Ammonia-absorption heat pump in U.S. tests

Stone Mountain Technologies, Inc. (SMTI), based in Johnson City, Tenn., is developing what it calls a “next-generation heating innovation” – a compressor-free, thermally driven heat pump that uses low-charge ammonia- water absorption, triggered by natural gas, to generate space heating and domestic hot water.

Having undergone a series of field tests in homes and restaurants, SMTI’s residential space heating and water-heating systems are slated to hit the market in early 2021, said Scott Reed, SMTI’s vice president of strategy and marketing. The restaurant unit, which also supplies cooling to the kitchen area, will have a later release, he said.

SMTI’s systems will be marketed by an HVAC manufacturer that has not been named.

The units comes in different sizes and configurations, including a 10,000 BTU/hr heat pump attached to a water tank; an 80,000 BTU/hr combination space/domestic hot water unit; and a 140,000 BTU/hr system that can handle space heating and domestic hot water for light commercial applications. The COP is about 1.6 (2.0 in the restaurant application), said Michael Garrabrant, founder and CEO of SMTI.

Garrabrant sees the SMTI unit mainly competing against gas-fired water heaters and boilers, using half the gas with twice the efficiency. He contends that his system works better than an electric heat pump in cold climates where the heat pump’s COP suffers. “We feel we have a better path forward to reducing carbon emissions for space heating in cold climates,” he said.

The growth of renewable natural gas will help make SMTI’s system a greener alternative, noted Reed. “Methane can be made in ways that are renewable and carbon neutral,” he said.