The paper discusses the issue of prediction of electric energy production using a photovoltaic system which is directly installed at the administrative building. The problem with solar energy, which has been transformed using photovoltaic systems for electricity, is the low capacity to accumulate an excess of produced electricity. This excess of electricity we link within the power grid to send outside the building where the energy was produced to be consumed elsewhere. In this way, we achieve the highest possible utilisation of electricity produced within the boundaries of thebuilding itself. One option is to create opportunities to recharge electric vehicles during working hours, at the time when the production of electricity is the highest but the consumption of electricity is not

Košičanová, Danica

Kušnír, Marek

Lojkovics, Ján

Vranay, František

Vranayová, Zuzana

Portal Czasopism Naukowych (E-Journals)

* Ph.D. Eng. Marek Kušnír, Doc. Ph.D. Eng. Danica Košičanová, Doc. Ph.D. Eng. Zuzana Vranayová, 
Ph.D. Eng. František Vranay, Eng. Ján Lojkovics, Department of Technical Building Equipment, 
Institute of  Architectural Engineering, Faculty of  Civil Engineering, Technical University 
of  Košice, Slovakia.
MAREK KUŠNÍR*, DANICA KOŠIČANOVÁ*, ZUZANNA VRANAYOVÁ*, 
FRANTIŠEK VRANAY*, JÁN LOJKOVICS*
ZERO ENERGY BALANCE PROPOSAL  
FOR OFFICE BUILDINGS
BUDYNEK BIUROWY O ZEROWYM  
BILANSIE ENERGETYCZNYM
A b s t r a c t
The paper discusses the issue of prediction of electric energy production using a photovoltaic system 
which is directly installed at the administrative building. The problem with solar energy, which has 
been transformed using photovoltaic systems for electricity, is the low capacity to accumulate an 
excess of  produced electricity. This excess of electricity we link within the power grid to send outside 
the building where the energy was produced to be consumed elsewhere. In this way, we achieve the highest 
possible utilisation of electricity produced within the boundaries of the building itself. One option is to 
create opportunities to recharge electric vehicles during working hours, at the time when the production 
of  electricity is the highest but the consumption of electricity is not.
Keywords: photovoltaic system, solar energy, heat pump, synergy
S t r e s z c z e n i e
W artykule przedstawiono analizę przewidywanej produkcji energii elektrycznej z system fotowoltaicz-
nego zainstalowanego bezpośrednio w budynku administracyjnym. Problemem z energią słoneczną, za-
mienianą przy użyciu systemów fotowoltaicznych w energię elektryczną, jest niska zdolność gromadzenia 
nadmiaru produkowanej energii elektrycznej. Ten nadmiar energii elektrycznej możemy przy połączeniu 
z siecią energetyczną wysłać poza granice budynku, w którym energia została wytworzona i zastosować 
w innym miejscu. W ten sposób możemy najlepiej wykorzystać energię elektryczną wytwarzaną w gra-
nicach budynku. Jedną z opcji jest stworzenie możliwości ładowania pojazdów elektrycznych w czasie 
godzin pracy, kiedy poziom produkcji energii jest najwyższy, a zapotrzebowanie na energię nie jest na 
wysokim poziomie.
Słowa kluczowe: system fotowoltaiczny, energia słoneczna, pompy ciepła, synergia
TECHNICAL TRANSACTIONS
CIVIL ENGINEERING
3-B/2014
CZASOPISMO TECHNICZNE
BUDOWNICTWO
260
1. Introduction
Renewable energy comes from natural resources that are all around us. It is up to us 
to discover how we can use these resources to our advantage. Through the right choice 
and combination of different sources of energy, we can achieve zero energy balance 
conditions for a building. In this article, we will deal with the synergy of renewable energy 
sources and how it affects and reduces energy consumption in buildings. Heat pumps and 
photovoltaics offer the most energy-efficient way to provide heating and cooling in many 
applications, as they can use the renewable heat sources in our surroundings. The experimental 
workplace of our Faculty of the “Economic Research Centre for Renewable Energy Sources 
and Distribution Systems” was founded with the purpose of investigating the possibilities to 
reduce the energetic costs of buildings tied to economy. The realised project of the Centre 
creates a real environment for effective implementation research of technologies in laboratory 
and operative conditions: technologies of co-generative elements, heat pumps, photovoltaic 
elements, thermal capillaries and technologies in the field of measurement and regulation. 
The solution is a project with the possibility to repeat this on other similar applications 
as well as the utilisation of experience and determination of the economical expedience 
of  implementation of researched technologies. In the contemporary phase of the research, 
we evaluate the operative behaviour of a zero energy balance building, interaction with 
building constructions and a study of the inner climate parameters and overall results for 
a central heat supply system.
At the heart of the ZEB concept is the idea that buildings can meet all their energy 
requirements from low-cost, locally available, non-polluting, renewable sources. 
At the strictest level, a ZEB generates enough renewable energy on site to equal or exceed 
its annual energy use. The following concepts and assumptions have been established to 
help guide the definitions for ZEBs.
2. Research methods of renewable energy sources – photovoltaic system
The existing photovoltaic system, made of monocrystalline photovoltaic panels, from 
which the measurements were taken, is located on the flat roof of an administrative building 
in Košice, Slovakia. Monocrystal photovoltaic panels have a rated efficiency of solar energy 
transformation at a level of around 20%. The system itself consists of 40 photovoltaic panels 
that are attached to two electric power converters. These converters record the measurement 
values of the amount of produced electricity at 5-minute intervals. Photovoltaic panels 
(2×2×10 pc.) are placed in rows on the flat roof of the building, supported by a metal frame 
structure. The resulting DC power from the photovoltaic panels is transformed into DC 
voltage with 2 inverters for a single-phase AC voltage and an automatically phased inverter 
for a single phase AC voltage to two phases of a low voltage distribution grid. Each inverter 
is equipped with fuses, which automatically disconnect the photovoltaic solar generator from 
the distribution network when subjected to critical deviations of the monitored parameters 
from the limits of standard values. The photovoltaic solar system is composed of 40 units 
of  photovoltaic panels. The peak power of one photovoltaic panel is 230 Wp (Fig. 1).
261
The PVGIS simulation program was used to simulate the photovoltaic system. In order 
to quantify the amount of energy produced, a mathematical method was developed to 
calculate the amount of incident solar energy on the Earth’s surface for any location and 
the inclination of solar panels. The measured and simulated values of produced electric 
energy are set for comparison with the calculated values. This methodology for calculating 
the amount of  electricity produced by the photovoltaic system partly used the measured 
values for the city of Košice (cloud cover, ambient temperature and direct sun glare).
Produced electric energy comparison
When comparing the all results from different sources (measurement, simulation 
and calculation) of the produced electricity during the year, there are clear variations 
in the amount of energy produced each month.
But when we look at the yearly produced electric energy balance of the measured values, 
we obtain approximately identical results. These results are processed in the following table, 
where the methodology of calculating the amount of electricity produced for the selected 
location is more favourable (Table 1).
T a b l e  1
Comparison of measured data
Data collection methods electric energy 
[kWh/year]
variation
[%]
Measurement 8752.505 –
Simulation 8920.000 1.88
Calculation 8840.974 1.00
Fig. 1. Installed photovoltaic system
262
3. Research methods of renewable energy sources – progressive 
indoor environmental system
The heating and cooling system incorporates a separate electricity meter. The electricity 
meter records the consumption of the electric energy source as well as the circulation pumps 
in the building. The area includes the heating source heat pump (HP), submersible pump 
(P1) and circulation pumps (P2-P5). The source cooling circuit includes a submersible pump 
(P1) and circulation pump source (P2 – P5) (Fig. 2). During the heating season, the largest 
consumer of electricity in the system is the heat pump. During the cooling period, water 
from the source well is used for cooling; thus, we are not producing cooling in the building, 
and in this case, the heat pump is decommissioned. On the other hand, we are also measuring 
the consumption of electricity in the heating system (Fig. 2).
where:
– HE – heat exchanger 
– HP –water/water heat pump, 0°C/35°C COP 3.8; heat performance 95.3 kW
– M1-2 – heat meter
– E1-2 – electricity meter
– ST – heating storage tank
– BHS - bivalent/backup heat
– S1-2 – source/suction well
– P1 – submersible pump
– P2-3 – circulation pumps – engine room
– P4-5 – circulation pumps – building
– D-C – distributor-collector
Requirements for supply of heat and cooling to the office building
1. Heat:
– Energy loss during the heating season: 1,000 GJ
– Requirement for maximum output power supply: 125 kW
Fig. 2. Depicted scheme of the connection of water/water heat pump and electricity consumption
263
2. Cooling:
– Energy loss during the summer: 330 GJ
– Requirement for maximum output power supply: 50 kW
Energy performance and technological annual energy input of energy source wells
Energy potential of the water source was measured via a hydrological test. Given 
the nature of the ground and the building above it, the test of a part of the sedimentation 
showed that the ground motion is not detected until the yield point of the water source 
at 7 l/s. A test for 7 days × 24 hours showed that suction wells are capable of such absorption 
of a volume of continuously pumped water. For the purposes of supply of heat, it is then 
possible to determine the energy performance of the wells as follows:
– Coverage of water source: 7 l/s 
– Water temperature: 14°C 
– Two heat pumps connected in series 
– The temperature difference for each heat pump: 4°C
– The number of heating days: 204 
– Days of cooling: 153 
– Temperature difference: 4°C
Proposal of a photovoltaic system in the evaluated administrative building
One part of the photovoltaic system will be placed in rows on the flat roof of the building 
on a metal framework structure, and the other part of the photovoltaic system will be placed 
on the inclined metal structure on the south side of the administrative building. This design 
increases the number of installed photovoltaic panels and also fills in the blank and unused 
space of the office building. The resulting DC power from photovoltaic panels is transformed 
into DC voltage with inverters for single-phase AC voltage and an automatically phased 
inverter for single phase AC voltage to two phases of a low voltage distribution grid. Each 
inverter is equipped with security protection, which in the case of deviations of the monitored 
parameters from the limits of standard values  automatically disconnects the photovoltaic 
solar generator from the distribution network. The photovoltaic solar system will be 
composed of 365 photovoltaic panels. The peak power of one photovoltaic panel will be 
230 Wp. Depending on the weather conditions for Slovakia, the entire photovoltaic system 
is inclined at an angle of 35° (Fig. 3).
Fig. 3. Photovoltaic system proposal and design
264
4. Conclusions
The electric energy demand for the administrative building during the heating season 
is 65 MWh per year, and during the cooling season, it is 19.4 MWh per year. Overall electric 
energy demand to drive the heat pump and other circulation pumps in the system is about 84.4 
MWh per year. The calculated amount of electricity produced by photovoltaic system is 80.7 
MWh. According to the annual energy balance of the heating and cooling system, we can say 
that energy demand will be 96% covered by the electric energy produced with the proposed 
photovoltaic system. If the parameters of photovoltaic panels increase in the future, there 
is the possibility to say that the entire system during the year will be fully covered by 
the electric energy that is produced through the photovoltaic system. On the other hand we 
should say that we need to cover additional energy demands for lighting as well as for electric 
equipment in the offices. This could be possible if the peak power of one photovoltaic panel 
is around 300 Wp. After these system modifications, we will be able to say that the evaluated 
administrative building will be a building with a zero-energy balance, which mean that 
the administrative building will be completely self-sustaining. This is effective if we could 
cover the energy consumption on the basis of the yearly energy balance.
This work was supported by VEGA 1/0450/12 Energy balance research on rainwater management 
in cities of the future; VEGA 1/0748/11 Theoretical and experimental analysis of building services 
and HVAC systems from the point of view of microbiological risk and regarding the effective use 
of  renewable sources.
R e f e r e n c e s
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Zero energy balance proposal for office buildings

http://www.ejournals.eu/sj/index.php/Cz/article/download/1481/1479

Zero energy balance proposal for office buildings

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