pneumatic control strategy

[airdata870]

hey guys, i'm looking for some help.i have two conference rooms next to one another on a perimeter wall,there is one hot water baseboard zone for both rooms with a 3 to 8# n.o. valve. each room will have a bypass vav n.c. with 8 to 13# actuator and a h.w. coil 3 to 8 # with a direct acting stat.my question is controling the heating.any sugestions? thanks

[crab master]

Is the baseboard hot water circuit and the reheat hot water circuit the same or are they controlled separately? IE can you reset the whole baseboard circuit at a different rate than the reheat circuit?

Also is the PSI ratings the stamped ratings or the measured values?

[tlp261]

You can use a higher of two pressures relay, with the two inputs being the thermostat branch lines, and use the output to control the baseboard valve. That way if either room does not need heat, particularly if only one of the two rooms is in use, the baseboard will close. The colder room will still get heat from its reheat.

Or use a lower of two pressures relay, so both rooms have to be satisfied before the baseboard will shut off. This scheme is more likely to cause overheating in the hotter zone.

Finally you can use an averaging relay so the baseboard will be controlled by ther average output of the two zone thermostats.

I'd suggest the first scheme as best for conference rooms where one mighht be occupied and the other not.

[airdata870]

Is the baseboard hot water circuit and the reheat hot water circuit the same or are they controlled separately? IE can you reset the whole baseboard circuit at a different rate than the reheat circuit?

Also is the PSI ratings the stamped ratings or the measured values?

crab master thanks for the reply,i do not know if the baseboardand reheat are on the same loop or not.i will find out.the PSI info are stamped ratings,barber coleman valves w/yellow springs.honeywell tp970a stats,kmc actuators mcp-8xxx series

[airdata870]

You can use a higher of two pressures relay, with the two inputs being the thermostat branch lines, and use the output to control the baseboard valve. That way if either room does not need heat, particularly if only one of the two rooms is in use, the baseboard will close. The colder room will still get heat from its reheat.

Or use a lower of two pressures relay, so both rooms have to be satisfied before the baseboard will shut off. This scheme is more likely to cause overheating in the hotter zone.

Finally you can use an averaging relay so the baseboard will be controlled by ther average output of the two zone thermostats.

I'd suggest the first scheme as best for conference rooms where one mighht be occupied and the other not.

tlp261 thanks for the reply, that is exactly what i was looking at,using the honeywell rp470a/b but was not sure which would control better,have you used any of these senerios before?thanks

[Control Man]

The YELLOW Barber Colman springs are 3 - 7 range

[airdata870]

The YELLOW Barber Colman springs are 3 - 7 range

thank you control man,you are correct, my mistake:D

[flange]

Ummm, the baseboardif on the same wall should really only be used for warmup, and extreme cold as a curtain wall. In most cases one stat should suffice.

[alex8863]

hey guys, i'm looking for some help.i have two conference rooms next to one another on a perimeter wall,there is one hot water baseboard zone for both rooms with a 3 to 8# n.o. valve. each room will have a bypass vav n.c. with 8 to 13# actuator and a h.w. coil 3 to 8 # with a direct acting stat.my question is controling the heating.any sugestions? thanks

How is the VAV going to open below 8#, to allow minimum air for the reheat coil?
Does it have a stopper for minimum position or a velocity controller?

[airdata870]

How is the VAV going to open below 8#, to allow minimum air for the reheat coil?
Does it have a stopper for minimum position?

yes they stops,no controller, they are bypass vav's pressure dependent ,engineer spec'd 30% min