Well, its been an unusual weather week up here in the Pacific Northwest (kinda sounds like Garrison Keillor doesn’t it) with snow on the ground and temperatures hovering at or below freezing most of the time. On the bright side, it brings a white Christmas experience to a place that typically doesn’t have it.
That opens the door to a lot of nice romantic stuff like a hand in hand walk with your bride to one of several local combination pub and theaters to watch a movie on a big screen while sipping wine and have a bite to eat (at least that’s what we did).
But, if you are operating HVAC systems right now in the Pacific NW, you are currently pushing the envelope in terms of what you normally might see. To give you some perspective on that relative to normal and to the rest of the country, based on information in my bin weather data CD:
- Portland, Oregon has about 430 hours per year below freezing with the coldest temperature for which there is any data being 9°F (0.1 hours) and the coldest temperature with more than an hour of occurrence being 14°F (2.5 hours).
- St. Louis, Missouri, where I lived and worked for about 25 years has about 1.282 hours per year below freezing with the coldest temperature for which there is any data being -17°F (0.1 hours) and the coldest temperature with more than an hour of occurrence being -7°F (1.8 hours).
- Minneapolis, Minnesota, a place that frequently comes to mind when people think of cold has about 2,638 hours per year below freezing with the coldest temperature for which there is any data being -31°F (0.1 hours) and the coldest temperature with more than an hour of occurrence being -24°F(1.8 hours).
For those of you who are visual people, these graphs for Portland, Oregon from City-Data.com paint a picture of the contrast.
As of this morning, the official snowfall total for yesterday’s little meteorological event is somewhere between 180% and 200% of our annual total, all in one fell swoop. If you look at the temperatures we have seen in Portland for the past week …
(this graph is straight from the NWS site for Portland; see my blog on Free Hourly Weather Data if you want to know more)
… and the Portland design conditions …
(this table is one of features of Akton Psych Chart; you just plug in your location and up pops the ASHRAE data)
… you can see that we have been flirting with freezing temperatures, design conditions, and extreme conditions all week.
If you do the math, in this week alone we have seen 35-40% of all annual hours below freezing. That’s a lot different than seeing them as an hour here and an hour there when the temperature bottoms out right before dawn on a clear night in the fall or spring.
Flirting with design and extreme conditions can be a real challenge to the folks operating buildings, especially if the design team focused more on the design condition with out much thought for the extremes. I shared some of my thoughts on this previously in a post titled Commissioning and Operations meet HVAC Design Theory; Design vs. Extreme Conditions.
The reality is that the operating team has to deal with the extreme conditions even if the design team didn’t. In discussing this with Rob Cole, the lead engineer at one of the projects I am working on he offered this amusing perspective on the dilemma.
Designers work with theory, operators work with reality. That’s why each group would like to throw the other off of the roof.
My thought at the time was that Rob’s theory might explains why there were days when I wanted to throw myself off the roof given that I have been both a designer and an operator.
But that aside, here are some of the very real issues that Rob and others like him have been dealing with this week as the operating envelope for the systems they work with are pushed to the limit and beyond.
- Economizer equipped air handling systems become difficult or impossible to start for a number of reasons including poor mixing, lack of a mixed air low limit cycle, excessive minimum outdoor air quantities, and control loop instability that emerges as the result of loops being challenged by new operating conditions.
- Previously un-noticed cracks in envelopes with pipes running by them come to the forefront when the line freezes, ruptures, and then thaws.
- Previously un-noticed openings in exterior soffits and reveals connect the outdoor environment with HVAC return plenums causing plenum and return temperatures to plummet. (On several projects, the holes have been big enough to walk through once you found them but you couldn’t see them if you were looking at the building from a normal observation point).
- Lobbies become “iceboxes” if building pressure relationships are not properly set and controlled causing numerous complaints and a lot of suffering for the folks that are stuck working in them.
- Stack effect accentuates all of these issues, especially on high-rises.
- Pneumatic lines and components that were installed outside but have not been protected with dryers that are capable of producing air with dew points below the current outdoor temperature freeze up and in some cases, rupture, causing control systems failures that can ripple out into damage in other areas.
- Coils that need to do preheating but have not been installed, piped, and controlled to deal with freezing air rupture.
- Cooling towers with no de-ice cycle that must run because the loads they serve need condenser water or chilled water 24/7 (clean rooms or computer room HVAC systems with out economizer cycles for instance) ice up, resulting in damaged fill, vibration safety cut-outs, and occasionally, fan blade disintegration, all of which ripple out to loss of service and more headaches.
- Dry pipe sprinkler systems freeze either because the condensate legs were not installed or properly located or they were installed properly but not maintained.
The final bullet makes an important point which is that maintenance is a critical aspect of dealing with extreme conditions. A system that has been designed with forethought to accommodate conditions beyond design but which has not been properly maintained will still fail to deliver when the extremes are encountered. But a solid design that considers the extremes is the first step down the path to success and sadly, experiences like the items in the list indicate that many of our facilities are lacking a good foundation in terms of being arranged to deal with extreme weather.
This list is not a theoretical discussion. Most of the items are actual problems that I know have happened this week based on direct conversations with the folks dealing with them. The ones that aren’t know events from the week are things that likely happened this week based on past experiences under similar conditions. And Murphy, subtle trickster that he or she is, usually triggers this stuff at the worst possible moment.
For instance, when I was a facilities engineer at Komatsu Silicon’s Hillsboro wafer fab (now Solar World’s manufacturing plant) in about 2 hours on one night of extremes, we had 4 dry pipe sprinkler systems rupture, discovered we could not keep most of the utility air handling systems serving critical support areas like RODI on line, and severely iced up the towers, creating problems with the chiller plant that lead to problems holding critical conditions in the fab. That night was Christmas Eve 1997.
So, as you settle in on a night where its “not fit for man nor beast outside”, with hot buttered rum in hand and visions of warmth, festivity, and romance complemented by a view of a winter wonderland outside your window, say a little prayer for the folks out there running facilities. There are a lot of them that are working because their facility has to stay on line round the clock no matter what. And they’re probably not quite as relaxed as you are since they are learning some things the hard way; things that you may want to consider as you develop your next design or preventive maintenance plan.
Senior Engineer – Facility Dynamics Engineering