dP Sensor Location & PICV's

[nuuvox000]

Is there anything wrong with locating the dP sensor in a hydronic heating/cooling system at the very farthest fan coil in the system when all of the fan coils have PICV's? As I understand it , the 2/3 rule of thumb was to prevent the coils closest to the pumps from having too much flow but with PICV's they never will have too much flow. Seems like if everything is on a PICV, then the farthest point makes sense. Am I missing anything? Thanks!

 

[GT-EGR]

The 2/3 rule always seemed like a vague way for someone to easily call out a sensor spot without putting too much thought into it, mostly because it can be complex in theory but then you can install it in different spots and still get it to work out.

The PICV will handle the over pressure issues, but you’d still be wasting pump energy. 2/3 location to me means - put it somewhat remote in the system so you see the real impact of pump speed change including some main losses - but don’t put it so far that you are in small piping much more susceptible to pressure jumps from small changes in flow.

Also if you have the capability of monitoring valve position and then resetting DP to keep the worst case one 95% open, then the DP location is moot and really just becomes a reference point. If you are using this I tend to place it early on in the system in easily accessible serviceable location (that you can find), or in the main with the most connected valves which gives me the most helpful information to troubleshoot with.

 

[HVAC-Novice]

If you use static pressure reset, which GT-EGR is describing, location doesn't matter

I put them around the pump to have high pressures to measure. Those sensors are 100 psi or so sensors. So at 5% accuracy you have 5psi +/-. So it is really hard to measure low pressures accurately.

With static pressure reset it is somewhat self healing and sensor accuracy matters less. But still, measuring larger pressures works better.