Q&A: Energy sucking pump

I got a rude shock the other day when I purchased a new water pump to supply my house with tank water. I put my energy meter on it for few days to get an idea of how much energy I would use on an average daily basis. When I went to disconnect it, I noticed that it was drawing 17 watts while it was doing nothing. I called the company that sold me the pump and they assured me that a pump should draw no power unless a tap was on and it was running, so I dismantled the whole thing and brought it in.

They plugged it in to their ammeter which said it was drawing nothing. Fortunately, I had brought my meter with me and showed them that it was drawing 17 watts. Then they noticed that it has a couple of LEDs on it that show power on etc and said that it has to draw some power for the LEDs. I would consider trying to break into the box and get rid of the LEDs, but 17 watts seems like more than needed for one LED.

Then they told me I was going to have to buy a pump with a pressure tank instead (the very pump they had previously told me I didn’t want to buy because it would cut in and out while having a shower). They then fitted this new pump with a pressure tank they had ‘sitting out the back’ and sent me on my way.

I am not overly excited about the outcome, not the least because I now have to build a whole new pump house as the pressure tank doesn’t fit under the previous one.

I did the calculations and given that I am getting 66 cents for PV power I put into the grid, it would cost me $63/year to have the first pump connected as purchased. The pump I had before this neither had a pressure tank nor drew power when it wasn’t running, but the same company that said it wouldn’t draw power when it wasn’t running, now say that all pumps either draw power when not running or have a pressure tank. Is this true? Is this power doing anything more than powering an LED power indicator? Do you know of pumps that don’t do this and if so, which ones?

Enga Lokey

If the pump has an electronic controller then it will draw some power even when off. The only pumps that won’t are those with simple electromechanical pressure switches. Some pumps are variable speed and are designed to eliminate the need for a pressure tank, but if it’s a simple on-off type controller then it should still have a tank.

The problem with many mobs selling pumps is they tend to undersize tanks for pumps that need them. If a tank is sized correctly, the pump won’t need to kick in during an average shower, unless it was almost empty (close to the pump’s cut-in pressure) anyway. For a whole house system, the minimum tank size you should look at to reduce pump cycling is around 100 litres, but with pressure tanks, the larger the better.

My personal preference with pumps is a simple electromechanical pressure switch and a decent-sized pressure tank. It’s simple, robust and effective.

Lance Turner

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