To reduce our consumption of energy in our Welcoming Center, we focused on both sustainable energy alternatives and on energy saving measures. It was important to not simply focus on obtaining our electricity from alternative means, but to also work on reducing the amount of energy we use in the first place. We are proud to say that our building uses 47% less energy than California Title 24 2001 Energy Code.
We have three types of solar energy collection at the Welcoming Center to supplement the electricity we buy from the grid, to supply the building with hot water, and to heat the building in the winter, drastically lowering energy consumption during the cold months:
- The south-facing portion of our roof is covered with photovoltaic cells, which supplement the electricity we buy from the grid.
- We also have solar thermal collectors to supply the building with hot water.
- Finally, the entire building incorporates passive solar design to heat the building in the winter, drastically lowering energy consumption during the cold months.
In addition to the on-site solar energy collection, we also wanted to help promote green power in general. As part of the Welcoming Center project, we purchased 223,580 kWh of clean, renewable off-site wind energy, in the form of Renewable Energy Credits (RECs). This prevents 311,223 pounds of carbon dioxide from being released into the atmosphere, and supports the movement towards a sustainable, clean energy solution.
List of Energy Efficient Measures:
- Passive Solar Building Design
- Non-Compressor Cooling
- Hydronic Radiant Floor Heating
- Solar Water Heating
- Photovoltaic Solar Panel System
- High-Efficiency Fluorescent Lighting (0.93 watt/sf)
- Motion Sensor Controlled Lighting in Bathrooms
- Best possible Energy Saving Kitchen Appliances
- Reflective Roofing (in areas not covered by our Living Roof)
- High Efficiency Exhaust Fans
- High Performance Glazing
- Double-Paned, High Performance Windows
- Avoiding Air Conditioning
- Our Welcoming Center has no air conditioning system. By not installing air conditioning in the building, we save large amounts of energy during the warm months. Two primary factors allowed us to avoid air conditioning:
- The high thermal mass of the building helps keep the temperature down when it’s warm and sunny out by absorbing excess heat.
- The living roof reduces the “heat island effect” that occurs with the black tar roofs found on most commercial buildings.
High Tech Cooling
We have high-tech windows, which are part of our demand-controlled ventilation system. If you look up at the ceiling in our dining room area—the central and also largest part of the building—you will see a row of smaller windows on the north-facing side of the roof (away from the sun). These windows open and close automatically depending on need. There is a sensor (also in the dining room) that tells the windows to open if the inside temperature is above 68º F and to close if it is below. This allows the hot air, which naturally rises to the top of the room, to vent out, keeping the building cool. The other part of our demand control ventilation system is a CO2 sensor. This does not serve to keep the building cooler but does regulate indoor air quality. This sensor determines if the levels of carbon dioxide in the building are too high (which can happen in the winter when the windows are all closed to keep the heat in), in which case air is pulled in from the outside until the levels return to normal.
Evaporative Cooling System
When all else fails, we have an evaporative cooling system that takes the place of a typical air conditioning system. The evaporative cooler (also known as a “swamp cooler”) pulls air from the outside through an earth-sheltered basement—pre-cooling the air—and then through a membrane that has water flowing over it. This cools the air down before it is blown into the interior of the building. Swamp coolers use about 75%—80% less energy to operate than an equivalent refrigerated air conditioning system. Our savings are in fact even greater because our other building features decrease the need to run an air-cooling system in the first place.
Hydronic Radiant Floor Heating
Our Welcoming Center does not have a forced air heating system. We used what is known
as hydronic radiant floor heating. In this system, hot water is circulated through polyethylene pipes installed in our concrete slab floor.
Heat is conducted to the surface of the floor where it broadcasts energy up into the room. Radiant floor heating is superior to convection heating because warm air will rise wastefully to the top of a room, especially in a large, two-story open space like our dining room. This is not only inefficient, but also tends to heat the head and the upper parts of the body, while leaving the lower parts of the body cold, which can lead to discomfort. Radiant floor heating warms the lower part of the room and the body, making more efficient use of the thermal energy and creating a more “natural” feeling of warmth. Underfloor heating is also more efficient than a traditional radiator system, because the large surface area of the heating element (i.e. the entire floor) means that the boiler water temperature can be set relatively low.
We had hoped to use the solar thermal collectors to heat the water that flows through the floor heating system, but we were unable to do so for permitting reasons. We were told that we would not be allowed to link the two systems because the solar thermal collectors are used to heat the potable water in the building, and the water running through the floors is not potable. So instead, the water is heated using a 97% efficient condensing boiler, which uses half the amount of energy as a traditional water heater to heat the same amount of water.
In the end, we estimate that our hydronic radiant floor heating system uses 21% less energy when compared to a standard heating system.
Passive Solar Design
Passive solar design is a general term for making use of various passive solar technologies to maintain a comfortable temperature range inside a building throughout the sun’s daily and annual cycles. By implementing passive solar design in our building, we minimized the need for traditional heating and cooling technologies such as a HVAC (heating, ventilation and air-conditioning) system, which would rely on power from our PV cells or grid power.
Passive solar systems are an ideal use of the sun’s energy because they have little or no operating costs, very low maintenance costs, and emit zero greenhouse gases when in operation.
For a year before ground was broken on the Welcoming Center project, surveyors came out to the site and did a sun path analysis. They looked at where the sun rose and set and at the altitude angle of the sun throughout the seasons. This analysis allowed the architect to design the building to absorb sunlight during the cold, winter months and to block sunlight during the warm, summer months. The Welcoming Center has a series of large, floor-to-ceiling windows that face due south for absorbing sunlight. However, the awnings over the windows, which house our solar thermal collectors, are designed so that they completely block the high-angle, summer sun while letting in the low-angle, winter sun.
The second part of our passive solar design is the large thermal mass present in the building in the form of the plastered straw bale walls, the concrete floor, and the living roof. Thermal mass is any mass that absorbs and holds heat. Properties of a good thermal mass are high specific heat, high density, and a low thermal conductivity, though not as low as for insulation materials. Because the walls, floor, and roof have a high thermal mass, they can take in excess thermal energy during sunny periods when you don’t want the interior of the building to be hot, and then release it during overcast periods or during the night. Basically, you can think of thermal mass as a “shock absorber” for the fluctuations in temperature outside the building, keeping the inside temperate at all times.
As you can see, both of these technologies utilize the energy from the sun directly, without complicated semiconductors, electronic systems, or even any moving parts.
Photovoltaic Solar Energy
We have a 6.4 kW photovoltaic array installed on the roof of our Welcoming Center that produces approximately 9,000 kWh of energy per year, effectively reducing carbon dioxide emissions by about 8.5 tons annually, or the equivalent of 33,792 gallons of oil over 30 years. The cells are situated on a south-facing roof, designed specifically for this purpose, with additional room to expand the solar array in the future, as funds become available.
The solar cells on our roof are photovoltaic laminates (PVLs) provided by Uni-Solar. There are two general classifications of PV cells—crystalline silicon cells and thin-film cells. The PVLs on our roof are the second kind. Crystalline silicon cells are the most common type solar cells and typically have better efficiency than thin-film cells. However, thin-film cells use less than 1% of the raw material (silicon or other light absorbers) compared to traditional crystalline solar cells. Thin-film cells like the ones on our roof are also shadow tolerant, meaning if the cell is in partial shade, the rest of the cell—the part still in direct sunlight—continues to produce electricity, a characteristic that is not true of traditional crystalline cells. The PVLs are lightweight and flexible and come in long strips that are easily “installed” on the roof by simply pealing off the backing to expose an adhesive and sticking them on.
After the sunlight is collected with our PVLs, the DC voltage produced by the array is converted to grid-compatible AC voltage and is then tied into the grid. In case the solar panels do not produce enough energy to fully power the building, then the additional necessary energy is drawn from the grid. However, if there is a surplus of energy from the solar panels, the excess energy is fed into the local grid and is available for use by other consumers. By tying our solar panels into the grid, we ensure that every single kilowatt-hour of energy produced by our solar panels is utilized, and we help ease the load on the electricity company’s power systems whenever possible.
For more specific information on the basics of photovoltaic technology, please read the related Wikipedia article.
Solar Thermal Collectors
The awnings on the south side of the Welcoming Center are actually an array of solar thermal collectors that, as the name implies, absorbs heat from sunlight. The thermal energy collected from the sun is used to heat water for the kitchen and bathrooms. The thermal collectors consist of glass tubes with aluminum pipes running through them. The tubes are evacuated to prevent heat loss during the winter, and the aluminum pipes have a special coating on them to help absorb specific frequencies of sunlight. The entire array consists of eight panels, containing six evacuated tubes each.
A heat transfer medium called “Downfrost” runs through the aluminum pipes at about 1 gallon per minute, absorbing large amounts of thermal energy and becoming very hot. “Downfrost” is a non-toxic antifreeze, consisting chiefly of propylene glycol with a small amount of inhibitor, dipotassium phosphate. The FDA generally recognizes both of these ingredients as safe as food additives, making “Downfrost” a safe and appropriate heat transfer medium for potable water. In other words, if the system breaks and for some reason and some of the fluid gets into the water system, no one will be harmed.
The heat is transferred to the potable water via coils in a water tank. After leaving the solar thermal collectors on the south side of the building, the heat transfer fluid runs into a heat exchange coil in the bottom of a large water tank. There is a second heat exchange coil in the top of the tank through which the potable water runs. Water is heated by the first coil in the bottom of the tank, then rises to the top of the tank and heats the second coil. Water will be 55º F when it enters the top coil and will exit at about 125-128º F, with a flow speed of 20 gallons per minute if all the faucets in the building are turned on.