Hotel Adapted to the Requirements of an nZEB Building—Thermal Energy Performance and Assessment of Energy Retrofit Plan

Abstract

Recently, emissions and the energy use of the building and construction sector globally increased. Therefore, energy retrofit processes and reducing the energy consumption of buildings are increasingly often discussed by the academic community, industry, and end-users. The application of high-performance technologies and highly insulating materials results in a low energy demand in newly constructed buildings. A crucial challenge is to reduce energy consumption in existing buildings. The article presents an energy analysis of the reconstruction of a historic building adapted to hotel functionality. Based on the available information on the design of the facility, and the annual demand for cooling and heating energy, simulations of the energy performance were carried out. The proposals to exchange the heat source and replace the existing systems were simulated and assessed. Three different retrofit options were analyzed, including the replacement of the air handling unit (variant 1—v1), bathroom fixtures (v2), and, in the last scenario analyzed (v3), the above-mentioned activities and the usage of tri-generation units. As the results show, such solutions allow for the reduction in final energy consumption of 20%, to 73% regarding the baseline variant.

1. Introduction

Due to tightening regulations in the construction sector, building concepts with higher energy standards are steadily gaining popularity. Newly constructed buildings must feature high levels of insulation and, equally, the highest energy standards for sanitary and electrical installations. The solutions attracting the interest of designers and users are zero-energy and near-zero-energy buildings (nZEB). Directive 2010/31/EU [1] requires member states to ensure that by 31 December 2020, all new buildings are nearly zero-energy buildings. Furthermore, by 31 December 2018, the new structures occupied and owned by public authorities should be nearly zero-energy buildings. Thermal modernization measures to reduce energy consumption, and consequently decrease operating costs and environmental impacts, are also becoming increasingly popular. The most common way to reduce the energy intensity of buildings is to increase the insulation of the building envelope and window and door frames. In many cases, reducing the transmittance of the building envelope is crucial to decrease the costs associated with heating or cooling spaces. In hot climates, the envelope insulation improvement may reduce the energy demand for cooling, while for cold climate conditions, it could be beneficial due to lower heating energy consumption. Moreover, a large part of the overall energy demand is related to the ventilation system, hence, mechanical ventilation with heat recovery gained popularity. Many innovative solutions are available on the market. Increasingly attractive options are heat pumps, which could significantly reduce the operating costs of the buildings. More advanced technological methods of reducing energy intensity are cogeneration and tri-generation installations, which decrease energy losses and allow the reuse of waste heat in other processes, such as domestic hot water (DHW) preparation. An exceptional case is that of buildings with historical value. Modernization measures in such facilities must consider not only the energy and economic reasons, but also the preservation of cultural heritage. Consequently, it leads to limited interference with the structure, building envelope, windows, and doors.

1.1. Energy Consumption in Hotels

As in the case of other buildings, the topic of energy consumption in hotels is becoming increasingly popular. It is directly related to the high operating cost caused by the increased energy demand. In addition to the aspect of achieving possible financial savings by decreasing the energy demand, the key factor is also to reduce air pollution. According to the report of the Association of Hotels, Restaurants, and Cafes in Europe (HOTREC) [2], it is assessed that about 5% of global greenhouse gas emissions are related to the tourism sector, and hotels are responsible for 20% of it. Moreover, it is forecasted that international tourist arrivals will increase by 43 million a year on average between 2010 and 2030. Increased tourist traffic will lead to increased energy consumption. Hence, it is crucial to modernize existing facilities, and reduce their energy demand. Hotels facilities, in contrast to other commercial buildings, are characterized by separate functional areas, as well as thermal loads that vary over time and are difficult to estimate. Therefore, determining the energy performance is crucial for selecting the best measures to reduce energy consumption and improve the building’s energy efficiency. The energy performance of buildings is the subject of many studies in different regions of the world. For example, the work of Santamouris et al. [3] was based on a study of 158 hotels in Greece, and the average annual energy consumption determined from them is 612 kWh/m². In comparison, Bohdanowicz et al. [4] determined the energy consumption rate for two hotel chains, Hilton and Scanidic, in Europe and they amount to 364 kWh/m² and 285 kWh/m², respectively. Priyadarsini et al. [5] report an annual average energy consumption of 427 kWh/m² when studying the energy characteristics of 29 hotels in Singapore. The study included hotels with different interior and comfort standards, which corresponded to three-, four-, and five-star hotels. Similarly, Yao et al. [6] conducted an energy analysis of hotels in Shanghai based on information about the buildings, functionality, service level, and energy consumption for 45 years. The authors determined the energy load in the unit of kgce, meaning kilogram carbon equivalent, and it is 61.95 kgce/m², 73.18 kgce/m², and 86.64 kgce/m², for three-star, four-star, and five-star hotels, respectively. After conversion, this provides values of 504 kWh/m², 596 kWh/m², 705 kWh/m², respectively. As the authors noted, the relationship between occupancy rate and energy load is difficult to identify. The level of energy consumption depends on many factors, so an in-depth analysis of building characteristics and use is crucial. The study of energy demand in hotel buildings was also dealt with by Tsoutsos et al. [7]. The authors presented the results of actual energy performance for seven countries: Greece, Croatia, France, Romania, Italy, Spain, and Sweden. In all sixteen pilot hotels, implementation of the proposed solutions toward nearly-zero energy buildings allows for decreasing the primary energy use from an average of 277 kWh/m² to an average of 102 kWh/m²—an average reduction of 63%. The analysis also shows that non-residential functions, i.e., other facilities requiring special indoor environmental conditions, such as spas, kitchens, etc., are more critical than hotel rooms; their primary energy consumption can drop from an average of 727 kWh/m² to an average of 374 kWh/m². The parameters that influenced the results identified in this study were hotel typology, climate zone, facilities offered, and seasonality of operation. Tsoutsos et al. [8] analyzed the pilot hotels of the European project “Nearly Zero-Energy Hotels”, which aimed to provide technical support and advice for the renovation of existing buildings towards nearly zero-energy buildings (NZEB). Among the main conclusions, the authors noted that the hotel sector is very diverse and highly dependent on climatic conditions in a country. During the project, the authors assumed an average energy consumption for the year-round operation of 350 kWh/m² and a reduction to 100 kWh/m² for nearly zero-energy hotels. Besides atmospheric conditions, the presence of hotel guests and their operating habits are also essential factors. As shown in the research in the article by Borowski et al. [9], at the stage of predicting the demand for cooling energy in the summer, in addition to external parameters, the occupancy level of the hotel, and also the day and time of measurement, significantly influence energy demand. The results show how characteristic hotel buildings are, where both the users and the time aspect are of great importance.

1.2. Energy Sources

The problem, which often arises during operation, is the variability of energy consumption and the variable operating parameters of the installation. The persistently high prices of electricity are also of great importance, which limit the use of many systems driven by electricity. These factors push designers to seek solutions that allow partial generation of the required heat or power directly on site. Due to the savings afforded by the technological association of multiple systems, cogeneration and tri-generation systems are steadily gaining popularity. Combined cooling, heat, and power (CCHP), also known as tri-generation, is the simultaneous production of more than one type of energy from a single fuel source. Proposals for the application of combined heat and power (CHP) and CCHP systems, along with the aspect of thermal energy management, are the subject of many scientific articles [10,11,12]. Li et al. [13] examined the effectiveness of CCHP systems for hotels, offices, and residential buildings in China. As the analysis shows, CCHP systems show the highest energy savings in hotels, due to their relatively stable electrical load (42.28% reduction in energy consumption). From an economic point of view, it is advantageous to implement such solutions in hotels and offices. However, in the case of residential buildings, they do not give satisfactory results. The undeniable advantage of these systems is the emissions reduction in each of the analyzed buildings. A study of the proposed CCHP system for commercial and office buildings in Iran by Hanafizadeh et al. [14] shows that the adaptation of this system results in a reduction in environmental impact, grid electricity consumption, and fuel consumption. The authors analyzed three possible generator power options. Due to economic reasons, the selection of four gas engines of 4MW each was considered the most cost-effective.

1.3. Energy Performance Evaluation—Energy Indicators

Directive 2010/31/EU [1] defines that an energy performance certificate indicates the energy performance of a building or building unit, calculated according to an adopted methodology. The document is recognized by a member state or by a legal body. Energy assessment of a building is possible through the use of energy indicators. The basic indicator used for the energy assessment determines the total primary energy (PE) demand per reference unit, such as floor area or room volume, most often expressed in kWh/m² per year [1]. The calculation separately determines primary energy from renewable and non-renewable sources, considering the individual energy carriers, namely fuel, heat, and electricity. Besides the primary energy, the usable energy required to ensure adequate indoor conditions is significant for assessment. The usable energy index (UE) indicates the quality of a building’s construction. In general, the lower the value of usable energy, the less heat is lost through the building envelope. The design of energy-efficient buildings requires achieving the lowest possible value of usable energy demand. The final energy (FE) indicator describes the energy needed in the house regarding the efficiency of the heating and DHW systems. If the value of the final energy index is slightly higher than the usable energy index, it means that there are highly efficient systems in the building. Figure 1 shows the relationship between the primary, final, and useful energy for a building. As can be seen in the figure, various losses occur across each transformation part of the energy chain. Conversion into another form of energy, its transport, transmission, and distribution, lead to losses in the stage between primary and final energy. The essential points are transformation losses. It depends primarily on the efficiency of conversion to electricity or heat. Before the energy is supplied to the final appliances, further losses occur. In this case, they are related to the efficiency of equipment, and the process of distribution or storage of energy.

1.4. Energy Simulation

An increasingly common method for optimizing energy consumption in buildings is energy simulation [15,16,17,18,19]. In their paper, González-Gil et al. [20] presented simulations using a specially developed and calibrated dynamic energy model. The results allow them to determine the average energy intensity of operating rooms and the potential for energy savings of 40% to 80%. In addition, they found that heating accounts for about 98% of the total heat demand, with about 80% of consumption corresponding to periods of inactivity. The topic of improving energy performance was also addressed in an article by Díaz-Torres [21]. Based on their calculations of thermal loads, they determined the efficiency of installations inside the hotel and found opportunities for improving energy performance, leading to energy, cost, and environmental impact savings. The analysis found that due to the nature of the load, changing the operating strategy of the heating, ventilation, and air conditioning (HVAC) system could result in total savings of 403.1 MWh/year, which is the average consumption of the hotel for three months. Various retrofit scenarios using simulation tools were also analyzed by Biserni et al. [22]. A residential building in northern Italy was examined for three retrofit scenarios: I: replacing windows; II: increasing exterior wall insulation; and III: replacing windows, and increasing wall and roof insulation. Optimization was carried out using TRNSYS software, and calibrated based on energy bills. Based on the analysis, the most cost-effective solution was to increase exterior wall insulation. A similar approach was used in a paper by Silenzi et al. [23]. The authors evaluated the energy requirements for both heating and cooling systems. The analysis included various retrofit solutions, including façade-void-insulated panels, smart rotating windows, and LED systems. Due to high solar gains and relatively high temperatures, smart rotating windows proved to be the most cost-effective solution. An educational building in Italy is the subject of an article by Ascione et al. [24]. The authors conducted an analysis, in which the most cost-effective energy retrofit configurations include the installation of an air-source heat pump for space heating and a photovoltaics (PV) system distributed throughout the roof. According to the analysis, implementation of the best solution may result in a decrease in the primary energy demand value of about 12 kWh/m²a. Cho et al. [25] described the method of a historical building retrofit. For this purpose, the authors used the DesignBuilder simulation program. Possible retrofit solutions considered in this study include passive and active measures, as well as renewable energy technologies. Replacement of windows, use of roof and wall insulation, interior blinds, LED lighting, and a high-efficiency HVAC system was considered the optimal solution to reduce the energy intensity of the building while maintaining its historical value and utility. Using one of the retrofit proposals reduced Underwood Hall’s average energy consumption by 54.2% in winter and 42.6% in summer. It also reduced Underwood Hall’s annual energy costs by 47.9%.

The paper analyzed the energy demand of buildings using building energy demand simulation. Chapter 1 presents the problem statement of the paper and a review of the literature of simulation and CCHP application. Section 2 presents the methodological approach adopted in the study, including a description of the software used and the scope of the measurements. Section 3 shows the obtained results. Section 4 discusses the results, while Section 5 provides a summary and conclusions.

2. Materials and Methods

2.1. Research Methodology

The article presents an analysis of the thermal modernization possibilities of the Turówka hotel, which is a building of high historical value. As part of the research, energy consumption measurements of domestic hot water, and the cooling, heating, and ventilation systems were carried out. Then, based on the available technical documentation of the building, a geometric model of the building was prepared, considering the dimensions of the particular rooms, construction materials used, their insulation properties, glazing area and properties, technical condition, and locations of the building. Using the Audytor OZC software, an energy model of the building was developed, and calculations were carried out to determine the energy performance of the building. The obtained results were compared with actual energy consumption measurements. In this way, the developed model was validated, and the correctness of the preliminary assumptions was confirmed. A description of the measurements carried out and details of the prepared energy model assumptions are presented in Section 2.4. Then, using the base model, modifications depending on the considered retrofit variant were introduced. The paper aimed to assess the application of various retrofit methods in the analyzed building, and evaluate the real benefits of the solutions. The study takes into account three possible modernization variants. The first of the variants only involved interference with the ventilation system, by replacing the air handling units with devices with higher efficiency. The second option included the exchange of air handling units, analyzed in variance 1, and the replacement of bathroom fittings, which reduced water consumption by 60%. The last of the analyzed variants included several modernization measures, including, among others, the implementation of tri-generation aggregates as the main source of energy. The selected solution allows for the generation of electricity, and provides heat and cooling energy to the heating and cooling system, respectively. Chapter 3 includes details of the analyzed retrofit solutions and a specification of the assumptions adopted for the model for each retrofit approach. The particular descriptions are presented together with the obtained results for each of the three measures variants in Section 3.2, Section 3.3 and Section 3.4. Figure 2 shows the procedure of the research methodology.

2.2. Case of Study

The subject of this work is the historic Turówka hotel. The building was to be part of the planned Wieliczka Salt Works, and now is in the register of monuments. After 2001, reconstruction of the saltworks and adaptation of the building began, adapting the building to the hotel and catering facility, while maintaining the original dimensions and materials. Due to the historic nature (listed in the register of monuments) of the building, the modernization of the hotel, adapting it to the prevailing energy standards, was a crucial challenge for designers. The hotel is a reconstruction of a building from 1812.

Table 1. Characteristics of analyzed building.

Parameter	Value/Description
Location	Kraków
Type	Hotel
Construction year	1812
Reconstruction year	2007
Number of floors	5 (basement and four ground levels
Useful floor area	5525.00 m2
Capacity	19,300.00 m3
Ventilation system	Mechanical ventilation with recuperation
Heating system	Gas boiler, radiators in rooms
Cooling system	Fan coils (individual) + ventilation (central)
Additional information	50 double rooms, a conference room, a restaurant, drink bar

summarizes the most important parameters describing the analyzed building. Figure 3 shows an exterior view of the hotel.

The building is equipped with mechanical supply and exhaust ventilation implemented with seven air handling units with rotary exchangers and one with a glycol exchanger. Currently, the average seasonal efficiency of this system does not exceed 45%. In summer, cooling is provided by a chilled water system with a chiller located outside the building. Air is treated centrally in an exchanger located in the air-handling unit and locally in selected rooms using fan coil units. A refrigeration unit with a module for cooling 35% glycol–water solution with parameters of 6 °C/12 °C pumps the refrigerant to the exchanger located in the machine room. The average seasonal energy efficiency ratio (SEER) is estimated at 2.4. The facility has a two-pipe central heating system, using two boilers (250 and 350 kW) with operating parameters of 80/60 °C. In the rooms are steel panel radiators equipped with single-regulation straight radiator valves. The hot water system is supplied from the gas boiler located on the top floor. The external walls do not meet the requirements of the technical conditions. However, due to the historic nature of the building, thermo-modernization could prove to be an expensive procedure, uneconomical with the current thermal standard of the partitions. A similar situation applies to the window and door woodwork.

2.3. Planned Modernization Activities

The proposed retrofit solution includes three fundamental components, i.e., the multifunctional reverse regenerator (MRR), the tri-generation gas power generator (GAT), and the NEURO+ control module. They are connected to other components of the ventilation system, including air-handling units, active air controllers, and air filters. The proposed modernization solution involves replacing the existing air-handling units with new ones equipped with countercurrent regenerative heat exchangers, with controllable moisture recovery from exhaust air and adiabatic cooling. The manufacturer assumes that the average seasonal temperature efficiency of the air-handling units will exceed 87%. An essential component of the system is the GAT, a gas-fired tri-generation unit. Its main advantage is the ability to recover energy from the burned fuel and use it to drive the refrigeration system and electrical components. It is assumed to achieve an energy utilization rate of 85%. The unit is equipped with a gas-powered engine of modern design, ensuring heat recovery through the supplementary cooling systems driven by the energy of the aggregate. The system uses the energy of the condensation of water vapor contained in the flue gas, consequently lowering its temperature and managing the recovered energy in the system.

The air-conditioning system’s fan coil units will provide adequate room temperatures in both winter and summer, as they will be used to heat and cool the air. The cooling system will be supplied with chilled water from an A/W pump, i.e., an air-to-water triple-generation chiller of 150 kW, and also a peak chiller of 200 kW. It is envisaged that condensing boilers and tri-generation units will be used. Standard water fixtures will be replaced with proximity-sensing elements (expected to reduce consumption by 60%). The new heating system is to be fully integrated with the cooling and hot water preparation system. The entire system is controlled by intelligent adaptive automation building energy management system (BEMS), using weather forecasts. One boiler will be replaced by three GAT tri-generation units. The system will be divided into two parts: high-temperature and low-temperature. For the high-temperature medium with operating parameters of 80/60 °C, the total power of 75 kW will be obtained from the gas engine cooling and the flue gas/water heat exchanger. The exchanger will be used to heat domestic hot water and pool water. A low-temperature medium with operating parameters of 50/40 °C from the reversible air/water heat pump will be used to power radiators and fan coil units. Each of the GAT units will be equipped with a power distribution system between the heat pump compressor and the generator. It will allow the gas engine to operate at constant optimum power.

2.4. Building Simulation and Validation

Audytor OZC software was used to perform the building energy summation both before and after the energy retrofit [26,27,28]. The design energy consumption of rooms, the seasonal energy demand for heating and cooling, and general energy performance were prepared using the software. The software calculated the building design heat load according to the PN-EN 12831 standard [29]. The energy performance certificates were prepared according to current Polish regulations. For each variant, the energy demand was calculated by ISO 13790 standard [30]. The energy demand for DHW preparation was calculated based on Polish regulations [31]. The total efficiency of the heating system was estimated as a multiplication of the seasonal energy efficiency ratios, which refer to the generation, distribution, regulation or usage, and storage of the energy. The outdoor design temperatures were adopted based on indications from the nearest meteorological station, i.e., Krakow Balice. The calculations considered natural infiltration, thermal bridges of building partitions, and losses and gains between rooms. Moreover, the program also used heat gains through opaque partitions, losses through long-wave radiation, and losses to the ground following EN ISO 13370. The consumption of natural gas and electricity was estimated based on the unit emission and calorific value. The values of particular indexes are related to the medium used and the applied technology. Based on these values, the emissions expressed in CO₂ equivalent were calculated. The calorific value of natural gas used in the calculations is 48 MJ/kg, and the specific emission for this carrier is 56.1 tCO₂/TJ.

Table 2. Basic simulation data.

Parameter	Value/Description
Climate zone	III
Meteorological station	Poland, Kraków, Balice
Design outdoor temperature, °C	−20.0
Average yearly outdoor air temperature, °C	7.6

summarizes the basic information of the simulation model in connection with the location of the facility and the calculated external parameters.

The results for the pre-retrofit configuration were compared with actual data to ensure the reliability of the calculations. The geometric model of the hotel and the energy performance was prepared in the software Audytor OZC version 7 Pro (Sankom, Warsaw, Poland). Figure 4 shows a 3D model of the analyzed building.

The energy balance included internal heat gains from people, lighting, and electrical equipment. The average energy demand was determined in the program based on room functionality and Polish regulations [31]. Since the weather conditions affect the energy demand, the analysis adopted data from the nearest meteorological station Kraków Balice.

All systems were defined in the software according to the original state of the building following the article [32] and the design assumptions described in the preceding chapters. The heat transfer coefficient for multilayer partitions was calculated regarding ISO 6946 [33]. Partition data was obtained from technical drawings from the reconstruction phase, and details of building envelope coefficients are summarized in

Table 3. Thermal characteristics of the building envelope.

Building Envelope	Overall Transmittance, W/(m2K)
External walls 1	0.281/0.314/0.349
Roof	0.190
Ground floor	0.365
Windows	1.800
Doors	2.000

¹ There are three types of exterior walls characterized by different wall thicknesses and corresponding transmission coefficients.

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Data for model validation were collected from January 1 to 31 December 2019. Measurements were made using MULTICAL heat meters by Kamstrup. Sensors were submitted to a type approval according to EN 1434 [34], which includes the 2400 h measurement stability test of the flow sensors. All chilled water and heating systems have Kamstrup Multical 403 ultrasonic heat meters with digital communication modules. Data are transmitted via a serial communications protocol, MODBUS RTU, and stored in a recording system. Detailed information on the measurement system is presented in the article [32].

3. Results

The use of Audytor OZC software made it possible to obtain a complete energy performance of the building. Based on the analysis, the most crucial data were extracted and presented in the sections below, both for the building before and after the modernization.

3.1. Energy Performance of Pre-Retrofit Building

Firstly, the geometry of the building, the characteristics of the building envelope, and primary efficiency coefficients of the systems were entered into the software. Then, the calculations of heating and cooling demand were carried out.

Table 4. Heat demand calculations—variant 0.

Parameter	Heating and Ventilation	Cooling	DHW	Lighting	Total
Useful energy, MWh/year %	343.16	156.35	169.55	-	669.05
	51.3%	23.4%	25.3%	-	100.0%
Final energy, MWh/year %	585.47	65.97	521.69	107.50	1280.64
	45.7%	5.2%	40.7%	8.4%	100.0%
Primary energy, MWh/year %	730.49	197.91	573.86	322.51	1824.77
	40.1%	10.8%	31.4%	17.7%	100.0%

summarizes the consumption by system: heating and ventilation, cooling, domestic hot water, and lightning. The values represent annual demand for both utility, final and primary energy. The pre-retrofit variant is referred to hereafter in the article as variant 0. It is the basis for further analysis. Table 4 summarizes the results of the primary, final, and useful energy consumption for each system in the analyzed building. The first line gives the values, while the second line contains percentages.

On this basis, energy performance indicators were determined. The values describe the consumption per m² of the facility. It allows for comparing the facility with each other. A summary of the indicators is presented in

Table 5. Energy performance indicators—variant 0.

Indicator	Value
Useful energy, kWh/(m2·year)	144.8
Final energy, kWh/(m2·year)	277.2
Primary energy, kWh/(m2·year)	395.0
Emission CO2, Mg CO2/(m2·year)	0.092

. The table also includes the estimated emissions resulting from the operation of the building expressed in CO₂ equivalents per building area.

As mentioned in Section 2.4, the simulation results were compared with actual measurements in the building. Before the model comparison and calibration phase, a preliminary data analysis was performed. At this stage, the monthly energy demand was determined for the three systems already mentioned: heating and ventilation, cooling, and DHW. An example of the actual energy demand over the year by month is shown in Figure 5. In addition, the average outdoor temperature each month is presented.

The next step was the verification of the energy model, which relied on comparing the actual measurements with the results of the calculations on an annual basis. Separately, the annual energy demand for each system and the total consumption for the entire building were determined. Figure 6 shows the results. The differences between simulated and actual values do not exceed 5%. It could be considered that the calculation results are reliable, and the model corresponds to actual conditions. This model became the base model. Subsequent simulations were compared to this variant.

3.2. Energy Retrofit—Variant 1

In variant 1, the energy performance of the building was examined in the case of limited modernization measures, where air-handling units were replaced. The new air-handling units are equipped with countercurrent regenerative heat exchangers, with controllable moisture recovery from exhaust air and adiabatic cooling function. The manufacturer assumes that the seasonal average temperature efficiency of the air handling units exceeds 86%. As in Variant 0, the initial energy demand was determined by the listed systems. The results are summarized in

Table 6. Heat demand calculations after replacing air handling units—variant 1.

Parameter	Heating and Ventilation	Cooling	DHW	Lighting	Total
Useful energy, MWh/year %	176.69	131.46	169.55	-	477.70
	37.0%	27.5%	35.5%	-	100.0%
Final energy, MWh/year %	323.51	55.47	521.69	107.50	1008.18
	32.1%	5.5%	51.7%	10.7%	100.0%
Primary energy, MWh/year %	442.45	166.41	573.86	322.51	1505.23
	29.4%	11.1%	38.1%	21.4%	100.0%

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Similarly, energy indicators were also compiled for the state after the replacement of the ventilation units. As in the previous case, the index of usable, final, and primary energy was determined. In addition, the estimated emissions associated with the generation of energy at this level. The results are shown in

Table 7. Energy performance indicators—variant 1.

Indicator	Value	Percentage Reduction Compared to Variant 0
Useful energy, kWh/(m2·year)	103.4	28.59%
Final energy, kWh/(m2·year)	218.2	21.28%
Primary energy, kWh/(m2·year)	325.8	17.52%
Emission CO2, Mg CO2/(m2·year)	0.078	15.22%

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3.3. Energy Retrofit—Variant 2

In variant 2, calculations were carried out according to the assumptions of variant 1, with an additional upgrade of the installation of supplying water to the premises. The modernization measure includes the implementation of timing and proximity automation and dynamic flow limiters < 2 L/min (sinks) and < 6 L/min (showers). The consumption reduction is assumed to be 60%.

Table 8. Heat demand calculations after replacing air handling units and water equipment—variant 2.

Parameter	Heating and Ventilation	Cooling	DHW	Lighting	Total
Useful energy, MWh/year %	176.69	131.46	67.82	-	375.97
	47.0%	35.0%	18.0%	-	100.0%
Final energy, MWh/year %	323.51	55.47	208.68	107.51	695.17
	46.5%	8.0%	30.0%	15.5%	100.0%
Primary energy, MWh/year %	442.45	166.41	229.55	322.51	1160.91
	38.1%	14.3%	19.8%	27.8%	100.0%

summarizes the results.

Next, energy indicators were also compiled for the condition after the replacement of the ventilation system and DHW system upgrade. The results are shown in

Table 9. Energy performance indicators—variant 2.

Indicator	Value	Percentage Reduction Compared to Variant 0
Useful energy, kWh/(m2·year)	81.4	43.78%
Final energy, kWh/(m2·year)	150.5	45.71%
Primary energy, kWh/(m2·year)	251.3	36.38%
Emission CO2, Mg CO2/(m2·year)	0.065	29.35%

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3.4. Energy Retrofit—Variant 3

Option 3 includes the application of all the measures described in Section 2.3. A detailed description of the activities, the assumed efficiencies, and expected effects are presented in

Table 10. Scope of modernization activities.

System	Modernization
Ventilation	The seasonal average temperature efficiency of the new air handling units will exceed 86%.
Heating	The facility will use radiators (10%) and fan coil units (90%).
Cooling	Chilled water from an air-to-water pump of a three-generation unit will supply the cooling system.
DHW	Timed, touchless automation will be installed with dynamic discharge limiters on the draw-off points. It is assumed water consumption is reduced by 60%.
Electricity	The use of three tri-generators with mechanical power of 60 kW with a system of smooth power distribution between the reversible heat pump. It will allow the generation of 120 MWh of electricity.

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In connection with the replacement of boilers, the efficiency of the facility’s high-temperature central heating system is expected to be 0.74, while the overall coefficient of performance (COP) efficiency of the heating system of fan coil units and the heat pump is 4.19. Assuming that the heating system relies 90% on heat exchange during engine cooling and 10% on heat removal in the flue gas-water heat exchanger, the overall COP efficiency of the heating system is 3.85. The overall efficiency of the heating system is calculated assuming that 90% of the heating load is covered by fan coils and only 10% by the high-temperature cooling system of the engine and the flue gas/water heat exchanger. The efficiency of the cooling system is also expected to increase, with the overall thermal efficiency after the upgrade being 5.0. It is more than double that of the state before the thermal upgrades. The transmission efficiency is 0.96 and has been determined, as in the case of heating systems, based on Polish regulations [31]. It is assumed that 85% of the energy demand is provided by the GAT system. Simultaneously, the rest of the consumption is drawn from the grid. The hotel’s detailed energy requirements are summarized in

Table 11. Heat demand calculations after all retrofit activities—variant 3.

Parameter	Heating and Ventilation	Cooling	DHW	Lighting	Total
Useful energy, MWh/year %	176.69	131.46	67.82	-	375.97
	47.0%	35.0%	18.0%	0.0%	100.0%
Final energy, MWh/year %	91.77	25.88	99.18	107.51	324.34
	28.3%	8.0%	30.6%	33.1%	100.0%
Primary energy, MWh/year %	100.95	28.46	109.10	174.05	412.57
	24.5%	6.9%	26.4%	42.2%	100.0%

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As in the cases above, the results of the energy consumption indicators were compiled, as summarized in

Table 12. Energy performance indicators—variant 3.

Indicator	Value	Percentage Reduction Compared to Variant 0
Useful energy, kWh/(m2·year)	81.4	43.78%
Final energy, kWh/(m2·year)	72.2	73.95%
Primary energy, kWh/(m2·year)	89.3	77.39%
Emission CO2, Mg CO2/(m2·year)	0.019	79.35%

.

3.5. Assessment of the Energy Retrofit

All the results of the calculations presented in Section 3.1, Section 3.2, Section 3.3 and Section 3.4 were summarized and tabulated. The projected effects of usable and final energy consumption are shown below. Figure 7 shows the structure of energy demand, considering such systems as heating and ventilation, cooling, domestic hot water, and lighting.

Figure 8 summarizes the crucial energy indicators calculated for each alternative. In addition, the estimated consumption of natural gas and electricity is also shown. Figure 8a also presents emissions expressed in CO₂ equivalent.

4. Discussion

According to the results, it is noticeable that the highest reduction in demand for usable energy is achieved as a result of replacing the air-handling units in the building. An obsolete ventilation system with a heat recovery module and low heat efficiency at such a significant airflow causes an increase in the cost of air treatment, particularly due to the heating of the ventilation airflow in winter. Replacing the air-handling units and increasing the recovery efficiency for this case reduces the energy demand by less than 50% per year. The use of automation in the domestic water system also proves to be a very effective measure. It allows an annual reduction in consumption of 101.7 MWh, assuming that water consumption is reduced by 60%. This measure is particularly economically beneficial for hotels, where water costs do not influence the room cost. Similarly, this is the case of bathrooms in common areas, for which increased water consumption is a common problem. However, the fundamental upgrade is the replacement of the heat source with a tri-generator, which provides sources not only of electricity, but also of heat and cooling energy. Variant 3, compared to the other solutions, is particularly distinguished by its final energy ratio. It is due to the increased efficiency ratios of the systems and the primary energy ratio. These values are related to the technology used, energy source, and fuel. Due to transmission losses, the primary energy factor for electricity drawn from the grid is much higher than for generation by burning natural gas directly on site. The use of the proposed solution results in a reduction in final energy compared to the second variant by more than 53%, and of primary demand by more than 64%. Concerning the baseline model, the application of the comprehensive retrofit results in a reduction of 293 MWh of usable energy per year, or almost 44%. The measures taken result in a reduction in final demand by practically 75% and primary consumption by 77%, thus, reducing emissions by 337.26 Mg of CO₂ per year. The modernization of the ventilation and DHW system allows for achieving the most significant benefits of reducing energy demand. In each of the variants, there is a reduction in gas consumption, but only the application of comprehensive modernization, variant 3, contributes to a noticeable decrease in the electricity demand. It is due to the above-mentioned electricity production in aggregates on site.

5. Conclusions

The energy performance of the building is an essential topic not only because of environmental aspects, but also because of the operating costs. Ensuring proper operating conditions while keeping the cost of use low is often a complex task that requires the consideration of many concepts. In such situations, designers face some opportunities to reduce heat losses resulting from the construction of the building and operating systems. However, the simplest methods of thermal modernization involving insulating the building or replacing door and window frames, are not always possible. As in the case of the Turowka Hotel, it would be unacceptable to disturb the structure and form of the historic building. Nevertheless, technological progress makes it possible to improve energy efficiency using modern solutions with higher efficiency.

According to the project, the proposed retrofit for the Turówka hotel does not include changes in partitions and woodwork elements. The plan is to replace the current gas boilers with tri-generation units designed to cover the needs of both the central heating system and low-temperature heat-supplying fan coil units on the premises. The chillers also provide the primary cooling source for the air-conditioning system, supported at peak by a free-cooling chiller. The thermo-modernization also includes the introduction of timed automation to reduce heat losses needed for hot water preparation. The ventilation system includes replacing the existing air-handling units with units equipped with counterflow heat exchangers with a seasonal efficiency of more than 87%. As simulation results show, the implementation of the proposed solution reduces emissions by less than 80%, as well as reduces the demand for gas and electricity, which translates into reduced operating costs.

As the energy characteristics performed for the conditions before the retrofit show, the building does not meet current building standards, which translates into costs associated with the use of the hotel. Therefore, technology changes are necessary, and the proposed system should provide indoor comfort conditions with low operating expenses. The question of how the proposed system will perform in reality does not have a clear answer, as the technology used is a new solution implemented in 2020. Unfortunately, due to the epidemiological situation and the periodic closure of hotel facilities, as well as the low number of guests, comparing these values with previous years and assessing the effectiveness of the solution based on actual results will only be possible after the pandemic is over and the hotel is operational. Nevertheless, as analysis shows, the proposed measures should contribute to a decrease in energy consumption and operating costs. As the analyzed case provides, each facility is individual, with its characteristic features. However, the measures in each facility should ensure the desired effect of reducing energy demand. The percentage demand reduction will depend on the initial consumption value, the scope of modernization measures, and the replacement of installations. Only a comprehensive approach will allow effective demand reduction, and the scale depends on the individual characteristics of the object and the solutions used.