ct circuits & vt circuits

[hotpants]

what are the fundamental differences in ct and vt circuits? why are rads on a vt circuit and radiant panels and the like on ct?

Can someone who understands this fully leave a detailed answer please, this has bugged me for ages!

Thanks!!!!!!!!!!!!!!

 

[Cds]

CT circuits that is Constant Temperature. These run at the same flow temperature all of the time (excluding initial heat up).

VT circuits that is Variable Temperature. These run with a flow temperature that varies based on the external temperature. So at an external temperature of -3ºC the flow temperature would be 80ºC and with an external temperature of 10ºC the flow temperature might be 46ºC.

Radiant panels require a high temperature to work so would be on a constant temperature circuit.

Other emitters, radiator, UFH etc work well with a variable flow temperature which will reduce the output as the external air temperature increases (higher external temperature the lower the heatloss).

Hope this helps.

 

[migoplumber]

cds is almost right and over complicated.

a ct circuit as said will run at a constant temperature - that of the boiler primaries

the variable temperature circuit is exactly what it says on the tin. the circuit temperature is controlled by a 3 way valve ( can be plumbed to recirculate water in circuit or just send the heated water back to the boiler ) somebody or something controls the setpoint of this water

later on as cds has stated you have compensators and optimisers to change this temperature and is another topic alltogether

 

[oldplumber]

cds is almost right and over complicated.



later on as cds has stated you have compensators and optimisers to change this temperature and is another topic alltogether

Please dont anyone ask, tmi, my little brain cant take this detail, this is for fellows at CIPHE Im only a simple old plumber

 

[hotpants]

why do radiant panels need a high temperature to work?

 

[migoplumber]

havnt heard that one yet, can only imagine youve been told there less effiecent so you have to pump hotter water through them ?

an emitting radiator is just that, some are more effiecent than others, they both take heat from the hot water and convert it to hot air.

you might need a larger radiant panel (single panel) than a double panel with single or double convectors but the heat output of said radiator is only relevant to sizing and MI's stated temperature difference at said levels.

 

[Cds]

migoplumber is correct the variable circuit could be controlled by a number of external factors but in some 30 years in the heating industry I have only ever seen it done with a weather compensation.

You do get constant temperature circuits that are at a lower temperature than the primaries such as with underfloor heating mixing stations but these are still controlled at a constant temperature.