90 minutes a day @ 5500 watts = 8.25kwh per day = $.90/day. Since I keep the desuperheater off from Nov-March, that's about $140 per year in tank warming cycles. The question is why is it coming on so often. Gary suggested that I might have a thermosyphon loop occurring and after some investigation I believe he is correct. The downstairs heatpump sits right next to the water heater and the plumbing between the two units looks like this:
When the valve on the cold water line at the top of the water heater is open (as it has to be when the desuperheater is on), there is an instant flow of hot water out of the top of the water heater, down through the heat pump and back into the base of the water heater. Shutting the valve stops the flow and the lines stay cool. Even though all the piping is insulated, shutting the valve had an immediate affect on the number of tank warming cycles that occur during the day as shown below.
The tank now cycles on for 7 minutes every 6 hours. The "on" time for warming cycles has been reduced from 90 minutes to 30 minutes a day. For my 5500 watt water heater, that's 825 kwh per winter that I'm not using and 982 pounds of CO2 that's not being pumped into the air. In addition I'm also saving $.60 per day or $90 a year.
what method are you using to record when your hot water heater is on, I would like to do the same.
ReplyDeletethanks, Sloane
sloanebiking@yahoo.com
I'm using a TED 5000 to monitor the electrical usage of the entire house. As part of that it can be configured to recognise certain loads and graph the usage of those devices. I did not have the best of luck with the built in load profiling of the TED 5000 and ended up pulling all of the "per second" data from the TED every 30 minutes and processing it myself for the loads I was interested in. Several posts detailing what I went through are here
DeleteI use an Allen Bradley SLC 5/04 PLC to measure temperatures and digital signals throughout the house, I looked at my water heaters last night and am going to install a240vac relay on each heater that will pass a low voltage signal to the PLC to measure when they cycle, this particular data will record in an on change data base, the temps go into a one minute data base. I want to measure the cycle time difference before and after I install a solenoid valve to fix the thermosiphon problem.
ReplyDeleteWhen I first installed the temperature sensors on the DHW tank and started monitoring when the DHW heater was on via my TED, it was coming on for 5-6 minutes every 90 minutes. After installing the solenoid valve, it comes on every 6 hours.
DeleteAs a side note, after installing the solenoid valve and looking at the tank temps, I realized that I could turn off the DHW heater from June - Sept and let the desuperheaters supply all of my hot water.
this week the weather has been in mid 80s for highs, 50's for lows and the heat pump runs about 4-5 hours a day on stage 1, none on stage 2. It is a 4 ton water furnace envision I think it is called. desuperheater feeds into 1st water heater which I leave on at minimum temp but sometimes turn off that element, I always have left on the 2nd tank which is in series with the 1st. 5 people in the house that shower about the same time. are you using a relay to capture the water heater on/off signal into your data logger? I guess I could have gotten a 240vac plc card but did not really want to run 240vac that far in my case. or are you using temp change in the tank to determine when it is coming on?
ReplyDeleteI'm using a TED 5000 to monitor the electrical usage of the entire house. It has the ability to do load profiling to determine when certain loads are on/off.
DeleteI can also tell from my temp sensor when the element is on by the jump in tank temperature. However, determining when it when off just by the temperature is more difficult.
Good Explanation on water heater!!
ReplyDelete