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I've got a hot tub in my garden with 1,500 litres of water in it and the target temperature is 38° centigrade.
The tub has two operating modes:
- Economy: circulate water twice for 3 hours within 24 hours (at 4AM and 4PM). While circulating, heat if necessary.
- Standard: same circulation but heat whenever temperature is dropping below 38°
Outside temperatures over here very between -15° at night (winter) and all the way up to +35° during the day (summer).
Usage of the hot tub is typically during the evening hours, the rest of the time the tub is covered with an insulated lid.
I observed that on warm days the economy mode consumes considerably less energy but I wonder if that will be true for colder days too and I would like to understand why this is the case.
I understand that the same amount of energy is needed to heat water, no matter how it's done. But isn't hotter water cooling down faster than cooler water? Does that have an impact on the decision of the mode?
Is it right that in an ideal world (which we don't live in), both modes should use exactly the same amount of power?