Optimization of large heat pumps using ambient air

Svenn Ole Kjøller Hansen

Your Contact

Contact me

Indtast venligst et validt navn
Or your phone number
Thank you for your message
Vi beklager

På grund af en teknisk fejl kan din henvendelse desværre ikke modtages i øjeblikket. Du er velkommen til at skrive en mail til Send e-mail eller ringe til +45 72 20 12 67.

Anlæg fra Tønder Fjernvarme

Optimization of large heat pumps using ambient air

Project start October 2019. The project is completed.

Purpose of project

A significant expansion of the capacity of electrically powered heat pumps in the district heating supply is a central strategic key point in the struggle to phase out fossil fuels in the heating of buildings, both at national level and for the local Danish district heating companies around the country.

The high efficiency (COP) of the heat pumps can reduce the energy consumption for heating of buildings (the district heating water is used for both heating and hot water), and at the same time the heat pump is adjustable which means that the possibility of phasing in more wind power and other renewable energy is increased.

Since the electricity production subsidy for district heating plants in Denmark is no longer available as per January 1, 2019, large heat pumps for district heating are even more relevant, since the district heating plants are experiencing a pressure on the district heating price, which challenges the competitiveness.

A heat pump using ambient air as a heat source is a flexible and simple solution, since ambient air is available everywhere, and it is less expensive to install compared to other heat sources.

However, using air as a heat source presents some challenges in terms of frosting of the evaporators and noise (as well as cooled air in the surrounding areas). Problems regarding frosting and defrosting of the evaporator pose a risk in terms of operational failures and have a significant influence on the energy efficiency of the heat pump.

The purpose of the project is to optimize and develop the evaporator design and control of heat pumps in relation to frosting, defrosting and noise (and cooled air).


  • To develop and demonstrate new innovative solutions that both address the challenges that have been identified on the market regarding large heat pumps using ambient air and to ensure the dissemination of this type of heat pump to smaller district heating plants, where other heat sources are either not available or cannot be used.
  • To develop standardized, economically optimized stand-alone heat pumps. The project will optimize and develop the evaporator design and control of heat pumps in relation to frosting and defrosting (and cooled air).
  • To optimize the overall system design of the heat pump to ensure the lowest possible inconveniences of noise and to conceptualise the design of the heat pump towards more standardized and compact installations that simplify the installation for the district heating plants.
  • To increase the number of ambient air heat pumps in the district heating network and speed up roll-out. First in Denmark and later in many other areas of Europe, where they also experience these problems.


The project is divided into the following phases:

  • Knowledge gathering and analysis of previous studies
  • Optimization
  • Test in laboratory and on-site
  • Demonstration at district heating plant
  • Dissemination of knowledge.



  • Innoterm – Palle Lemminger (project manager)
  • Danish Technological Institute
  • DTU Mechanical Engineering
  • Fincoil Lu-Ve Oy
  • Fjernvarme Fyn
  • Planenergi
  • Brædstrup Fjernvarme.



The project is funded by EUDP.