Stiebel Eltron Accelera 300 Heat Pump Water Heater

Stiebel Eltron Accelera 300
The Accelera 300 is an air-source heat pump with an 80-gallon tank that heats and stores domestic water.
Stiebel Eltron Accelera 300

Stiebel Eltron’s ( Accelera 300 is an air-source heat pump with an 80-gallon tank that heats and stores domestic water. It is designed to heat about 50 gallons to 140°F; a 1,700 W electric backup heating element provides supplemental heating when more hot water is needed.

Heat pump performance is evaluated by the “coefficient of performance” (COP) ratings (the higher the value, the better). A typical conventional tank-type electric water heater’s efficiency may range from 0.8 to 0.95; the Accelera’s COP is 2.51, which means it uses about one-third of the energy of an electric water heater. (Note that the COP is greater with higher ambient air temperatures and higher relative humidity.) 

As a side benefit, in warm climates, the water heater can be placed inside the home and it will cool the air around it, reducing the air-conditioning load. In cold climates, the unit can be placed in a basement to act as a dehumidifier. The Accelera 300 carries a 10-year warranty.

Comments (4)

nospam's picture

Does anyone have any long term experience on the reliability of this brand and these Accelera 300 units? Does Stiebel-Eltron stand behind their warranty?

Fred Golden's picture

I worked on and installed a couple of Airtemp heat pump water heaters, they where last manufactured by Crysler Corp back in 1979. They are not "New" but are extremely efficient. The one I installed was in a Arizona home, where it collected heat from the house, providing both additional free cooling, and very low cost water heating.
Heat pump water heaters are most efficient when heating water to only about 110F. They would require a lot more energy to heat to 115. So the 80 gallon tank makes sence, because taking a 105F shower you will be using mostly water from the hot tank instead of mixing 130F with about 20% cold water.
Another application the heat pump was located in a unheated garage. Because it was southern California, the garage was normally never below 50F, so it worked out well.

I plan on installing a heat pump water heater in my garage in Portland Oregon area, and plan on installing under the floor solar hot water heating system in the garage, to use in the spring and fall when I have excess heat. The solar system should provide almost all of my domestic hot water, so the heat pump would only see most of it's use in the middle of winter.

I don't think the COP of 2.51 takes into account that you will also be saving 18,000 Btu's of cooling energy while cooling a home and heating hot water at the same time.

Michael Welch's picture

Hi Fred. Just some thoughts from a layperson who is not an expert in heating and heat pumps.

One problem with these is that you cannot turn them off. At my home, I turn my water heater way down until about an hour before shower or bath time. Doing the dishes, washing hands etc. works fine with whatever water temp is left over after turning the water heater down again. I save a fair amount of energy by not keeping the water hot all the time.

But with a HPWH, they slowly build up the heat to the point that it is hot enough to use, so they should not be turned off or down between use. And since they are hot longer, more energy is lost through the heater walls than when employing my strategy with a non-HPWH tank heater. So the bottom line is that I save more energy by not having a HPWH.

Also, yes you can save on summer cooling with a HPWH. But it also means that you will have to put more heat into the home in the winter, which offsets at least to some degree, if not all, the summer savings.

Fred Golden's picture

Running a typical water heater for 1 hour a day will consume about 4,000 watts, and transfer about 13,600 Btu's into the water.

Run a heat pump for 2 hours (just before you want a shower, you can put it on a timer, such as turn on at noon, until 2 or 3 pm) and it will transfer about 7,000 Btu's per hour, and only consume about 700 watts per 7,000 Btu's or 1,400 watts for 14,000 Btu's. Of course the Btu rating has to do with the size of the compressor. The 1979 Airtemp that I have worked on looked much like a upright 12,000 Btu window A/C with a water cooled condenser in the back, and a small water pump. It has a mechanical timer that turns on the pump every 15 minutes, and samples the water temp. If below the set point, it will run the compressor until the setpoint is reached, then shut off and wait 15 more minutes before sampling again. The compressor and fan and pump motor combined amp draw was about 10 amps at 110 volts, or around 1,100 watts. This compares very favorably with a 4,000 watt 240 volt heating element that it replaced. About 1/3 the power consumption for a given amount of water heated.

You really do not need to run it 24/7. Running it only during warm days will save power in that you collect more Btu's per watt when the air temp around the heat pump is warmer. Cooler nights, and you get less Btu's per watt.

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