This is what I was thinking. Your HHW Valve should be starting to open. No way you want to send 33 F air to the space, unless this is process cooling and if it is, then it wasn't designed correctly.
Originally Posted by chillerout1
True but you never know
Originally Posted by Trane Tech NYC
Originally Posted by bdivell
I'm surprised it doesn't have an OA low limit on it?
One other thing I was just sitting here thinking about..... Is the zone sensor/thermostat in question in a good spot? Away from coffee pots, copiers, printers, space heaters, etc? Not dealing with a false load here are we?
Originally Posted by access_max
1) Yes - Modulate the OAD's slowly to maintain a MAT above freeze stat trip level.
No - go to 2
2) Yes - Close OAD's and open CHWvlv to cool the area.
No - CHW system is locked out on OAT stat. See #3
3) install stand along supplemental cooling in problem zone.
Life is too short, Behappy!
That's essentially what I did, I set the stpt of the MAT to 45 and controls is backing off of OA before the freeze trips, essentially maintaining 45 SA. And unit works great. Thx for all who helped.
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Sounds if possibly the space's cooling load has outgrown the ability of the unit to handle it as installed. Do either the heating or cooling loops contain antifreeze? If so to what protection?
If you do the math and maximum outside air will handle the cooling load of the space then you'd need to find a way to eliminate the need to have freeze protection. 1) Isolate the coil(s) with their own HE, pump and antifreeze circuit. 2) Add additional means to cool the room that doesn't move air past the coils. 3) Possibly a bypass around the coils triggered by the freeze stat 1st stage with the 2nd stage shutting the unit down to protect the coils as is now the case.
If the building has use for the excess heat, maybe a sales pitch could be to "move" it somewhere it's needed. Making an expensive job look as green as possible sometimes shakes loose money that otherwise isn't available. Sell it as FREE heat.
Posted between your figuring a way to make it work. Congrats!
Last edited by firecontrol; 01-31-2013 at 02:17 PM.
Reason: Slow typer
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.
You will have to control it by mixed air temp., ensuring that the mixed air sensor is not situated close to the heating coil (if it has one). Also, you will have to make your minimum 0% when economizing because even at 5-10% it can be too much cold air to keep it above freezing.
Typically a preheat coil will be used to prevent the the cooling coil from freezing in cold weather
Mixed air setting could be the problem. Check and reset above 500F
most of the hi rise Manhattan buildings are running a mixed air temp before the filters if your trying to control from a space sensor that is why your tripping the FS.you should be "mixing" return and OA to make a 55F discharge air into the space..return dampers should be 100% opposite the OA in action.