Abstract
Gas-fired heat pumps are a potential replacement for condensing boilers, utilizing fossil-fuel resources more efficiently and reducing the amount of biogas or hydrogen required in sustainable gas grids. However, their adoption has been limited due to their large size and high capital cost, resulting in long payback times. For adsorption-based heat pumps, the major development challenge is to maximize the rate of heat transfer to the adsorbent, whilst minimizing the thermal mass. This work develops a modular finned-tube carbon–ammonia adsorption generator that incorporates the adsorbent in highly compacted 3-mm layers between aluminum fins. Manufacturing techniques that are amenable to low cost and high-volume production were developed. The module was tested using the large temperature jump (LTJ) method and achieved a time constant for adsorption and desorption of 50 s. The computational model predicted that if incorporated into two adsorption generators of 6 L volume each, they could be used to construct a gas-fired heat pump with a 10 kW heat output and a gas utilization efficiency (GUE, the ratio of useful heat output to higher calorific value of gas used) of 1.2.
Highlights
Fossil fuel boilers providing space heating and domestic hot water production are responsible for a substantial proportion of global carbon dioxide emissions [1,2]
Whilst the ultimate aim may be to replace them with electric heat pumps operating on renewable electricity, for many countries this would require substantial upgrading, or even the complete replacement, of their electrical grids [3]
Gas grids provide substantial built-in storage to cope with prolonged periods of adverse weather—similar levels of capacity and storage would be expensive and difficult to provide in a wholly renewable manner, in an electrical grid
Summary
Whilst the ultimate aim may be to replace them with electric heat pumps operating on renewable electricity, for many countries this would require substantial upgrading, or even the complete replacement, of their electrical grids [3]. Gas-fired heat pumps offer the possibility to more efficiently utilize fossil fuel resources and reduce carbon dioxide emissions in the meantime. They may be made partially or wholly renewable by the introduction of hydrogen or biogas into the gas grid. Gas grids provide substantial built-in storage to cope with prolonged periods of adverse weather—similar levels of capacity and storage would be expensive and difficult to provide in a wholly renewable manner, in an electrical grid
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