Physics Guy

Now I'm a Plumber
Bangor Daily News Op Ed 2/9/06
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Where to Start
Buying Stuff
Ground Work
Now I'm a Plumber
Now I'm an Electrician
The Moment of Truth
Summary and Conclusions

I installed the inlet and outlet header system in the basement. See picture under Ground Work, Drilling 12 – 1 inch holes.  I used clear plastic pipe here so I could see water flow and air pockets in the pipes. This would be very important later when filling the pipes as I’d be able to see the flowing water and trapped air in the pipes. I then connected the header pipes to the circulator pump and then to the heat pump input and output lines. I used the header pipe coming from the deeper part of the trench as the return to the heat pump since water from here should be warmer in winter than the other pipe. I installed fill ports with valves for filling. I had to put some thought into designing this part of the system. I needed to fill the pipes with water and antifreeze while allowing air to vent out of the pipes. The first step was to run a lot of water through the pipes to clean them. So I needed a drain valve placed at a low point in the system. I also installed a high point in the system for venting trapped air and injecting antifreeze.


Next I installed pressure gauges and a temperature sensor near the heat pump. Inexpensive pressure gauges were installed on the inlet to the heat pump and on the outlet to the heat pump. The pressure drop across the heat pump inlet and outlet can be used to calculate water flow. The manual had a chart that converted pressure drop to flow. Too large a pressure drop can also tell if the water in the heat pump coil is frozen. I had to wait 12-24 hours for it to thaw out when this happens. The heat pump should not be run when the coil is frozen because it will take that much  longer to thaw.


Water pressure goes up on both the inlet and outlet gauges as the temperature goes down. I suspect this is because the plastic pipe contracts as the temperature goes down. Decreased pipe volume means increased pressure. So I’ve found that a high pressure on both gauges means its time to turn off the heat pump and wait for the pressure to go down and the temperature to go back to ground temperature. I’ve wired the heat pump with a switch that allows the circulator pump to remain on even though the heat pump is off. This allows the coil to warm up to ground water temperature faster. This switch may not be needed with a higher horsepower circulator pump.



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