Recirculating loop DHW - control

[JamesPa]

There have been a couple of posts recently about recirculating loop DHW.  I dont have it and thought it was confined to hotels etc, but it appears not, so I'm intrigued.

 

The issue seems to be one of control.  If you have the pump on continuously you drain the heat out of the DHW.  In summer this adds unnecessary heat to the building, in winter the lost heat goes towards heating the building, but at a lower efficiency particularly if you have ASHP.

 

Some people seem to put the pump on timer, I have seen one who puts the pump on manual switches and then waits for the water to come through before turning on the tap (thus saving the water from going down the drain) but I cant see how thats going to work with teenagers.

 

One could imagine a smart tap which, when you switch it on, starts the pump but then only opens when the water comes through hot.  However you dont get the 'instant hot water' that surely is the main attraction, it needs a mind reading tap to do this.

 

Overall it feels to me like a bit of a dogs breakfast in a domestic scenario.  Has anyone got the perfect control strategy and if not, what control strategy do you use?  Is this a technology looking for a problem?

[JohnMo]

Buy a pump with built in thermostat and timer. Set thermostat so water is at a comfortable level - not super hot. Only time when you are likely to be there to use the tap. We have to our ensuite (20m from cylinder), only have it on first thing in the morning. I shower at night, and don't have secondary circulation on then as it's not needed, start shower when a go into room, by the time I'm undressed and finished messing about, the shower is almost hot anyway.  A visual of what it does, from this morning, a temperature measure of the cylinder in orange and the other is the water flowing out of the top of the cylinder. So pump effectively does two short runs over a 3 hour period.

 

 

[Wil]

Use PIR (or mmWave) in the bathrooms to switch the recirc pump? On only when room in use.