Ask Energenie

December 1998

Table of Contents

1. What does "wood waste-to-energy" mean?
2. In extremely cold weather my furnace seems to run all the time, even though I have the setting on automatic. Will this continuous operation hurt my furnace?
3. Please describe the concept of low temperature air distribution in commercial buildings for minimizing equipment and energy costs.
4. May I cover the louvered openings in my boiler room to prevent adjacent pipes from freezing?
5. We are having zone valves go out on the hot water heating system in our business. I know they stick because of calcium deposits, but what is causing this build-up of calcium?
6. What causes seals in a double-glazed window to fail?
7. I have a yard light I turn on at night for security purposes. Often I forget to turn it off during the day. When I'm gone, I leave it on all the time. Can you suggest a cost-effective automatic control?

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1. What does "wood waste-to-energy" mean?

"Wood waste-to-energy’ refers to the production of thermal energy using wood scrap or waste wood," said Richard Nelson, extension specialist in energy at Kansas State University. "The wood wastes can be from forest logging operations or from those businesses that process lumber into finished products such as cabinets, tables, chairs, and so on."

The wood wastes are combusted in a special burner and the energy produced from this combustion is usually in the form of hot water or steam. In some instances, the steam has been used to produce electricity.

"Usually the wood wastes are considered a negative-value by-product that costs the wood processing facility to dispose of them, generally at the local landfill," Nelson said. "Using the wood wastes as an alternative energy source either at the wood processing facility or at a local industrial business or school that requires the use of hot water or steam can possibly help alleviate the financial burden the wood processing facility faces in disposing of these wastes."

For example, wood wastes generated by a cabinet production facility have been used as an alternative energy source for a cement operation. Both business gain financially because the wood processing operation delivers the wood wastes for free, thereby eliminating their landfill disposal cost. And the cement operation gains a free fuel source.

"The economic benefits of using wood wastes for energy are dependent on the landfill disposal fee, electric and steam costs and whether hot water, steam or electricity is produced," Nelson said.

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2. In extremely cold weather my furnace seems to run all the time, even though I have the setting on automatic. Will this continuous operation hurt my furnace?

"No. A furnace is designed to run as long as necessary to satisfy a home's heating load. In fact, the longer it runs during each cycle, the more closely it operates to its designed efficiency," said Doug Walter, president of Kansas Building Science Institute, Manhattan. Frequent cycling caused by partial loads during mild weather or by an over-sized furnace reduces the overall efficiency of the furnace.

"The colder it is outside, the longer your furnace must run to provide the heat needed to maintain your home's comfort," Walter said. A properly sized furnace will maintain an indoor temperature of 70 degrees when it's 0 degrees outside.

"It is not uncommon, therefore, for the furnace to operate continuously when the temperature is below zero, but this does not harm or stress the furnace," Walter said.

"It is critical to maintain your furnace in good operating condition during cold weather," Walter advised. "Keep filters clean, service motors annually and check belts for proper tightness. Your furnace will not provide its maximum heating potential if it is not in optimum condition."

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3. Please describe the concept of low temperature air distribution in commercial buildings for minimizing equipment and energy costs.

"In an attempt to reduce air conditioning energy requirements as well as the installed cost of equipment and systems, engineers are designing low temperature air distribution systems for large commercial building applications," said Richard B. Hayter, director of Engineering Extension at Kansas State University.

The concept is as follows. Some portions of large commercial buildings may require year-round cooling. Typically the air temperature in the ductwork is 55 degrees. If the temperature of the supply air is reduced, less air is needed to provide the same cooling. This permits the use of smaller fans or air handlers as well as smaller ductwork. Less air handling equipment and ductwork may reduce the floor-to-floor height and may lower the cost of the building structure.

"In addition, moving less air reduces energy requirements. This savings is partially offset by the lowered efficiency of the air conditioning equipment," Hayter said.

Low temperature air conditioning systems are particularly attractive when the building has an off-peak thermal storage system. This system cools at night when utility rates may be lower and stores ice or cold water for daytime cooling.

"Low temperature air systems can be comfortable and cost effective," Hayter said, "but when designing the system, take care to avoid problems like condensation on ductwork and undesirable distribution of cold air within a room."

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4. May I cover the louvered openings in my boiler room to prevent adjacent pipes from freezing?

"The louvered openings you are referring to probably supply the boiler’s combustion air," said Gene Meyer, extension mechanical engineer at Kansas State University. "Any device that burns fuel must also have air for combustion. Building codes require air inlets to boiler or furnace rooms. The size of the inlets is determined device.

"If you restrict these inlets, you inhibit complete combustion, resulting in sooting and production," he said. "Consult with a professional engineer before making any changes. You may be able to duct air to the pipes instead of reducing the size of the opening."

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5. We are having zone valves go out on the hot water heating system in our business. I know they stick because of calcium deposits, but what is causing this build-up of calcium?

"Mineral deposits are a potential problem in all hot water heating systems," said Gene Meyer, extension mechanical engineer at Kansas State University.

In systems that don’t have leaks, the minerals in the initial fill of water are all that are available to be deposited, and this amount usually isn’t enough to cause problems.

"If the system leaks, however, you must add water either manually or automatically," Meyer said. "The minerals introduced with the additional water are deposited in the system and may cause build-up problems in valves, pumps and even the boiler itself."

If you have an automatic fill system, you may not know that water is being added. One method of checking for the addition of water is to watch the expansion tank. "If you occasionally have to bleed air from the tank, your system has a water leak," Meyer said.

"If you have a bladder type tank, you won’t be able to detect leaks in this fashion and may have to rely on close inspection of valves and pumps. Mineral deposits on valve stems and around pump shafts are an indication of leaks," Meyer said.

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6. What causes seals in a double-glazed window to fail?

"Seals usually fail because of sealant deterioration, thermal stress or structural stress," said Bruce Snead, extension specialist in residential energy at Kansas State University.

Most double-glazing consists of aluminum spacers and sealing around the outside edge, usually with a polysulfide sealant.

"If the sealant did not cure properly, a leak can develop and let in moisture," Snead said.

Thermal stresses cause seal failure if the temperature between the two panes differs significantly. Thermal stress may occur if you apply solar film to sealed glazing.

"Due to the film’s absorptivity, the pane with the film gets much hotter than the other pane, and thermal expansion forces bending, which breaks the sealant bond," Snead said.

Structural stresses may cause glass breakage or sealant failure.

"These stresses usually occur over a long period of time due to header deflection, wood shrinkage or overloading a structural member," he said.

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7. I have a yard light I turn on at night for security purposes. Often I forget to turn it off during the day. When I'm gone, I leave it on all the time. Can you suggest a cost-effective automatic control?

"You have a choice of three devices to automatically control the operation of your security light," said Doug Walter, president of Kansas Building Science Institute, Manhattan.

"The least expensive of these devices is a timer. For about $10 you can replace the regular switch with a timer control that will operate the light on a schedule you determine," Walter said.

"You will have to reset the timer after any power outage and periodically adjust it for varying daylight hours," he said. A more expensive timer with battery backup can eliminate resetting after power failures.

"A second, completely automatic unit is a photoelectric switch, which costs about $20," Walter said. This device, installed in the electrical circuit near the lighting fixture, turns the light on at dusk and off at dawn. It is not affected by power outages and automatically adjusts to varying daylight hours.

The third option is a motion-sensing switch installed to "scan" the security area. This device senses infrared heat, such as that given off by a person. If someone walks through the scanned area, they activate the security light. While moving branches won't activate the sensor, movement of small animals sometimes can.

"The light is controlled by a photoelectric sensor which prevents it from being turned on during the day, and a timer adjustment, which limits the 'on' time to 1 to 20 minutes. A motion-sensing switch costs about $30," Walter said.

All three of the devices present significant energy savings. "For example, a 150-watt security light operating 24 hours a day at 7.6 cents per kilowatt-hour (kwh) costs $100 a year," he said. "But operating only during non-daylight hours (10 hours a day) reduces your annual energy cost by more than half — to $42."

The motion-sensing switch could reduce operating time to less than an hour each night since the light is activated only when it detects movement. Operating one hour a night, the annual energy cost would be about $5.

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Ask Energenie is produced by the Kansas Energy Extension Service through Kansas State University. This material was prepared with the support of the U.S. Department of Energy (DOE) Grant No. DE-FG47-92-CE60210. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the view of DOE.