Piña Coolada
Project undertaken in course year 2018-2019 with Precourt Institute for Energy
Project Goal
Provide an efficient method of storing thermal energy to heat water and cool a home in southern Texas, enabling home owners to minimize peak power usage, cost, and carbon footprint
Project Motivation
Global carbon dioxide emissions have been steadily growing and have resulted in changing climate and severe weather. Renewable energy systems currently in place cannot meet 100% of the demand
There is a discrepancy between renewable energy generation and energy demand in certain areas, demanding more efficient, inexpensive methods of energy storage
Background
Texas uses over a quarter of its energy expenditure for air conditioning and is facing a problem with overgeneration of wind energy at night and undergeneration during the day.
High Priority Requirements
Cool a 2000 sq. ft. home from 92F to 75F within 3 hours
Adequate daily cooling capacity considering needs and costs
System can be installed as a retrofit
Ethical Considerations
Installation and maintenance safety
Expense and customizability
Material selection safety
Solution
We designed and built a heat recovery chiller using a phase change material energy storage system that stores the waste heat from the cooling cycle in an A/C unit and deposits it in the hot water tank, eliminating the need to produce that energy from a separate heat pump. The system would be installed inline in a home HVAC system.
To provide cold air to a home, air conditioners are typically used, also generating waste heat. Our system design runs the air conditioner when electricity is clean and inexpensive, which in Texas is after midnight when wind energy is plentiful:
the waste heat is moved to a Heat Recovery Unit designed to heat water in a hot water tank for later domestic use,
the cooled air is run through our Piña Coolada system cooling the phase change material. When cooling is desired in the day, only a lower-power fan is required to blow air through the Piña Coolada system to lower the air temperature.
System schematic
The flow of heat starts at the Air Conditioner. Waste heat is moved to the HRU, while cool air is moved through the Piña Coolada Box. Air coming out of the Piña Coolada box can be reinserted in to the Air Conditioner to furhter cool it, continuing to cool the phase change material in the box.
System schematic
The Piña Coolada box CAD design, with air inlet shown.
PCM Material
The Phase Change material we worked with is a HeatStaxx Air system with an 15C melt temperature
PCM Material
The HeatStaxx is designed for air flow through the stacked material
The Piña Coolada system
The Piña Coolada box is in the middle, air conditioner on the right blowing air into the box. Air is recirculated in to the air conditioner for recooling.
Test schematic
Air is blown in via a fan into the box. The blue rectangles represent the HeatStaxx elements, and thermocouple locations shown
Discharge time
Test looking at the time required for the outlet air temperature to match the inlet air temperature. HSR (Heat Staxx) is compared to two other materials, and is shown to be most effective with a total time of 60 minutes.
Charge time
Test looking at the time to charge the HeatStaxx, or cool it to 15C its phase change temp. At 80 minutes, the PCM is just below 15C.
Payback
In conjunction with a Heat Recovery Unit, the payback period for such a system is less than 5 years
Student team
Future Work
Evaluate the full system with hot water tank to determine impact on the tank's function
Develop control system to automatically shift between cooling via the A/C system and the Piña Coolada box
Develop method to recirculate air in home HVAC for charging