Seawater Heat Pump Demonstration Project - An Emerging Energy Technology Grant Project
This project investigates the demonstration of a seawater heat pump system at the Alaska SeaLife Center (ASLC). Heat pumps, a technology with limited cold climate applications, have been successfully utilized in countries such as Canada, Norway and Sweden utilizing seawater as a heat source. There is much interest in this technology for Alaska given these relative applications and the opportunity to displace expensive heating fuel in the state’s coastal communities with access to (relatively) inexpensive electricity.
The ASLC has been operating on the shoreline of Resurrection Bay in Seward since 1998 in pursuit of its four primary objectives: research, rehabilitation, education and display of exhibits. As a nonprofit organization, energy and operation costs represent a significant concern. The primary goal of ASLC during this project was to reduce monthly heating costs in the long term. Because ASLC is well aware of the impact excess amounts of carbon dioxide have on the climate, another important objective of this project was to decrease the carbon footprint of its facilities. Prior to 2009, the ASLC heated its facility with three oil-fired boilers. On average, the facility used nearly 130,000 gallons of fuel for heating each year.
Heat pumps are devices that transfer heat from a lower temperature reservoir, usually the ambient environment, to a higher temperature sink. The low temperature reservoir is usually the air, the ground, or a body of water. This heat, however, does not come without cost; work in the form of electricity is required to pump it to the high-temperature sink. Seawater heat pumps are water-to-water systems that operate by using electric compressors in combination with the physical properties of an evaporating and condensing fluid known as a refrigerant.
The opportunity for this project came from the proximity of ASLC to Resurrection Bay, which was determined by YourCleanEnergy (YCE) and a tremendous utility-grade heat resource, Seward’s dependence on heating oil, and access to relatively inexpensive electricity. Based on evaluation recommendations by YCE, ASLC pursued a project with the Denali Commission EETG to install and demonstrate a seawater heat pump system to displace a majority of ASLC’s heating oil need.
The overall goal of the project was to reduce expensive and rising heating costs at the ASLC. Specific to the EETG program, the goal was to demonstrate a commercial-scale seawater heat pump system in an Alaska environment. To this end, data collection was a priority during design and installation of the system in order to provide enhanced system and performance monitoring as well as recommendations for future projects in Alaska.
Key project tasks and relevant activities included the following:
- Installation of two 90-ton heat pumps
- Installation of supporting infrastructure (heat exchangers, pumps, etc.)
- Commissioning of integrated monitoring and controls system
- Reconfiguration and integration of supporting mechanical and electrical systems
- Rehabilitation and integration of ASLC’s seawater intake system
- Demonstration of the technology
Project activities commenced in May 2010, final design was completed in November 2010, with primary system installation and commissioning completed by June 2012 and substantial system commissioning completed by February 2013. The project underwent active performance monitoring through May 2013.
The ASLC successfully met original project objectives, particularly the installation of a seawater heat pump system and supporting infrastructure, controls and instrumentation. The project did experience some delays in commissioning as a result of minor instrumentation and controls issues, which were successfully addressed by February 2013. Over the course of three months of monitoring since that time (1,900 hours of system operation), the average COP was 2.90, displacing a total equivalent of 20,000 gallons of heating oil while consuming 300,000 kWh of electricity. Of note, it was reported by the ASLC that the existing fuel boilers were turned off on December 9, 2012 and have not been used for heating needs since.
Full demonstration of the technology will require a minimum of one year of monitoring data to adequately assess system performance and to inform future project considerations such as heat pump sizing, operation and system performance as a function of seawater temperature. A preliminary assessment shows that the economic viability of this project depends primarily on the price of electricity since 76% to 80% of the cost over the life of the project is electricity. It is projected that the project can potentially prove cost-effective with benefit-cost ratios ranging from 0.65 to 1.87 and payback periods ranging from 3.3 years to longer than the project lifetime depending on the future price of electricity, the price of displaced fuel oil and social cost of carbon (SCC). Higher electricity price negatively impacts the cost effectiveness of the project, while higher fuel oil and higher SCC positively impact the cost effectiveness of the project. More data monitoring, along with updated electricity and fuel oil pricing information, is needed to refine project viability projections.
One area that could benefit from further investigation is the effect on system of seawater temperature colder the 37°F on system COP. The ASLC system has a minimum allowable temperature of 37°F, which is equivalent to the historical minimum of Resurrection Bay since 2003. Over the course of the monitoring period for the project (the coldest period for seawater temperatures in the bay), the minimum temperature reached was 38.9°F. While the system operated successfully at this temperature, deployability of the technology in cooler temperatures, or the scope of suitable resources juxtaposed to suitable project sites, warrants further investigation.
This project and others in Alaska capitalized on existing seawater intake infrastructure. Presumably, the number of facilities with such existing infrastructure and the opportunity to implement a seawater heat pump system is limited. It is unclear how expensive such intake systems can be, but they could potentially add a significant capital and operational cost to a project. The ASLC system utilizes a wet well and gravity siphon system, which reduces the need for pumping. This system could reduce costs for other projects. YCE has recognized the need to develop a cost-effective intake system and has even applied to such programs as the AEA Emerging Energy Technology Fund for funds to investigate and develop low-cost wet wells. This is an area that needs to be researched further in terms of costs, best practices in current designs, innovations in design, replicability and scalability.
One promising application for this technology is district heating. Seawater is a utility-grade heat source and, as mentioned previously, has been successfully utilized for district heating in Sweden and Norway. Coastal communities that have access to (relatively) inexpensive electricity, but are dependent on high-cost fossil fuels for heating, and have higher-density commercial, business or residential districts close to a viable ocean resource are likely candidates for this scenario. District heating, however, can be expensive. Potential barriers to implementation include the cost of seawater intake infrastructure and distribution piping and pumping equipment, and the need to retrofit customer heating systems. The City of Seward has expressed interest in this concept since there is a business district in close proximity to the ASLC that may be a potential candidate for a district heating loop. However, the true potential of district heating in Alaska is unknown; economics, public support and interest in the technology, and business models for operating a heat utility all warrant further investigation.
Photo 1: Two Trane heat pumps installed and operational at ASLC. Courtesy of Jason Meyer, ACEP.
Photo 2: The heat pump system seawater heat exchanger. Courtesy of Jason Meyer, ACEP.
Photo 3: Pumping seawater from the ASLC wet well. Courtesy of Jason Meyer, ACEP.