Condenser Water Systems, Air Entrainment, and Pump Cavitation

This post is the result of a discussion I was having as the result of a comment made on a previous post about commissioning a condenser water system.  The initial question was to ask if the solution I had suggested to the problem that was the focus of the post – basically air venting problem – had worked.  The answer to that is “yes”.   The manual air vents were replaced with automatic air vents and, to the best of my knowledge the problem was resolved.


You can find some more details and close-up photos of the air vents in my reply comment in the original post if you are interested.

The person I was corresponding with thanked me and mentioned that they thought they had a similar issue in a system they were working with and that one of the symptoms was that there was a crackling noise in the pump suction when it was running at full speed/design conditions.  I started to reply because there are a number of things that can cause a noise like they were describing.  But as the reply grew in length, I realized it would probably make a good blog post or two. touching on a number of condenser water system topics, so here we are.

The links below will take you to the various topics that I ended up discussing.  The end of each section has a “Back to Contents” link that will bring you back here.

Air Entrainment

Air can definitely cause a noise like the one that was described in the comment. Condenser water pumps that are located very close to the tower they serve are particularly prone to this if the tower outlet is undersized or the flow rate is higher than the tower is designed to accommodate because a vortex forms in the tower basin at the suction connection and entrains air into the piping leading to the pump.

This exciting video clip is one I recently shot that shows a vortex starting to form at the connection to a sump in a cooling tower.

Back to Contents


Having said all of that, sometimes a crackling or banging sound on the suction side of a pump is cavitation, which is related to the velocity at the inlet of the pump and occurs because of the reduction in static pressure associated with the increase in velocity that occurs as the water accelerates into the eye of the impeller.

In general terms, the conversion of static pressure to velocity pressure that occurs as the water accelerates through the smaller cross-sectional area (relative to the pipe) of the pump impeller eye and impeller channels can cause the static pressure at those locations to approach and drop below the vapor pressure of the fluid that is being pumped.  The is especially true for condenser water systems where the pumps are only slightly below the elevation of the tower basin (meaning not much static pressure available to keep things positive at the pump suction) and especially if there are a lot of things in the pipe between the tower and the pump that can drop the pressure (like a plugged strainer).

The image below is from a pump manual that I have – The Durco Pump Engineering Manual – that shows the pressure gradient as a fluid approaches and moves through a pump impeller.  As a frame of reference, the upper image is a cross-section through the pipe and pump with the pipe to the left and the impeller, volute, and pump discharge just to the right of center.   The chart below the image shows the pressure gradient through the cross section;  the letters on the x axis of the pressure gradient diagram correspond to the locations referenced by those letters on the pump cross section.

Impeller pressure profile from Durco Pump Engineering Manual

If the absolute pressure at any point gets below the vapor pressure of the fluid being pumped, then the fluid will “flash”; i.e. change phase from liquid to vapor.

There is a tremendous volume change associated with a phase conversion from liquid to vapor and vice versa. For instance, if you convert a cubic inch of liquid water to water vapor at atmospheric pressure, the volume changes by a factor of about 1,600; i.e. 1 cubic inch of liquid water becomes 1,600 cubic inches of water vapor. When that happens in a confined area, like a pump impeller for instance, there is a force generated, which can make noise and also cause damage.

Of course, since pumps are designed to pump liquid, not vapor, as soon as the liquid flashes, the flow produced by the pump is reduced significantly. And, since it was the pressure drop due to flow that caused the low pressure that triggered the flashing, as soon as the flow drops, the pressure goes back up, and the vapor implodes back to a liquid, so another huge volume change and more noise and force.

When cavitation is triggered, the phase change phenomenon I described above is happening over and over again and that is what is causing the noise and what also can cause damage to the pump.

I should also note that while cavitation is most common in the pumps in our systems, it can also happen at the control valves, especially in situations where the valve imparts a large pressure drop to the fluid going through it.   The results are similar;

  • There is a lot of noise, and
  • The valve can be damaged, and
  • Since the valve is probably not as firmly anchored as a pump, the valve and pipe can actually start moving around.

The pipe movement can alarming; inches, not just fractions of an inch, and definitely will catch your attention.  At one point, Fisher Controls published a bulletin on the topic, which is how I learned about it.  If you are interested, I have a copy of it on my website and you can download it from there.

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Compound Gauges

The potential for sub-atmospheric pressures at the pump suction flange in situations like the one I just described and the ensuing potential for cavitation make it a good application for a compound gauge.  Most pressure gauges have the low end of their range at 0 psig.  The “g” in psig means “gauge” and indicates that the pressure indication is relative to atmospheric pressure.

But it is also possible to reference a gauge pressure reading to an absolute vacuum and those readings are termed psia, with the “a” indicating the reference is a vacuum.   For example, a reading of 0 psig at sea level is the same as a reading of 14.7 psia or 30 inches of mercury.

A compound gauge is a gauge that references a vacuum as the low end of its range.  Typically, the range will start at 30 in.hg, which stands for 30 inches of mercury vacuum (Hg is the chemical symbol for mercury if you look on a periodic table of the elements). The range will typically convert to psi at when it reaches atmospheric pressure, where it will have a zero, to indicate 0 psig.   From there, the range increases to full scale with the numbers representing psig.  Here is an example of a compound gauge along with a picture of what the internal workings of a typical gauge look like right below it.

DSCF5194 Gauge guts 01

This particular gauge has a handy feature called a “Maximum Indication Pointer”.  The red pointer is not directly connected to the internal mechanism.  Rather, it is arranged so that the black pointer (which is connected to the internal mechanism) can push it clockwise.   By turning the little brass knurled nut you can see sticking out of the center of the gauge, you can manually turn the red pointer counter clockwise so that it rests against the black pointer.

So, if you have the gauge connected to a manifold that allows you to take a number of readings using one gauge, like this ….

Preheat pump gauge piping

… then if you take the high reading first – say the pump discharge pressure – the red pointer will be pushed to that indication.  If you then take the suction pressure reading, the high reading is “retained” by the red pointer while the lower pressure reading is shown by the black pointer, which allows you to directly read the difference in pressure off of the gauge, which is usually the number you are actually interested in.

I should mention that one benefit of using one gauge to take multiple readings on a given piece of equipment is that it automatically will eliminate gauge accuracy as a source of error since you are subtracting readings taken with the same gauge.  And, you also don’t have to account for the impact of elevation differences on the gauge, which you need to do if you are using two gauges that are at different elevations to measure a pressure drop across something.

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Impeller Damage from Cavitation

Aside from making a pump under-perform, cavitation can do significant damage to the impeller.  Below are a couple of pictures that Jeff Mahin – a student in one of the classes I teach – shared with me. They were taken through an open suction diffuser associated with a condenser water pump.

Cavitated Impeller on Middle CW Pump Cavitated Impeller on Middle CW Pump Zoomed

As a part of a field exercise, his project team had run a pump test and the numbers were not adding up.  So we opened up the suction diffuser to see if there were any clues as to why. The second image is a close-up from the image to the left that zooms in on the impeller. In it, you can clearly see how the impeller has been chewed up by cavitation which is likely the reason the pump was not performing per the published curve associated with it.

The next string of pictures where shared with me by another student – Jay Cmiel – who has been trying to understand issues he has been having with a domestic water booster pump. At this point, he believes there are a number of things going on, including system configuration issues and possibly metallurgical issues. But he also suspects that cavitation is a major player behind the failures he is seeing.

These first two pictures illustrate what the impeller in one of his domestic booster pumps looked like back in June of 2016 after it was installed to replace a damaged impeller. The new and old impellers are shown side by side in the second picture.

Damaged Impeller 05 Damaged Impeller 02

This picture is what the impeller looked like in September of 2016 when they opened up the pump to replace a seal that had failed.

Damaged Impeller 06

These last two pictures are what the impeller looked like a couple of weeks ago (late April/Early May 2017) when they had to replace it again.

IMG_5214 IMG_5216 IMG_5217

So clearly, the message from the field is that cavitation is a thing to be avoided!

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Net Positive Suction Head (NPSH)

One way to understand if the potential exists for cavitation is to do a Net Positive Suction Head Available (NPSHa) calculation.   The basic idea is to do a calculation that tells you what the absolute pressure will be at the inlet flange to the pump in question at its design flow rate given the configuration of your system and its warmest operating temperature.   That number is is the Net Positive Suction Head Available or NPSHa.

You then compare that to the Net Positive Suction Head Required a.k.a. NPSHr for your pump.   That information shows up as a line on the pump curve.  For example, in the curve below, the design point for the pump is 1,000 gpm at 45 ft.w.c..  At that condition, it will be about 83.5% efficient, use about 13.25 bhp, and will require about 11.2 ft..w.c. of net positive suction head (or more if you want to be on the safe side) to avoid cavitation.


Notice how the NPSHr curve is read off of a secondary axis to the right and that it tends to rise as the flow increases because for a given cross-sectional area, an increase in flow will cause an increase in velocity.  And since the velocity pressure is  function of the square of the flow, the curve is not linear and really starts to take off as the flow increases.

The latter item is an important consideration in the field because it means that a pump that is just fine at it’s design condition can cavitate a lot if it runs out its curve.  That phenomenon is quite common in systems where large pumps are piped in parallel and serve common headers.  Consider the system illustrated below.


The three relatively large pumps (one is a back-up pump) serving the system are piped in parallel and deliver water to and from the chillers they serve via a fairly long piping run.  If both chillers are running, then the pumps need to deliver the design flow for the chiller at the head generated by that flow in the long piping run;  in this particular case, the total flow requirement was 2,400 gpm and the head requirement was 65 ft.w.c..

But if only one chiller is running, the required flow drops in half and as a result, due to the square law, the head required at the lower flow rate for the common piping that the pumps share is only one quarter of what it was (one half squared or half of a half).  As a result, in this particular case, when one pump was running, it ran out its curve and delivered significantly more flow that was required by a single chiller when it was in operation;  about 1,920 gpm at 47.5 ft.w.c. when only 1,200 gpm was required by the chiller.


That turned into an energy conservation opportunity that was worth anywhere from $1,100 to $15,000 a year depending on how you captured it.  If you want to know more about that, there is a PowerPoint case study on my website that you can look at which includes the cost/benefit metrics for the various options that were possible for capturing the savings.

My point in bringing this up here is that when system dynamics cause a pump operating point to shift out its curve significantly, the operating point on the NPSHr line can shift from a condition that was satisfied by the NPSHa to a condition where the NPSAa is not sufficient to prevent cavitation.   If you don’t fully comprehend the dynamic behind what is going on, then the cavitation problem can appear to mysteriously come and go.

For the system in the example above, this turned out not to be an issue.   But I have seen it be an issue on other systems with similar configurations and similar dynamics, which is why I bring it up.

The first time you do a NPSHa calculation, it can seem a little intimidating because you are working with absolute pressures and things like that;  it kind of seems like you are on a different planet or something. But Bell and Gossett publishes a handy little nomograph (chart that lets you graphically determine a solution) that makes it pretty easy.

B&G NPSH Nomograph

Us old folks have it in our Bell and Gossett Engineering Design Manual.

Bell and Gossett Manual

But you can now download electronic copies of the various bulletins that are in the manual from the Bell and Gossett website.  The nomograph shows up in the one on cooling tower pumping and piping, which also includes a lot of other very useful, practical information about cooling tower and condenser water system design and operation and how to apply pumps in them.

Back to Contents

So, I guess that ended up being a pretty long discussion for something that started out as answering a question about air venting.  But hopefully, the information is useful;  if it is, you can thank Kam for asking the question.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Posted in Chillers and Chilled Water Systems, Operations and Maintenance, Retrocommissioning Findings, System Diagrams | Tagged , , | Leave a comment

A New Commissioning Resource Website

For a while now, I have had this idea for a commissioning resource website floating around in the back of my head.  It seemed like there would be things that I could do with the way a website is organized that are challenging or simply not possible on the blog.   So, I finally dipped my oar and tried to create one and the result is now “live” as they say.


The URL is and as you can see from the image above, the theme is basically the same as the blog’s theme;  i.e. we stand to learn a lot from the reality the buildings we work in are trying to communicate with us.

I am certainly not a web developer by any stretch of the imagination and what is up currently is something that seemed “good enough” as the result of the combination of my skill set and the tools Weebly provides.  Part of the impetus for doing this was a need to figure out a way to shift content from lecture to a “find the details out yourself” format, which is what I am trying to do with the “What’s That Thing” page, the “Tools” page, and the “Useful Formulas” page I have linked from my “Resources” page.

This is an evolving work in progress so you will currently find a lot of stuff “under construction” (which I admit may be an excuse for me to post pictures of cranes and construction sites).  But hopefully, I will be able to fill out that structure over the course of the next year or so as I go through a round of the classes I teach at the Pacific Energy Center, which are a primary driver behind my doing this.

Incidentally, I have included a training page, which I plan to keep current with the dates for the classes I help teach in public venues for the upcoming four to five months.  Many, but not all, of these classes are free of charge, so if you are new to the industry and trying to learn, you may find  value in them. 

I also plan to include links to the materials from past classes and presentations under the Resources tab.  That is still  under construction but you can also get to those resources from the blog using the link on the right side of the home page under the 03- Materials from Classes and Presentations topic.


The advantage of moving things like that to the new website is that it makes them easier to organize and find and allows the blog to be more focused on the articles I write vs. the resources I reference.

The website includes an entry point to the blog in the navigation buttons on the upper right, or you can simply continue to use the actual blog URL, which is and which you probably already know if you are reading this.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Posted in Resource List and other Resources | Leave a comment

Learning about Relay Logic; What’s a Relay?

Author’s Note:  I edited this to put in pictures with better contrast for the relay images further down the post and for some reason, instead of just replacing the original post, the system put it up as a new post.   So, I am just going to let well enough be.  But bottom line, this is just a repost of the original of the same title with a bit better relay pictures.

In my last post, I talked about the Jeopardy game I had built that used relay logic and gave you a copy of my wiring diagrams in case you were interested in learning about relay logic by building your own version of the game.  In this post, I thought I would talk a bit about what a relay is since I am asked that question on occasion.  That will also set the stage for a discussion of Boolean algebra, which is the algebra of 1s and 0s and is the basis of doing logic with relays (excitement, excitement, excitement).

Relay logic has been with us for a long time, as you may have garnered from a post I did a while back titled Control Technology; a Glimpse Backwards and Some Thoughts on the Future where I discussed a legacy control system I had run into.

Old panel 01

What you are looking at represented the state of the art in the 1970s when I first started working in this business and is a far cry from the current approach to the control system implementation.   The control panel in the picture above originally sat behind where the blue chair is in the picture below.  All of its functionality, and then some, was replaced by a PC that is not visible in the picture below due to the camera angle, other than the display and keypad, which you can see sitting there on the desk.


If you looked inside the old panel, you would have seen what appears below;  hundreds of discrete electric and pneumatic control elements that were wired piped together so that they performed the desired control functions, some of which were analog (meaning the output of the devices was continuously variable) and some of which were digital (meaning the output of the device was in one of two states, like on or off, or open or closed).

Old panel 11 Sharpen

The yellow plastic cubes sitting on a gray base towards the bottom of the picture are electro-mechanical relays.  If you are wondering what the rest of the stuff is, I talk about it more in the post I mentioned previously.  For this post, I want to focus on the relays.

I have always, for what ever reason, kind of liked relays.  I didn’t know it at the time, but as a kid, I was making them out of nails with wire wrapped around them for an armature that moved pieces of tin can that connected other nails with wires on them to control my toy trains.  (Its probably a miracle that I did not electrocute myself).  In any case, I sort of have this weird natural curiosity and interest in them, so fair warning for what is to follow.

The picture below is a close-up of what one of the little cube relays in the picture above typically looks like.  The one after it labels all of the parts.  Incidentally, a common term used to refer to these relays is “ice cube relay” because in size and shape, its similar to an ice cube.



As you can see, its really a collection of levers and wires and the  “electro-mechanical relay” term I used previously is appropriate.  And as you might suspect, it depends on both electrical and mechanical principles to operate.

Fundamentally, a relay is simply an electrical switch that is operated by another  electric circuit instead of a lever that someone moves manually.  Thus, they provide a way to automate the operation of equipment using circuits that are electrically isolated from each other.  We use them a lot in building systems for that reason.  The isolation feature is important because it allows a low power, low voltage control signal to operate a high voltage, high amperage piece of machinery.  this makes things safer and keeps costs because the low voltage wires can be smaller and used for the long runs to the high voltage/amperage equipment point of use.  That is their other big application in building systems with prime examples being the interface a DDC control system output and a motor starter or lighting contactor. 

And, the motor starter or lighting contactor themselves are also relays, allowing high amperage, high voltage loads like 1,000 ton chillers or a 277 volt lighting distribution panel to be controlled by a 120 vac control circuit that is in turn, controlled by a 24 vdc DDC control system output.  So, ultimately, a  little tiny transistor or op-amp ends up controlling a 4 kV chiller motor.

The relay in the picture is a control relay like you apply as the interface between a DDC control system and a starter (or in a Jeopardy game).  Its not intended to handle heavy currents like three phase motor or lighting loads,  But having said that, the operating principle is fairly straight-forward an very similar to that associated with a motor starter or a lighting contactor:

  1. The armature is connected to a moving contact and swivels on a pivot, just like the see-saw you used to play on when you were a kid.  The contact is called the “common” contact since it will be in the circuit no matter what the state of the relay is (On or Off).
  2. When the relay is “off” (the coil has no power applied, which is termed “de-energized), a spring on the left side of the armature pulls that side down, causing the armature to rotate counter-clockwise. which moves the contact it is attached to up until it hits the fixed contact above it, which is termed the “normally closed” contact.  This completes a circuit through the common contact to the normally closed contact.  So wires that were hooked to the blades associated with these two contacts could be connected to light a light or sound a buzzer or start a motor if the relay was off.
  3. When the relay is “on” (the coil has power applied, in other words, it’s energized) a magnetic field is created.  This attracts the right side of the armature towards the coil and the armature rotates clockwise on the pivot until the common contact hits the fixed contact located below it, which is termed the “normally open” contact.  This opens up the circuit from common to normally closed and completes the circuit from common to normally open.  And, as was the case for the normally closed contact, wires could be attached to the blades associated with these contacts to perform useful functions.

The blades sticking out of the relay are designed so that you can solder wires to them in many cases.  But in most applications, they will also plug into a base that allows wires to be terminated under screws.  You can see these bases in the picture at the beginning of the post;  they are the gray squares with all of the wires hooked to them that are under the yellow relay cubes. 

This arrangement allows a failed relay to be quickly replaced with out having to re-wire anything.  In addition to saving time, this arrangement ensures the persistence of the logic created by the relay circuit because you never lift a wire to change a relay.  You just unplug it and plug in a new one.

Note that this “plug in” feature is something generally found with low voltage control relays vs. motor starters and lighting contactors.  But, in a motor control center, the entire enclosure containing the motor starter is often designed to be removable and simply plugs into the buss bars inside the motor control center, so again, the concept is similar.

The relay in the pictures also has a couple of handy features that are options for most manufacturers.  One is the LED that lights up when the coil is energized.   This is a good news/bad news thing.  The good news is that it tells you there is power to the coil.  But, the bad news is that it doesn’t really tell you if the coil actually moved the armature.

That is the benefit of the orange colored plastic lever.  If you look closely, you will notice that it is connected to the armature.  It turns out that the connection is arranged in a way that causes a little window on the top of the relay to turn orange if the armature has moved and keep it clear if the armature has not moved, as illustrated in this picture.

Slide Show 12162011 123148 PM

The blue lever allows you to manually move the contacts with out energizing the coil, a handy feature for verifying your wiring and trouble shooting problems.  Its also handy in an emergency when the control system is down and you want to force the output that it would have controlled had it been up and running to do something.

The terms “normally closed” and “normally open” are used because this is the state the relay will be in when no power is applied to the coil;  thus, the circuit through the “normally closed” contact would allow current to flow through that path as shown below.

Slide Show 12162011 123204 PM

Meanwhile, no current could flow through the “normally open” contact since it is not touching the common contact.

As you can surmise, when the relay is energized, the contacts switch and the normally closed contact opens and the normally open contact closes and current goes the other way as illustrated by the red line in the figure below, when contrasted with the yellow line in the figure above.

Slide 12162011 52943 PM

If you think about that for a minute, you might (correctly) conclude that in a way, the relay can “think”.  If it has power it reaches one conclusion represented by the normally closed contact being open and the normally open contact being closed.  If its not powered, then it reaches a different conclusion represented by the contacts being in their “normal” state.  Its this simple decision making capability that is the basis of relay logic, another major application for relays in buildings, especially in legacy control systems.

Its also important to note that the coil can control more than one set of contacts.  For instance, in a three phase motor starter or a three phase lighting contactor, the coil controls a set of contacts for each phase.  And in the control logic world, as you will notice if you study the wiring diagrams in my previous post, one coil controls three or four different contacts, meaning it can influence three of four different streams of relay “thought”.

Each set of contacts that can serve an independent circuit is called a pole.  So, in the drawings in the previous post for the Jeopardy game, the relays are three pole and four pole relays.

And while most control relays have a contact that can have two states as shown in the pictures above and in the wiring diagrams for the Jeopardy game, it is also possible to have a contact that is only “normally open” or only “normally closed”. Motor starters and lighting contactors are common examples, containing three normally open contacts (one for each phase) that close when the contactor coil is energized and open, but do not (typically) complete a different circuit, when the contactor coil is de-energized.

A set of contacts that completes one circuit when it is energized and a different circuit when it is de-energized, like in the pictures above and in the Jeopardy game is called a “double throw” contact.  A contact that completes or opens up only one circuit when it is energized and does not directly impact a second circuit when it is de-energized is called a “single throw” contact.

Relay engineers have combined these two terms and will say, for instance, that a relay is a four pole double throw relay, meaning it is a relay that can control four independent circuits and that it can connect each circuit in a different way depending on if the relay is energized or de-energized.  The relays in the Jeopardy game wiring diagram are three pole double throw and four pole double throw relays. In contrast contacts like those in motor starters and lighting contactors are usually what is termed “single throw”.

And, being engineers, relay engineers have created a set of acronyms to describe all of this.  A Double Pole Double Throw relay is abbreviated as DPDT.  A 4 Pole Single Throw relay would be called a 4PST relay.

If you really are interested in this (and who wouldn’t be), then you may want to poke around and see if you can find a copy of the Engineer’s Relay Handbook.  I, as you may have guessed (perhaps with some alarm) happen to have a copy and I can tell you that it contains everything you want to know and more about relays.  

In the course of developing this post, I looked around to see how easy it was to find a current copy and it seems to be not that easy.  My guess is its not published anymore so you will probably only find one at a used book store or a garage sale.

The good news is that the most relevant chapters seem to have been posted on line as HTML files on the Easterline Power Systems web site.  This includes the chapters on terminology and on principles of operation.  The files can be downloaded to your hard drive for off-line reference.

So there you have it;  probably more than you care to know about relays.  The next post will look at how we can use them to “think” just like I did in the Jeopardy game.

David Sellers
Senior Engineer – Facility Dynamics Engineering

Click here for an index to previous posts

Posted in Controls | Leave a comment

The Other Side of Life

I really enjoy working on this blog because the technical things I discuss are of interest to me and by sharing what I know, I am sharing what my mentors have shared with me, sort of playing it forward I guess.   But or a while now, I have felt that there were non-technical things I wanted to share and I decided to create a second blog called The Other Side of Life as a way to do that.

So the good news for followers of this blog is that I will no longer write any of those non-technical, philosophical posts that some might find to be annoying on this site.  Rather, I will use The Other Side of Life as my venue to fulfil those urges when they strike (except for the post I do around Christmas I suspect since its kind of like sending a Christmas card).

One of the reasons for doing this is to somehow document the events that triggered my desire to create the second blog, things like my early childhood memories from the family farm, finding my Dad’s letter’s home from the days leading up to and after the Normandy invasion, and most recently, the passing of Riley, our puppy.

When I think about why I felt compelled to document those events, a number of things come to mind.

  • They are part of the legacy of my family and if nothing else, might be of interest to our kids and grand kids
  • Some of the things that have moved me seem like things that should not be forgotten somehow
  • My thoughts and feelings, if I can express them clearly enough, may be of help to others, just as the expressed thoughts and feelings of others have been a help to me
  • Figuring how how to do this may help me understand myself a bit better

In the context of my technical blog, I have know for a while now – since I was a lab assistant for flight line maintenance labs when I was in college – that it is one thing to understand something and a totally different thing to be able to explain it to someone else.  Being able to write down an explanation requires an even deeper level of understanding.   Meaning that technically, I learn a lot by writing the technical blog.

So I suspect that there is a part of me that hopes to understand myself better along with my feelings and what motivates them by doing this.   So, we seem to have an engineer trying to understand his feelings;  who would have thunk it.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Posted in Uncategorized | Leave a comment

Hourly Weather Data Website Update

Frequently, when operating buildings or doing energy calculations for their systems, it is very handy to be able to obtain hourly weather data for a given location.   That is why I think the post I did a while back on the topic is one of my more popular posts, perhaps even more so since NOAA subsequently stopped charging for the data.

This weekend, I discovered a couple of things I didn’t know about the website I refer you to.   One is that they moved it and its not so easy to find where it went.  The good news is that I finally found it and updated the link in the previous post.   But to save you the trouble of going back to it, I wanted to put it into this post and also mention a few other pertinent things I learned.

The point of entry for the new data location is now via this web page.


If you are like me, your initial reaction is to pick the search tools or data tools and start looking there.  But, while those links have a lot of useful data available, none of them had the global hourly weather data link I was looking for.  It turns out, you have to page down a bit to find it.


If you click on the Legacy Climate Data Online, you are taken to this page.


If you pick the Data Set/Product option, and then pick Surface Data, Hourly Global (Over 10,000 worldwide sites)*  in the selection window that appears …


You will be taken to the page that I use as the starting point in my earlier post on the topic.


After that, the process is the same as what I outlined in my first post with two exceptions.  One is that you no longer have to pay for the data, which I mentioned when I discovered it after my original post.  Click here for a direct link to this page.

The other is that the process currently won’t work in Internet Explorer.  You can go all of the way through the selection and ordering procedure, but when you Submit Request, you get an error page;  Machines 1, David – 0.


At first, I thought I had done something wrong, but after carefully repeating the process several times with the same result, I started to suspect there was some sort of issue with the way the browser was interacting with the web site.

So, on a hunch, I tried using Google Chrome instead of Internet Explorer, and it worked;  Machines – 1, David – 1.

I subsequently e-mailed the NOAA help desk, just to be sure and very quickly, received a response confirming my hunch and suggesting I use another browser.

Since there is a note on the new home page under the Legacy Climate Data Online topic that says…

The first version of Climate Data Online which provides access to several datasets which have not yet been migrated to the current version

… I suspect we will go through this process one more time before all is said and done.  I’ll keep you posted if I run into the problem again and what I do about it.

On a related note, I also discovered, sadly, that Bill Koran’s weather data query spreadsheet no longer works (I mentioned it in a number of posts, including Using Scatter Plots to Assess Building Performance–Part 3).   Bill is a friend of mine, so I e-mailed him to see what was up.  The issue there is similar to the issue I discuss above; i.e. the location of the data that the query targeted had shifted.  Unfortunately, he thinks the problem is unfixable, so a really great tool has been laid to waste I am afraid.

Bill did mention that ECAM (another really great tool that Bill has been the driving force behind) has a download tool built into it  But currently, that also has been affected by the shuffling of web pages and he is still working go fix that.  Meanwhile, he suggested using the following links to do manual downloads.

This first link …

… will take you a web page on the new site that I mention in the opening of the post.


If you pick the purple Datasets button in the black banner (the one below the blue banner), it will take you to this page.


If you page down on that page, and expand the Global Hourly Data topic, you will discover that the Search Tool link will take you to the same place I describe above.


This second link …

… takes you to a location that will allow you to access data from airport automated weather observation systems (ASOS) around the world.  Its pretty slick;  all you have to do is pick your station and fill out the form using the drop-down menus provided.


When you get to the bottom of the form, you hit the Get Data button and  your file is made available for download (or viewing in a web browser if you pick that option).


Machines – 1, David – 2.

I’ve modified the links under 02 – Weather and Climate Resources to reflect the information above.

So that should give you a number of options for obtaining hourly weather data for your building commissioning work and energy calculations.   Thanks to Bill for the links he shared;  The second one really is nicely done and probably the fastest and cleanest approach if the location you are looking for is included in their site list.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Click here for a recent index to previous posts

Posted in Weather and Climate Interactions with Buildings and Systems, Weather and Climate Resources | Leave a comment

Control System Fundamentals

This post evolved to support a string of posts I will start next to support an exercise in one of the classes I am involved with at the Pacific Energy Center.  In those posts, we will look at how you can use Eikon for Educators or WindLGC to develop and verify control logic.


Applying these packages as a design tool is very useful since they both allow you to simulate your logic before it goes to the field.  Having that ability to allows you to find and fix any bugs that might exist.    And designer or not, using the tools will help you learn about logic and how control systems work. 

If you are involved with building systems in any way, be it as a designer or an operator or a commissioning provider or a field technician, it is very helpful to have a basic understanding of control system fundamentals and the building blocks used to develop control logic. My hope is that the slides modules provided with this post will facilitate that a bit by providing you with the slides I generally use when I do a control system basics class. 

These slides are not narrated but I think the graphics and links to resources in them can facilitate understanding the basic idea behind the slides.  They certainly are not a comprehensive presentation of the control system topic.   But they do provide information on most of the fundamental principles you might need to design or understand a control system and the logic and programming behind it.

The post is divided into three main parts.  Module Organization provides an overview of the content in each module.  Using the Modules explains how you go about downloading and running the modules if you are interested.  Taking Notes on Slides explains how you can use Microsoft One Note if you want to add  your own notes to the slides as you work through them. 

Module Organization

The slides are divided into seven modules, as listed below.  If you click on the link, it will take you to a description of the module and there will be a link from there to the actual module on my Google Drive.  The “Back to Contents” link and the end of the description will bring you back here.

Introduction and Overview

This module starts out by defining the basic, functional goal of a control system.


It then looks at what we have been able to do with control systems historically, from fairly early in the industrial age to something representing the epitome of technology and compares that to where we seem to be in terms of applying control systems in the HVAC industry currently, which many (including myself) would say is not particularly good.

The module then proceeds to explore why (in my opinion) the current process may be dysfunctional and proposes a process (that I and others I know have used) to address what I believe might be the causes of the dysfunction.  We should and can do better than we are on most projects these days.  A narrative that complements the information in the slides (which is basically what I talk about as I go through them) is included in the second chapter of the Control Design Guide.

Next, the module looks at some of the National Electric Code requirements that impact the installation of a current technology control system, including a case study that illustrates how these requirements might affect an installation in a tight equipment room.  Current technology control systems are basically electrical systems.  Thus we need to make sure we install then in accordance with the requirements of the codes that govern electrical systems.

From there, the module looks at some basic functional testing requirements that will help ensure that your design goals are realized.  As the Designer or Owner of a control system, you should have a fairly good sense of what you expect it or need it to do.   It turns out that if you know that, and test for it, you can find out if the system you have is delivering or not, even if are not up to speed on the details, networking, and theory behind a modern DDC system.

The module concludes by introducing the basic building blocs for most control systems;

  • Inputs
  • Outputs
  • Control Processes
  • Set Points

The modules that follow explore these topics in more detail.

Click here if you want to download the Introduction module from my Google Drive.

Click here to go back to contents.


This module focuses on the “Inputs” building block and starts out by looking at some of the basic concepts behind sensors and transmitters.  All though we tend to use those terms interchangeably, at a technical level, there actually is a difference and understanding that is important from an application stand point.


The module then looks at how the dynamics that are going on in an operating system might impact what a sensor and transmitter “see”.  It turns out that for accurate results, you need more than an accurate sensor and transmitter.  It needs to be installed correctly and arranged so that the data it picks up is truly representative of what is going on in the system.  The accuracy can also be impacted by application considerations for the sensor and transmitter itself, including position effects and the effect of mass.

Calibration is an important component of accuracy, but there is often more to it that simply verifying the sensor at one operating condition.  For one thing, the accuracy of many sensors will vary over their range.  And even if that is not the case, a single point calibration may not deliver accuracy over the entire range.  These topics as well as others are focused on in the Calibration and Accuracy section of this module.

The bottom line is that there are a lot of things between what we see at the work station and what is actually going on out in the field.  All of them can make a difference and of particular importance is the sampling frequency.  The Nyquist Theorem allows you to predict and appropriate sampling frequency and if you don’t pay attention to it, then you may be misled by your data.  The final section of this module explores this topic, including examples of what can go wrong.

Click here if you want to download the Inputs module from my Google Drive.

Click here to go back to contents.


Outputs are another important building block in our control systems and this post starts out by looking at the types of actuators and the signals that are typically used to cause them to move, both pneumatically and electrically.


Just because an actuator has a linear signal applied to it does not mean that the response in the system it is controlling will be linear.   In fact, most of the time it won’t due to they way system pressures and flows interact with the valves and dampers, the characteristic curves for the valves, dampers, and other final control elements in our systems, and the linkages that connect the actuators with the final control elements.  These topics, including examples, are explored as a part of this module.

Click here if you want to download the Outputs module from my Google Drive.

Click here to go back to contents.

Control Processes

Control processes manage our outputs based on our inputs and the set point for the process.  So they are a pretty important part of the control system.  This module starts by looking at where we came from in the HVAC industry, starting with the analog days, as illustrated below in the photo, which is an analog, pneumatic PID (Proportional plus Integral plus Derivative) controller and moving forward through the evolution to DDC.


The content in this module includes a section that takes a detailed look at how pneumatic one pipe and two pipe controllers work and their pro’s and con’s relative to each other, the pro’s and con’s of pneumatic vs. electric actuators (pneumatic control is not the same as pneumatic actuation) and pneumatic control resources before moving on the DDC systems.

The module then explores digital and analog control processes, including floating control, Proportional control (P-only), and Proportional plus Integral plus Derivative (PID) control.  This part of the module includes examples illustrating what happens when you narrow down the throttling range on a P-only control process and what happens when you take a P-only process and add integral gain and derivative gain to it,including the units of measure associated with both types of gain.

The open and closed loop tuning methods are also explored including illustrating what the response of a well tuned control process should look like.  It turns out that lags in the control process can have a huge impact on your ability to tune it tightly and get it to settle out in a reasonable period of time.  The module illustrates this along with showing how the open loop tuning method can be used to identify the lags in your system, which will provide a lot of insight into where you can expect to end up in terms of response and settling time once you have tuned your process.

The module concludes by providing you with some resources that will give you a deeper understanding of PID control and all of its variations as well as some general rules to apply as you go about tuning control loops and starting up control systems.  The rules are generally the same as the rules you would use in any functional testing process, probably because the control system plays such an important role in virtually all of our HVAC systems.

Click here if you want to download the Control Processes module from my Google Drive.

Click here to go back to contents.

Control Logic

This module supports the previous module by taking a closer look at the logic behind control processes, including how that logic is developed for a current technology system.


Having a sense of the logic required to implement and improvement to a system is very helpful if you are involved with commissioning and operations, new construction, existing building, or otherwise, which is one of the points that is made early-on in this module via an EBCx (Existing Building Commissioning) case study.

The module then looks at relay logic, which is how digital logic was accomplished in the “olden days”, and which is the foundation for modern digital logic.   This includes an example that compares a narrative sequence with the relay logic required to accomplish it.  It then contrasts the relay logic with the DDC logic that would be used to accomplish it.

The module concludes by comparing the two primary ways logic is implemented in current technology systems along with guidelines and resources you can use to help you develop the logic for the systems you are working with.

Click here if you want to download the Control Logic module from my Google Drive.

Click here to go back to contents.

Set Points

Set points are critical in terms of coordinating a logic sequence that might apply to a given system type in any location with the specifics of a given location, the loads the system serves, and the nuances of the equipment serving the system.


For example, the perfect set point to return an economizer process to minimum outdoor air on a hot and humid day in San Francisco, California could be an energy efficiency disaster if you used it on an a similar air handling system serving a surgery in St. Louis, Missouri.

This module uses a number of case studies to illustrate why the set point you select for a given control process needs to consider the operating environment, the nature of the load, and the characteristics of the equipment serving the system if your goal is optimal performance and efficiency.

Click here if you want to download the Set Points module from my Google Drive.

Click here to go back to contents.

An Exercise

This module is the exercise that I will be working with in the blog posts that follow.


The intent of the module is to let you work with Automated Logic’s Eikon for Educators or Idec’s WindLGC to build and test some basic logic and then modify it to achieve energy savings.  Both of these tools are free resources and are fully functional versions of their respective manufacturer’s programming software, including the ability to simulate and test your logic once it is complete.  They only thing you can’t do is download the logic to an actual controller.

The exercise starts by having you put together the logic for a control loop that will modulate the steam valve on the heat exchanger serving the hot water system in the system diagram above so that a constant discharge temperature is maintained.  Once you have that working, you modify the logic to add two energy saving features.

The point of the exercise is to help you become familiar with logic by working with it.  While the building blocks you will be working with are specific to the manufacturer’s software you will be using, I think you will find that once you understand how to develop logic for one vendor, the knowledge is easily transferable to other vendors, at least that is how it was for me when I first started going control system programming.

The other point of the exercise is to illustrate how having the ability to understand, work with, and communicate logic can open the doors to some very low-cost/no-cost savings opportunities.   I plan to illustrate this by developing the cost/benefit metrics for the two improvements you will make to the logic.  So, not only will you learn about logic, you will learn a bit about energy savings calculations and cost estimating by the time you are done with the exercise and related blog posts.

Click here to download the Exercise Module from my Google Drive.

I have provided the system diagram that goes with the exercise as both a PowerPoint file and a .pdf file.   The reason is that if you have PowerPoint and are interested in developing system diagrams, having the system diagram in the PowerPoint format will give you a start on some symbols since you can copy and paste them from my diagram.  If you don’t have PowerPoint, the .pdf version of the diagram is really all you need to do the exercise (along with the programming software mentioned above).

Click here to  download the system diagram that goes with the exercise as a PowerPoint file.  Click here to download the system diagram that goes with the exercise as a .pdf file.

Click here to go back to contents.

Using the Modules

The modules are PowerPoint slides that have been converted to html and flash files to allow you to view them even if you do not have PowerPoint.  I believe they should work on PCs and IOS devices but currently, I don’t have a way to verify that so let me know if you have problems with running them on a MAC.

The various modules are saved on my Google Drive (the link takes you to the location) as zip files.   I created the files with Winzip, but they typically will open with the standard Windows file compression utility.   If you have problems getting that to work, you can download the free trail copy of Winzip for a PC, Linux, or a Mac off the internet.

Downloading the Modules

In the paragraphs that follow, I am going to show the download process on a Windows PC using Internet Explorer.  Other operating systems and web browsers should look similar to what I show.  I should mention that I have run into an occasional problem working with Google Drive using Internet Explorer, but I was always able to solve them by using Google Chrome instead.  So if you run into a problem try doing the steps in Google Chrome.

To use the modules, you should down load them and then extract the files to the location of your choice, making sure to preserve the file structure.    Specifically, you should navigate to the Google Drive location where the module of interest is located by clicking on the Click here to download the …  link at the end of each section describing a module. which should give you a window that looks something like this.


To download the zip file containing the files listed in the window, you click on the download icon at the upper right side of the Google Drive window.  When you select the download option, you should be asked if you want to open or save the file. To get them on your computer, you need to save them and if you are doing that, you are given the option of where to save it, at least that is how it works for a Windows PC.   Here is what that looks like on my system.


If you select “Save” on most systems, the file will end up in your default “Download” folder.   If you pick “Save As”, then you an select any location on your system’s hard drive (or drives).  Here is what that looked like on my system when I created a folder on my Desktop named “Download Example” and then saved the Introduction and Overview module there.


The next step is to extract the files from the compressed folder that you downloaded.   To do that, you highlight the folder of interest, which in this case, since the folder is a compressed file folder, will open up a set of “Compressed File Tools”. 

I’m sure that what this looks like and the specific steps involved with vary from PC to PC and operating system to operating system and may even vary with the file compression tool set as the default tool on your system.  But here is what that looks like on my system, which is running Windows 8.1 Pro.


To extract (unzip) the files in the folder, select the “Extract” menu and then the “Extract All” option. 


When you do that, you will be given the option of selecting a location for the extracted files.  The default is typically a normal (non-compressed) folder of the same name in the same folder (location) as the zipped file, but you can put them anyplace you want by using the “Browse” button.


When you select “Extract”, you typically will get a little window showing the progress of the operation …


… and then a window with the folder that you extracted the files to open, showing the files you extracted.


For the “Play” function to work, it is important that the files be in the structure shown above.  For most systems, that will happen automatically if  you extract the files using the process I illustrated, but I mention it just in case somehow, in the process of doing this, you don’t end up with something that looks like the preceding.

Click here to go back to contents.

Playing the Modules

If you double click or otherwise open or run the file with the name that starts with Run This …, it should launch your html viewer (Internet Explorer, Firefox, Google Chrome, etc.) and allow you to play the slide show.

Note that, depending on your security settings, you may get a message asking you if you want to allow blocked content to execute.  To get the slides to run, you will need to click the “Allow Blocked Content” button.  Ultimately, you should end up with a window that looks like this.


You can display the slides “Full Screen” by clicking the little square button with the diagonal arrows as shown below.


You can advance the slides in a number of ways including pressing the “Play” button, pressing the “Previous” or “Next” buttons, pressing the “Page Up” or “Page Down” keys on your keyboard, or pressing the “Space Bar” on your keyboard.


Note that there is a subtle but significant difference between using the “Play” button or “Space Bar” to advance the slides vs. the “Previous” or “Next” buttons, or pressing the “Page Up” or “Page Down” keys.  Specifically, the “Previous” or “Next” buttons and the “Page Up” or “Page Down” keys will literally advance to the next slide even if the animation associated with the current slide has not run.

In contrast, using the “Play” button or “Space Bar” will step through each animation (if they are not automatically triggered by the previous one) and only advance to the next slide after you have seen all of the content on the current slide.   So, I would recommend using the “Play” button or “Space Bar” to move through the slide deck.

To facilitate things when I teach using these slides, I have hyperlinks set up to jump between the various slide decks and back to the table of contents.   So far, I have not been able to figure out how to make those links work in the html versions of the slides.  Meaning that to open the next module, you will literally need to go to the location that the Run This to Play the …. Module.html file is located in and launch the module that way.   To return to a previous module, you will need to manually navigate to it if it is still open or simply launch it again.

Click here to go back to contents.

Taking Notes on Slides

Frequently, when you are working through a presentation or listening to a webinar, you might find it handy to be able to take notes on a particular slide or anything that you have showing on your monitor for that matter.  OneNote makes this pretty easy (the link takes you to web page the describes some of the features) so I thought I would close this post by illustrating how you go about using OneNote to make notes on the slides if you want to do that.

What follows is specific to OneNote, which is a free Microsoft utility. I use it a lot for taking notes in meetings, keeping a phone journal, taking notes as I work through projects, taking notes when I am listening to presentations or webinars, etc.  OneNote will not run natively on a MAC, but you could run it in a Windows Shell.  But I believe there are MAC specific programs that have the same basic functionality as OneNote.

Lets say I was working through the Inputs module and got to this slide and wanted to make a note reminding myself that one of the points of the image was to illustrate that while the two devices appeared to be similar a closer examination of the nameplate reveals that they actually have different ranges.


To do that, select the window you want to capture so that it is on top on your monitor.  Then switch to OneNote window and select “Insert” and then “Screen Clipping”.


When you do that, OneNote is hidden and your entire screen is covered by an opaque white layer.


You can now use your mouse to drag a window on what-ever portion of the screen you would like to capture …


… and when you release the left mouse key, OneNote will re-appear, but now, the portion of the screen you selected will be included on the OneNote page and you can add your notes to it by simply clicking anyplace on the page and typing.


Pretty cool and really fast once you know how to do it.  

Incidentally, when I say “drag a window with your mouse” what I mean is that you use your mouse to put the little cross-hairs that appear with the opaque screen over one corner of the area you want to capture.   Then, while holding down the left mouse key and moving the mouse to the other corner, you will discover that you will “make a hole” in the opaque screen defined by your use of the mouse.

Click here to go back to contents.

In closing, I should mention that this is the first time I have tried doing this (putting slide modules up on line in a format that should allow you to view them).   Everything seems to work on the machines I have tried it on, but please let me know if you have are having problems getting the slides to open up via a comment on the blog and I will try to figure it out.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Posted in Controls, HVAC Fundamentals, Operations and Maintenance, Pneumatic Controls | 2 Comments

Happy Holidays, 2017; Recollections of George Hinke

For the past couple of years, around this time of year, I have tried my hand at writing a non-technical thing that has some measure of seasonal appropriateness, like the post last year about snow crystals.  So, this post is my effort at that this year and will be totally not about engineering.  So, if you are follower that finds my occasional forays into non technical topics to be annoying, you probably should stop reading this right about here.  But, if you are starting to feel “the holiday spirit”, you may enjoy what follows.

My parents really enjoyed Christmas and when I was little, they made it pretty magical, especially my Mom who did a lot of decorating and baking around the holiday.   One of the traditions was that Dad would always get Mom a copy of the Christmas Ideals magazine. The magazine was more like a book than not and had color pictures, poetry, stories and a generally nostalgic air to it.  It turns out they are still being published and the link above will give you a sense of what they were like.

As near as I can tell, in 1958 (when I was about 4 years old), Ideals published a book titled Jolly Old Santa Clause.   I found this image of the original title page on an Esty site called Tinsel and Trinkets.

The book told the story of the days leading up to and through Christmas Eve as seen by Sparkie, one of the elves at the North Pole and had these really detailed, wonderful pictures by an artist named George Hinke.  When I looked at them, I just knew that is what it must look like up at the North Pole right about this time of year.

So, I have a lot of pleasant memories of being snuggled up with my Mom and brother reading this book (probably a lot) during the weeks and days leading up to Christmas with Christmas music playing in the background and the smell of pine in the air from the garlands my Mom decorated with and the candles she burned at that time of year. 

On the musical side of things, the one album that sticks out was called Twas the Night Before Christmas by Fred Waring and the Pennsylvanians.


It was this eclectic mix of secular and sacred holiday music sung by a vocal choral.   My favorites, being 4 or 5 at the time, were Twas the Night Before Christmas and Rudolph the Red Nosed Reindeer, which were the perfect songs to accompany the reading of Jolly Old Santa Clause.

I especially liked Rudolph the Red Nosed Reindeer, which, in the second chorus adds all kinds of silly sound effects to the song that still make me smile (as they did my Grandson, when I played it just now) (The links take you to sound clips from the songs to give you a sense of them if you want).

As I grew older, of course, the number of times I found myself snuggled up with Mom reading the book declined.  But frequently, around this time of year, I found myself remembering them and Jolly Old Santa Claus in particular.  So, on trips home, I would often dig around for a bit trying to find the copy of the magazine, and was always disappointed because it seemed to have disappeared.

The good news is that in 1996, someone republished the book and copies of it were all over the place.  So I happily bought one for myself and one for Mom, giving it to her as a Christmas present in honor of the happy Christmas memories she and Dad created for me as a kid.  Now, I have bought copies for all of my grandkids (and maybe in hindsight, twice for Piper and Arabella; what can I say;  I’m getting old).  Hopefully, they are creating a few happy holiday memories for them.

So, I thought for my holiday post this year, it would be fun to scan some of the images and share them here.  The first was one of my favorites because it reminded me of my Mom and all of the Christmas cookies she baked.


We had this tradition of having a “cookie tree” which was this little artificial tree that we set up someplace and decorated cookies that Mom had made.  When one of our friends came over to play, they got to take a cookie home with them.

These cookies were no ordinary cookies thought.  Each one was a little work of art.  They were all decorated with colored sugar, but when I say that, I don’t mean that the snowman, for instance, hand white sugar crystals all over it.  Rather, the snow balls on the snowman had white sugar, the scarf had red or green sugar, the hat had blue sugar and there were little brown dots –the tip of a clove I think – that made the eyes, nose, smile, and buttons down the front of the snowman.

There were cookies shaped like snowmen, stockings, Santas (with rosy cheeks), Christmas Stars, Trumpets and Drums (after the little drummer boy), and Christmas Trees.  Each one was individually decorated and then wrapped in cellophane with ribbon tying the cellophane in place and making a loop to hang it on the tree. 

After Mom passed, when Kathy and I were helping my brother sort through the stuff in her house, we found a tray of them in the freezer, which made me happy because Kathy, who is an artist, had never seen them and really appreciated what it took to make them.  Mom would have appreciated that because she and Kathy became pretty close.  Like, I learned stuff about Mom from Kathy because Mom had told her about it (vs. Mom telling me;  not an problem, just saying she came to love and trust Kathy a lot).

This next picture was another favorite because for our family, heading out to find and cut down our own Christmas tree out in the Pennsylvania woods was another tradition; sort of a sane version of one of the opening scenes in Christmas Vacation.


The tree was set up by the family on Christmas Eve right before we went to church.  Magically, the next morning, we rushed down stairs to find it beautifully decorated by Santa and his elves while we slept.   At the time, I was sure most of our ornaments had originated in a scene like this (and still think that may be the case).


When I was a bit older and snuck down the stairs one Christmas Eve, I even saw “Mommy kissing Santa Clause”, which is one of my more romantic memories of Mom and Dad. 

The tree decorations were another one of my Mom’s works of art.   Each year, we had this tradition of buying a special ornament for my brother and I.   That was started by my Grandparents, who typically sent us a special ornament each year.   I still have this little glass clown (I’m not afraid of clowns) that is as old as I am and plastic stars (back when plastic was a scientific break-through) that had a little spinning propeller in them that spun in the thermal created by a Christmas Tree light if you hung them over the lights.

Spinny Star Ornament   Spinny Star Ornament 02

So part of the tradition when I was younger was that we would hang our special ornaments after we set up the tree;  the rest of the decorating happened over night, as I mentioned above.

When I was older and saw my Mom decorate the tree, I discovered that each individual ice cycle was placed by hand.  Back then, icicles were strips of shiny stuff (originally lead which could explain a few things about me, and later on acetate) that were about 1/16” wide and maybe 18 –24 inches long.   So hanging each one individually (and retrieving them for  use the following year) was a pretty painstaking process.  But the result was a really spectacular looking tree, at least to my childhood’s and memories eye.

This next scene was one that tended to be emphasized by Mom when she was reading the story to us in the days leading up to Christmas.


In the original painting, if you look closely at the book where Santa is making his notes, you discover that it is a list of nice girls and boys and naughty girls and boys.   My Mom’s point at the time was that we should err on the side of “Nice” given that my brother and I were probably running around like “wild men” in our excitement (and sugar high).

The picture that follows is an example of one of the things that, to this day, I love about George Hinke’s pictures;  there is an incredible amount of detail to them, as can be seen in this one.

George Hinke 01

Clearly, its the day after Christmas, and the reindeer are being groomed and bedded down after their long night’s work, not the day before, as can be seen from the date on the calendar. 

And then, there is (at least for me), the primary thing you focus on when you look at the picture, which (for me in this picture) is the sleigh and reindeer.  But if you look closely, you see all sorts of other things going on, like the elves polishing bells and lanterns and feeding the reindeer who are already in their stalls (with their names over them, of course).   I think you will notice the same sort of thing in the other pictures I have shared.

This final picture is the closing picture in the book, and, to my mind, when Mom was finishing the book, was exactly what it would look like on the roof of our house on Christmas Eve.


So, with that, I will leave you to the holiday and wish everyone a happy holiday season.   And thanks, as always, for visiting the blog.


David Sellers
Senior Engineer – Facility Dynamics Engineering

Posted in Uncategorized | Leave a comment