Interlocking 2 BARD units

[Sn00ze]

Hello everyone,

Our HVAC supplier is providing 2 HVAC units (BARD W36AA) 240V 15KW heating with one being 100% redundant. hey ome with a TEC40 controller which alternates teh units every 200hrs.

The problem is that this controller may activate both units if temperature falls below design temp.

What i need is some way to intelock both units so that only one is runnign at any given time. otherwise i will ahve to size up my TX srvice for jsut this unecessary load.


any suggestions?

 

[itsmoked]

There are contactors to run each heater. Add an auxiliary N.C. contact onto each contactor that "conditions" the coil on the other contactor. With that installed the first contactor to close will prevent the other contactor from ever closing.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Sn00ze]

Hi itsmoked,

Thanks for replying. That works in interlocking but i forgot to mention i also want it to work incase of a fault of the first unit. Will this work if the otehr unit can't heat the building??

 

[lukaiENG]

can you just use offset set points?

 

[Sn00ze]

Hi LukaiENG,

I believe this is the way the Tec40 controller works (Lead/Lag). The problem is (or is it a problem?) that if for some reason the first unit can't keep up, it will eventually kick in the second unit so there is a chance that both will work concurrently.

At the same token, i am against disabling this feature as it could save the building from potentially freezing if the first unit 1)cant keep up. 2) is malfunctioning.


Thus the conundrum.

My current train of thought is that for
1) that possibility is small.
2) this will happen during extreme cold circumstances so the service transformer could potentially run hotter than usual? not that this is a good thing.

weighing in my options right now.

 

[itsmoked]

I'm sensitive to that right now as one of our private rail cars just lost power up by the great lakes. One night of that caused probably $60k in freeze damage!

Seems you want your cake and to eat it too.

You want to limit to one heater to prevent the need of up-sizing the service but then you want both to be able to operate if one can't keep the place above freezing. No question, you should up the service. It gets you the redundancy AND the capacity.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[lukaiENG]

I agree with Keith. alternately you could add staging/SCR control to the heaters. That way at least they will stage back if both are running.
I don't know if this is a thing with Bard units, I would hope it's an option

 

[itsmoked]

I could see the customer coming back at you for damages if you limited the heat available to something less than enough.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Sn00ze]

hi guys,

itsmoked - wow! way off. Sorry for the misunderstanding.

Each unit is sized to heat the whole building. The other one is 100% redundant but because the controller does not function this way. it only alternates them very 200hrs and leads/lags. so i am told that there is a possibility that it may turn both of them on at the same time during extreme conditions. I dont suppose this will be for longer than 15 mins, because, again. Each unit is sized to supply the whole of the heating need.

 

[itsmoked]

Ah okay.

A couple of things:

Why every 200 hours? I'd want them to directly alternate every cycle. That reduces weird smells. Set the change period to 1 day.

I'd call them and ask how to handle if one heater element dies.

I suspect the only available option is the staged control method where if one unit can not maintain setpoint the second unit is called ON. In the case that one unit's heater fails - temp won't be maintained and the second unit will be called ON. Of course since it's the only unit heating it will continue to run and the facility may end up a degree or two lower but not pipe breaking cold.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Sn00ze]

Thanks itsmoked.

The 200 hours is the settings the HVAC company is settings but i will request to make it a day. While im at it i will ask about the heater elements.

So far i've told them to leave the Tec40 as it is.

Yeah i suspect the cycle will run longer to try and maintain the set point/.