The life & times of an HVAC Engineer

Life has been a little busy of late, I’ve moved house, changed job role (I’m currently on a secondment as a ‘Project Engineer’ on some BP projects) and had a few other things on my mind. I hadn’t realised quite how long I’d been away from the blogging though until a colleague from another office commented on how they were missing my blog. So, this one is for you Stuart.

One of the challenges on my previous project was to ensure that no air could pass from room A to room B or vice versa. Not especially difficult you might think, considering there was a wall between the rooms without any doors or windows in. What there was though was a large hole in the wall between these rooms for a conveyor belt to pass through. This was made into even more of an interesting challenge given that the objects on the conveyor belt were very lightweight, meaning that they could easily be sucked up if you had very low pressure air.

Here’s a little sketch to explain:

Don't let the air move between A & B

To make sure that no air could ever go from room B to room A we just made sure that room B was at a lower air pressure. You can see this on the sketch above, room A is at 15 Pascals and room B is at 0 Pascals.

But how do you make sure that air isn’t going from room A to room B? Especially now that you have higher pressure in room A…this means that the air is pushing to get into room A. Normally you would deal with this by having a small airlock room between the two, but here we have a conveyor belt that is constantly running so you can’t do that. What we did instead was to install an extract duct within the wall so air was being pulled into the duct from both rooms, like this:

Use an extract duct to capture air in the opening

It’s a simple idea, but one that is difficult to get right. If suction airflow is too small then you will still have air flowing between the two rooms, if it is too high then you will suck all of the lightweight items on the conveyor belt into your duct. And of course it’s not just about the speed and volume of the airflow, it’s also about the shape of the opening and what airflow patterns that makes – much like the aerodynamics of a formula one car. And, much like the aerodynamics of a formula one car we had to model our designs using ‘Computational Fluid Dynamics’ (or CFD).

Doing this modelling allows us to see what the patterns of the airflows around our design will be, as well as how fast they will be. Usually the results are displayed using colours to indicate direction, pressure, speed or temperature depending on what you’re trying to find out. As it turned out, it was a very good job we did do the modelling, because the first design gave us this result:

The direction of the arrow shows the direction the air is flowing in, and the colour shows you how fast it is. So the red arrows going straight across the middle of the picture from left to right show air flows going straight through the opening at nearly 10 metres per second! This obviously isn’t what we were trying to achieve. We tweaked the design of the opening, and the volume of the air being extracted, and ran the model again. The final version shows flows like these:

Final airflows - x cross section view

Final airflows - y cross section view














So now we can see that the design should work. The arrows/airflows come into the opening from the sides and upwards into the extract duct as we want them to. Though of course a model is only as good as the information you put into it, so we need to make sure that the construction, installation and commissioning makes the reality as close to the modelled design as possible.

With thanks to Richard Ozaki at Mentor Graphics for the modelling and the images


{February 21, 2011}   Here’s one I made earlier

When I was picking my degree course I chose engineering, rather than something more theoretical/’academic’, because I like to get hands on. I like to apply my knowledge to something real and, occasionally, I like to get a bit grubby. I’ve always been like that. When I was little I shunned pre-made toys in favour of playing with scissors, glue & felt tips to create something. When I was in primary school I was the goalkeeper for the girl’s football team not because I had any real football talent but because I was one of the few girls who didn’t mind getting muddy. At secondary school I delighted in subjects like ‘resistant materials’ because I got to use my maths skills to work out the dimensions for something real, and then go & use my hands to actually physically make it real.

These days, though the maths and drawings I create do finally end up being made into a building it’s not me that gets to go and lay the bricks or install the ductwork. Most of the time that’s fine, I still take great pleasure in seeing a building or system that I was involved in the design of, being installed. There’s something truly satisfying about seeing your designs working hard and being useful. But sometimes I feel like I missing something…and that something is getting hands on. Last week though, was a week where there was nothing missing and where I was working with a huge smile on my face. Why? Because I was crawling around on the floor sticking down carpet tape to mark out the full scale dimensions of a cold work area I’m designing.

Part of being a good engineer is being able to communicate clearly to other people, and when those people aren’t engineers it’s important to find ways of getting information across to them in ways they can really understand. As I’m in the middle of designing something that will be completely new to out client, something unlike anything else they have, now is a particularly vital time to get the communication right. One of the areas that people who aren’t familiar with looking at drawings can sometimes struggle with is scale. As we all know from looking at a map it can sometimes be hard to get a realistic sense of size from looking at a scaled down image.

So, I spent last Thursday afternoon creating this:

It’s a full scale outline of a ‘cold work enclosure’ which is essentially a giant fridge, the diagonal lines are the doors. The squares within the big rectangle show where the weighing scales and table will go. The little square in front shows where there will be a column within the room. On the right, making our model 3 dimensional, is the existing piece of equipment which will go into the space next to the cold work area once it has been build.

Laying the equipment out full size like this meant having to calculate all the little clearance sizes that are needed to make sure everything fits in together without clashing, and allowances for construction tolerances (as few things of this kind of size are ever made millimetre perfect). It gave me a brilliant opportunity to give some very in depth thought to the detailed design of the equipment, and to be able to reflect on it once it was complete. It actually resulted in us changing which direction one of the doors opened as it became obvious once it was laid out that the column was less of an obstacle that way.

Most importantly though, it has given our client the chance to get a feel for how big the area will be and whether they will be able to fit and operate all the necessary items into it. Doing that now means we’re far less likely to run into issues once it equipment has been made and it’s too late to change. Also, clambering around on the floor and playing with sticky tape reminded me hugely of my Blue Peter loving days…so I had a lot of fun!

One thing I have to take into account as an HVAC engineer is how noisy the air distribution is going to be. You can’t usually see or feel air, but if it’s got some force behind it you can sometimes hear it – think about the sound of the wind howling around tall buildings, the squeal you can get out of a deflating balloon, the background noise around the car on the motorway (it’s not all from the tyres & engine!) or even the beautiful noise you can get from flutes, clarinets & the like.

Well since my job is often to make rooms more comfortable, by providing them with fresh air and keeping them at a nice temperature, it would somewhat defeat the object if I then made them really noisy. So to avoid the whoosh & hum of fast moving air it’s important for me to design the ducts to be big enough to keep the velocity low, and to avoid obstructions & corners (much like in my earlier post: Die Hard School of Ductwork Design). The lower the air speed, and the smoother the ductwork, the quieter the air will be…but the ductwork will take up more space – so there is a balance to be had. I also need to make sure there are attenuators before and after the fan to make sure the noise generated by the fan isn’t passed into the rooms. On top of this if there are quiet/private meeting rooms I need to consider installing ‘cross-talk’ attenuators to stop conversations from travelling from one room to another via the ventilation. If there is noisy equipment in the plantroom (the room that contains all the boilers, air handling units & other equipment to keep the facility working) then I might also need to consider acoustic louvres to make sure air can get in, but not much sound can get out.

But where else in engineering is sound critical? There’s some relatively obvious roles like sound engineer or telecommunications engineer…but have you thought about the impact of acoustics on car design? Many automotive engineering companies now employ NVH (noise, vibration & harshness) engineers to make sure cars give good feedback and a safe, enjoyable experience to their drivers and passengers.

But what if your car makes no noise? There is a lot of debate at the moment about what noise electric vehicles ought to make. There are concerns that if cars are silent they’re a far greater risk to pedestrians, especially blind & partially sighted pedestrians, who may not be aware that the vehicle is there. Also, many drivers actively enjoy the sound of their engines, so may not wish to drive silent electric vehicle. Not to worry, Elvin from Warwick University has come to our rescue. “Who is Elvin?”, I hear you ask. Elvin is and ELectric Vehicle with Interactive Noise, and he looks like this:

image credit: Warwick University

He’s a bit of a test project to gauge opinion on the acoustics (whether artificially added, or left ‘silent’) of electric vehicles and he lives on the campus of Warwick University. If you’d like, you can go and listen to Elvin and give Warwick your feedback on what you think he should sound like. As electric vehicles are likely to be the transport of tomorrow I think this is a brilliant opportunity to be involved in a little bit of engineering design. I’ll certainly be taking part!

{November 8, 2010}   Is this thing switched on?

In the facility I am currently working on, part of the process is to spray the product with a fine mist of 70% Isopropyl Alcohol, ‘IPA’. As you can imagine, that poses something of a hazard. To paint a picture of how much of a hazard, here are a couple of facts:

Lower Explosive Limit of IPA = 2%
[i.e. only 2% of the air volume needs to be IPA for it to still be flammable]

Flash Point of IPA = 12oC
[i.e. the room temperature only needs to be 12oC for the gas to vaporise & be ignitable]

Image credit: bruce7 from istockphoto

So, as it’s critical to spray the product with this hazardous substance, how do you go about making sure the operators don’t get blown up? Well there are a variety of different ways, so to name just a few;

  • Minimise the amount of spray used
  • Ensure all equipment within the hazardous zone created is safe for that environment (i.e. it is non-sparking / intrinsically safe / ATEX rated)
  • Provide extract ventilation to keep the amount of IPA in the room below the lower explosive limit

Well as a building services engineer, and thus a designer of ventilation systems the latter is the most relevant to me. So off I went & designed the ventilation to remove the IPA and protect the operators. Brilliant, Chloe saves the day…just one problem though…how do we know it’s working? And if it’s not working, how do we stop the machine from continuing to spray IPA into the room? Aah. Yes. Well…best do something about that hadn’t we.

So to make sure the machine doing the spraying knows that it’s safe to spray, we’ve included a flow sensor in the extract duct. The machine receives a signal from the sensor to say there is air flow, and then it can safely spray the product with IPA. We can all breath (an IPA free) sigh of relief. But no…what if the sensor is broken?! Okay guys…we’re getting into double jeopardy here, but as it’s for safety then the more the merrier, what do you suggest?

A couple of process engineers later and to ensure we have a double layer of protection to check the ventilation is working we are installing a sensor on the fan motor – that way we know it’s running. If the fan motor isn’t running then you know it’s not safe to spray the IPA.

I can’t help but thinking though, just because the fan motor is running doesn’t mean that there is extract ventilation…the fan or drive shaft could be broken. A little bit of me thinks that a few ribbons (perhaps that’s giving way to my girly side though) around the ventilation intake would be a visible indicator of the extract working that could never give a false signal. It would be reliant on the operators stopping the machine from spraying though, as ribbons can’t give a signal directly to the machine!

Image credit: The Seattle Times

I came to the realisation recently that engineers are very good at thinking everyone knows what they’re talking about…and I’m sure that criticism can be applied to me too. For all I write about what I’m thinking and doing as an engineer I don’t always remember that most people outside the process industry have never seen the innards of a process facility, and people outside of engineering generally haven’t had the chance to stick their head into any ductwork. So, for many folk their only experience of what an air-conditioning system looks like on the inside comes from Bruce Willis in Die Hard, Tom Cruise in Mission Impossible, Milla Jovovich in Resident Evil or even Homer & Bart escaping from Willy after stealing grease in the Simpsons. Now those scenes are not entirely accurate, though there was an escape from Alcatraz that utilised the ventilation shafts, but they can still be very helpful in explaining a few fundamental bits of ductwork design. So, without further ado, let me begin the Die Hard School of Ductwork Design:

From an HVAC engineer’s perspective it’s really important when designing ductwork layouts that you ensure air flows are as smooth as possible. The smoother they are, the more energy efficient and quieter the system will be…and the more likely the system is to work properly! The same goes for designing the ductwork from Bruce Willis’ perspective though. After all, whatever gets in the way of air is bound to get in the way of Mr. Willis, no matter how much of an action hero he is! So…if you were clambering around in air-conditioning ductwork, trying to escape from the bad guys, what might get in your way?

1) Corners

Right angles bad, curves good

Obvious as it may seem, it’s still worth a mention. It’s never really possible to lay all the ductwork out in straight lines with no corners, so they are a necessary evil. However, putting yourself in John McClane’s shoes (or lack thereof), how would you like the corners to be designed? Personally I think a nice gentle curve would be alot easier to get around than a sharp right angle, and from the look of this I think Mr. McClane agrees:
It’s certainly the case that airflow is alot smoother around a curve, which means it looses less pressure so less power is needed to get the air to wherever its going.

2) Joints

Internal flanges bad, smooth insides good

Anything that gets in Bruce’s way, and makes his life more difficult when navigating buildings via the ventilation will get in the way of the air. So when joining the lengths of ductwork together it’s best to put the joints on the outside. The same goes for any other obstructions in the duct work – if Mr Willis would have to put in extra effort to squeeze through then so will the air.

3) Access Hatches

Obstacles bad, access good

When trying to sneak up behind the bad guy through cunning use of ductwork the last thing you want is to be stopped by some impassable obstacle. So to make it possible for Bruce Willis/John McClane to out manoeuvre his enemies you should always put in an access hatch nearby. These access hatches are also rather essential for maintenance staff to keep everything in order without having to take down the duct work to access moving parts – in this instance a damper.

You can also help Bruce, Milla, Tom & Homer out by making ducts large with nice smooth inside surfaces. The less of a squeeze it is for Hollywood stars or air then the less energy it takes, and the same is true for keeping the friction low.

So if you’re ever asked to design some ductwork, bear Bruce in mind and think “What would John McClane want?”.

[Artwork created by my fiancé James Agg from my terrible sketches]

Ingenious Donkey

Making an ass out of me

A week or so ago I thought I’d finished writing the specification and producing the drawings for the air handling units for the project I’m currently working on. Then I sat down to review all of the specifications with engineers from other disciplines, and with the buyers. It quickly became apparent that I, and many of the other engineers, had made assumptions about what items had been included in other department’s specifications. It’s really not a problem discovering these things at the current stage of the project – we just add, or occasionally delete, items into our specifications to make sure that all the interfaces are covered. If we hadn’t stopped to have that review though, there would have been a few gaps that would have left us looking pretty silly once items were installed on site. After all, it’s no good specifying, paying for, and installing equipment if no-one provides a power supply to it!

One of the items that had been left out for example was the mesh in the low level extract scoops. You normally extract air from a room via grilles in the ceiling and the ductwork contractor provides all the necessary items. However, in clean rooms it’s often preferable to extract air at a low level, in which case the architectural contractor forms the ducts within the room as they’re making the rest of the room. That’s fine so long as they’re aware of all the bits you need within that ductwork – like a mesh to stop pieces of paper or rubber gloves or cleaning cloths being sucked up into the air extract system. Thankfully we found out that they hadn’t included the mesh in their specification and now it is in there. I wouldn’t have envied the commissioning engineers trying to figure out what was wrong with the new system only to discover the filters, which are intended for very tiny particles, were covered in rubber gloves!

Another assumption which has been made a few times recently is that I’m a secretary or document controller. Or more simply, when people haven’t seen me in a room, they often assume the meeting room or office is going to have no women in it. It can be a little frustrating having to regularly put people straight & explain that I’m not just there to take the meeting minutes but can also make useful contributions to the discussions as well. That said, I’m sure part of that is my age & youthful looks rather than just my gender – I have been ID’d when buying alcohol within the last 6 months after all! The second assumption, that there will be no women in any given engineering office/meeting room can actually provide a certain amount of amusement. The mischievous, mould-breaking streak in me rather enjoys seeing people blush beetroot red as they’ve said ‘morning gents’ then realised I’m there. I also find it rather curious how embarrassed many male engineers become having realised they’ve sworn in front of a woman as well. It’s not like my delicate donkey ears haven’t heard such words before after all…

Last but not least, I went on mentor training last week in preparation for having a 16-19 year old mentee from the local school’s Engineering Diploma programme. One of the main aspects of the training was about not assuming the mentees will know what we consider to be the most basic of work place behaviour. It was fascinating listening to previous students’ testimonials. Prior to the help of a mentor they had made mistakes on work experience such as answering a work phonecall by saying “yo”, or accidentally making a cup of mixed tea and coffee and then being too embarrassed by their error to do anything but drink the horrible concoction.

As you can see, over the last week it’s becoming increasingly clear to me that the saying, and title of this blog, “when you assume, you make an ass out of you and me” really is rather true. If I can try and make a few less assumptions perhaps I’ll avoid some embarrassing moments, not just for myself but for others too. After all, who wants to be an ass?

{October 5, 2010}   What’s behind door number 3?

As I’ve said on this blog before, it’s really important to keep pharmaceutical facilities clean. That means that when they are in production you can’t take down any of the ceiling tiles, and if you take one down outside of production hours then there must be a full clean down afterwards…which can take as long as 3 days, which is a lot of expensive lost production time. That might not sound like a particularly big problem, after all how often do you need to take a ceiling tile down? If you design the facility well, and keep items requiring maintenance out of the ceiling void wherever possible then there’s usually no need. Until you decide to refurbish or upgrade the facility that is. “What’s the problem with that?” I hear you cry – “Surely if you’re carrying out a refurb you’re going to stop production & take down the ceiling tiles anyway?!”. The problem is with doing the design.

Of course most facilities have “as-built” drawings of all the services that are in the ceiling void, so you should already know what is up there, and that is what you base your design around. More often than not though, until production is stopped and construction begins there are no opportunities for a full survey and there are almost always a few surprises along the way. Sometimes it’s little things like a cable tray where you didn’t expect one, sometimes the ducts or pipes have taken a slightly different route than is shown on the drawings. Or perhaps you just can’t find the smoke detectors, or the control panel for the doors. All of these things result in needing to tweak your designs, and tweak them fast…you probably have 3 months worth of work to fit into a 6 week shutdown (if you’re lucky) and now your lovely, simple, quick to install designs are out of the window.
That though, for me, is when things get exciting, I love a bit of a challenge, I enjoy solving problems…and when the team pulls together, and everyone from the client, to the contractor and ourselves in between is trying to make something new work as quickly as possible it’s actually quite a thrill. It’s even more pleasing when your fast maths and new layouts are being approved, then installed and before you know it you’re watching them operating successfully.

Yesterday morning the unexpected find revealed was an entire fan coil unit, moving over one thousand metres cubed of air each hour. By the afternoon I was busily working on the maths for a new solution, this morning the layouts were completed, now I’m working on client approval and getting contractor buy-in. It may only be a matter of days before the design is being installed, and right now I have a huge smile on my face.

{September 28, 2010}   Reasons to be picky, one, two, three

We’ve all been there, stood in a shop we’re bored of, next to someone we normally care about but right now is driving us up the wall, wondering when we’ll be able to leave….all because someone likes that chair but thinks it’s not quite right because they’d like it to have a straighter back, or a lamp paler shade, or a heavier door knocker or more stripy wallpaper…or some other tiny detail that you think is utterly unnecessary but they’ve become obsessive over.

If you’ve ever thought that your parents, wife, flatmate or anyone else taking on some interior design were being overly pedantic when picking an item have you ever discussed with them why that detail is quite so important to them? It may be that they’ve got spinal problems so need a very upright seat, or are struggling to see well enough their evening hobby of embroidery so need a brighter light, or they’ve started to go a little deaf so need a door knocker that makes a louder noise. Or perhaps it’s just that they really like stripes…or have low ceilings that they want to appear higher.

You see sometimes it’s the very fine details of an interior that are the most important aspects of the design as a whole. I’m currently working on a pharmaceutical project, and we’ve gotten to the stage of selecting the “finishes”, and it’s a very prolonged process over which people are very exacting. That’s not because we’re working with fussy people who want a precise shade of magnolia to match their cream leather sofas, it’s because the finishes in a pharmaceutical facility play a vital role in its cleanliness. Of course there are many other aspects, such as good air-conditioning systems supplying well filtered air, good control systems and well trained staff, to name but a few but right now I’m working on finishes.

When you’re talking about whether a wall covering, flooring or ceiling tile contains crevices in which dirt can gather it suddenly becomes very important to specify exactly the right product so that you know you’re manufacturing in a truly clean environment…after all, you wouldn’t want dirty drugs. To maintain this clean, safe facility there are a lot of very exacting standards that the finishes must live up to. Not only must they be smooth and crevice free now, but they need to be robust enough to keep that finish as they are subjected to years of trolleys and people moving over them, or bumping into them. They must be sufficiently waterproof and chemical resistant to withstand the arduous cleaning regime, which includes everything from floors to ceiling lights. It’s also really important to be very precise about details like light switches and door handles to ensure that there are a few horizontal surfaces for dust to settle on as possible.

It’s a very time consuming decision making process, but it’s one that is hugely important and, albeit indirectly, lives depend upon…they’ll certainly be adversely affected if you get it wrong after all. So maybe next time your parents or partners are dragging you into the 5th DIY shop of the day, searching for that perfect kitchen cabinet door because they want to be able to clean it easily, you’ll have a little more patience…I know I certainly will. I’ll also be thinking along very different lines when I’m next getting the kitchen re-fitted!

et cetera
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