Simple Cheap High Voltage High Current Control

[brotsten]

Good point and I should have clarified my request for additional information for this cost calculation. I'm not too concerned about calculating the cost to operate the pump itself (I can just put my Kill-O-Watt meter on it and see how many watts it is using for this simple calculation). I was more concerned about running hot water continuously (pump just left on) as now the hot water is circulating over many, many feet of non-insulated pipe. This would not be an easy calculation as one would have to do a thermal model of the pipe (thermal resistance), then de-rate the hot water tank’s performance based on this value (i.e. beyond me :blink.

I’m not a thermodynamic expert, but I’m thinking the cost of having to re-heat the water that is outside the tank (running through the pipes) is more than the cost of running the pump itself. This is the main reason I only run the pump on demand as described above.

Perhaps someone more familiar with these models can give further guidance (as I also stated above, my thinking on this may be wrong)!

I would think a ballpark figure could be derived from measuring the watts consumed of an idle hot water tank for several hours and then again with the pump running. Assuming an electric tank.

Brian

 

[BraveSirRobbin]

Yes, but I have a gas hot water heater. Michael McSharry provided THIS How-To on monitoring gas water heater usage, but still, this seems complicated to measure let alone calculate. :blink:

 

[BDHall]

Where did you find that relay for $15?

B&B Electronics is another supplier for solid state relays. I have purchased quite a few from them.

Brian

 

[ctay]

To arrive at the $3 a month figure I simply did the math on the max draw of the pump * my electric rate. I did not calculate the loss of heat which as many have pointed out can possibly be higher. We just built our house and all the hot water lines are insulated but there clearly is loss or there wouldn't be any point to having the recirc pump in the first place.

I think it is a good idea to shut off the pump when it is unlikely to be used but really the whole point of the recirc pump was to make sure to have hot water on tap when I wanted it. If shutting down the pump reduces the likely hood that I will have hot water when I want it I have reduced the value of the pump. Basically I am saying I would only want to shut it down when I am sure no one would use it and thus would not receive great enough of savings to make it worth my time just now. This is on the list to do at some point, just got kicked down a couple notches when I realized the cost of the electricity was so low.

Brian did a great job with a clever low cost solution!

 

[ckindt]

Recirculation pumps?? I circulate my hot water through a loop without a pump. Do you know if your water heater is the lowest point of your water circuit (in the basement typically) you can use the effects of convection currents to circulate the water? Of course if your heater is not at the lowest point you can't take advantage of this natural effect.

Now to get back on track with the topic, I haven't automated my loop, but I do have a manual valve I can shut off to eliminate the water flow returning to the heater and reduce my heat loss/gas usage, but I usually leave it on. I could automate the valve I guess.

 

[politics123]

I´d bet that eventhose with insulated hot-water pipes (like me!) have less insulation and of poorer quality than exists around newer tanks. The insulation around tanks is pretty good, but pipe insulation is notoriously not, unless you foamed them. My tankhas something like R12 around it, my pipe insulation is R3.5, and even though I applied the pipe insulation well, there are still air pockets and air can easily move around the pipes.

We pay $10 for every 1000 gallons of water used (water + sewer); remember to include wasted water saved in your cost calculations. If it takes 1 minute to get H/W to your shower, and you have a low flow 2.5gpm fixture, and you shower 1 per day, you´d save 912 gallons of water, which in my area would save me almost $10.

As far as automation rules:
1) You can detect the flow of water and have the pump turn on automatically to accelerate the delivery of HW to the fixture.
2) you can detect motion in areas that use H/W and have that trigger the pump

 

[brotsten]

I´d bet that eventhose with insulated hot-water pipes (like me!) have less insulation and of poorer quality than exists around newer tanks.

My pipes have a little fiberglass wrapped around them. I know an hour after the pump shuts off, the water is cold.

As far as automation rules:
2) you can detect motion in areas that use H/W and have that trigger the pump

That's an interesting idea...

Brian

 

[hucker]

Good point and I should have clarified my request for additional information for this cost calculation. I'm not too concerned about calculating the cost to operate the pump itself (I can just put my Kill-O-Watt meter on it and see how many watts it is using for this simple calculation). I was more concerned about running hot water continuously (pump just left on) as now the hot water is circulating over many, many feet of non-insulated pipe. This would not be an easy calculation as one would have to do a thermal model of the pipe (thermal resistance), then de-rate the hot water tank’s performance based on this value (i.e. beyond me ).

I’m not a thermodynamic expert, but I’m thinking the cost of having to re-heat the water that is outside the tank (running through the pipes) is more than the cost of running the pump itself. This is the main reason I only run the pump on demand as described above.

Perhaps someone more familiar with these models can give further guidance (as I also stated above, my thinking on this may be wrong)!

Just to add complexity, if the heat loss from the recirc water is into the house AND the house is in need of heat then it really isn't a loss, it is just a poor man's hydronic heating system. If it is summer and you are running AC then it is a double loss!