Cooling of Air in Outdoor Areas of Human

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1. Introduction

The issue of human thermal comfort in urban outdoor spaces is becoming increasingly important for many cities worldwide, largely due to the combined effects of global climate change and rapid urbanization [1,2,3]. Rising temperatures in outdoor environments affect not only physiological and psychological stress, but also the incidence of human morbidity and mortality [4,5,6].

The urban heat island (UHI) effect is a climatic phenomenon in which the air temperature in an urban area is higher than in the surrounding rural areas. The shape and intensity of the urban heat island are the result of the interaction of many factors [7,8,9,10,11]:

the high heat capacity of the building materials,
the altered structure of thermal radiation,
the limited presence of natural vegetation,
the prevalence of tall buildings and vertical surfaces,
and human activities, such as the use of heating and air conditioning equipment, industrial processes, and transportation.

The above factors and processes result in the accumulation of significant amounts of heat in the urban environment during the day. This heat is then released into the atmosphere at night, resulting in a slower rate of cooling in these areas compared with the surrounding regions. Recorded air temperature differences between the city center and non-urban areas have been observed to be as high as 8–10 K [12]. The UHI effect not only affects the local climate, but also contributes to the occurrence of extreme weather events by increasing the electricity consumption for cooling [13,14]. This increased energy demand, combined with increased greenhouse gas emissions, serves to accelerate the ongoing phenomenon of global warming [15,16].

High temperatures make urban spaces not only uncomfortable for human habitation, but even dangerous [17]. To mitigate the effects of the UHI, city managers are forced to take a number of strategic measures to protect residents from the heat [18]. These can be divided into two groups. The first are natural methods, which include, among others, increasing the area of green infrastructure [19,20,21], the appropriate selection of building materials to reduce heat absorption, and the proper design of urban developments, including shading elements [22,23]. The second group includes artificial methods or improving the energy efficiency of existing energy systems [24,25]. As shown in Table 1, among the available technical cooling systems, the following may be of interest for outdoor use:

the classic compressor unit, due to its popularity and availability on the market, may have a disadvantage due to high operating costs,
adsorption chillers to use heat from the district heating network in summer, but the low availability of this type of equipment can be a problem,
evaporative air conditioners, which are environmentally friendly but require a water supply system,
indirect evaporative cooling due to its low running costs and lack of use of harmful refrigerants; only the low availability of the equipment can be a problem.

The neutralization of the UHI phenomenon is particularly important from the point of view of sustainable development policies and the promotion of sustainable urban environments, with the aim of making cities more resilient to climate change [43,44,45].

Improving the accessibility of public transport, and thus facilitating the creation of interchanges, is a crucial aspect of urban development. Local interchanges are typically located in the city center, surrounded by a variety of roads, pavements, car parks, and buildings. In addition, the presence of vehicles in the interchange area contributes to the overall heat generation due to the heat emitted by their engines or air conditioning systems. These factors combine to create a significant level of thermal discomfort for passengers waiting on interchange platforms for their chosen mode of transport on hot days. In the majority of cases, the only element that serves to mitigate the sensation of heat is the canopy, which provides protection from direct sunlight [22,23]. Nevertheless, remaining in the shade when the air temperature exceeds 30 degrees Celsius is an uncomfortable situation for humans. It is therefore reasonable to consider the implementation of an air-cooling system in the outdoor human habitation zone in such a case.

In the available literature, the authors did not come across similar solutions for air cooling in outdoor human settlements or a methodology for selecting cooling devices. The closest publications are [46,47], where the authors designed and built a prototype bus shelter with a radiation cooling system and evaluated the effectiveness of this system under artificial conditions in a climatic chamber. A detailed analysis based on real climatic conditions in short-stay outdoor areas has not yet been carried out.

The aim of the research presented here is to identify the best available technical system (artificial method) for cooling an outdoor area where people are present, taking into account the energy consumption, environmental impact, investment, and operating costs. As an example of an object with a common problem of excessively high temperatures, places of communication infrastructure are taken. An additional problem for many people can be the significant temperature difference between the outside temperature on the platform of a bus station and the inside temperature of a heavily cooled (air-conditioned) bus.

Given the need to supplement the primary energy demand for cooling in the outdoor zone, it may be advantageous to use solar energy for this purpose. This is based on the assumption that the period of cooling demand coincides with the period of increasing solar radiation intensity.

2. Study Object

2.1. Description of the External Area Under Study

The subject of the study is the local bus station in Rzeszow (Poland). It is the center of local, long-distance, and international transport. An important element of the station, from the point of view of this study, is the platforms, which form the external zone of human habitation. The platforms are arranged along the perimeter of the forecourt, on two opposite sides: north and south. Figure 1 shows the layout of Rzeszow station and the location of the research facility.

The northern platform was chosen as the object of study. The reference area is an area of 144 m² lined with granite slabs, fully roofed, and not limited by walls. The study area is covered from above with frameless photovoltaic modules using glass/glass technology. There are 104 modules installed in the canopy, each with an output of 275 Wp. The rated power of the platform canopy photovoltaic system for STC conditions is 28.6 kWp. Figure 2 shows an actual view of the test installation. Table 2 shows the basic data characterizing the installation.

2.2. Cooling Installation Options

In order to analyze the cooling potential of the external zone under study, 10 variants for the cooling plant were proposed. A description of the variants is presented in Table 3.

Group I options

The first group of plant variants for air cooling in the outdoor area consisted of chilled water systems, generated using a classic compressor unit. The cooling in the form of water at a suitably low temperature is transported through the hydraulic system to the cooling consumers. The final cool receivers are exchangers that cool and then transfer the air directly to the space to be cooled. The cooling receivers are fan cooling units (AS-WL-AC variant; Figure 3). The chilled water generator, in this case a compressor unit, can be powered entirely by electricity from the electricity grid (AS-WL-AC variant) or partly by electricity generated by a photovoltaic installation (AS/PV-WL-AC variant).

Group II options

In the second group of installations, an adsorption chiller was proposed as the chilled water production device. The adsorption chiller produces chilled water mainly using heat (e.g., waste heat from the district heating network). The heat from the district heating network can be produced by the company in cogeneration from the combustion of fossil fuels (variant: AA-PK-WL-AC, AA/PV-PK-WL-AC) or in energy-efficient systems with more than 50% RES or as a combination of CHP and RES (variant: AA-OZE-WL-AC, AA/PV-OZE-WL-AC). The adsorption chiller also requires electricity to operate, which can be drawn from the grid, as in the case of the AA-PK-WL-AC and AA-OZE-WL-AC variants, or from a photovoltaic system, as in the case of the AA/PV-PK-WL-AC and AA/PV-OZE-WL-AC variants. The produced chilled water is transported to the exchangers, which produce and deliver the cooled air to the reference space. The final consumers of the cooling are the fan-coil units. A simplified diagram of an air-cooled system with a chiller unit is shown in Figure 4.

Group III options

A common feature of the installations belonging to Group III was the use of evaporative air conditioning for air cooling, using the natural process of water evaporation. This type of cooling can take place in two ways:

(a). in the form of cooling by indirect evaporation, without changing the humidity of the air—variant PKW-CP-KW, PKW/PV-CP-KW, using a central device producing cool air, transported through ventilation ducts and supplied to the occupied zone through ventilation grilles (Figure 5);
(b). by direct evaporative cooling, adiabatic cooling—variant BKW-CP-KW, BKW/PV-CP-KW, using evaporative air conditioners supplying cool and humidified air through a short duct directly to the occupied zone (Figure 6).

The primary source of cooling for these units is water, while electricity is only required to drive the fan and circulating pump. Due to the source of electricity, two additional variants are proposed:

PKW-CP-KW, BKW-CP-KW—use of grid electricity,
PKW/PV-CP-KW, BKW/PV-CP-KW—use of photovoltaic electricity.

In all the cooling system variants considered in the analysis, it was assumed that the cool air would be distributed throughout the study space by means of fans and diffusers. The role of the cool air is to lower the temperature of the air in the outdoor zone and to create an air curtain.

Table 4 shows the main technical parameters characterizing the equipment adopted.

3. Research Methodology

3.1. Defining the Thermal Comfort Range

3.1.1. Analysis of the Meteorological Data

Data on the outdoor air parameters for the meteorological station Rzeszow-Jasionka (Poland) with geographical coordinates 50°06′ N 22°03′ E, obtained from the Institute of Meteorology and Water Management in Warsaw [48], were used for the analysis. The collected data included both daily and hourly measurements of air parameters, such as the temperature (T, °C), relative humidity (RH, %), and wind speed (w, m/s), recorded between 2005 and 2019. In climatology [49], there is a temperature criterion that distinguishes particularly hot days. A hot day is a day with a maximum daily temperature equal to or higher than 25 °C, while a hot day is a day with a temperature equal to or higher than 30 °C. On the basis of meteorological data [48] on the maximum daily temperature for the period from 2005 to 2019, the months in which hot days occurred were selected. For the Rzeszow-Jasionka meteorological station, these were the months from May to September.

3.1.2. Calculation of the TE Indicator

As the research [50] has shown, a very large number of human thermal climate indices have been proposed over the past 100 years. The indices used vary in their approach depending on the number of variables considered, the rationale used, the evolution of the theory of heat transfer between the body and the atmosphere, and the specific design of the application. As indicated in [50], an example of an index that is considered a universal index for assessing bioclimatic conditions is the Universal Thermal Climate Index (UTCI) [51]. It takes into account the combined effect of meteorological conditions and related human physiological responses. The detailed method of determining the UTCI involves multiple calculations of the human heat balance, which is time-consuming for a large set of meteorological data. The use of a simplified form of the calculation of the UTCI index is also problematic because of the nature and quality of the input data required. While data on air temperature, relative humidity, or even wind speed are readily available, determining the average radiant temperature [52] is a major difficulty. Another index that takes into account human thermal physiology and can be used to assess thermal comfort in cities is the Physiological Equivalent Temperature (PET) [53]. However, as with the UTCI index, it is difficult to obtain a complete set of input data to determine the PET.

In [51], a comparison was made between various thermal sensation indices and the UTCI index value. This comparison showed a high correlation coefficient between the UTCI and most of the other indices. In the case of the indices calculated on the basis of heat balance models, this correlation was as high as 0.975. Interestingly, a very high correlation coefficient (0.98) [51] occurred in the case of the simple Missenard Effective Temperature (TE) index [54]. This index does not require advanced calculations or a large amount of input data. The TE index takes into account commonly available meteorological data, such as air temperature, relative humidity, and wind speed. In order to compare the selected cooling systems and decide which is the most suitable for further experimental research, the TE index was chosen. The calculation of this index does not require advanced calculations and a lot of data and is a common reference for all cooling systems.

The effective temperature index, TE, based on the Missenard formula [54], was used to determine the outdoor thermal comfort zone:

For w < 0.3 m/s:

(1) $T E = T - 0.4 (T - 10) (1 - \frac{R H}{100})$

for w ≥ 0.3 m/s:

(2) $T E = 37 - \frac{37 - T}{0.68 - 0.0014 R H + \frac{1}{1.76 + 1.4 w^{0.75}}} - 0.29 T (1 - \frac{R H}{100})$

The value of the TE index was calculated between 1 June 2012, and 31 August 2019, for 8 years, based on meteorological data [48]. Three summer months were chosen: June, July, and August. Air temperature and humidity were collected from the Rzeszow-Jasionka meteorological station, while the wind speed was reduced to the speed at a height of 1 m [55].

Wind speed depends on the height of the measurement zone above the ground. Wind measurements are taken at a height of 10 m at a weather station. Wind speeds at other heights are calculated using the formula [56,57]:

(3) $w_{Z} = w_{W} \cdot {(\frac{h_{Z}}{h_{W}})}^{Z_{0}}, m / s$

The assumed reference area is the immediate footprint of each of the three bus bays at a height of 2 m. The wind speed for this area was reduced to half the height, i.e., 1 m above the ground surface. The value of Z₀ was chosen based on the aerodynamic roughness of the terrain, as for a city of 100,000–500,000 inhabitants with an average built-up area, with Z₀ = 2 [58].

3.1.3. Thermal Comfort Range

The effective temperature index (TE) was used to determine the thermal comfort, using the Mikhailov scale [59] to categorize human thermal sensations, as shown in Table 5.

A range of 21–22.9 °C was postulated as the optimal temperature for humans in the reference area. For all the hourly events where the TE index reached higher values, the air of the selected research object had to be cooled.

3.2. Calculation of the Cooling Power

3.2.1. Cooling Power Components

The cooling power requirement was calculated based on the assumption that the cooling provided to the study zone Q_CH should balance the total heat gains Q_ZC occurring in the outer zone. The total heat gains Q_ZC consist of variable heat gains (Q_(ZC-Z)), calculated from the instantaneous outdoor air parameters, and fixed gains (Q_(ZC-S)), calculated from the heat sources present in the test installation according to the equation:

(4) $Q_{C H} = \sum Q_{Z C} = Q_{Z C - Z} + \sum Q_{Z C - S}$

3.2.2. Variable Heat Gains

The variable heat gains result from the amount of heat received by the flowing airflow Q(_ZC-Z) and were calculated based on the instantaneous outdoor air parameters using the relationship:

(5) $Q_{Z C - Z} = \dot{m} \cdot ∆ h = \dot{m} \cdot (h_{2} - h_{1}), kW$

The supply air mass flow rate was calculated based on the relationship:

(6) $\dot{m} = \frac{\dot{V}}{ρ}, k g / s$

The supply air volume flow rate was calculated using the formula:

(7) $\dot{V} = F \cdot w_{z}, {m / h}^{3}$

(Assumption: F = 72 m²).

The starting point of the cooling process (P1) was taken from the actual outdoor air parameters [48] occurring during the hours when air cooling was required. The end point of the cooling process (P2) was the air parameters described by the T2 parameter. The value of the T2 parameter was calculated from the transformation of the relationship (2) to the TE index according to the formula:

(8) $T 2 = \frac{T E - 37 + \frac{37}{0.68 - 0.0014 R H + \frac{1}{1.76 + {1.4 w_{z}}^{0.75}}}}{\frac{1}{0.68 - 0.0014 R H + \frac{1}{1.76 + {1.4 w_{z}}^{0.75}}} - 0.29 + 0.0029 R H}, °C$

The end point of the cooling process (P2) was the actual air parameters for which the index value TE = 22 °C, which is the middle value of the range considered comfortable for humans dressed in summer clothing and performing light work.

3.2.3. Permanent Heat Gains

In order to determine the fixed heat gains Q_ZC-S resulting from the heat gains occurring in the area of the designated outdoor zone during the summer period, calculations were performed according to the formula:

(9) $\sum Q_{Z C - S} = Q_{N} + Q_{L} + Q_{P} + Q_{K}, k W$

Heat gain from insolation

The assumed reference area is shaded by the photovoltaic panel structure, so the solar heat gains were ignored:

(10) $Q_{N} = 0, kW$

Heat gains from people

The total heat gain depends on the number of people (No) in the zone and their physical activity and was calculated as:

(11) $Q_{L} = N_{o} \cdot q_{c} \cdot φ_{o}, W$

(Assumptions: N_o = 180 persons, q_c = 174 W/person, φ_o = 0.7).

Heat gains from motor vehicles

Given the characteristics of the chosen test object, it was necessary to take into account the heat gains from the motor vehicles (in this case, buses) located in the immediate vicinity of the chosen occupancy zone. The internal combustion engines of these vehicles release heat to the environment both directly and through exhaust emissions. For the purposes of this study, it was assumed that there could be three buses in the immediate vicinity of the reference area at the same time. Buses with the following technical data [60] were selected for further calculations:

total seating and standing areas: 105,
dimensions: 12.135 × 2.55 × 3.12 m,
engine power: 220 kW at 2200 rpm,
cooling power in passenger compartment: 39 kW,
cooling power at the driver’s seat: 8 kW.

From the point of view of the heat gains generated by a running internal combustion engine located directly next to the reference area, the exhaust loss (Q_ns) and the heat radiation loss to the surroundings (Q_ot) are important. Therefore, the amount of heat transferred to the surroundings was taken as 40% of the primary energy value and calculated according to the formula:

(12) $q_{a} = Q_{w} + Q_{o t}, k W$

(Assumptions: Q_w = 30% of the engine power at 1000 rpm, Qot = 10% of the engine power at 1000 rpm).

Heat gains from motor vehicle engines located immediately adjacent to the reference area were calculated according to the formula:

(13) $Q_{P} = φ_{1} \cdot q_{a} \cdot N_{a}, k W$

(Assumptions: φ₁ = 0.3, N_a = 3).

When calculating the heat gain from operating motor vehicles, the heat emitted by the air conditioning system must also be taken into account. The cooling system removes a certain amount of heat from the conditioned space and gives it back to the environment. For the purpose of calculating the heat balance of the reference area, the heat gains from the running air conditioning in the selected bus were assumed to be equal to the maximum cooling capacity of the air conditioning, as read from the vehicle technical data [60], expressed by the formula:

(14) $Q_{K} = q_{K} \cdot φ_{1} \cdot N_{a}, k W$

3.3. Determination of the Solar Radiation Potential

In order to ascertain the potential for solar radiation at the research facility, the actual electricity yields of the existing photovoltaic installation, which forms the canopy over the outdoor cooling zone, were subjected to analysis. The technical data pertaining to the installation are presented in Section 2.1. The energy produced by the photovoltaic installation was quantified using the energy management system, which enabled remote observation of the installation’s operational status.

In order to fulfil the objectives of this thesis, the daily electricity yields from the three summer months of June, July, and August 2019 were selected for the analysis. Only those days were selected for analysis during which cooling was required, as indicated by an effective temperature index exceeding 22.9 °C.

3.4. Identification of Effects

3.4.1. Energy Effect

The energy effect of the different cooling variants was determined on the basis of the primary, final, and useful energy demand according to the guidelines in the work [61]. For this purpose, the following relationships were used:

annual primary energy demand EP:

(15) $E P = \frac{Q_{p}}{A}, k W h / (m^{2} \cdot r o k)$

annual final energy demand EK:

(16) $E K = \frac{Q_{k}}{A}, k W h / (m^{2} \cdot r o k)$

annual energy demand EU:

(17) $E U = \frac{Q_{u}}{A}, k W h / (m^{2} \cdot r o k)$

The annual primary energy demand Q_p was taken as the annual non-renewable primary energy demand for the cooling system Q(_p,C):

(18) $Q_{p} = Q_{p, C}, k W h / r o k$

(19) $Q_{p, C} = Q_{k, C} \cdot w_{C} + E_{e l, p o m, C} \cdot w_{e l}, k W h / r o k$

The following relationship was used to determine the annual final energy demand for the cooling system:

(20) $Q_{k} = Q_{k, C}, k W h / r o k$

(21) $Q_{k, C} = \frac{Q_{C, n d}}{η_{C, t o t}}, k W h / r o k$

(22) $η_{C, t o t} = S E E R \cdot η_{C, s} \cdot η_{C, d} \cdot η_{C, e}, -$

(23) $S E E R = {S E E R}_{r e f} \cdot (1 + \sum_{i} c_{i}), -$

The coefficient values adopted for the calculation of the energy effect, depending on the installation variant, are shown in Table 6.

3.4.2. Life Cycle Assessment (LCA) Method

The proposed outdoor air-cooling options were compared from an environmental point of view and their environmental impact was assessed. A Life Cycle Assessment (LCA) developed in accordance with standards [62,63] was used for this purpose. The environmental impact of the selected cooling options was assessed using the eco-indicator method. This method distinguishes three main categories of damage:

(1). human health—takes into account factors affecting human health, i.e., climate change, ozone depletion, carcinogenicity, the presence of harmful organic and inorganic substances causing respiratory problems, ionizing radiation. The values of the indicators were calculated on the basis of the number of years lost due to premature death or the number of years lived with the disease, as well as the severity of the disease and the number of cases per year;
(2). ecosystem quality—includes the impact of ecotoxicity, acidification, and land surface transformation;
(3). natural resources—takes into account the damage caused by the extraction of natural resources and fossil fuels, resulting in the necessary surplus energy required to extract the resource again.

The environmental impacts were assessed under the assumption of an egalitarian cultural version and a long-term technological development perspective. The eco-indicator value was calculated for each impact and damage category for each proposed air-cooled plant variant. The non-renewable primary energy demand was used as the functional unit, i.e., taking into account the own demand of each cooling plant variant. A service life of 25 years was assumed.

It should be emphasized that the environmental analysis only covers the operating phase of the assumed air-cooled plant variants. The manufacturing phase of the equipment and the decommissioning phase of the plant were not included in this study. For the calculation of the environmental impact, unit environmental impact coefficients were applied in the form of an eco-indicator related to the GJ of useful energy consumed. The values of these indicators are shown in Table 7.

3.4.3. Life Cycle Cost (LCC) Method

To analyze the cooling system variants for the research facility, we used the Life Cycle Cost (LCC) method [63,64]. This method compares the total investment and operating costs of different design variants throughout the product life cycle, allowing the optimal solution to be selected. In this study, the following formula was used for the LCC analysis [66,67]:

(24) $L C C = K_{N} + \sum_{n = 1}^{t} \frac{K_{P}}{{(1 + s)}^{n}}, PLN$

This method involves a discounted cash flow analysis and takes into account cost elements such as energy supply, maintenance, upkeep, and price volatility over the operating period. Therefore, for each cooling plant variant analyzed in the study, the following were determined:

investment costs;
costs of ownership (maintenance, servicing, cleaning, possible repair costs, operating costs related to electricity consumption, district heating, and mains water);
increases in the prices of energy carriers;
lifetime of the investment.

4. Research Findings

4.1. Thermal Comfort Range

Thermal Comfort Index

To illustrate the frequency of cases where the TE value exceeded the thermal comfort threshold (TE > 22.9 °C), Figure 7 shows the frequency of hourly occurrences. For comparison, a TE value was calculated for the hourly air parameters based on a typical meteorological year, TRM. This value was derived from a database of typical meteorological years provided by the Ministry of Investment and Development [68], which was developed for energy calculations in the building industry.

The TE value calculated for the actual data of the period analyzed (2012–2019) exceeded the values calculated for the TRM by an average of 2.1 times.

This was due to the fact that the TRM is, by definition, a year representing long-term average conditions. Given the significant underestimation of the prevalence of unfavorable human climatic conditions during the summer heatwave, the use of the TRM to assess thermal comfort is questionable. An accurate calculation of the energy demand of ventilation and air conditioning systems can only be achieved by using the most recent climate data. This, in turn, has a significant impact on the cost-effectiveness of investments and the efficiency of these systems during operation.

In the context of the outdoor zone studied, the need for cooling occurs during the three summer months of June, July, and August. In the period considered (2012–2019), the number of hours per season when cooling is required ranges from 332 to 537. This is typically a few hours per day. Appendix A includes graphs showing the value of the effective temperature index (TE) calculated for the consecutive hours of the summer season based on a typical meteorological year (TRM). For comparison, the same calculations were performed based on actual meteorological data [48] from an analogous period of eight years in the period 2012–2019. The horizontal dotted line in each graph indicates the range of human thermal comfort according to the Mikhailov scale [59].

It is important to note, however, that the number of such hours is likely to increase significantly in the coming years as a result of climate change. This confirms the need to develop systems to cool the air in occupied outdoor spaces.

4.2. Cooling Power Requirement

The variable heat gains (Q_ZC-Z) were determined based on the meteorological data occurring in the area of the research facility and the assumed thermal comfort temperature. The calculations were carried out according to the methodology described in Section 3.2.2 of this document. The results of the calculations are shown in Figure 8.

The instantaneous cooling demand, taking into account only the data on air parameters in the area of the research facility and the assumed maximum thermal comfort temperature, was in the range of 0–50 kW during the analyzed season. However, the cooling load for the selected zone was significantly influenced by additional permanent heat gains (QZC-S) generated by people and running vehicle engines located directly in the outdoor zone, calculated on the basis of a heat balance (point 3.2.3).

Table 8 shows the results of the heat balance calculations for the local station research facility during the summer, at approximately 15:00.

The total cooling demand required to achieve thermal comfort in the outdoor zone under study is the sum of the variable heat gains Q_ZC-Z, calculated on the basis of the air parameters, and the fixed heat gains Q_ZC-S, calculated on the basis of the heat balance, equal to 94 kW. The total cooling demand QCH for the reference area is shown in the graph in Figure 8.

For the period analyzed, the vast majority of the results were less than 130 kW. However, the maximum calculated value was 144 kW, which forms the basis for the selection of the cooling system components.

4.3. Electricity Yield from PV Panels

Figure 9 illustrates the electricity yields of the existing photovoltaic system installed at the research facility. The actual daily electricity yields are specific to the three summer months. The data pertain to the period between June and August 2019. Furthermore, the same graph (Figure 9) illustrates the maximum daily air temperatures recorded during this period.

The minimum daily electricity yield from the existing PV installation for the period of June–August 2019 was 15 kWh, while the maximum was 152 kWh. Considering only days with a minimum of one hour of cooling, the minimum PV electricity yield was 47 kWh. By analyzing the data in Figure 9, it can be seen that, in most cases, the PV electricity yields follow a similar trend to the maximum daily air temperature. This confirms the existence of synergies between the solar irradiance and the cooling demand.

An analysis of the potential of the existing photovoltaic installation in terms of cooling generation by the proposed systems (Figure 10) showed that the highest electricity demand was generated by the compressor chiller and adsorption chiller variants. It can be seen that the existing photovoltaic installation was able to cover 42% and 43% of the daily electricity demand for these variants, respectively. The remaining installation concepts, based on evaporative cooling, required a much lower amount of electricity for cooling. It was found that the existing photovoltaic installation was able to cover up to 84% of the total electricity demand for the indirect evaporative cooling. A comparison of the yields of the existing PV plant with the electricity demand for the different options is included in Appendix B.

The PV yields analyzed refer to PV modules installed in 2018, with an electrical output of 132 Wp from 1 m² of surface area. Today (2024), PV modules with more than 60% more power are available on the market (218 Wp from 1 m² surface) [69]. This means that more of the electricity needed for cooling can be provided by a PV installation with a similar surface area.

4.4. Comparative Analysis of the Cooling Options

4.4.1. Energy Effect

The energy impact analysis of the selected outdoor air-cooling options allowed the seasonal final energy demand (FED) and primary energy (PED) to be calculated. The values of the EP and EK indices are presented in the accompanying diagrams (Figure 11 and Figure 12). The calculations were carried out according to the methodology presented in Section 3.4.1.

The value of the primary energy indicator EP for each variant was divided into two parts:

EP (main)—calculated on the basis of the primary final energy demand required to produce cooling by the refrigeration unit in question,
EP (auxiliary)—calculated based on the amount of auxiliary electricity required for the operation of the proposed refrigeration plant, e.g., to power the chilled water circulating pumps, to power the final cooling consumers or the cooling system of the primary chiller.

The lowest demand for non-renewable primary energy is generated by the evaporative cooling variants (PKW-CP-KW, PKW/PV-CP-KW, BKW-CP-KW, BKW/PV-CP-KW). In these systems, primary energy is used only as auxiliary power, while the main source of cooling is water. The primary energy indicator EP is 106 kWh/(m²·year) for the variant using indirect evaporative cooling and 111 kWh/(m²·year) for the variant using evaporative air conditioning. If the use of electricity from an existing photovoltaic system is taken into account, the index value for both variants drops by more than 80%. A higher EP value of 246 kWh/(m²·year) is shown by the variant where the cooling source is a classic compressor chiller (AS-WL-AC) supplied with electricity from the grid. The energy produced by the photovoltaic system is able to completely cover the auxiliary electricity demand (necessary for the operation of the circulating pump in the chilled water system and the fan chillers) and part of the energy required for the production of cooling, reducing the EP value by 42%.

The variants with an adsorption chiller as the primary chiller were the worst performers in terms of energy. Assuming that the heat is obtained from the combustion of fossil fuels and the electricity from the grid, the variant AA-PK-WL-AC obtained the highest EP value compared with the other variants: EP = 814 kWh/(m²·year). On the other hand, if we assume that the heat is obtained from an efficient district heating system—variant AA-OZE-WL-AC—the rate of non-renewable primary energy decreased to 555 kWh/(m²·year). The production of electricity from the installation of photovoltaic cells in both cases of installation with the adsorption chiller AA/PV-PK-WL-AC, AA/PV-OZE-WL-AC reduced the EP value by 43%.

The final energy indicator EK also reached the lowest value and at the same time was the most favorable for variants from Group III, based on evaporative cooling (20 kWh/(m²·year)—variant PKW-CP-KW, PKW/PV-CP-KW and 19 kWh/(m²·year)—variant BKW-CP-KW and BKW/PV). A higher final energy rate was demonstrated by an installation with a compressor unit (AS-WL-AC, AS/PV-WL-AC): EP = 84 kWh/(m²·year). A more than six times higher final energy rate, EK = 519 kWh/(m²·year), in relation to an installation with a compressor unit was calculated for the variants with the adsorption chiller AA-PK-WL-AC, AA/PV-PK-WL-AC, AA-OZE-WL-AC, AA/PV-OZE-WL-AC.

The ranking of the different variants of the outdoor air-cooling plant by the final energy EK ratios is similar to the ranking by the non-renewable primary energy EP ratios, as shown in Figure 12.

The value of the annual EU useful energy demand is the same for all the systems and is 350 kWh/(m²·year).

The analysis showed that the evaporative cooling variants (Group III) are the most energy-efficient solutions. In terms of the final energy indicator EK, the BKW-CP-KW, BKW/PV-CP-KW variant—installation of evaporative air conditioners—was the most favorable. On the other hand, in terms of the use of non-renewable primary energy (primary energy indicator EP), the variant with the use of an indirect evaporative cooling unit extended with a PKW/PV-CP-KW photovoltaic system was the most effective.

4.4.2. Environmental Effect

For the proposed variants of outdoor air-cooling installations, the indicator values of each impact category were calculated and then grouped into damage categories. Figure 13 illustrates the impact category index values of the installations that influence the eco-indicator value.

Fossil fuel consumption, inorganic compounds, and carcinogenicity, as well as climate change and ecotoxicity, are of primary importance when calculating the summed eco-indicator values for the variants analyzed. The results obtained indicate a minimal negative environmental impact for the Group III variants with evaporative cooling. This is due to the fact that these systems use a small amount of electricity and the natural refrigerant of water to produce cooling. The most negative environmental impact is generated by the variants with adsorption cooling, which use district heat from fossil fuel combustion (112,346 Pt) to produce cooling. If it is assumed that the district heating is produced by a company using energy-efficient systems (RES share above 50% or a combination of CHP and RES), as in the case of the AA-OZE-WL-AC variant, the total value of the ECO decreases by about 30% (amounting to 70,389.88 Pt). Taking into account the partial coverage of the electricity demand by the photovoltaic installation for the variants based on adsorption cooling, we reduce the value of the indicator by 11%, variant AA/PV-PK-WL-AC, and 15%, variant AA/PV-OZE-WL-AC. The cooling system using a compressor chiller—AS-WL-AC variant (28,471 Pt), which produces cooling entirely using grid electricity— also has a high environmental impact. The use of a photovoltaic system, as foreseen with the AS/PV-WL-AC variant, reduces the value of the negative environmental impact of this variant by 42%.

The results show that for all the variants considered, the impacts of organic compounds, ionizing radiation, ozone depletion, and mineral resource consumption are negligible in the final values of the indicator. Figure 14 shows how the eco-indicator values of the individual damage categories change for the air-cooling plant variants studied.

The impact of the proposed air-cooling options on human health and natural resources can be seen when they are considered in the context of the wider damage they cause. The impacts on the ecosystem quality are minimal. Human health is most affected by inorganic compounds and carcinogens, while climate change has a lesser impact. The main environmental problem is the extraction of fossil fuels.

A summary of the results shows that the operation of the systems proposed in Group III, based on evaporative cooling and using electricity from PV systems, is the most environmentally beneficial. This is shown by the results for the PKW/PV-CP-KW variant (1948 Pt) and the BKW/PV-CP-KW variant (2427 Pt). It is important to note that the analysis presented here concerns only the operation of the proposed installation variants, without taking into account the production of the equipment and its subsequent dismantling and final disposal. In such a scenario, the eco-indicator value increases, indicating a greater environmental impact.

4.4.3. Economic Impact

The economic analysis of the proposed variants for cooling the air in the outdoor zone was conducted in accordance with the Life Cycle Cost methodology, as detailed in Section 3.2.3. The calculations were performed using the assumptions outlined in Table 9.

The unit prices of the utilities and their quantities over the life of the installation are shown in Table 10.

The results of the life-cycle cost analysis showed large discrepancies between the different variants of the outdoor air-cooling system. The LCC values, calculated as the sum of the acquisition and operating costs, are shown in Figure 15.

The BKW/PV-CP-KW variant—an installation with direct evaporative cooling and the use of photovoltaics (LCC = €55,539)—had the lowest LCC and thus the best economic efficiency. The absence of photovoltaics increases the total life-cycle costs of this installation by 21% (BKW-CP-KW variant). The compressor chiller variant (AS/PV-WL-AC) comes next in the economic balance, with an LCC of €226,068 when combined with the PV system. The system with indirect evaporative air cooling has similar life-cycle costs: PKW-CP-KW-without the use of a PV system, €274,729; and PKW/PV-CP-KW–extended with PV cells, €246,907. The variants using adsorption cooling had the least favorable total cost ratios, with estimated costs of around €900,000 per variant. Both the initial investment and subsequent running costs are significantly higher than for the other variants. The installation of a photovoltaic system had a positive effect on the overall life-cycle cost (LCC) result, reducing its value for each variant of the proposed installations. It is also worth noting that the variant with a compressor unit (AS-WL-AC) has a significant share of the holding costs over the life cycle of the installation, amounting to 77% of the total LCC value.

The results of the analysis show that the BKW/PV-CP-KW variant, which uses direct evaporative cooling with evaporative air conditioners and a photovoltaic system, is the most economically advantageous solution.

5. Conclusions

Based on the research conducted, the following was concluded:

(1). For the study outdoor zone, the need for cooling occurs during the three summer months of June, July, and August. In the period analyzed (years 2012–2019), the number of hours per season when cooling is needed ranges from 332 to 537. This is usually a few hours per day. However, it should be noted that the number of such hourly occurrences is likely to increase significantly in the coming years due to climate change. This confirms the need to develop systems to cool the air in outdoor areas of human habitation.
(2). The additional sources of heat gain exert a considerable influence on the maximum cooling load, which serves as the foundation for the selection of cooling plant components at the selected research facility. These sources account for 65% of the total cooling demand as calculated in the overall heat balance. These are the heat gains associated with the utilization of the outdoor zone.
(3). The most favorable solutions from an energy point of view are those that use evaporative cooling. In terms of the final energy indicator EK, the BKW-CP-KW and BKW/PV-CP-KW evaporative cooling variants were the most advantageous. However, in terms of the use of non-renewable primary energy (primary energy indicator EP), the variant with an indirect evaporative cooling unit extended with a PKW/PV-CP-KW photovoltaic system proved to be the most effective.
(4). From the point of view of environmental impact, the most favorable solutions are those based on evaporative cooling-and using electricity from PV systems: the PKW/PV-CP-KW variant: 1948 Pt and the BKW/PV-CP-KW variant: 2427 Pt. It should be stressed that the analysis concerns only the operation of the proposed system variants themselves, without taking into account the manufacture of the equipment and its dismantling and final disposal.
(5). An analysis of investment and operating costs showed that the BKW/PV-CP-KW cooling system variant, based on direct evaporative cooling using evaporative air conditioners and a photovoltaic system, had the lowest total costs.
(6). The analysis is based on the TE indicator, which does not take into account the temperature of reflected radiation. Taking this factor into account as an additional heat gain will increase the cooling demand and extend the operating time of the cooling system. This will be important in the context of the results of the energy, economic and environmental analysis, but will not change the ranking in terms of choosing the preferred cooling system variant.

As a result, the following final conclusions have been drawn:

Solar energy can be used to cool outdoor zones in Poland during the summer.
The most energy efficient, cost-effective, and environmentally friendly cooling solution for the outdoor zone is evaporative cooling using photovoltaics.
It is recommended that an evaporative air-conditioning system, based on direct evaporative cooling and cooperating with a photovoltaic system, should be installed at the adopted research facility for the purpose of cooling the air.
The photovoltaic system can provide 81% of the electricity for the recommended cooling system. Technological advances in photovoltaic cells could increase the proportion of electricity from PV systems used for outdoor cooling.

Author Contributions

Conceptualization, E.B., R.S. and B.B.; methodology, R.S. and E.B.; software, E.B. and B.B.; validation, E.B.; formal analysis, R.S.; investigation, E.B.; resources, E.B., R.S. and B.B.; data curation, E.B.; writing—original draft preparation, E.B.; writing—review and editing, R.S. and B.B.; visualization, R.S. and E.B.; supervision, R.S.; funding acquisition, E.B. and B.B. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Nomenclature

A	study area (m²)
c_i	correction factor depending on the cooling system (-)
E_el,pom,C	annual support final energy demand for the cooling system (kWh year⁻¹)
EK	annual final energy demand indicator (kWh m⁻² year⁻¹)
EP	annual primary energy demand indicator (kWh m⁻² year⁻¹)
EU	annual usable energy demand indicator (kWh m⁻² year⁻¹)
EER	energy efficiency ratio (-)
F	horizontal airflow area (m²)
H	height of the study area (m)
h_w	height of the wind meter measurement (m)
h_Z	height under study Z (m)
K_N	capital costs (euro)
K_P	ownership, operating costs (euro)
L	length of the study area (m)
n	lifetime of the installation (year)
N	number of photovoltaic modules (number)
N_a	number of buses (number)
N_o	number of people staying in study area (-)
P_j	unit power of the photovoltaic cell (W)
s	discount rate (%)
q	specific sensible heat (W person⁻¹)
q_A	unit heat gains from running the bus engine (W)
q_K	unit heat gains from running the bus air conditioning (W)
Q_CH	cooling power (kW)
Q_C,nd	annual utility energy demand for cooling (kWh year⁻¹)
Q_K	heat gains from the air conditioning equipment in motor vehicles (kW)
Q_k	annual demand for non-renewable final energy supplied for technical systems (kWh year⁻¹)
Q_k,C	annual final energy demand for the cooling system (kWh year⁻¹)
Q_L	heat gains from people (kWh)
Q_N	heat gains from sunlight (kWh)
Q_ot	radiative heat loss from the vehicle engine to the environment (W)
Q_P	heat gains from motor vehicles (kWh)
Q_p	annual primary energy demand (kWh year⁻¹)
Q_u	annual useful energy demand (kWh year⁻¹)
Q_w	amount of heat removed with exhaust gases (W)
Q_ZC	total heat gains for the research facility (kWh)
Q_ZC-S	constant heat gains calculated on basis of heat balance (kWh)
Q_ZC-Z	variable heat gains calculated on basis of heat balance (kWh)
RH	relative humidity (%)
S	width of the study area (m)
s	discount rate (%)
SEER	average seasonal coefficient of energy efficiency of cooling production (-)
SEER_ref	reference average coefficient of energy efficiency of cold production (-)
T	air temperature (°C)
T2	real air temperature to be reached at the cooling end point (°C)
TE	effective temperature (°C)
V	volume of the study object (m³)
w	wind velocity (m s⁻¹)
w_c	coefficient of non-renewable primary energy input for the generation and delivery of the energy carrier or energy for the cooling system (-)
w_el	coefficient of input of non-renewable primary energy for the generation and supply of electricity, specific for the annual auxiliary energy demand of the cooling system (-)
w_w	wind velocity at wind meter height (m s⁻¹)
w_Z	wind velocity at height Z (m s⁻¹)
Z ₀	aerodynamic roughness coefficient (-)
$\dot{m}$	mass flow rate (kg s⁻¹)
$\dot{V}$	volume flow rate (m³ s⁻¹)
Greek Symbols
η_C,d	seasonal average efficiency of cooling distribution from cooling source to the cooled area (-)
η_C,e	average seasonal efficiency of control and use of cooling in the cooled area (-)
η_C,s	seasonal average cooling storage efficiency (-)
η_C,tot	seasonal average total efficiency of the cooling system (-)
φ_o	occupancy simultaneity factor in the cooling zone (-)
φ ₁	coefficient considering the contribution of the vehicle’s surface area to heat transfer to the cooling zone (-)
ϴ	length of the period considered (year)
Abbreviations
AA	adsorption chiller
AA-OZE-WL-AC	a cooling system consisting of an adsorption chiller, using district heat from energy-efficient systems, a share of RES above 50%, or a combination of CHP and RES, a chilled-water installation, and fan-based chillers.
AA-PK-WL-AC	a cooling system consisting of an adsorption chiller, using district heat from cogeneration–fossil fuels, a chilled water installation, and fan cooling units
AA/PV-OZE-WL-AC	a cooling system consisting of an adsorption chiller, using district heat from energy-efficient systems with an RES share of more than 50%, or a combination of CHP and RES, a chilled water installation, and fan-based chillers, combined with a photovoltaic installation
AA/PV-PK-WL-AC	a cooling system consisting of an adsorption chiller, using district heat from cogeneration–fossil fuels, a chilled water installation, and fan-cooling units, cooperating with a photovoltaic installation
AC	fan-cooling apparatus
AS	compressor chiller
AS/PV-WL-AC	a cooling system comprising a compressor chiller, chilled water installation, and fan-cooling units, combined with a photovoltaic installation
AS-WL-AC	a cooling system consisting of a compressor chiller, a chilled water installation, and fan cooling units
BKW	indirect evaporative air conditioners (local units)
BKW-CP-KW	a cooling system consisting of indirect evaporative air conditioners (local units), short ventilation ducts, and supply air vents
BKW/PV-CP-KW	a cooling system consisting of indirect evaporative air conditioners (local units), short ventilation ducts, and air vents, combined with a photovoltaic installation
CHP	combined heat and power
CP	cool air distribution
DEC	direct evaporative cooling
EC	heat energy
IEC	indirect evaporative cooling
IW	chilled water system
KW	air diffuser
LCA	life-cycle assessment (Pt)
LCC	life-cycle cost (euro)
OZE	renewable energy sources
P1	starting point of the cooling process
P2	end point of the cooling process
PKW	indirect evaporative air conditioner (central unit)
PKW-CP-KW	a cooling system consisting of an indirect evaporative air conditioner (central unit), ventilation ducts, and air vents
PKW/PV-CP-KW	a cooling system comprising an indirect evaporative air conditioner (central unit), ventilation ducts, and air vents, combined with a photovoltaic installation
PV	photovoltaic cells
SEN	electricity grid
STC	standard test cell
TRM	typical meteorological year
UHI	urban heat island
VRF	variable refrigerant flow
VRV	variable refrigerant volume

Footnotes

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Figures and Tables

Figure 1. Site plan of the Rzeszow local bus station (a) and the top view and vertical cross-section of the research facility (b).

Figure 2. Rzeszow local train station—north shelter.

Figure 3. Diagram of the air-cooling system proposed in the AS-WL-AC, AS/PV-WL-AC variant.

Figure 4. Diagram of the air-cooling system proposed in variants AA-PK-WL-AC, AA/PV-PK-WL-AC, AA-OZE-WL-AC, AA/PV-OZE-WL-AC.

Figure 5. Diagram of the air-cooling plant proposed in the PKW-CP-KW, PKW/PV-CP-KW variant.

Figure 6. Diagram of the air-cooling plant proposed for BKW-CP-KW, BKW/PV-CP-KW variant.

Figure 7. Frequency of episodes when TE exceeded 22.9 °C by year [48].

Figure 8. Total cooling demand QCH for the reference area.

Figure 9. Electricity yield from an existing photovoltaic installation.

Figure 10. Degree of coverage of energy needs from PV.

Figure 11. EP values for the different alternatives.

Figure 12. EP, EK, and EU values for the different options.

Figure 13. Comparison of the E-indicators of the different impact categories for the analyzed options.

Figure 14. Comparison of the eco-indicators of the different damage categories for the analyzed options.

Figure 15. The value of the LLC index for the different options.

Table 1

Feasibility of existing air-cooling solutions for outdoor cooling.

Artificial Cooling Method	Disadvantages	Advantages
classic split compressor air conditioner	low unit cooling capacity in relation to open spaces, high electricity consumption [26], presence of harmful refrigerant [27]	easy installation and simple operation, high availability of devices
precision air conditioning cabinet	high investment cost, high precision in maintaining the required air parameters, which is not significant in the case of open spaces [28,29], presence of harmful refrigerant [27]	no advantages for outdoor areas
rooftop compressor air conditioner	high electricity consumption [30], presence of harmful refrigerant	can be used for large areas [31], easy installation
VRF (VRV) system	high electricity consumption, but less than the classic split system [32,33], presence of harmful refrigerant [27]	no advantages for outdoor areas
compressor chilled water systems	advanced installation, high energy consumption, presence of harmful refrigerant	possibility of using buffer tanks, limiting the consumption of electricity necessary for cold production [34], small size of installation
sorption (absorption or adsorption) cooling units	high investment cost [35], large dimensions, low availability on the market	possibility of using district heating in the summer [36]
evaporative air conditioner (DEC)	efficiency dependent on climatic conditions (highest efficiency in case of hot dry air) [37], possibility of microbiological contamination [38], necessity of water supply to the device, efficiency dependent on climatic conditions (highest efficiency in case of hot dry air) [37]	refrigerant is water [39], low operating cost, high reliability, easy installation and operation
adiabatic cooling in ventilation units	complex structure of the device, possibility of microbiological contamination [40], necessity of water supply	environmentally friendly (the refrigerant is water) [39], low electricity consumption compared with compressor units
indirect evaporative cooling (IEC)	necessity of supplying water to the device, large dimensions	refrigerant is water, no direct contact with water of the cooled air [41], low operating costs [42], high failure-free operation, simple construction

Table 2

Basic data on the research object.

Element	Symbol	Unit	Value
Length	L	m	36
Width	S	m	4
Height	H	m	2
Surface	A	m²	144
Volume	V	m³	288
Number of photovoltaic modules	N	-	104
Dimensions of photovoltaic modules	-	m	2.135 × 0.975
Unit power of photovoltaic modules	Pj	W	275
Number of people in the reference area	N_o	-	126

Table 3

Summary of proposed air-cooling plant options.

Group No.	Symbol of the Variant	Energy Supply	Production of Cooling	Cooling Carrier	Cooling Receivers
I	AS-WL-AC	SEN	compressor chiller	chilled water	fan-cooling apparatus
I	AS/PV-WL-AC	SEN/PV	compressor chiller	chilled water	fan-cooling apparatus
II	AA-PK-WL-AC	district heat from cogeneration—fossil fuels/SEN	adsorption chiller	chilled water	fan-cooling apparatus
	AA/PV-PK-WL-AC	district heat from cogeneration—fossil fuels/SEN/PV	adsorption chiller	chilled water	fan-cooling apparatus
	AA-OZE-WL-AC	district heat from energy-efficient systems with an RES share of more than 50%, or a combination of CHP and RES/SEN	adsorption chiller	chilled water	fan-cooling apparatus
	AA/PV-OZE-WL-AC	district heat from energy-efficient systems with an RES share of more than 50%, or a combination of CHP and RES/SEN/PV	adsorption chiller	chilled water	fan-cooling apparatus
III	PKW-CP-KW	water/SEN	indirect evaporative cooling	cool air	air diffuser
	PKW/PV-CP-KW	water/SEN/PV	indirect evaporative cooling	cool air	air diffuser
	BKW-CP-KW	water/SEN	direct evaporative cooling	cool air	air diffuser
	BKW/PV-CP-KW	water/SEN/PV	direct evaporative cooling	cool air	air diffuser

Table 4

Technical parameters of the equipment adopted in the 10 cooling plant variants analyzed.

Device	Technical Data
PV module	power: 275 Wp.
compressor chiller	nominal cooling capacity: 162 kW, electricity consumption: 66.1 kW,EER = 2.48.
fan-cooling apparatus	nominal cooling capacity: 21.8 kW, air flow range: 2000–4200 m³/h,electricity consumption: 550 W,
adsorption chiller	cooling capacity: 75 kW,electricity consumption: 1543 W,EER up to 0.65.
indirect evaporative air conditioner (central unit)	air flow: 23,040 m³/hnominal cooling capacity: 160 kW, water consumption: 423 L/h, electricity consumption: 11.8 kW.
indirect evaporative air conditioners (local units)	nominal cooling capacity: 18.4 kW, water consumption: 70 L/h, electricity consumption: 13.5 kW.

Table 5

Mikhailov scale [59].

TE (°C)	Thermal Sensation
<1.0	very cold
1.0–8.9	cold
9.0–16.9	chilly
17.0–20.9	refreshingly
21.0–22.9	comfortably
23.0–26.9	warm

Table 6

Summary of the adopted coefficients for energy effect calculations [61].

Group No.	Symbol of the Variant	SEER_ref[-]	C_i [-]	η_C,s [-]	η_C,d [-]	η_C,e[-]	at_c [-]	at_el[-]
I	AS-WL-AC	4	0.1	1	0.98	0.96	2.5	2.5
I	AS/PV-WL-AC	4	0.1	1	0.98	0.96	2.5	0/2.5
II	AA-PK-WL-AC	0.65	0.1	1	0.98	0.96	1.1	2.5
	AA/PV-PK-WL-AC	0.65	0.1	1	0.98	0.96	1.1	0/2.5
	AA-OZE-WL-AC	0.65	0.1	1	0.98	0.96	0.6	2.5
	AA/PV-OZE-WL-AC	0.65	0.1	1	0.98	0.96	0.6	0/2.5
III	PKW-CP-KW	13.56	0.5	1	0.9	0.96	0	2.5
	PKW/PV-CP-KW	13.56	0.5	1	0.9	0.96	0	0/2.5
	BKW-CP-KW	12.27	0.5	1	1	1	0	2.5
	BKW/PV-CP-KW	12.27	0.5	1	1	1	0	0

Table 7

Coefficients used in the calculation of the E-indicators of the impact category and the injury category [64,65].

Impact Category-E-Indicator, EkW, Pt/GJ			Damage Category-E-Indicator, EkW, Pt/GJ
	Electricity-SEN	District heating		Electricity-SEN	District heating
Carcinogenicity of the substance	49.445	12.862	Human health	130.806	36.186
ChUO-Organic compounds	0.014	0.006
ChUO-Inorganic compounds	51.524	14.166
Climate change	29.738	9.128
Ionizing radiation	0.039	0.011
Depletion of the ozone layer	0.045	0.013
Ecotoxicity	5.938	1.549	Quality of the ecosystem	9.090	2.461
Acidification	1.981	0.576
Land use	1.171	0.335
Mineral consumption	1.365	0.361	Natural resources	83.001	29.081
Fossil fuel consumption	81.636	28.721	Natural resources	83.001	29.081
Total	222.897	67.728	Total	222.897	67.728

Table 8

Results of the fixed heat gain calculations Q_ZC-S for the test facility.

Element	Symbol	Unit	Value
Heat gain from insolation	Q_N	W	-
Human heat gain for the reference area	Q_L	kW	22
Gains from running mechanical engines of vehicles immediately adjacent to the reference area (including running air conditioning in the vehicle)	Q_P	kW	72
Constant heat gains	*Q_ZC-S*	kW	94

Table 9

Summary of the assumptions used to calculate the economic effect.

A	Q_CH	n	ϴ	s
144 m²	68,223 kWh year⁻¹	490 h	25 year	5%

Table 10

Unit prices of the utilities and their quantities during the operation of the installation.

Group No.	Symbol of the Variant	Demand for Energy Carriers			Price of Energy Carriers
		Electricity	Heat	Water	Electricity	Heat	Water/Sewage
		[kWh year⁻¹]	[kWh year⁻¹]	[m³ year⁻¹]	[EUR kWh⁻¹]	[EUR GJ⁻¹]	[EUR m⁻³]
I	AS-WL-AC	14,192	0	0	0.21	-	-
I	AS/PV-WL-AC	8255	0	0		-	-
II	AA-PK-WL-AC	14,017	101,421	0		26.67	-
	AA/PV-PK-WL-AC	8056	101,421	0
	AA-OZE-WL-AC	14,017	101,421	0
	AA/PV-OZE-WL-AC	8056	101,421	0
III	PKW-CP-KW	6080	0	205		-	2.23
	PKW/PV-CP-KW	971	0	205
	BKW-CP-KW	6413	0	309
	BKW/PV-CP-KW	1210	0	309

Appendix A

Figure 15. The value of the LLC index for the different options.

Appendix B

Date	PV Yields Whole Study Area	Electricity Demand	PV Electricity Demand Coverage	Electricity Demand	PV Electricity Demand Coverage	Electricity Demand	PV Electricity Demand Coverage	Electricity Demand	PV Electricity Demand Coverage
		AS/PV-WL-AC		AA/PV-PK-WL-AC, AA/PV-OZE-WL-AC		PKW/PV-CP-KW		BKW/PV-CP-KW
	[kWh]	[kWh]	[kWh]	[kWh]	[kWh]	[kWh]	[kWh]	[kWh]	[kWh]
2 June 2019	135.98	83.07	52.90	88.53	47.45	38.4	97.58	40.5	95.48
3 June 2019	149.72	197.71	−47.99	206.57	−56.85	89.6	60.12	94.5	55.22
4 June 2019	140.80	201.65	−60.85	206.57	−65.77	89.6	51.20	94.5	46.30
7 June 2019	119.09	139.70	−20.60	147.55	−28.46	64	55.09	67.5	51.59
8 June 2019	143.88	316.49	−172.60	324.61	−180.73	140.8	3.08	148.5	−4.62
9 June 2019	95.72	82.81	12.91	88.53	7.19	38.4	57.32	40.5	55.22
10 June 2019	149.95	372.73	−222.78	354.12	−204.17	153.6	−3.65	162	−12.05
11 June 2019	130.43	337.72	−207.29	324.61	−194.18	140.8	−10.37	148.5	−18.07
12 June 2019	143.92	368.02	−224.09	354.12	−210.20	153.6	−9.68	162	−18.08
13 June 2019	148.43	435.35	−286.91	413.14	−264.71	179.2	−30.77	189	−40.57
14 June 2019	133.66	441.62	−307.97	442.65	−308.99	192	−58.34	202.5	−68.84
15 June 2019	144.33	459.16	−314.84	442.65	−298.32	192	−47.67	202.5	−58.17
16 June 2019	133.83	308.83	−175.00	295.1	−161.27	128	5.83	135	−1.17
18 June 2019	99.60	27.47	72.13	29.51	70.09	12.8	86.80	13.5	86.10
19 June 2019	86.36	280.69	−194.32	295.1	−208.74	128	−41.64	135	−48.64
20 June 2019	118.80	235.77	−116.97	236.08	−117.28	102.4	16.40	108	10.80
21 June 2019	114.96	232.79	−117.84	236.08	−121.12	102.4	12.56	108	6.96
22 June 2019	127.67	86.24	41.43	88.53	39.14	38.4	89.27	40.5	87.17
23 June 2019	118.13	84.65	33.48	88.53	29.60	38.4	79.73	40.5	77.63
25 June 2019	149.45	370.90	−221.45	354.12	−204.67	153.6	−4.15	162	−12.55
26 June 2019	141.40	517.21	−375.82	501.67	−360.27	217.6	−76.20	229.5	−88.10
27 June 2019	137.06	377.27	−240.22	354.12	−217.06	153.6	−16.54	162	−24.94
30 June 2019	152.10	409.97	−257.87	383.63	−231.53	166.4	−14.30	175.5	−23.40
1 July 2019	143.70	548.23	−404.53	472.16	−328.46	204.8	−61.10	216	−72.30
2 July 2019	120.49	174.75	−54.26	177.06	−56.57	76.8	43.69	81	39.49
7 July 2019	113.97	27.88	86.09	29.51	84.46	12.8	101.17	13.5	100.47
19 July 2019	129.30	141.78	−12.48	147.55	−18.25	64	65.30	67.5	61.80
20 July 2019	115.20	145.18	−29.97	147.55	−32.35	64	51.20	67.5	47.70
21 July 2019	89.57	203.94	−114.37	206.57	−117.00	89.6	−0.03	94.5	−4.93
22 July 2019	117.43	56.21	61.22	59.02	58.41	25.6	91.83	27	90.43
25 July 2019	125.54	312.26	−186.73	324.61	−199.07	140.8	−15.26	148.5	−22.96
26 July 2019	99.19	196.94	−97.75	206.57	−107.38	89.6	9.59	94.5	4.69
27 July 2019	99.44	232.61	−133.17	236.08	−136.64	102.4	−2.96	108	−8.56
28 July 2019	136.05	431.68	−295.62	413.14	−277.09	179.2	−43.15	189	−52.95
29 July 2019	98.45	174.29	−75.84	177.06	−78.61	76.8	21.65	81	17.45
30 July 2019	123.92	364.23	−240.31	354.12	−230.20	153.6	−29.68	162	−38.08
31 July 2019	76.02	166.68	−90.66	177.06	−101.04	76.8	−0.78	81	−4.98
6 August 2019	109.68	206.78	−97.10	206.57	−96.89	89.6	20.08	94.5	15.18
7 August 2019	90.62	213.04	−122.42	206.57	−115.95	89.6	1.02	94.5	−3.88
09 August 2019	126.33	118.20	8.13	118.04	8.29	51.2	75.13	54	72.33
10 August 2019	91.88	358.09	−266.21	354.12	−262.24	153.6	−61.72	162	−70.12
11 August 2019	128.06	227.93	−99.87	236.08	−108.02	102.4	25.66	108	20.06
12 August 2019	109.99	508.92	−398.93	501.67	−391.68	217.6	−107.61	229.5	−119.51
18 August 2019	113.03	172.56	−59.53	177.06	−64.03	76.8	36.23	81	32.03
19 August 2019	121.36	397.81	−276.44	383.63	−262.27	166.4	−45.04	175.5	−54.14
20 August 2019	109.79	372.21	−262.41	383.63	−273.84	166.4	−56.61	175.5	−65.71
21 August 2019	46.95	28.83	18.12	29.51	17.44	12.8	34.15	13.5	33.45
25 August 2019	110.80	241.66	−130.86	236.08	−125.28	102.4	8.40	108	2.80
26 August 2019	110.00	298.16	−188.16	295.1	−185.10	128	−18.00	135	−25.00
27 August 2019	107.63	308.47	−200.84	295.1	−187.47	128	−20.37	135	−27.37
28 August 2019	98.66	316.97	−218.31	324.61	−225.95	140.8	−42.14	148.5	−49.84
29 August 2019	90.26	369.46	−279.20	383.63	−293.37	166.4	−76.14	175.5	−85.24
30 August 2019	90.82	178.21	−87.39	177.06	−86.24	76.8	14.02	81	9.82
31 August 2019	63.42	329.25	−265.83	324.61	−261.19	140.8	−77.38	148.5	−85.08
Total electricity demand		14,191.01		14,017.25		6080.00		6412.50
Surplus electricity from PV			386.41		362.05		1214.07		1120.14
No coverage of electricity demand from PV			−8254.62		−8056.50		−971.27		−1209.84

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Abstract

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This paper deals with the issue of air cooling in outdoor areas of human habitation. An analysis of air parameters during the summer season was carried out to determine the thermal comfort zone for a part of the northern platform of the local station in Rzeszow (Poland). The cooling capacity required for thermal comfort was calculated using outdoor air parameters and heat gains in the vicinity of the research object. Ten potential air-cooling systems were proposed for the outdoor zones. The systems differed in terms of cooling equipment, primary energy source, cooling medium, and recipients. They were divided into three categories: compressor, adsorption, and evaporative cooling. The electricity yield of the existing photovoltaic installation at the research facility was evaluated to identify potential synergies between the cooling demand and solar energy. An analysis assessed the energy, economic, and environmental impact of each proposed option. The best option for cooling the outdoor areas was found to be an evaporative cooling system with a PV system. Solar radiation can be effectively used for cooling outdoor zones in Poland in the summer. The optimal solution for the research facility is an evaporative cooling system based on direct evaporation combined with a photovoltaic system. The subject matter covered can be used as an effective tool for the optimal selection of outdoor air-cooling systems to ensure the thermal comfort of the occupants.

Details

Title

Cooling of Air in Outdoor Areas of Human Habitation

Author

Barnat, Ewelina¹

; Sekret, Robert²

; Babiarz, Bożena¹

¹ The Faculty of Civil and Environmental Engineering and Architecture, Rzeszow University of Technology, Powstancow Warszawy Street 12, 35-959 Rzeszow, Poland; [email protected]
² Faculty of Infrastructure and Environment, Czestochowa University of Technology, J.H. Dabrowskiego Street 69, 42-201 Czestochowa, Poland; [email protected]

First page

6303

Publication year

2024

Publication date