ENGINEERING FOR TOMORROW
Team ASUNM’s house, SHADE, is both AC and DC wiring infrastructure. Many people are accustomed to AC wiring in their homes because AC electricity from large power plants is cheaper than energy derived from more sustainable sources. Many devices and appliances that we currently use (computers, cell phone chargers, etc.) use DC power.
To maximize energy production and use, both AC and DC wiring is implemented in SHADE. AC and DC wiring serves different dedicated loads throughout the house. The goal will be to ensure that DC loads (such as LED lighting, small DC consumer electronics and optional battery storage) are serviced from DC power available from solar modules, while loads that are more efficient in AC operation (such as fans and motors) are served from AC through micro-inverters.
This effort is the first time that complex optimization of power consumption and power flow between AC and DC loads is implemented and analyzed simultaneously with a detailed monitoring of PV production.
SHADE’s envelope and energy balance is modeled using available software packages including TRNSYS, Energy Plus, HOMER, and others. Modeling for this project coincides nicely with other projects at UNM and ASU.
SHADE when completed, will continue serving as a living test bed for these projects. Team ASUNM will incorporate self-learning, remote programmable, and web-accessible devices, including state-of-the-art thermostats.
Whole Building Management
Whole building energy management, enabled by smart sensors and controls, is the number one priority for sustainable building. SHADE has an extensive energy management and monitoring system, all integrated in one Home Area Network (HAN).
The HAN monitors instantaneous power generation and load demands from various appliances and make optimized power management decisions based on programmable pre-settings saved by the residents. Team ASUNM incorporates utility-interactive principles into the home design even though it is not required by the Solar Decathlon competition.
Heating and Cooling
Unlike the majority of American homes, the SHADE home is incorporating a radiant cooling system used concurrently with an air cooling unit. The team of cooling systems will work together to create a stable, consistent and desirable thermal environment. Radiant cooling will maintain a cool temperature in each zone of the house by running cold liquid through a system of small capillary tubes which make mats. These mats will be placed in the ceiling and the rooms will be cooled by the thermal contact of the cold water and the warm air, and by radiation. An air cooling unit will be used when the cooling load is higher than the radiant cooling output, and to help control humidity.
Radiant cooling was chosen as the primary system for several reasons. Research has shown that occupants prefer the sensation of radiantly cooled spaces over traditional air-conditioning. Radiant cooling has also been shown to reduce energy use, compared to using air-only systems. At peak demand, one study showed that a combined radiant-air system used 50% of the energy used by an all-air system, to meet the same cooling requirement. Using a radiant system gives greater efficiency and reduces energy costs. This combination of advantages of thermal comfort and reduced energy consumption led to the ultimate decision of radiant cooling used as the primary source of cooling.
The heating and cooling system for SHADE includes thermal storage system as well. Previously, thermal storage has been applied primarily to commercial buildings. Team ASUNM is exploring its application for residential use. The main idea of thermal storage is to store thermal energy during one time period and use it over a different span of time. This is accomplished by charging a thermal storage unit by freezing water to make ice. The chiller will run during the night, when temperatures are lower and energy prices are at their lowest, in areas that have time-of-use pricing for electricity. During the day, the ice is used to cool a glycol solution which is carried to both the radiant and air cooling systems.
In the past, thermal storage has shown potential benefits in energy savings for commercial use. Other factors that have to be considered in weighing energy savings include the efficiency of the chiller at temperatures low enough to freeze water and the effectiveness of insulating material around the thermal storage unit. The chiller that charges the thermal storage unit of the SHADE house will not be directly fed by electricity made from photovoltaic panels; however, thermal storage encourages renewable energy by storing thermal energy when it is available and using the stored thermal energy to avoid large peaks in electricity demand. In states such as Texas, Kansas and North Dakota, electricity from wind turbines is primarily created at night. Thermal storage has the potential to maximize the use of this electricity by storing the thermal energy during the night and utilizing it during the day. Because energy is in its highest demand around mid-day, thermal storage systems could use this wind energy created at night and potentially lower peak electrical loads during the day. The various energy benefits that thermal storage offers makes this option an innovative challenge for Team ASUNM.