Hx & buffer tank

[panelman]

Gents

it's bit of an open question but....

We have a Hx, primary fed by boiler with control by diverting valve, secondary is DHW fed into a storage/buffer tank. Controls temp sensor is attached to buffer tank and there is a circulating pump in the Hx/buffer circuit.

at times of low demand is is better to turn the circulating pump off and allow stratification in the tank or better to leave it running to ensure good mixing?

all thoughts welcome

 

[MintJulep]

Better for what?

 

[panelman]

that's the open bit of the question, it's not my field so I was hoping for some pros & cons of each method

 

[MintJulep]

Constant running pump incurs constant pump operating costs, lower pump life and increases stand-by losses for the whole system.

Turning the pump off may result in a perception of differing "hot" water temperatures by users.

 

[willard3]

The end use characteristics/requirements will govern whether you leave the pump on or off.

 

[panelman]

it's DHW in residential.

my thoughts were that if the pump goes off then thermal stratification will reduce the amount of stored HW available when demand resumes and once the pump comes back on it will mix everything up thus further reducing the amount of HW available.

might there also be legionella issues?

 

[willard3]

There will be legionella issues, probably at the faucet.