Gas Grids Can Decarbonize through End-Use Technologies

Utilities are challenged to provide cold weather heating capacity while meeting decarbonization goals. End-use electrification has been promoted as a solution, but a key question remains around how to cost-effectively meet heating demand without the use of fossil fuels. Demand from electric heating end uses can increase peak load at times when gas-fired electricity generation may be used to meet marginal demand, contributing to emissions increases. Although hydrogen, renewable natural gas (RNG), and power-to-gas gain traction in gas utilities’ efforts to decarbonize, long-term emissions reductions will benefit from end-use demand for these fuels in the form of heating technologies that are more efficient than electric systems but cleaner than traditional gas. 

Gas absorption heat pump (GAHP) technology is unproven in mass market conditions and may not outperform electrified heating under many circumstances. However, this technology is worth a look for gas utilities and equipment manufacturers. A diversified set of decarbonization solutions for gas utilities is valuable in the short term, and in the long term, may also provide a demand source from the decarbonized fuel products in development. 

A New Look at an Old Technology

Such technologies already exist but need further R&D as well as commercialization to reach a mass market. A key example is the GAHP, which can function at high efficiency under cold ambient conditions, according to industry and academic studies. Both legacy and startup HVAC companies are developing this technology for mass market adoption. Patented in the mid-1800s, the gas absorption cycle was a dominant cooling system through World War II, after which vapor compression gradually took over. Both cycles are also capable of heating, but GAHPs can do so more efficiently under certain conditions in cold climates. According to studies performed by the Gas Technology Institute (GTI), GAHPs have received ratings as high as 140% annualized fuel utilization efficiency, the U.S. Department of Energy metric for residential furnaces and boilers. At this efficiency level in cold conditions, there may be many regions where GAHPs outperform electric heat pumps on an energy equivalent basis. 

This possible advantage gets around the price ratio between electricity and gas, which usually favors the latter as a source of heat. In another recent study, GTI evaluated a GAHP residential furnace and water heater replacement application (combined, or combi) alongside other existing building heat technologies using hourly weather data and actual heat pump performance curves for a Chicago single-family residence. Assuming a US national gas price range from $0.76/therm-$1.14/therm, and electricity at $0.13/kWh-$0.17/kWh, the GAHP’s annual operating costs were significantly lower than standard electric equipment and in many cases electric heat pumps.

Figure: Comparing Annual Operating Costs for GAHPs, Baseline Electric, and Electric Heat Pumps in US Urban Markets
  

(Source: Gas Technology Institute, Stone Mountain Technologies and Purdue University)

Cost and Carbon Emissions Concerns

Several forms of thermally-driven heat pumps (including GAHPs) are on the market or being commercialized by vendors such as Stone Mountain Technologies, ThermoLift, Homy Building Solutions, Robur, and Yanmar Energy Systems. These vendors are leveraging cost and performance improvements to create economics that are expected to eventually overcome traditionally high upfront purchasing costs. Cheaper and more efficient GAHPs could eventually challenge traditional gas heating appliances’ residential market position in cold weather regions as well as reduce the costs of electric grid infrastructure upgrades needed to service cold weather heating loads. As long-term supply-side plans in gas grid retrofitting develop in RNG, hydrogen production, and power-to-gas, new end-use demand will likely be a beneficial part of the equation.