u/Conscious_Break8269

I’m an HVAC designer working on a retrofit where we’re replacing constant speed pumps (with a bypass valve) with sensorless pumps.

Right now, the DP sensor is located right across the pump, not out in the system (like the usual 2/3 longest run location).

From the pump selection, the minimum control head is about 40% of design — so in my case ~16 ft out of 40 ft.

I’m trying to figure out what kind of control logic people typically use for the bypass valve in this situation. Especially since the DP sensor isn’t in the system.

My thinking was:

• Keep bypass valve closed during normal operation
• Once pump hits minimum speed / minimum controllable head
• If DP starts rising (low flow condition), start opening bypass
• Basically use it as a protection to avoid overpressure / no-flow

Is this how it’s usually done? Or is there a more standard approach for this setup?

I’m an HVAC designer working on a retrofit where we’re replacing constant speed pumps (with a bypass valve) with sensorless pumps.

Right now, the DP sensor is located right across the pump, not out in the system (like the usual 2/3 longest run location).

From the pump selection, the minimum control head is about 40% of design — so in my case ~16 ft out of 40 ft.

I’m trying to figure out what kind of control logic people typically use for the bypass valve in this situation. Especially since the DP sensor isn’t in the system.

My thinking was:

• Keep bypass valve closed during normal operation
• Once pump hits minimum speed / minimum controllable head
• If DP starts rising (low flow condition), start opening bypass
• Basically use it as a protection to avoid overpressure / no-flow

Is this how it’s usually done? Or is there a more standard approach for this setup?

I switched to HVAC design 6 months ago. However, at my current job I am just following up only instructions on drafting as most of stuff from schools and institutional buildings, like renovating washrooms, rtu replacements with on same curb etc. I am just wondering, is there any platform from which I can get freelance or internship work? I want to upgrade my skills to do understand calcs more and able to do more task.

Hi Guys,

I am working as MEP engineer, however I used to work for combustion process company. My previous company has sister company which work on building automation. I got some training on how to program building automation controller - only reliable controller. While programming we used to put setpoint as AV and occupied status as BV. However, at my current most people getting hard time to understand controls and I was through with most of task. They told me they getting hard time to integrate bacnet controller from Engineered air controller. Long short story I was given task to see if we can integrate some of these controller with Trane bacnet. I never done integration but while reading manual for points it seems like that most of r/W points are AO and BO even occupancy, setpoint? Is it because to write these we need to do with priority array. When I got training from reliable they did talk about bacnet priority for outputs. Just wondering a reason for that and is this give hard time to integrate these controllers? Also, how it possible to make AV as AO without hard points?

Thanks in advance,