Reducing greenhouse gas emissions from the heating supplied to a city in Sweden required a sea change in thinking by a major power company, using GEA’s energy-efficient heat pumps.
After testing the water, a sewage plant was considered the best source for heating homes in an innovative approach for turning waste into usable energy.
Under the banner of ‘Clean 2025’,energy companyE.ON Sweden has been working towards ambitious climate protection targets first set in 2017. It intends to provide to its customers 100 per cent recycled or renewable energy by 2025.
As the ideal option the company decided that GEA’s ammonia heat pumps were ideal for district heating in southern Sweden, along with biomass and other renewable technologies to mitigate greenhouse gas emissions from heating.
With a heating capacity of 10MW each, four GEA heat pumps were installed next to a sewage treatment plant and waste incinerator in the harbour area of the city of Malmö, where they are now providing eight per cent of the total energy to approximately 100,000 homes, the yearly equivalent usage of 10,000 households, contributing to around 50,000 tonnes of CO2 savings per year.
Heat pumps are fast becoming the technology of choice for renewable district and domestic heating to meet increasingly stringent environmental regulations and reduce CO2 emissions and operating costs.
The heat pumps operating in Malmö use waste heat from sewage and waste incineration plants. E.ON decided to use recycled sewage water for the system due to the higher temperatures emitted by the sewage plant (14˚C) – making the water warmer than the seawater near the city which was too cold for efficient use.
Withdrawing 30MW of heat from the sewage water, the energy harvested is upgraded to useful heat for the district heating network, with the integrated heat pumps working in conjunction with the nearby waste incinerator plant. The heat pump is designed for delivering up to 80˚C but will rarely be required to deliver temperatures above 71˚C.
As fluorinated gases are phased out to meet with European F-Gas regulation, also designed to reduce greenhouse gas emissions, natural refrigerants are becoming more popular - especially ammonia, a climate-friendly refrigerant which is readily available, inexpensive and has no impact on global warming or ozone depletion.
Whilst this is not the first time that heat pumps have been used in Sweden, the Malmo project is the first in the country to specify ammonia. E.ON opted for ammonia rather than chemical-based refrigerants due to the EU F-Gas regulation, which aims to phase down HFCs by 79 per cent by 2030.
Mats Egard, project manager at E.ON Värme Sverige AB, said it would have been cheaper to install an R134a heat pump, but the goal is to become 100 per cent renewable. “We’re going to supply district heating energy that is either recycled or renewable by 2025,” he said.
Kenneth Hoffmann, GEA’s product manager heat pumps, said ammonia is the way forward into a sustainable future.
Hoffmann summed up the science behind the cost-effective heat pump technology.
“The four heat pumps work in parallel to deliver the promised temperatures. Each has a coefficient of performance (COP) above 3.5, so for each 1kWh of electricity used by the heat pump, 3.5 kWh of heat is produced for the city,” he said.
A heat pump system requires comprehensiveanalysis of the requested temperatures and assessment of the right process parameters. Every degree counts with a heat pump and the more accurate the initial design, the more energy can be saved. Instead of focusing on small pipes with large temperature difference to keep the initial cost down, a heat pump investment is based on continuous savings every day.
E.ON Malmö-project at a glance:
GEA solution: Customized heat pump system (4 heat pumps)
Heating capacity: 40 MW
Heat source: Sewage water (10°C -20°C)
Heat sink: district heating water (42°C -63°C)
Coefficient of performance (COP): >3.5 (yearly average)
Compressor type: GEA Grasso Screw compressors
Natural refrigerant: Ammonia