Low temp manual reset freezestat 2

[vmarho]

I am on a job where the control engineer requires manual reset freeze-stats on an ahu that has glycol in both heating and cooling systems.Initially standard freeze-stats were purchased with range of approx 15 to 60 deg with factory stop at 35 deg.The AHU is very large (24 supply "fan wall" fans and 16 return "fan wall" fans),and very minimal area in mixing section to prevent stratification of very large outside air intakes.
He has since decided standard freeze-stats would cause frequent trips and now says he wants manual reset devices that can be set to 0 to 10 deg. also need 20 ft. cap tubes as we have 4 - 100 square ft coil sections to protect, each 20 ft long, so 1-20 ft cap tube makes it across 1 time. We need 12 freeze-stats of his specs.
He said he doesn't know where to get these, and we are faced with a deadline of 1 week to complete ahu control installation, and my engineer / boss says i'm to procure this device?????
I am not a new comer to this industry.Worked for Honeywell
20 yrs.
I have searched far and wide , and have come to conclusion the specified device is nothing that is availible.
Came close with Emerson Climate Controls custom configurable, but they say can't do.
Any help from any forum , or a general consenus of issue would be greatly appreciated.
VMarho

 

[DRWeig]

Think you can fool him with a Celsius scale? It'll read -10 to +15C instead of +15 to 60F...

Seriously, I don't believe there's any such thing as a manual-reset device all in one package for your application. As an old Honeywell dude, you should be familiar with the T6031 series. One of those comes with a range you can use and a 20-foot capillary, and there are equivalents from JCI and a couple others. You'll just have to add a latching relay into your control logic to make it happen in manual-reset fashion.

Or maybe one of our other friends out there knows something we don't!

Good on ya,

Goober Dave

 

[ChasBean1]

These look like the freezestats I've seen everywhere. Looks like 20' is standard. Did I miss something?

http://www.southsidecontrol.com/aca...ell_L480B1239_Freeze_Stat_L480B1239_2610.html

 

[DrRTU]

ChasBean, The problem 0-10 deg F. The common JC and Honeywell units are designed for 35 deg F (the unit may read to a lower level but cannot adjust lower than 35). I believe the only way to do this low temp. requirement, is to use numerous bulb controllers w/latching relay in series as DRWeig pointed out or use an average sensor(s) and a controller(s) with the logic in the controller. A DI could be used as the local manual reset.

http://www.kele.com/Temperature-Sensors-and-Transmitters/Thermistors/ACI-Series.aspx

The key is how to lace the average sensor to pickup low entering air temp in a zone to protect the coil bank.

 

[vmarho]

Thanks to all for replies,
Our company, in this instance,is the control device provider and installer.The engineer requesting this requirement is in charge of the control system design and programming.
You have confirmed that the exact device specified is not a standard, readily available control, as I pretty much knew, but I wanted to see if there was a control to meet the exact spec out there somewhere.
Thanks again for the replys.
VMarho

 

[ChasBean1]

So I did miss something. I focused more on the 20' cap tube than the very low temp range. With glycol protected systems, chilled water disabled in the winter, why not go with a low temperature trip device in the discharge section of the AHU instead of the typical between-the-coils location? DAT set point will be 55-65; monitor a one-point location (no averaging sensor required) and trip at 40°F in the discharge duct downstream of the fan...

 

[danw2]

You might find an industrial temperature switch that could be custom made to those requirements.

Check out a United Electric E100 or F100 temperature switches (pg 9), available as capillary and bulb assemblies; with option 1530 for external manual reset (pg 10);

data sheet at

http://www.ueonline.com/bulletins/100-b.pdf

Whether the factory can put one together in the time frame is an open question.

Dan