Saturday, December 19, 2009

Can't have everything

In the alternative energy world, sometimes everything doesn't mesh all that smoothly.

You can never do just one thing.

Installing a tankless water heater seemed like a good idea. In many ways it was. When it worked, it saved energy compared to a regular heater with a tank. There was one important unforeseen consequence. Picture my first shower. I run the water until it gets toasty warm. I jump in. It soon becomes icy cold -soon followed by scalding hot. Repeat. Repeat. Repeat.

Scream. Gasp for breath. Jump out of the shower.

What happened?

The shower is located fairly far away from the heater, causing some pressure drop from friction loss. New shower heads come with flow restrictors to save water -another noble goal. The well pump is on a pressure switch. Depending on the point in the on/off cycle, the water pressure varies by about ten PSI.

Between the distance, the flow restrictor and pressure switch cycle, the tankless water heater had a problem. At the high end of pressure, the flow was enough to turn the water heater on and it would make hot water. At the low end of the cycle, the flow was too little to activate the burner. Hence, the painful cycle of hot and cold.

To fix this problem the flow restrictors were removed, allowing more volume to flow through the water heater. While this improved the situation, it didn't quite make it go away. Turns out even just a little blast of cold water in the middle of a shower is no fun.

Adjusting the household water pressure upwards and shortening the on/off cycle of the pressure switch did the trick. Finally, I was able to enjoy endless hot water without the cold water surprise.

Two problems:

Without the flow restrictors, the shower used a lot more water. Fortunately, my well is productive. New Hampshire isn't the desert Southwest.

The second unforeseen consequence was higher electrical usage. Pumping more water took power, and running at a higher pressure also took more energy. I did not realize how much until after the tankless water heater died and I went to a regular tank for a short while. Reducing the pressure and lengthening the spread between the high and low end of the switch cycle put much less strain on the solar electric powered water pump.

At the time, even with the changes needed to make it work, the tankless water heater paid off. It cost more in unexpected ways so it wasn't a 100% gain.

At least I had an interesting problem to solve. Good thing I like solving puzzles.


No comments:

Post a Comment