System Diagrams: Moving on from the Roof at the Pacific Energy Center

The past two posts moved away from the “how to develop a system diagram” example I had started, and focused a bit more on some concepts that are applicable to system diagrams in general.  In this post, I want to get back to our Pacific Energy Center example and discuss how you might go about moving forward from where we left off.

As you may or may not recall, our goal was to develop a system diagram for the ice storage system at the Pacific Energy Center, which would physically look like this if you had the super duper X-ray vision I alluded to in the post were I started to discuss this process.

We had arbitrarily selected the roof as our starting point and traced out all of the related piping, ending up with some notes that looked like this …

… which cover the highlighted portion of my version of the system diagram illustrated below.

The question at this point is “what next?”  Like other questions we have encountered in the system diagram discussion, this is another one where there is no particular right or wrong answer.  What matters is that you move forward in some way.

This can be a bit intimidating in a facility that you are unfamiliar with.   How can you possibly find where pipes that disappear into the roof end up, especially if there is no one with you to help point you in the right direction?   My approach to this is to assume that if the pipes disappear into the roof, then they probably re-emerge on the floor or floors below in about the same location.

That leads to a field challenge;  how do you transfer the location on the roof to the same point on the floor below?  That is not too difficult in the paper world of floor plans, and certainly, if you have a set of plans at your disposal, one approach to the problem is to simply look on them and see what they say and then find that location in the physical world you are working in.

Unfortunately (or fortunately if you like challenges and puzzles) we frequently do not have a set of drawings to work with, in the field, especially when we are working with existing buildings or solving a problem “on the fly”.   And, even if we do have a set of drawings, it is not uncommon at all for the piping arrangement they depict to be different from what we are finding in the field due to modifications that were made subsequently to original project or simply because the installers performing the original work found it necessary to use a different piping route and arrangement.

My approach when confronted with this challenge is to use some measuring equipment I carry with me at all times;  my legs, eyes, and my brain.  This technique is one of those things that seems obvious in hindsight, but when I first came up with the approach, it seemed like a real break-through.

Step 1 – Identify a Consistent Point of Reference

Most buildings have vertical elements that can provide a consistent point of reference throughout the facility.  The exterior walls are the obvious ones, but the ones I find particularly useful are elevator shafts, mechanical shafts, skylights and stairwells.

Stair wells are particularly handy because you can pick up an exact floor to floor height from them if you need it.  One way to do that is to literally measure the distance between landings.  But sometimes, the nature of the construction makes that impossible and/or your measuring implement is too short.

For instance, I carry a little wooden pocket tape measure with me that Kathy gave me as gift one time.  (Its from a store called The Real Mother Goose, which is a really fun place if you are ever in Portland or through the airport with some time on your hands).  But its only 6 feet long;  great for small dimensions, figuring out pipe diameters, etc. but a bit cumbersome for measuring long (relative to its length) distances.

So, another way to get an exact floor to floor height at a stairwell when you only have a short measuring device is to measure the rise of the stair and then count the steps.  For a give run of stairs, the rise will be very consistent;  it has to be or we would trip because our brains quickly get used to a regular step as we climb a set of stairs.  The acceptable ergonomic tolerances are fractions of an inch that are actually governed by building codes.

That said, the rise can vary from floor to floor, especially if floor to floor heights vary.  So if you are using this technique, don’t assume that the rise you measured on the stairs from the third to the fourth floor is the same as the rise for the stairs from the basement to the first floor.

For the PEC, there are several skylights and there is an elevator that runs all of the way from the roof to the basement.  There are also several stair shafts that run, in one instance, from the roof to the basement and in the other instance, from the roof to the first floor, adjacent to the elevator.

Since I knew that there was equipment on the 2nd floor as well as in the basement, I chose the elevator shaft as my frame of reference at the PEC since it was relatively close to the AHU and piping I was interested in and because it covered all floors of the facility.

Step 2 – Determine the Length of your Pace

This is the part where your legs come into play.  Once you have identified a vertical frame of reference that you can use, you need to locate the point you know about relative to it.  If you happen to have two people and a hundred foot tape with you, then you can get pretty exact.  But if you are missing one or more of those elements or are under a time crunch, then you can simply pace off the distance.

It turns out that for most people the distance between footsteps when they are walking at a steady speed is pretty consistent.  Mine is typically 32 – 34 inches for instance.  To find out what yours is, revert to your child hood for a few minutes, or go find your grand kids, and stomp around in a puddle.  Then, walk out of the puddle onto dry pavement and measure the distance between your foot prints.

A couple of points to bear in mind when you do this.

  • Dry pavement and puddles often do not occur together, so you may have get out the hose and make your own puddle; just more fun with the grand kids, so not a big problem.
  • I discovered that if I think about what I am doing, it affects my pace;  I think I concentrate on trying to make it consistent or something and throw it off.  So, think about something else when you walk through the puddle and down the sidewalk.
  • For consistent results in terms of distance between footsteps, you need to be walking at a steady pace, not just starting.  So, its probably best to start walking ahead of the puddle to establish a steady gait by the time you get to it and walk through it.

Step 3 – Obtain Coordinates from the Object of Interest to the Frame of Reference

Having established the length of your pace, we can now leave the lofty realms of high technology and return to the practical world of ducts, pipes, and system diagrams and establish our coordinates.

Usually, this involves some “eye-balling” because frequently, you can not get right up to the pipe or duct you are using as a frame of reference.  For instance, at the PEC, all three of the pipes we are interested in go through the roof under the structural steel supporting the air handling unit and chiller.

And, in the case of the PEC, the elevator shaft I was using as a frame of reference was actually inside the portion of the building protruding up above roof level.  So, I needed to establish an approximate location on the outside wall that corresponded to a corner of the elevator shaft.

Once I had done that, to get my coordinates, I “eye-balled” my position relative to the pipes and then paced of a dimension parallel to the elevator shaft until I was in line with my reference point on the exterior wall.  Then, I lined myself up with the pipe in the other direction and also with the door into the building so I could walk through it and right up to the elevator shaft, and paced off the distance.  If I had walked through puddles on the roof, you might have seen something like this.

The elevator shaft is dirty yellow colored cube in case you were wondering.  The dotted red lines are the “eye ball” projections I made from my reference points.

At this point, I could convert the paces into physical distances by multiplying the number of steps times the typical pace distance.  Or, I could simply remember the count and replicate it on other floors.

Step 4 – Apply Your Coordinates on a Different Floor

Having established an approximate location on the roof, you can now transfer it to a different location by going there and working backwards from your frame of reference.  If the floor plan at your new location is open, then you probably can pace each dimension off in one fell swoop.

Frequently, this is not the case as there may be walls or partitions or furniture between you and where you are headed.   My approach to dealing with that is to pace up to the object that is in the way, move over until there is a clear path in front of me again, being careful to keep in line with the point where I stopped pacing, and continue pacing.

You may have to do this once or twice in a congested area, and this can throw your measurements off a bit, but this is not an exact science anyway, and if you are careful in your offsets and eye-ball alignments, you will get close to where you want to be.

When I applied this technique at the PEC on the 2nd floor, and looked up, here is what I saw.

Darn the luck;  no pipes, at least not any going through the roof.  But, bear in mind, this is not an exact science what with all the eye-balling, pacing and offsetting to get around obstacles.  (I actually ended up a bit to the left of where I took this picture; sort of under the space between the two plywood platforms.  But a picture taken from that exact vantage point did not illustrate what I wanted to talk about very well, so I moved a bit.)

What I did notice were two things.  One was that there was a small line running horizontally from the wall with the cupboards on it that turned and then went through the other wall above the door;  you can see it towards the center of the picture between the two yellow ducts.  Since one of the lines I was following was smaller than the others, and since one of the pieces of equipment that the ice storage system served was in the room behind the door, my suspicions were aroused.

The other thing that I notices was that the cupboards seemed to have a gap between them and the wall they were recessed in;  notice the vertical black line to the right of the cupboards.  Upon closer examination, I discovered that there were wheels under them.  In fact, the entire book case that you see in the picture below – the one with the boxes of drawings on it – was on rollers.

So, I had found a hidden door with a clue in the form of a suspicious pipe leading into it, kind of like those Hardy Boys books I read when I was a kid. (I told you this could be fun, right?)

When I pushed the moving book case aside I found a storage area and when I looked up, I found my pipes.

The smaller pipe is towards the top of the picture and heads out through the wall into the room that the other picture was taken in.  The large pipe turns and heads to the same area that the smaller line does after it turns in  the other room.  The 2nd larger pipe is above the duct and you can’t see it from this camera angle.  But its there and runs in parallel with the other large line.

So, I poked my head into the room behind the not so hidden door and here is what I saw.

The two larger lines simply passed through the room and disappeared again.  The smaller line headed across the room and dropped to serve the air handling unit that was located there.

Then a second smaller line came back from the unit and disappeared through the wall below the larger lines.

Having found another load on the system, I took a few minutes to make a sketch of that piping using techniques similar to the ones I discussed for the effort on the roof.

Note that the reference points match up to points in the first sketch, which shows up at the beginning of the post.

Step 5 – Re-apply Your Coordinates at Other Building Locations

At the PEC, I knew there was equipment only on the roof, the 2nd floor, and the basement.  But if I hadn’t, I would have used my coordinate technique on each floor to locate the mains, and see if there were any loads associated with them as they passed through that location.

Given my knowledge of the PEC, after sketching up the piping on the 2nd floor, I proceeded directly to the elevator and made my way to the basement.  When I got off, and paced off my coordinates, I ended up with a view that looked about like this.

I say “about like this” because where I actually ended up was a bit to the left of where I was standing when I took the picture.  I moved a bit so that the picture would show the the two lines coming through the ceiling from the floor above.  They are in the upper left hand corner of the picture.  These are the two large lines we have been following through the building from the roof.

The fact that my pacing strategy did not put me closer to the lines coming through the ceiling could be due to inaccurate technique;  miss-counting paces, loosing count when I shifted around an obstacle, inaccurate “eye-balling” reference points, etc.   But being this far off (probably 5 to 10 feet in each direction) could mean there was an offset someplace that I had not found.  More on that later.

Having found the lines in the basement, along with the pumps and ice tanks that are major elements in the system, I proceeded to take more notes using the techniques we have been discussing.  Here they are along with a few pictures of the equipment to give you a feel for what I was seeing.  I took the pictures at the time as a memory jogger and as a way to quickly document details that I could add later on when I developed my system diagram final draft.

Here is a view of the pumps as seen from behind;  sort of directly opposite from where I took the first picture, looking back towards the location I took it from.

Here is a picture of the piping around the ice storage tanks, which are behind the pumps.  The silver “thing” in the mid and lower right side of the picture above is one of the tanks.

I tossed this picture in to illustrate the “elbows don’t matter much in system diagrams” concept I discussed previously.

Clearly, there are a bunch of elbows in the piping in this area.  And while they were necessary to get everything to fit in the physical space and undoubtedly impact the pump energy required to move water, or in this case, glycol through the system, from an operational standpoint, they don’t have much potential to cause a problem so my system diagram does not include them.

Filling in the Gaps and Checking Out the Offset On the First Floor

After finishing my sketch in the basement, I went back to the first floor to see if I could find the offset.  What I knew at this point was that on the 2nd floor, 1 small line and two larger lines disappeared into a wall, which I suspected contained a mechanical shaft on the other side.

I suspected this partly because in general terms, its a reasonable expectation given that I knew the pipes needed to get to a lower level.  Plus, I had looked at a set of architectural and mechanical drawings and they both showed a shaft in that area.  But, as if often the case, the actual pipe route was very different from the generalized route shown on the mechanical drawings.

Since I knew that one of the larger lines ended up going back to the return side of the evaporator on the roof, and since I knew that the smaller line going into the shaft was the return line from the AHU in the mechanical room on the 2nd floor, I also suspected that the small line connected to the larger return line in the shaft on the other side of the wall.  The fact that the smaller line penetrated the wall directly below the larger line that was labeled as the return tended to support that conclusion (you can see what I mean if you look closely at the previous pictures of the piping in the 2nd floor mechanical room).

I should mention at this point that you need to take labels on pipes and equipment with a “grain of salt”;  more than once, I have found them to be wrong.  But in this case, I could see the physical arrangement of the lines where they came through the roof and it correlated with the arrangement at roof level, which also correlated with the labeling.

I mention all of these details because short of cutting a hole in the shaft, I physically could not see the connection and thus, was making an assumption.  Its a pretty good assumption backed up by a lot of facts.  But it still an assumption and its important to not loose sight of that.

There have been occasions where I’ve made an assumption like this, and, based on other measurements and tests, concluded that there was something wrong with it and cut a hole in the shaft wall, opened up a pipe or duct, or took some other fairly radical step which ultimately revealed the assumption was not correct and also resolved the mystery I was investigating. But, cutting holes in fire rated walls or welded pipe should be a measure of last resort.  If the evidence suggests that the assumptions you are making are reasonable, as is the case here, then it’s probably best to wait on destructive observation and testing techniques.

One of the best examples of going to implementing a measure of last resort because things were not adding up happened to Bill Coad, one of my mentors.  Bill was troubleshooting an intermittent loss of flow problem and became convinced that there was an obstruction between an elbow and a reducer in a welded piping system.  So, he had the contractor cut the pipe open, a request that was not greeted with enthusiasm I might add.

But when they opened up the pipe, they found a beer can that was trapped between the elbow and reducer.  And since it could float and move around with the flow, it acted like a check valve and stopped flow if the flow carried it towards the reducer and allowed flow if the flow carried it towards an elbow. But the dimensions of the can and the elbow were such that the flow could not carry the can past the elbow.  So it spent its days floating back and forth between the two fittings.   That was one project where the elbow and the reducer that one would normally not show on a system diagram turned out to be quite significant.

All of this is to say that when I went to the first floor, I went looking for the two larger lines and expected them to show up fairly close to my paced off coordinates, but maybe shifted a bit in one direction due to the offset I had observed on the 2nd floor, a shift I might add that was away from where I expected to find them them coming through the ceiling in the basement.   After “eye-balling” my way around the first floor a bit, I found myself in a storage area behind the kitchen and found the offset I was looking for.

The two smaller lines are the heating hot water system serving reheat coils through out the facility.  The larger lines are the lines we have been following, which exit the shaft we saw them enter on the 2nd floor in the mechanical room …

… and offset through the storage area and disappear again into the wall that was, near as I could tell, directly over the pumps and tanks in the basement.  Thus, I felt satisfied that I had see all there was to see of the system and had the information I needed to make the first draft of my system diagram.

I actually made a sketch of what I thought that would look like while I was standing out in the field in a blank spot on the 2nd page of my notes.

I did that partly so I could begin using the diagram right away and partly to make sure things made sense when you put them together and I had everything I needed.  It’s a lot easier to walk back up to the roof to verify something when you are at the site versus at home, especially if home is about 800 miles north.

When I made it back home, I made my first draft of the diagram, which showed the major elements in the system and their general arrangement.

As you can see, this diagram has much less detail than the final draft I have been using through out this string of posts (there’s a copy of it at the beginning of this post and you can download it and the other diagrams from the public folder on my Picasa web account).  But this first draft was good enough to get started and was a useful tool as we began our effort to test and optimize the system.

I’ll walk through the process I used to get from the first draft to the detailed draft in a future post.  But first, I an going to devote a few posts to applying the concepts we have been discussing to an air handling system.  The general idea is the same, but there are some nuances associated with air handling systems that make developing a system diagram for them a bit different from the way I go about developing a diagram for a piping system.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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