Technical and social challenges in the grid-friendly and economic optimization of heat pump systems

Heat pumps are a key technology in the heating transition. As electrical power consumers that supply heat for households and industry, for example, they can also make an important contribution to sector coupling. The economic optimisation of heat pumps is the most important factor for market success. However, this is relatively complex, as the COP is highly dependent on ambient conditions.

Surpluses in electrycity generation due to high renewable production are becoming more common, which limits their usability. Heat pumps can utilise these surpluses to benefit the system and the grid thereby operating more economically over their life cycle.

Time-dependent electricity tariffs are currently rarely used, and particularly in the over-50 kW range, little research has been done into the effects of dynamic electricity prices and how heat pumps can be optimised to respond to them.

Fluctuating electricity prices mean that heat pumps with an optimised SCOP are not automatically the most economically solution. Relevant influencing factors include:

• Dimensioning
• Control strategy
• Heat source
• Technical restrictions (on-off times, cycling, ramps)
• Interaction: heat demand profile - generation profile - storage masses
• Usage requirements (comfort, et cetera)
• Tariff model

The main project objective is to analyse from various perspectives such as

• GHG emissions,
• energy generation from renewables in the electricity system (energy system model),
• load shifting potential,
• storage requirements in the electricity system (energy system model or comparison with pumped storage and batteries),
• annual performance factor
• longevity of the heat pump system and
• user requirements (comfort, process reliability, et cetera)

to investigate the extent to which the economically optimised dimensioning of heat pump systems over the life cycle is desirable in the case of time-varying electricity prices in the context of spot and balancing energy markets.

To this end, generic case studies will be selected to cover a broad spectrum within the following framework:

• Required heat output over 50 kW
• Commercial operators
• Three types of buildings or uses: for example large residential complexes, non-residential buildings (commercial, schools, museums, hotels), industrial process heat
• Various heat sources (air, geothermal, waste heat), distribution systems (air, radiators, underfloor heating, component activation) and, where applicable, storage systems (water and ground source heat pumps); up to eight relevant combinations will be selected with stakeholders and then simulated and optimised.

The following questions, among others, need to be clarified:

• Which heat pump design is economically optimal depending on the electricity tariff model?
• Which tariff models can facilitate participation in short-term markets (control reserve, intraday trading, balancing energy minimisation)?
• Which control strategy should be chosen to make the best use of time-dependent electricity tariffs?
• How much efficiency is lost with an operating mode that is economically optimised for time-dependent electricity tariffs?

With regard to energy markets, at least three use cases will be developed and translated into a control strategy. The heat pump system of each case study will be optimised for each use case.

Furthermore, legal, financial and information-related deficits will be analysed in interviews with market players and an analysis of existing findings, and solutions will be developed.

This project will lay the foundation for the implementation of a system-oriented heat pump approach, including monitoring, in real projects.

Update of the project

Technical and social challenges in the grid-friendly and economic optimisation of heat pump systems

The project investigates the extent to which the economically optimised dimensioning of heat pump systems with time-variable electricity prices is desirable from an ecological and operational point of view as well as with regard to the electricity grid over the life cycle.

As part of the WPOpt4Grid project, specific case studies were selected and analysed in detail in order to investigate the flexible and grid-friendly use of large heat pumps under realistic technical boundary conditions.

Selected case studies and key technical data

For WPOpt4Grid, seven case studies were defined, covering a broad range of building types, system capacities and technical requirements. Both generic model buildings and existing buildings are examined.

Case studies at a glance

Case study	Building type	Heat pump technology applied	Heat pump capacity (th)	Heat delivery system (temperature level)	Special characteristics
FS01	Multi-storey residential building (generic)	Air-water HP or brine/geothermal HP	~ 60 kW	Low-temperature radiators (45/38 °C)	Sensitivity analysis (HP size, storage, Room temperature)
FS02	production site/non-residential building	well HP, air HP, booster HP, high temperature HP	> 300 kW	process HP, ventilation heating coil (up to > 60 °C)	process heat, several temperature levels
FS03	multi-storey residential building	brine water HP + booster HP	~ 130-170 kW	FBH/BTA (35-28 °C), High-temperature sub-areas (65-50 °C)	combination of space heating & special uses
FS04	educational facility	brine water heat pump + domestic hot water heat pump (+ chiller)	~ 280 kW (+ cooling)	radiators & ventilation (40-45 °C)	additional cooling
FS05	office building	well water heat pump	~ 50 kW	Floor heating (45/35 °C)	Distinct daily load profiles
FS06	Public building (Generic)	Geothermal HP	~ 110 kW	Floor heating (40/30 °C)	Type model for municipal buildings
FS07	Sales outlet (Generic)	Water well HP	~ 75-110 kW	Fan coils (55/45 °C)	High simultaneity, long opening hours

Analysed use cases

Four central use cases are analysed in WPOpt4Grid for the structured evaluation of different operating strategies. They differ in terms of tariff model, control logic and flexibility options:

Use Case UC00 - Fixed electricity tariff (reference):

The reference case depicts a conventional heat pump operation with a fixed electricity tariff and constant grid charge. The heat pump operates on the basis of the heating curve without targeted time optimisation. UC00 serves as a basis for comparison for all other use cases.

Use Case UC01 - Optimisation of self-consumption of photovoltaic electricity:

In this use case, the operation of the heat pump is adapted to the local PV generation. Surplus PV electricity is used to charge thermal storage units or to preheat the building mass. The aim is to maximise self-consumption while ensuring stable system operation.

Use Case UC02 - Dynamic electricity price:

A dynamic electricity tariff with hourly varying prices is assumed here. The heat pump reacts to price signals and shifts heat generation to hours with low electricity prices. Cost reductions, load shifting potential and effects on efficiency and comfort are analysed.

Use Case UC03 - Interruptible tariff:

This use case analyses time-limited off-peak periods for heat pump operation, for example during critical grid load situations. The heat supply is ensured during off-peak periods by means of targeted pre- and post-charging of the thermal storage tanks. Comfort, operating costs and system flexibility are assessed.

Objective of the project update

By analysing these case studies and use cases, WPOpt4Grid provides concrete, practical findings on the technical and operational behaviour of large heat pumps under variable market conditions. The results form a sound basis for

• the further development of dynamic electricity tariffs,
• the design of grid-friendly operating strategies
• as well as energy and climate policy decisions in the heat and electricity sector.

Client / Funding organisation	FFG on behalf of BMIMI and BMWET
Project management	Franziska Zimmer
Project team	Petra Lackner Konstantin Kulterer Franz Zach
Project partners	AIT Austrian Institute of Technology GmbH
Project duration	May 2025 to April 2026