Energy Conservation and Renewable Energy in Homes

Chemical Education Today

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Energy Conservation and Renewable Energy in Homes

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by Danny Aerts and Betsy True

Energy is an important topic in today’s world. Dependence on petroleum and coal has had many side effects, including air pollution, global warming, and political strife between oil-producing and oil-consuming countries. Many people are concerned about the increasing costs of energy. To illustrate some possible actions individuals can take, we will describe the process we went through on our house to reduce our energy consumption and to use renewable energy sources. Our house is a two-story ranch style built in 1985 (see Figure 1). It was fairly energy efficient for homes in that era, having R-19 insulation in the walls, double-paned windows, and a high-efficiency gas furnace.1 One thing the house did not have was a wood stove. We enjoy having a wood fire on cold days, and there are many of those days here in Wisconsin. Also, wood is a renewable fuel source and is nearly CO2 neutral, so it does not increase global warming. So we began to plan a remodeling project to include a wood stove. The project grew when Betsy suggested we add a plant room on the south side of the house. With the southern exposure we thought we could have enough passive solar energy collection to keep the plant room warm year round. As we talked more about our energy consumption, we decided to do as much as possible to reduce our use of fossilfuel based energy. This would involve energy conservation and use of renewable energy. Our first step was to have a renewable energy site assessment, which we did in June 2003. We are fortunate that the state of Wisconsin has a program to encourage the use of renewable energy. Trained energy auditors visit your home and conduct a site assessment at a very reasonable cost. The Wisconsin Focus on Energy Web site2 has information on various Wisconsin energy programs. Many other states have similar programs.3 The items we were interested in were: • Passive solar energy collection in the new plant room • Solar hot water heating • Solar photovoltaic energy collection and conversion • Wind energy generation • Heating and cooling with a geothermal heat pump • Using a wood stove for heating

Figure 1. Photograph of house with a view of the new south wall and showing the solar panels on the roof.

We added a sun room/plant room on the south side of our house because we needed a lot of sunlight for the plants. The room is earth-bermed two feet high on the outside to reduce heat loss through the walls. Exhaust fans were added in the ceiling to provide ventilation during the summer. Window size, position, and type all affect solar thermal gain. We chose double-paned, argon-filled, low-e (emissivity) glass. For the plant room we used all vinyl windows because of the high humidity in that space. In the rest of the house we used wood windows with exterior vinyl cladding. The roof overhang is a key element of our design. It extends far enough to block direct sunlight during the summer, yet allows as much direct light as possible in during the winter. This is possible, of course, due to the tilt of Earth’s axis and the sun’s varied position in the sky during the year. The amount of overhang necessarily varies with latitude. A passive solar design generally incorporates a way to store heat during the short days of winter and to release this heat to warm the room during the long night. Objects with high thermal mass can provide this storage. They are materials with high mass and high heat capacity. For our room we poured a 0.30 m thick slab of concrete for the floor. We insulated under this slab to minimize heat loss to the ground. The back wall of the plant room is limestone, which also provides a large thermal mass. Water storage barrels can also help to moderate the temperature swings.

Passive Solar Design

Solar Hot Water Heating

Passive solar collection is one of the most cost-effective ways to reduce your energy consumption. By considering the sun’s position you can design elements into your house that maximize solar heat gain during the cold season and minimize heat gain during the warm season. We hired an architect experienced in passive solar design to assist us with our project. Three main considerations are the windows, the overhang of the eaves, and the thermal mass.

Solar domestic hot water (DHW) heating is a great way to incorporate renewable energy into your home. Modern systems are very reliable and the cost payback is very reasonable. A DHW system consists of solar collector panels in a sunny location, typically on a roof, a storage tank with a heat exchanger, a pump to circulate the fluid, and some simple controls (see Figure 2). We have four panels on a south-facing roof. The panels have a total surface area of 8.2 m2. Support

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Figure 2. Schematic diagram of a solar DHW system.

Figure 3. Schematic diagram of geothermal system.

brackets hold the panels at an angle of 45 degrees. This is an optimum collection angle for year-round performance for our latitude (43 degrees, 46 minutes North). This is also a steep enough angle to prevent excessive snow accumulation during the winter. The renewable energy site assessor used a solar pathfinder to estimate our solar energy collection potential. This handheld device gives a quick, accurate, visual indication of how much direct sunlight you will have at a specific location at different times of the year. For example, we have a relatively clear line of sight to the south from 10 a.m. to 6 p.m. However the pathfinder showed that one small oak tree would be a major interference problem in a few years. So before we installed the panels, we moved the tree to a new location.

Energy Features of This Residential Retrofit • Passive solar designed sun room and greenhouse • Solar domestic hot water system: 4 panels, 8.2 m2 total collector area, 300 L storage tank • On-demand, gas-fired water heater for backup hot water • Ground source heat pump heating and air conditioning system: 3 ton, 4 geo-loop wells, 180 m total length • High efficiency, gas-fired furnace for backup heat • Energy recovery ventilator • Whole-house fan • Wood stove • Low-e windows

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This information is also available on the solar pathfinder Web site.4 A glycol-water solution circulates from the panels to the heat exchanger in the storage tank. Circulating potable water is not recommended because it can cause corrosion and deposition in the collection system. The storage tank is 300 L, larger than a standard hot water heater tank. Water can be heated up to 80 ⬚C, so a mixing valve is required at the tank outlet to cool the water to less than 50 ⬚C for household use. Temperature is measured in the tank and at the panels. A controller turns on the pump when the panel temperature is higher than the tank temperature and turns the pump off when the panel temperature drops below the tank temperature. There is also a check valve in the line to prevent natural circulation from the hot tank to the cold roof panels at night. As a backup for the solar system, we installed a tankless, gas-fired water heater. The solar system provides all our hot water during the summer, but we do need the backup heater during the winter. Heating with Geothermal A geothermal (also called ground-source) heat pump system uses the energy in the earth to help heat or cool your home. An overall schematic of the geothermal system is shown in Figure 3. As can be seen, the main components are the underground wells, the pump, the compressor unit, and the furnace unit. Vertical wells are drilled into the ground. The depth and number of wells depend on the heat load required and the type of soil. Our three-ton cooling system required


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Report four wells, each 45 m deep. Tubing is run down and back up to each well. A refrigerant in a vapor compression cycle provides the heating or cooling for the house. Figure 4 is a schematic diagram of the system operating in cooling mode. A warm glycol solution is pumped into the wells in the colder ground, which reduces the temperature of the solution. The cooled glycol solution then goes to the compressor unit where it passes through a heat exchanger and cools and condenses the refrigerant fluid. The warm glycol solution then returns to the pump. The cool, liquid refrigerant goes through an expansion device that decreases the pressure and the temperature of the refrigerant. The cold refrigerant passes through another heat exchanger where it evaporates and cools the house air. The warm refrigerant, which is now a vapor, goes to the compressor, which increases the pressure of the refrigerant and sends it through the cycle again. The house fan moves the cold air throughout the house. The fan also pulls warm air from the house to be cooled by the refrigerant. To provide heating to the house, the compressor unit operation is reconfigured so that warm refrigerant in the con-

denser heat exchanger goes to the house side of the cycle and cool refrigerant in the evaporator goes to the ground side, as shown in Figure 5. To provide air to the house that is warmer or cooler than the ground temperature (depending on the season) the condenser and evaporator must be at different temperatures. This is done by maintaining different pressures in the heat exchangers, which results in different refrigerant saturation temperatures. Incorporating Insulation, Ventilation, and a Wood Stove We installed a whole-house fan to help ventilate and cool the house on warm days. To accommodate the air flow, vents were added in the gables at each end of the attic. We also added more insulation in the attic to achieve a level of R-38. We also added an energy recovery ventilator. This is a heat exchanger that pulls in fresh outside air during the winter and preheats it with warm exhaust air from inside the house. It is an efficient way to provide fresh air in a home that otherwise would have little fresh air during the winter.

Figure 4. Geothermal system operation in cooling mode.

Figure 5. Geothermal system operation in heating mode.

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The wood stove was installed and has worked very well, greatly reducing our need for fossil-fueled heat in the winter. Systems We Did Not Use We considered installing a solar photovoltaic (PV) system. However, there is a much higher initial cost, with a correspondingly longer payback period with PV systems than with DHW. We did not have enough prime roof space for both PV and DHW, so we decided against PV. We also considered a wind energy system. We live at a very windy location, near the top of a hill, so it seemed like a logical choice. However, the initial cost of these systems is high. To obtain optimal performance the turbine should be mounted on a high tower above the boundary layer, where the wind is faster and more consistent. A tower this tall would not fit on our lot.

9. The State of Wisconsin, Department of Administration– Energy Division Web site is available at http://www.doa.state.wi.us/ energy/. 10. The Renewable Energy Policy Project–Center for Renewable Energy and Sustainable Technology Web site is available at http://www.repp.org/ and maintains a green-building discussion list. 11. The American Solar Energy Society Web site is at http:// www.ases.org/; it is a useful, knowledgeable organization and publisher of Solar Today magazine. 12. A Web site with consumer information on solar energy is available at http://www.findsolar.org/. 13. The article, Remodeling—Art and Science, appeared in the June 2006 issue of the Energy Center of Wisconsin newsletter at http://www.ecw.org/prod/e2/jun2006.pdf.

Danny Aerts and Betsy True live in Middleton, Wisconsin; [email protected], [email protected].

Summary We are very satisfied with the renewable energy and energy-saving features we added and would recommend them to others. For those interested in obtaining more information, much is available online. A few sources we found useful appear in Notes and Web Resources.5–12 The newsletter of the Energy Center of Wisconsin recently published an article about someone’s experience in energy conservation during remodeling. This was similar to our experience, but addressed different issues.13 W

Supplemental Material

A PowerPoint presentation that visually describes our project to make our home more energy efficient is available in this issue of JCE Online. Notes and Web Resources (all sites accessed Aug 2006) 1. The R-value indicates how well a material resists heat transfer; the higher the R-value, the better the insulation. The U.S. Government Energy Saver Web site at http://www.energy.gov is an extensive Web site that covers many different topics. It has information on various insulation materials, R-value definition, and links for finding R-values of different materials. 2. Wisconsin Focus on Energy may be found at http:// www.focusonenergy.com/. 3. Information about energy agencies in the individual United States may be found at http://www.eere.energy.gov/states/. 4. The Solar Pathfinder Web site is available at http:// www.solarpathfinder.com. 5. The Energy Savers Web site at http://www.energy.gov/ taxbreaks.htm has information on tax credits available in 2006. 6. The U.S. Government Energy Star site can be found at http://www.energystar.gov/. 7. The National Renewable Energy Lab Web site is at http:// www.nrel.gov. 8. The Midwest Renewable Energy Association Web site can be found at http://www.the-mrea.org/.

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