Config for Hot Water cylinder

[Chris Moir]

Hi,

So got the heating controls all up and running on the latest project but want to set up the hotwater controls. 

Have got a one wire probe into the hot water cylinder but can anyone advise me on the config I need.

 I have started to casll the demand via a schedule ( easy enough) but I cant work out what function block I need to set the cylinder temperature demand. eg. if it is less than 65/70 degrees call for heat.

Can anyone advise

thanks

[Duncan]

use a 2 position controller which adds hysteresis to avoid too much on/off cycling

T is your target value eg 65

AI is the real temp input from your sensor

H is the hysteresis value  eg 2 so the target is T +/- H 65deg +/- 2

Q is the on/off output to drive the motorised valve and boiler/heat demand

[Dan Orange]

Chris, i personally wouldn’t use a 1-wire probe. I’d use a standard hot water cylinder temp sensor and put your heating of the hot water on a schedule in series with the sensor.

You don’t want that cylinder ever getting too hot and exploding putting the temp sensor in series just like a plumber would prevent any incidents.

Loxone with a 1-wire will work but we always install heating with the standard fail safes and leave Loxone to just turn heating on and off when required.

[RSinn]

Agree. Read building regs (if UK based). Part G3. You have to have the cylinder temp sensor linked to the power on the 2-port valve. If it gets too hot the power gets cut to the valve which shuts it so no more hot water can come from the boiler. I think you may have to use an approved sensor that comes with the cylinder, but check that.

That being said, nothing wrong with monitoring from Loxone, you just have the safety back up.

[Duncan]

most tanks have an on/off stat and newer ones have a 2nd backup stat, plus an open tube for you to add a temperature sensor

i dont think the building regs specify that you cant have some electronics/logic between the tank stat and the 2port valve, its just that most homes will have a simple series wiring running at 240v and dont have the facility to do anything else

in a modern house with ufh and hot water storage, the boiler hot water will only be running hot enough to get the hot water up to 60deg minimum so it spends more time in condensing mode, so the boiler primary and secondary thermal controls limit the hot water as well as the tank stat - no danger there of 80deg plus water coming out of the taps

the 1-wire temp sensor allows loxone to measure (and adjust if necessary) the water temperature, and the 2nd stat can act as a safety cut-off, say if it gets the 70deg the stat trips and cuts power to the 2port valve

[RSinn]

3.18 An acceptable approach might consist of:
a. a non self-resetting energy cut-out to
disconnect the supply of heat to the storage
vessel in the event of the storage system
over-heating; and
b. a temperature relief valve or a combined
temperature and pressure relief valve to safely
discharge the water in the event of serious
over-heating.
Alternative approaches to this are acceptable
provided that they provide an equivalent degree
of safety

The bit I was referring to (but couldn't remember detail) was the non-self resetting cut out.this should come with the cylinder.

The way mine is set up is Loxone relay to the cylinder stat box, power then comes from this (via it's internal relay) to the 2-port valve. So If Loxone has hot water demand AND the cylinder is below the safety limit power will flow to the 2-port. If either of these are negative then no extra heat from the boiler.

The 2nd part is the temp safety valve that will run to the tundish (black plastic cone with opening) if it senses cylinder is too hot it dumps a load of hot water thereby causing an inrush of cold water which lowers the overall temp.

Not sure how Loxone could satisfy non-self resetting but I guess it's only a guide. I like things like this to be easy for building control to understand!