Heat Pump vs Electric Geyser

[TheOracle]

I have created a Heat Pump vs Electric Geyser Calculator.

Every heat pump quote leans on a spec-sheet coefficient of performance measured on a warm test bench, not a Highveld morning in July, and none of them ask whether the tank you're buying can actually keep up with two teenagers showering back to back. The calculator sizes the swap first, the tank and recovery rate you actually need, then shows the running-cost payback next to the number you'll likely get quoted, and what closes the gap between them.

Anyone interested can have a look here:

Heat Pump vs Electric Geyser Cost Calculator SA

How much a heat pump geyser costs installed in South Africa, what it saves a month vs your electric geyser, and how long until it pays back.

southafricafacts.co.za

 

[Lupus]

I've had my heat pump since September last year, you still use the geyser tank for the storage. On the coldest day we had in August this year it took 45 minutes longer than usual to get the water back to 55 degrees. You're not buying a tank? It's your original geyser, so if that could handle two teenagers showering then the heat pump would do the same, unless you're referring to a IHP?
Currently the heat pump runs for an hour most of the time and uses a third of the power the geyser would do, even when it runs for almost two hours it tops out at 2/3rds of the geyser.
At the worst of the usage it has hit 3.5 units used vs the geyser equivalent 12.

 

[TheOracle]

I've had my heat pump since September last year, you still use the geyser tank for the storage. On the coldest day we had in August this year it took 45 minutes longer than usual to get the water back to 55 degrees. You're not buying a tank? It's your original geyser, so if that could handle two teenagers showering then the heat pump would do the same, unless you're referring to a IHP?
Currently the heat pump runs for an hour most of the time and uses a third of the power the geyser would do, even when it runs for almost two hours it tops out at 2/3rds of the geyser.
At the worst of the usage it has hit 3.5 units used vs the geyser equivalent 12.

I was talking about the integrated units. If you retrofit onto the existing cylinder you are not buying a tank, and the first two showers off a full tank are the same as before. The calculator defaults to IHP because that is the quote when the geyser's had it, but retrofit is in there as the other option.

What does change is recovery after that, which matches what you saw. 45 minutes extra to get back to 55 on the coldest August day is the heating output dropping with the air temp. A 3 kW element is still 3 kW in July. If the tank is already down and two showers land close together, that is when the backup element can sneak in. Sounds like yours is keeping up though.

3.5 units against a 12 unit geyser equivalent on the worst day is a COP of about 3.4. That is better than the winter number I used, so the unit is doing well.

 

[spit]

I have created a Heat Pump vs Electric Geyser Calculator.

Every heat pump quote leans on a spec-sheet coefficient of performance measured on a warm test bench, not a Highveld morning in July, and none of them ask whether the tank you're buying can actually keep up with two teenagers showering back to back. The calculator sizes the swap first, the tank and recovery rate you actually need, then shows the running-cost payback next to the number you'll likely get quoted, and what closes the gap between them.

Anyone interested can have a look here:

Heat Pump vs Electric Geyser Cost Calculator SA

How much a heat pump geyser costs installed in South Africa, what it saves a month vs your electric geyser, and how long until it pays back.

southafricafacts.co.za

I've had my Stiebel Eltron WWK 304 ZA heat pump for about 14 months now. We're three adults in the house, all taking showers between 6:00 and 7:00 in the morning.

We've never run out of hot water, and the backup element doesn't even kick in under normal use. I keep the setpoint around 60°C – 65°C depending on the season. The only time the backup element ever kicked in was back when we had a top-loader washing machine pulling hot water, but we've since replaced that with a front-loader since it broke.

I'm down in Mossel Bay, so we obviously don't get the extreme Highveld winter freezes, but the unit is rated to operate down to -5°C (though COP naturally drops at lower ambient temps).

Zero issues so far. The big win for me is the flat ~500W power draw—even on overcast days, our solar setup easily covers it without pulling from the grid or battery.

 

[kolaval]

If you know his videos he goes pretty deep into testing stuff.

 

[SauRoNZA]

Must say mine seems to be at a constant 58-60% saving over the old one in the year before, but yet to hit summer and see how that differs.

Have pretty much settled on 55-degrees now and then I just pump that up to 65-degrees between 12:00-16:00 to get the bigger benefits of solar. Haven't even done that in Home Assistant to make it fancy, may just do that sometime this month so it only does this when there is actually solar pumping.

If I wasn't at the lowest electricity tariff due to my solar then this thing would have been a no-brainer basically paying for itself in 2-3 years. There is of course the question of whether it will last beyond the 10 years like they claim it should and what maintenance might pop up then.

 

[SauRoNZA]

What does change is recovery after that, which matches what you saw. 45 minutes extra to get back to 55 on the coldest August day is the heating output dropping with the air temp. A 3 kW element is still 3 kW in July. If the tank is already down and two showers land close together, that is when the backup element can sneak in. Sounds like yours is keeping up though.

I do think there's something to be said for thermostats and their accuracy. I have a strong feeling the thermostats in most normal geysers aren't particularly accurate and the one in my IHP is.

So yes recovery time is a thing, but 1 bath and 2 showers back to back it's pretty much imperceivable and just like the old geyser the 4th person in line is going to feel the difference regardless so it's not like the conventional geyser didn't have this at all it's just a case of maybe waiting 15min instead of half an hour.

This will almost certainly be camouflaged entirely by running higher temperatures as I haven't experienced it with 4 people since starting to boost it to 65-degrees until 16:00 and then keeping it at 55-degrees.