Documenting my attempt to cut my energy usage in half.

Friday, April 1, 2011

Water Heater Analysis

Since I've been able to work around the load profile problems with the TED 5000, I've started collecting enough data that I can start to change some things and see what affect it has on my hot water heater. 

This is a typical load profile for my hot water heater for a single day.  The heater was on for about 125 minutes of which 34 minutes was due to the shower at 8am.  The other 90 minutes of run time during the day was mostly just the tank keeping the hot water that I'm not using... hot.

I then turned on the desuperheater for the heat pump.  I usually keep this turned off during the winter and really had no way in the past of telling how much heat it supplied to the hot water tank.  Tank run time for this day was 68 minutes for the two showers.  Note that at no time during the day did the hot water heater come on to keep the tank warm.

Is this good?  I'm not sure.  During the summer months the desuperheater is always on as any heat that I can pull off the coil and put in the hot water tank is heat that doesn't get pumped out to the ground loops.  But during the winter, any heat that I pull off the coil and put in the tank is heat that's not going into the house.  So either the hot water tank comes on more often, or the heat pump runs longer.  I'm not sure which option is better.

Some of the issues/thoughts with using the desuperheater during the winter that I see are:

  1. If the desuperheater is off, the hot water heater will only come on when the temperature in the tank drops below a certain level and the water actually needs to be heated.
  2. If the desuperheater is on and it's a nice day outside such that the heat pump doesn't come on, it's the same as having the desuperheater off and the hot water heater supplies all of the hot water.
  3. If the desuperheater is on and it's cold outside, whenever the heat pump comes on, heat is pulled off of the coil and pumped into the tank even if it doesn't need it.
This last thought is the one that I have the most trouble with as it seems that I'm wasting money.


  1. So it seems you have figured out a way to do load profiling outside of TED with your HA software. I'm wondering what HA software you are using and if you can show more details as to how you did it? I'm running Indigo and thought I'd might be able to do something similar. Would really like to get some load profiling going for some appliances and can't seem to get it to work within TED so this seemed promising.

  2. The Home Automation/Home Monitor software I use is something I have written myself. There is a brief description of it Here.

    It uses the TED API to retrieve per second data and processes it every 15 minutes.