Co-production with a gas engine driven heat pump in Tønder, Denmark

This case study is part of a project catalogue produced by ReUseHeat to inspire how to utilize excess heat from urban sources for heating and cooling purposes. The catalogue contains 25 existing or planned projects, 12 of which are Danish and 13 from other European countries.

Description

A gas engine-driven heat pump unit in Tønder is expected to begin co-producing cooling and district heating in November 2017. Heat is supplied to the local district heating company, Tønder Fjernvarmeselskab, and cooling is supplied to the local company SAPA Extrusion*. Previously, heat production in Tønder was solely based on natural gas boilers.

Depending on economic conditions, the heat pump unit consists of two parallel mechanical heat pumps driven by natural gas engines or an electrically powered engine. Depending on the cooling needs at SAPA, the heat pumps can be driven by either ambient air or cooling water from SAPA. Using ambient air with a temperature of 7 degrees Celsius, the thermal capacity of the gas engine is 4.3 MW, and for the electric motor, it is 3.3 MW. Using more than one heat source makes the heat pump investment more robust, in the case of SAPA withdrawing their cooling needs. However, the two heat sources enable the heat pumps to operate with a larger heat pump capacity compared to the sole utilization of excess heat from SAPA.

Tønder Fjernvarmeselskab has approximately 2700 consumers connected to the district heating network, and the annual heat production is currently 92,000 MWh. Using ambient air, the annual heat production from the heat pumps is expected to be at least 36,100 MWh, corresponding to nearly 40% of the total heat deliverance. If cooling water from SAPA is to be used, the potential is larger, as the efficiency of the heat pumps would increase. Water from SAPA can be delivered at approximately 20 degrees Celsius, which is cooled to a temperature between 6 and 10 degrees Celsius. When using the gas engine, the heat pumps are natural gas boilers with average annual efficiencies above 200%.

In addition to the heat pumps, an accumulation tank has been established to store cold water, ensuring the supply for SAPA. The heat produced cannot be stored, meaning that the heat pumps must deliver supply temperatures around 70 degrees Celsius directly to the district heating network. Nonetheless, the heat pumps decrease the natural gas used by the district heating company. Simulations predict annual savings between € 725,000 and € 950,000, depending on the natural gas price. If the gas price increases, the savings increase as well.

While SKAT, the Danish Customs and Tax Administration, which is Denmark’s tax authority, has stated that the heat is not excess heat, co-production is still used to exploit an industrial heat source, thus resembling the reuse of heat from an urban source.

*SAPA Extrusion is today Hydro Extrusion

Tønder, Denmark

ReUseHeat

Finished in 2017

IVL Swedish Environmental Research Institute

Names of stakeholders

Tønder Fjernvarmeselskab

External links:

Tønder Fjernvarmeselskab A.m.b.a., Hydro Extrusion (former SAPA Extrusion), The Danish Customs and Tax Administration (SKAT), Handbook – 25 cases of urban waste heat recovery