All Electric in Cold Climate- Combining High-Performance Energy Recovery and Heat Pumps

Rudolf Zaengerle, Konvekta USA Inc.

Recent changes in building codes seem to push toward all-electric buildings even in cold climates. With HVAC in winter being the largest consumer of fossil fuels, replacing these with electricity only will reduce carbon footprint if the building is equipped with a high-performance energy recovery system and the balance of heat input is provided by heat pumps.

Ground-source heat pumps seem energetically a preferred solution, but capital cost is very high and in a dense setting may not be feasible at all. Utilizing the remaining heat in the exhaust air (after energy recovery) is a solution which will lower the electric input significantly as compared to outside air heat source for the heat pump. This concept consists of two heat recovery coil banks in the exhaust air: the first a "normal" energy recovery coil tied into the high-efficiency energy recovery system, the second a coil bank that will decrease the exhaust air temperature to a few degrees above outside air temperature, serving as the heat source for the heat pump. Because the temperature level of this heat source is always significantly higher than outside air, the COP of the heat pump is also significantly higher and the electric consumption thus significantly lower. As a side benefit, this second coil bank in the exhaust can be utilized for heat rejection of the chillers in summer, reducing or eliminating the need of cooling towers.

Learning Objectives

  • Understand the underlying thermodynamics of an high-performance energy recovery system;
  • Understand the benefit of using exhaust air as heat source for a heat pump vs. using outside air in winter (cold climate) operation;
  • Understand the benefit of a combined run-around/wrap-around energy recovery system for summer high-performance; and
  • Evaluate the advantage of indirect evaporative cooling for heat rejection in summer operation.


Rudolf Zaengerle is the President of Konvekta's US operation, a subsidiary of the Swiss based Konvekta AG. He holds a Master of Mechanical Engineering degree and a PhD in Business Administration, both from the Swiss Federal Institute of Technology, Zurich. He has also studied at Harvard Business School. He was an Assistant Professor at the Swiss Federal Institute of Technology's Energy Sustainability Institute before relocating to the USA over 25 years ago to manage Swiss technology businesses.


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