ENERGY CENTS
By James Dulley
James Dulley
UPS systems back up “smart house” controls “Smart house” controls run by a personal computer are becoming more commonplace in homes, and they can significantly reduce energy usage. By controlling the timing and operation of the heating and cooling systems, ventilation, lights and some appliances, even a house of typical efficient construction can operate on less energy overall. With an older house, installing smart controls may be more cost-effective than trying to improve the energy efficiency of the building envelope. For example, trying to add insulation to old solid masonry walls can be an expensive project. If the older house is on a historic register, you may be limited as to the external improvements you can make to it. There are many different levels of sophistication for smart-house controls, and not all of them require a personal computer or central electronic brain to operate. One of the simplest smart home controls uses new Z-wave technology to control the timing of lighting or appliances in a house. The main control unit runs on just four AA batteries. Keep in mind, if you use compact fluorescent bulbs many types of electronic timers and controls do not work properly. It can take only a very short-duration power outage to cause a personal computer or other electronic control system to lose its settings, possibly requiring reprogramming. If the electric power flutters on and off quickly while the computer hard drive is accessing data, the files can become corrupt or, even worse, the hard drive can be damaged. Older-design hard drives are more susceptible to damage from a power outage. It would be wise to install a UPS (uninterruptible power supply) at each of your electronic devices that are sensitive to power outages or low-voltage conditions. If the utility power goes off during a storm or accident, the UPS kicks in almost instantaneously to keep the electronic device, usually a computer, running without a glitch. If the beeper alarm did not alert you, you would not even notice the power had gone off. If you installed a standard large standby backup generator with an automatic transfer switch, this will not save your data or your computer. The automatic transfer switch, which starts the generator and disconnects your house from the utility grid, has a delay period until it starts and restores electric power. This delay is too long to keep the computer running and files opened. A UPS system uses a powerful rechargeable battery pack. These are usually lead-acid batteries of a deep cycle design so they can handle repeated discharging. When plugged into the UPS, the computer continues to run on the 120-volt 40 SEPTEMBER 2008 Carolina Country
A 1,500-volt-amp UPS system (at left) is placed under a printer stand so it can be connected by a control cable and power cords.
house power until there is a power outage or significant voltage drop. Instantaneously, power from the batteries kicks in. The amount of electricity used to keep the batteries charged is very small, even for large, powerful UPS units. When selecting a UPS for your computer or control system, size it properly for efficiency and lower initial cost. The two factors to consider are the maximum power it must provide and for how long. A UPS includes an inverter that converts the low-voltage direct-current battery power to 120-volt alternating-current house power. If your computer or smart house control draws more power than the inverter is designed to provide, it may overheat and shut off to protect itself. Then there is no electric power again until it cools and you reset it. The maximum power of a UPS is indicated by its VA (volt-amp) rating. Most electronic equipment lists its VA requirement on the nameplate or packaging. Sum the VAs for all the items to be plugged into the UPS. A VA rating for a device is slightly different from just multiplying its rated voltage times its amperage, so don’t try to calculate it yourself. I recommend selecting a UPS with about 20 percent more VA capacity than you need. The UPS should contain cables and computer software that close computer files and safely shut down the computer when the power goes off. This should take less than five minutes, so the UPS does not have to keep the computer running for long. For longer run times, add additional batteries or purchase a larger unit. Send inquiries to James Dulley, Carolina Country, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.
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James Dulley is an engineer and syndicated columnist for the National Rural Electric Cooperative Association.