Some of you nerds might be interested in this. Since I've been tracking geyser water temperature for more than a year now I thought I could look at standing loss, especially to see how it varies by temperature. e.g. it's only going to be "0.5 degrees per hour" under certain conditions. What conditions?
This chart takes evening water temperature (8-9pm average), and then looks at the loss overnight (to 7-8am). We never heat the geyser overnight, so this is just it cooling down from different starting points. (It's not the SANS 151 test!)
So if the geyser is at 55 degrees at 8:30pm it'll be 50 degrees by 7:30. But if it starts the night at 37, it'll only lose about half that.
It loses 0.5 degrees per hour on average over this period only when it starts at 60 degrees. Over a longer period, or lower temperature, it's a slower loss.
If the geyser were a battery, it's like it has a ~90 W parasitic load when it starts hot vs. about 45 W when it's colder.
Some caveats:
- It's not really a linear function, but close enough.
- Ambient temperature is not constant in these data. Actually highly correlated. The curve would probably be a bit steeper if that was controlled.
- Since we use the geyser, it's never really at equilibrium. I've tried to exclude data points that are obviously "corrupted" by e.g. a late shower but some mixing effects and other noise will have slipped in.
- I'm not sure what to make of the SANS 151 rated 1.2 kWh/24 hour standing loss but the important differences are that test is done at equilibrium with the thermostat actively maintaining a temperature delta of 45 degrees.
This chart takes evening water temperature (8-9pm average), and then looks at the loss overnight (to 7-8am). We never heat the geyser overnight, so this is just it cooling down from different starting points. (It's not the SANS 151 test!)
So if the geyser is at 55 degrees at 8:30pm it'll be 50 degrees by 7:30. But if it starts the night at 37, it'll only lose about half that.
It loses 0.5 degrees per hour on average over this period only when it starts at 60 degrees. Over a longer period, or lower temperature, it's a slower loss.
If the geyser were a battery, it's like it has a ~90 W parasitic load when it starts hot vs. about 45 W when it's colder.
Some caveats:
- It's not really a linear function, but close enough.
- Ambient temperature is not constant in these data. Actually highly correlated. The curve would probably be a bit steeper if that was controlled.
- Since we use the geyser, it's never really at equilibrium. I've tried to exclude data points that are obviously "corrupted" by e.g. a late shower but some mixing effects and other noise will have slipped in.
- I'm not sure what to make of the SANS 151 rated 1.2 kWh/24 hour standing loss but the important differences are that test is done at equilibrium with the thermostat actively maintaining a temperature delta of 45 degrees.
