Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The BEopt result seems reasonable to me. The difference between electric tankless and tank water heaters is not that great, just look at their respective Energy Factors, which differ by ~5 percentage points. As electric tank water heaters can be insulated quite well, there aren't high tank losses that can be eliminated by going tankless.
Contrast that with gas tankless water heaters, which are significantly better than gas tank water heaters, with Energy Factors that can differ by up to 30 percentage points. This is because gas tank water heaters have multiple penetrations (gas line, flue), so they have high tank losses even when insulated well. By eliminating these tank losses, there is a large benefit to going tankless for gas water heaters.
Thus, gas tankless water heaters generally save a lot of energy while electric tankless water heaters provide marginal benefit. It's also pretty uncommon to install/use electric tankless water heaters because they have huge power draws. Thus, heat pump water heaters are a more common solution to improving on a conventional electric tank water heater. (One could focus on reducing hot water usage via low flow fixtures, hot water pipe insulation, drain water heater recovery, etc.)
| | 2 | No.2 Revision |
The BEopt result seems reasonable to me. me.
The difference between electric tankless and tank water heaters is not that great, just look at their respective Energy Factors, which differ by ~5 percentage points. As electric tank water heaters can be insulated quite well, there aren't high tank losses that can be eliminated by going tankless.
Contrast that with gas tankless water heaters, which are significantly better than gas tank water heaters, with Energy Factors that can differ by up to 30 percentage points. This is because gas tank water heaters have multiple penetrations (gas line, flue), so they have high tank losses even when insulated well. By eliminating these tank losses, there is a large benefit to going tankless for gas water heaters.
Thus, gas tankless water heaters generally save a lot of energy while electric tankless water heaters provide marginal benefit. It's also pretty uncommon to install/use electric tankless water heaters because they have huge power draws. Thus, heat pump water heaters are a more common solution to improving on a conventional electric tank water heater. (One could focus on reducing hot water usage via low flow fixtures, hot water pipe insulation, drain water heater recovery, etc.)
| | 3 | No.3 Revision |
The BEopt result seems reasonable to me.
The difference between electric tankless and tank water heaters is not that great, just look at their respective Energy Factors, which differ by ~5 percentage points. As electric tank water heaters can be insulated quite well, there aren't high tank losses that can be eliminated by going tankless.
Contrast that with gas tankless water heaters, which are significantly better than gas tank water heaters, with Energy Factors that can differ by up to 30 percentage points. This is because gas tank water heaters have multiple penetrations (gas line, flue), so they have high tank losses even when insulated well. By eliminating these tank losses, there is a large benefit to going tankless for gas water heaters.
Thus, gas tankless water heaters generally save a lot of energy while electric tankless water heaters provide marginal benefit. It's also pretty uncommon to install/use electric tankless water heaters because they have huge power draws. Thus, heat pump water heaters are a more common solution to improving on a conventional electric tank water heater. (One could focus alsofocus on reducing hot water usage via low flow fixtures, hot water pipe insulation, drain water heater recovery, etc.)
