120 V Heat Pump Water Heater Replacement Solution for 30- to 40-Gallon Gas Water Heaters

This project will focus on laboratory development of a 120 V electric heat pump water heater (HPWH) that can be a direct replacement solution for existing 30–40-gallon gas water heaters. Of particular interest is the so-called 'tall and slim' form factor gas water heaters, which are approximately 60 inches in height and 20 inches in diameter. ENERGY STAR qualification criteria for 120 V (15 Amp circuit) HPWH include UEF of at least 2.20, and FHR of at least 45 gallons. However, the ENERGY STAR criteria does not specify a physical size, and many replacement installations are space constrained to use a same-sized replacement unit. This project will develop of a 120 V (15 amp circuit) HPWH that can be a drop-in replacement for 'tall and slim' gas water heater, that meets ENERGY STAR efficiency criteria, and has water delivery capacity similar to the gas water heater it replaces. To accomplish the goals of this project, ORNL will combine the best available technologies and techniques, and develop innovative new technology where necessary. The most critical performance metrics in this project are the first hour rating (FHR), the physical external product dimensions, and the ability to use a 120 V (15 amp) circuit. Matching the space constraints of the existing 'tall and slim' form factor will allow for easier retrofit installations, thus the developed HPWH must fit in the physical envelope typical of 30-40 gallon gas water heaters. There are 167 products in the ENERGY STAR qualified products list powered by natural gas and having storage size from 28 to 39 gallons. Of these, 149 are from 58 to 60 inches tall and most are 20 inches in diameter. These have FHR ranging from 62 to 93 gallons, with an average FHR of 75 gallons; they have input ratings from 36,000 to 60,000 Btu/hr, with an average input rating of 42,000 Btu/hr. By the end of the first year, a breadboard prototype will be evaluated. The team will identify what further innovations would be needed to make this prototype meet the project objectives. If the next prototype meets those objectives, the team will turn their attention to identifying opportunities to minimize the cost of the unit.