5 ms·

Heating water with electricity is the literally last thing we should do. That is, once clean electric energy is cheap, we can do it. But we are not there yet. H

Heating water with electricity is the literally last thing we should do. That is, once clean electric energy is cheap, we can do it. But we are not there yet. Hence we should at least use heat pumps or similar technology.

WalterBright 6y ago
Meanwhile, there are hot water heaters in use everywhere. That isn't going to change anytime soon. Besides, in many places during peak solar there isn't anyplace to dump the electricity. Electric hot water heaters can take care of that problem, as water will stay hot in one for a couple days (I know from experience).
- dharmab 6y ago
  A heat pump can approach 500% efficiency and is powered by outdoor ambient air (using direct heating as a fallback). https://www.youtube.com/watch?v=-vU9x3dFMrU https://www.youtube.com/watch?v=-vU9x3dFMrU
  - WalterBright 6y ago
    It still uses electricity, and can be shut off during electric rate spikes, acting just like a "grid battery" without the expense.
war1025 6y ago
I was talking with someone recently and they recently bought a new electric water heater. I asked why they didn't go with a heat pump option, and they said the dealer told them that heat pump water heaters are basically a "robbing Peter to pay Paul" situation where you end up taking heat you would have added to your house and putting it in your water instead. I guess in warm climates / seasons that is probably a net benefit, but I've noticed our electric co-op also promotes highly-insulated electric water heaters instead of heat pump water heaters. Not sure what I think of it all. We have an electric water heater and at first I was grumpy about the relative cost to run relative to natural gas, but I've come to terms with it. It's about the simplest device possible, and that has some value I think.
- MayeulC 6y ago
  A conventional heater can, at best, use 100% of the energy to heat both the water and the house. A heat pump would use some of that energy to capture some more from a heat source (outside air, or geothermal, ground temperature). It gets less efficient as the heat source becomes cooler, so it might not be such a good idea in very cold climates. Theoretically, though, it shouldn't get lower than 100%, and efficiencies can reach 300% pretty easily. I haven't done an extensive search on the topic, here is one of the first sources I found with the kind of graph I wanted: https://www.nordicghp.com/2017/01/heat-pump-effective-temperature-range/ https://www.nordicghp.com/2017/01/heat-pump-effective-temper... I read about 270% at -4°C (25°F). 1 watt of electricity in, 2.7 watts of heat out, not bad. The same graph reads about 480% at 18°C(65°F), and 150% at -20°C (-5°F). I know that gas heat pumps exist as well, and some systems are hybrid, so it sounds like a no brainer to me. On the flip side, they can be quite expensive, so do your calculations relative to the temperature history, and hourly electricity hours. It would be more efficient to heat when the air is warmer during the day (assuming air pump), and combine that with a well-insulated house. Solar (thermal or electric) is pretty interesting too, I wonder what kind of efficiency one can get with photovoltaic + heat pump (photovoltaic is more versatile, being more useful during summer).
  - semi-extrinsic 6y ago
    I think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Very different from what you are suggesting. It could still make sense if it is installed in a room with lots of waste heat, e.g. next to a clothes dryer and other appliances.
    - war1025 6y ago
      > I think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Correct. Every heat pump water heater I've ever seen has the heat pump directly on top of the water tank. It's possible they make ones that tie into an external heat pump, but I've never seen one.
war1025 6y ago
The way the parent comment is worded, he is actually advocating for not doing activities like running hot water heaters during peak load times. I know many utilities in my area have a program you can sign up for where they will cycle through the registered AC units to balance out peak load in the summer. I'm not entirely sure how they manage that, I suppose they have to have some sort of sensor switch they install in your circuit.
- WalterBright 6y ago
  > you can sign up for where they will cycle through the registered AC units to balance out peak load in the summer This is inefficiently attempting to solve the problem in the same way while trying to maintain that flat electric rate. We need to get past the idea that electric rates must be flat.
  - war1025 6y ago
    > We need to get past the idea that electric rates must be flat. I'm not aware of anyone that does minute to minute electricity pricing, but I know for many utilities you can sign up for alternate price schedules that have different rates based on the time of day. I would guess as much as anything it's a metering issue.
    - WalterBright 6y ago
      price schedules that have different rates based on the time of day. That's better than 24/7 flat, but is not a solution for dealing with spikes in demand or fluctuations in supply. Minute-by-minute spot pricing is the solution for that. With the ubiquity of the internet, and low cost for IoT, it's feasible, practical, efficient, and effective.
    - alach11 6y ago
      Griddy (in Texas) offers 15-minute wholesale price for electricity.
      - 6y ago
conk 6y ago
Heat pump is heating water with electricity... And it’s not the last thing we should do, it’s economical today if you live in a mild climate. I installed one in my house a year ago. The initial cost was ~$500 over a similar gas water heater but it qualified for a $1000 rebate making it cheaper than a gas unit. Cost of heating is less than I used to pay for an old gas water heater. It might not make sense in a region with cold winters, but in a moderate region they make a lot of sense.
- choeger 6y ago
  In a heat pump, the heat does not come from the electricity but from an environmental source. The electricity moves and compresses but does not heat anything. Your usage of dollars indicates you live in the US. I hate to tell you but your definition of "economic" is probably not sustainable. Your price of electricity would probably double or even triple when switching to (cheap) renewables.
  - corty 6y ago
    > Your price of electricity would probably double or even triple when switching to (cheap) renewables. Finally someone who recognized that renewables are a magnitude more expensive instead of the usual "muh, renewables are cheaper!" fallacy. Look at the typical price per kWh in Germany (around 32ct/kWh) and tell me again how that is cheap...
mianas 6y ago
> Heating water with electricity is the literally last thing we should do. Would you consider electric showers an exception? They only heat whatever water you're using. I've lived in houses with no hot water in the taps for months, but could still take a hot shower whenever.
- alecmg 6y ago
  I think it was a reference to the way we get electricity. Burn gas at the plant to heat water to run steam through turbine to get electricity ... and then use electricity to heat water again? Just use gas at the end point. Getting heat from fuel (or sun) is easy and efficient. Converting it to electricity isn't. If electricity comes from a non-fossil-fuel source - it is even more expensive/valuable.

WalterBright 6y ago

Meanwhile, there are hot water heaters in use everywhere. That isn't going to change anytime soon. Besides, in many places during peak solar there isn't anyplace to dump the electricity. Electric hot water heaters can take care of that problem, as water will stay hot in one for a couple days (I know from experience).

dharmab 6y ago
A heat pump can approach 500% efficiency and is powered by outdoor ambient air (using direct heating as a fallback). https://www.youtube.com/watch?v=-vU9x3dFMrU https://www.youtube.com/watch?v=-vU9x3dFMrU
- WalterBright 6y ago
  It still uses electricity, and can be shut off during electric rate spikes, acting just like a "grid battery" without the expense.

war1025 6y ago

I was talking with someone recently and they recently bought a new electric water heater. I asked why they didn't go with a heat pump option, and they said the dealer told them that heat pump water heaters are basically a "robbing Peter to pay Paul" situation where you end up taking heat you would have added to your house and putting it in your water instead. I guess in warm climates / seasons that is probably a net benefit, but I've noticed our electric co-op also promotes highly-insulated electric water heaters instead of heat pump water heaters. Not sure what I think of it all. We have an electric water heater and at first I was grumpy about the relative cost to run relative to natural gas, but I've come to terms with it. It's about the simplest device possible, and that has some value I think.

MayeulC 6y ago
A conventional heater can, at best, use 100% of the energy to heat both the water and the house. A heat pump would use some of that energy to capture some more from a heat source (outside air, or geothermal, ground temperature). It gets less efficient as the heat source becomes cooler, so it might not be such a good idea in very cold climates. Theoretically, though, it shouldn't get lower than 100%, and efficiencies can reach 300% pretty easily. I haven't done an extensive search on the topic, here is one of the first sources I found with the kind of graph I wanted: https://www.nordicghp.com/2017/01/heat-pump-effective-temperature-range/ https://www.nordicghp.com/2017/01/heat-pump-effective-temper... I read about 270% at -4°C (25°F). 1 watt of electricity in, 2.7 watts of heat out, not bad. The same graph reads about 480% at 18°C(65°F), and 150% at -20°C (-5°F). I know that gas heat pumps exist as well, and some systems are hybrid, so it sounds like a no brainer to me. On the flip side, they can be quite expensive, so do your calculations relative to the temperature history, and hourly electricity hours. It would be more efficient to heat when the air is warmer during the day (assuming air pump), and combine that with a well-insulated house. Solar (thermal or electric) is pretty interesting too, I wonder what kind of efficiency one can get with photovoltaic + heat pump (photovoltaic is more versatile, being more useful during summer).
- semi-extrinsic 6y ago
  I think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Very different from what you are suggesting. It could still make sense if it is installed in a room with lots of waste heat, e.g. next to a clothes dryer and other appliances.
  - war1025 6y ago
    > I think GP is talking about heat pump water heaters that are working between the air in the room where heater is installed and the hot water. Correct. Every heat pump water heater I've ever seen has the heat pump directly on top of the water tank. It's possible they make ones that tie into an external heat pump, but I've never seen one.

war1025 6y ago

The way the parent comment is worded, he is actually advocating for not doing activities like running hot water heaters during peak load times. I know many utilities in my area have a program you can sign up for where they will cycle through the registered AC units to balance out peak load in the summer. I'm not entirely sure how they manage that, I suppose they have to have some sort of sensor switch they install in your circuit.

WalterBright 6y ago
> you can sign up for where they will cycle through the registered AC units to balance out peak load in the summer This is inefficiently attempting to solve the problem in the same way while trying to maintain that flat electric rate. We need to get past the idea that electric rates must be flat.
- war1025 6y ago
  > We need to get past the idea that electric rates must be flat. I'm not aware of anyone that does minute to minute electricity pricing, but I know for many utilities you can sign up for alternate price schedules that have different rates based on the time of day. I would guess as much as anything it's a metering issue.
  - WalterBright 6y ago
    price schedules that have different rates based on the time of day. That's better than 24/7 flat, but is not a solution for dealing with spikes in demand or fluctuations in supply. Minute-by-minute spot pricing is the solution for that. With the ubiquity of the internet, and low cost for IoT, it's feasible, practical, efficient, and effective.
  - alach11 6y ago
    Griddy (in Texas) offers 15-minute wholesale price for electricity.
    - 6y ago

conk 6y ago

Heat pump is heating water with electricity... And it’s not the last thing we should do, it’s economical today if you live in a mild climate. I installed one in my house a year ago. The initial cost was ~$500 over a similar gas water heater but it qualified for a $1000 rebate making it cheaper than a gas unit. Cost of heating is less than I used to pay for an old gas water heater. It might not make sense in a region with cold winters, but in a moderate region they make a lot of sense.

choeger 6y ago
In a heat pump, the heat does not come from the electricity but from an environmental source. The electricity moves and compresses but does not heat anything. Your usage of dollars indicates you live in the US. I hate to tell you but your definition of "economic" is probably not sustainable. Your price of electricity would probably double or even triple when switching to (cheap) renewables.
- corty 6y ago
  > Your price of electricity would probably double or even triple when switching to (cheap) renewables. Finally someone who recognized that renewables are a magnitude more expensive instead of the usual "muh, renewables are cheaper!" fallacy. Look at the typical price per kWh in Germany (around 32ct/kWh) and tell me again how that is cheap...

mianas 6y ago

> Heating water with electricity is the literally last thing we should do. Would you consider electric showers an exception? They only heat whatever water you're using. I've lived in houses with no hot water in the taps for months, but could still take a hot shower whenever.

alecmg 6y ago
I think it was a reference to the way we get electricity. Burn gas at the plant to heat water to run steam through turbine to get electricity ... and then use electricity to heat water again? Just use gas at the end point. Getting heat from fuel (or sun) is easy and efficient. Converting it to electricity isn't. If electricity comes from a non-fossil-fuel source - it is even more expensive/valuable.