Legionella

[buffalobillpatrick]

Is it Safe To Turn Down Your Water Heater Temperature? : TreeHugger

[NiHaoMike]

As I mentioned before, it's a non issue on city water due to the chlorine in it added specifically to avoid that issue. If you're on well water or have whole house filtering that removes chlorine, then set your heat pump to ramp up to 130F every few days.

[buffalobillpatrick]

I'm still on a well.

I think "then set your heat pump to ramp up to 130F every few days"
means: adjust heat pumps aquastst on thermal accumulator up?

Not too many people adjust their hot water heater every few days!

As far as controlling heat pump throughput,
I think that controlling water flow in/out is all I can do + aquastst controlling power?

BBP

[NiHaoMike]

I was just mentioning the city water for others reading this.

It's pretty easy to adjust the temperature electronically. Pretty much all you do is let the heat pump run until it gets to where you want it to be. The evaporator water flow should be as much as the pump can manage except when it's necessary to throttle to prevent compressor overload and the condenser water flow is a tradeoff between keeping condensing temperature low and maintaining stratification in the tank.

[buffalobillpatrick]

NiHaoMike, Thanks!

Can you explain this: "except when it's necessary to throttle to prevent compressor overload" ? R U talking about liquid propane going into compressor?

For the condenser water, I can pull cooler water from low in thermal accumulator, as that should help with heat exchange & select pump size for 5-6 gpm? Possibly throttle back to control the water temperature back to thermal accumulator?

[NiHaoMike]

If the source water is too hot (probably around the 100F mark in your design), you'll have to slow down the flow to prevent the compressor from becoming overloaded.

You'll have to try different condenser flow settings to find the right balance. There are too many factors involved to just give a value.

[buffalobillpatrick]

does "compressor overload" mean liquid propane being sucked in or something else?

[NiHaoMike]

It means the suction pressure going too high and the vapor getting too dense for the compressor design. It's a little analogous to why airplanes fly high to save fuel.

[Mikesolar]

That article has a lot of info in it. They reference the Walkerton issue but that has nothing to do with legionella. It was caused by e-coli because too many dairy farms were letting cattle poop close the source of the water and a breakdown in chlorine (which only masked the problem).

I've seen the HydroQuebec study for years and it actually shows that all water heaters have issues at the bottom of the tank and that legionella is quite rare anyway.

Sometimes we over estimate the risks. When i mentioned upping the temps every day or couple days, this comes from a European solar controller regulations that state that if the temp is brought to 60C -70C for 2 hours every couple of days, the bacteria won't survive. It can be done automatically so it you cannot forget to do it.

I would just use an electric element to do that.

[NiHaoMike]

The system I designed for him can do 140F and above, at least if the evaporating temperature is high enough to keep the compression ratio low enough. At 140F, half an hour is enough, but if the tank is well insulated, it would likely stay there for hours if not days.