing inverter? Switch on the ac via relay off the controller? I'm working day time hours now so may get off my backside and set this up shortly. May families and individuals aren't around during the day and might get by with day time charging. I had no problem keeping hot water much of the year when working 2nd shift manually turning on the water heater. I am a single guy and the water, even with cold inrush in winter would be hot enough for showers 2 days if sparse other uses off my 30 gallon tank.

Hi Photowhit,
Because the Outback vfx will make lights and other electronics flicker when his controller will start to PWM at the begining of absorb. I'll have the same problem as I would like to change my DC fridge for a brand new Ac one under 1kwh/day and would like the heater (electric) system to be more efficient for short days in winter or cloudly periods all year round, my magnum 4.4kw would be overloaded and I'd need to add an old vfx3648. I'd want to use this vfx to only supply resistive loads and avoid this problem, water heater (2000 watts), water line heater (600 watts), toaster (1200 watts) and keep the magnum for submersible and septic pumps, fridge and all other electronic loads. The only guy that I know who had success heating from his primary inverter system was Chris Olson with his XW6048 inverter, all others on Outback, Magnum have had this flickering problem and ended with a second dedicated inverter (msw or psw) to make it work.
I may be wrong, it wouldn't be the first time .
Erik
PS: There are several ways to do it, in your case I would use Classic aux1 non pwm and I'm pretty sure that it will work nicely with 900 watts elements on a 4kw array.

SolarMusher

Anawa wrote: »

Erik, I'm still contemplating DC vs AC, as well as, some of the issues you mentioned in prior post. Your thoughts on:
1- Setting the controller aux relay to start on absorb, or float? Is the difference 60v vs. 50v+, or other considerations?
2- If I'm running AC mini-splits simultaneously with the water heating load (which is reality), what kind of issues will I expect to encounter?

Anawa

Anawa, I'm not sure how FM aux pwm works now, I'm on Classic and only have an old spare 2007 MX60.
1- In my case (3.2kw PV), a small 1300/1000 watts DC opportunity really needs to start as soon as possible on absorb because of the 6 hours it needs to heat, float would not be long enough. Mine works on single Classic aux1 non PWM (on/off) because aux2 pwm is already used for WBjr monitoring. Difference between 60V/50V is around 250/300 watts at the elements, to me these 300watts are useful to reach a correct temp. If you choose 2000 watts Ac elements through a dedicated inverter, I believe that float only would be long enough to reach a good temp. Take a look on this forum or Midnite forum at Chris.Olson and Eric.L posts about diversion/opportunity loads through ssr.
2- If you're using these mini-splits as real loads and have enough inverter power to supply them, these loads would still have piority vs your opportunity/diversion load so this should not be a problem.

There are not good or wrong ways to do it, there are pros and cons in each way. It's all depend on your PV power available at a given time and how fast and hot you would like this heater to work.
Erik

Anawa

Erik, does the light/electronic flicker occur through the VFX, thus only with AC diversion loads? What about flicker with a DC diversion load?
Anawa

SolarMusher

Yes, its only hapen on Ac diversion when the controller is in pwm mode and loads are supplied through the inverter but there's no flickering problem on DC pwm diversion from batteries. That's why you'd better use a dedicated inverter (a cheap 2500 watts msw will be great for that use).
Erik

Photowhit

Thanks Erik, I'll go read as well, when I get a chance, seems odd particularly with a pure resistance load that you would, some how, get a fluctuation from a relay connection that takes such a small amount of current to hold closed. I guess since Chris had the problem, it's with both classics and outback charge controllers.

Anawa

As I consider the factors in deciding between DC and AC water heating solutions, both require additional equipment, such as, dedicated inverter vs expensive DC element, additional breaker box (I have one space available in my DC cabinet for a breaker), for me, I'm leaning to the DC method. Other things I'm factoring in to my decision is "more stuff" means "more stuff to maintain and repair" down the road. Also, I look at the solar water heating as a secondary heating source and there will be times that my family and I will not be using hot water during the day at all this location.

I've come to learn that every one of us off-gird'ers get to this point from many world views and varied perspectives. It's how we make it work for our unique situations is what is important. Not a profound statement, but a simple reflection.

SolarMusher

Anawa wrote: »

As I consider the factors in deciding between DC and AC water heating solutions, both require additional equipment, such as, dedicated inverter vs expensive DC element, additional breaker box (I have one space available in my DC cabinet for a breaker), for me, I'm leaning to the DC method. Other things I'm factoring in to my decision is "more stuff" means "more stuff to maintain and repair" down the road. Also, I look at the solar water heating as a secondary heating source and there will be times that my family and I will not be using hot water during the day at all this location.

I've come to learn that every one of us off-gird'ers get to this point from many world views and varied perspectives. It's how we make it work for our unique situations is what is important. Not a profound statement, but a simple reflection.

If you're leaning to DC, a first step would be to try with 3000 watts/120V elements that's what I did to begin, they are cheap and would give you 1300 watts when simultaneously used. Yesterday, at 5h30pm my tank was hot enough to keep the propane unit from starting for the evening and is still a bit warm this morning. Works great when sunny and would be even better if I could use a pwm signal in cloudly weather.
Erik

Anawa

Erik, would appreciate some more of your expertise in going the "DC way".

Help me keep it simple. My water heater is only 20 feet from my DC power source and CC's and that's the length of the cabling (overhead and down). I think I will be okay with the heat-up time, my water source is well water from above ground water tanks that are consistently about 64 degrees year round.

1- I would like to use the single available slot in my DC panel for a breaker, thus will I be terribly disappointed with a single DC heating element?

2- I've been looking at DC elements and find the pickin's are a bit slim. What would be your recommendation for voltage and/or wattage?

3- One of your previous posts suggest that I use the "manufacturers mechanical thermostat", I presume you mean the water heater manufacturer rather than the heating element companion thermostat?

4- What are the SSR selection criteria? Should the max amperage of the SSR be balanced to max amps of the element? Is Mosfet technology important?

Thanks
Anawa

SolarMusher

Anawa wrote: »

Erik, would appreciate some more of your expertise in going the "DC way".

Help me keep it simple. My water heater is only 20 feet from my DC power source and CC's and that's the length of the cabling (overhead and down). I think I will be okay with the heat-up time, my water source is well water from above ground water tanks that are consistently about 64 degrees year round.

1- I would like to use the single available slot in my DC panel for a breaker, thus will I be terribly disappointed with a single DC heating element?

2- I've been looking at DC elements and find the pickin's are a bit slim. What would be your recommendation for voltage and/or wattage?

3- One of your previous posts suggest that I use the "manufacturers mechanical thermostat", I presume you mean the water heater manufacturer rather than the heating element companion thermostat?

4- What are the SSR selection criteria? Should the max amperage of the SSR be balanced to max amps of the element? Is Mosfet technology important?

Thanks
Anawa

1- Use both elements in parrallel, 3000 watts/120Vac, each one will draw something around 10.5 amps. So a max 21 amps when used in parallel (verified).
2- The expensive 1265 watts DC elements would be your best configuration because it allows you to make these heater elements to work non-simultaneously (2/3 upper first, 1/3 later) and it should be faster. But at the end, using 2x 600 watts in parallel (2x 3000W/120V) will provides the same result, its just a little less efficient (I believe, not verified).
3- Yes the eco thermostat that's already in place, for security I've prefered to add another eco one, this way each element can work independently and has its own cut out security (150°F), you'll just have to wire the aux signal in parallel on each thermostat (do not connect 60V on these thermostats or they will burn).
4- I've used 2x D1D40 from Crydom (40A each) but one was defective, so I had to connect both elements in parallel (21 amps) on the same 40A SSR for a little time. It was working fine, may be a little hot to me. Now each of my ssr is running cool at only 25% of their rated power. I believe that Mofset is important for DC pwm but I'm not an expert, some guys here are far more knowledgeable than me...
You're very lucky to have this well that supplies water at this temp, it will help you to heat faster than mine.
No matter how you do it, do it safely.
Erik

Anawa

Thanks to all contributors on this thread, especially to Erik and PhotoWhit.
Anawa

Photowhit

I think, I learned more than I contributed, so let me thank Erik, too!

Anawa

Erik, just now getting around to installing the wiring for the water heater using the aux on the FM80. I've done some prelim wiring and tested the aux ports with my MM at various settings and verified the 12V signal works when Auto is on.

I like the DC route, but have some reservations. My proposed set-up has 2x 3000W-120v elements and 2x eco thermostats. I have single Crydom 60amp mosfet SSR (with heat-sink) with 10awg pulled to the elements through a 35 amp DC breaker. Since the elements will be pulling about 21amps, your thoughts on this appreciated.

Also, I want to be sure that I'm understanding your previous posts concerning the final wiring configuration. I understand parallel wiring to engage the elements simultaneously, but confused about how the "power" wiring is configured. I always thought that the 240V or 120V power to the elements was regulated for temperature when wired to the "top" of the thermostat, but, if I'm understanding your post, you are suggesting that for this application that the 60V DC can not be wired this way. I do not want to do anything dumb, but I'm not sure how to proceed. If this application requires more wiring from the aux ports at each if the thermostats, I!m not sure how to do it. This is a new water heater and the internal wiring is enclosed in foam insulation eliminating all slack, almost impossible to add any more inside the casing. I have not powered anything to the water heater.

Thanks Paul

Alaska Man

For what it's worth, an On Demand Hot Water Heater will be far more efficient, less money and way less of hassle, both now and in the future. Making hot water with electric is something to be avoided. A Solar Water heater I can see,

Unless you have a Wind/Hydro turbine and just need a dump load or something?

Photowhit

Alaska Man wrote: »

For what it's worth, an On Demand Hot Water Heater will be far more efficient,

While I could argue the "less money" since you would be supplying heat from solar that would be wasted so your costs are just the relay and a tiny bit of wiring over it's life time...

...I don't know how you can get "more efficient" than using energy potential that would be wasted over gas that must be harvested and transported!

SolarMusher

Anawa wrote: »

Erik, just now getting around to installing the wiring for the water heater using the aux on the FM80. I've done some prelim wiring and tested the aux ports with my MM at various settings and verified the 12V signal works when Auto is on.

I like the DC route, but have some reservations. My proposed set-up has 2x 3000W-120v elements and 2x eco thermostats. I have single Crydom 60amp mosfet SSR (with heat-sink) with 10awg pulled to the elements through a 35 amp DC breaker. Since the elements will be pulling about 21amps, your thoughts on this appreciated.

Also, I want to be sure that I'm understanding your previous posts concerning the final wiring configuration. I understand parallel wiring to engage the elements simultaneously, but confused about how the "power" wiring is configured. I always thought that the 240V or 120V power to the elements was regulated for temperature when wired to the "top" of the thermostat, but, if I'm understanding your post, you are suggesting that for this application that the 60V DC can not be wired this way. I do not want to do anything dumb, but I'm not sure how to proceed. If this application requires more wiring from the aux ports at each if the thermostats, I!m not sure how to do it. This is a new water heater and the internal wiring is enclosed in foam insulation eliminating all slack, almost impossible to add any more inside the casing. I have not powered anything to the water heater.

Thanks Paul

Paul, here is how I did it.
#1 Build a remote DC power point with #4awg Alu wire through a 50Adc breaker (midnite) to avoid voltage drop. For this I've used one MNPV6 (or MNPV3) combiner from midnite (6x breakers) and wired it as a DC load center.
#2 From this combiner, I 'd wired 2x lengths of #10awg wires through 2x 30Adc breakers (Midnite). Each 30A circuit goes to its own element through its own 40ADC SSR. Each signal wire goes to its own Eco thermostat. Classic Aux is connected to the upper thermostat and then paralled to the lower thermostat (upper part).
#3 I had to drill a new 1 inch hole through the casing to wire the lower element circuit and signal.
I know that it's all over protected but that's the way I like it.
I have to leave.
Erik
Attachment not found.

Attachment not found.

Alaska Man

Photowhit wrote: »

While I could argue the "less money" since you would be supplying heat from solar that would be wasted so your costs are just the relay and a tiny bit of wiring over it's life time...

...I don't know how you can get "more efficient" than using energy potential that would be wasted over gas that must be harvested and transported!

less expensive.. Compare my Girard On Demand Water heater total cost installed was $425.00 with the above from Solar Musher dollar for dollar.

Electric Elements are less efficient than On Demand Direct heaters. Holding 40 gallons of heated water even warm, takes multiple times the energy to keep it warm.

Granted if all the components are already bought and installed then Extra Capacity is free in the present. a Cost/lifetime analysis I bet will show I'm still "More Efficient" and "Cost Less" with a $34.00USD cost per year of propane to heat my water.

So Installed $425, yearly cost to heat water $34.00 US. I'll put that up against Electrical Production by any means and a Hot Water tank any day.

The only way I see to beat that is, Solar Hot Water Heater. I could build a Glass covered Black Box and run some copper for way less than $425.00 and as long as the sun shines the hot water is free. Just shower in the evenings.

Photowhit

Alaska Man wrote: »

Electric Elements are less efficient than On Demand Direct heaters. Holding 40 gallons of heated water even warm, takes multiple times the energy to keep it warm.
.

FWIW - I can take a shower 3 days in a row, off one heating to capacity on a sunny day, with no additional charging, it's barely warm the last day, you don't have to have the water kept hot, warm is easy with out additional heating cycles. Anyone who is on the grid should have a 'grey box' to limit the amount of time your water heater runs.

Of course family size and structure feed into it, my cost of a relay and some network wire, most of which I have should be pretty minimal, and be fine for me, and do away with the hot water off the wood stove for most of the winter. So my cost will be under $100...

BTW - if you had some one install a water heater LPG lines a regulator for $425 in Missouri, I wouldn't trust it, in Alaska, it must have been slave labor and used equipment!:D

... For me I don't have or want gas, I even gave away my low flow LP gas heater I bought for my cabin. In the hard water here they don't last very long...

SolarMusher

Anawa wrote: »

Also, I want to be sure that I'm understanding your previous posts concerning the final wiring configuration. I understand parallel wiring to engage the elements simultaneously, but confused about how the "power" wiring is configured. I always thought that the 240V or 120V power to the elements was regulated for temperature when wired to the "top" of the thermostat, but, if I'm understanding your post, you are suggesting that for this application that the 60V DC can not be wired this way. I do not want to do anything dumb, but I'm not sure how to proceed. If this application requires more wiring from the aux ports at each if the thermostats, I!m not sure how to do it. This is a new water heater and the internal wiring is enclosed in foam insulation eliminating all slack, almost impossible to add any more inside the casing. I have not powered anything to the water heater.

Thanks Paul

Paul, with 2x 3000 watts 120Vac elements, you will only have 1000/1100 watts if used simultaneously at 52/53V when in float. If you wire this heater non simultaneously, that means that you will only have the upper element heating at only 10A (530 watts) and it would need 12 hours if you're lucky to heat a 40Gls, forget it. If you want to keep it the way it was wired (non simutaneously), you would need to install real 60V elements (2x 1265 watts), that way your heater will work exactly the same as if it was wired with 120/240Vac: upper starts first and lower starts only when upper is hot/disconncted and it will work fine and heat from 70°F to 140°F in 4 hours. As you can see, with 2x 3000 watts 120V elements, you have no other choices than to make it work simutaneously. As said before, install a new eco thermostat on the lower element (same as the upper) and it will work independently: when water is cold => both elements are heating, when upper part is hot=> upper element/ssr will disconnect and lower element/ssr will continue to heat at 500/600 watts until lower part is hot (in fact it will keep on heating in pwm mode since you'll have extra PV power available).
I had kept existing wiring for paralleling aux signal from/to each thermostat, don't need to use new wire.
Hope this helps,
Erik
PS:
Simultaneous wiring
L1-L3 (from FM60-80 aux 12V) are aux paralleled on each Eco therm (L1 pos, L3 neg).
T2= aux pos to ssr pos.
L4= aux neg to ssr neg.
Element pos x2 to DC ssr 40A (2x 10AWG).
Element neg x2 to batt neg or load center neg (2x 10AWG).
Add a diode between both positive negative elements.
. Attachment not found.

SolarMusher

Photowhit wrote: »

FWIW - I can take a shower 3 days in a row, off one heating to capacity on a sunny day, with no additional charging, it's barely warm the last day, you don't have to have the water kept hot, warm is easy with out additional heating cycles. Anyone who is on the grid should have a 'grey box' to limit the amount of time your water heater runs.

Of course family size and structure feed into it, my cost of a relay and some network wire, most of which I have should be pretty minimal, and be fine for me, and do away with the hot water off the wood stove for most of the winter. So my cost will be under $100...

BTW - if you had some one install a water heater LPG lines a regulator for $425 in Missouri, I wouldn't trust it, in Alaska, it must have been slave labor and used equipment!:D

... For me I don't have or want gas, I even gave away my low flow LP gas heater I bought for my cabin. In the hard water here they don't last very long...

Photowhit, I fully agree with what you said. Yesterday my tank was at 140°F (with classic aux1 on-off ) and we take two showers + my wife washed all the buckets for the dogs x40 (take a lot of water) and the tank was still at 28°C on next day. Of course propane heater didn't start at all. Forgot to say that the overall cost was around $800 can (+ taxes) with brand new safe material including the heater with new elements and heatsink ssr, I am pretty sure that this will be paid in 2 or 3 years.
Just like you I hate propane.
Erik

Anawa

Photo is lousy! I'll try something else in a few minutes
Paul

Anawa

I have a PDF of the drawing, but I do not know how to post it on this forum. Suggestions anybody?
Paul

Anawa

Let's try this.

Paul

SolarMusher

Anawa wrote: »

Let's try this.

Paul

Yes Paul, you've got it! Except that you need to add 30A breakers on each element pos lines and a 50A/60A breakers to protect your 6AWG from batteries to combiner. A good advice that you can find on Crydom DC ssr diagram is to add a diode between pos/neg of the element connections to protect the controller. I've tested 140°F setting and it disconnects the upper element at 57.7/58.4°C (a bit under 140°F) safely, this morning (7h45am) tank is still at 32°C (90°F) and should reach 130/140°F easily.
Erik
PS: My next update before fall will be to change only the lower element for a real 60V/1265 watts and still run the heater simultaneously at something around 1800 watts to heat faster, this would be the best for me. Just need to add some PV and my old mx60 in pwm diversion to make it perfect .

Anawa

Thanks Erik. It takes time for an ole guy like me to get this stuff. I've got a mountain of other things to do and not much time to devote to my solar activities.

Your help has been immeasurable and I do appreciate you sharing your time and expertise. I may end-up with something a bit different than your configuration, but I think I grasp the basics.

PS: The diagram helped me to fully understand your 2 SSR design; basically, necessary for simultaneous operation of the 2 elements. Otherwise, shut-off of both elements controlled by only one. Apparently, there is a temperature disparity between the two even when they both receive the same load.

Thanks
Paul

MarkP

I have an SW4048 and an MPPT 60 150.  I just hooked up a 119 gallon electric resistance water heater as an opportunity load.  I bought a 12vdc/120vac DPDT relay to turn the heater on and off with.  I use the 12 vdc/200ma from the aux terminals in the MPPT to control the relay.  I am running the heater on 120 vac instead of 240vac because at 120 volts the heater draws only about 1000 watts rather than the 4500 watts it would draw at 240 volts.

I programmed the aux settings to turn on at 55.0 volts (float) and off at 54.0 volts with a 5 minute delay when turning off, so that the battery voltage must remain below 54 volts for  the 5 minute delay time before the load is disconnected.  When there is sun there is sufficient power to run the heater AND charge the batteries.  With less PV power coming in the heater will come on and the battery voltage will get dragged below 54 volts for 5 minutes.  It then takes another few minutes to come back up to get back up to 55 volts.  This is sort of a crude PWM style of control in a way.  I just turned the heater on late yesterday and had a couple of hours to work out bugs before sundown.  Today was partly cloudy with long sunny periods so I got to see the system operate in all situations.  On mostly cloudy days the average battery voltage would be less than the float voltage because it would get dragged down each time it did reach the float voltage but on sunny days like today the heater would come on prior to even reaching absorption voltage and would slow everything down but absorption would still take place normally, reaching float later in the day, exactly like I want.

Elsewhere on these pages there are discussions about how you don't need to reach float every day.  I'm not saying it would be good to never reach float but given a mix of sunny and less sunny days with the heater shutting off below 54 volts it seems like you would be OK with a couple of good sunny days a week.  Remember that on those particularly cloudy days the heater will never come on.

Forgot to say that I calculated 14.5 kwh required to heat 120 gallons from 75 degrees F to 125 degrees.  I figure I got a couple kwh yesterday and another 10 or so today so the tank should shut off tomorrow morning on its own.  I have not actually used any hot water from it yet but during the summer I hope it will provide for all my hot water needs.  How many kwh per day it will draw remains to be seen.  My point is that the last couple of days is a rare situation in that the water heater has run every minute that the battery voltage was above 55.0 and then some.  Most days it will only run a couple of hours a day.

I have the electric heater hooked up in parallel with a Bosch LP on demand instant water heater.  The LP heater will not work with a pre-heated water source as it can't turn down well enough so I must decide ahead of time which heater I will use.  I have a fair number of panels which charge my batteries in the first 3 or 4 hours of the day on sunny days so using an electric resistance heater is not wasting anything that wasn't going to get wasted anyway.  I need all the panels and more in fact because we get frequent cloudy days where having lots of panels means we can run the generator less.  With more panels on those days I will heat with LP instead of generating with gasoline like I used to.

Estragon

I'm curious - why doesn't the on demand LP heater work with preheated water?

I have a Rennai unit which I use for both domestic hw and to heat a w-w heat exchanger for radiant in floor space heating. When heating only (no DHW in use), water circulates in a loop to the hx with return water quite warm. The temp of return water depends on the drop caused by heating load, and the on-demand heater cycles accordingly to keep supply water at set temp (140°f winter when I don't have visitors to scald on the DHW supply, 120 otherwise). It works fine, but you have me wondering if there's a problem with doing it.

I have an old LP tank I might change to a PV and/or direct solar opportunity/preheat which I would pipe in series ahead of the Rennai. If direct solar I would add a mixing valve to keep preheat supply temp below Rennai.

BB.

The LP/NG Tankless water heaters... There are the type that input xxx,000 BTU per hour of heat (some are adjustable, but still fixed output). Others have a sensor or two (input/output water temperature sensors) that varies the amount of heat from x,000 to xxx,000 BTU per hour.

The first type will not do well with preheated water of variable temperatures (warm water->hot output; cold water->cooler output). Also, the ones with variable flame levels, they will be less sensitive to water flow. The "simple" heaters, you need a pretty much fixed flow to get stable output water temperature (at one place, I would open the hot water to 3/4 on, then adjust the cold water flow for the correct shower temperature).

-Bill

Estragon

That makes sense. I believe the Rennai is variable output, something like 50,000 to 180,000 btu. Once the infloor water and floor around piping gets hot it cycles on and off. The load is probably only about 10-15,000 btu at that point.

Presumably, if I do the preheat in series ahead of the LP heater, it shouldn't hurt it.

BB.

For many (most?) solar hot water systems, you need a tempering valve on the output of the solar hot water tank. The system may heat the water to ~180F, but you do not want much more than 120F or so at the shower/bath tube fixture.

The tempering valve can limit the maximum temperature to the Rinnai--But you will always be using LP. Another option would be to have a solinoid switch--When the solar tank drops below 110F, it switches the input to the LP Rinnai.

Looking around on the web, I see Rinnai US has a "hybrid" booster. Connect to your water heater (gas/electric, possibly solar?):

https://www.rinnai.us/hybrid-tank-tankless-water-heater

And Rinnai in Australia and New Zealand seem to offer solar solutions (solar collector+storage tank+Rinnai):

http://www.rinnai.com.au/hot-water/solar-hot-water-systems/

And a few years ago, they had a RH360 system that appeared to be designed for solar hot water support, but I do not find any current information about the product:

http://www.ecobuildingpulse.com/products/solar-tankless-water-heating-backup-from-rinnai_o

-Bill