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Smart control of PV and exhaust air heat pump systems in single-family buildings
Uppsala University.ORCID iD: 0000-0003-0402-8433
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Recently, decentralized household photovoltaic (PV) systems have become more affordable and there is a tendency to decrease subsidies for the PV excess electricity fed into the grid. Therefore, there is growing interest in methods to increase the self-consumption (SC), which is the part of the electricity produced by PV and directly consumed on buildings. It has been found that battery storage is an effective way to achieve this. When there is a heat pump system installed, thermal energy storage using the thermal mass of the building or hot water tanks, can also be used to increase the household self-sufficiency and minimize the final energy use. The main aim of this thesis is to develop operational control strategies for the heating system of a single-family house with an exhaust air heat pump, a photovoltaic system and energy storage. In order to accomplish this a detailed system model was developed in TRNSYS 17, which includes a six-zone building model and the heat pump control. Moreover, these control strategies include short-term weather and price forecast services.  Another objective is to evaluate the impact on the benefit of these control strategies in terms of energy use and economic performance for a wide range of boundary conditions (country/climate, electricity prices, occupancy and appliance loads).  Results show that the control using a forecast of dynamic electricity price in most locations leads to greater final energy savings than those due to the control using thermal storage for excess PV production. The exception is Sweden, where the result is the opposite. Moreover, the addition of battery storage leads to greater decreases in final energy than the use of the thermal storage (TH mode), which is limited to the thermal mass of the building and small hot water tank of the compact heat pump. As far as the impact of the advanced control (combined use of TH and PRICE) on cost savings is concerned, savings (up to 175 €) are possible in Spain and in Germany. The design of the TH and PRICE mode show low computational complexity that can be easily implemented in existing heat pump controllers. Additionally, the PRICE mode should have no capital and running cost for the end user while the TH mode might require an external electricity meter. Another yet implication with the TH mode is the need to activate the room thermostatic valve.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2019. , p. 50
Keywords [en]
photovoltaics, heat pump, forecast services, thermal storage, electrical storage, control algorithms
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:du-32581OAI: oai:DiVA.org:du-32581DiVA, id: diva2:1427007
Opponent
Supervisors
Funder
Knowledge Foundation, 20160171Available from: 2019-12-17 Created: 2020-04-28 Last updated: 2020-04-29Bibliographically approved
List of papers
1. Control algorithms for PV and Heat Pump system using thermal and electrical storage
Open this publication in new window or tab >>Control algorithms for PV and Heat Pump system using thermal and electrical storage
2016 (English)In: Proceedings of the 11th ISES EuroSun 2016 International Conference on Solar Energy for Buildings and Industry, Palma de Mallorca, Spain, 11-14 October 2016, International Solar Energy Society , 2016Conference paper, Published paper (Other academic)
Abstract [en]

In this study a detailed model of a single-family house with an exhaust air heat pump and photovoltaic system is developed in the simulation software TRNSYS. The model is used to evaluate three control algorithms using thermal and electrical storage in terms of final energy, solar fraction, self-consumption and seasonal performance factor. The algorithms are tested and compared with respect to energetic improvement for 1) use of the heat pump plus storage tank for domestic hot water and space heating, 2) use of the electrical storage in batteries and 3) use of both electrical and thermal storage. Results show the highest increase of self-consumption to 50.5%, solar fraction to 40.6% and final energy decrease to 6923 kWh by implementing the third algorithm in a system with 9.36 kW PV capacity and battery storage of 10.8 kWh. The use of electrical energy storage has higher positive impact compared to the thermal storage with the settings and component sizes used. The combined use of thermal storage and batteries leads to final energy savings that are nearly the same as the combined savings of thermal storage and batteries separately, showing that they are mostly independent of one another for the settings of this study.

Place, publisher, year, edition, pages
International Solar Energy Society, 2016
Keywords
Photovoltaics, heap pump, thermal storage, electrical storage, solar fraction, self-consumption
National Category
Energy Engineering
Research subject
Energy, Forests and Built Environments
Identifiers
urn:nbn:se:du-25960 (URN)10.18086/eurosun.2016.08.13 (DOI)000426895100130 ()
Conference
EuroSun 2016 International Conference on Solar Energy for Buildings and Industry
Available from: 2017-08-16 Created: 2017-09-05 Last updated: 2020-04-28Bibliographically approved
2. Techno-economic analysis of control algorithms for an exhaust air heat pump system for detached houses coupled to a photovoltaic system
Open this publication in new window or tab >>Techno-economic analysis of control algorithms for an exhaust air heat pump system for detached houses coupled to a photovoltaic system
2019 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 249, p. 355-367Article in journal (Refereed) Published
Abstract [en]

Operational control strategies for the heating system and “smart” utilization of energy storage were developed and analyzed in a simulation based case study of a single-family house with exhaust air heat pump and photovoltaic system. Rule based control algorithms that can easily be implemented into modern heat pump controllers were developed with the aim to minimize final energy and maximize self-consumption by the use of the thermal storage of the building, the hot water tank and electrical storage. Short-term weather and electricity price forecasts are used in some of the algorithms. Heat supply from an exhaust air heat pump is limited by the ventilation flow rate fixed by building codes, and compact systems employ an electric heater as backup for both space heating and hot water. This heater plays an important role in the energy balance of the system. A typical system designed for new detached houses in Sweden was chosen for the study. This system, together with an independent photovoltaic system, was used as a base case and all results are compared to those for this base case system. TRNSYS 17 was used to model the building and system as well as the control algorithms, and special care was taken to model the use of the backup electric heater as this impacts significantly on final energy use. Results show that the developed algorithms can reduce final energy by 5–31% and the annual net cost for the end user by 3–26%, with the larger values being for systems with a battery storage. Moreover, the annual use of the backup electric heater can be decreased by 13–30% using the carefully designed algorithms.

Keywords
Photovoltaics, Heat pump, Forecast services, Thermal storage, Electrical storage, Control algorithms
National Category
Energy Systems
Research subject
Energy and Built Environments
Identifiers
urn:nbn:se:du-30003 (URN)10.1016/j.apenergy.2019.04.080 (DOI)000472692200029 ()2-s2.0-85065118179 (Scopus ID)
Available from: 2019-05-09 Created: 2019-05-09 Last updated: 2020-04-28Bibliographically approved
3. Impact of Boundary Conditions on the Performance Enhancement of Advanced Control Strategies for a Residential Building with a Heat Pump and PV System with Energy Storage
Open this publication in new window or tab >>Impact of Boundary Conditions on the Performance Enhancement of Advanced Control Strategies for a Residential Building with a Heat Pump and PV System with Energy Storage
2020 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 13, no 6Article in journal (Refereed) Published
Abstract [en]

Operational control strategies for the heating system of a single-family house with exhaust air heat pump and photovoltaic system and “smart” utilization of energy storage have been developed and evaluated in a simulation study. The main aim and novelty of this study is to evaluate the impact on the benefit of these advanced control strategies in terms of performance (energy use and economic) for a wide range of boundary conditions (country/climate, occupancy and appliance loads). Short-term weather data and historic price data for the same year as well as stochastic occupancy profiles that include the domestic hot water load are used as boundary for a parametric simulation study for the system modeled in detail in TRNSYS 17. Results show that the control using a forecast of dynamic electricity price leads to greater final energy savings than those due to the control using thermal storage for excess PV production in all of the examined locations except Sweden. The impact on self-consumption using thermal storage of heat produced by the heat pump using excess PV production is found to decrease linearly with increasing household electricity for all locations. A reduction in final energy of up to 842 kWh year−1 can be achieved just by the use of these algorithms. The net energy cost for the end-user follows the same trend as for final energy and can result in cost savings up to 175 € year−1 in Germany and Spain due to the use of the advanced control.

Keywords
photovoltaics, heat pump, thermal storage, electrical storage, control algorithms, forecast services, self-consumption, final energy
National Category
Energy Systems
Research subject
Energy and Built Environments
Identifiers
urn:nbn:se:du-32340 (URN)10.3390/en13061413 (DOI)2-s2.0-85082712162 (Scopus ID)
Available from: 2020-03-19 Created: 2020-03-19 Last updated: 2020-04-28

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Psimopoulos, Emmanouil

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