We have a building in our organization to be retrofitted with new chiller, boilers, AHUs, VAVs with reheats added to new multizone AHUs which currently are single zone hot/cold deck AHUs. Zones are created from the single zone AHUs by have duct dampers pass or restrict airflow, acting in reverse or direct mode depending on the temp of the AHU's discharge air.
I sat in on a meeting about the DDC controls aspect of the project. They'll be starting from scratch on the controls in this building, completely replacing a legacy DDC system. Other buildings in our organization have Niagara/legacy or Tracer Summit controls. I'm not involved with most of the Trane controls.
A mechanical engineer has been directed to provide an open, non-proprietary control system specification for the DDC. He is recieving spec writing assistance from a DDC vendor branch rep that has no Niagara, and has LON equipment available, but installs very little LON (all bacnet. except to accomadate Trane Com 5 equipment.) His truck was blue.
When it comes to the VAV controller spec, I asked what was planned. "Bacnet VAVs" were the answer. Having only read the LON/Bacnet controversy threads, I've no actual experience having Bacnet certified products on our systems.
I asked them to look ahead 8 to 10 years from now, to a time when one of the VAV Bacnet controllers has failed, and assume that the original Bacnet VAV controller for some reason can't provide a new Bacnet VAV controller, can we go to another manufacturer and have one other their Bacnet VAV controllers installed on the Bacnet serial com link, have the new VAV controller programmed to take the place of the old failed VAV controller?
I was told by the DDC vendor "I don't know, I'll look in to that". The engineer's response was basically that to keep the VAV's within one network, we'd need to have any replacement VAV controllers be installed by the original supplier of the DDC system.
I said I thought LON VAV controllers of different manufacturer origin could be interchanged on the same network, though possibly some controllers may need proprietary software to get them setup onto the LON network. The engineer was fairly certain that no manufacturer or network type could provide this ability.
Allowing for some miscommunication between myself and the engineer and the DDC vendor, how locked in to the original manufacturer of Bacnet VAV controllers will we be? Can it really be possible that to intermingle different manufacturer's VAV controllers in a building we have to provide separate comm trunk, supervisory controller, head-end software, or even a protocol gateway between the comm trunks?
Secondarily, can we 8-10 years from now replace the supervisory controller and software from different manufacturer without replacing all the field controllers ?