Completed Demonstrations - Fort Stewart
New Residential Water Heating Technology Demonstrated at Fort Stewart
Gas-Fired Products' Seahorse, a natural gas hot water conversion system, was installed in base housing at Fort Stewart, near Savannah, Georgia, and monitored from April through November 1994.
Seahorse is relatively recent addition to residential water heating market
The Seahorse gas hot water conversion system is a relatively recent addition to the residential water heating market that allows a residence or small building to easily convert an existing electric resistance water heater to a water heating system fueled by natural gas or propane. The Seahorse consists of a natural-gas-fired tankless water heater and a small water pump, both housed in a metal case installed outside the home. The conversion system includes adapters which allow plumbing the input and output water flows from the Seahorse to the existing electric hot water tank.
The heater is equipped with a freeze protection device (freezestat), which will turn on the pump and circulate the water in the system for a short period of time during sub-freezing conditions. Auxiliary freeze protection, available as an accessory, has been used in the solar industry as freeze protection for over 25 years, and does not require any electricity.
The Seahorse has a nominal gas input of 60,000 Btu/h and is available in either propane or natural gas models. According to Robert Glass, Vice President of Engineering and Manufacturing, Gas-Fired Products, the large input is about twice the input of a standard gas water heater, so it lends itself to innovative installations. For example, Gas-Fired Products has hooked one Seahorse to multiple storage tanks, and has also used the technology for both home heating and water heating. In addition, the American Gas Association has certified the Seahorse for installations including manufactured (mobile) homes.
Seahorse evaluated using several parameters
Seahorse hot water heater installed at Fort Stewart.
The Seahorse system was installed in a three-bedroom, two-bathroom duplex, with approximately 1,300 square feet floor area; two adults and two children occupy the home. Hot water use is limited to three sinks, two tub/showers, a clothes washer, and a dishwasher. The technology was installed in March 1994 and monitored until November 1994.
The Seahorse installed in the demonstration used a two-stage gas valve and a direct spark ignition device to ignite the gas flame. The thermostat used to trigger operation of the Seahorse can be either the original tank thermostat or a submersible thermostat, or aquastat, supplied by Gas-Fired Products.
Through the demonstration, staff of the Pacific Northwest National Laboratory measured the electric and gas consumption of the Seahorse, the hot water energy supplied to the storage tank by the Seahorse, and the hot water energy supplied to the house from the storage tank. From this data, researchers generated a performance map relating the energy consumption of the Seahorse to the residential hot water energy requirements as well as the outside temperature.
The researchers then used the performance map to calculate the efficiency of the Seahorse and the Seahorse system ("system" implies the new technology and existing hot water tank combined). The cost to meet typical hot water requirements with the Seahorse system and the cost to meet the same requirements with conventional electric and gas residential water heaters were then compared on a life-cycle cost basis.
Hot water delivery efficiencies included in demonstration results
The average hot water consumption during the testing period was 60.7 gal/day resulting in a hot water energy use of 28,100 Btu/day or 68% of the Department of Energy's estimate for typical residential hot water energy consumption. The average hot water delivery temperature to the residence during the testing period was 128°F.
The final average hot water delivery-to-residence efficiency of the Seahorse system was determined to be 46.8%. High standby losses and the relatively low hot water consumption contributed to the relatively low delivery-to-residence efficiency recorded during this test. Much of the standby losses could be reduced through the addition of a simple check valve, which would increase the delivery-to-residence efficiency in future Seahorse installations.
The final average hot water delivery-to-tank efficiency (Seahorse alone) was determined to be 77.4%. The delivery-to-tank efficiency is defined as the hot water energy provided by the Seahorse to the hot water storage tank, divided by the gas energy input to the Seahorse. The manufacturer obtained an average thermal efficiency of 83.9% as determined by an independent laboratory.
Observation of the demonstration unit suggests that attaining this efficiency level requires properly setting the Seahorse temperature control during installation. Larger thermostat differentials between the Seahorse and tank reduce the cycling of the Seahorse unit and provide higher efficiency. Short cycling times and sporadic cycling occurred during the earlier stages of the demonstration, allowing researchers to try several compensatory strategies. Because reduced efficiency and short-cycling operation occurred when the tank thermostat was used for control, the demonstration results indicate that an aquastat be used for any new Seahorse installations.
Seahorse system nets significant life-cycle energy cost-savings of $778
Based on the measured performance, the Seahorse gas hot water conversion technology demonstrated at Fort Stewart was estimated to net a life-cycle energy cost-savings of $778 for a typical residence at that site with a hot water consumption equivalent to 64.3 gallons/day of 135°F water. The estimate was calculated using avoided energy costs of $0.025/kWh for electricity, $8.85/kW for electric demand, and $0.30/therm for natural gas.
Based on national average electrical costs of $0.0867/kWh and natural gas costs of $0.604/therm, the life-cycle energy cost savings for the Seahorse system would be $1,365.
After analysis, the cost savings were not enough to offset the initial estimated installation costs of $835 at the Fort Stewart location. Marginally higher water consumption or electric energy costs would make the technology a life-cycle cost-effective retrofit for electric water heaters at Fort Stewart.
Seahorse proves comparable to tank-type gas water heaters, with potential for greater efficiency
A comparison of the Seahorse performance with more typical tank-type gas water heaters suggests that the installed Seahorse system at Fort Stewart performed at roughly the same level of efficiency as a typical 40- gallon gas water heater with an energy factor of 0.54, the minimum efficiency level allowed for installation at a Federal site. Improvements in system design in the present generation of Seahorse units may make new Seahorse models more efficient than base tank-type gas water heaters. In addition, installation of a check-valve in the Seahorse flow loop would also improve the Seahorse efficiency beyond what was measured in the Fort Stewart demonstration. Similar levels of improvement are available in residential tank-type gas water heaters but often at higher costs.
Based on the measured data, the author of the technical report on the demonstration, Dave Winiarski of the Pacific Northwest National Laboratory, recommends that the decision to purchase a Seahorse versus a tank-type gas water heater be based primarily on capital and installation cost consideration. A life-cycle cost comparison with gas-fired, tank-type water heaters will depend heavily on the installation costs for the tank-type gas water heaters, particularly the cost of providing an exhaust flue for ventilation of the gas water heater.
In the technical report, Mr. Winiarski presents two nomographs, one showing the electric and natural gas costs leading to a positive net present value for the Seahorse conversion, and one illustrating which gas water heater type would be more cost effective based on the cost to provide a flue system for the tank-type water heater.
Demonstration indicates that Seahorse is robust technology
In conclusion, the Seahorse gas hot water conversion system appears to be a robust technology for which there are cost-effective applications in the Federal sector. Federal energy managers supervising areas with the right combination of energy costs should consider the Seahorse as an alternative to electric resistance water heaters for residences that have natural gas or propane gas available to them.
For a copy of the technical report summary, call the FEMP Help Desk at (877) 337-3463. International callers please use (703) 287-8391.