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Article

Energy Performance Analysis of a Heat Supply System of a University Campus

Faculty of Energy Engineering and Industrial Management (Romania), University of Oradea, 3700 Oradea, Romania
*
Author to whom correspondence should be addressed.
Energies 2023, 16(1), 174; https://doi.org/10.3390/en16010174
Submission received: 2 December 2022 / Revised: 16 December 2022 / Accepted: 19 December 2022 / Published: 23 December 2022
(This article belongs to the Section G: Energy and Buildings)

Abstract

:
The energy efficiency of a system and the performance level of its equipment and installations are the two key elements based on which the investment decision in its modernization is made. They are also very important for setting up optimal operation strategies. The energy audit is a well-known and worldwide recognized tool for calculating energy performance indicators and developing improvement measures. This paper is a synthesis of the energy audit results performed for a district heating network that uses geothermal energy as its primary source of energy. The location of the heating system is inside a university campus. The first part explains the necessity of a comprehensive study on district heating networks and introduces the defining elements that characterize the analyzed equipment and installations. The complex energy balance methodology that has been developed and applied to this district heating system is presented in the second part of the paper. Next, the methodology for collecting the input data for the energy and mass balance is explained. In the final part, the numerical values of the performance indicators and the technical measures that must be applied to improve energy efficiency are shown, and conclusions are drawn.

1. Introduction

Energy is vital for the economic and social development of a nation [1]. If an accelerated economic growth scenario is considered, the global energy demand is expected to increase by 20% between 2020–2050 [2]. Although this scenario is unlikely to happen for various political, social, and economic reasons—including the environmental impact restrictions—the pressure on the planet’s energy resources will remain high for decades to come. The major levers for moderating the energy consumption from depletable resources, such as fossil fuels, might be more restrictions with respect to environmental impact, increasing the price of fossil fuels, intensive promotion of renewable energy sources, and increasing the energy efficiency of the end-users.
According to information published by the World Watch Institute, buildings are responsible for 40% of annual global energy consumption [3]. Therefore, an optimal energy management both inside the buildings and outside it, in all systems that transport and distribute heat is essential to temper the energy consumption [4,5].
Energy losses in the transmission and distribution networks of heat carrier agents depend directly on the condition of the pipes and the quantity of thermal agents transported through the pipeline or needed by the buildings. For this reason, in energy efficiency analysis of heating fluids networks, buildings cannot be circumvented. Currently, the energy efficiency issues of the heating network-building is treated holistically, in accordance with the international standards ISO 50001 [5] and ISO 50006 [6].
According to the two standards, the holistic approach of energy management of an entire company or parts of it, is to identify the influence factors for energy consumption and energy losses, to establish and characterize—from both technical and economic point of view—the appropriate measures to reduce energy consumption while having as main objectives the increase of energy efficiency, reducing environmental impact and sustainable development. This involves at least the following influence factors: weather conditions, buildings occupancy, construction materials used and type of insulation, duration of use and degradation degree of the buildings, applied air conditioning solutions, and the type of activities carried out. University campuses—as spaces for educational services—consist of specific groups of different type of buildings having a significant energy consumption [7]. Therefore, as an important measure of energy efficiency on university campuses, energy audits have been proven to be a topical issue [8,9,10,11,12,13,14,15,16].
This paper presents the methodology and results of the energy audit performed on a university campus heating system. It follows the recommendations ISO 50001 and ISO 50006 for establishing the energy baseline, evaluating energy performance indicators, and identifying and characterizing the potential for energy efficiency. The main contributions of the authors are:
  • Find the energy consumption area for which the detailed energy audit should be done;
  • Identify the systems to be analyzed together with their components and related technical specifications;
  • Develop the actual complex energy balance based on the measurements and specific data of the equipment and installations;
  • Identify measures to reduce energy consumption in order to develop an optimized energy balance;
  • Perform economic efficiency calculations for the identified optimization measures;
  • Calculate the greenhouse gas emissions and assess the environmental impact.

2. Description of the Analyzed System

The university campus to which this article refers belongs to the University of Oradea (UO), a higher education institution of public interest in Romania, certified for education services and scientific research. Sustainability is an important element for the development of UO, and because it is privileged to have access to a renewable energy source, the UO central campus is heated using geothermal water [17]. The UO campus uses both electrical energy (EE) and thermal energy (TE), but this paper is focused on the latter since it is based on the results of a detailed energy audit having the TE consumption system as its target. Because within this heating system with geothermal water as the primary energy source (HSGWPE) there are several electric-driven pumps for water circulation, the energy audit becomes a complex one. So, even if the electricity consumption is significantly lower than the thermal energy, it is still considered in the analysis. Figure 1 shows the components of the heating system with geothermal water as the primary energy source (HSGWPE), including the transmission pipeline (for the geothermal water), the heat exchangers inside the thermal substations, and the distribution network that connects the main thermal substation (TS1), and the end-users (campus buildings and other users).
All the equipment needed to perform the extraction, circulation, and energy transfer of the GWT is located inside the geothermal extraction well station (EWS) and thermal substations (TS1, TS2). The energy depleted geothermal water (DGW) from TS1 is transferred to the injection well station (IWS), while DGW from TS2 (HEx5 and HEx6) is discharged to sewer. The circulation pumps for the secondary circuit are located in TS as well.
Inside the thermal substations (presented in Figure 2 and Figure 3), the geothermal water transfers its heat to either a secondary circuit for building/space heating or to cold water (CW) to prepare DHW. Each of the 10 installed plate HEx covers the demand of specific end-users and are designed for:
1.
Production of secondary fluid for space heating:
  • HEx1.1 and HEx1.2 (2 × 100%)—for buildings: A, C, D, E, F, G, H, I, L, K, houses, and block of flats;
  • HEx2.1 and HEx2.2 (2 × 100%)—for buildings: B, N, M, O, P, R, C1, C2, S, T, U, V, X, Y, Z, shooting room (TIR), IMT research laboratory (L-IMT), ID printing house (T-ID), sports field, and wooden church;
  • HEx4—for building J (floor heating);
  • HEx5.1 and HEx5.2 (2 × 100%)—for the new students’ dormitory (C3).
2.
DHW production:
  • HEx3—for buildings: C1, C2, O, R, L-IMT, D, E, F, S, U, L, B, C, shooting room, and locker rooms;
  • HEx6.1 and HEx6.2 (2 × 100%)—for the new students’ dormitory (C3).
The technical information of the HSGWPE equipment and components are specified in [17], Table 1 just exemplifying a synthesis of the HEx technical data.
The geothermal water that is used by the University of Oradea is extracted from drilling no. 4796, located inside the campus (Figure 4). The drilling length is 2900 m, and the well is equipped with a line-shaft vertical pump. It produces a maximum flowrate of 45 l/s, while the geothermal water has a wellhead temperature of 86 °C. Currently, the TS demand for geothermal water does not exceed 30 L/s.
The geothermal water transmission network consists of a pipeline through which the primary thermal agent (geothermal water) is circulated from the extraction well station to both TS1 and TS2. The aerial steel pipeline of the TN1 has a length of 150 m and an inner diameter of Φ = 250 mm. It is insulated with reinforced mineral wool, covered with a protective steel sheet, and mounted on metal supports. The TN2 is a pre-insulated steel pipe having a nominal diameter of Φ = 114 mm and a length of 135 m out of which 80% buried directly into the ground.
As for the thermally depleted geothermal water, the Municipality of Oradea recently implemented a project to enhance the utilization factor of the geothermal energy. A new geothermal well was drilled and used as an injection well, thus creating a geothermal doublet that significantly increases the efficiency and durability of geothermal water use [18,19]. The geothermal well inside the UO campus was selected to discharge its heat-depleted geothermal water back into the reservoir [20]. Therefore, DGW from TS1 is no longer flushed to the sewer but reinjected.
The pipes of the secondary fluid distribution network (DN) are mostly made of steel, insulated with mineral wool, or pre-insulated. They are laid underground at a depth of 60–80 cm. The distribution network is of the radial type [21]. The circulation of the secondary water along the distribution network and inside the buildings is provided by the pumps located inside the thermal stations.
The heated secondary water exiting from HEx1 is transmitted through a main supply (flow) pipeline made of steel and insulated with mineral wool (Φ = 250 mm), placed inside an underground concrete duct (UCD1) for thermal and mechanical anti-corrosion protection. Connecting sections of the distribution network separate from this main flow pipe, supplying the above-mentioned buildings. Additionally, buildings C and L are supplied directly from HEx1. Similarly, the heated secondary water form HEx2 is transmitted through a main steel pipeline, mineral wool insulated (Φ = 278 mm), placed inside a main underground concrete duct (UCD2) that separates into two other concrete thermal ducts (UCD2.1, UCD2.2) hosting the pipelines from which the connections to the above-listed buildings are made. From HEx4, the heated secondary water is sent directly to building J through an underground buried steel pipeline insulated with mineral wool. The central heating installation of building C3 is supplied directly from HEx5.
The DHW prepared in HEx3 is transmitted to the students’ dormitories (C1, C2) through a pipe placed inside UCD2 and, respectively, through underground direct buried pipes to the other consumers. DHW produced by HEx6 is injected directly into the piping system of students’ dormitory C3.
Most of the distribution network piping is made of steel pipelines insulated with mineral wool, but some DN parts that were more recently commissioned, together with the connection to buildings, use pre-insulated steel pipes (Table A1). Nevertheless, some connections are made of a PPR (polypropylene) pipe. The heating elements inside the buildings are wall-mounted, except for building J, where floor heating was installed. About 90% of the radiators are made of cast iron, with the rest being made of aluminum or steel.
The main technical data used in this study for both the heat distribution network and heated buildings are summarized in Table A1.
When passing through the radiators, the heated secondary water is cooled down, becoming thermally depleted. Then, it returns to the TS and is reintroduced back into the circuit by using the electrical driven pumps from pumping stations PS1 and PS2. Here is also the place where make-up water from the municipality utility is introduced into the heating circuit to compensate for water losses.
According to thermal energy balance models [22,23,24,25,26,27,28,29], the reference measurement unit is “1 second,” therefore the energy components are usually assessed using kJ/s ≡ kW. Considering the specificity of the activities carried out by the UO and the available information, the annual, monthly, and hourly detailed energy balance (CEB) was prepared. The energy load of each piece of equipment and installations targeted by the CEB has been within normal range.
Some of the data needed for CEB have been collected from the UO database, where important information has been recorded for years. This is the case with the operating data related to geothermal water. For the other electrical and non-electrical input data, the following instrumentation has been used:
  • Network Analyzer, Chauvin Arnoux CA 8334, that is equipped with 3 voltage measurement channels and 3 current measurement channels, capturing and recording all the parameters, transients, alarms, and waveforms simultaneously. The current sensors connected are actually transformer clamps with a round jaw shape and uniformly distributed winding that offer a high level of accuracy and a minimum phase difference. For voltage measurements, crocodile clips were used.
  • Thermocamera Fluke Ti20 has a temperature range of −20 °C to +250 °C and an accuracy of ±2 °C or 2%. The spatial resolution (IFOV) is 2.5 mRad and the view field is 23° × 17°.
  • Measuring devices existing in HSGWPE:
    • Thermal energy meter for the geothermal water (SONTEX type), EN1434, θϵ (20 °C–200 °C), Δθ = (3–150) K and an accuracy of 2%;
    • Flow meter for cold water (for DHW preparation and make-up water), SENSUS type, with a a HRI-Mei-B3 sensor reading device that provides a high-resolution pulse output with a flow direction signal, and a maximum flow rate of 25 m3/h;
    • Electromagnetic flow sensors Isomag MS 5000, compact version, together with its MV 800 transducer;
    • Industrial analogic manometers having a pressure range of 0 to 12 bars.
All these sensors are metrologically checked, and if necessary, calibration is performed.
The measurement errors do not exceed 2%, thus being below the allowed error margins (regulations for energy balances).

3. Calculation Methodology for Energy Efficiency Indicators

According to the usual practice [22,23,24,25,26,27,28,29], if the energy carrier agent is hot water (as it is in the HSGWPE), both energy balance and mass balance are suitable.

3.1. Energy Balance

The general equation is:
WI = WU + Wp + WCPT,
where WI—input energy entered into the system [kJ]; WU—useful energy [kJ]; Wp—energy losses [kJ]; WCPT—own consumption [kJ].
  • Input energy (WI)
WI = WGTW + WEE,
where WGTW—thermal energy of geothermal water (GTW), recorded by the energy meter, [kJ]; WEE—electrical energy to drive the pumps [kJ].
  • Useful energy (WU) is the thermal energy supplied to end-users within the UO campus and, also, to third parties, and is calculated as follows:
W U   = i = 1 n W Ui = W U , SH = W U , DHW ,
where i = 1 , n   ¯ —buildings supplied from this source, as described in Table A1, WU,SH—energy used for space heating [kJ]; WU,DHW—energy used to produce domestic hot water (DHW) [kJ].
  • Own consumption (WCPT) represents the energy needed to drive the pumps within HSGWPE, therefore:
WCPT = WEE,
  • Energy losses (WP) are expressed as follows:
Wp = Wp,TN + Wp,TS + Wp,DN,
where Wp,TN—energy losses on the transmission network (geothermal well—thermal stations) [kJ]; Wp,TS—energy losses inside thermal stations [kJ]; Wp,DN—energy losses on the distribution network (heat exchangers—buildings) [kJ].

3.2. Mass Balance

It can be written for each circuit, as follows:
  • In the primary circuit (EWS-HEx), the geothermal water is circulated through the transport network pipeline and heat exchanger. Therefore, the equation is:
DGTW = DE,HEx + Dp,1,
where DGTW—the input flowrate of the geothermal water [kg/s]; DE,HEx—geothermal water output flowrate when exiting the HEx [kg/s], Dp,1—geothermal water mass losses in transmission network and heat exchanger [kg/s].
  • In the secondary circuit (distribution network), the mass balance equation is:
DS,DN = DR,DN + Dp,2,
where DS,DN, DR,DN—DN supply and return flow rate [kg/s]; Dp,2—water losses inside DN piping and HEx [kg/s]
All the flow rates (DGTW, DE,HEx, DS,DN, DR,DN) are directly measured, while water losses (Dp,1, Dp,2) are calculated.

3.3. Calculation of the CEB Components

3.3.1. Energy Inputs

Geothermal water (GWT) is the main energy carrier agent through which energy flows into the analyzed system, according to [11,12,13,14,15,16,17,18], therefore it can be written:
WGTW = DGTW (iEWS − iDGW) τ,
where iEWS—enthalpy of the well-head geothermal water (just exiting the EWS) [kJ/kg]; iDGW—enthalpy of thermally depleated geothermal water, when exiting the HSGWPE [kJ/kg]; τ—duration of analysis [h]
The electricity input will be calculated as follows:
W EE = i = 1 m P med τ ,
where Pmed—mean power absorbed by the “i” receiver of the analyzed system [kW].

3.3.2. Energy Losses

  • Transmission network (TN) losses will be calculated as follows:
W p , TN = W GTW W I , HEx ,
W I , GS = D I , GS ( i I , GS i DGW ) τ
where DIGS, iIGS—geothermal water flowrate and enthalpy at TS (or HEx) inlet [kg/s], [kJ/kg].
  • Thermal substation (TS) losses have 2 components:
    a.
    Energy losses for the HEx—are calculated based on the heat exchanger energy balance.
The energy of the HEx geothermal water outlet:
WE,GS = DE,GS (iE,GS − iDGW) τ,
Energy transferred by the primary circuit agent-GWT (through the HEx):
W1,HEx = WI,GS − WE,HEx,
The input and output energy of the secondary fluid (WI,SF, WE,SF):
WI,SF = DI,SF iI,SF τ,
WE,SF = DI,DN iE,SF τ
where DI,SF—HEx input flow rate for the secondary fluid [kg/s], (iI,SF, iE,SF)—enthalpy of the HEx input and output of secondary fluid [kJ/kg]
Energy received by the secondary fluid inside the HEx:
W2,HEx = WE,SF − WI,SF,
HEx energy losses:
Wp,HEx = W1,HEx − W2,HEx,
  • b.
    Energy losses in TS piping
W P   pipe = j = 1 n D pipe ,   j · c a · Δ θ j ,
where Dpipe, j, Δθ j—flow rate and temperature drop in pipe section “j” [kg/s, °C]; ca—specific heat of water [kJ/kg·°C].
It results that overall energy losses for TS is:
Wp,TS = Wp,HEx + Wp,pipe,
  • Distribution network (DN) energy losses is calculated using:
W p , DN = i = 1 n W p , i ,
Wpi = [(DS,Ii iS,Ii − DS,Ei iS,Ei) + (DR,Ii iR,Ii − DR,Ei iR,Ei)] τ
where (DS,Ii, DS,Ei)—SF flow rate at inlet and outlet of the “i”section of DN, supply line direction [kg/s]; (iS,Ii, iS,Ei)—SF enthalpy at inlet and outlet of the “i”section of DN, supply line direction [kJ/kg]; (DR,Ii, DR,Ei)—SF flow rate at inlet and outlet of the “i”section of DN, return direction [kg/s]; (iR,Ii, iR,Ei)—SF enthalpy at inlet and outlet of the “i”section, the return direction [kJ/kg].

3.3.3. Useful Energy

It is calculated for each building (WU,i) and for the entire HSGWPE (WU), as follows:
WU,i = (DS,Ei iS,Ei − DR,Ii iR,Ii) τ,
W U = W I ( W P + W CPT + W EWS ) = i = 1 n W U , i
To determine the enthalpy values (i) for energy carrier agents (GTW, DHW, SF) properties table for water will be used [30].

3.3.4. Energy Performance Indicators

They are expressed in accordance with [22,23,24,25,26,27,28,29]:
  • HSGWPE gross energy efficiency:
η b = W U + W CPT W I · 100 [ % ] ,
  • HSGWPE net energy efficiency:
η n = W U W I · 100 [ % ] ,
  • HEx efficiency:
η SC = W 2 , HEx W 1 , HEx · 100 [ % ] ,
  • Pipeline temperature (heat) losses (percentage):
p i = θ Ii   θ Ei θ Ii · 100 [ % ] ,
  • Pipeline specific temperature losses:
p Si = θ Ii   θ Ei l i [ ° C / m ] ,
where θIi, θEi—inlet and outlet temperature for section “i” pipeline [°C], li—length of section “i” pipeline [m].
  • Specific thermal energy consumption of buildings (per area unit or volume unit):
C A , Wi = W Ui S di [ kWh / m 2 ] ,   C V ,   W i = W ui V i [ kWh / m 3 ] ,
This indicator can also be calculated for the entire analyzed system:
C A ,   W = W U i = 1 n S di [ kWh / m 2 ] ,   C V , W   = W U i = 1 n V i [ kWh / m 3 ] .

3.3.5. Environmental Impact Assessment

Since the primary energy source is a “clean” one, the thermal energy being transferred from the geothermal water, the assessment is limited to the calculation of the amount of pollutants released into the atmosphere while the electricity needed to drive the pumps is generated. Therefore, the energy mix should be considered. By the time this study was developed, the average energy mix specific to Romania had the following GHG values [31]:
  • CO2 = 314.52 g/kWh;
  • SO2 = 34.74 g/kWh;
  • NOX = 0.64 g/kWh.

4. Survey, Measurements, and Results

Most of the data required for the assessment of the CEB components were measured using the devices presented in Section 2, while the others were taken from the beneficiary’s database.

4.1. Gathered Data from the UO Database

In order to perform the energy audit, historical data and offline recordings were gathered from the UO database. Table 2 shows the values of the geothermal water supplied to the campus heating system for the 2018 and 2019 periods, without including private consumers (houses, blocks).
Figure 5 shows the monthly distribution of GTW consumption in 2018 and 2019.
Analyzing the GTW consumption, it can be found that it is much higher in the winter time than the rest of the year, which means that most of the GTW is used for heating.
To increase the accuracy of the analysis, Table 3 and Table 4, respectively, and Figure 6 and Figure 7 show the most important measured data (temperatures and flowrates) that characterize the daily consumption of thermal energy for a winter month and a summer month in the year 2019.

4.2. Data from Direct Measurements

Additional measuring devices (mentioned in Section 2) were used to collect on-site data that was added to the already existing ones (gathered from the databases). Direct and detailed measurements on HSGWPE equipment and components were performed in the interval 20–22 January 2020.

4.2.1. Power Analyzer Recordings

Measurements were performed in order to determine the amount of EE consumed by HSGWPE. Figure 8 shows the daily load curves for TS1 electricity consumers. They were monitored, and data was recorded by the power analyzer [17].

4.2.2. Thermal Camera Measurements

Using a Ti20-Fluke infrared thermometer, temperature measurements were performed at 40 points of HSGWPE equipment and installations [17]. These points have a precise location—exactly the places where temperature values are important in order to describe HSGWPE status, the partial consumption and losses, and to be able to identify measures to reduce energy losses. Figure 9 and Figure 10 show a selection of images taken by the thermal camera.

4.2.3. Synthesis of Measured Data

Direct measurements performed on the HSGWPE equipment and components, using the power analyzer, the thermal camera Ti20, and the existing measuring devices, resulted in the following values, presented in Table 5 and Table A2 (in the Appendix A).

5. Results

Using the methodology for CEB presented in Section 3, the numerical values of CEB components were determined. The obtained results were structured as follows:
  • CEB—current load (hourly);
  • CEB—maximum load (for a winter month);
  • CEB—minimum load (for a summer month);
  • Annual CEB.
CEB components are shown in energy flow tables and diagrams (Sankey). The last part of this Section shows the values of the energy performance indicators and GHG indicators.

5.1. Hourly Complex Energy Balance

It is performed based on the data collected from direct measurements, by applying the methodology for calculating CEB presented in Section 3.

5.1.1. Details and Clarifications with Respect to the Calculated Values

a.
SF flow rate inside the distribution networks as well as at the entrance point to buildings were not measured because of their inaccessibility, therefore:
  • SF flow rate inside the HEx was estimated based on the rated values, considering the GTW flow rate as well;
  • SF flow rate inside the buildings (Di) was estimated as a share of the total flow rate (Dt) using the quasi-empirical equation:
D i = k i · D t ; k i = di S di li di S di li
where di—supply pipe diameter [mm]; Sdi—the gross floor area of the building [m2]; li—the length of the SF pipeline [m]; ki—calculation constant
Because UCD2.2 piping has got a circulation pump for the secondary fluid, the length of its pipeline was not considered. When calculating the total useful flow rate of the secondary fluid (buildings inlet), distribution network losses were cosidered, as well. During CEB survey and performed measurements, no secondary fluid leaks were reported.
b.
SF temperature was not measured directly. Temperature measurements were performed on the non-insulated surface of heating pipes placed inside the underground concrete thermal duct, on sections connected to buildings. When comparing the directly measured temperatures of GTW and SF with the measurements of the pipe temperature, a negligible deviation has been found for SF and deviations of (2–4) °C—for GTW.
c.
GTW flow rate
  • Based on the measured data, the shares of GHW between TS1 and TS2, for a winter month, is:
    DGTW = DI,GS1 + DI,GS2 = 72 m3/h,
    So, DI,GS1 = 64.44 m3/h (89.5%), DI,GS2 = 7.56 m3/h (10.5%).
  • Similarly, for a summer month: DI,GS1 = 10.5 m3/h; DI,GS2 = 2.32 m3/h;
  • For TS1, the shares of SF for space heating and DHW is: DI,GS1 = 57.53 m3/h (winter) and DI,GS1 = 10.5 m3/h (summer) exclusively for DHW preparation (18.2%). Therefore, the GTW flow rate used for space heating in thermal substation TS1 is about 81.8% of the total flow rate in January 2019, representing 47.03 m3/h;
  • The shares between HEx1, HEx2 and HEx4 are: 1%—for HEx4 (GWT input to this HEx is controlled); between HEx1 and HEx2—depending on their capacity: 63.2% for HEx2 and 36.8% for HEx1;
  • For TS2, for the most represantative winter month—January—the share of GTW between HEx5 and HEx6 is calculated according to the above results: HEx5 (DHW): 2.32 m3/h (30.7%); HEx6 (space heating): 7.56—2.32 = 5.24 m3/h (69.3%).
d.
Wellhead GTW temperature in EWS (outlet pipe from EWS) is 85 °C, according to drilling 4796 documentation [21].
e.
Distribution network losses (sections connected to TS1) were calculated based on the average values [28], resulting in Dp,2 = 11.33—10.9 = 0.43 m3/h; Dp,2 = 10.32 m3/day (3.8%). No losses were reported for the transmission network, distribution network supplied from TS2, or inside the buildings. So, all SF losses belong to the DN and for calculations purposes, it was proportionally split between the two underground concrete thermal ducts: UCD1: 0.16 m3/h (1.4%); on UCD2: 0.27 m3/h (2.4%).

5.1.2. Enthalpy Values

The key data for any thermal energy balance is enthalpy. Based on the measured values for temperature, and using the specific tables [30], the enthalpy values for the involved energy carrier agents were determined (Table 6).

5.1.3. Flow Rates

Based on the above hypothesis and results, the following flow rate values are obtained for the detailed analysis period, 20–22 January 2020:
a.
GTW flow rate
  • GTW inlet pipe to TS1: DI,GS1 = 64.44 m3/h; split between the four heat exchangers as follows: HEx1: 19.2 m3/h; HEx2: 33 m3/h; HEx3: 11.7 m3/h; HEx4: 0.54 m3/h;
  • GTW inlet pipe to TS2: DI,GS2 = 7.56 m3/h; out of which HEx5: 5.24 m3/h; HEx6: 2.32 m3/h.
Usually, high-capacity heat exchangers (HEx1, HEx2) have very good energy efficiency. In [32] a value of 98% is indicated when operating at nominal load. Additionally, the variation in energy efficiency with respect to load is presented. Therefore, for the HEx load during the detailed analysis period, the following efficiency values were considered (HEx + connecting pipes inside TS): HEx1, HEx2 and HEx3—95%; HEx5, HEx6—65%; and HEx4—50%.
b.
SF flow rate has been calculated based on the energy balance equation for each heat exchanger and its connections using:
ηHEx × WI,HEx = WE,HEx,
where: WI,Hex—HEx energy input (GTW energy); WE,Hex—HEx energy output (SF energy); ηHEx—HEx + connecting pipes efficiency
The obtained values are shown in Table 7.

5.1.4. Systemic Assessment of Useful Energy

Based on the measured and collected data and applying the dedicated equations, the useful energy for each building has been calculated. The resulting values are presented in Table 8.

5.1.5. Real Hourly Energy Balance

a.
HSGWPE input energy was calculated according to the CEB methodology, considering the flow rate and enthalpy variation values. Average power values were used to calculate the electricity input [28]. The results are listed in Table 9.
b.
Energy losses in HEx and its connecting pipes were calculated based on their estimated efficiency:
Wp,SCD = (1 − ηSCD)·WGTWHEx,
c.
DN energy losses were calculated using the energy balance equation and the results are shown in Table 10:
WI,DN = WU + Wp,DN,
Synthesis of CEB components is shown in Table 11 and Figure 11.
d.
DN input energy was calculated as a difference between the energy input and energy losses. For example, the energy input to the distribution network through HEx1 is:
WI,DNHEx1 = (2.547 − 0.127)·106 kJ = 2.42·106 kJ,

5.2. Annual Energy Balance

To calculate the CEB components, data from 2019 were used, as this is the most relevant in terms of the current state of HSGWPE performance. The annual consumption of thermal energy, and subsequently geothermal water, decreased in 2019 compared to 2018 (as shown in Table 2), mainly because of energy efficiency improvements to thermal substations and buildings. Additionally, the outdoor temperatures in that winter were slightly higher than usual, resulting in a lower heat demand. The electricity consumption in the analyzed system is much lower than the thermal energy consumption and is considered to be proportional to the handled energy carrier agents.
The results of the energy calculations are presented in Table 12, while in Figure 12 the annual CEB diagram is represented.

5.3. Energy Performance Indicators (EnPI)

They were calculated applying the methodology given in Section 3, based on the data presented in Section 4, respectively 5.1 and 5.2. The results are shown in Figure 13 and Table 13.

5.4. Environmental Impact Assessment

In Romania, the primary energy comes from fossil fuels for the vast majority of thermal energy end-users. This is not the case in UO, where—for the moment—the thermal energy source is geothermal water that does not release GHGs into the atmosphere. Nevertheless, the UO campus may be connected to the Municipality of Oradea district heating network in the near future. This is more likely because the wellhead station is not the property of UO, and in other similar cases in Oradea, the produced thermal energy is injected into the municipality’s district heat network. Therefore, the environmental impact will be assessed considering the hypothesis that UO is supplied from the same source of energy as the municipality’s district heating system. This is a cogeneration power plant firing natural gas. About 90% of the total thermal energy is produced by natural gas combustion that results in CO2 and NOx emissions. The following values of the emission factor [33] εCO2 = 50·10 3 g/GJ; εNOx = 150 g/GJ are considered.
The results are presented in Table 14, considering the environmental impact of the electricity consumption as well.
This assessment was made considering that the current TS will continue to operate and SF will be supplied from the municipality’s district heating system as the primary energy agent.

6. Recommended Measures to Improve Energy Efficiency

Most of the big Romanian cities have large district heating systems to serve their populations, and their thermal energy flows are huge. Centralized heating systems can also be found in industrial parks and platforms, as well as on university campuses. Therefore, the energy efficiency of heat carrier networks is a topical issue, both for the managers of the district heating companies and for the end-user. The performed measurements and calculations, together with the analyses of energy use for HSGWPE on the UO campus, allow the assessment of installations and equipment states, and their efficiency levels. To identify and develop energy conservation opportunities and recommend measures to improve energy and economic efficiency, while reducing the negative impact on the environment are the key elements of this energy audit. The conclusions refer to both the thermal network (transmission network + thermal substations + distribution network) and the buildings, but the recommendations are made only for the thermal network as the buildings have not been analyzed in detail as they are not the object of this paper.
Based on the calculated data, the following measures to improve energy efficiency were identified (Table 15).

Work Assumptions

Hypothesis 1 (H1). 
Keep the present renewable energy source (geothermal water).
Hypothesis 2 (H2). 
The source of thermal energy is going to be the municipality district heating network.
To analyze the economic efficiency of the proposed measures and to assess the payback period, the net present value indicator was applied [33]. The assessment was made for the year 2020, considering a 30% increase in thermal energy consumption for space heating on the UO campus with respect to 2019 values.
By applying the recommended measures presented in Table 15, a predicted optimized CEB is developed, with its components highlighted in Figure 14a,b.
The estimated EnPIs are shown in Table 16, while the estimated GHGs emissions for Hypothesis 2 are shown in Table 17.
The reduction of GHG emissions by implementing energy efficiency improvement measures will be in line with the 2020 forecast:
  • ΔCO2 = 862 tons/year;
  • ΔSO2 = 5.1 tons/year;
  • ΔNOx = 2.49 tons/year.

7. Conclusions

Conceptually, the University of Oradea heating network is compatible with the principles of sustainable development, the source of thermal energy being a renewable one (geothermal water), rationally exploited, and mostly reinjected (after use), so that the reservoir maintains its energy potential.
In operational terms, the University of Oradea heating network has a number of technological and functional deficiencies, requiring substantial rehabilitation/modernization. A more rigorous settlement of the thermal energy consumption of private consumers (blocks of flats, houses) is recommended.
The buildings supplied by the UO heating network have not been analyzed in detail in terms of energy efficiency, not being included in the subject of this analysis. Estimates of the specific consumption of buildings (Table 14) show:
  • The average value of the indicator “specific consumption of thermal energy per square unit” ( c A , W   = 161 kWh/m2 year) is competitive for the current state of educational buildings in Romania, for which average values of total energy consumption (TE + EE) are recommended [23,24,25] in the range [200–296] kWh/m2·yr;
  • A large dispersion of the energy efficiency of buildings can be observed, values in the range: c A , W = [39 ÷ 364] kWh/m2·year for thermal energy only. The buildings having higher values c W S than the national average (248 kWh/m2·year) are: C3, Y, P, R, Z, and S;
  • Most of the buildings included in this study have a higher value of c A , W than the maximum recommended for nZEB public buildings [34], but some of the buildings included in the national statistics are equipped with complex systems: heating, ventilation, and air conditioning.
According to the energy audit methodology, the energy balance components are divided on energy types and HSGWPE components. The largest amount of the input energy (about 98.5%) is renewable, namely geothermal water, with electricity having a much lower share (about 1.5%). The input energy is transferred to end-users, mainly through thermal substation TS1 (about 89.5%) and about 10.5% through TS2 and is used for space heating (about 64%—annual average) and domestic hot water production (36%—annual average).
Energy losses are calculated for the system components (transmission network, thermal substations, and distribution network) and during different periods of operation (winter season—when both SF for space heating and DHW are produced, respectively, and summer season—when only DHW is produced). Atypically, there is a better energy efficiency during the lower demand period, respectively in the summertime when only DHW is produced, which mainly highlights the very advanced wear of the DN pipeline insulation.
Energy losses (% of input energy) are distributed as follows: presented in Figure 15.
For all the highlighted components (TN, TS, DN), the energy losses exceed the rated values [35] and usual values [28,36]. The worst component is the distribution network of secondary fluid, having very high losses.
These DN losses are either flow losses (leaks) or heat transfer losses (mainly conduction). The latter ones are dominant and are caused by the total absence of pipeline insulation or a highly degraded one. Nevertheless, flow losses have significant values (about 0.43 m3/h) meaning about 3.8% in winter months. The values of the “temperature drop” indicators (pT, pS, Table 13) are pointing out very probable flow losses on sections UCD1, UCD2 and the connecting sections to buildings M and N.
DN sections highlighted in Table 14—meaning the great majority of the heating network—has energy losses through insulation above the standardized limit of the newly commissioned heating networks (where pSmax = 0.5 °C/km) [35].
Based on the values listed in Table 14, a hierarchy of DN sections can be carried out, indicating the degradation degree of the pipelines’ insulation, thus setting the priority order for rehabilitation.
TS energy losses are significant and consists of both radiation losses of connecting pipes (mostly without insulation) and the inevitable losses in HEx which often work at partial loads.
TN energy losses are above the standard limit for new heating network [35]. This is both because there are areas without insulation, and the poor quality of insulation. For instance, the insulation of section TN1 is mineral wood—probably wet, while section TN2 has pre-insulated pipes that seems to be degraded.
Thermally depleted geothermal water still has a significant energy potential. The largest part (89.5%—peak load in wintertime and 81.9%—summer lower demand) is reinjected into the reservoir by using the injection well, but the recommendation of this study is to introduce the cascaded uses of geothermal water in order to further cool it by extracting more energy. Additionally, thermally depleted geothermal water discharged from thermal substation TS2 is sent as waste water into the sewer system. This is not a sustainable solution. Therefore, it is recommended to collect it and send it to the injection well.
So, based on all the above findings resulting from the measurements and calculations of BEC, a set of measures to improve the energy performance of the heating system were recommended in Section 6. In order to determine the impact of these proposed improvement measures, a predicted optimized energy balance is developed. It shows a reduction of energy losses both in TN and DN, leading to an increase of about 30% for the energy performance indicators (from 56.1% to 85.9%).
Modernization and rehabilitation works are under way at the University of Oradea campus, targeting the heating system as well. As a future work, the authors intend to do a new analysis in order to calculate the real impact of the implementation of our recommended measures and compare those values with the ones calculated in this paper in the predicted optimized BEC.

Author Contributions

Conceptualization, G.B., I.F. and C.H.; Data curation, A.F. and A.B.; Formal analysis, C.H., C.B. and A.B.; Funding acquisition, G.B.; Investigation, I.F., A.F. and A.B.; Methodology, G.B., I.F. and C.B.; Project administration, C.H.; Resources, C.H.; Supervision, G.B.; Visualization, C.B. and A.B.; Writing—original draft, I.F.; Writing—review & editing, C.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

CEBcomplex energy balance
CSthermal energy consumer
CWcold water
CWScold water source
DGWdepleted geothermal water
DHWdomestic hot water
DNdistribution network
EEelectrical energy
EWSextraction well station
GHGgreenhouse gases
GWTgeothermal water
HExheat exchanger
HSGWPEheating system with geothermal water as primary energy
IWSinjection well station
PPRpolypropylene
SEWsewer
SFsecondary fluid
TEthermal energy
TNtransmission network
TSthermal station
UCDunderground concrete duct
UOUniversity of Oradea

Appendix A

Table A1. Components of the heat distribution network and buildings involved in HSGWPE.
Table A1. Components of the heat distribution network and buildings involved in HSGWPE.
DN Section Building
FromToLength
[m]
Diameter [inch]Pipe and Insulation MaterialCodeArea
Sd [×103 m2]
Volume [×103 m3]
TS1/HEx1C254St/MWC4.316.13
TS1/HEx1L254St/MWIT1.314.22
TS1/HEx1UCD1808steel/no insulation---
UCD1A553St/MWA2.138.3
UCD1D + E384St/MWD + E4.721.9
UCD1F213St/MWF1.778.04
UCD1I22steel/no insulationI0.732.65
AH41.5steel/no insulationH0.0610.15
EG41.5St/MWG0.0530.11
TS1/HEx2UCD21808St/MW---
UCD2.1UCD2.11101.5steel/no insulation---
UCD2.2UCD2.22854steel/no insulation---
UCD2B74steel/no insulationB3.5213.04
UCD2M91.5steel/no insulationM0.963.1
UCD2N101.5St/MWN0.110.41
UCD2.1A132steel/no insulationA0.863.29
UCD2.1P52steel/no insulationP0.744.46
UCD2.1R72St/MWR0.150.42
UCD2.1Shooting room21.5steel/no insulationShooting room0.120.37
UCD2.1Sports field571.25PPRSports field0.040.04
UCD2.1L-IMT381.5St/PIL-IMT0.592.01
UCD2.1T-ID372PPRT-ID0.270.78
UCD2T2393St/PIT2.739.69
UCD2S958St/PIS5.8731.6
UCD2C2554St/MWC23.8810.11
UCD2-C2C11514St/MWC13.8810.11
UCD2.2U124St/MWU1.043.77
UCD2.2V92St/PIV2.879.98
UCD2.2X182St/PIX0.672.54
UCD2.2Y242St/PIY0.230.68
UCD2.2Z162St/PIZ0.391.48
C1Wooden church1061.5St/MWWooden church0.050.18
TS1/HEx4J652PPRJ0.541.92
TS1/HEx1K642PPRK0.100.39
TS2/HEx5C343PPRC32.687.22
TS1/HEx1C254St/MWC4.316.13
Where: UCD1, UCD2 (UCD2.1 UCD2.2)—underground concrete thermal duct; (d, l)—diameter and length of the section; (Sd, V)—surface area and volume of the heated building; St/MW—steel pipe, insulated with mineral wool, St/PI—steel pipe, pre-insulated; PPR—polypropylene pipe.
Table A2. HSGWPE temperature measurements using thermal camera.
Table A2. HSGWPE temperature measurements using thermal camera.
Measurement PointTemperature [°C]Measurement PointTemperature [°C]
GTW inlet pipe, HEx181.1i/o pipe/ambient building R49.2/44.3/17.1
GTW inlet pipe, HEx281.5i/o pipe/ambient shooting room49.2/44.3/17
GTW inlet pipe, HEx380.4i/o pipe/ambient L-IMT45.2/35/25.2
GTW outlet pipe, HEx444.7i/o pipe/ambient T-ID48.6/36.2/20.6
GTW outlet pipe, HEx247.2i/o pipe/ambient building T45.2/35.2/23.7
SF supply pipe from HEx156.7i/o pipe/ambient building S49.2/34/21
SF supply pipe from HEx257.2i/o pipe/ambient building C149.4/45/26.7
SF return pipe from DN, to HEx139.7i/o pipe/ambient building C249.5/43/26.1
SF return pipe from DN to HEx241.1i/o pipe/ambient building U47.7/33.8/20
GTW outlet pipe, HEx340.1i/o pipe/ambient building V49.7/41.1/24
CW inlet pipe in HEx312.4i/o pipe/ambient building X51.1/43.8/22.7
DHW supply pipe from HEx343.2i/o pipe/ambient building Y46.9/34.4/21.6
i/o pipe/ambient building C57/46.6/25.6i/o pipe/ambient building Z49.2/40.7/22.8
i/o pipe/ambient building J36.6/26.6/20i/o pipe/ambient building C346/41/25
i/o pipe/ambient building K55.9/50.6/22i/o pipe/ambient block of flats47.7/42.8/25
i/o pipe/ambient building I53.5/39.2/27i/o pipe/ambient private houses47.7/42. /25
i/o pipe/ambient buildings D + E56.1/42.2/23i/o pipe/ambient building M47.5/40/19.2
i/o pipe/ambient building F53.4/40.6/25.8i/o pipe/ambient building L50.4/37.9/25
i/o pipe/ambient building A55.6/42.9/24.7GTW pipeline at EWS80.8
i/o pipe/ambient building B50.1/44.2/25.1GTW, HEx5 and HEx6 i/o pipe81/44.1
i/o pipe/ambient building N47.2/42.5/17.5DHW supply pipe from HEx640.1
i/o pipe/ambient building O49.7/45.2/23.3DHW inlet pipe in (C1 + C2)35.6
i/o pipe/ambient building P49.2/40.5/23SF supply pipeline from HEx5/ inlet pipe to C3/ambient C350/41/25

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Figure 1. HSGWPE diagram: EWS—geothermal extraction well station; IWS—injection well station; TS1, TS2—thermal substations; CS1, CS2—TE end users; CS—other TE consumers; TEM—TE meter, GTW—hot geothermal water; DGW—depleted geothermal water; TN—transmission network (for GTW); DN—distribution network; SF—secondary fluid; CWS—cold water (CW) source; SEW—sewer.
Figure 1. HSGWPE diagram: EWS—geothermal extraction well station; IWS—injection well station; TS1, TS2—thermal substations; CS1, CS2—TE end users; CS—other TE consumers; TEM—TE meter, GTW—hot geothermal water; DGW—depleted geothermal water; TN—transmission network (for GTW); DN—distribution network; SF—secondary fluid; CWS—cold water (CW) source; SEW—sewer.
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Figure 2. Main thermal station diagram (TS1): DHW—domestic hot water; PS1, PS2—pumping stations; CWS—cold water source (for water losses and DHW); SFS, SFR—secondary fluid supply and return pipes; TEM—own TE meter; HE,i, HEi.j—heat exchangers; UCD1, UCD2—underground concrete ducts; CS1.1, CS1.2—TE consumers for TS1.
Figure 2. Main thermal station diagram (TS1): DHW—domestic hot water; PS1, PS2—pumping stations; CWS—cold water source (for water losses and DHW); SFS, SFR—secondary fluid supply and return pipes; TEM—own TE meter; HE,i, HEi.j—heat exchangers; UCD1, UCD2—underground concrete ducts; CS1.1, CS1.2—TE consumers for TS1.
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Figure 3. Second thermal station diagram (TS2).
Figure 3. Second thermal station diagram (TS2).
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Figure 4. UO central campus plan and HSGWPE components.
Figure 4. UO central campus plan and HSGWPE components.
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Figure 5. HSGWPS geothermal water monthly consumption.
Figure 5. HSGWPS geothermal water monthly consumption.
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Figure 6. TE daily consumption for TS1 [January 2019].
Figure 6. TE daily consumption for TS1 [January 2019].
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Figure 7. TE daily consumption for TS1 [July 2019].
Figure 7. TE daily consumption for TS1 [July 2019].
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Figure 8. Daily load curves for TS1 electricity consumers.
Figure 8. Daily load curves for TS1 electricity consumers.
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Figure 9. HEx1 geothermal water inlet pipe.
Figure 9. HEx1 geothermal water inlet pipe.
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Figure 10. HEx1 geothermal water outlet pipe.
Figure 10. HEx1 geothermal water outlet pipe.
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Figure 11. Energy flow diagram of the real hourly CEB, 20–22 January 2020.
Figure 11. Energy flow diagram of the real hourly CEB, 20–22 January 2020.
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Figure 12. Energy flow diagram of the real CEB for HSGWPE [overall year 2019].
Figure 12. Energy flow diagram of the real CEB for HSGWPE [overall year 2019].
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Figure 13. Energy performance indicators for HSGWPE.
Figure 13. Energy performance indicators for HSGWPE.
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Figure 14. Energy flow diagram of the predicted optimized annual energy balance (a) forecast 2020—Hypothesis 1; (b) forecast 2020—Hypothesis 2.
Figure 14. Energy flow diagram of the predicted optimized annual energy balance (a) forecast 2020—Hypothesis 1; (b) forecast 2020—Hypothesis 2.
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Figure 15. Energy losses in transmission network, thermal stations and distribution network.
Figure 15. Energy losses in transmission network, thermal stations and distribution network.
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Table 1. Technical data of the plate heat exchangers installed into the UO thermal stations.
Table 1. Technical data of the plate heat exchangers installed into the UO thermal stations.
DataHEx1.1
HEx1.2
HEx2.1
HEx2.2
HEx3HEx4HEx5.1
HEx5.2
HEx6.1HEx6.2
Rated capacity [kW]2400140058050058022796
Primary flowrate [m3/h]63.2737.23161015.762.1
Secondary flowrate [m3/h]175.09121.94251625.377
Transfer area [m2]69.9240.81714.613.64.954.35
Table 2. HSGWPE geothermal water input.
Table 2. HSGWPE geothermal water input.
YearGTW Consumption [m3]Price [Euro/m3]
2018272,6020.76
2019259,8050.77
Table 3. Temperatures and flowrates of the GTW, SF (space heating and DHW) in TS1 (January 2019).
Table 3. Temperatures and flowrates of the GTW, SF (space heating and DHW) in TS1 (January 2019).
DateθIGS1
[°C]
θEGS1
[°C]
DIGS1
[m3/h]
θISF1
[°C]
θESF1
[°C]
DSF
[m3/h]
0184.245.650.447399.7
0284.245.650.447399.7
0384.245.650.447399.7
0484.245.650.447399.7
0584.245.650.447399.7
0684.245.650.447399.7
0784.445.650.447399.7
0884.446.652.2463911.96
0984.546.659.4524312.3
1084.347.555.8504012.3
1184.849.864.8504212.2
1284.753.373.8514411.8
1384.753.373.8514411.8
1484.753.373.8514411.8
1584.751.668.4514412.2
1684.651.166.6514412.2
1784.449.461.2514212.1
1884.349.359.4514312
1984.551.463514211.6
2084.551.463514211.6
2184.551.463514211.6
2284.550.763514312
2384.652.468.4524312
2484.75372524411.9
2584.75372524411.9
2684.551.263504211.6
2784.551.263504211.6
2884.551.263504211.6
2984.451.663504211.9
3084.349.755.8494011.9
3184.34957.6504212
Average value84.549.657.5349.841.711.33
Table 4. Temperatures and flowrates of GTW and SF (DHW) in TS1 [July 2019].
Table 4. Temperatures and flowrates of GTW and SF (DHW) in TS1 [July 2019].
DateθIGS1
[°C]
θEGS1
[°C]
DIGS1
[m3/h]
DSF
[m3/h]
0176.841.810.89.9
0277.142.4910.1
0376.94210.810.4
047743.310.810
0576.942.4910
0676.946.910.89.96
0776.946.910.89.96
0876.946.910.89.96
0976.544.510.810.2
1076.742.2911.1
1176.741.9910.2
1276.743.110.810.3
137744.312.610.3
147744.312.610.3
157744.312.610.3
167742.710.810.7
1776.942.810.810.7
1876.942.310.810.7
197742.410.810.8
2076.943.310.810.6
2176.943.310.810.6
2276.943.310.810.6
237742.910.810.96
2477.142.710.810.92
25774198.92
2677.142.5911.13
2777.443.910.810.94
2877.443.910.810.94
2977.443.910.810.94
3077.444.312.611.12
3177.344.810.811.2
Average value7743.510.510.9
Table 5. Measurement data collected 20–22 January 2020 (average values).
Table 5. Measurement data collected 20–22 January 2020 (average values).
Name/SymbolMUValue
Well head GTW flow rate [DGTW]m3/h72
GTW flow rate at TS1 inlet [DIGS1]m3/h64.44
GTW temperature at TS1 inlet [θIGS1]°C84
Themally depleated GTW outlet temperature [θEGS1 ≡ θE,HEx]°C52
CW flow rate at TS1 inlet [DAI1]m3/h13.35
CW temperature at TS1 inlet [θAI1]°C12.4
GTW pressure at TS1 inlet [PIGS1]bar3
SF temperature on the heating circuits connected to TS1
DN supply pipe [θI,SF1]°C54
DN return pipe [θE,SF1]°C42
SF pressure on the heating circuits connected to TS1
DN supply pipe, after HEx [PI,SF1]bar3.2
DN return pipe, before HEx [PE,SF1]bar3.6
Outdoor temperature (ambient) [θa]°C1.5
Table 6. Enthalpy values of energy carrier fluids inside TS at hourly load.
Table 6. Enthalpy values of energy carrier fluids inside TS at hourly load.
Energy Carrier Fluid/Measurement Point/Calculation Areai
[kJ/kg]
Δi [kJ/kg]Measurement Point/
Calculation Area
i
[kJ/kg]
Δi
[kJ/kg]
GTW—well head356.83-SF return to HEx2171.6
GTW—TS1 inlet352.63-SF in UCD2 and CS1.2 67.5
GTW—TS2 inlet352.63-GTW—HEx3 output167.4
GTW on TN1-4.2GTW—HEx4 output187.9
GTW on TN2-21.31CW—HEx3-inlet pipe52
GTW—TS1 outlet (HEx1 + HEx2)217.26 DHW—supply line from HEx3180.4
GTW—TS2 outlet179.53 DHW—end-user inlet (C1 + C2)148.6
GTW on TS1—(HEx1 + HEx2) 135.37GTW on HEx3 185.23
GTW on TS2 173.1GTW on HEx4 164.73
SF supply from HEx1234 DHW on HEx3 128.4
SF return to HEx1165.7 DHW at end users C1 + C2,
temp. range 25–35.6 °C
44.23
SF in UCD1 and CS1.1 68.3DHW at end user C3, 63
SF—supply from HEx2239.1 temp. range 25–40.1 °C
Table 7. Average SF flow rate in 20–22 January 2020.
Table 7. Average SF flow rate in 20–22 January 2020.
Heat ExchangerSF Flow Rate [m3/h]
HEx262.36
HEx315.87
HEx40.64
HEx514
HEx63.7
Table 8. Hourly values of useful energy components in 20–22 January 2020.
Table 8. Hourly values of useful energy components in 20–22 January 2020.
BuildingD
[m3/h]
Δi
[kJ/kg]
Wu
[106 kJ]
C1243.60.523
J0.6441.70.026
K0.522.10.011
I1.0460.60.06
(D + E + G)5.1254.70.277
F2560.11
(A + H)2.67530.14
B13.0624.60.315
M2.0231.30.062
N0.5919.60.011
O1.5418.80.029
P3.7836.30.136
R1.2420.50.025
Shooting room0.4220.50.008
Sports field0.04820.50.001
L-IMT0.342.60.013
T-ID0.351.80.015
T4.7441.70.155
S13.0663.40.813
C25.3327.30.142
C14.4518.40.081
U2.96580.17
V3.5535.50.126
X1.5430.50.047
Y0.8152.20.043
Z1.1535.50.043
L3.7752.30.156
Total SF for space heating—HEx1 1.277
Total SF for space heating—HEx2 2.235
Total SF for space heating—HEx4 0.026
(C1 + C2)/DHW (HEx3)15.87971.532
Total TS1 5.07
C3/SF for space heating1437.60.521
C3/DHW3.7630.23
Total TS2 0.751
Total TS1 + TS2 5.821
Table 9. Average hourly values of WI 20–22 January 2020.
Table 9. Average hourly values of WI 20–22 January 2020.
Name/EquipmentSymbolMUValue
Total GTW energy input in TS1 of which:WGTW1GJ9.136
HEx1 + HEx2WGTW1,2GJ6.925
HEx3WGTWHEx3GJ2.124
HEx4WGTWHEx4GJ0.087
GTW energy input in TS2WGTW2GJ1.282
ElectricityWEEkWh43.47
EWSWEEEWSkWh11.65
TS1WEETS1kWh31.82
Total TN energy losses of which:Wp,TNGJ0.324
Between EWS and TS1 (TN1)Wp,TN1GJ0.265
Between EWS and TS2 (TN2)Wp,TN2GJ0.059
Table 10. Average hourly values of DN energy losses, period 20–22 January 2020.
Table 10. Average hourly values of DN energy losses, period 20–22 January 2020.
DN Thermal Energy ComponentSymbolMUValue
DN-SF from TS1-HEx1, to CS1.1Wp,DN1.1106 kJ1.143
DN-SF from TS1-HEx2, to CS1.2Wp,DN1.2106 kJ1.924
DN-SF section from TS1-HEx4, to building JWp,DNJ106 kJ0.0175
DN-DHW from TS1-HEx3, to CS1.2Wp,DN DHW1106 kJ0.486
DN-SF from TS2 to C3Wp,DNC3106 kJ0.083
Table 11. HSGWPE real hourly energy balance, period 20–22 January 2020.
Table 11. HSGWPE real hourly energy balance, period 20–22 January 2020.
Name/EquipmentSymbolValue
106 kJ%
1. Energy inputWI10.898100
 1.1. GTWWGTW10.74298.57
 1.2. EEWEE0.1561.43
2. Energy outputWE10.898100
 2.1. Useful energyWU5.82153.41
  a. From TS1WU,TS15.0746.5
  b. From TS2WU,TS20.7516.9
 2.2. Energy lossesWp4.92145.16
  a. TNWp,TN0.3242.97
  b. TS (HEx and connecting pipes)Wp,TS0.94358.66
  c. DNWp,DN3.653533.53
3. Own energy consumptionWCPT0.1561.43
Table 12. Results of the real CEB, for maximum load, minimum load, and average [(overall year 2019).
Table 12. Results of the real CEB, for maximum load, minimum load, and average [(overall year 2019).
Load LevelEnergy [×106 kJ]
WIWGTWWEE = WCPTWUWU,SHWU,DHWWpWp,TNWp,TSWp,DN
Max. (December)6025.8593590.83186.542355.6830.94242748.5188.2548.12012.1
Min. (June)1131.31114.217.644804.2-804.231035.1102.9171.9
Average (year 2019)37412.936850.2562.721004.114646.1635815846.111693404.511272.5
Table 13. Supply pipe temperature drop (hourly load) and TE specific hourly consumption for space heating 20–22 January 2020.
Table 13. Supply pipe temperature drop (hourly load) and TE specific hourly consumption for space heating 20–22 January 2020.
Section (Delimitation Points)Temperature DropBuildingTE Specific Consumption for Space Heating
pspT c A , W c V , W
[°C/m][%] [Wh/m2][Wh/m3]
TN between EWS and TS10.0071.18A + H17.764.6
TN between EWS and TS20.0071.18D + E + G16.23.5
DN-UCD1, between TS1 pt 10.0050.35F17.263.8
DN-UCD1, between pts 1–20.0755.31I22.836.29
DN-UCD2, between TS1 and pt 30.07112.4J13.373.76
DN-UCD2, between pts 3–40.0040.6K30.567.84
DN-UCD2.1, between pts 4–50.0070.8C33.789
DN-UCD2 (pts 4–6)0.00080.4IT33.110.27
UCD1—buildings (A + H)0.0222.1B24.866.71
UCD1—buildings (D + E + G)0.0050.35M17.945.56
UCD1—building F0.0050.19N27.787.45
TS1—building K0.01251.4A9.372.45
UCD2—building B0.0140.2P51.058.47
UCD2—building M0.295.2R46.316.53
UCD2—building N0.295.8Shooting room18.56
UCD2.1—building O0.0080.2Sports field6.96.9
UCD2.1—building P0.080.8T15.774.44
UCD2.1—building R0.0290.4S38.477.15
UCD2.1—Shooting room0.050.2C210.173.9
UCD2.1—L-IMT building0.118.5C15.82.23
UCD2.1—T-ID building0.0221.62L-IMT6.121.8
UCD2—building T0.029.24T-ID15.45.34
UCD2—building S0.0061.2U4.541.25
UCD2 – students dormitory C20.0050.6V12.23.5
UCD2—students dormitory C10.0030.8X19.55.14
UCD2.2—building U0.133.25Y51.917.57
UCD2.2—building Y0.0964.7Z39.88.07
TS1—building L0.25211.1C35420
Total23.886.35
Yearly value 20187118.9
Yearly value 201962.216.6
Table 14. Pollutants estimated to be released in the energy production process (TE—from the municipality district heating network) [tons].
Table 14. Pollutants estimated to be released in the energy production process (TE—from the municipality district heating network) [tons].
Pollutant20192020
EETEEETE
ConsumedTotal LossesDN LossesConsumedTotal LossesDN Losses
CO249.21840.7791.556363.92392.91029731.9
NOx0.15.52.41.70.137.13.12.2
SO25.4---7---
Table 15. Recommended measures to improve energy efficiency on the UO campus HSGWPE.
Table 15. Recommended measures to improve energy efficiency on the UO campus HSGWPE.
The Proposed MeasureEnergy Saving [toe/yr.]Investment Required [×103 lei]Return on Investment [Years]
Replacement of the existing energy carrier network at UO campus, with a new one, so that the technical norm I13—2015, point 8.88 to be met (heat losses should not exceed 0.5 °C/km). Detachable thermal insulation will be used on flanges/valves/other parts [17]379.14113.749—Hyp1
2.5—Hyp2
Replacement of TS connecting pipes with pre-insulated pipes that have specific losses according to norm I13—2015, and insulation for connections and flanges/valves/other parts with removable thermal insulation [17]31.72005.6—Hyp1
1.5—Hyp2
A share of GHW from TS1 to be supplied to HEx4, after the manifold and before the geothermal injection well station7.54.20.5—Hyp1
Hyp2—not suitable
Table 16. Estimated EnPI—according to the predicted optimized CEB.
Table 16. Estimated EnPI—according to the predicted optimized CEB.
AssumptionEnPI
ηgross [%]ηnet [%]
Hypothesis 186.785.1
Hypothesis 286.585.9
Table 17. Estimation of pollutant emissions developed for the consumed energy [forecast 2020 – optimized CEB—Hypothesis 2.
Table 17. Estimation of pollutant emissions developed for the consumed energy [forecast 2020 – optimized CEB—Hypothesis 2.
PollutantEnergy Component
EETE
DeliveredTotal LossesDN Losses
CO217.31577.5213.550.4
NOx0.044.70.640.15
SO21.9---
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Bendea, G.; Felea, I.; Hora, C.; Bendea, C.; Felea, A.; Blaga, A. Energy Performance Analysis of a Heat Supply System of a University Campus. Energies 2023, 16, 174. https://doi.org/10.3390/en16010174

AMA Style

Bendea G, Felea I, Hora C, Bendea C, Felea A, Blaga A. Energy Performance Analysis of a Heat Supply System of a University Campus. Energies. 2023; 16(1):174. https://doi.org/10.3390/en16010174

Chicago/Turabian Style

Bendea, Gabriel, Ioan Felea, Cristina Hora, Codruta Bendea, Adrian Felea, and Alin Blaga. 2023. "Energy Performance Analysis of a Heat Supply System of a University Campus" Energies 16, no. 1: 174. https://doi.org/10.3390/en16010174

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