|Energy Demand: Intelligent Control|
|Part 2 of 2|
by Dan Schafer
(Production Manager for Fine Enamels, Thailand)
You probably know someone who is a control freak. They can't stand surprises. I had a friend who couldn't even appreciate a surprise birthday party, because it was an interruption to her plans. But she didn't have to live too long to discover that, like it or not, she was bound to meet some unexpected things. Yet again, as is often the case, those of us who tend to be more easy-going, rolling with the punches, discover that there is something we can learn from our control freak friends. Life goes more smoothly, we get more accomplished and we are less tense if we can bring some control into the random circumstances of our lives.
Last issue (Energy Demand: Knocking off the Peaks) I started discussing bringing some control into our electrical demand. You will remember that electrical utilities make a charge, particularly to industrial customers, for their highest usage in the billing period. That is because it reflects a cost for the utility to have to maintain enough capacity to meet their customers' highest demand. The northeastern US and southeastern Canadian utilities would, I am sure, have something to say about the cost as they start to sort out meeting that part of the world's electrical demand. So apart from altruism there are very real (read dollar signs and heads rolled) incentives for both us as customers and utilities as providers to bring some control into electrical demand.
An example of "random circumstances" in electrical use is the thermostat that turns a heating or cooling system on and off. Of course it isn't really random, but if nobody intervenes and tells it differently, there is nothing to prevent it from turning on just when some kiln in the factory is also clicking on and the air compressor cutting in and those all while we were doing some energy hungry processes like electroplating and silver casting. The end result is a tremendous spike in our electrical demand that we will have to pay for at the end of the month.
I explained last issue how we took some steps to take the randomness out. 1. We started scheduling processes with high consumption so they didn't all take place at the same time. 2. We got an electrical meter that could tell us in real time and also keep a record of what our electrical demand was like. 3. That meter had some relays that we could preset to shut down some big air conditioner compressors if demand exceeded a certain level.
This third level of control had its drawbacks. I had to be very careful at what level I set the cut off points for those relays. On the one hand if I set them too high we got very little reduction in our demand. On the other if I set them too low I could and did start causing problems in the factory. Sometimes what should have been air conditioned rooms started getting stuffy and hot. Then I would find the workers had all the windows open about the time the relay let the air conditioner back on. So I ended up continually readjusting. It was some help to our electrical bill, but time consuming for me and pretty tricky for public relations.
About that time we learned there was a Thai-developed software for controlling demand. It required a meter like ours feeding its signal into a computer. But instead of depending on a relay to switch off power at a set cut point, with the potential chaos already described, it could give us intelligent control.
In almost every system there is some electrical consumption that is not specific time dependent. Most commonly there are consuming units that control temperature, such as water heaters and air conditioners. They normally don't have to run all the time to maintain a preset temperature. The principle, then, in controlling demand is to not let every consuming unit come on just the moment its thermostat calls for it, i.e. "randomly". But rather one attempts to bring order into when the different loads are carried. If we know the normal requirements of each unit, we can estimate how long it can be shut down and how long it needs to operate to maintain the required temperature.
That was the beauty of this softwarewe could control as many circuits as we liked. In the computer we just needed to set up each switchable load with minimum "on" times and maximum "off" times. In a factory like ours we have a lot of heaters and a lot of air conditionersideal for bringing into order to reduce our demand. However, to simplify things we combined the loads we would control into eight groups, with the loads within the group having similar "on-off" parameters. Then through a PLC (programmable logic controller) to do the actual switching, the computer could automatically control these loads making use of the normal "on-off" times, but in an order that kept a cap on our demand. The software enables us to set a target demand figure in kilowatts, and then also to prioritize which loads get shut down first by setting at how many kilowatts over or under that demand figure a particular load can be switched off.
Controlling demand is not without its cost. Think of the wires to run - all over the factory to air conditioners, heaters, air compressors, water pumps. Then there were relays to install on each of those units. Of course we also had to buy the meter, the computer interface, the software, the PLC. Then when lightening struck our incoming electrical wire and burned up a meter or an interface they had to be repaired or replaced. So special surge protection had to be installed.
Has it all been worth the time and cost? Of course a big gain came just with an awareness that led us to schedule processes. Theoretically that wouldn't have required any meters, computers or software. But we are continually amazed, as we fine-tune our settings, how smoothly our demand is controlled. When I think of the scrambling I sometimes had to do when some room was getting too hot, because our meter relay had shut the air conditioner down too long, I realize the value of "intelligent" control. Artificial intelligence it may be, but this is an ideal job for a computer. There is no point in a human brain struggling like an air traffic controller with which units should be turned on when. Of course we've had our bad months when something like lightening has messed up our equipment, and consequently our demand has swung free for a few hours. But the bill we have to pay in a month like that is another good reminder of what saving we are making when the system is working properly.
I can say this, that estimating the savings conservatively and excluding the savings we had already achieved just by rescheduling, even with all the extra costs of not only buying equipment, but replacing it when damaged, we will easily recoup our investment in less than two years. Note the accompanying graph and charts.By way of explanation I should point out that although we had our demand control software in force in the last half of 2002, we had two or three disasters (mainly lightening) in that period that threw our system out of order. Therefore I have made the graph as though we began control in January 2003. On the "Demand Control Investment" chart I have listed a computer purchase, though in fact we were able to enlist an old computer with fairly low specs that we no longer used for the business. So that $800 could be removed from the cost for anyone in a similar position with a spare old computer. On the chart "2000 to 2002 Compared 2003" on which the graph is based, I have extrapolated our 2003 demand charge to a full year for a comparison with the yearly average of 2000 to 2002. It is on that basis that I project a yearly saving of over $2200.
For a growing company and a technology acquiring company, even holding our own in electrical demand would be an effective result, but being able to reduce it has been remarkable. That is in part because, in fact, the demand control software now gives us very good feedback on what even more precise scheduling we can do.
These are all good results for us. But they are also good for the electrical utility and the environment, because they are a little contribution to keeping the capital investment in electricity generation capacity from going up too much too soon. Besides that, it is an expression of what our Creator asked us to do in the very beginning, "fill the earth and subdue it" (Gen. 1:28). In effect He says, "Let the order of My life which is in you be expressed in the work of your hands."
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