(experiment) Circulation pump effects on...

[Slaz]

... water heater operation. I did a little experiment I thought wold be handy to refer to when questioning weather or not to place a timer/demand or other device on a circulating pump. I placed one sensor on the hot water feed coming out of the water heater. The second sensor on the return line which is run to the cold water supply line directly above the water heater. Each sensor was programed to record a temp every 5 minutes for 2 days and placed between the pipe and insulation. The hot water lines are insulated throughout the building with 1 inch fiber insulation.This is a commercial building with about 75 employees in 50 offices operating 8am to 5pm / M-F. The system is about 25 years old. The WH is a newer 480v Rheem. The chart below doesn't have the actual sample numbers because that was just too much to attach. However, what this shows is that during non business hours the heat loss from circulating the water made the water heater operate 2 hours each night. This 2 hours of time was split up over the night where the heater ran for 15 minutes then would sit idle for a couple hours before needing to heat back up. The temperatures on the chart are in Celsius. The blue line labeled cold is the return water and the red line labeled hot is the supply. If I did my calculations properly this means an operating cost of around $300/yr just for the nighttime hours. Anyway have fun with this and let me know if you have questions. I am in no way a professional plumber/HVAC person. I'm just the guy in charge here to try and make sense out of all the facility issues.

[jadnashua]

Seems like less than $1/day is probably worth it to have hot water available everywhere. If you used something like an occupancy sensor to turn the circulation on, you could cut that cost down without compromising the convenience (and possible code issues). A timer might not work best to account for nighttime maintenance crews, or the occasional late night operations.

A typical residential system would probably not be using 1" pipe, or have as far to pump things, so the costs would be lower since there'd likely be less pipe length to radiate heat and the WH temp might be lower than your are running.

[hj]

The ONLY purpose for a circulation line and pump is provide "instant" hot water at the faucets when it is needed. IF there are no occupants of the building "after hours", then the pump has no function and should be shut down. It would be restarted shortly before occupancy begins in order to stabilize the system's temperature.