Separate feeder for DOAS's Heating and Motor equipment

[Salvador Santos]

Good day!

In our approved design drawings, the electrical design is calling for separate feeder for DOAS (Dedicated Outdoor Air System) unit. The DOAS unit will be powered by two electrical panels, one providing for the DOAS electric heater and the other one will be powering the DOAS fan motor.

In my experience, DOAS units always comes with a control panel and that is the only part that you need to feed since it will be the control panel's job to run the whole system. Our Electrical system is 400V/3ph/50Hz, our DOAS supplier is providng the DOAS unit with a Control Panel, rated 400V/3ph/50Hz, that will handle all the powering of the electric heaters, fan motors, VFD and other components that makes up the DOAS. Our DOAS supplier does not agree with our approved designs.

I want to ask if it is accepted by the code to have a separate feed for a single DOAS unit? I tried checking art. 430 and 440 but did not get a clear understanding if a separate feed is allowed. Could someone also provide some link DOASs that has separate power provisions.

Thank you

 

[Fitzdrew516]

Good day!

In our approved design drawings, the electrical design is calling for separate feeder for DOAS (Dedicated Outdoor Air System) unit. The DOAS unit will be powered by two electrical panels, one providing for the DOAS electric heater and the other one will be powering the DOAS fan motor.

In my experience, DOAS units always comes with a control panel and that is the only part that you need to feed since it will be the control panel's job to run the whole system. Our Electrical system is 400V/3ph/50Hz, our DOAS supplier is providng the DOAS unit with a Control Panel, rated 400V/3ph/50Hz, that will handle all the powering of the electric heaters, fan motors, VFD and other components that makes up the DOAS. Our DOAS supplier does not agree with our approved designs.

I want to ask if it is accepted by the code to have a separate feed for a single DOAS unit? I tried checking art. 430 and 440 but did not get a clear understanding if a separate feed is allowed. Could someone also provide some link DOASs that has separate power provisions.

Thank you

I'm still somewhat unsure what the exact question is. I would install it as the manufacturer has told you, but it seems as if an RFI to the engineer is in order here. Did you get a returned submittal on this equipment and if so what were the mark ups or the response?

 

[jeremy.zinkofsky]

Good day!

In our approved design drawings, the electrical design is calling for separate feeder for DOAS (Dedicated Outdoor Air System) unit. The DOAS unit will be powered by two electrical panels, one providing for the DOAS electric heater and the other one will be powering the DOAS fan motor.

In my experience, DOAS units always comes with a control panel and that is the only part that you need to feed since it will be the control panel's job to run the whole system. Our Electrical system is 400V/3ph/50Hz, our DOAS supplier is providng the DOAS unit with a Control Panel, rated 400V/3ph/50Hz, that will handle all the powering of the electric heaters, fan motors, VFD and other components that makes up the DOAS. Our DOAS supplier does not agree with our approved designs.

I want to ask if it is accepted by the code to have a separate feed for a single DOAS unit? I tried checking art. 430 and 440 but did not get a clear understanding if a separate feed is allowed. Could someone also provide some link DOASs that has separate power provisions.

Thank you

The code does not specify a standard way of powering mechanical equipment. Each type of equipment is different, there are split systems that require a single feed and systems that require two seperate feeds. Both are used frequently. It is the engineer's job to make sure that the right equipment was selected not the supplier. As was previously stated, an RFI is warranted here.

 

[Jraef]

Besides that, I doubt there are many people in this forum familiar with whatever codes exist in Bahrain...
This seems to be something that a local engineer familiar with the Bahranian Electrical Code should be consulted on.

 

[Salvador Santos]

Fitzdrew516/jeremy.zinkofsky/Jraef,

Thanks for the responses.

Apologies for the confusion. To make it clear, this is a US Navy project and our main Client is USACE. I'm the QC Electrical Engineer here and our project requirement and the design needs to conform to NEC 2011. In the 95% Design, the DOAS manufacturer have submitted their product and was approved with a single feed requirement, just a power provision to the DOAS control panel. When the 100% Design came out, the Panel schedules showed separate power provision for the DOAS equipment just like I said earlier. I want to know where is our Designer coming from since they were also the one who approved the submittal but did not comment that it must have a separate feed for the DOAS heater and the DOAS fan motors. We have sent an RFI and our designer is now insisting that the control panel must be modified to have a supplementary feeder for the DOAS heater without disclosing the actual basis of the requirement. The DOAS Manufacturer started the fabrication when the submittal got approved and now, the Manufacturer is in a dilemma since they are not sure why they must separate the feeds.

 

[Jraef]

OK, got it. There is nothing in the Code stating that you must, or must not, separate the feeds, but if you have one feeder, there are possible issues (see below). The closest you will get to anything will be the generality that says, "As per manufacturer's instructions." So given the flip flop in your situation, guidance is difficult. Your designer made a change between the 95% and 100% stages, but to be quite honest, the 100% design is the one that counts, that's why you call the other one "95%", meaning, it's not complete yet. As to why the designer made that change, you would have to ask him (her).

Now, IF the original control panel was not designed for a single feed, meaning a main breaker for that feed, then branch breakers down stream for the individual loads, then that might be the reason. It could be, given the 400V 50Hz indicating a non-US based supplier, that the OEM control panel design met some IEC regulation, but would not meet NEC requirements. So the designer was forced to change the feeder situation. That's purely speculation on my part, I'm just postulating a possible scenario.

 

[jeremy.zinkofsky]

Fitzdrew516/jeremy.zinkofsky/Jraef,

Thanks for the responses.

Apologies for the confusion. To make it clear, this is a US Navy project and our main Client is USACE. I'm the QC Electrical Engineer here and our project requirement and the design needs to conform to NEC 2011. In the 95% Design, the DOAS manufacturer have submitted their product and was approved with a single feed requirement, just a power provision to the DOAS control panel. When the 100% Design came out, the Panel schedules showed separate power provision for the DOAS equipment just like I said earlier. I want to know where is our Designer coming from since they were also the one who approved the submittal but did not comment that it must have a separate feed for the DOAS heater and the DOAS fan motors. We have sent an RFI and our designer is now insisting that the control panel must be modified to have a supplementary feeder for the DOAS heater without disclosing the actual basis of the requirement. The DOAS Manufacturer started the fabrication when the submittal got approved and now, the Manufacturer is in a dilemma since they are not sure why they must separate the feeds.

So, if the original submittal was approved by the design engineer then he is on the hook for any changes or discrepancies. If he is changing the power requirement for the DOAS system then his engneering firm has to credit back the manufacturer and contractor for any work that has been done and also pay for any additional work. Sounds like the design engineer doesn't quite understand what he's designing here and you should comment on the discrepancy in your Quality Review. Bring attention to the conflicting information and put the ball in the design engineers court, that's all you can really do.

 

[Salvador Santos]

Jraef/jeremy.zinkofsky,

Thank you for the guidance :thumbsup:.

The previous RFI did not really got in to the chronological sequence of the approval of the submittal. We simply asked why the change.

Now my plan is to generate an RFI with bullet points on the time sequence when the submittal got approved and ask the Designers the clear issue on what caused the changes to see how can we move forward with less cost and time delay.

Again, my thanks,
Salvador

 

[Jraef]

Sounds like a good plan.