As opposed to unofficially confused and only finding out later that I'm confused.

I set up rules in SmartLife to allow the guest geyser (2kW element) to run, but not whilst the main geyser (kwikot heatpump) is running. Can't have them both on at the same time.

These are on separate circuits. Both circuits have a CBI Astute smart controller (ASC). For the main geyser the ASC just monitors. For the guest geyser the ASC also switches the geyser on and off.

The heat pump has a built in control unit which I use for scheduling and for setting the temperature. The temperature is set to 57.

The guest geyser has a conventional element. This is set by eye to 60 (half way between the 50 and 70 marks. I accept that this is not precise).

The first time the guest geyser ran under this rule it consumed 6.45 kWh (according to the ASC). And something like that is to be expected because that geyser had been switched off a long time so the water was cold.

Thereafter we can start doing more fair comparisons between the two systems. Though there are still differences. Main geyser has an insulating blanket. We never use the guest geyser, so once that is heated no hot water is drawn from it.

But the consumption figures in kWh (according to the ASCs)

Date	Total for pump	Total for element
8th	1.71	1.12
9th	1.25	1.53
10th	2	1.69
11th	1.38	1.23

Not what I was expecting. 3 days out of 4 the element has won the prize for lower consumption.

Also the run times are surprising. Here's my system on the 8th. I've reduced this to load only

We see

1. the heat pump turn on at 6:30 and run for 50 minutes.

2. the element turns on at 10:00 as per the automation and runs for 35 minutes. The automation allows the ASC to be on until 12:00

3. The heat pump comes on again at 13:30 and runs for 15 minutes

4. Although the automation switches the ASC on again at 13:00, no more power is drawn on that circuit.

OK... it is possible that the spike at 13:30 is actually the guest geyser. I was not sitting watching devices all day. But we see a similar pattern the next day, and this time the midday spike cannot be the guest geyser because that ASC is turned off from 12:00 to 13:00

Possibilities

1. The numbers from those ASCs are not worth the money they are printed on

2. Not drawing hot water from the guest geyser makes a big difference

3. My heat pump (13 - 14 years old) is not what it was

As regards point (1) above, looking at the area beneath the line on the graphs should give a rough figure. So for the 8th the heat pump is adding about 1.4 kw to the load for 50 minutes - that's about 1.16 kWh. Then the 2nd run it adds again about 1.4 kW for 15 minutes. That's another 0.35 kWh. That's a rough 1.75 kWh, and that's in the same ballpark as the figure from the ASC, and also supports the spike at 13:30 being the pump.

At no time do we see the guest geyser running for the allotted 2 hours between 10:00 and 12:00, nor coming back for more after 13:00.

#notWhatIExpected.

OK... the test that would really tell us what we need to know is kWh per degree rise in temperature. I don't have a way to monitor that. Such a figure would compensate for cooling down of the geyser contents because of hot water being used.

NB! Both geysers are 200l (I can't edit my original post - browser session just hangs and eventually I get a warning about an unresponsive site).

43 minutes ago, Bobster. said:

Not drawing hot water from the guest geyser makes a big difference

This is probably the biggest factor.

It sounds like you're comparing replenishing the standing loss of the guest geyser (typically 1.5kWh-2kWh radiated losses per day) to the energy of re-heating the main geyser with a heat pump after drawing out hot water and cold water comes in.

Perhaps the best comparison would be to see how much energy it takes to re-heat the main geyser from cold to 60 degrees. If it takes 6.45kWh to heat 200l with a conventional element, then your heat pump should be doing the same using only about 2kWh.

58 minutes ago, GreenFields said:

Perhaps the best comparison would be to see how much energy it takes to re-heat the main geyser from cold to 60 degrees. If it takes 6.45kWh to heat 200l with a conventional element, then your heat pump should be doing the same using only about 2kWh.

Then I have to let the main geyser get cold. Which will take days 😢

I have just made a rod for my own back and confusion for my own brain.

The figures you give for standing loss are bang on for what we see with the guest geyser.

Is also have a heatpump (5.4kw ITS), also on a 200L geyser (installed outside the house on the flat garage roof)

I left the heatpump on when we were away from home in December, so basically no one used any of the hot water. It ran for 55 minutes each morning to heat the water up to 60°C again. It did not turn on again until the next morning.

When we are home and use the hot water it takes about 90 minutes to get the water up to 60°C in the morning and then it will turn on again round about 3PM and run for about 25 minutes.

Don't know the C to which the water inside the geyser is cooled to when used. We are 4 people. Heatpump is set not to run between 5PM and 7AM.

3 hours ago, I84RiS said:

Is also have a heatpump (5.4kw ITS), also on a 200L geyser (installed outside the house on the flat garage roof)

I left the heatpump on when we were away from home in December, so basically no one used any of the hot water. It ran for 55 minutes each morning to heat the water up to 60°C again. It did not turn on again until the next morning.

When we are home and use the hot water it takes about 90 minutes to get the water up to 60°C in the morning and then it will turn on again round about 3PM and run for about 25 minutes.

Don't know the C to which the water inside the geyser is cooled to when used. We are 4 people. Heatpump is set not to run between 5PM and 7AM.

Some figures are in line with my experience like 45min for my ITS to reheat from about 26-30 deg up to 55 during the day from PV. My heat loss seems much lower and surprised to see you used so much power during Dec with no hot water used. My heat loss during say 12 hours during the night is only 8 deg. About 3 deg loss from 14h to 18h. I do have a long 30min of very little increase in temp after switching it on but once it starts heating it heats up very fast. This 30min is not present if it heats up from around 42 deg up to 55.

Also having a 150L geyser and 4.7kw heating power ITS now 14yrs old.

11 hours ago, Scorp007 said:

Some figures are in line with my experience like 45min for my ITS to reheat from about 26-30 deg up to 55 during the day from PV. My heat loss seems much lower and surprised to see you used so much power during Dec with no hot water used. My heat loss during say 12 hours during the night is only 8 deg. About 3 deg loss from 14h to 18h. I do have a long 30min of very little increase in temp after switching it on but once it starts heating it heats up very fast. This 30min is not present if it heats up from around 42 deg up to 55.

Also having a 150L geyser and 4.7kw heating power ITS now 14yrs old.

My geyser is installed outside the house on the garage roof so it is exposed to the cool night air in Cape Town.

It used to be inside the roof, but could not fit the 200L through the trap door when we changed form a 150L to 200L about two years ago. Also actually prefer the outside install since it is now right next to the HP and a lot easier to replace once the inevitable happens and it starts leaking. I have not yet insulated it,

I do heat to 60°C, I have noticed that changing this to 55°C has a disproportionate impact on the running time.