New carbon-ammonia adsorption heat pump to help reduce emissions

The IOR webinar was organised in conjunction with Angeles Rivero Pacho of the University of Warwick, who presented her award-winning case study on an innovative carbon-ammonia heat pump.

“One way of helping to reduce emissions of CO₂ is to develop a more efficient heat or refrigeration technology for domestic use,” said Rivero, a project manager and research fellow at the university.

She was presenting a summary of her PhD project on ammonia gas-driven absorption heat pump technology. Her research won the IOR’s Ted Perry award in 2014 and was described as “a practical research project with a high potential for commercial exploitation”.

Rivero explained that the UK is committed to reducing CO₂ emissions from buildings by 80% by 2050 (as stated in the Carbon Plan and the Strategic Framework). “This will require promoting more efficient gas heating in the short to medium term, with gas use reduced to close to zero by 2050,” she said.

The main goal of her research project was to develop commercially feasible, heat-driven carbon-ammonia heat pump technology with a high efficiency and specific heating power using a shell and tube heat exchanger, an appropriate choice of adsorbent material and a four-bed cycle.

“The main objectives of my project were to carry out the computational modelling of a four-bed heat pump cycle; to conduct a heat transfer study of the active carbon available for the heat pump in order to identify the best sorbent sample; and to design, manufacture and test the heat pump cycle in order to validate the computational modelling”.

Product specification

The new prototype targets the UK market and aims to provide heating for a typical British 3 bedroom semi-detached house.

“We wanted to develop a heat pump that is going to be commercialised in the short term in the UK. The system has to deliver at least 7 kW for the domestic building that needs to be kept at least at 18 °C in winter. This means that with the new ammonia heat pump, the household will be able to reduce gas consumption between 30-40%.”

The evaporator will be placed outside the house and the remaining heat pump components will be placed inside. Rivero wanted to develop a very compact heat pump, similar in size to a conventional gas boiler. The prototype machine is 1x0.5x1.5m³, with an ammonia charge of 1.5 kg.

The new heating system can deliver hot water at 60 °C (with a heating coefficient of performance [COP] between 1.25 – 1.45 depending on the evaporating temperatures). The system can achieve higher temperatures, although in such cases the heating COP falls. It can also be used to deliver small amounts of hot water by adding a storage tank.

“We are going to target the retrofit market, which would represent more than 90% of annual sales in the UK,” said Rivero.

At £10,000, Rivero’s prototype technology is priced rather highly. However, if her heat pump is commercialised and mass-produced, prices are expected to fall to £2,000-5,000 depending on the scale of production.