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Auxiliary energy

Electrical energy used by heating, cooling, ventilation, and/or domestic hot water installations to support energy conversion to meet energy requirements.

NOTE 1: This includes the energy for fans, pumps, electronics, etc. The electric energy supplied to the ventilation system for air transport and heat recovery is not considered auxiliary energy but the ventilation energy requirement.

NOTE 2: In EN ISO 9488 [15], the energy requirement for pumps and valves is called “parasitic energy”.

NOTE 3: Within the present standard, the drive energy for electrically-operated heat pumps within the system threshold of the COP in accordance with EN 14511 and for an electrical auxiliary heater is not termed parasitic energy but merely as the additional supply of electrical energy not covered by the COP. DIN EN 15316-4-2:2008-09

Auxiliary heater

An additional heater used for generating heat when the heat pump’s power is insufficient. Ensures that the target temperature is reached. The energy supplied by the auxiliary heater must be reduced to a minimum, e.g. less than 5% of the total energy generated by the heat pump if the auxiliary heater’s energy source is not renewable. DIN EN 15450:2007-12

Bivalence point

The lowest standard outside air temperature at which the heat pump output power and the heat requirement (heating load) of the building are equal.

NOTE: A second heat generator is used at lower outside air temperatures to meet part or all of the building’s heat requirement.

Bivalence temperature

With outdoor temperatures lower than the bivalence point, additional heating takes over partly or at all. The heat pump covers the heat demand only for temperatures above the bivalence points. Therefore, the bivalence point is used for system design. Usually, it is about -5°C. There is no such temperature in monovalent operation.


A heat transfer medium with a freezing point lower than that of water. DIN EN 14511-1:2008-02, e.g. ethylene glycol and water (liquid to -13 °C)

Coefficient of performance

The ratio of usable heat flow produced under specific operating conditions in relation to the electrical energy used for driving the compressor and the auxiliary drives in accordance with DIN EN 14511/DIN EN 255-3. VDI 4650-1 draft 2008-09

Cold water temperature

Domestic hot water setting, dependent on season; DIN EN 15450:2007-12

Combination tank

Tank used both for hot water supply for domestic use and indoor heating. DIN EN 12977-3:2008-11


Key power-consuming part of a heat pump

Depth-dependent temperature increase

Typically 3 K per 100 m

Design temperature

Temperature stipulated by the prevailing climatic zone in accordance with DIN EN 12831 supplementary sheet 1 table 1a. DIN EN 12831

Drilling depth

DIN EN 15450:2007-12

Domestic hot water requirement

DIN EN 15450:2007-12

Double U-tube

Property of the geothermal probe

EN 15316-4-2

Heating systems in buildings – method for calculation of system energy requirements and system efficiencies – part 4-2: heat generation for indoor heating, heat pump systems.

Extraction factor, annual specific

In addition to the specific extraction power, the extraction factor must be considered for longer periods and should be between 50 and 70 kWh/(m2∙ a) for geothermal heat collectors and between 100 and 150 kWh/(m ∙ a) for geothermal heat probes. VDI 4640-2:2001-09

Extraction power [W / m²]

i.e. heat pump vaporization power. VDI 4640-2:2001-09

Ground temperature, undisturbed

DIN EN 15450:2007-12

Geothermal energy, near-surface

to 400 m depth

Heating energy requirement

Calculated amount of energy which must be supplied to a building’s heating system in order to be able to meet heating requirements. DIN V 4108-6:2003-06

Heating limit temperature

Base temperature, outside air temperature, above which a building at a set indoor air temperature need no longer be heated. DIN V 4108-6:2003-06

Heating load Ф~HL~ [kW]

The heating load is the power that a heating system must provide, to maintain the indoor temperature at the specified standard outdoor temperature in a building. DIN EN 15450:2007-12, VDI 4640-2:2001-09

Heating output

The heating output is calculated from the heating load multiplied by the operating hours. The operating hours of the system depend on the building and thus on the heated useable area, the indoor temperature, the heating limit temperature, and the standard outdoor temperature.

Heating requirement

Computed heat input via a heating system required to maintain a specific average indoor temperature in a building or a zone within a building. This value is also known as the net heating energy requirement. DIN V 4108-6:2003-06

Heat power

In accordance with DIN EN 12828:2003, 4.2.2: ΦSU = fHL ⋅Φ HL + fDHW ⋅Φ DHW + fAS ⋅Φ AS The heat power of the heat pump can be maintained at a low value by avoiding additional heating loads caused by periodic heating (e.g. by preventing nighttime reductions). DIN EN 15450:2007-12

Heat pump

Assembly or assemblies enclosed in a housing for supplying heat and ready for connection. The device contains an electrically-operated cooling unit for the heat supply. It can also be equipped for cooling, circulating, purifying, and humidifying the air. Cooling operation is effected by reversing the cooling loop. DIN EN 14511-1:2008-02

Heat pump systems, small

up to 30 kW. DIN EN 15450:2007-12

Heat source

Amounts of heat with temperatures above the indoor temperature which are supplied to the building zone or arise within the building zone. Not included are regulated heat inputs supplied via the system (heating, ventilation) to maintain the indoor temperature. DIN V 18599-1:2005-07

Heat transfer medium

Any medium (water, air, ..) used for heat transport without a change of state EXAMPLE ⎯ cooled liquid circulating in the vaporizer; ⎯ cooling agent circulating in the condenser; medium circulating in the heat exchanger for heat recovery. DIN EN 14511-1:2008-02


Heat pump. VDI 4650-1 draft 2008-09


high temperature, used in “HT heating loop”

Inside air temperature

Air temperature within the building. DIN EN 12831:2003-08

Loss, system thermal

Thermal loss of a heating, cooling, DHW heating, humidifying, dehumidifying, ventilation, or lighting installation, or another application, which does not contribute to the usable power of the system. NOTE: Thermal energy that is immediately recovered in the subsystem is not considered as a thermal loss of the system but as heat recovery and is addressed directly in the relevant system standard. DIN EN 15316-4-2:2008-09

Low temperature disconnection → see Heat pump > Control

Temperature at which the operation of the heat pump is interrupted, and the entire heat requirement is met by auxiliary heating. DIN EN 15316-4-2:2008-09


low temperature, used in “LT heating loop”

Monoenergetic operation

The heat distribution system is supplied by two heat generators, which both use the same type of energy (e.g., electricity). From an outside temperature (e.g., -5 °C) up to one which at which the heat pump can meet the heating load on its own, the auxiliary heating is switched on as required at low outside temperatures. The two heat generators work in parallel. The operating mode is suitable for all heating systems up to the maximum supply temperature of the heat pump.

Monovalent operation

Operating mode in which the heat pump is configured in such a way that it alone meets the entire heat requirement of the heating system. NOTE: the heat pump output power is here the same as the standard heating load calculated in accordance with EN 12831. DIN EN 15450:2007-12

Rated power

Capacity measured under standard rated conditions.

Outside temperature

Outside air temperature used for calculation based on meteorological measurements and analyses. DIN V 18599-1:2005-07


The pre-simulation generates the settled state following the initial operation phase. The length varies on the basis of the differing inertia of the heat sources:

Brine-water HPs: pre-simulation = 120 days.

Air-water HPs: pre-simulation = 3 days

Primary energy savings

The report shows on page [Results of the annual simulation* the primary energy savings. It is calculated by comparing the heat pump system with a natural gas boiler system:

$\eta_{Boiler}$= 0.7 for systems without DHW; $\eta_{Boiler}$= 0.9 for systems with heating support & DHW
$\eta_{Power station}$: 0.42

source: http://de.wikipedia.org/wiki/Stromkennzeichnung

$ Primary energy savings = (E_{HP}+ E_{Collector loop})/ \eta_{Boiler} - $
$( E_{HP,compressor } + E_{Heater}+ E_{EAuxiliary power})\eta_{power station} $

$CO2_{Natural gas} = 1/(40.0e6)*2.75; mit Hu = 40MJ/kg; Natural gas ; 2.75 gCO2/gNG$

$CO2_{Natural gas} = Primary energy savings * CO2_{Natural gas}$

Primary pump

Pump incorporated in the cycle which contains the generator and the hydraulic decoupling, e.g., in the form of a heat tank in parallel construction or a hydraulic distributor. DIN EN 15316-4-2:2008-09

Seasonal performance factor SPF

Ratio of the total energy amount QHP supplied from the heat pump to the distribution system for indoor heating and/or to other connected systems (e.g., domestic hot water).

DIN EN 15450:2007-12; DIN EN 15316-4-2:2008-09

Seasonal performance factor ß

Ratio of usable heat produced annually in relation to the electrical energy used for driving the compressor and the auxiliary drives. VDI 4650-1 draft 2008-09

Solar fraction (α)

Dimensionless energy component that a heat pump contributes to meeting the annual space heating and hot water heating requirement of a building or area. VDI 4650-1 draft 2008-09


Difference between T~supply~ and  T~return~.


Not standardized but common term for the seasonal performance factor (ß)

Standard outside temperature

Outside air temperature used for calculating standard heat loss. DIN EN 12831:2003-08

Standard indoor temperature

Operative room temperature in the center of the heated room (between 0.6 m and 1.6 m height), used for calculating standard heat losses. DIN EN 12831:2003-08

System technology losses

Losses (heat loss, cold loss) in the technical process steps between the usable energy requirement and the final energy requirement, i.e., during transfer, distribution, storage, and generation. Losses in the system technology, as long as they occur in the conditioned space, count as heat sources or heat sinks. DIN V 18599-1:2005-07

Useable energy requirement for domestic hot water

Computed energy requirement resulting from the building zone being supplied with the amount of domestic water at the necessary supply temperature defined in the use profile. DIN V 18599-1:2005-07

Useable heating requirement

The useable heating requirement = space heating requirement Computed heating requirement necessary to maintain the defined thermal indoor conditions within a building zone during the heating period. DIN V 18599-1:2005-07