Air Conditioning in Professional Heating – Combination with Heat Pump and Heating
Climate control in professional heating – combination with heat pump and heating
When it comes to "air conditioning", most people imagine cooling in the summer. Professional heating system designers and technicians, however, know that modern climate control technology is much more – it is a full-fledged element of the overall energy strategy of a building, which can significantly reduce operating costs, increase comfort and eliminate the need to install several separate systems in the right design. In this part of the Knowledge Center, we focus precisely on this intersection: where air conditioning, heat pump and classic or modern heating meet, why it makes sense and what it looks like in practice – including specific numbers, diagrams and scenarios from practical experience.
Why combine air conditioning with heating at all?
Historically, air conditioning and heating were two separate disciplines. The air conditioner installed a split unit on the wall, the heating engineer dealt with the boiler and radiators. These two professions rarely met. In the last decade, this has changed fundamentally – and the reason is simple: physics. An air-to-air heat pump (i.e. a classic split air conditioning system with a heat pump) works on the same principle as a refrigerator: it transfers heat from one place to another. In summer, it takes heat from inside and discharges it outside, in winter it reverses – it takes heat from outside (even from freezing air) and brings it in.
Modern inverter split systems with heat pump technology have a COP (coefficient of performance) of 3.0 to 5.5 in heating – this means that from 1 kW of electrical energy, they produce 3 to 5.5 kW of heat. Compare this with an electric heater (COP = 1.0) or even a condensing gas boiler (efficiency ~95 %, i.e. COP ~0.95 in terms of primary energy). From a purely energy point of view, an air-to-air heat pump is clearly more economical at favorable outside temperatures. And since modern air conditioners work in heating mode down to –15 °C outside temperature (premium models even down to –25 °C), covering the Slovak climate is not a problem.
From the perspective of a professional heating system, we are therefore interested in several scenarios:
- Air conditioning as a primary heat source (monosystem) – suitable for low-energy and passive buildings
- Air conditioning as a bivalent (supplementary) heat source – combined with a boiler or floor heating
- Air conditioning as part of an air-to-water heat pump system – where the "air conditioning" outdoor unit is actually a heat pump for the entire system
- Air conditioning for finishing cooling in a building where an air-to-water heat pump provides heating
Air-to-air heat pump vs. air-to-water heat pump – key differences for the designer
In a professional environment, it is important to understand the differences between these two systems and where their natural place is. An air-to-air heat pump (i.e. a split air conditioning system with a heating function) distributes heat directly through air – the indoor unit blows warm air into the space. It is fast, flexible and economical to install. The disadvantage is that it does not work with a hot water system, so it does not solve hot water or radiators or underfloor heating without additional components.
An air-to-water heat pump, on the other hand, heats water, which then circulates in a classic heating system. It is more expensive to install, but it solves the complex needs of a building – heating, hot water preparation and sometimes even cooling via chilled ceilings or fan-coils. Air conditioning in the sense of this article (split systems, multi-split systems) belongs to the air-to-air category, but can be an excellent supplementary system even where the primary source is an air-to-water heat pump.
Example from practice: a customer has a new building with underfloor heating and an air-to-water heat pump. Underfloor heating in summer cannot cool efficiently (it is technically possible, but suitable subfloors are needed and condensation has to be solved by a dehumidifier). Solution? Install 2–3 split air conditioners in the living rooms for cooling in summer and as a backup in transitional periods. Result: comfort all year round, the system works efficiently and the customer is not dependent on one source.
Bivalent systems – when air conditioning makes sense as a boiler supplement
A bivalent system means that two heat sources are used for heating and work together. The classic combination in Slovak conditions: gas boiler (or pellet boiler) + air conditioning with heat pump function. How does it work? During the transitional period (spring, autumn) and in milder winters, only the air conditioning runs, which is much cheaper to operate. When the temperature drops below –10 to –15 °C, the system automatically or manually switches to the boiler, or both sources operate simultaneously.
The bivalent point (bivalent temperature) is the outside temperature at which the heat pump's output drops to the level of the building's heat loss. For well-insulated new buildings, this can be –12 to –18 °C, for older buildings with poor insulation even –5 to –8 °C. Key principle for the designer: if the bivalent point is set correctly, air conditioning covers 70–80 % of the annual heat demand (since such cold periods when it would not be sufficient occur only a few weeks per year), while the boiler capacity remains sufficient to cover the peak. Savings on gas or pellets can be 30–50 % compared to heating with a boiler alone.
From practice: an administrative building (offices, 600 m², Liptov) – before reconstruction, a gas boiler, annual gas costs about 8,500 €. After installation of a multisplit system (8 indoor units, total output 28 kW in heating) and keeping the boiler as a backup: annual electricity consumption for air conditioning about 4,200 kWh, gas savings 65 %, total heating costs reduced by 42 %. The winter was mild, but in the following season (colder) the savings were 38 %. The boiler was used only at temperatures below –13 °C, which was a total of 11-day period in that year.
Air conditioning integrated into VRF/VRV systems for large buildings
For larger commercial and industrial buildings (shopping centers, hotels, administrative complexes, production halls with office areas), VRF (Variable Refrigerant Flow) or VRV (Variable Refrigerant Volume) systems are relevant. These are extensive air conditioning systems where one or more outdoor units supply dozens of indoor units of different types (cassette, ducted, wall-mounted, ceiling-mounted) through a refrigerant distribution system.
Modern VRF systems with heat recovery are particularly interesting: they can simultaneously cool some zones and heat others, transferring heat from cooled areas to those that need heating. During the transitional period (autumn/spring), a server room or kitchen can heat an office, significantly reducing overall energy consumption. The efficiency of such systems in heat recovery mode can reach COP 6 to 8 – an incredible result from an energy perspective.
For heating system designers, it is important to know that VRF systems can be integrated with BMS (Building Management System), which allows for centralized control, consumption monitoring, schedule setting, and coordination with other building systems (ventilation, lighting, security).
Dimensioning of a combined system – how to calculate it
Dimensioning is key and the most common mistakes are made here. In a full professional project, the process is as follows:
1. Heat load of the building (heat loss calculation)
According to STN EN 12831, the design heat loss of the building is calculated at the design outdoor temperature (for most of Slovakia –15 °C, for northern areas –18 to –22 °C). For example, for a single-family house (150 m², low-energy standard), it can be 5–8 kW, for an older apartment block (1,000 m², original insulation) 60–120 kW.
2. Setting the bivalent point
Air conditioning (air-to-air heat pump) should cover the heat load at temperatures of –5 to –10 °C. The performance of air conditioning drops at low temperatures – always check the performance table from the manufacturer at –7 °C and –15 °C, not only at 7 °C (which is a standard laboratory condition, not a Slovak winter). Quality inverter air conditioners retain 80–90 % of their nominal output at –7 °C.
3. Selection of air conditioning capacity
If the heat loss of the building at –15 °C is, for example, 10 kW and the air conditioning achieves 70 % of its nominal capacity at –15 °C, you need at least a nominal capacity of 10 / 0.7 = 14.3 kW. If you set the bivalent point at –10 °C (where the air conditioning achieves 85 %), you need only an air conditioning system of 9 kW to cover the demand at –10 °C (while the boiler covers the rest).
4. Cooling capacity in summer
In summer, you need to calculate the heat load in reverse – solar gains, people, appliances, ventilation. For office spaces, it is typically 60–120 W/m², for shops even more. Dimensioning of air conditioning for cooling can therefore differ from dimensioning for heating, which is why these calculations are done separately and the resulting capacity is the higher of the two requirements.
In practice: during the renovation of a multifunctional building (Banská Bystrica, 3 floors, 800 m² in total), the heat loss calculation at –15 °C was at the level of 48 kW. The customer wanted to use air conditioning to the maximum for heating and minimize dependence on gas. We designed a multisplit system with a total nominal output of 38 kW in heating (covering the load at –5 °C), the boiler remained as a backup for peaks. Result: air conditioning covered 74 % of the annual heat volume, gas was used only in December and January.
Protection of the outdoor unit – an essential part of a professional system
The outdoor unit of the air conditioning is the heart of the entire system. In a professional environment, the demands on the protection of this unit against external influences are increased. It is not just about aesthetics – an incorrectly placed or unprotected outdoor unit can have a shorter lifespan, reduced performance and higher service costs.
For IVAR.2.0 air conditioners, specialized protective accessories are available. RAIN PROTECTION KIT for IVAR.2.0 air conditioners protects the outdoor unit from direct rain, ice and snow from above – it extends the life of the heat exchanger and reduces the risk of corrosion damage. Equally important is BUG PROTECTION KIT for IVAR.2.0 air conditioners, which prevents birds, insects and small rodents from entering the area of the outdoor unit. In summer, this is particularly relevant – wasps and bees like to build nests directly in the unit, which can lead to a failure of the fan or electrical system.
For the completeness of the installation, especially in professional mounting on walls or roof structures, it is also recommended to check the condition of the bottom cover of the outdoor unit. For the IVAR.2.0 series, Bottom cover for IVAR.2.0 is available and for smaller models Bottom cover IVAR.2.0 9HP MINI – these parts prevent the penetration of dirt, moisture and insects from below the unit, which is especially important when placed close to the ground or in a dusty environment. More about this accessory can be found in the article Accessories for IVAR.2.0 air conditioners – overview of parts and their functions.
Correct placement of the outdoor unit in terms of system efficiency is also critical: the unit must not suck in its own exhaust (recirculation), must have enough space for air flow (at least 30 cm from the obstacle at the back, 60–100 cm in front), must not be directed to a place where snow accumulates in winter, and ideally should be on the north or east side of the building (lower temperature in summer = higher cooling performance and lower consumption). Details on the protection of the outdoor unit are covered in a separate article Protection of the outdoor unit against rain and insects – why and how to do it.
Control and integration – air conditioning as part of a smart home
Modern air conditioners (split and multisplit) are in the vast majority of cases equipped with a Wi-Fi module or the possibility of its installation. This allows integration into smart home systems – Apple HomeKit, Google Home, Amazon Alexa, KNX, Modbus and other protocols. From the perspective of professional heating, it is important to be able to connect the air conditioner to a central thermostat or building control system.
A specific example of integration: a family house with floor heating controlled by Loxone, an air-to-water heat pump as the primary source and two split air conditioners in the living room and kitchen. Loxone controls the distribution of heat in the floor heating, as well as both air conditioners – based on weather forecasts (API), it automatically switches the air conditioner to heating mode when the forecast indicates cooling, while the floor heating is still not able to react (it has a large thermal inertia). The result is immediate comfort without wasteful switching of sources.
Control must also be addressed in simpler systems: if the air conditioner is a bivalent source to a gas boiler, it is necessary to set the hysteresis and priority so that both systems do not conflict. Most modern boiler controllers (e.g. Bosch/Buderus EMS, Viessmann Vitotronic, Wolf BWL) have an input for an external heat source, which allows the boiler to be turned off when the air conditioner is sufficient to cover the load.
Energy certification of buildings and air conditioning
In the context of energy certification of buildings (Act No. 555/2005 Coll. and related decrees), air conditioning with a heat pump plays a positive role. Systems with a high SCOP (seasonal coefficient of performance) – typically 3.5 to 4.5 – significantly improve the energy balance of the building and can decide whether the building receives a certificate A1 (ultra-low energy) instead of B (low energy). In new buildings, where the law since 2021 requires the nearly zero energy consumption standard (NZEB), integration of a heat pump (in any form) is practically essential.
It should be noted, however, one practical aspect: when combining air conditioning and a boiler, both systems are included in the energy performance certificate. If the boiler is old or has low efficiency, the resulting certificate class may be worse than would correspond to the actual operation (since the boiler is "backup" and is in fact used very little). A competent designer solves this either by reducing the boiler's capacity (and thus its smaller share in the certification calculation) or by replacing the old boiler with a modern condensing one.
Practical scenarios from the field – interviews with technicians
Scenario 1 – School, Central Slovakia: An old municipal school, 1,200 m², central heating with a natural gas boiler, radiators. Problem: the boiler is at the end of its life, the school has no money for a complete renovation, but wants to save. Solution: procurement of 4 VRF outdoor units + 24 indoor cassette units. The boiler remained as a backup, but was generally set to only minimal performance. Annual gas savings of 58%, and the school also gained cooling, which it did not have at all before.
Scenario 2 – Retirement home, Orava: The owner planned to install an air-to-water heat pump for the entire building (20 rooms). The designer explained that at –20 °C (Orava!), the air-to-water heat pump would operate at the limit of its capacity and with low COP. He proposed a hybrid solution: a condensing gas boiler as the primary heat source for the entire building + 6 split air conditioners for common areas (reception, dining room, lounge) for cooling in summer and bivalent heating in the transitional period. The customer saved on the initial investment (air-to-water heat pump is 3× more expensive) and has a system adapted to the specific harsher climate.
Scenario 3 – Apartment building after insulation, Bratislava: A 24-apartment building, fully insulated, new windows. Original solid fuel boilers replaced by a gas boiler. However, the apartment association wanted to also address cooling – every summer, the apartments had unbearable temperatures. Instead of central cooling (complicated ducting, expensive), each apartment could individually decide to install a split air conditioner. 18 out of 24 apartments did so, 14 of them with inverter air conditioners equipped with heating. These apartments now do not need gas heating at all during the transitional period – they regulate the heat themselves with the air conditioner. The community's gas costs have decreased, even though the boiler remains fully functional for apartments without air conditioning and for the coldest periods.
Most common mistakes in the design of a combined system
- Overdimensioning of air conditioning: Customers think that the higher the capacity, the better. The opposite is true – a large air conditioner in a small room cycles (turns on and off), does not achieve seasonal condensation of moisture, is noisier and wears out faster. A correct calculation is essential – see also the article What air conditioning capacity do I need – calculation according to area and type of space.
- Ignoring performance at low temperatures: Manufacturers state performance at 7 °C outdoor temperature (A7/W20 standard). At –15 °C, the performance is completely different. Always request performance curves at actual design temperatures.
- Lack of source priority regulation: Without properly set regulation, both sources may work simultaneously or interfere with each other, increasing costs instead of reducing them.
- Poor location of the outdoor unit: Recirculation of exhaust air, snow accumulation, direct sunlight – all of this dramatically reduces performance and lifespan. More in the article Installation of air conditioning step by step – procedure and installation requirements.
- Not including maintenance in the plan: A combined system has more components and requires regular inspection of both sources. This is discussed in detail in the article Maintenance and service of air conditioning – what to do regularly and what to leave to a professional.
Economics of the investment – return on a combined system
Economic analysis of a combined system (air conditioning + existing boiler) is usually very favorable, precisely because you do not need to replace the entire boiler system. A typical investment for a family house (3–4 split air conditioners, including installation and electrical work) ranges from 4,000 to 8,000 €. Annual savings on heating (at current energy prices) can be 800–2,000 € per year, giving a payback period of 4–8 years – and that without the cooling effect in summer, which also has economic value (no need to purchase mobile air conditioners or other cooling devices).
For larger buildings (schools, administration, hotels), the investments are higher, but the savings are also proportionally greater. Many municipalities and companies use grant schemes – SIEA, Obnovme Slovensko, or EU fund regulations. Air conditioning with heat pump function is usually an eligible expense within insulation projects or projects aimed at increasing energy efficiency.
What influences the choice of a specific solution
The following factors decide the choice of a suitable combination of air conditioning and heating:
- Type of building and its energy balance: New buildings (low-energy, passive) can easily cover the thermal load with air conditioning alone; older buildings require a hybrid approach.
- Existing heating system: If the boiler is relatively new and functional, there is no reason to remove it – air conditioning can simply be added as a bivalent source.
- Climatic zone: In warmer parts of Slovakia (Podunajsko, Záhorie), air conditioning can cover heating almost the entire winter. In the north (Orava, Kysuce, Tatry), a backup source is much more important.
- Requirements for domestic hot water: Air-to-air air conditioning does not provide DHW. If this is a requirement, you need either an air-to-water heat pump with a water heater, solar collectors, or a combination.
- Noise restrictions: Outdoor units produce noise of 45–65 dB(A). In dense urban areas or near neighbors close to windows, quiet models and proper placement are necessary. More on selection in the article How to choose air conditioning for professional use – what to focus on.
- Number and type of rooms: Split vs. multi-split systems – this topic is discussed in detail in the article Split vs. multi-split air conditioning – which is more cost-effective.
Frequently asked questions (FAQ)
Can air conditioning completely replace a boiler in a standard family house in Slovakia?
Yes, in a low-energy or passive house in a warmer part of Slovakia – modern inverter air conditioners with heating function operate reliably down to –20 °C outdoor temperature and, when properly dimensioned, can cover the entire thermal load of the building. In an older building with higher heat loss or in mountainous areas, it is safer to keep the boiler as a backup. The decision depends on a specific heat loss calculation and location – there is no universal answer.
How are air conditioning and boiler coordinated in a bivalent system – manually or automatically?
Ideally automatically, via a boiler controller with an external input or via a smart home system. The setup is simple: the controller monitors the outdoor temperature, and when it drops below the bivalent point (e.g., –10 °C), the boiler is turned on. Above this point, only the air conditioning operates. Many air conditioners also have an integrated thermostat with a function to control an external source. For simpler installations, manual operation is also sufficient – users quickly learn when to switch.
Does the presence of air conditioning affect the energy certificate of the building – positively or negatively?
Positively, if the air conditioning with a heat pump is included in the energy balance as a renewable energy source (which technically it is, since it uses heat from the outside air). The certification calculation takes into account the SCOP of the system and the share of renewable energy in the total delivered energy. A system with air conditioning and a boiler usually gets a better class than a system with a boiler alone – provided the energy audit is properly processed.
What are the legislative requirements for the installation of air conditioning with a heat pump in Slovakia?
Air conditioning with F-gas refrigerant (e.g. R32 or R410A) must be installed by a certified person with an F-gas certificate according to EU Regulation No. 517/2014. The electrical installation must comply with STN 33 2000 and must be carried out by an electrician with the appropriate license. For capacities above 12 kW, a building permit or notification of a building change is usually required. We always recommend checking the current requirements at the local building office, as local regulations may vary.
Is a combined system worth it even at low gas prices?
Yes, even at lower gas prices, a combined system is economically viable, although the payback period will be longer. Air conditioning also brings a value that a boiler cannot provide: cooling in summer, which is a reason for investment on its own. However, if you are calculating the return on investment purely at low energy prices, in some cases it may be better to wait for a more favorable subsidy program or to spread the investment – first air conditioning for cooling, later integration into the heating logic.
What to do if the outdoor unit of the air conditioner freezes in winter?
The defrost cycle is a standard function of every air-to-air heat pump. When the temperature of the heat exchanger drops below a certain point, the unit automatically switches to defrost mode (reverse cycle) for 2–5 minutes, melts the ice and returns to normal operation. During defrosting, the indoor unit temporarily stops blowing warm air (or changes mode). If defrosting occurs too frequently or the unit remains frozen for a long time, it may indicate a fault – temperature sensor, refrigerant deficiency, dirty heat exchanger. More in the article Common air conditioning faults and how to recognize them.
Conclusion – air conditioning as a strategic element of modern heating
Air conditioning is no longer just a summer luxury. In a professional context, it is now a full-fledged technical system that can significantly change the energy balance of a building, reduce dependence on fossil fuels and provide comfort throughout the year. Combining it with a heat pump and existing heating is economically and technically viable for the entire range of buildings – from single-family homes to large commercial properties.
The key to success is precise design: correct calculation of thermal load, realistic assessment of air conditioning performance at low temperatures, correct setting of the bivalent point, quality control and not least careful protection of the outdoor unit from external influences. Every project is different – and that is why it makes sense to consult with an expert who knows the specific products and their proper application on site.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.