Energy Savings Comparison Myths
Almost every day someone asks how much energy an Energy Management System (EMS) will save or wants to know if our XtraVision system will save more energy than brand X. The answer is always, “it depends”. There are too many factors that go into determining how much energy can be saved to make it a simple answer. Look around long enough and you’ll find folks claiming to have achieved 30%, 40% and even 50% energy savings with their EMS. We’ve also seen savings like that, but not from where you might expect. The following are a few cases for why “it depends” and hopefully explain the various factors that affect it.
CASE #1
Maintenance Issue
As a rule, we tell our clients that they should expect 10-15% in direct energy expense savings from the XtraVision system. We’ve seen the same high level of savings claimed by some in our industry, but it had nothing to do with our EMS performance over the next guy. It had to do with a large sump pump running 24/7 due to a water leak. Or there was the time we found every roof top AC had its compressors electrically jumpered so that they were running 24/7. Even when the XtraVision system was trying to turn them off. And my favorite, broken ductwork in the ceiling space causing the units to run 24/7 but never quite reach setpoint. No matter how many times they called the service guy out to repair the unit he only looked at the unit on the roof, he never looked at the ductwork in the ceiling. These are all items that our Voyant Cloud Analytics identified and the client corrected resulting in huge savings. So, while the Voyant Cloud did detect the problem it was not the direct result of the energy savings. Building maintenance is what raised energy usage and ultimately reduced it. Said another way, these savings were available to the client without ever installing an EMS. So, unless your building has a problem your savings are likely to be in the 10% to 15% range.
CASE #2
Design Issue
In many places, we’ve seen poor building design result in high energy usage. One example is a dining room with four AC units and thermostats located and configured so that they can be influenced by the other units. During the shoulder months, one unit blows cold air on the thermostat of another unit causing it to start a heating cycle. This added heat causes the cooling unit to start another stage of cooling which causes the heating unit to start yet another stage of heat. I know what you’re thinking, we would know if that was happening. The truth is you don’t. The air from the units mix and it’s not that noticeable during the shoulder months. All EMS have something, or they should, to prevent this. Once the EMS is installed the condition will be corrected. But can we say that every building will benefit from this and save energy? The answer is no. Unless the same design flaw is present with the setpoints set just so, the condition will not be replicated and therefore the same savings will not be available.
CASE #3
Inefficient Process or Equipment
The type of equipment used between various buildings can have a dramatic effect on energy usage. Let’s take two quick serve restaurants of the same size serving the same menu located directly across the street from each other with the same operating hours and generating the same number of sales. The only physical and operational differences are the exhaust hoods used. Both buildings exhaust 3000 cfm of air through their hoods but one building (Building A) uses integrated supply fans with their hoods for the makeup air and the other (Building B) uses exhaust only hoods and brings the makeup air in through the AC units. Remember that for every cfm of exhaust air removed from the building by the exhaust hoods you must have a slightly greater amount of makeup air put back into the building to maintain a positive pressure. Integrated hoods like the ones used at Building A provide a curtain of unconditioned air from the roof around the exhaust hood that’s then drawn back into the hood and exhausted back to the roof. Buildings with exhaust only hoods like the ones at Building B rely on the AC units for their makeup air. If we have 3 AC units capable of 3000 cfm each and we need 3000 cfm of makeup air then the AC units at Building B will need to bring in 1000 cfm of makeup air each. That’s 33% of their total capacity dedicated to conditioning makeup air brought directly into the store from the roof. This air is then dragged from the
diffusers to the hoods interacting with all your customers and employees along the way. This means that the Building B AC units will need to run their fans and at least one stage of cooling the entire time the hoods are operating in the summer to condition the air. This conditioned air that you’ve invested all these energy dollars into will then be exhausted right back out of the building through the exhaust hoods. During the winter much higher setpoints will be needed to keep the customers comfortable as the cold makeup air from the diffusers falls on them creating a wind chill effect inside the building. I know you’re thinking this is crazy, nobody would do this. You would be wrong. Many of our customers are building brand new buildings that operate just like this today. They do it to save on construction costs as the integrated hood systems are much more expensive. Clearly we see that Building B will use substantially more energy with less opportunities to leverage traditional EMS strategies for saving energy. Yet we see folks trying to compare the savings between “similar” buildings all the time and claiming victory when one saves more than the other. Most of the time the truth is it had nothing to do with the EMS. Bottom line, there are way too many variables to just use size, weather and revenue to compare one quick serve concept against another to evaluate what the best EMS is.
CASE #4
Taking all the Credit
Another common mistake when evaluating various systems is to give the EMS all the credit for the savings. Lets say someone made the following upgrades to their building.
The total savings are $13,209. Assuming there are two AC units the EMS saved $1,960. It would be inaccurate to say the EMS saved $13,209 in the first year but that’s exactly what lot’s of folks are doing. They attribute all the savings to the EMS. I know, that’s crazy, but at least once a month we’re shown this exact scenario. When comparing systems you must weed through the data to see exactly what the EMS is responsible for and what it’s not. When someone starts throwing around these kind of numbers ask to see the data.
Where would 30% Savings Consistently Come from Anyway?
SDGE conducted a study of quick serve restaurants and found that the number one consumer of energy was the cooling process at 40% followed by cooking and refrigeration at 31% and lighting at 13%. A little common sense tells us that the only way to consistently save even 30% would be to turn off all the cooking and refrigeration. Another way would be to turn off 75% of your air conditioning. Or you could turn off half the air conditioning, cooking, and refrigeration for a savings of 35.5%. But ask yourself, can you really operate your building that way? Of course not, you can’t operate your building that way and neither can your EMS. So where do these 30%, 40% and 50% savings come from? Typically, they come from an ill-conceived comparison where things are not as they seem, or they’re taking credit for a maintenance or design problem that didn’t have anything to do with the installation of an EMS. If someone tells you they consistently save over 30% you should ask them to show you the math. For example, if their EMS was limited to the lighting and AC units then they’re limited to 53% of the total energy spend. So how did they consistently reduce the lighting and AC by 57%, 75% and 94%? No amount of pixie dust will make that wish come true.
Other Considerations
Who Will Operate It? An EMS is not maintenance free and there will be setpoints, schedules, alarms, users, repairs, upgrades, network changes, and service dispatch to manage. Will you do this? Some systems offer these services as part of the system and some do not. We offer these services through our Voyant Energy Services package.
Any good EMS package should have internal bypass and fault detection. If someone bypasses the EMS control the EMS should know this and report it. You don’t want to invest in an EMS only to find that it’s controls have been bypassed a year later. The Voyant Cloud Analytics package tests all aspects of the XtraVision system and reports any bypassed or faulted components keeping the energy savings at expected levels.
An EMS will not fix a broken building. If, for example, your HVAC is undersized and running all day just to keep up, installing an EMS will not fix that problem or lower your energy bill. Properly sized and maintained equipment is a must if your EMS is to have any impact on energy usage.
As we’ve shown, the biggest energy consumer is poor maintenance. A system with the ability to detect these problems through a robust analytics package can save more energy in detection and quick resolution than an EMS can in process control. We call this indirect savings. For example, our Voyant Cloud Analytics package automatically tests each AC unit’s ability to cool efficiently during the winter so cooling repairs can be made before summer arrives. This prevents inefficient cooling cycles from draining your energy budget and allows you to better manage your repair and maintenance budget by making repairs on your own timetable.
Conclusion
Bottom line, it’s silly to compare EMS to EMS based on energy savings alone and even more ridiculous to compare concepts against concepts with various EMS in an attempt to determine the best EMS. Everything must be taken into consideration to truly answer the question. So, what EMS saves the most energy? It depends… For the most part all of them are going to provide savings at about the same rate of 10-15%. There’s lots of system out there to choose from and like every industry there’s a few bad apples. Pick someone with a good reputation and set of features that best fits your organization. Take your time and try a few out.
Voyant Solutions
PO Box 12275
Research Triangle Park, NC 27709
p: 800.757.0299
f: 866.757.0299
