Freezestat Questions Pro/Cons

[theoldman]

You have to be careful when the cooling coil is downstream from the heating coil in the winter even when units are not in freeze. If you have chiller pumps running and a chiller not running and you build heat in the chilled water system because a chilled water valve is also open,or just from pump friction , you can actually build enough heat to blow the rupture disk out of a chiller. I've seen it happen on large centrifugal chillers and it cost a fortune to replace the refrigerant, not to mention the environmental issues with the release.

[n8atk]

If connected to BAS and your chw has proper glycol mixture to prevent freezing coil. Simply close dampers and mod hcv to maintain 15c in the duct.
No BAS you gotta close dampers fail heat open 100% and hope nothing melts.

[CHAMBERS87]

What temp do you recommend not to go over with the above mention issue within the pump CHW System, to avoid the rupture disc from blowing? Thx Bob

[Control Man]

Have lots of units like that in a lot colder enviroment ( - 32'F OA temp the other day )

Heating Valves N O ( Normally open ) Cooling Valves N C ( Normally closed ) on freeze stat trip AHU shuts down OA damper closes ,HEATING valve goes open , Cooling valve goes closed.

[Cphreak]

What I do especially when it is steam heat is on a low limit trip I modulate the heating valve to maintain 45 degf mixed air temp. The heating valves have spring return actuators so on a loss of all control power they fail wide open.

[CHAMBERS87]

What about 100% OA Units? With Steam preheat no reheat. Still recommend just preheat valve to open?

[CHAMBERS87]

What about a) Roof Top Units and b) 100% OA Roof Top Units? With Steam preheat no reheat. Still recommend just preheat valve to open?

[CHAMBERS87]

What temp would it take roughly to blow a rupture disk?