The Hungarian capital of Budapest is planning to install an ammonia heat pump system, utilizing riverbank-filtered water and geothermal water, for a district cooling and heating project.
The use of these “free” heating and cooling sources will give the system a combined coefficient of performance (COP) in heating mode of 12.7 and a combined COP of 15.6 in cooling mode. This information was shared in a presentation by Akos Murin, Managing Engineer at QPlan in Hungary, speaking at the online Eurammon Symposium last week.
The Budapest South Gate project, where the new ammonia heat pump will be installed, covers a mixed use area, which includes residential areas, shops, a new stadium, a theatre and a number of sports and recreational facilities. The area is divided in two by a tributary to the Danube river.
According to Hungarian law (TNM Decree 7/2006 v24) 25% of the total energy for a new building must come from renewable energy sources. This means that during peak demand around 40% must come from renewable sources, a fact that is one of the main drivers behind this heat pump project, said Murin.
The ammonia heat pump solution installed for the project is set up to provide either heating or cooling. “The two are not concurrent; the heating and cooling are not required at the same time – that’s the demand in this area,” Murin explained.
The solution will consist of eight individual units, with each unit designed for 2.5MW (711TR) of cooling and 2.5MW (711TR) of heating, including the “free” cooling element obtained from the two water sources. The system is designed to provide 80°C (176°F) water for heating and 5-7°C (41-44.6°F) water for cooling. The return temperatures are 40°C (104°F) and 17°C (62.6), respectively.
The units use single-screw compressors due to their part-load efficiency. “I think they have better part-load efficiency than twin screw, especially without VFD [variable frequency drive],” Murin said. “I personally like to avoid VFD because they introduce an additional 3-5% power loss into the system, and are more complex and expensive. These compressors can go down to 10% capacity, so VFD is not really required.”
For the cooling part of the project, the riverbank-filtered water – with a relatively constant temperature of 10-12°C (50-53.6°F) – is used for direct cooling throughout the year, with additional cooling from the heat pump as needed.
The river water supplies 2,792MWh of direct cooling and 200MWh via the heat pump. The installed cooling capacity is 1.45MW (412TR).
For the heating required, the heat pump uses warm water from thermal wells. This warm water, obtained from 650m (2,133ft) deep wells, is also used for direct heating of domestic hot water, meaning that for this part, the heat pump isn’t needed. “We have a lot of thermal water, so most of the heating can be done with the thermal well water,” explained Akos Murin.
The thermal waters provide 4,300MWh of direct heating and 3,223MWh of domestic hot water production. The waters have a temperature of 55-57°C (131-134.6°F) and can be used directly for the heating through a heat exchanger. After use, the thermal water is pumped back into the soil layer it was collected from. For peak demand times, gas boilers are utilized.
The heat pump has a capacity of 2,46MW (699.5TR), and in the first phases of the project was supplying 1,670MWh.
If necessary, it will also be possible to use treated waste water as a heat source and sink for the heat pump, in a later expansion phase of the project, Murin explained. This waste water is readily available in quantities 5-10 times larger than needed, he said. “In my experience thermal wells do not always supply the quantity and quality of water they promise at the beginning,” Murin said about the potential need for waste water.
“We have a lot of thermal water, so most of the heating can be done with the thermal well water,”Akos Murin.
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