How to Make Almost Any Rooftop Unit Run Better Than New
The Building Operators Guide to Saving Time & Money with Advanced Rooftop Controls (ARC)
It’s the Friday of Canada Day weekend and you’re thinking about the well-deserved 3-day break coming when the phone in your pocket starts buzzing.
There’s a problem.
It’s 36°C outside, and the main floor of your building has been swelteringly hot since early this afternoon.
Your manager has been flipping breakers, tinkering with thermostats and cursing up a storm for hours – all to no avail.
This can only mean one thing: one of your rooftop air conditioning units is out of commission. Again.
Then your HVAC technician delivers even worse news…a $5,000.00 repair estimate. And all you can think of are the words you heard loud and clear in that department meeting yesterday: “We need to save money on operations.”
Rooftop HVAC units (also known as RTUs, air handlers or air handling units) are the single most popular form of commercial heating and cooling in North America. You’ll find them everywhere from offices to warehouses to retail stores. Altogether, almost 70% of all indoor commercial space is serviced by RTUs.
The reason behind their popularity is simple: convenience.
- They’re an all-in-one-solution. Packaged rooftop units combine heating, ventilation and air conditioning functions (including humidity control) into one convenient package.
- They’re unobtrusive. Once installed, your rooftop system is essentially out of sight and out of mind.
- Most importantly, they’re affordable. RTUs are almost always cheaper to install than other systems with comparable capacity.
Because of this, it’s likely that rooftop systems will remain the HVAC equipment of choice for most commercial and industrial facilities for a long, long time.
Unfortunately, as you’ve seen for yourself…commercial rooftop HVAC units (RTUs) are notoriously difficult to monitor and maintain.
You’re not alone if you’ve thought of flinging the thing off the roof.
Of course, you can’t make up a budget for a brand-new RTU out of thin air. RTUs are supposed to last 10 -15 years minimum, so you’ll probably going to have to live with this situation for a while.
It’s for these reasons that more building owners and operators are turning to Advanced Rooftop Controls (ARC) retrofit kits as a way to extend equipment operating life and reduce operating costs.
So, what is ARC? Simply put, ARC describes a category of retrofit systems that convert an RTU into a “smart machine.” The heart of this system is a device that adapts the RTU’s operating mode in real time to match the actual needs of the space its serving.
Six years ago, the US Department of Energy commissioned a groundbreaking study on ARC technologies that has changed the way we think about rooftop systems. I’ll cover the main points for consideration in this blog, but for those of you who want to get into the weeds, I encourage you to check out the report as well.
ARC retrofit kits, which incorporate technologies like variable frequency drives (VFD) and advanced economizer controls, are also much faster to implement and far more cost-effective than equipment replacement. They also improve energy efficiency and lower the operating costs beyond the level typically available with new RTUs.
With electricity rates forecast to increase by another 30% – 40% over the next 10 years, this is the next best place to implement cost savings after LED lighting.
So, how exactly do these retrofit kits work and what do you need to consider?
More importantly…do they actually make rooftop units (and your hectic schedule) better?
Let’s break down these questions, along with:
- Why rooftop units seem so prone to unexpected breakdowns
- The various technologies available to upgrade your RTU
- Why RTU management isn’t the same as building management
Retrofits aren’t right for every situation, but it’s worth investigating if you’re tired of paying to repair a different RTU malfunction every month…feeling the pinch of rising energy costs…or just plain sick of day-to-day operational pains.
- i. Variable Frequency Drive (VFD)
- ii. Demand Control Ventilation (DCV)
- iii. Advanced Economization
- iv. Peak Demand Shaving
- v. RTU Management Software
- vi. Automated Fault Detection and Diagnostics (AFDD)
- vii. Energy Accountability
First time dealing with a rooftop unit? You might just think you’ve got a particularly faulty unit or especially bad luck. In reality, RTU breakdowns are frustratingly common.
Trust me: part of my business involves rescuing people when their rooftop system needs repair. Over the years, we’ve seen just about every RTU repair problem under the sun: failing bearings, busted blower fans, frozen coils, clogged filters, “interesting” DIY repairs…you name it.
All of these problems follow an interesting trend. Spend enough time repairing these units and you’ll find you can trace just about every RTU headache back to one fatal flaw.
This flaw, ironically, also happens to be one of the biggest RTU selling points.
What’s Really Causing Your RTU to Break Down?
Put simply, rooftop units are invisible.
And at first, that sounds like a good thing.
Property owners don’t want to sacrifice valuable square footage for a big, noisy air conditioner. Besides, a grounded HVAC unit can be unsightly and susceptible to vandalism.
All are points in favour of a rooftop unit.
The downside is this: because they’re up on the roof, RTUs tend to receive little attention from the maintenance crew. Neglected and forgotten, a failing rooftop unit is often left to struggle along until it breaks.
This is the #1 reason RTUs are so prone to catastrophic failure when you need them most.
How RTUs Waste Energy, Even When They’re Working Perfectly
To make matters worse, rooftop HVAC systems are pitifully inefficient.
In fact, RTUs actually consume more total energy than any other cooling technology. Depending on the size, the compressor unit alone can run you hundreds or even thousands of dollars per month to operate.
Poor-quality parts and shoddy installation can play a role in this inefficiency, but it isn’t the primary cause. Most of it simply comes down to the fact that RTUs aren’t very smart.
- Run at a constant speed regardless of the heating/cooling demand.
- Take themselves out of use by frosting condenser coils.
- Constantly over-ventilate the building.
- Do not fully utilize ‘free cooling’ when it’s readily available.
So, not only is your rooftop behemoth tough to manage, it’s gobbling up thousands more in energy dollars than it should every year.
It’s a lose-lose situation.
Are There Any Reliable RTU Retrofit Options?
The HVAC industry has known about these problems with RTUs for years.
Unfortunately, manufacturers have never offered a satisfactory solution. How many times have you been told that you ought to just replace an expensive RTU that you installed just 10 years ago?
It’s only recently that RTU retrofit technology has evolved to the point that there are proven solutions backed by real-world trials and objective studies.
The latest generation of RTU retrofit technology – known as Advance Rooftop Control (ARC) systems – are designed to rein in these issues by taking control of each key system component. They turn your unruly rooftop beast into a smart, connected machine.
To date, thousands of businesses have adopted this technology in order to make their existing rooftop units more energy-efficient, easier to manage and more reliable.
Let’s dig into why.
Independent field tests by the U.S. Department of Energy (DOE) and the National Renewable Energy Laboratory have confirmed that Advance Rooftop Controls can deliver total energy savings of 25-75%. This extensive report contains all of the gory statistical analysis for those that are inclined – but I’ll stick to the high level here.
As with any new technology, it’s essential to verify that any product claims are backed by hard data and understand exactly what’s going on under the hood. This is why I turn to organizations such as NRCan and the U.S. DOE for information and independent validation before selecting a solution to add to our toolkit.
ARC systems aren’t the first or only kind of controls that have been applied to HVAC equipment. When you’re in this field long enough, you start hearing all kinds of claims about retrofits. Some well-informed, some not so much.
In the sections below, I’ve put together a quick rundown of the key features you’ll find under the hood of an ARC retrofit kit, how they work, the problems they’re designed to address and some things to watch for:
- I. Variable frequency drives: Pros & cons.
- II. Demand Control Ventilation: What’s the big deal?
- III. Economizers/free cooling: If you have it, how do you know it’s working?
- IV. Peak demand shaving: What is it and why?
I’ve also laid out an overview of how these technologies relate to your building management system (BMS), which is another key piece of the retrofit puzzle:
- V. RTU management systems: Wouldn’t it be nice to know what’s going on up there?
- VI. Automated fault detection and diagnostics: Save yourself some more money and a lot of frustration.
- VII. Energy accountability: Be a hero with hard data to justify your recommendations.
i. Variable Frequency Drive (VFD)
A variable frequency drive (VFD) is a device that controls the speed of a motor based on a control signal. In ARC systems, they are used to control the speed of either the fan motor or both the fan and compressor.
Variable Speed vs. Single-Speed Operation
An RTU is essentially an air conditioner and a furnace packaged in one box. ASHRAE standards dictate that they are designed to provide for peak cooling or heating demand, which happens on only one or two very hot or very cold days…some years. A constant volume system (single speed) runs both the fan and compressor at 100% capacity regardless of outdoor air temperature.
This means that most of the time, your RTU’s fan and compressors are working harder and consuming more energy than necessary.
There has been a lot of discussion about the wisdom of applying VFDs to motors that are not “VFD rated”. There is also a lot of manufacturer data that shows a general-purpose motor is not at risk of failure so long as operation is limited to a minimum 30% of rated speed.
Running compressors at variable speeds is another matter, and has a few more failure modes to worry about. In our business, we have stuck to systems that apply a VFD to the fan motor only.
How Much a Variable Frequency Drive Can Save?
Given the risks associated with retrofitting old compressor motors with VFDs, we’ll stick to the fan motor savings opportunity. No sense in introducing a new potential failure mode, especially when the majority of the savings opportunity is in the fan speed control.
A single 3HP fan motor on a 12.5 ton RTU costs roughly $1,000/yr to operate (@ $0.15/kWh). The fan affinity law shows that the power consumed by a fan is the cube root of the fan speed.
This means that at 50% speed the energy consumed is only 12.5% of the same fan running at full speed. Even at a modest 10% reduction in fan speed, the energy savings is an incredible 30%! This is shown in the graph below.
To simplify system operation and keep costs down, there is no need to have the fan operate at all possible points on this curve. Remember, 30% is the safe lower limit and the gains below 50% diminish rapidly, so a system with the low-end limit set to 40% seems like a great choice.
Similarly, there is no need to run at 100% speed when 90% will be more than adequate 99% of the time…and on those few extreme weather days, the unit will just run a little longer to reach the set point.
Seems like a reasonable tradeoff to save 30% of the cost of spinning the fan!
Finally, a lot of packaged RTUs have two stages of cooling and heating. On most days of the year, first stage operation is enough to satisfy demand, but during the warmest and coldest months, the 2nd stage kicks in to allow temperature set points to be achieved within a reasonable amount of time. The ARC systems we evaluated operate the fan at an intermediate speed for first stage heating & cooling. To reduce the risk of the heat exchanger overheating and cracking 75% seems to be a common choice. Check the graph to see what the power reduction of that mode is.
Bottom line, applying these 3 fan settings to a 12.5 ton RTU will reduce the operating cost of that unit by $500 – $600 every year. Not bad.
A demand control ventilation (DCV) controller opens and closes the unit’s dampers to regulate the amount of fresh air drawn from outdoors to ventilate the space. When the amount of ventilation is reduced, your heating and cooling costs drop accordingly.
Why Rooftop Units Over-Ventilate
Supplying fresh air and venting out CO2 is a core function of any rooftop unit. Similar to heating and cooling capacity, ASHRAE dictates rooftop units provide enough ventilation for peak building occupancy.
But as you well know, most buildings are rarely full to the brim — so you end up spending a lot of money heating or cooling more fresh air than you need.
Further, in ventilation mode, single speed systems run the fan at 100%, wasting even more energy and money. It’d be kind of like flooring your car between stop lights…that’s a big deal when it comes to unnecessary waste!
There are several methods deployed to achieve DCV, but they all share common flaws: they can only estimate a building’s current ventilation need and they don’t address the fan speed issue (in single zone systems).
- Scheduled ventilation adjusts the ventilation rate based on time of day and/or day of the week.
- Occupancy counters, like turnstiles and key card readers, can count the number of people entering and leaving the building and adjust accordingly.
- Occupancy sensors, like motion-detectors, can also provide an occupancy estimate.
Demand controlled ventilation is superior when it employs a CO2 sensor in the space combined with reducing the fan speed during vent mode. The sensor provides an accurate gauge of the level of ventilation needed in real-time, allowing the RTU to ventilate as needed. In practice 40% fan speed is more than adequate.
As you can imagine, these savings add up significantly over time in colder climates like ours in Canada.
How Much Demand Control Ventilation Can Save
The savings offered by demand control ventilation varies greatly depending on the building size, shape and operating schedule. However, in climates with many more heating than cooling days (like the Northern U.S. and Canada), rooftop units using CO2-based DCV technology have been proven to achieve energy savings ranging from 14 to 49% – with a median savings of 34%.
Economization, often called free cooling, monitors the ambient temperature and humidity using sensors. When the conditions are right, the sensor signals the rooftop unit to open a damper and allow outdoor air to mix with the return air.
Not all RTU’s come equipped with an economizer, and those that do typically have only two settings: 10% minimum opening and 100% maximum. An all or nothing approach.
Further, the temperature at which the open/close decision is made is 55°F (13°C) to avoid warmer humid air being brought into the space. There is a lot of cooling power to be used between 13°C and 18°C…if it’s properly controlled.
Finally, experience shows economizer controllers are the most common component to fail, and if your service tech doesn’t explicitly check its operation, you have no way to know. Even if it was checked, the economizer could fail the very next day and miss a whole season of savings! I’ll get back to the whole visibility and monitoring topic later.
So What’s Advanced Economization?
Advanced economization takes the whole process a step further by linking how far the economizer vent is open to the fan speed, temperature set points and humidity sensor.
This allows a finer degree of control and enables the use of all that cool air between 13°C and 18°C that off-the-shelf units cannot. No doubt you can see how this reduces compressor run time (free cooling) and save even more energy by controlling fan speed and damper opening to the ideal points.
How Much Can Advanced Economization Save?
The savings associated with economization depends on many factors, including a building’s location, construction materials, use, and occupancy. The cooling capacity of your current HVAC equipment will also have an effect.
This NRCAN report outlines how a properly installed and maintained economizer can reduce your need for mechanical cooling by a whopping 75%. That could easily shave off hundreds of dollars a month in the summer and Advanced Economization only makes things more attractive.
In an effort to lower retail electricity costs and reduce carbon emissions, most utility companies offer incentives to businesses that participate in peak demand shaving. Demand response or peak demand shaving means reducing or shifting your electricity use out of the peak hours as part of a contract you have with your local utility. In most cases, this is achieved through an aggregator – a third party company that manages the contracts of many companies to maximize results and minimize the work you have to do.
What You Can Save By Shaving Demand
An independent field test by the National Renewable Energy Laboratory (NREL) showed that using demand response for just three hours a day achieved savings of 12 to 27%.
A DR contract requires that you reduce consumption by an agreed amount in response to a demand from the system. Some organizations achieve this by manually turning down/off systems like lighting & HVAC and some use automated systems like a building management system (BMS).
Another version of the same concept is managing your Global Adjustment costs through reducing peak loads (you can download a backgrounder on Global Adjustment costs written IESO here). If you’re a Class A user in Ontario (>500KW peak load for manufacturers, >1MW everyone else) and have opted in to “chase peaks,” you understand the need to accurately control your electric loads during the warmer months. Similarly, some use automated systems to avoid peaks and some curtail activity that involves heavier loads.
I opened with the point that the “out-of-sight, out-of-mind” nature of RTUs is the root of most of the issues discussed here.
Global Adjustment peak shaving and Demand Response both require visibility and control over your rooftop assets to capture these savings. But these aren’t the only savings you can realize with the visibility and control that comes with cloud-based controls and diagnostic tools… so let’s get into that next.
In addition to the physical components we’ve looked at so far, more companies are beginning to introduce management software developed specifically for rooftop HVAC units.
You’re not the first to wonder why someone might invest in such specific software. There are already dozens of building management programs on the market, and there’s a good chance you’ve mastered one already.
In truth, not everyone who wants to improve an RTU will necessarily need an RTU management platform. The software is most beneficial in buildings with multiple rooftop units or for people responsible for multiple facilities.
Still, these management systems often come as part of the retrofit package (like the eIQ software that comes with CATALYST) – so if you’re already thinking about an upgrade, it’s well worth considering the potential benefits.
Building Management Software vs. RTU Management Software
Building management systems (BMS) or building automation systems (BAS) are computer-based control systems that bring all of a building’s systems into one platform: HVAC, electrical, lighting, fire, security, elevators and so on. BMS are designed to centralize the controls for these separate systems and provide feedback on all of them. When electronic / PLC systems were introduced back in the 1980’s, they were a complete game-changer in the messy world of facility operations.
Beneath the surface, a contemporary BMS is made up of several interconnected layers of tech:
- At the field or device level, physical input sensors and output actuators are connected to the equipment to monitor and control the environment (such as CO2 sensors, hygrometers and economizers)
- Behind the scenes, microprocessor-based control devices (such as Advanced Rooftop Controllers) respond to the information collected at the field level and send signals to the management level
- Computer or cloud-based software provides an overview of each of these systems individually and as a whole, allowing for real-time monitoring and control of the system.
At a macro-level, building management systems greatly simplify and streamline the building management process. However, most systems are not designed to address the specific challenges presented by rooftop HVAC units.
A typical BMS will enable control of thermostat set points and schedules but beyond that, they don’t really solve the biggest problem with rooftop units: the ‘invisibility factor.’
RTU management systems go a step beyond traditional building controls in several significant ways:
- Web connectivity: Connecting operators with RTUs over the web to control each of an RTU’s individual components remotely, such as testing those pesky economizers for proper operation.
- Automated fault detection and diagnostics: Actively monitoring the performance of these components to flag potential performance issues as soon as they arise – allowing for proactive maintenance, easier diagnostics and asset management.
- Energy accountability: Collecting huge volumes of data on the unit’s energy use and performance – and, most importantly, presenting that data in a way that’s easy to digest and act on
It’s essentially a smart HVAC master controller designed specifically for rooftop units. The best systems interconnect multiple RTUs in a wireless network, allowing you visibility of all units at a glance.
When you’re running multiple RTUs at once, it’s not uncommon for some units to be in heating mode and others in cooling mode simultaneously (I see this problem in big box retail stores all the time.) Wouldn’t it be nice to know when that happens and be able to adjust settings from your desktop or phone to prevent that waste of money? Not to mention the benefits to customer and employee comfort!
If you already have a BMS, it would be best for your RTU management platform to be compatible. Many RTU systems are designed to integrate with existing BMS platforms over standardized control protocols such as BacNet, making it possible to control RTUs along with automating your lighting and other building systems.
These systems typically offer web-based tools similar to traditional BAS systems, but go beyond simple set-point and schedule control. System like the eIQ platform from Transformative Wave offer Advanced Fault Detection & Diagnostics (AFDD) capability. These tools provide visibility of RTU operating condition and save money on service calls by identifying potential issues before they turn into hard fault conditions.
An automated fault detection system uses embedded sensors and continuously monitors the ‘health’ of a rooftop unit. It checks up on how the unit is performing as a whole and its individual components, paying particular attention to indicators like airflow, motor speed and power consumption.
When something looks off – say airflow is restricted, or a compressor is suddenly working overtime – the system automatically notifies you. Depending on how you’ve configured it, these notifications may come in the form of a popup, email or text message to your phone.
An automated diagnostic system, meanwhile, works in tandem with fault detection sensors to help troubleshooting the source of the problem. It can for instance, provide a list of potential problems sources and a list of items to check before deploying a service tech.
Remember those notorious economizers faults I mentioned earlier? The best AFDD systems test and exercise the economizer on a regular basis to help prevent them from seizing up. If the fault detection flags that a damper has indeed failed, you can have it repaired immediately rather than wasting money and energy until the next regularly scheduled maintenance.
Obviously, you can’t expect an onboard AFDD to replace the eyes, ears and intuition of a well-travelled technician. It won’t cut your service calls down to zero. What it can do is empower you to become proactive – which can seriously cut down the time and money you spend dealing with your RTUs.
Proactive vs. Reactive RTU Maintenance
Think back to the story you read off the top.
You’re just about to head out on the Friday of a holiday weekend when one of your rooftop units kicks the bucket.
You aren’t sure what went wrong or even which unit is causing the problem, but you’ve got to get it fixed ASAP.
Here’s how things could have gone differently using the proactive approach made possible by AFDD.
You arrive at work Wednesday morning and login to your RTU management platform. Immediately, you see that Trane #2 is detecting low airflow conditions because the “delta T” is out of spec. So, you dial up the fan speed and turn off the compressor to keep the evaporator from icing over and call your service company…and this assumes you caught it before the system had already done this and alerted you via text!
Knowing exactly what to look for, the technician wastes no time spotting a loose, ailing fan belt. Easy problem to fix. The issue is resolved before the day is out, and your long weekend isn’t cut short by even one minute.
Such a simple adjustment, like fixing a worn fan belt before it breaks, can instantly save you hours of downtime to defrost the coil and hundreds of dollars in emergency repairs.
Proactive maintenance means identifying the issue right as it happens and fix it before you’ve got an expensive problem on your hands. It allows you to cut your operational costs drastically. Might be a great thing to talk about at your next budget meeting!
Go back ten or fifteen years and you’ll find that most small-to-medium businesses saw so-called ‘green’ initiatives as a sort of fluff.
It felt good to save, sounded great to eco-conscious customers, and looked great in the quarterly newsletter. It wasn’t, however, seen as something that got results.
Even today, the business case for energy-efficiency can still be a hard sell. We’ve always just accepted utility cost as the cost of doing business and passed it on to our customers.
It’s only recently that small and medium size companies are beginning to catch on to what big business has seen all along: energy conservation retrofits are some of the highest-return, lowest-risk investments you can make. And since rooftop HVAC units are such heavy energy consumers, boosting your rooftop unit’s efficiency should be a top priority.
This is where RTU management comes in. Along with detecting and diagnosing malfunctions, this software also collects and analyzes information on all things energy: including your day-to-day usage and historical trends.
What You Can Do with Your Energy Data
Advanced Rooftop Controls are the next generation of HVAC control software. It’s the single most accurate way to track what you’re spending on heating and cooling – which gives you the power to reduce energy consumption well beyond that initial retrofit.
- You can prove that your energy retrofit project is actually achieving the promised savings. In other words, it holds your system accountable to your installer’s estimate. You’ll know for sure if your business is getting its money’s worth.
- You’ll be better equipped to meet conservation and demand management goals. Once you’re able to definitively show how your business is saving energy, you’ll have more opportunities to cash in on incentives through your utility provider or government.
- It’ll be easier to get support for future retrofit projects. Nothing gets through to management like cold, hard statistics! You’ll have a much better time making a business case for your next big upgrade.
Everyone wants to reduce their energy consumption (and costs.) But many companies struggle to roll out energy-saving initiatives in a way that can be effectively tracked and accurately measured.
Having access to conservation data creates a world of new possibilities in this regard.
Your savings potential is definitely going to be top-of-mind when it comes to procuring a retrofit kit for your pre-existing rooftop system. But it’s important to note that these kits come in a range of different specs and configurations, and not all of them will be the right solution for you.
Like any new technology, you’ve got to do some research and ask the right questions to get the most bang for your buck. Specifically:
What’s in the box?
You know your equipment better than anyone, so you’ll definitely have a few must-have features in mind. Don’t assume it’s all there – ask! Make sure your kit will give you multi-speed fan control (VFD), demand control ventilation, economization and Demand Response capability.
Is it easy to install?
Some kits are pre-wired kits that enable a qualified installer to quickly and confidently install and configure the system. Others require more extensive electrical work. This extra wiring could increase your upfront costs.
Is it compatible with my existing BMS?
HVAC control systems are supposed to make your job easier…but that’s not going to happen if you’re juggling two incompatible building management systems and use interfaces. If you aren’t using building automation solutions yet a system like the eIQ platform can become your platform of the future.
Can I network my RTUs?
Depending on the kit, your RTU upgrade may work only as a standalone unit or have the option to operate as a hardwired/wirelessly networked system. This is a crucial consideration when your facility has more than one rooftop unit.
Can I see your case studies?
Advance rooftop controls are relatively new, but they’ve been around long enough to be put to task. Ask to see energy efficiency case studies about a business like yours – or, better yet, independent studies by the Department of Energy or the IESO.
To date, I know of only one RTU retrofit package that answers “Yes” to all of the above: CATALYST and the eIQ platform. If you’ve read the independent report at the link provided WAY back at the start of this you’ll see that’s not just my opinion
The CATALYST ARC comes from two guys with years of HVAC / mechanical contracting experience who saw the problem with RTUs firsthand. They weren’t happy with the other upgrade options on the market, so they decided to develop one themselves – which eventually became the CATALYST Advance Rooftop Unit Control Solution.
At Tradeforce Tech, we invest a considerable amount of our time and resources to stay ahead of the game by identifying new and emerging technologies. Once we’ve know we’re onto something great – like CATALYST – we work as closely as possible with the people behind the tech to bring the benefits of these amazing systems to you.
So, in answer to the question, “How do you get the CATALYST upgrade for your RTU?”
It’s simple: get in touch with one of our expert reps today and we’ll help get you on the right path.
Tradeforce Tech is a proud partner of Transformative Wave and the leading supplier and installer of the CATALYST HVAC system here in Ontario.