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Smart House Safety Nets

I added “smart house” computer controls to make my house more efficient. During even a brief power outage, the settings are lost. Are there backup power supplies that don’t waste electricity, and are big ones better?—Al S.

Smart house controls run by a personal computer are becoming more common, and can significantly reduce energy use. By controlling the timing and operation of heating and cooling systems, ventilation, lights, and some appliances, even a house of typical efficient construction can use less energy.

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, adding insulation to old, solid masonry walls can be expensive.

There are many different levels of sophistication for smart house controls, and not all of them require a personal computer or central electronic brain. One of the simplest uses new Z-wave technology to control the timing of lighting or appliances. 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 takes only a very short power outage to cause a personal computer or other electronic control system to lose settings. If the power flutters on and off quickly while the computer is assessing data, files can become corrupt or, 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 all of your electronic devices that are sensitive to power outages or low-voltage conditions. If the utility power goes off, the UPS kicks in almost instantly to keep the electronic device, usually a computer, running without a glitch.

If you installed a standard large standby backup generator with an automatic transfer switch, this will not save your data. The automatic transfer switch, which starts the generator and disconnects your house from the utility grid, has a delay period until it restores electricity. 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 to handle repeated discharging. When plugged into it, the computer runs on the 120-volt house power until there is a power outage or significant voltage drop. The amount of electricity used to keep the batteries charged is small, even for large, powerful units.

When selecting a UPS, 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 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 currently needed.

The UPS should contain cables and computer software that close computer files and safely shut down the computer when the power goes off.

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