Optimal Design and Control of Residential Airconditioning Equipment With Integrated Thermal Storage
Although thermal energy storage (TES) has been integrated with commercial building cooling systems, it is rarely considered in residential buildings. In recent years, though, variable utility rates have become more available to residential customers to incentivize demand reductions during midday peak hours. TES allows consumers to store cooling during hours with low demand and reduce the peak demand from air conditioning. From an economic perspective, the integration of storage can result in reduction in the installed cost of the primary cooling equipment because of the reduction in the peak cooling requirement. However, this is counteracted by the additional costs associated with TES and a secondary loop. Furthermore, variable utility rates are not mandatory for residential buildings, so the operating costs of a cooling system with TES must be competitive with the operating costs of a conventional split air conditioner under traditional flat utility rates. In this thesis, a system model consisting of a packaged chiller, ice storage, and building load is used to simulate the operating costs of a residential sized cooling system with ice storage. In order to minimize the operating cost of this system, a generalized rule-based control strategy is developed for TES in residential buildings. This control strategy is based on a combination of existing heuristic control strategies and considers the occupancy and power consumption of residential households. A benchmark comparison against an optimal controller showed the generalized rule-based controller performs within 20% of the minimal operating cost, and a seasonal evaluation showed up to 40% reduction in off-peak demand when compared to existing heuristic control strategies. The ice storage system is compared against a conventional split A/C system in terms of installed costs and operating costs. The installed costs based on currently available products showed the ice storage system is more expensive than a split A/C, and most simulation results showed higher operating costs for the ice storage system when considering the same SEER rating xiii for both systems. Optimal system design from minimizing the simple payback period showed higher SEER rating for the ice storage system. This compensates for the loss of capacity when operating the system in charging mode to charge the ice storage tank. These results showed optimal simple payback exceeding 10 years in all simulations. Additional parametric studies showed the optimal system design is dependent on the combination of the utility rate structure and climate. The work done in this thesis has shown that the generalized rule-based control strategy developed for residential buildings provides more operating cost savings than existing control strategies primarily due to reduced off-peak demand charges. Even though the simple payback results are unfavorable, payback periods are highly dependent on the system cost model as well as available utility rates. Future studies can consider different storage media, refrigerants, and integration of TES cooling systems with renewable power generation.
Braun, Purdue University.
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