# Improving the Energy Performance of Public Buildings Equipped with Individual Gas Boilers Due to Thermal Retrofitting

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## Abstract

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## 1. Introduction

^{−2}∙year

^{−1}. The analysis of these indexes and their comparison with the indexes characterizing other buildings, as well as comparing them to national standards, allows the energy quality of a building to be determined. Calculating the energy balance of a building, taking into account the total efficiency of the heating system, as well as the type of fuel or energy used for heating, allows for the determination of three energy indexes. The first one is related to the usable energy demand index for heating and ventilation (UE

_{H}). The second one, which takes into account the total efficiency of the heating system, is called the final energy consumption for heating (FE

_{H}). The third is called the non-renewable primary energy index for heating (PE

_{H}), the value of which additionally depends on the type of fuel or energy used to cover the heating needs of the building [8,17].

_{H}index characterizes only the quality of the external envelopes of the buildings, which is influenced, among other things, by the insulation of building partitions, the degree of glazing, the shape of the body, and orientation towards the directions of the world [18,19]. On the other hand, the FE

_{H}index represents the quality of the building along with its technical system, so the value of the index depends on the efficiency of heat-generating devices in the building, the amount of heat distribution losses and the efficiency of heat regulation and use, i.e., the quality of technical parameters and solutions in general. In operational conditions, this index can be determined on the basis of the measured values of the fuel used or the energy used to heat the building. The PE

_{H}index should rather be used in assessing a building’s environmental impact and considering environmental aspects [9,12,15].

_{H}index, and on the basis of its value, it is only possible to calculate the PE

_{H}value in accordance with applicable legal acts [20,21,22]. Estimated PE

_{H}values ought to be compared with the national EPBD requirements to verify the environmental quality of the building. In Poland, maximal allowable values of the primary energy index were successively decreased by the Regulation of Polish Ministry of Transport, Construction and Maritime Economy [23]. In case of the newly erected non-healthcare public buildings PE

_{H+W}(heating and hot water production) limits changed from 65 kWh·m

^{−2}∙year

^{−1}in 2014 to 45 kWh·m

^{−2}∙year

^{−1}in 2021. For the old, refurbished buildings, the only limitation is the overall heat transfer U coefficient value of the external barriers. For walls, it equaled 0.25 W·m

^{−2}·K

^{−1}in 2014 to reach the value of 0.20 W·m

^{−2}·K

^{−1}(since 2021); for the roofs, 0.20 W·m

^{−2}·K

^{−1}(in 2014) and 0.15 W·m

^{−2}·K

^{−1}(since 2021); windows, 1.30 W·m

^{−2}·K

^{−1}(in 2014) and 0.90 W·m

^{−2}·K

^{−1}(since 2021); doors, 1.70 W·m

^{−2}·K

^{−1}(in 2014) and 1.30 W·m

^{−2}·K

^{−1}(since 2021).

## 2. Materials and Methods

#### 2.1. Characteristics of the Analyzed Buildings

^{−1}(marked with M1 group, and buildings with numbers from 1 to 4), while ten are assigned to stations with the number of 3825.2 (days∙K)·year

^{−1}(marked by the M2 group and buildings by numbers from 1 to 10). In eight cases, boiler rooms are single-function and cover the thermal needs of buildings only for heating purposes. In the remaining six cases, boiler rooms are dual-function and cover the needs for heating and hot water.

#### 2.2. Calculation Method

#### 2.2.1. Evaluation of Heat Consumption Indexes

- In the case of school buildings that had a common gas consumption measurement for heating and the gas cookers, consumption by cookers was subtracted from the total annual consumption readouts in the following way: readouts from the months outside the heating season (May–September) were subtracted in full, and for the months of October–April, the average monthly gas consumption for cookers for three months was calculated (May, June, September, when the schools were still running) and subtracted for each month.
- In the case of school buildings with common gas consumption for heating and hot water preparation, a similar method was applied as for the gas cookers.
- In case of the office building, average consumption for all months outside the heating season was evaluated, because they perform similarly during summer period as during the rest of the year.
- There was no circumstance within the investigated objects where gas consumption measurements would cover three purposes (heating, hot water preparation, gas cookers).

_{1}and φ

_{2}correction factors were used and were calculated using Equations (1) and (2).

_{1}= 3963.4 (days∙K)·year

^{−1}:

_{1}= 3825.2 (days∙K)·year

^{−1}:

_{01}and SD

_{02}are values calculated for a particular year on the basis of the monthly average outdoor air temperatures (θ

_{em}) measured in an appropriate meteorological station, L

_{D}is the number of heating days in particular month and indoor air temperature θ

_{i}= 20 °C.

_{01}and SD

_{02}results from the fact that in standard conditions the stations have different average monthly temperatures θ

_{em}, while the number of heating days is the same, which equals 222 days for the whole period (Table 5).

_{1}and φ

_{2}correction factors enable us to adjust energy consumption to the standard year. SD

_{1}and SD

_{2}are the standard values from the long-term measurements. SD

_{01}and SD

_{02}values represent the number of degree-days in a given year, and they were calculated using the following equation:

_{1}and φ

_{2}correction factors for the following years were as follows (Table 6):

_{01}in case of M2 group V

_{02}and can be calculated using the following equations:

_{P1}and V

_{P2}are the measured values of gas consumption in a selected building in a particular year (m

^{3}·year

^{−1}) decreased for the consumption by gas cookers or hot water preparation.

^{3}·year

^{−1}) into heat consumption (GJ·year

^{−1}), the average calorific value of medium given by gas supplier was assumed:

_{0}= 35.5 MJ·m

^{−3}= 0.0355 GJ·m

^{−3}

_{FH1}(for M1 group of buildings) and Q

_{FH2}(for M2 group of buildings) expressed in GJ·year

^{−1}can be evaluated using the following:

_{H}) was evaluated according to the following equation:

_{H}—Final Energy Consumption Index for Heating, kWh·m

^{−2}·year

^{−1};

_{f}—usable heating area, m

^{2}.

_{H}value, Annual Primary Energy Consumption Index for Heating (PE

_{H}) was evaluated according to the following equation:

_{H}= w

_{H}∙ FE

_{H}

_{H}—primary energy input factor, according to Polish regulations [20,21] assumed 1.1 for all objects (heating system powered by gas boiler located in the investigated building).

_{H,0}) was calculated according to Polish regulations from the period when thermal refurbishment was conducted, according to the following equation [20]:

_{H,0}= 1.15 · [55 + 90 · (A/V)]

^{−1}] or:

_{H,0}= 1.15 · 149.5 = 171.93

^{−1}],

^{−1}].

#### 2.2.2. Energy Audits

_{FH}) and annual primary energy consumption index for heating (PE

_{H}).

#### 2.2.3. Statistical Analysis

_{FH}, FE

_{H}and PE

_{H}indexes) before and after thermal refurbishment. Basic descriptive statistics such as minimum, maximum, mean, median and standard deviation were estimated. Boxplots illustrating the distributions of the replacement were also used. The significance of the differences was verified using the Wilcoxon test for dependent variables [43], which is a non-parametric equivalent of the Student’s t-test. The choice of the test was dictated, firstly, by the relationship between the measurements before and after thermal refurbishment and, secondly, by the lack of meeting the assumptions about the normality of the distribution of the studied features in the groups and the lack of homogeneity of variance. In such a situation, it was reasonable to use this test [44].

_{before}, x

_{after}are the readings, respectively, before and after thermal retrofitting.

## 3. Results

_{FH}), the percentage decrease in final energy consumption for heating was calculated. The trends are shown in Figure 1, while the average values before and after and the percentage decrease (savings) in Table 7.

^{−2}·year

^{−1}and denoted as FE

_{H}. The decrease in FE

_{H}index value is presented in Figure 2, while its averaged values before and after thermal refurbishment are presented in Table 8.

_{H}index obtained after thermal-refurbishing in the M1 group was 95.5 kWh·m

^{−2}∙year

^{−1}, while in the M2 group it was 107.9 kWh·m

^{−2}∙year

^{−1}. With the assumed value of the non-renewable primary energy input index of w

_{H}= 1.1 (energy production in the building, energy carrier in the form of natural gas), the consumption rate of non-renewable primary energy was calculated in each building. It was expressed in kWh·m

^{−2}∙year

^{−1}and denoted as PE

_{H}. The values obtained in the condition before and after thermal refurbishment in each building are presented in Table 9. The average, minimum, maximum and median values of the PE

_{H}index divided into M1 and M2 groups before and after thermal-refurbishment are presented in Table 10.

_{H}index after thermal refurbishment are 1.1 times higher than the FE

_{H}values due to the assumed value of the coefficient w

_{H}= 1.1. In the M1 group, the PE

_{H}index was 105.1 kWh·m

^{−2}∙year

^{−1}, while in the M2 group it was 118.7 kWh·m

^{−2}∙year

^{−1}.

- estimated decreases, under operating conditions, in final energy consumption Q
_{FH}with forecast drops calculated in energy audits; - FE
_{H}, PE_{H}values calculated on the basis of gas consumption measurements with values calculated in energy audits; - the obtained results of improving the energy quality of buildings in operational conditions to the requirements contained in legal acts in force during the period of thermal-refurbishment works.

_{H}values resulting from legal acts.

_{H}index in each building, obtained under operating conditions based on the results of gas consumption measurements, to the decrease predicted by the audit.

_{H}index with the calculated values included in the audits before the retrofitting.

## 4. Discussion

- estimation of the level of final energy savings obtained in operating conditions for heating the building due to the implementation of the thermal refurbishment investment and comparing it to the calculation values contained in the energy audit,
- comparison of the value of the PE
_{H}energy index determined on the basis of actual measurements before and after the thermal refurbishment of the building with the theoretical values obtained in an energy audit prepared on the basis of the applicable algorithms, standards and calculation guidelines, - comparison of the forecasted and actual values of the PE
_{H}index with the Polish requirements of the energy standard applicable in the period of thermal refurbishment of the building.

^{−2}·K

^{−1}), while in the final state, they were similar to each other. The calculations and analyses carried out show that, as a result of thermal retrofitting in each building, a decrease in final energy consumption in operating conditions was achieved, ranging from 21.8% to 60.5%. The lowest value in this range applies to building M1-2, in which only building partitions were thermo-modernized, while the largest one concerns building M2-10, which among all the buildings had the highest U coefficients of partitions before the retrofitting. The obtained average value of final energy savings for heating in the M1 building group was 35.0%, while it equaled 42.7% in the M2 group. The comparison of final energy consumption before and after thermal refurbishment showed significant differences (p = 0.002) for buildings from the M2 group. This is confirmed by a noticeable decrease in final energy consumption resulting from the performed investments.

_{H}index obtained on the basis of measurements in operating conditions with the same index calculated in the building energy audit was compared in 12 buildings (in two the audit results were not available), in the condition before thermal refurbishment (Figure 4). The comparison of the values of the PE

_{H}index shows that in eleven cases examined in this respect, they were higher in the audit than in the operating conditions. These differences ranged from 9.4% to 47.7%, and the average for both groups was 26.1%. It turned out that in the examined group of buildings, only in the case of M2-3 were the theoretical values of the indicator describing the energy performance of the building lower than the results obtained on the basis of measurements. In the remaining cases, these results were much higher, as presented in Figure 4. It should be assumed that before the thermal retrofitting, the buildings were heavily underheated, and the standard indoor air temperature was not reached in the rooms. This means that the thermal needs of the building were not fully covered in the conditions before thermal refurbishment, so the level of final energy savings achieved in operating conditions was lower than the forecast calculated in the audit. The final effects of energy savings are influenced by user behavior, as evidenced by literature reports [51], especially the use of control fittings of radiators (thermostatic valves) and programming of internal temperature. However, this influence of individual behavior is greater in residential buildings than in public buildings, where one person is responsible for energy management.

_{H}index values shows that its decrease in each building was significant. The mean value of the index in the M1 group of buildings decreased from 152.1 kWh·m

^{−2}∙year

^{−1}to 95.5 kWh·m

^{−2}∙year

^{−1}, which means a decrease by 37.2%, while that in the M2 group decreased from 190.2 kWh·m

^{−2}∙year

^{−1}to 107.9 kWh·m

^{−2}∙year

^{−1}, which is a decrease of 43.3%. The same percentage reductions were obtained for the PE

_{H}index, because in each building, the input coefficient w

_{H}was equal to 1.1, which in this case means a linear relationship between the two indexes. Additionally, since FE

_{H}and PE

_{H}values are derivatives of the Q

_{FH}index as its linear combinations, the comparisons of energy consumption decreases expressed by the above-mentioned indexes are also characterized by the same level of significance of differences. The study comparing the PE

_{H}value obtained in real conditions with the one calculated in the audit after thermal refurbishment shows that the relations between them developed in different ways. In three buildings, the PE

_{H}value resulting from gas consumption measurements was lower than the one specified in the audit, from 6.1% to 11.4%; in the remaining nine buildings, it was greater than 6.8% up to 86.8%, and on average, for both groups, it is a 28.4% higher value. A comparison of the PE

_{H}index values obtained on the basis of measurements with the values required in legal acts as for reconstructed buildings shows that after thermal retrofitting in nine buildings the requirement was met with an excess of 0.4% to 29.4%, while in four buildings, 1.4% to 19.1% was missing. However, on average for both groups in total, the value was 6.4% lower. There may be several reasons for this, e.g., inadequate adjustment of the central heating system, maintaining higher temperatures in the rooms than required, not using the heating weakening outside the building’s working hours or worse than assumed thermal parameters of the building partitions and lower overall efficiency of heating systems. Considering the impact of thermal refurbishment on the improvement of the energy performance of a building, it should be clearly stated that it is diversified but always leads to a reduction in energy consumption and thus its carriers.

_{H,0}values depending on the building shape factor (A/V), and the values obtained on the basis of measurements. The continuous red line indicates the required values of the index at a given value of the A/V ratio, while the points on the graph show the average values of the PE

_{H}index obtained after the thermal refurbishment of the building. Additionally, the relation between the building shape ratio and Annual Primary Energy Consumption Index for Heating PE

_{H}was checked. From the diagram, it can be noticed that after the refurbishment, the values of PE

_{H}index were in most cases lower than required. It was noticed that in the case of low A/V ratio values, the influence of building shape was not significant for PE

_{H}. Hence, it can be interpreted that analyzed buildings functioned differently, and some of them could be underheated before the retrofitting. In the case of the high value of A/V ratio (building M2-5), energy consumption expressed as Annual Primary Energy Consumption Index for Heating PE

_{H}was higher than in other cases and exceeded the required PE

_{H,0}index value, which may result from both building shape ratio and the manner of operation. These relations are similar to those previously described in the literature [7].

## 5. Conclusions

- After thermal retrofitting, a decrease in final energy consumption in operating conditions was achieved, ranging from 21.8% to 60.5%. The obtained average value of final energy savings for heating in the M1 building group was 35%, while it equaled 42.7% in the M2 group.
- The estimated values of energy savings for heating obtained under operating conditions are in each case lower than the forecast calculated in the energy audits. The decrease in final energy demand calculated in audits was much greater and ranged from 37.6% to 77.1%.
- Despite the planned and implemented similar scope of works aimed at reducing energy consumption in buildings, both the forecasted (resulting from the audit) and the actual (resulting from the measurements) PE
_{H}indexes are highly diversified. This is confirmed in the case of forecasting values ranging from 63.6 kWh·m^{−2}∙year^{−1}to 148.6 kWh·m^{−2}∙year^{−1}, while in real conditions, the values ranged from 72.4 kWh·m^{−2}∙year^{−1}to 177.1 kWh·m^{−2}∙year^{−1}. - A comparison of the PE
_{H}index values obtained on the basis of measurements with the values required in legal acts for reconstructed buildings shows that after thermal retrofitting in nine buildings, the requirement was met with an excess of 0.4% to 29.4%, while in four buildings, 1.4% to 19.1% is missing. However, on average, for both groups in total, the value is 6.4% lower. There may be several reasons for this, e.g., inadequate adjustment of the central heating system, maintaining higher temperatures in the rooms than required, not using the heating weakening outside the building’s working hours or worse thermal parameters than assumed of the building partitions and lower overall efficiency of heating systems. - Although the decrease in final energy consumption in operating conditions was achieved in all the examined cases, investors cannot expect theoretically calculated savings in the real conditions. At the same time, thermal refurbishment will certainly ensure the additional effects of improving the thermal comfort in rooms and achieving the required internal conditions, which is very important from the point of view of the users.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 3.**Decrease in the value of the PE

_{H}index calculated on the basis of measurements from the operation of buildings and indexes calculated on the basis of audits.

**Figure 4.**PE

_{H}values obtained from measurements and calculated in the audit before thermal refurbishment.

**Figure 5.**Comparison of the obtained PE

_{H}index values with those calculated in the audit after thermal refurbishment and with the technical requirements.

Object | Function | Usable Area [m^{2}] | A/V [m^{−1}] | Construction Year | Retrofitting Year |
---|---|---|---|---|---|

M1-1 | School | 1464.0 | 0.38 | 1962 | 2004 |

M1-2 | School | 1804.2 | 0.49 | 1955 | 2007 |

M1-3 | Office | 1397.0 | 0.53 | 1981 | 2003 |

M1-4 | School | 2160.0 | 0.50 | - | 2003 |

Object | Energy Needs | Heating System Refurbishment | Measuring Period | Expected Savings, [%] | |

M1-1 | heating, cooking | Yes | 2001–2010 | 66.5 | |

M1-2 | heating, cooking | No | 2001–2010 | 37.6 | |

M1-3 | heating, cooking | Yes | 2001–2010 | 67.0 | |

M1-4 | heating, hot water | Yes | 2001–2010 | - |

Object | Before Thermal Retrofitting U, [W m^{−2} K^{−1}] | After Thermal Retrofitting U, [W m^{−2} K^{−1}] | ||||||
---|---|---|---|---|---|---|---|---|

Walls | Roofs | Windows | Doors | Walls | Roofs | Windows | Doors | |

M1-1 | 1.15; 0.97 | 2.75; 1.08 | 2.60 | 2.50 | 0.25; 0.24 | 0.22 | 1.60 | 2.50; 1.60 |

M1-2 | 1.15; 0.96; 0.30 | 0.24; 0.22 | 2.60; 2.00; 1.80 | 2.50; 1.80 | 0.25; 0.30; 0.96 | 0.24; 0.22 | 2.00; 1.80 | 1.80 |

M1-3 | 2.59; 1.12 | 2.37 | 2.80; 1.30 | 1.30 | 0.25 | 0.21 | 1.30 | 1.30 |

M1-4 | No data | 0.25 * | 0.22 * | 1.30 * | 1.30 * |

Object | Function | Usable Area, [m^{2}] | A/V, [m^{−1}] | Construction Year | Refurbishment Year |
---|---|---|---|---|---|

M2-1 | School | 890.2 | 0.66 | 1962 | 2004/5 |

M2-2 | School | 1117.2 | 0.63 | 1965 | 2004/5 |

M2-3 | School | 535.6 | 0.57 | 1980/1996 | 2007/8 |

M2-4 | School | 989.7 | 0.52 | 1974 | 2008 |

M2-5 | School | 220.0 | 1.10 | 1970 | 2007 |

M2-6 | School | 684.3 | 0.52 | 1965 | 2007 |

M2-7 | School | 820.0 | 0.52 | 1962 | 2004 |

M2-8 | Kindergarten | 1566.0 | 0.47 | 1987 | 2008 |

M2-9 | Office | 448.8 | 0.64 | 1960/1974 | 2004/5 |

M2-10 | School | 1702.7 | 0.51 | 1964 | 2004/5 |

Object | Energy Needs | Heating system Refurbishment | Measuring Period | Expected Savings, [%] | |

M2-1 | heating | Yes | 2001–2010 | 74.3 | |

M2-2 | heating, cooking | Yes | 2001–2010 | 77.0 | |

M2-3 | heating, hot water | No | 2004–2010 | 50.6 | |

M2-4 | heating, hot water | Yes | 2003–2010 | 73.6 | |

M2-5 | heating, cooking | Yes | 2001–2010 | - | |

M2-6 | heating, hot water | Yes | 2003–2010 | 67.7 | |

M2-7 | heating, hot water | Yes | 2001–2010 | 79.0 | |

M2-8 | heating, hot water | Yes | 2002–2010 | 77.1 | |

M2-9 | heating | Yes | 2002–2010 | 60.5 | |

M2-10 | heating | Yes | 2002–2010 | 71.5 |

Object | Before Thermal Retrofitting U, [W m^{−2} K^{−1}] | After Thermal Retrofitting U, [W m^{−2} K^{−1}] | ||||||
---|---|---|---|---|---|---|---|---|

Walls | Roofs | Windows | Doors | Walls | Roofs | Windows | Doors | |

M2-1 | 0.93 | 1.04 | 2.60; 1.60 | 2.50 | 0.24 | 0.22 | 1.60 | 1.60 |

M2-2 | 0.93 | 1.15; 1.04 | 2.60; 1.60 | 2.50; 1.60 | 0.24 | 0.22; 0.21 | 1.60 | 1.60 |

M2-3 | 1.15 | 0.25 | 2.60 | 2.50; 1.80 | 0.25 | 0.25 | 1.80 | 1.80 |

M2-4 | 1.15;1.13 | 0.21 | 2.60 | 2.50 | 0.25 | 0.21 | 1.80 | 1.80 |

M2-5 | 1.15 * | 0.90 * | 2.60 * | 2.50 * | 0.25 * | 0.22 * | 1.80 * | 1.80 * |

M2-6 | 1.21; 1.18 | 0.90 | 2.60; 1.80 | 2.50; 1.80 | 0.25; 0.24 | 0.21 | 1.80 | 1.80 |

M2-7 | 1.25 | 0.99; 0.70 | 3.00 | 3.00; 2.50 | 0.25 | 0.22; 0.37 | 1.30 | 2.50; 1.30 |

M2-8 | 0.80; 0.79 | 0.77 | 2.60 | 5.60; 2.50 | 0.24 | 0.22 | 1.80 | 1.80 |

M2-9 | 1.13; 0.74 | 1.13; 0.94 | 5.60; 2.60 | 2.50 | 0.25 | 0.21 | 1.60 | 1.60 |

M2-10 | 1.43 | 1.25 | 3.00; 2.60; 1.60 | 2.50 | 0.24 | 0.22 | 3.00; 1.60 | 1.60 |

Month | Group of Buildings | |||
---|---|---|---|---|

M1 | M2 | |||

θ_{em} | L_{D} | θ_{em} | L_{D} | |

January | −2.6 | 31 | −2.6 | 31 |

February | 0.0 | 28 | −1.9 | 28 |

March | 2.5 | 31 | 3.2 | 31 |

April | 6.7 | 30 | 9.2 | 30 |

May | 11.4 | 5 | 14.4 | 5 |

September | 12.7 | 5 | 12.8 | 5 |

October | 6.4 | 31 | 8.5 | 31 |

November | −0.1 | 30 | 1.3 | 30 |

December | −1.2 | 31 | −2.1 | 31 |

Year | Group of Buildings | |
---|---|---|

M1 | M2 | |

φ_{1} | φ_{2} | |

2001 | 1.028 | 0.961 |

2002 | 1.091 | 1.020 |

2003 | 1.039 | 0.971 |

2004 | 1.102 | 1.030 |

2005 | 1.098 | 0.995 |

2006 | 1.077 | 1.010 |

2007 | 1.117 | 1.040 |

2008 | 1.169 | 1.080 |

2009 | 1.113 | 1.043 |

2010 | 1.023 | 0.897 |

Group | Object | Final Energy Consumption | Decrease in Consumption % | |
---|---|---|---|---|

GJ·year^{−1} | ||||

Before | After | |||

M1 | M1-1 | 620.4 | 347.1 | 44.1 |

M1 | M1-2 | 857.6 | 670.5 | 21.8 |

M1 | M1-3 | 1107.4 | 537.7 | 51.4 |

M1 | M1-4 | 1075.7 | 824.3 | 23.4 |

M2 | M2-1 | 587.9 | 347.6 | 40.9 |

M2 | M2-2 | 724.6 | 380.5 | 47.5 |

M2 | M2-3 | 413.0 | 255.2 | 38.2 |

M2 | M2-4 | 594.2 | 395.8 | 33.4 |

M2 | M2-5 | 194.1 | 127.5 | 34.3 |

M2 | M2-6 | 337.3 | 217.6 | 35.5 |

Group | Object | Final Energy Consumption | |
---|---|---|---|

GJ·year^{−1} | |||

Before | After | ||

M1 | M1-1 | 117.7 | 65.8 |

M1 | M1-2 | 132.0 | 103.2 |

M1 | M1-3 | 220.2 | 106.9 |

M1 | M1-4 | 138.3 | 106.0 |

M2 | M2-1 | 183.5 | 108.5 |

M2 | M2-2 | 180.2 | 94.6 |

M2 | M2-3 | 214.2 | 132.4 |

M2 | M2-4 | 166.8 | 111.1 |

M2 | M2-5 | 245.1 | 161.0 |

M2 | M2-6 | 136.9 | 88.3 |

Group | Object | Final Energy Consumption | |
---|---|---|---|

GJ·year^{−1} | |||

Before | After | ||

M1 | M1-1 | 129.5 | 72.4 |

M1 | M1-2 | 145.2 | 113.5 |

M1 | M1-3 | 242.2 | 117.6 |

M1 | M1-4 | 152.2 | 116.6 |

M2 | M2-1 | 201.8 | 119.3 |

M2 | M2-2 | 198.2 | 104.1 |

M2 | M2-3 | 235.6 | 145.6 |

M2 | M2-4 | 183.5 | 122.2 |

M2 | M2-5 | 269.6 | 177.1 |

M2 | M2-6 | 150.6 | 97.2 |

Group | Refurbishment | PE_{H} Index | |||
---|---|---|---|---|---|

kWh·m^{−2}∙year^{−1} | |||||

Min. | Max. | Median | Mean | ||

M1 | Before | 129.5 | 242.2 | 148.7 | 167.3 |

M1 | After | 72.4 | 117.6 | 115.1 | 105.0 |

M2 | Before | 145.6 | 272.8 | 203.6 | 209.2 |

M2 | After | 90.2 | 177.1 | 111.7 | 118.7 |

**Table 11.**Summary of calculation results, data from audits and required values of the PE

_{H}[kWh·m

^{−2}∙year

^{−1}] ratio and the decrease in energy Q

_{FH}[%].

Group | Object | Values of PE_{H} Index kWh·m^{−2}·year^{−1} | Decrease in Energy Q_{FH} % | |||||
---|---|---|---|---|---|---|---|---|

Measured | Calculated | Required | ||||||

Before | After | Before | After | After | Measured | Calculated | ||

M1 | M1-1 | 129.5 | 72.4 | 238.9 | 80.0 | 102.58 | 44.1 | 66.5 |

M1 | M1-2 | 145.2 | 113.5 | 205.3 | 128.1 | 113.97 | 21.8 | 37.6 |

M1 | M1-3 | 242.2 | 117.6 | 267.4 | 88.2 | 118.11 | 51.4 | 67.0 |

M1 | M1-4 | 152.2 | 116.6 | - | - | 115.00 | 23.4 | - |

M2 | M2-1 | 201.8 | 119.3 | 329.5 | 84.9 | 131.56 | 40.9 | 74.2 |

M2 | M2-2 | 198.2 | 104.1 | 329.1 | 75.6 | 128.46 | 47.5 | 77.0 |

M2 | M2-3 | 235.6 | 145.6 | 182.8 | 90.3 | 122.25 | 38.2 | 50.6 |

M2 | M2-4 | 183.5 | 122.2 | 247.4 | 65.4 | 117.07 | 33.4 | 73.6 |

M2 | M2-5 | 269.6 | 177.1 | - | - | 164.45 | 34.3 | - |

M2 | M2-6 | 150.6 | 97.2 | 207.1 | 66.9 | 117.07 | 35.5 | 67.7 |

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## Share and Cite

**MDPI and ACS Style**

Życzyńska, A.; Majerek, D.; Suchorab, Z.; Żelazna, A.; Kočí, V.; Černý, R.
Improving the Energy Performance of Public Buildings Equipped with Individual Gas Boilers Due to Thermal Retrofitting. *Energies* **2021**, *14*, 1565.
https://doi.org/10.3390/en14061565

**AMA Style**

Życzyńska A, Majerek D, Suchorab Z, Żelazna A, Kočí V, Černý R.
Improving the Energy Performance of Public Buildings Equipped with Individual Gas Boilers Due to Thermal Retrofitting. *Energies*. 2021; 14(6):1565.
https://doi.org/10.3390/en14061565

**Chicago/Turabian Style**

Życzyńska, Anna, Dariusz Majerek, Zbigniew Suchorab, Agnieszka Żelazna, Václav Kočí, and Robert Černý.
2021. "Improving the Energy Performance of Public Buildings Equipped with Individual Gas Boilers Due to Thermal Retrofitting" *Energies* 14, no. 6: 1565.
https://doi.org/10.3390/en14061565