If you've been following this activity, you know that I finished adding a recirculation pump to my water heater. Here is a chart of the activity on a typical desert day.
The normal day
The red spikes are the power reading of the system when the 5500 watt element goes off. The orange area is the solar heating pump running. The gray area is the recirculation pump running. The green line is the bottom of the tank temperature. The blue line is the top of the tank temperature. The two pumps actually use around 45 Watts, I multiplied them so they would appear in the chart; otherwise, they would have been too low to see because of that 5500 Watt draw of the helper element.
Let's discuss what all this stuff means. Starting off on the left notice the big difference between the top and bottom temperatures. That is because we used the hot water at the top for the dishwasher and such and pulled colder water into the bottom of the tank. Overnight, the top of the tank dropped a bit in temperature, setting off the helper element, which raised the temperature back to the setting of the thermostat. That happened four times during the evening.
Then, the sun got high enough for the solar heating to kick in. The solar pump ran, increasing the temperature of bottom of the tank considerably as well as nice kick-up to the top temperature as the hot water rose in the tank.
The helper element kicked on during the solar period once because the solar just hadn't transferred enough energy into the water and the top temperature needed a little boost. Once the solar had transferred enough energy into the bottom, there was not any further need for the helper element.
I fired the destrat pump up and watched as the water mixed. The bottom temperature rose immediately to match the top temperature and stayed there as long as the pump ran, then when I turned off the pump, it settled in a much smaller difference between the top and the bottom for the rest of the measurement period. I had a full tank of usable hot water for whatever purpose without having the high current helper element kick in at all for the rest of the day. Plenty of hot water without the power company sticking their hand in my wallet.
Let's discuss what all this stuff means. Starting off on the left notice the big difference between the top and bottom temperatures. That is because we used the hot water at the top for the dishwasher and such and pulled colder water into the bottom of the tank. Overnight, the top of the tank dropped a bit in temperature, setting off the helper element, which raised the temperature back to the setting of the thermostat. That happened four times during the evening.
Then, the sun got high enough for the solar heating to kick in. The solar pump ran, increasing the temperature of bottom of the tank considerably as well as nice kick-up to the top temperature as the hot water rose in the tank.
The helper element kicked on during the solar period once because the solar just hadn't transferred enough energy into the water and the top temperature needed a little boost. Once the solar had transferred enough energy into the bottom, there was not any further need for the helper element.
I fired the destrat pump up and watched as the water mixed. The bottom temperature rose immediately to match the top temperature and stayed there as long as the pump ran, then when I turned off the pump, it settled in a much smaller difference between the top and the bottom for the rest of the measurement period. I had a full tank of usable hot water for whatever purpose without having the high current helper element kick in at all for the rest of the day. Plenty of hot water without the power company sticking their hand in my wallet.
Now, I could easily have shut down the water heater completely for the night and eliminated some of the high current spikes, but for the testing period, I wanted to track the mixing and how it helped rather than strictly limiting the power consumption. That will change with experience. Probably to a schedule that turns it off entirely from midnight to the bedside alarm to save even that little bit of power usage.
Also, notice the width of the spikes from the helper element. The larger-sized element made short work of keeping the top temperature stable. They turn on for less than 15 minutes and avoid the 15 minute measuring period the power company uses to track usage. So, if a spike did show up during the peak period from 4 PM to 7 PM on weekdays, it won't raise my demand charges. That's unlikely though since I turn the entire system off completely during peak periods. It's just my 'belt and suspenders' attitude toward power bills.
What did it do for cloudy days? Well, it works, but I can't show you a graph because they are so rare here that Home Assistant doesn't hold data that long. I had a couple of them over a month ago, when the solar panel didn't capture enough energy to actually do much. When that happened and the recirc pump kicked in, it caused the helper element to fire and warm the water all by itself. The larger element and the circulating water raised the temperature of the hot water to 130F in a short amount of time and removed the stratification. It did eventually separate into a cool bottom and a hot top, but there was plenty of hot water available to last well into the evening. If another cloudy day happens, I'll capture the chart and do another post showing how well that works.
But, the weather will determine when I'll be able to discuss that.
Also, notice the width of the spikes from the helper element. The larger-sized element made short work of keeping the top temperature stable. They turn on for less than 15 minutes and avoid the 15 minute measuring period the power company uses to track usage. So, if a spike did show up during the peak period from 4 PM to 7 PM on weekdays, it won't raise my demand charges. That's unlikely though since I turn the entire system off completely during peak periods. It's just my 'belt and suspenders' attitude toward power bills.
What did it do for cloudy days? Well, it works, but I can't show you a graph because they are so rare here that Home Assistant doesn't hold data that long. I had a couple of them over a month ago, when the solar panel didn't capture enough energy to actually do much. When that happened and the recirc pump kicked in, it caused the helper element to fire and warm the water all by itself. The larger element and the circulating water raised the temperature of the hot water to 130F in a short amount of time and removed the stratification. It did eventually separate into a cool bottom and a hot top, but there was plenty of hot water available to last well into the evening. If another cloudy day happens, I'll capture the chart and do another post showing how well that works.
But, the weather will determine when I'll be able to discuss that.
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