A solar cooling strategy for net-zero energy buildings

Abstract

Within the commercial building sector, the largest consumption of primary energy is driven by cooling and ventilation requirements. Renewable cooling strategies utilizing solar energy could present an attractive alternative to grid source HVAC systems, due to the abundance of solar energy (1050 kWh/m2/yr) incident on buildings relative to building energy demand (150 kWh/m2/yr).

Lastly, a third question in low-energy cooling, and in low-energy heating as well, is whether localized radiant panels can provide thermal comfort with less energy than traditional HVAC approaches which condition large spaces and prioritize narrow comfort regions. Energy modeling results of a simulated office space in New York, NY show that cooling loads could be reduced 10-15% by expanding the cooling temperature setpoint from 21°C to 25°C while still providing thermal comfort with a localized cooling device. Additionally, in order to assess the comfort perception of a localized thermal comfort delivery system, an experimental installation was constructed at the 2016 Smart Geometry Conference in Gothenburg, Sweden. Since the investigation of cooling was not an option for this installation, thermal comfort related to heating was examined instead. Mean occupant thermal comfort results showed an increase on the thermal sensation scale from 0.13 to 0.88 after 20 minutes of sedimentary activity underneath the installation, indicating that the localized heating system was able to shift occupant thermal perception.

The energy modeling results of the solar cooling experiments demonstrate that these strategies, whether independent or in concert, should be further explored in the context of cooling for net-zero energy buildings with physical experimentation to validate preliminary findings. Additionally, further tests are needed in order to determine if localized radiant cooling panels can achieve similar thermal comfort results as the localized radiant heating installation.

The second phase of the research addressed solar thermal cooling with building-integrated energy harvesting systems. Related work has recently demonstrated the potential for 400-500 watts of thermal energy collection with a prototype of a Building envelope-Integrated, Transparent, Concentrating Photovoltaic and Thermal collector (BITCoPT) installed in New York, NY. Additionally, while this work outlined an experimental framework to test the solar cooling potential of a 10 kW adsorption chiller, the chiller’s performance has not yet been characterized when driven by the solar collector. In order to evaluate the chiller’s performance with similar thermal contributions from a fully operational solar prototype, a preliminary assessment of the chiller was completed with 1 kW of thermal driving energy at 60°C. Experimental results from this effort show that there are still many limitations with building envelope-integrated solar cooling, however, recommendations are made for future solar cooling experiments.

Since peak cooling loads within commercial buildings tend to coincide with solar intensity, current approaches to solar thermal cooling use collected solar energy to power air-conditioning almost instantaneously. This is potentially an ineffective use of solar energy as heat rejection during cooler parts of the day, such as the nighttime, may improve solar cooling efficiency. To determine whether nighttime transformation of solar thermal energy into cooling is more efficient than existing daytime approaches, an energy model of an office space in New York, NY was simulated in EnergyPlus. Preliminary energy modeling results show that solar thermal cooling efficiency in commercial office buildings could increase 10-15% in humid continental climates, like New York City with the proposed nighttime solar cooling strategy.