FEASIBILITY ASSESSMENTS OF COMBINED COOLING, HEATING, AND POWER (CCHP) SYSTEMS FOR COMMERCIAL BUILDINGS
Open Access
- Author:
- Ahn, Hyeunguk
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 14, 2019
- Committee Members:
- James Freihaut, Dissertation Advisor/Co-Advisor
James Freihaut, Committee Chair/Co-Chair
Donghyun Rim, Committee Member
Gregory Scott Pavlak, Committee Member
Nilanjan Ray Chaudhuri, Outside Member - Keywords:
- Distributed energy system
Microgrid
Trigeneration
Energy saving
Energy resiliency
Carbon dioxide emission - Abstract:
- Distributed energy systems produce energy on-site considerably reducing energy loss that would occur when energy is supplied from centralized systems. One of the distributed energy technologies is a combined cooling, heating, and power (CCHP) system. In a CCHP system, electricity is generated near end-users and the recovered heat from a power generation unit is utilized for cooling and heating in a building. Therefore, CCHP systems can increase primary energy utilization efficiency and energy reliability while reducing adverse environmental impacts. CCHP systems can be applicable from a building to community level. However, the feasibility of CCHP systems can largely vary with building type and location as well as other integrated sub-systems such as hybrid chiller and solar photovoltaic (PV) systems. This dissertation focuses on feasibility assessments of CCHP systems integrated with hybrid chiller and PV systems. Specifically, the work in this dissertation consists of investigations of energy, environmental, and economic performances of CCHP systems applied to various commercial building types in different climatic regions in the U.S. The first investigation evaluates the energy and environmental performances of CCHP systems operating with two distinct cooling systems (i.e., absorption chiller vs. hybrid chiller) based on primary energy consumption and carbon dioxide emission. This study focuses on a hospital and an office building in San Francisco, CA and Long Island, NY. The results show that CCHP hybrid chiller systems can reduce a significant amount of primary energy consumption than traditional CCHP systems that utilize only an absorption chiller, especially when the systems are applied to a hospital building. The significant reduction of the primary energy consumption is mainly because a hybrid chiller system can minimize undesirable boiler operations for absorption cooling. The reduced primary energy consumption can also lead to a decrease in carbon dioxide emissions although regionally-varying emission factors of the grid electricity notably influence the environmental performance of CCHP hybrid chiller systems. The second investigation focuses on the economic feasibility of different-sized CCHP hybrid chiller systems for large office buildings considering realistic electricity tariff structures in different geographic regions including San Francisco, CA; Boston, MA; and Miami, FL. The results show that CCHP hybrid chiller systems can be economically justifiable for regions with relatively high electricity price and low natural gas price such as San Francisco and Boston. The cost savings are mainly attributed to electricity cost savings. Specifically, if a local electricity tariff estimates demand charges as high as energy charges (e.g., a tariff structure in San Francisco), demand charges can contribute to about 40% of the electricity cost savings; thus, using simplified tariff structures that neglect demand charges can result in a noticeable discrepancy in economic analyses of CCHP systems or other analogous distributed energy systems. However, for regions with relatively high natural gas price and low electricity price (e.g., Miami), the operation cost of CCHP hybrid chiller systems is higher up to $0.4 million per year compared to that of a conventional separate heat and power (SHP) system. The third investigation integrates solar PV panels with CCHP hybrid chiller (CCHP+PV) systems as applied to a large office building in San Francisco, CA and examines the impacts of variabilities in energy demands and solar irradiance on the energy and economic performances of CCHP+PV systems. According to the results obtained in this study, the associated uncertainties marginally influence the energy performance of CCHP+PV systems whereas they can increase the operation cost by up to $75,000 per year. Such a great increase in the operation cost is mainly attributed to demand charges that tend to increase as the uncertainties are considered. This result implies that a deterministic model of a CCHP+PV system may significantly underestimate its operation costs and overestimate economic savings, thereby leading to overly optimistic economic viability.