Hydronic heating systems control

[marko333]

Hello,

I understand that with 'low pressure hot water' (hydronic) heating systems fed from water heaters (boilers) it is not good practice to have a mixture of forced draft fan convectors (i.e. heating coil with fan- as per Dunham Bush units) on the same piping circuit as flat panel radiators (as per Stelrad models). I seem to recall that as there water to air output ratios are not the same, different circuits are required in order to achieve the best control. It is my understating that these are best served from the constant temperature circuit of the system and control is by regulating the fan only.
Can anyone confirm this?

 

[friartuck]

A few years ago I would have agreed, but now there are a number of options.

a. You can now get fcus that operate at lower flow and return temps (I think Dunhams do one)
b. You can design yout controls to have a minimum flow temp ...say 60 degrees so the low outlet temps are not a problem.
c. You can fit LTC low temp cut outs to the fcus anyway so that at low flow temps they cut out and stop the drafty fcu problem.

The output of the fcu's and rads vary to diffrent powers.

Rads very output at a power of 1.3 to 1.35

natural convectors to the power of 1.5

and fcus to the power of 1.0

if i could figure out how to put equations onto this screen i would

(Anybody help with that??)



Friar Tuck of Sherwood

 

[imok2]

Fan coil units are available in a number of different styles to suit any design layout. Water systems are generally called hydronic and use a network of pipes to deliver water to hot water radiators, radiant pipes set
in floors or fan coil cabinets which can give both heating and cooling.
Boilers produce hot water or steam; chillers produce chilled water for use with fan coil units. Thermostats control the temperature by zone valves for
radiators and radiant floors. Fan coil units have individual controls.
Take a look here:

http://www.lonmark.org/products/datasheets/sbt_FNC18.pdf