Testing and Demonstration of a River-Water-Heat-Pump With Partial Freezing and District Heating Feed-In:

Seasonal Testing of the AQVA-HEAT-System

Abstract

Many cities are located near bodies of water. Lakes, rivers, and seas often represent powerful, efficient, and cost-effective heat sources for heat pumps, even for systems with high output. However, existing hydrothermal heat pump systems cannot be operated at low water temperatures because of the risk of evaporator freezing. This restricts their use precisely when heating demand is at its highest.

The triple point process is implemented in a vacuum ice slurry plant. As water freezes, it releases energy that drives the evaporation of nearby water molecules. The water vapour is compressed by a turbo compressor to a higher temperature level where it can be used in the downstream stage of the heat pump cascade. Heat extraction in the evaporator produces a pumpable water–ice mixture (ice slurry), which is returned to the water body. This allows the water body to serve as a powerful and efficient heat source even at temperatures close to freezing. The water body can therefore be used as a heat source for the heat pump all year round. The installation of an additional heat generator is not necessary. At the same time, the amount of water circulating between the water body and the heat pump is significantly reduced.

The AQVA HEAT project combines a 350 kW vacuum ice generator with a two-stage ammonia heat pump. River water from the Mandau serves as the heat source. 500 kW of heat at 92 °C is fed into the district heating network of the city of Zittau.