Hi all,
I’d like to set up an automation to lower the utility bill of our heat pump water heater. Right now it’s set to run 5-8am and 3-10pm, at 120F. We also have a time of use rate with higher costs 4-9pm. It kills me to see it run during those hours “just in case” even when we don’t use it. Has anyone done this before?
Thank you,
Ben
Hello Ben,
how many litres are in your heater?
And…
How many people in your household?
2 mins showers or long baths? …morning and/or evening?
,…what other hot water usage do you have?
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Do you have chlorinated city water? If not you may want to keep it hot to keep microbe growth down and periodically run it at 140f.
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Hello PeteRage,
we don’t have chlorinated city water. But I have only 56l and with one bath it will be full replaced. 
Here’s what I do:
The way the manufacturer designed my heat pump hot water system, no matter how many times you power it on a day it only runs one cycle. It cuts off when the heat exchanger water inlet temperature reaches 60 degrees C.
I start the heat pump at 11 am each day, which is when I am on the off-peak power tariff and am usually producing an excess of solar power.
I only run the heat pump until the heat exchanger inlet to outlet differential drops to 30 degrees C. Below this efficiency drops rapidly. It heats enough water to a high temperature (60C) for my needs.
On Friday I let the heap pump cycle to completion to allow the entire tank to reach 60 degrees C to kill off any legionella bacteria. Nasty stuff you definitely don’t want. Once per week is enough according to the Australian standard. Friday is good as it is more likely that there may be more people in the house on the weekend.
I also have an override input boolean that allows running the full cycle if I have guests and will be using more hot water than normal.
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My heat pump runs on weekdays from 5:30 to 8 am and 5 to 8 pm. On weekend even longer. I have an addictional pump for circulation. The circulation works independent to the heat pump and hasn’t automations in ha.
The 56l tank keeps the water in temperature the whole day, even if someone wants to take a shower.
The circulation can be triggert by a button and runs for 15 minutes.
I have also the dishwasher connected to hot water.