We come across the words UPSTREAM and DOWNSTREAM in the HVAC ductwork, pipework, and other flow process systems.
These words are used to define the location of nearby equipment /inline items with respect to some reference point.
Sometimes we got confused about which one was on the UPSTREAM side and which one was DOWNSTREAM.
Let us understand the terminology through the below explanations and supporting pictures.
To define the location (UPSTREAM or DOWNSTREAM), we should know the FLOW DIRECTION and the REFERENCE POINT.
In the below example, three line items (cooling coil, heating coil, and shut-off damper) and a reference point-A have been considered. However, this can be explained or understood by considering a reference point-A and only one line item or one equipment.
1) Downstream:
In this, the inline items (cooling coil, heating coil, and shut-off damper) are located after Reference Point-A, along the flow direction. In simple words, we can say that, firstly the flow crosses the Reference Point-A and then it crosses the inline items.
Note that the flow direction is from left to right.
2) Upstream:
In this, the inline items (cooling coil, heating coil, and shut-off damper) are located before the reference point-A, along the flow direction.
In simple words, we can say that, firstly the flow crosses the inline items and then it crosses the Reference Point-A.
Note that the flow direction is from right to left.
