Hybrid heat pump (HHP) represents a heating system (HS) that simultaneously utilises two or more energy sources. The key novelty is the integration of an optimised control strategy, effectively maximising the efficiency of both the heat pump and gas boiler segments. In this study, a HHP system that consists of an air-source heat pump (ASHP) and a condensing-type gas boiler (GB) for a two-story single-family house was calculated and validated. The results from three different calculation methods were obtained: the heat pump manufacturer’s calculator, the simulator programme, and the calculations based on real measured data. Two operation modes were tested: economic mode, where the cheapest energy resource becomes the priority, and ecological mode, where the system operates using the energy resource with lowest CO₂ emissions. When comparing consumed energy, there was a 15.36% variance between the manufacturer’s program and the actual measured data, while for produced energy, the difference amounted to 25.81%. It was found that the balance point temperature is −7 °C, where the heat pump unit of the HHP system can cover necessary heat losses until that point, while the gas boiler operates at lower temperatures. Changes in electricity price can significantly influence the point of the system switch, but the possibility to cover heat loads of the heat pump unit always has to be taken into account.

The most significant increase in construction volumes in Latvia was registered in the time period from 2005 to the middle of 2008. Many large suburban areas around Riga were landscaped for building single-family-type houses. People have been using these properties for 12–15 years, and now, the challenge for the inhabitants is to find the most efficient way to maintain a high level of living comfort. Deteriorating systems require investments, so it is in the interest of owners to ensure that the benefits of such investments are maximized and that energy consumption is as low as possible. In this study, the authors simulated various scenarios where HVAC system parameters were changed, and the thermal performance of building structures was improved. Annual energy consumption, indoor quality and thermal comfort were analyzed. The importance of this work is justified by the need to realize and define the energy efficiency levels of existing single-family houses and demonstrate the amount of investment required to move closer to established energy efficiency targets.

Gas condensing boiler and air to water heat pump hybrid unit is an optimal way to introduce renewable energy resources in existing buildings. Two energy sources (gas & electricity) give hybrid unit higher flexibility in comparison to typical air to water heat pump. In hybrid solution air heat pump can be used in locations with low temperature heating seasons. Hybrid unit can output higher heat carrier temperatures, because of this, it can be used in combination with older radiator heating systems. There are many parameters that can influence the performance of hybrid heating unit. This paper investigates heat terminal type, heat carrier temperature, and outdoor switchover temperature setting (outdoor temperature at which hybrid unit switches from electricity to fossil fuel) influence on air to water heat pump and gas condensing boiler hybrid heating unit performance parameters (total efficiency - ηhybrid and primary energy factor - PEFhhp). Hybrid heating units performance is evaluated by using a computer model created in program IDA ice 4.8. The created computer model represents a real building, located in Latvia, that uses the previously mentioned hybrid heating unit. The model is verified by comparing its results with energy meter data from the real building, for time period from 01.03.2022 to 28.02.2023.The verified model is used to simulate how hybrid heating units performance is influenced by changes in heating terminal type, heat carrier temperature and outdoor switchover temperature setting. According to simulation data, at constant heat carrier temperature, heat terminal type has no influence on hybrid heating unit’s performance parameters. It has been found that increased heating system volume can reduce hybrid heating unit’s run time. In this case replacing panel radiators with floor heating, there is a 33% reduction in unit’s annual running time. In simulated scenarios, heat carrier temperature reduction by 15°C, increases ηhybrid by 8.7% and decreases PEFhhp by 17.5 % (at temperature graph 40/35°C). Switch over temperature increase from -7 to 3°C decreases ηhybrid by 47% and increases PEFhhp 7 %. Switch over temperature increase also reduces ηhybrid and PEFhhp change magnitude, when changing heat carrier temperature graphs. When changing the temperature graph from 40/35 to 55/50 °C the changes are as follows: at switchover temperature setting of -7°C, drops by 14,33 %, but PEFhhp increases by 23,42%; at switchover temperature setting of -2°C (actual setting), drops by 8,7 %, but PEFhhp increases by 17,51%; at switchover temperature setting of +3°C, drops by 1,74 %, but PEFhhp increases by 6,45%.

One of the main goals of heat and electricity producers in Latvia is to reduce the use of fossil fuels and introduce alternative fuel types that could help in reducing carbon dioxide emissions. This work focuses on addressing the set issue for a medium-capacity automated gas boiler plant, which provides heat for a local residential district. The following solutions were selected for boiler plant optimization: an electric boiler, a heat storage system, and solar collectors. Operating mode simulations were conducted for the electric boiler and solar collectors using Excel and Polysun (Standard) software. Simulations were created based on energy resource demand data obtained from a residential district located in Latvia and local energy resource prices/heat energy tariffs for the year 2024. The results from the simulations were used for technical and economic calculations to determine the payback period of the project. The electric boiler, together with the thermal energy storage tank and solar collectors, can produce 5903.04 MWh/year (~70% of local district heat demand) of thermal energy. This reduces the CO₂ emissions of the boiler plant by at least 1186.51 tCO₂ per year, which, at an emission quota price of 63.80 EUR/tCO₂, allows for savings of 75,699.34 EUR per year (12.82 EUR/MWh heat energy). The project’s discounted payback period is 4.12 years, considering the reduction in the cost of the CO₂ emission quota. The results of this study show that the chosen technologies are straightforward solutions that can be used to optimize existing boiler plants with limited space and can provide financial benefits to heat energy producers.