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Ask the Energy Wiz!

Q: Dear Energy Wiz,
Could you explain what biomass, geothermal, and solar energy are? Could you explain how they work and what the advantages and disadvantages for each are?
The Energy Wiz!
The Energy Wiz!

A: Biomass energy is energy that comes from organic material such as plants and animals. Biomass would include: ethanol from corn or grasses, biodiesel from soybeans or vegetable grease, methane from animal waste, or wood for burning in a stove.

Solar energy is energy received directly from the sun. Solar energy could be electricity from collector panels on a roof, hot water from solar collectors that face the sun and circulate water through them, or the heat that enters homes through windows that face the sun.

Geothermal energy is energy extracted from the earth. The center of the earth is very hot, and there are places on the earth where this heat is closer to the earthís surface than others. In those places, holes have been drilled down and the extracted heat is used to generate electricity. There are also geothermal heat pumps which can be used almost anywhere on the earth to gather the earthís heat for heating and cooling homes. In a sense, geothermal energy is also a form of solar energy because the earth stores some of the sunís energy.

The advantage of these three energy sources is that they are renewable. Renewable means we can grow more plants each year, the sun supplies energy whether it is used or not, and the earth's surface is continuously warmed by the sun.

The disadvantage of these energy sources is that we have not yet found economical ways of extracting the energy from these sources. With biomass, in some cases, we have to use energy to produce the energy. In other cases for biomass, solar, and geothermal, it takes expensive equipment to extract the energy. More efficient ways of using these types of energy are also needed. How we use the energy from these sources, once we have gathered it, can be problematic.

For more information on these types of energy, visit the following web sites:

The Energy Wiz

Q: Dear Wiz:
I use an 80% efficient natural gas furnace to heat my home. The home also has a heat pump that is used in addition to the gas furnace. The heat pump has a SEER rating of 10. In the past, I have switched from the heat pump to natural gas heat at 34 degrees so that the heat pump would not use natural gas to defrost. With the increase in natural gas prices should this setting be lower? A relative has a similar arrangement, but uses resistance heat in addition to a heat pump. What temperature setting should be used in this instance?

A: The simple answer is that backup heat, whether gas or electric, should not come on until the heat pump can no longer provide enough heat to keep the home warm.

How do you find that point where the heat pump can no longer keep up with the heating load? There are several methods: trial and error, calculation and a special type of thermostat. For trial and error method, take the following steps:

  1. Set the temperature for the backup heat very low at zero degrees.
  2. Wait for the temperature outside to become low enough that the heat pump will no longer keep up with the heating level you have set. You will know when this happens because the temperature inside your home will be less than the thermostat setting and the heat pump will have been running for more than 20 minutes.
  3. Note the outside temperature when the heat pump could no longer keep up with the heating load.
  4. Set the temperature for the backup heat to come on at one or two degrees above the outside temperature you noted in methods #2 or #3 (The outdoor temperature where the heat pump could no longer keep up with the heating load). Or, if you don't mind your home being a little cooler, set the temperature at or just below the temperature you noted.
  5. If your home ever becomes colder than you would like because the heat pump is not keeping up, set the temperature for the backup heat several degrees higher: 20 to 22, or from 10 to 12.
The second method is for a heating and cooling contractor to perform a load calculation to determine what temperature your back up heat needs to turn on. You may also want to use the trial and error method to optimize the setting.

There are thermostats that will monitor whether your heat pump is making set point. Set point is the temperature you set for inside your home on a thermostat. With this type of thermostat, the trial and error method is done automatically. This can be beneficial since the amount of wind outside can affect the temperature at which your heat pump can no longer keep up. Changes in your heating load from wind are due to infiltration or air leaks, not from wind chill. Wind chill does not apply to inanimate objects. The effect of wind on a totally sealed enclosure will be very little on the heating and cooling load.

An additional note: Most heat pumps with electric heat as a backup are set to run even after the electric backup heat comes on. For this to occur, the air flow in your homes heating system must hit the heat pump coil before it hits the electric backup strips. So, if your heat pump continues to run even after your electric backup heat comes on, you should not be alarmed. If your heat pump does not continue to run after your electric backup comes on, you may want to contact your heating and cooling contractor to be certain the unit is operating properly. The opposite is true of a heat pump with natural gas as a backup. A heat pump with natural gas backup must shut down when the gas backup heat comes on. If your heat pump continues to run after the natural gas backup heat has come on, you should contact your contractor to fix this problem.

The Energy Wiz
Editor's Note:
The staff at the Energy Office respond to many inquiries on a variety of topics from Nebraskans. From time to time, the Quarterly will share some questions — and the answers — with readers.
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