Attack of the 20-foot Maintenance Man!

Now it may be of some surprise to designers and engineers that HVAC rooftop equipment needs to be serviced, so I have come up with the solution: genetically-enhanced maintenance people that are 20 feet high.  Alright, so my solution has some flaws, like door handles being broken off the AC units by those giant hands, but seriously now, why such a drastic idea.  Two reasons and both reared their ugly heads recently on my projects, namely roof and equipment access.

Let’s talk about roof access first.  I know it’s not the engineer’s job to specify and layout roof access, but it should be at least reviewed by them.  Try to put yourself in the shoes of the maintenance staff when they go to service the equipment or when something goes wrong.  Typically this does not happen on a nice sunny Tuesday afternoon, it will usually occur in the middle of the night in a downpour or a blizzard.  And to add insult to injury, work has to be performed in those conditions on roofs that are made from that white, plastic, slicker-than-a-greased-pig roofing material.  All these conditions can quickly turn a simple situation into a worker’s compensation claim, with the maintenance or repair still left undone.

ACTION ITEM #1: In design, check all roof surfaces that have roof drains or HVAC equipment and make sure that you can reach all areas without carrying a ladder around.  Remember even a three foot elevation change can be dangerous in some weather conditions.  This check can be effectively done by checking the architectural roof plan and making sure that they have permanent ladders noted where you would require them.  Also, in addition to checking for changes in elevation look for access to the roof itself.  Man-doors are preferred, but a hatch and a ladder also work.

Second is the HVAC equipment access.  In the age of high-efficiency systems, I have seen my fair share of the heat-wheel type energy recovery units; these are my number one access offenders.  These AC units can be as tall as a double-decker bus, with a fan, motor, filters and possibly other components located on the top deck, and all of which require maintenance.  Add in that white roof and the inclement weather and your recipe for disaster shows up again!

ACTION ITEM #2:  Also in design, check the height on the rooftop HVAC air-handlers (cooling towers, chillers and anything else for that matter). If they require a ladder for proper service then consider adding a permanent catwalk system.  If that isn’t possible because of budget reasons, try to get good walk-way pads all around the unit that aren’t slippery and add some permanent ladder tie-off points to the equipment casing.  Other ideas may include removable or moveable scaffolding, but a lot depends on what can be easily moved to the roof and the available storage.  I would also check out what OSHA has to say about this as part of your due diligence.

These simple things are easy enough to gloss over in your efforts to get you designs out the door but if you want your design to stand the test of time, with consistently low energy consumption, it has to be maintained and for that to happen you have to make it easy for the people working on you equipment to properly access to it.



HVAC 360 - Episode 010 - Owner Training

In this episode, I dole out some tips about Owner Training.  It's really amazing to me that in this age of higher energy efficiency and green technology, that the easiest energy savings can be attained by making sure that the building is being run properly.  Honestly, without looking at any studies I think its safe to assume that you can probably trim 10% off your energy useage with some good owner training.  The fact is that building managers need to be able to motivate their staff to care about this and easier said then done.  But I at least wanted to point out a few things that I have seen in the field that seem to make sense.  So have a listen and let me know what you think.

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Until next time know what you build, and share what you know.

HVAC Freezestats - A Coil's Best Friend

A freezestat is a safety device that protects a water coil from freezing (DX coils do not require them).  Another name for a freezestat is a low-temperature cut-out, limit, or detector, take your pick.  In my years of inspecting these simple devices, the installations have been like snowflakes, no two were alike.  This seems odd because they all come with installation instructions that are pretty clear, to me at least. Here's how they should be laid out.

1. Mount the body of the unit outside of the ductwork and near the top.  The rule of thumb is that each sensor is about 20 feet long (exact lengths may vary) so at a ratio of 1 linear foot of element per 1 square foot of coil, one sensor should cover about 20 square feet.  And at a standard coil velocity of 500 feet per minute, one sensor should cover the coil area for a unit supplying approximately 10,000 cfm.  Now this doesn't mean that if you have a 11,000 cfm unit you should use two sensors to cover a coil, but if you have a bigger unit, realize you may have multiple sensors (I saw one the other day with five).

2. Where the sensing element enters the case you should have some sort of rubber grommet or bushing.  Airflows within the unit's casing can cause the element to vibrate and damage itself.

3. Don't crimp, pinch or crush the sensing element.  This capillary tube is delicate and care should be taken to install in properly with the approved turning and mounting devices.  Failure to do so may render the element ineffective. Resulting in a burst coil.

4. Install the element mostly in the horizontal plane and in a downward direction from the body of the device.  You should first layout how you are going to install it on the coil.  Then starting at the bottom, you should work your way back to the body of the unit.  A lot of times I have seen the opposite type of installation where you work from the body to the end of the tail.  Often this results in ending up with a foot or so of extra element and the tendency is to just wrap the tubing back on itself.  This is not correct.

5. The bottom of the coil will freeze first.  The row with the end of the sensing element should be six inches from the bottom of the coil with the next row 12 inches above the last.  The elements cover six inches above and below, that's where you get the one linear foot to one square foot ratio.  Also, if the bottom is most likely to freeze and the top is the least likely to freeze if you don't cover the very top of the coil its really not that critical (unless the designer says so).

6. Freezestats should be installed on the downstream side of the heating coil.  This assumes that you have a heating coil or that you heating coil is in the pre-heat position (i.e. before the cooling coil as seen by the flow of outside air). If you cooling coil is the only coil or if you have a heating coil in the re-heat position (after the cooling coil) then I would say put in on the downstream side of the cooling coil.

Once installation is complete, the operation of the freezestat is pretty simple.  If a portion of the element (typically 12-18 inches depending on the manufacturer) falls below the temperature set on the sensor body (which typically is adjustable from 15-55 deg F) then two sets of contacts will open.  The first line voltage contact shuts the unit down and should return all components to the unoccupied conditions (i.e. outside air damper 100% closed, etc) and the second low-voltage contact will send the alarm to the building automation system.  Once the freezestat is tripped it requires a manual reset from the building staff.  This ensures that someone visually inspects the unit prior to returning it into service.  This reset button also typically doubles as the test button to make sure that the freezestat is working properly.

This manual reset is really important, but it can also be the bane of the building operators.  Because if the freezestat is not properly installed it can cause nuisance tripping that may cause the operators to start a series of corrective measures that could result in poor system performance or safety violations. So it all starts with proper installation.

Turn down the heat! I'm melting!

One of the perennial struggles as a commissioning agent is to understand what the owner wants the range on the thermostats to be set at.  One rarely sees it in the specifications of the design engineer and it typically falls to the controls contractor to set up the range. This is where an Owner's Project Requirements (OPR) document should clarify this question, but is all to often omitted.

So what happens in the real world?  Well I have seen +/-10 deg F, so should you elect to hang meat or start a steam shower you have been given the power.  However, I more commonly see that the temperatures are set at +/- 2 to 3 deg F.  This narrow range can still be problematic, as it was for one of my clients.  You see shortly after opening their new building they started getting temperature complaints.  As the building has three identical wings the maintenance staff decided to play around with the systems controls. They took the temperature adjustment control away from one of the wings and a strange thing happened, the complaints stopped from that wing, but still remained in the other wings.  They then removed control from another wing and again the complaints stopped. Now, the entire building has fixed setpoints and everyone seems happy.  If you are confused about why they were happier with less control, let me explain.  First off, the staff doesn't know that they no longer have control, shhhh!  Second, what seemed to be happening is that the staff would be cold in the morning, and turn the thermostat up.  Then, during the day they would get hot and turn the temperature down.  Now at the end of the day would they turn the thermostat back to the normal setpoint? Nope.  They would forget and the temperature the next morning would be cold again, so the cycle continued.

In the end I think that the best bet is to just set it and forget it.  Most higher educational facilities implement this as a policy already and I think one of the best by-products of doing this is truly knowing where your problems lie in your facility and you don't end up covering them up through system manipulation. 

AHR Expo 2010 Recap

I stayed to the end of the show this year just so that I wouldn't feel that I had missed some aspect of the expo.  The result, nothing new.  If you have ever been to any trade shows or participated in them, then you know the feeling of wanting to get out of there and back to your families. With the expo ending at 4pm, by 3pm exhibitors were starting to pack up and the traffic was very light.  Overall it was still a good day to ask questions as there was less competition for exhibitors.  Most of them also used the time to talk and network with each other.  So hear are my lessons learned from the expo:

Big Surprises

1. No Carrier, Trane, York, Titus, Price, Cook, Greenheck at the show.  One thought was that the investment to "show big" at the expo was not worth the outlay of cash.  Can't say that I blame them and in the end, it wasn't a detractor.

2. A lot of OEM's, by that I mean that a good portion of the exhibitors sold pieces parts for larger HVAC equipment.

3. Quit a bit of exhibitors were the target of contractors.  Showcasing tools, plasma cutters, spiral duct machines, and estimating software just to name a few things.

Must do's if you attend the conference

1. Comfortable shoes! Need I say more?

2. Pick up an AHR Expo Book listing all the exhibitors and includes a map.

3. Get there for Day One and the opening of the show, I liken it to the running of the bulls, with hoards of people flooding down the isles.

4. Get your questions answered.  Here's your chance to meet with the people who know the most about a product all in one place.  In fact, the expo gives you a unique opportunity to ask 3 different exhibitors with the same products and get a consensus answer, just like a second and third opinions.

5. Go through the AHR Expo to get your rooms not only will you get a discounted expo rate but you will also get free transportation to and from the event saving cash on parking.

6. Most importantly have fun, ask questions, start conversations with vendors like, "What makes your product the best?" or "Explain what that is and why would I use it?" or even "How much of you own booth candy have you eaten?".

Special thanks to Tim Ward and his team for helping, and hosting me, at my first AHR Expo.