Canadian Consulting Engineer

Building HVAC & Controls: Trouble Shooting

August 1, 2012
By Canadian Consulting Engineer

CCE interviews commissioning expert Bill McCartney of

CCE interviews commissioning expert Bill McCartney of

Toronto to discuss some of the worst common problems he

finds with existing buildings’ HVAC systems and controls.

Bill McCartney, CPMP is a partner of Isotherm Engineering in Toronto and director of commissioning services with the company. He has 46 years of experience in the HVAC & R industry and has been active with several industry organizations, including the Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

He is certified by ASHRAE as a Commissioning Process Management Professional (CPMP), currently a member of the ASHRAE TC 7.9 Building Commissioning Committee, and immediate past chair of the ASHRAE Handbook Committee. He is also a recipient of ASHRAE’s Distinguished Service Award. He is currently serving as a director-at-large for the Building Commissioning Association, a non-profit international association based in Oregon.

CCE interviewed Bill McCartney in July.

Q. When re-commissioning existing buildings, what are some of the worst problems you have seen with the HVAC design?

The most common and difficult hurdle is the lack of documentation for the existing HVACR and energy consuming systems.

When we’re doing a new building, we work with the owners and design team to figure out the Basis of Design. But in existing buildings, a lot of the documents that were created originally, perhaps 20 or 25 years ago, have disappeared. In fact in those days what we call a “basis of design” was probably never written. It’s only because of the ASHRAE commissioning process that the terminology of the “owner’s project requirements, “and “basis of design” have come to exist and have eventually found their way into LEED.

Without that documentation, when we come to re-commissioning and figuring out the problems we are sort of re-engineering the building and working backwards.

Oversized equipment

Q. Why do you think there are so many problems with the HVAC systems in existing buildings?

When we do component and system performance verification testing we often discover that the chiller and heating plant are oversized. This is especially true when lighting and energy efficiency retrofits have been done, or when the system has been tightened up through updated building automation.

Unfortunately, this patchwork, band-aid approach over a period of time may create incompatible and inefficient operations that often threaten the life-cycle of the components.

A lot of the buildings I’ve seen lately were designed in the mid-1980s and built in the late 80s and early 90s. The design criteria in those days were a lot different. Lighting levels were a lot higher, ventilation had started to improve and there wasn’t as much attention paid to the envelope. And the building systems were, as we have discovered, extremely oversized.

When air-conditioning equipment is oversized it is not operating efficiently. It starts and ramps up until the building is cooled, and then it turns off. With the equipment off, the air is not being dehumidified and so the space begins to feel damp and uncomfortable.

Oversizing is still a problem. If you talk to the chiller manufacturers they’ll tell you that they rarely see a chiller operate above 60%. So owners often lay out a lot more capital on equipment than they need to.

For example, we commissioned a complex of two residential high-rise towers that had been built just four years ago. We found out through our discovery that when the HVAC system was originally started up, in one of the buildings the chiller malfunctioned after an hour and didn’t work properly for a year. So they piped in chilled water from the other tower. Guess what, that equipment carried both buildings, which tells us the chiller was double the size it should have been.

In another case, we found that the systems were delivering 30,000 cfm too much air. Well, heating or cooling, and dehumidifying or humidifying 30,000 cfm when it is not required is very expensive.

Systems often switched to manual

Q. What are the worst problems you have found with building automation systems and controls?

When nobody has the documentation as to how to run the building, eventually the operators will run the building the best way they can, and in the case of a commercial office building the operation is based on reacting to tenant responses. The operators don’t want people complaining to their boss that they’re uncomfortable in the building. So the system is often being run manually.

Q. What’s the problem with that?

It’s not the intent, and it’s not efficient. Let’s say if somebody complains it’s not warm enough, bringing up the boiler temperature is not the solution unless it’s a problem at the system end. If the terminal doesn’t work properly then turning up the boiler does nothing but waste energy.

In a lot of cases the controls design is strictly done by the controls manufacturer or his secondary supplier. Some designers will write a description of what they want to happen, but then they rely on the controls manufacturer to do the work. There will be a basis of design, or a schematic, or a picture drawn, or a philosophy written. But it’s up to the actual controls supplier to decide, “What components do I need and where do I put them?” The controls suppliers might be one of the big manufacturing companies or an independent secondary supplier.

Then when we come to do the commissioning we’ll find that the equipment or the system is not capable of responding to the requests of the designer.

When you see, for example, that the manufacturer instructions say: “put the duct sensor two-thirds of the way down the main run,” and then the engineer turns around and designs the duct to split at about 3 feet, you know that the system can’t do what the controls manufacturer requires.

A lot of the people who work in building controls are new, they’re young. It’s because that industry has grown so fast. Someone might take a two-week programming course, then he goes out and takes “the product” and applies it to “the building,” but he hasn’t a clue what he’s looking at.

Here’s an example of what can happen. Say you have a gas-fired appliance, whether it’s a boiler or a heating unit, that usually operates at a minimum firing position of around 30%. The individual who is applying the new building automation system was probably told that the unit was modulating, so they set the operating signal to go from 0 to 100%. Well it actually starts at 30% which will likely be greater than the heat required, so the system will overheat the space.

Or if you look at cooling: if it’s direct expansion and it’s in stages, the controls programmer doesn’t understand why [the building] is not getting his air-conditioning because he doesn’t understand what happens when he turns the stages of cooling on or off.

It’s a systemic thing. You have got to understand the system — not just your little piece.

Variable frequency drives not always the right fit

Q. Is there an issue with compatibility when they mix and match different systems?

Yes. There is a fallacy out there that the BACnet protocol solves all problems, but it doesn’t. There’s still a gap of understanding.

Another common problem we come across is that variable frequency drives are being installed in many cases where they’re not appropriate. The designer reads an article that says you can save 20% to 30% of your energy by using a VFD, but he doesn’t think about what it does to the system.

If you pu
t a VFD on a direct expansion system it might freeze up the compressors because there isn’t enough airflow. I’ve seen this happen numerous times. If you put a VFD on a gas-fired appliance you have to remember that there is a minimum airflow requirement for gas-fired appliances [set] by the Canadian Gas Association.

VFD is a good idea — it’s a great idea — but you have to understand what the impact is on the system and how it operates.

I was out in Saskatoon two weeks ago where VFDs had been added to all the air handling equipment. The building operator was complaining that the motors were burning up. When I looked I saw that they were set at 15 Hz. The motor manufacturers recommend that you should run a motor at no less than 20 Hz.

Q. Are you in favour of high-tech sophisticated controls, or more simple systems?

It depends. I have designed control systems where we control the temperature within plus or minus 1 degree F.

With an older building that is just single-stage heating, and single-stage cooling, then you only need a single-stage heat-cool thermostat. You don’t need a building automation system. But if you have a building where they want to control the energy consumption range, then, yes, you need a building automation system.

Q. Do you ever find good systems in existing buildings?

Oh yes, but it’s only when they have been properly designed in the first place, correctly installed, and appropriately maintained, and where any changes to the systems have been documented and operated.

And don’t forget, [as building re-commissioners] we only get called in because it’s a bad building; we don’t normally get called in when a building works well.

Sometimes it is just a matter of going through the existing system’s programming, sorting out all the issues, training the building staff and walking away.

We did that with a hospital and long-term health care complex in the east end of Toronto, for example. It had two groups of operators, one in the hospital, one in the long-term health care building, who were operating totally independently of each other with systems that were 10 years apart in age. All we did was go in and figure out how the systems worked, wrote the systems manual, trained their people, and walked away. We saved the hospital approximately 15% of the energy according to the feedback from the owner’s new building services engineer.

Monitoring and verification (M & V) is a market we’ve become certified in and moved into quickly. It is a LEED credit for new buildings, but it’s also becoming something that we’re adding to existing buildings.

Who should do building commissioning?

Q. What kind of experience do you believe qualifies an individual to hang up their shingle as a recognized Commissioning Authority?

I contend that 15 years of experience is the minimum. My view is that an individual who has five years in design, five years in construction, and five years in operations and maintenance should have the overall experience required to serve the role properly. Then they still need to take courses or get involved with a commissioning firm to learn the process.

I was asked recently what I consider to be the most important requirements for someone to be a commissioning authority. I didn’t hesitate to say that understanding the value of communication and controls are the keys. You have to be able and comfortable in communicating with the owner (or their representative), the architect, their sub-consultants, project manager, general contractor, major sub-contractors, controls, TAB [testing, adjusting, balancing] contractor, manufacturers representatives, and the eventual users of the building, the operations and maintenance personnel. If any one of them senses weakness you are doomed to be regarded as ineffectual and in essence ignored.

If you can’t write the systems manual based on meetings with the controls sub-contractor and design team prior to the issuing of the control shop drawings, you’re in the wrong business.— BPcce


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