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.