Tankless water heaters are terrible....

[nwdiver]

While wood burning during cold snaps ought to end up being carbon neutral, I'm not sure it's otherwise ideal from a local air quality perspective.

And I also forgot to point out that solar panels tend to have less output in the winter than the summer, if we're going to rely on solar plus batteries (where the batteries are not really sized to shift energy by more than about 15 hours) for a substantial fraction of our power.

But if we end up wanting to remove carbon from the atmosphere through a process powered by renewable electricity, maybe we can suspend that carbon removal process during cold snaps to balance the grid.

EPA rated stoves re-burn the flu-gas. Probably even cleaner than car exhaust.

Solar output falls in the winter but wind output rises.

 

[Joel Weber]

Burn Wise - Frequently Asked Questions | US EPA seems to be saying that propane and natural gas stoves are cleaner than EPA certified wood stoves. That leaves me wondering if a renewable process for producing propane from atmospheric carbon dioxide during the fall might be the best approach to dealing with cold snaps.

Where I live, it's likely that most wind farm construction will happen off shore, and http://www.aweablog.org/analysis-fi...-prices-low-during-the-coldest-winter-months/ claims off shore wind production is strong both during the cold parts of winter and also hot summer afternoons. I think maybe off shore wind has stronger summer production than on shore wind.

 

[SDRick]

Wood-burning, even in certified stoves does not appear to be very health or environmentally friendly even compared with ICE. At least based on these statistics:

Traffic, Cigarettes and Heating

 

[brkaus]

So - this is probably a stupid question... but...

Could one tie a PV panel (or two) to an inverter and then a electric hot water tank (perhaps pre-heat extra tank)? What would be the minimum components required, micro inverter? Guess if it isn’t grid tied, it wouldn’t be on. What happens when there is nothing drawing power?

Just curious. Can you have a small off grid inverter with no battery?

 

[Joel Weber]

In principle, it ought to be possible to connect a resistance heating element in a hot water tank directly to solar panels without an inverter; resistance heating elements shouldn't care whether they're fed AC or DC. However, if you want to have something to cut off the power if the tank gets too hot, it's not clear to me that anyone is currently building the control system you'd need for that. (Switching off DC is potentially harder than switching off AC with a mechanical switch / relay because a flowing current ionizes air, and ionized air becomes a conductor; with AC, the brief moment of 0V that typically happens 100 or 120 times a second while reversing polarity apparently will break the flow of current through the ionized air.) And if you feed the DC directly to the heating element, you'd have to make sure that there's no weird case where the solar panels output more voltage than the heating element can safely deal with.

I suspect if we could get an all DC path from solar panels to Powerwall to heat pump / oven / EV charging station / etc there'd be a slight energy efficiency improvement over the current AC conversion steps, but no one seems to be working on that.

 

[brkaus]

In principle, it ought to be possible to connect a resistance heating element in a hot water tank directly to solar panels without an inverter; resistance heating elements shouldn't care whether they're fed AC or DC. However, if you want to have something to cut off the power if the tank gets too hot, it's not clear to me that anyone is currently building the control system you'd need for that. (Switching off DC is potentially harder than switching off AC with a mechanical switch / relay because a flowing current ionizes air, and ionized air becomes a conductor; with AC, the brief moment of 0V that typically happens 100 or 120 times a second while reversing polarity apparently will break the flow of current through the ionized air.) And if you feed the DC directly to the heating element, you'd have to make sure that there's no weird case where the solar panels output more voltage than the heating element can safely deal with.

I suspect if we could get an all DC path from solar panels to Powerwall to heat pump / oven / EV charging station / etc there'd be a slight energy efficiency improvement over the current AC conversion steps, but no one seems to be working on that.

I'm guessing 300w isn't that hard to switch DC. But it's a good point that I forgot about how relays operate.

Looks like someone has a solution -

http://www.sunbandit.us/Portals/0/P...t_AC-MicroGrid-Inverter_IOM-Manual_062216.pdf

Are there any other off-grid microinverters that require no additional equipment?

 

[Topher]

>70% reduction with a heat pump.

This very much depends on where the heat is coming from. We should not be confused by claims of 3 COP when installing a heat pump water heater in a heated space.

It’s easy to fully insulate

This makes no sense, heat loss is inversely proportional to insulation value, there is no such thing as 'full insulated'.

When you're doing calculations with R value of insulation, isn't it the case that the absolute value of the temperate difference between inside and outside is proportional to the number of BTU/h that leaks through the insulation, and thus if you're trying to keep a building heated to 72F when the outside temperature is -8F you have an 80F difference, whereas if the outside temperature is 99F and you're trying to cool off the building to 72F, you only have to deal with a 27F difference, which means you need roughly 3 times as much BTU/h capacity in the winter than in the summer?

Yes. But the problem with air-conditioning is that isn't about simply lowering temperature, it also needs to condense humidity. It takes vastly more energy to condense water than to cool air.

While wood burning during cold snaps ought to end up being carbon neutral

That is a lot more difficult than it might first appear. Very few wood lots are sustainably harvested. Is your wood ash going back to the forest where your wood came from?

Thank you kindly.

 

[Topher]

EPA rated stoves re-burn the flu-gas. Probably even cleaner than car exhaust.

Sadly, an EPA approved stove is not sufficient. Even for them, the operator can make a hundred-fold difference in pollution output. If you use a wood stove, PLEASE learn how to operate it properly.

That leaves me wondering if a renewable process for producing propane from atmospheric carbon dioxide during the fall might be the best approach to dealing with cold snaps.

Methane, Methanol, or Hydrogen are probably better candidates than propane. But yes, when all efficiencies are eventually accomplished, there will probably be a seasonal (winter) energy imbalance that requires long term storage, for which the leading candidates are sand based thermal storage and fuel creation.

Can you have a small off grid inverter with no battery?

Sure. Especially if you connect it to a load that doesn't care about quality of the electricity. Heating, of course, doesn't care enough to even worry about AC versus DC.

Thank you kindly.

 

[brkaus]

This makes no sense, heat loss is inversely proportional to insulation value, there is no such thing as 'full insulated'.

You are correct - I was referring to the point that a propane/natural gas tank water heater has the burner vent pipe right up the middle. Not possible to insulate that part at all.

If it’s in a cold place, it can pull quite a draft.

Sure. Especially if you connect it to a load that doesn't care about quality of the electricity. Heating, of course, doesn't care enough to even worry about AC versus DC.

I did find someone that made such a product. Off grid micro inverter powered water heater. Price is a crazy $7k though.

http://www.sunbandit.us/Portals/0/P...t_AC-MicroGrid-Inverter_IOM-Manual_062216.pdf


If it’s DC, are there any code issues or diez that magically make it easier?

 

[ohmman]

I have an electric tankless in our pool house. It's a rarely used space that has occasional very low demand (washing dishes, washing hands from time to time) and infrequent medium demand (guests showering). It's a good solution but it's a high consumer of electricity, as has been mentioned here. I don't think a heat pump would be a good choice considering the infrequent and unpredictable usage pattern.

Meanwhile, we have a natural gas tank water heater in the main house which I am itching to replace. A heat pump unit makes a lot of sense for us and I'll be checking out options. For those who want a centralized tank heater but "instant" hot water, or wasteless hot water at the faucet, there are some options for on-demand recirculating systems using legacy plumbing. For instance, ones like this that tie together your hot and cold supply in order to recirculate until a thermostatic control stops the pump.

Thanks for the thread, @nwdiver. It's been educational.

 

[brkaus]

I do enjoy this off topic thread. @ohmman comment does reiterate that there is no one correct solution.

Regarding recirculating systems, I know mine puts about $0.35 worth of heat into the slab every day.

 

[nwdiver]

I do enjoy this off topic thread. @ohmman comment does reiterate that there is no one correct solution.

I should have been more specific in the thread title. 'ELECTRIC' tankless heaters are terrible.

For applications that would see use only a few times a month electric tankless heaters make more sense. But for whole house applications even in cold climates they'll be more cost effective overall than any resistance heater. Even if they suck warm air out of the home in the winter those losses will be more than made up for in the summer and if the home is heated with a heat pump even in the winter it will be more efficient over-all.

 

[cybergates]

has anyone tried this for a traditional water heater - Aquanta smart water heater controller (it sounds interesting but too gimmicky/gadgety to work?)

 

[S'toon]

So - this is probably a stupid question... but...

Could one tie a PV panel (or two) to an inverter and then a electric hot water tank (perhaps pre-heat extra tank)? What would be the minimum components required, micro inverter? Guess if it isn’t grid tied, it wouldn’t be on. What happens when there is nothing drawing power?

Just curious. Can you have a small off grid inverter with no battery?

It'd be more efficient to just use a solar water heating panels.

 

[mspohr]

So - this is probably a stupid question... but...

Could one tie a PV panel (or two) to an inverter and then a electric hot water tank (perhaps pre-heat extra tank)? What would be the minimum components required, micro inverter? Guess if it isn’t grid tied, it wouldn’t be on. What happens when there is nothing drawing power?

Just curious. Can you have a small off grid inverter with no battery?

You could hook up a solar panel or two directly to a standard electric water heater. They have a simple thermostat to prevent overheating and the heating elements don't care about AC or DC. The voltage will be low but that's not a problem. It will heat slowly all day.
Just don't use a heater with a fancy control system.

 

[mongo]

This very much depends on where the heat is coming from. We should not be confused by claims of 3 COP when installing a heat pump water heater in a heated space.

Agreed, it's helpful in summer, but increases house heat load in winter.

Yes. But the problem with air-conditioning is that isn't about simply lowering temperature, it also needs to condense humidity. It takes vastly more energy to condense water than to cool air.

Once target temperature is reached, the only additional latent heat load is due to leakage/ respiration/perspiration. Thermal resistance should be the dominant factor (depending on ventilation strategy). Looking at original quote, I think the discussion was electrical load to the heat pump, not heat load. With the diminishing COP at low temp, I can see cold night exceeding hot day even under that criteria, but depends on climate.

That is a lot more difficult than it might first appear. Very few wood lots are sustainably harvested. Is your wood ash going back to the forest where your wood came from?

The carbon for the trees came from the atmosphere. The carbon remaining in the ash is semi-sequestered. So it could be viewed at carbon negative overal (ignoring harvesting energy). My firewood comes from my back yard, same place the ash goes.

 

[mongo]

Does anyone here have experience with using something like a Chiltrix CX34 to heat hot water?

I'm looking at using that in my barn (radiant floor and DHW). Might also loop it to a swim spa (with heat exchanger). Interested in any data you dig up.

 

[Merrill]

There seems to be lots of folk on this forum that are very informed, I have a question that maybe someone could answer. I’m all electric and need to replace my hot water heater (50 gal). I actually have had it on a timer for 30 years and have it come on in the morning for 2 hours and in the evening for 2 hours. There is only two of us and it has seemed to work and save us some electricity. As I read this thread it looks like an on demand electric hot water heater is not very efficient or reliable, it would be nice to have instant hot water but not sure I want to deal with a pump. I’m thinking of just replacing the old heater with the most efficient unit on the market. Any input is welcome.
Merrill

 

[mongo]

There seems to be lots of folk on this forum that are very informed, I have a question that maybe someone could answer. I’m all electric and need to replace my hot water heater (50 gal). I actually have had it on a timer for 30 years and have it come on in the morning for 2 hours and in the evening for 2 hours. There is only two of us and it has seemed to work and save us some electricity. As I read this thread it looks like an on demand electric hot water heater is not very efficient or reliable, it would be nice to have instant hot water but not sure I want to deal with a pump. I’m thinking of just replacing the old heater with the most efficient unit on the market. Any input is welcome.
Merrill

How much hot water would you like? Sink level, shower level, other?

 

[mspohr]

There seems to be lots of folk on this forum that are very informed, I have a question that maybe someone could answer. I’m all electric and need to replace my hot water heater (50 gal). I actually have had it on a timer for 30 years and have it come on in the morning for 2 hours and in the evening for 2 hours. There is only two of us and it has seemed to work and save us some electricity. As I read this thread it looks like an on demand electric hot water heater is not very efficient or reliable, it would be nice to have instant hot water but not sure I want to deal with a pump. I’m thinking of just replacing the old heater with the most efficient unit on the market. Any input is welcome.
Merrill

All electric tank heaters are equally inefficient.
Heat pump is most efficient.