Key Words and Abbreviations
Key Definition
Heat Sources

Key Words and Abbreviations:

  • Apartment/Dwelling/Flat
    • Used interchangeably. Living unit in a multi-family building. Can include several rooms.
  • COP = Coefficient of Performance
    • Describes the efficiency factor of the heat pump. For example, a COP of 3.5 means that for every 1 Watt (W) of electric power put into the heat pump, 3.5W of heating output are produced.
  • Building(s)
    • Usually the complete multi-family builing, sometimes multiple buildings. Includes all the buildings and flats therein that are thermally supplied by the studied heat pump solution.
  • HP = Heat Pump
    • A device that absorbs energy from a heat source, multiplies it and then emits it as thermal energy to the flat (as DHW and/or SH).
  • DHW = Domestic Hot Water
    • The part of heating that aims to supply the flat with usable/potable water, for the faucet, the sink, showering et cetera.
  • SH = Space Heating
    • The part of heating that aims to achieve a warm temperature in the flat. Usually distributed by (wall-mounted) radiators, underfloor heating or fancoils.

Key Definitions

Building Size

  • Small
    • up to 10 flats in the system
  • Medium
    • 11 – 20 flats in the system
  • Large
    • 21 and more flats in the system

Insulation

  • Poor
    • Never renovated, built before 1995 (roughly above 120 kWh/m²)
  • Average
    • Partly renovated, built between 1995 and 2010 (roughly 61-120 kWh/m²)
  • Good
    • Completely renovated, newly built after 2010 (roughly up to 60 kWh/m²)

Operation Modes1

  • Monovalent Operation
    • All of the heat is supplied entirely by the heat pump. It must have a heating capacity that can cover the load of the whole system.
  • Mono-energetic Operation
    • Up to a certain determined output, the heat pump supplies the entire thermal heat. After that point is reached, a second heat generator that is also powered electrically switches in. Heat pump and additional generator then work together (parallel).
  • Bivalent-alternative Operation
    • Up to a certain determined output, the heat pump supplies the entire thermal heat. When that point is reached, the heat pump switches off and a second heat generator using a DIFFERENT final energy (e.g. fuel oil) takes over. They do not run at the same time (alternative, not parallel).
  • Bivalent-parallel Operation
    • Same as bivalent-alternative, except after the determined output and thus a higher heat demand are reached, both the heat pump and the second heat generator with a DIFFERENT final energy (e.g. fuel oil) work together (parallel).
  • Bivalent-partly-parallel Operation
    • Same as bivalent-parallel, except if the heat pump reaches one of its operation limits (e.g., minimum outdoor temperature, maximum supply temperature), the second heat generator with a DIFFERENT final energy takes over alone (first parallel, then alternative).
  1. According to and cited from: Verein Deutscher Ingenieure VDI (04/2023). VDI 4645: Heating Systems with Heat Pumps in Single and Multi-Family Houses: Planning, Construction, Operation. Beuth Verlag. Berlin ↩︎

Heat Sources

  • Air
    • Ambient Air = Whatever air is available around the heat pump system.
    • Exhaust / Waste Air = Air that, before “feeding” the heat pump, had specifically already been used elsewhere. For example gathered in a parking garage from running cars.
  • Ground
    • ATES (groundwater) = Warm water is pumped directly out of the ground to be used in the heat pump cycle.
    • BTES (boreholes)= There is a closed loop in the heat pump cycle that transfers the heat from the bedrock to the hp via an array of boreholes
  • Ice = The latent heat principle is exploited in order for an ice storage to serve as the heat source for the hp.
  • Internal Loop = A central hp (or several) is sourced by any of the named heat sources. It then heats up a water-loop inside the buildings which in turn serves as the heat source for individual hps throughout the building/system. (see more)
  • Solar = Solar Thermal units (mostly on the roof) are used to heat up the medium in the hp cycle.
  • Water = If not used in a geothermal sense (e.g. ATES), water, for example from a lake, is used to “feed” the hp.
  • Others are available. This list is not exhaustive.