FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT
Department of Building Engineering, Energy Systems and Sustainability Science
Lina Björklund 2020
Degree project, Advanced level (Master degree, one year), 15 HE Energy Systems
Master Programme in Energy Engineering, Energy Online
Supervisor: Nawzad Mardan
Energy Audit and Energy Saving Measures of a Large Office Building
Bern 9 in Örnsköldsvik
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Abstract
There is a large potential in making the residential and service sector more energy efficient and the first step towards achieving a more efficient use of energy is to implement an energy audit. In this study a property with an approximate area of 8 000 m2, consisting of a main building and three building extensions from different eras has been examined. The main building and its extensions were built in different stages and the first one in the early 20th century and some parts of the last building extension were modified at the time that the examination was carried out. This indicates that there is a vast energy savings potential in the property and an energy audit was performed.
The main aim of the study was to examine where the energy was being used and where energy could be saved. Energy saving measures has been suggested together with a calculated approximate energy decrease and payback period.
The total energy savings potential for the measures is approximately 146 MWh. The energy audit showed that a large amount of electricity was being used during non-work hours and that energy was lost through the building envelope. The electricity use during non-work hours was examined during the night walk, however, it is suggested to carry out further examinations
regarding the property’s vast electricity use during non-work hours. To add loose wool in the roof of B2 has an energy savings potential of 33 000
kWh/year. Another measure is to clean the heat exchangers, this measure has an energy savings potential of 26 000 kWh/year. Also it is suggested to optimize the operational hours for the lighting by implementing presence control and to decrease the energy use for ventilation by cleaning the heat exchangers. Further examinations that would improve the study would be to do measurements of the electricity and temperatures to get a better
understanding of the buildings energy use. Also to model the building in a simulation tool would give a calculated energy loss that is more like the actual energy loss of the building and make the results more reliable.
Keywords: Building energy use, Energy audit, Energy use, Electricity use, Heat exchanger, LED, Presence control, U-value
Preface
This thesis is part of the examination of the Master’s programme in Energy Engineering Online at the University of Gävle. The study has been performed at a property owned by Nordiska Centrumhus AB.
I would like to give a special thanks to Håkan Martinell at Nordiska
Centrumhus AB for providing the property that has been used in this study. I would also like to give a special thanks to Niclas Asplind and Olle Lindgren at AFRY for supporting and answering questions throughout the work with the thesis. Lastly I would like to express my gratitude towards Nawzad Mardan for answering questions and for the valuable input that has improved the thesis.
Nomenclature
MVHR – An abbreviation for mechanical ventilation with heat recovery.
Luminaire – The complete electric light unit including light source and armature.
Old lighting – In this study this is referred to T8-luminaires.
HVAC – An abbreviation for Heating, Ventilating and Air Conditioning.
AHU – An abbreviation for Air Handling Unit.
ACH – Abbreviation for Air Changes per Hour.
Contents
1 Introduction ... 1
1.1 Background ... 2
1.2 Literature review ... 2
1.3 Aim and objective ... 4
1.4 Delimitations ... 4
1.5 Approach ... 5
1.6 Object description ... 5
2 Theory ... 8
2.1 Energy audit ... 8
2.2 Building energy balance ... 8
2.2.1 Transmission heat loss ... 8
2.2.2 Ventilation heat loss ... 9
2.2.3 Infiltration heat loss ... 10
2.2.4 Internal heat generation ... 10
2.3 Atemp ... 11
2.4 Ventilation ... 11
2.4.1 Mechanical Ventilation with Heat Recovery ... 11
2.4.2 Rotary heat exchanger ... 12
2.5 Indoor environment ... 12
2.6 Lighting ... 12
2.7 Payback period ... 13
2.8 Degree hours ... 13
3 Method ... 14
3.1 Field study ... 14
3.2 Night walk ... 15
3.3 Calculations ... 15
3.3.1 Transmission energy losses ... 15
3.3.2 Ventilation energy losses ... 16
3.3.3 Internal heat generation ... 16
3.3.4 Night walk ... 17
3.3.5 Measures ... 17
4 Results ... 20
4.1 Energy use ... 20
4.2 Electricity use ... 20
4.3 Transmission energy losses ... 21
4.4 Ventilation energy losses ... 22
4.5 Internal heat generation ... 22
4.6 Night walk ... 22
5 Measures ... 24
5.1 Turn off lighting when not needed ... 24
5.2 Presence controlled lighting ... 24
5.3 Energy efficient luminaires and presence control ... 25
5.4 Clean the heat exchangers ... 25
5.5 Optimize the operational hours for LA02 ... 26
5.6 Change the windows in building extension B2 ... 26
5.7 Change the display windows in building B2 and B3 ... 27
5.8 Additional insulation ... 27
5.9 Lower the indoor air temperature with one degree ... 28
5.10 Investigate further the electricity use during non-working hours 28 5.11 Summary of the measures ... 28
6 Discussion ... 29
6.1 Energy use ... 29
6.2 Transmission energy losses ... 29
6.3 Ventilation energy losses ... 30
6.4 Internal heat generation ... 30
6.5 Electricity use ... 30
6.6 Heat exchanger ... 31
6.7 Windows ... 31
6.8 Lighting ... 31
7 Conclusions ... 33
7.1 Study result ... 33
7.2 Outlook ... 34
7.3 Perspective ... 34
References ... 35 Appendix A Night walk ... A1 Appendix B U-values ... B1 Appendix C Calculations ... C1 Appendix D Integrated controls ... D1 Appendix E Actual energy use ... E1
1 Introduction
The global energy use increased with 2.3 % in 2018. This increase is due to a strong global economy and also the higher needs of heating and cooling in some parts of the world. The trend of a higher electricity demand is also a factor to the increased energy demand and was responsible for more than half of the increased global energy use in 2018. This resulted in an increasing CO2 emission of 1.7 % in 2018 which is a new record (International Energy Agency, 2019). A global aim towards combating climate change resulted in the Paris Agreement which entered into force on the 4th of November in 2016. The Paris agreements main goal is to keep the global temperature rise in this century at well below 2 °C above the pre-industrial levels. Also to support countries who will suffer the most by the effects of climate change and to assist developing countries (UNFCCC, 2020).
The worlds total final energy use in 2017 was 102 792 TWh. The residential and service sector stands for 37 326 TWh which is 36 % out of the total energy use.
This makes the residential and service sector the largest sector regarding the worlds final energy use in 2017 (Energimyndigheten, 2020).
Buildings have become one of the most rapidly growing energy using sectors in the European union (Doukas, Nychtis & Psarras, 2009). The building sector uses approximately 30 % of all of the raw materials and energy produced in Europe and more than 50 % of the electricity (Balaras et al., 2007). Almost 35 % of the European Union’s buildings are over 50 years old and almost 75 % out of the building stock is considered energy inefficient. Nearly 1 % out of that building stock is renovated each year (European Commission, 2019). A large fraction of the energy savings potential in buildings are accomplished by renovating the existing building stock. Thus this will be vital to achieve the energy efficiency targets (Dineen &
Gallachóir, 2011).
In Sweden the total final energy use in 2018 was 373 TWh. The residential and service sector is the largest sector in Sweden with a total energy use of 147 TWh which is 39 % of the total final energy use (Energimyndigheten, 2020). There is a large potential in making the residential and service sector more energy efficient and the first step towards a more efficient use of energy in a real estate is to implement an energy audit. However the higher living and working standards together with the introduction of new appliances and equipment might counterweight these energy saving measures and in some cases increase the energy use. Thus the attempt to reduce a buildings energy use while restoring an optimal indoor environment as well as securing the energy balance is a constant struggle (Balaras et al., 2007).
1.1 Background
Sweden has a goal to reduce the buildings energy use per heated floor area with 20
% by 2020 and with 50 % by 2050 both relative to the reference year in 1995.
There is a potential of reducing the final energy demand in the Swedish residential sector by 53 % by implementing selected energy savings measures. These energy saving measures would also reduce the CO2 emissions with 63 % (Mata, Kalagasidis
& Johnsson, 2013). The main aim with this study is to perform an energy audit of the property Bern 9. Bern 9 is a property with extensions from different eras and has a large energy savings potential. The property is owned by Nordiska
Centrumhus AB and the company works mainly with property development, property management and corporate development. Nordiska Centrumhus AB operates in Umeå, Örnsköldsvik and Åre (Nordiska Centrumhus, 2020). AFRY is an engineering and consulting company that is operating across the globe. The
company has extensive experience in working with energy audits and they are going to be supporting the study.
1.2 Literature review
This section will examine energy saving measures from previous scientific articles.
Especially, the expected energy savings potential for the measures will be
considered. The database that was used when searching for scientific articles were the Umeå University’s Library Search Tool. Key words that was used when searching was “energy audit”, “energy saving measures”, “lighting”, “energy use” and “heat exchanger”.
There is mainly three different categories of energy saving measures: technology, construction and management. Energy saving measures in the technology and management categories are the ones that are most commonly used. Some of these measures that are most commonly used are modification of lighting, Heating, Ventilation and Air Conditioning (HVAC) system modifications, use of renewable energy sources, changed behavior and optimization of management system (Zhang, Yuan & Mao, 2018). According to Mata, Kalagasidis & Johnsson (2013) measures with heat recovery systems and reduced indoor air temperature are the ones that generates the greatest energy saving of about 22 % and 14 % respectively. Measures that would upgrade the U-value of the windows and the envelope would both generate an energy saving of 7 % (Mata, Kalagasidis & Johnsson, 2013).
The lighting in a building stands for a large fraction of the buildings energy use.
With an energy use of 10 % out of the total energy usage in residential buildings and 20 % of the total energy usage in commercial buildings (Byun & Shin, 2018).
Luminaires also has a standby effect which means that they have an energy usage even when the luminaires are switched off, for old lighting this amounts to
approximately 30 % of the lightings total energy use. The study also showed that the standby effect can raise up to 55 % in some extreme cases (Gentile & Dubois, 2017). Thus there is a large energy saving potential when old lighting is replaced with new energy efficient lighting (Byun & Shin, 2018). However, Mata, Kalagasidis
& Johnsson (2013) mean that a reduction of the use of electricity for appliances and lighting would increase the need for heating. This since the electricity use for lighting and appliances also generates heat which needs to be heated by for example district heating when this electricity usage is reduced (Mata, Kalagasidis & Johnsson, 2013).
According to Wei et al. (2017), when building performance simulations for energy saving measures are carried out there is a gap between the predicted building performance and the actual building performance. This gap seems to be due to occupant behavior such as heating behavior and window opening behavior. Wei et al. (2017) mean that the window opening behavior do not have a vast impact on the building performance. However the heating behavior had a significant impact on the energy savings potential and the buildings energy savings potential was doubled with the case of passive heating users (18°C) instead of active heating users (24°C) (Wei et al. 2017). Furthermore, according to Masoso and Groebler’s (2010) study more than 50 % of the buildings energy use is used during non-work hours. The study showed that the ventilation, equipment (mostly computers that were left on after the work day) and lighting that where the largest energy users during non-work hours. This points out the importance of occupant behavior to achieve a decreased energy usage.
Another study shows that cleaning of heat exchangers has a potential of increasing the thermal exchange efficiency with about 8.1 %. Thus there is considerable energy savings potential by simple cleaning of the existing heat recovery units. It is
recommended to clean these units more frequently in commercial buildings since they collect contaminants in a faster pace than for units in residential buildings.
Buildings in cold climates uses more energy for heating which results in a higher energy loss when the heat recovery units gets contaminated (Abdul Hamid, Johansson & Lempart, 2020).
The literature review also shows that there is a wide range of energy saving
measures that can be implemented to reduce the energy use of a building. Some of them are simple and has no cost while some of them are more complex with a higher cost. This study will examine all of the energy saving measures that has been mentioned in this section, although for some of them there is not enough
information to investigate the expected energy decrease for the property.
1.3 Aim and objective
The main aim of this study is to perform an energy audit of a property called Bern 9 in Örnsköldsvik and to examine where the supplied energy is being used. This knowledge will be used to find where energy can be saved and different measures to make the property more energy efficient will be recommended. Furthermore these measures will reduce the cost and the energy use for the property. The cost savings can be invested in implementing more energy savings measures or other investments within the company. A reduced energy use will be beneficial for the environment both locally and globally since reduced energy use results in less greenhouse gas emissions. The aim is partitioned into the following objectives:
• Calculate the energy use of the building and get an approximate comprehension of where the energy is being used
• Ascertain the parts of the building that has a high energy use
• Establish measures with energy savings potential
• Suggest which measures that should be carried out and in what order they should be implemented
• Calculate the payback period for the measures
1.4 Delimitations
The calculations in this study are based on floor plan drawings and information about the building that was found during the field studies. Since the floor plan drawings of the building might not represent the reality and due to insufficient information about the property some assumptions were required. Energy saving measures regarding lighting in the office spaces are not included due to limited information and access in those spaces. Although there is an energy savings potential in investing in presence controlled lighting in all the offices, however this savings potential is not included in the study. The property’s use of district cooling is not going to be handled in this study, since there has already been measures
implemented to lower the use of district cooling.
Complete information about the energy saving measures such as overall costs and how the energy saving measures will affect the building after they have been
implemented are not included in this study. This needs to be investigated further by the real estate company by consulting professionals in each field that is of interest.
1.5 Approach
The first step was to study how energy audits are carried out and to collect material such as checklists from the Swedish Energy Agency. After that an inventory,
collection of materials and measurements of temperatures was performed at the property. The property’s transmission and ventilation losses was then calculated.
The energy saving potential for the energy saving measures was then calculated for some of the measures. Thereafter a payback for the measures was calculated.
1.6 Object description
Bern 9 is a property that is situated in the central of Örnsköldsvik. The real estate was previously owned by Mittmedia and Nordiska Centrumhus bought the real estate in 2015. Bern 9 consists of one initial building with three extensions from different eras with an approximate area of 8 000 m2. Bern 9 is an office building with approximately 200 occupants in the building and after the conversion of the third building extension into an office the total number of occupants are estimated to be 300. The occupant hours for the building is 07.00 – 17.00. There is an editorial office in the building and some of their staff also works between the hours 05:00 – 07:00 and 17:00 – 24:00. Studieförbundet vuxenskolan has study circles with gatherings in the evening a few times a week. The exterior of Bern 9 is shown in figure 1, the initial building is on the right, the first extension in the middle and the second extension is on the left. The third extension cannot be seen from this view since it is behind the first and second building extension.
Figure 1. The property’s initial building to the right together with the first building extension in the middle and the second building extension on the left.
Building 1 (B1) was built in about 1930 (See figure 2) and the indoors was renovated in 2016. In conjunction with the renovations 40 cm of loose wool insulation was added to the attic. The initial building B1 consists of four storages including a basement. Most of the windows are triple glazing types and the rest are double glazing types.
Building 2 (B2) as shown in figure 2 was built in 1960 and some renovations were carried out in 2008. The building extension consists of seven storages including one basement and one garage. The windows are both double glazing and triple glazing types. A building extension called New Örnskölsviks Allehanda (ÖA) room was built in 1999 and is located on the first floor on top of the old printing extension and is connected to B2.
Building 3 (B3) was built in 1980 the indoor has not been renovated since it was built, figure 2. The building extension consists of five storages including a garage.
All the windows are triple glazing types.
Building 4 (B4) as shown in figure 2 is a printing house that is going to be converted into an office building. The printing business was downsized after the change of ownership and the entire printing business was dismantled in the beginning of 2019.
All the windows of this building extension are triple glazing types.
Figure 2. Bern 9 from above, B1 is the initial building, B2 is the first extension, B3 is the second extension and B4 is the third extension. Source: Hitta.se, 2020.
The property has five main air handling units (AHU) four larger units and one that is a bit smaller, which is LA04. All the AHUs are Mechanical Ventilation with Heat Recovery (MVHR)-systems with rotary heat exchangers. As shown in table 1, LA01 serves B1, LA02 serves B2, LA04 serves New ÖA, LA08 serves B3 and VentB4 serves B4. The AHUs operational hours are presented in table 1, the AHU LA04 has been turned off since the space that it serves is not in use at the moment.
Table 1. The names of the ventilation AHUs and the part of the property that they serve. Also the type of ventilation and the type of heat exchanger.
Name Serves Ventilation Heat exchanger Operational hours
LA01 B1 MVHR Rotary 06:00 –
18:00
LA02 B2 MVHR Rotary 05:00 –
24:00
LA04 New ÖA MVHR Rotary Turned off
LA08 B3 MVHR Rotary 06:00 –
18:00
VentB4 B4 MVHR Rotary 06:00 –
18:00
2 Theory
This section presents the theory that has been used to perform the energy audit, together with the theory that are the basis for the chosen measures. The theory behind the calculations that has been performed in the study are explained to give the reader an enhanced understanding of the study.
2.1 Energy audit
An energy audit is the first step when a company wants to reduce their energy use or use it more efficiently. The energy audit should include an energy balance and a list of measures with profitability calculations. The energy balance shows the amount of bought energy and how it is used. The amount of bought energy is given by
collecting energy bills for the past 2 -3 years. The next step is to examine where the energy is being used. When that is accomplished it is time to analyze the energy use and find where there are energy savings potentials.
A list of measures can then be developed. The type of measures vary and some are simple and cheap while others are more extensive and expensive. A common perception is that it is the process that uses the most energy that has the highest energy savings potential, but that is not always the case. Measures that do not need an investment cost should also be studied such as change in behavior of the
occupants and changed operating routines. The last step is to calculate the decreasing costs that the measures entails and what the measures will cost to implement (Energimyndigheten, 2019).
2.2 Building energy balance
The buildings energy balance is based on the buildings heat losses and heat gains.
The heat losses of a building is due to transmission heat losses, ventilation heat losses, infiltration heat losses which is due to leakages in the building envelope and losses due to waste water. The heat gains of a building is due to internal heat
generation and heat supplied by the heating system (Warfvinge & Dahlblom, 2010).
2.2.1 Transmission heat loss
Transmission is heat flows through floors, walls, roof, windows and also through thermal bridges where different parts of the building is connected. Transmission will also occur if an adjacent room is colder even though they are part of the same
envelope (Warfvinge & Dahlblom, 2010). The specific heat loss factor 𝑄"[W/K]
for transmission is given by
𝑄" = % 𝑈 ∙ 𝐴 + % 𝜓 ∙ 𝑙 + % 𝜒 [1]
where 𝑈[W/m2·K] is the coefficient of thermal transmittance, 𝐴 is the area in square meter [m2], 𝜓 [W/m·K] is the coefficient of thermal transmittance for the linear thermal bridge, 𝑙 [m] is the length of the thermal bridge towards heated indoor air and 𝜒 [W/K] is the coefficient of thermal transmittance for the punctiform thermal bridge. ∑𝜓 ∙ 𝑙 +∑𝜒 represents the thermal bridges for the building and an approximate value for the thermal bridge is 20 % of ∑ 𝑈 ∙ 𝐴 (Boverket, 2012).
The U-value sometimes needs to be calculated and is then given by
𝑈 = 1 𝑑𝜆
= 1 𝑅
[2]
where 𝑑 is the thickness of the material in meter [m], 𝜆 is the thermal conductivity in [W/m·K] and 𝑅 is the thermal resistance in [m2·K/W].
The annual energy loss due to transmission 𝐸"34567866895 [MWh/year] is given by
𝐸"34567866895 = 𝑄"∙ 𝐺" [3]
where 𝑄" [W/K] is the specific heat loss factor for transmission and 𝐺" [°Ch] is the degree hours for the property.
2.2.2 Ventilation heat loss
The buildings ventilation is determined by driving forces such as various pressures from wind, stack effect and the ventilation system. The buildings air tightness and the design of the ventilation system is also of importance. The calculation of the specific heat loss factor 𝑄; [W/K] for the ventilation with a heat exchanger is given by
𝑄; = 𝑞;=5"8>4"895∙ 𝜌 ∙ 𝑐A∙ (1 − 𝜂) [4]
where 𝑞;=5"8>4"895 [m3/s] is the air flow for the ventilation, 𝜌 is the air density in [kg/m3], 𝑐A is the thermal capacity of air with the unit [kJ/kg·K] and 𝜂 is the efficiency of the heat exchanger.
2.2.3 Infiltration heat loss
The infiltration heat losses are the losses that are due to air leakages. Which is determined by the air tightness of the buildings different components such as windows and wall sections and how well they are fitted together (Abel & Elmroth, 2007). The calculation of the specific heat loss factor 𝑄> [W/K] due to air leakage is given by
𝑄> = 𝑞>=4F4G= ∙ 𝜌 ∙ 𝑐A [5]
where 𝑞>=4F4G= [m3/s] is the air flow of the air leakages of the building. The air leakage in a building is approximately 0.05 air changes per hour (ACH).
The air leakage of the building was calculated by the following equation
𝑞>=4F4G= = 𝑛 ∙ 𝑉
3600
[6]
where 𝑛 [h-1] is the air changes per hour and 𝑉 [m3] is the volume of the building.
The annual energy loss due to ventilation and air leakage 𝐸;=5"8>4"895 [MWh/year]
is given by
𝐸;=5"8>4"895 = M𝑄;∙ 𝑡O + 𝑄>P ∙ 𝐺" [7]
where 𝑡O is the amount of operating hours each week for the ventilation divided by the total amount of hours per week.
2.2.4 Internal heat generation
The buildings internal heat gain is the heat that is transferred to the room air directly from people, equipment and lighting and indirectly from the buildings walls, floor and ceiling if their surface temperatures are higher than the room air temperature.
Solar radiation is not absorbed by the room air directly although when the solar radiation strikes a solid surface the radiation is converted into heat and this raises the temperature of the surface. After a while this heat raise might lead to convective heat emission into the room air (Abel & Elmroth, 2007). Approximately 70 % of the electricity usage is going to be converted into useful heat (Howell, 2017)
2.3 Atemp
Atemp is the area that it used to calculate the buildings energy performance. The area for all the floors including attic and basement that is heated more than 10 °C is defined as the Atemp of the building. This area is used to calculate the buildings specific energy use which is the buildings total energy usage divided by the buildings Atemp. The area of the garage is not included in Atemp. BBR has determined maximum values for the amount of supplied energy per square meter and year for different types of buildings (Boverket 2014).
2.4 Ventilation
A well designed ventilation should supply the property with fresh air and remove the polluted air. Furthermore it should make sure that pollutions are not spread in the building and to create a under pressure in the property. The ventilation can in some cases be used for heating or cooling. The Swedish work environment authority has established a minimum value for the supply air for facilities such as offices
(Warfvinge & Dahlblom, 2010). This minimum value has been used when calculating the supply air for the ventilation and is given by
𝑞;=5"8>4"895 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑜𝑐𝑐𝑢𝑝𝑎𝑛𝑡𝑠 ∙ 7 𝑙
𝑠 ∙ 𝑜𝑐𝑐𝑢𝑝. + 𝐴 ∙ 0.35 𝑙 𝑠 ∙ 𝐴 1000
[8]
where 𝑞;=5"8>4"895 is in [m3/s] and the floor area 𝐴 is in [m2].
2.4.1 Mechanical Ventilation with Heat Recovery
An MVHR-system is a supply- and extract system with heat recovery. This system is commonly used in offices, schools, hospitals and other buildings that requires a heavy ventilation. All the parts of the AHU needs to be controlled and taken care of regularly to be able to operate efficiently. Filters need to be changed often to avoid that the air flows are decreasing and that the fan work is increased (Warfvinge &
Dahlblom, 2010).
2.4.2 Rotary heat exchanger
A rotary heat exchanger consists of wheel with a large amount of small ducts. The wheel rotates around its own axis and captures heat from the exhaust air flow in one half of the rotation and released heat to the supply air flow on the other half of the rotation. The effect of the rotary heat exchanger only affects the ventilation flow rate and will not affect the air infiltration. The rotary heat exchanger has efficiencies of about 80 %. Dust in the heat exchanger will significantly decrease the efficiency which results in that more heat energy needs to be bought (Warfvinge & Dahlblom, 2010). It is recommended to clean the heat exchangers in commercial buildings every two years (Abdul Hamid, Johansson & Bagge, 2018). The efficiency of a heat exchanger is given by
𝜂_=4" =`a_45G=3 = 𝑇6cAA>d− 𝑇9c"e993
𝑇=`"34a"− 𝑇9c"e993
[9]
where 𝑇6cAA>d is the temperature of the supply air after the heat exchanger and before the heating battery in degree Celsius [°C], 𝑇9c"e993 is the temperature of the outdoor air in degree Celsius [°C] and 𝑇=`"34a" is the temperature of the air that is extracted from the building in degree Celsius [°C].
2.5 Indoor environment
There are several factors that affect the perception of well-being in an indoor environment. The indoor air temperature is easy to measure, although on its own the indoor temperature cannot fully describe the perception of the thermal climate.
The movement of the indoor air and the temperature of the surrounding surfaces does also affect the thermal climate (Abel & Elmroth, 2007). To decrease the indoor air temperature gives an approximate energy saving for heating of 5 % per degree (Energimyndigheten, 2018).
2.6 Lighting
Sweden uses 14 TWh of electricity for lighting every year. The largest fraction is used by companies and public sector. Old lamps has an energy usage that is 5 times higher than new energy efficient lighting. A lot of these old lighting systems are still in use and a conversion of this old lighting such as T8-luminaires into energy
efficient luminaires has a saving potential of 40 %. Approximately 90 % of old lightings impact on the environment is from their electricity usage when the
luminaires are operating and 10 % is from production, transports and recycling. In a
An investment in daylight- and presence controlled lighting is one of the most profitable ways to decrease the use of energy. Presence control uses one or more motion sensors that notices when someone is entering the room and immediately turns on the lighting in the room when a movement is detected. The lighting is then turned off automatically after a predetermined time after the latest movement was registered (Belysningsbranschen, 2013). The lightings annual energy use 𝐸>8G_"85G
in [kWh] is given by
𝐸>8G_"85G = 𝑃>8G_"85G ∙ 𝑡9"∙ 1.3 [10]
where 𝑃>8G_"85G is the installed power in Watt [W] for the lighting, 𝑡9" is the annual operation time from lighting in [h/year] and 1.3 is used to take into account the standby effect for lighting, which is about 30 % of the total energy.
2.7 Payback period
The payback period shows how long it takes for an investment to repay itself. In other words it is the time for the increased profit or decreased cost to compensate for the investment cost. Although this method do not include the inflation, interest rate or what happens after the payback period. The payback period 𝑇g is given by
𝑇g = 𝐶85 𝑎
[11]
where 𝐶85 is the investment cost and 𝑎 is the difference between the annual cost before and after the investment (Soleimani-Mohseni, Bäckström & Eklund, 2014).
2.8 Degree hours
The degree hours are the summation of the difference between the indoor and the outdoor temperature for each hour of the year. It is used when calculating a buildings heat energy use (Soleimani-Mohseni, Bäckström & Eklund, 2014). The degree hours can be retrieved from a table when the annual average temperature and balance temperature is known. An approximate annual average temperature
𝑇44" [°C] for Örnsköldsvik is 3.4 °C and the balance temperature 𝑇i [°C] is given
by
𝑇i = 𝑇8− 𝑄̇klm 𝑄"+ 𝑄;+ 𝑄>
[12]
where 𝑄̇𝐼𝐻𝐺 [W] is the property’s internal heat generation and 𝑇𝑖 [°C] is the indoor air temperature.
3 Method
The first step towards achieving a well accomplished energy audit was to get a more profound knowledge about energy audits. Information about energy audits was found in associated literature and from information such as checklists at the Swedish Energy Agency. The Umeå University’s data was used to find energy saving
measures from previous scientific articles. As mentioned in the previous section, the key words that was used when searching was “energy audit”, “energy saving measures”,
“lighting”, “energy use” and “heat exchanger”.
Information about the property’s energy usage was collected at Övik Energy’s website. The district heating, district cooling and electricity usage for 2018 and 2019 was retrieved, the energy use for each month in 2019 is presented in Appendix E table 2. Furthermore the hourly electricity usage for 2019 was also retrieved and showed that the electricity usage was relatively high during the hours when the property was not occupied, see Appendix E table 1 and Appendix E figure 1.
3.1 Field study
Two field studies at the property has been carried out to collect data, do an inventory of the equipment and to get an understanding of how the property was constructed. At the first field study an inventory of lighting in the garage, basement and the stairwells was performed. Also some information about the lighting in the offices was collected. Information from old drawings about the outside wall
construction for the extension built in 1980 was found. At the second field study an inventory of windows and ventilation was carried out and a night walk was
performed. Measurements of the buildings and the windows dimensions such as height and width was performed with the distance meter Cocraft HD 400-2 shown in figure 3. The indoor air temperatures in the main building and all the extensions was measured.
All the lighting in the stairwells in B2 and B3 were switched on during both field studies. The building extension B2 and B3 has skylights that provides the stairs with natural light and makes the use of lighting unnecessary as shown in figure 4.
Figure 4. Lighting that was switched on in the stairwell in building extension B3.
3.2 Night walk
The night walk was performed after office hours between 19:15 – 20:30. The main focus of the night walk was to examine if there were lighting and ventilation that was operating when the building was not in use. The inventory of the luminaires that was operating during the night walk are presented in Appendix A table 1.
3.3 Calculations
The calculations in this study was carried out to examine the property’s heat losses due to transmission heat losses and ventilation heat losses. Also some calculations regarding the energy saving measures was performed to get an approximate image of the energy savings potential and their cost saving.
3.3.1 Transmission energy losses
The U-values that was used in the calculations was collected from building regulations for the different eras. Except for the U-values of the new outer wall construction of B4 and the outer wall construction of B3 where there were drawings of the construction available and the U-value could be calculated by using equation [2]. The U-values for B1 was collected from Byggnadsstyrelsens anvisningar till byggnadsstadgan (BABS) from 1947 (Boverket, 1945). The U-values for B2 was collected from Byggnadsstyrelsens anvisningar till byggnadsstadgan (BABS) from 1960 (Boverket, 1960). The U-values for B3 and B4 was collected from Svensk byggnorm (SBN) from 1983 (Boverket, 1983). The results from the calculations are presented in Appendix C table 1 and table 2. When all the U-values and areas had been obtained the specific heat loss factor for transmission could be calculated by using equation [1], the U-values are presented in Appendix B table 1.
The balance temperature was then calculated by using equation [12], using an indoor temperature of 22 °C (Sveby, 2013). The calculations resulted in a balance
temperature of approximately 17 °C, which together with the annual average temperature of 3.4 °C gives the degree hours of about 125 400 °Ch for the property in Örnsköldsvik (Soleimani-Mohseni, Bäckström & Eklund, 2014). Thereafter the annual energy loss due to transmission could be calculated by using equation [3].
The areas for all the building parts are presented in Appendix B table 1. The
calculations of the annual energy loss due to transmission are presented in Appendix C table 3.
3.3.2 Ventilation energy losses
The floor areas from floor plan drawings and the estimated number of occupants for each extension was used to calculate the controlled ventilation air flow. The
controlled ventilation air flows were calculated by using equation [8]. The
calculation of the specific heat loss factor for ventilation could then be calculated by using equation [4]. The specific heat loss factor due to air leakages was calculated by using equation [5]. As mentioned earlier the ACH for air leakages is assumed to be 0.05 h-1. The calculated volume of the building is approximately 29 100 m3 and this gives an air flow for the air leakage of 0.4 m3/s by using equation [6]. Thereafter the calculation of the annual energy loss due to ventilation was carried out by using equation [7], the density for the air used in the calculations were 1.2 kg/m3, the specific heat capacity 1000 J/kg·K and the degree hours 125 400 °Ch (Soleimani- Mohseni, Bäckström & Eklund, 2014).
According to Abdul Hamid, Johansson & Lempart (2020) the thermal efficiency of a heat exchanger can be reduced by approximately 8.1 % if they are contaminated.
The efficiency of a rotary heat exchanger is about 80 % (Warfvinge & Dahlblom, 2010). Thus, the efficiencies for the heat exchangers were estimated to be 70 % for all the heat exchangers, since there is no information of them being cleaned. The results from the calculations and the data that was used is presented in Appendix C table 4.
3.3.3 Internal heat generation
The property’s internal heat generation was calculated by using the values from table X, together with the Atemp of the property. The Atemp of the property was calculated by using floor plan drawings and the calculations resulted in a Atemp of 7 000 m2 for the property. The property has two elevators and 200 occupants.
Table 2 shows some values that can be used when calculating the internal heat
Table 2. Values that was used when calculating the heat gains of the property (Sveby, 2013).
Parameter Value
Effect per person [W] 108
Number of office days per year [days/year]
250
Length of office day [h/day] 9
Occupancy during office days [%] 70
Equipment and lighting [kWh/m2, year]
50
Elevator [kWh/year, elevator] 5 500
3.3.4 Night walk
The energy use calculations for the lighting that was switched on during the night walk was carried out by using equation [10]. When calculating the energy use of the luminaires that was operating during the night walk the worst case scenario was assumed. Which is that these luminaires are switched on at all time during the year.
3.3.5 Measures
The calculations of the reduced annual energy use when implementing each
measures are presented in this section. The payback period for all the measures with an estimated investment cost was calculated by using equation [11].
A. Presence controlled lighting in garage and stairwells in B2 & B3 The calculations of the lightings annual energy use has been carried out by using equation [10] and the annual cost saving was then calculated. The calculations together with the data that has been used for the calculations are presented in Appendix C table 5.
B. Convert the existing T8-luminaires in garage and the railing in the stairs in B3 into LED-luminaires together with presence controlled lighting
The calculation of the reduced energy use for this measure was carried out by using equation [10] and data from Appendix C table 6.
C. Clean the heat exchangers
The heat exchangers before the cleaning was estimated to have an efficiency of 70 % and after the cleaning the efficiency was estimated to 80 %. The annual energy loss due to transmission was then calculated with the new efficiency. The actual efficiencies of the heat exchangers in the AHUs LA01 and LA08 were calculated by equation [9]. Table 3 shows the temperatures that was used in the calculations. The temperatures were collected from integrated controls on each AHU, see Appendix D figure 1 and figure 2.
Table 3. Temperatures that was used when calculating the efficiencies of the heat exchangers.
LA01 LA08
𝑻𝒔𝒖𝒑𝒑𝒍𝒚 [°C] 19.1 15.9
𝑻𝒆𝒙𝒕𝒓𝒂𝒄𝒕 [°C] 22.3 21.2
𝑻𝒐𝒖𝒕𝒅𝒐𝒐𝒓 [°C] 3.8 5
D. Change the windows in the offices in building extension B2 into triple glazing windows with a U-value of 1 W/m2·K instead of the existing double glazing windows with a U-value of 2.9 W/m2·K There are 37 windows in the offices in B2 that is estimated to have double glazing windows, these are converted into windows with triple glazing. The U-value of the new windows with triple glazing in B2 were estimated to have a U-value of 1 W/m2·K. The annual energy loss due to transmission was then calculated with the new U-value.
E. Change the display windows in building B2 and B3 into windows with triple glazing and a U-value of 1 W/m2·K instead of
windows with double glazing with a U-value of 2.9 W/m2·K The display windows in B2 and B3 are of double glazing type, those are converted into windows with triple glazing. The U-value of the new display windows with triple glazing in B2 and B3 were estimated to 1 W/m2·K.
The annual energy loss due to transmission could then be calculated with the new U-value for the windows.
F. Additional insulation of 0.2 m loose wool to receive a U-value of 0.13 W/m2·K in the roof of B2
When implementing measures regarding the building envelope the aim is to achieve the following U-value of at least 0.13 W/m2·K for the outer roof (Boverket, 2019). This U-value was used when implementing the measure
be 0.4 W/m2·K. To achieve the new U-value of 0.13 W/m2·K, 0.2 m of loose wool was added. Equation [2] was used to calculate the thickness of the loose wool, the data that was used in the calculations are presented in
Appendix C table 7.
4 Results
This section presents the property’s actual energy use and the calculated energy losses due to transmission and ventilation. There is also the results from analyzing the buildings hourly electricity usage and a summation of the findings from the night walk that was performed at the property.
4.1 Energy use
The buildings total annual electricity, district heating and district cooling use in 2018 and 2019 is shown in table 4, this data was collected on the website of Övik Energy. The total annual electricity use in 2019 is approximately 130 MWh and has been lowered with 18 % in comparison to the previous year. District heating and district cooling usage for the property in 2019 is approximately 438 MWh and 81 MWh respectively. The district heating use in 2019 has decreased with 15 % and the district cooling use has decreased with 34 % compared to the previous year as shown in table 4.
Table 4. The property’s annual energy use of electricity, district heating and district cooling in 2018 and 2019.
Bern 9 2018 2019
Electricity [MWh] 158 130
District heating[MWh] 518 438
District cooling [MWh] 122 81
4.2 Electricity use
The electricity use when the building is not occupied is relatively high as shown in figure 5. The buildings electricity usage is higher when the building is not occupied for all the months of the year. Total annual electricity usage for weekdays between 06.00 – 18.00 is 56 148 kWh and the total annual electricity usage for the rest of the time is 73 594 kWh. Thus the fraction of the electricity use for other time is approximately 57 % out of the total electricity use. The hourly values regarding the electricity use for all months of the year are presented in Appendix E figure 1. A night walk was performed to investigate if there where lighting and ventilation operating during the time when the building was not occupied, to find out why the electricity use is high during non-work hours.
Figure 5. The property’s electricity use for weekdays between 06-18 and the electricity use for the rest of the time for each month in 2019. Also the property’s total electricity use for each month in 2019.
4.3 Transmission energy losses
The property’s annual energy loss due to transmission is 586 MWh as shown in table 5. The building extension B2 has the highest annual energy loss as stands for 43 % of the total energy loss or approximately 253 MWh/year. The building extension with the lowest energy losses due to transmission is B4 as stands for 14 % of the total energy loss or about 82 MWh/year. B1 has an annual energy loss as stands for 23 % of the total energy loss or 132 MWh/year and B3 has an annual energy loss as stands for 20 % or 118 MWh/year, see table 5. The annual cost for the energy loss is approximately 430 000 SEK with the district heating price of 0.735 SEK/kWh.
Table 5. The specific heat loss factors for transmission for the building extensions and building components. The property’s total annual energy loss due to transmission and the annual energy loss for each building extension.
Building extension
Qt, windows
[W/K]
Qt, outer walls
[W/K]
Qt, outer roof
[W/K]
Qt, floor
[W/K]
Et
[MWh/year]
B1 245 458 43 130 132
B2 505 714 295 168 253
B3 294 252 91 159 118
B4 89 55 105 297 82
Total 586
0 2000 4000 6000 8000 10000 12000 14000
Jan Feb Mar Apr May Jun jul Aug Sep Oct Nov Dec
Electricity use [kWh]
Month
Weekdays 06-18 [kWh] Other time [kWh] Total [kWh]
4.4 Ventilation energy losses
The total annual energy loss due to ventilation and air leakage is 139 MWh/year as shown in table 6. LA02 has the highest energy loss of 28 MWh/year and LA01 has the lowest energy loss of 13 MWh/year. The AHUs LA08 and VentB4 has an annual energy loss of 19 and 18 respectively. The annual cost for this energy loss is
approximately 102 000 SEK when using the district heating price of 0.735 SEK/kWh.
Table 6. The annual energy loss due to ventilation for each AHU and the total annual energy loss where the total annual energy losses due to air leakages are included.
Name Ev [MWh/year]
LA01 13
LA02 28
LA08 19
VentB4 18
Total 139
4.5 Internal heat generation
The property’s calculated internal heat generation is 287 MWh/year as shown in table 7. The internal heat generation from people is 34 MWh/year. The internal heat generation from equipment and lighting and from the elevators are 245 MWh/year and 8 MWh/year respectively.
Table 7. The property’s annual internal heat generation by source in MWh.
Source Internal heat generation
People [MWh/year] 34
Equipment and lighting [MWh/year] 245
Elevators [MWh/year] 8
4.6 Night walk
The lighting that was operating during the time when the night walk was performed amounted to approximately 4 100 W. The luminaires that was operating during the night walk results in an annual energy loss of approximately 47 000 kWh/year and an annual cost of 61 000 SEK, using an electricity price of 1.3 SEK/kWh.
Table 8 shows the operation of the four main ventilation systems during the night walk. The ventilation AHU LA01 was turned off between 19:17 and 20:31 and the ventilation AHU LA04 was operating at 19:35 and was still operating at 20:35. The ventilation AHU LA08 was turned off at 20:19 and LA02 was operating at 20:19 as shown in table 8.
Table 8. The operation of the main ventilation systems during the night walk.
Name Serves Time Operation
LA01 B1 19:17 On
20:31 Off
LA04 New ÖA 19:35 On
20:35 On
LA08 B3 20:19 Off
LA02 B2 20:19 On
5 Measures
This section presents the results from calculating the potential annual energy saving and payback period for the measures.
5.1 Turn off lighting when not needed
Turn off the lights in the garage and the stairwells after office hours. Also during the time when those areas are not in use during office hours. The total installed power of the garage and the stairwells is approximately 4 950 W.
5.2 Presence controlled lighting
As mentioned in the previous section the lighting was operating during non-working hours and one way to reduce the electricity use is to have presence controlled lighting in garage and stairwells in B2 and B3. The calculated energy savings potential by installing presence controlled lighting in the garage and stairwells is about 11 000 kWh/year which is a cost saving of about 15 000 SEK/year, the calculations are presented in Appendix C table 5. When comparing the presence control lighting with the old lighting without presence control and that the old lighting is operating at all time when the offices are in use. The estimated
investment cost for the sensors for the presence controlled lighting is 10 000 SEK (Eldirekt, 2020) where labor cost is excluded which gives a payback of
approximately 8 months. The energy savings potential for the presence control is 52 000 kWh/year and the cost saving is 67 000 SEK/year, see Appendix C table 5.
When comparing the presence control lighting with the old lighting without presence control and assuming the worst case scenario that the lighting without presence control in garage and stairwells are operating at all time. The estimated investment cost for the presence control is 10 000 SEK where labor cost is excluded which results in a payback time of approximately 2 months.
5.3 Energy efficient luminaires and presence control By converting the existing T8-luminaires in the garage and in the railing in the stairs in B3 into LED-luminaires together with presence controlled lighting, the electricity use can be further reduced. The energy savings potential when converting the old T8-liminaires into new energy efficient LED-luminaires is 10 000 kWh/year and the cost savings potential is 13 000 SEK/year, the calculations are presented in
Appendix C table 6. When assuming that the old luminaires are operating at all time when the offices are occupied. The estimated investment cost for new LED-
luminaires and presence control is according to information from LamporNu (LamporNu, 2020a) and (LamporNu, 2020b) approximately 48 000 SEK where labor cost is excluded. This results in a payback time of approximately 4 years. The energy savings potential when using the worst case scenario is approximately 38 000 kWh/year and the cost savings potential is 49 000 SEK/year, the calculations are presented in Appendix C table 6. When assuming the worst case scenario, when the old luminaires are operating at all time during the year. The estimated investment cost for new LED-luminaires and presence control is 48 000 SEK where labor cost is excluded this gives an payback time of approximately 1 year.
5.4 Clean the heat exchangers
When calculating the energy saving it was assumed that all the heat exchangers had an efficiency of 70 % before the cleaning and 80 % after the cleaning. The annual energy loss due to ventilation is then 113 MWh/year as presented in table 9. This results in an annual energy saving of 26 000 kWh/year and a cost saving of
approximately 19 000 SEK/year. The investment cost for cleaning the heat exchangers are estimated to 16 000 SEK based on data from Abdul Hamid,
Johansson & Lempart’s (2020) study and this results in a payback time of about 10 months. As mentioned earlier, it is recommended to clean the heat exchangers in commercial buildings every two years (Abdul Hamid, Johansson & Bagge, 2018).
Table 9. The calculated annual energy losses due to ventilation when the efficiency for all the heat exchangers are 80 %.
Name Ev [MWh/year]
LA01 9
LA02 19
LA08 13
VentB4 12
Total 113
The actual heat exchanger efficiencies were calculated for LA01 and LA08. The efficiency for the rotary heat exchanger in LA01 was 83 % and the efficiency of the rotary heat exchanger in LA08 was 67 %. Unfortunately the efficiencies of the other heat exchangers could not be calculated since there was not enough information.
5.5 Optimize the operational hours for LA02
The operational hours for the ventilation that serves B2 are operating between 05:00 – 24:00. Most of the occupants are using the building between 07:00 – 17:00. However as mentioned earlier there are some of the editorial staff that works between the hours 05:00 – 07:00 and 17:00 – 24:00. Furthermore,
Studieförbundet vuxenskolan has study circles with gatherings in the evening a few times a week. Hence the longer operational hours for the LA02 AHU. An
examination of the number of occupants that uses the building during these hours every week should be carried out. This information can then be used to find out if there is a possibility to reduce the operational hours for the AHU. Also the
possibility to implement different operating modes for the AHU LA02 during these hours should also be examined. Another suggestion is to implement CO2 control sensors to the ventilation system.
5.6 Change the windows in building extension B2 Changing the windows in the offices in building extension B2 into windows with a U-value of 1 W/m2·K instead of the existing windows with a U-value of 2.9 W/m2·K, will reduce the transmission losses. The total annual energy loss due to transmission is 573 MWh as shown in table 10. Which means that the annual energy loss has been decreased with 13 000 kWh. This results in a reduced annual energy cost of approximately 10 000 SEK by using the district heating price of 0.735 SEK/kWh. The total investment cost for this measure is estimated to 222 000 SEK based on data from Kostnadsguiden (Kostnadsguiden, 2020) and this gives a payback time of about 22 years.
Table 10. The energy loss due to transmission when the windows with double glazing in the offices in B2 is converted to windows with triple glazing and a U-value of 1 W/m2·K.
Building extension Qt, windows [W/K] Et [MWh/year]
B1 132
B2 418 240
B3 118
B4 82
Total 573
5.7 Change the display windows in building B2 and B3
The change of the display windows in building extension B2 and B3 into windows with a U-value of 1 W/m2·K instead of the existing windows with a U-value of 2.9 W/m2·K, will reduce the transmission losses. The property’s annual energy loss due to transmission when the measure has been implemented is 558 MWh as shown in table 11. Which corresponds to an annual reduction of 28 000 kWh and results in a cost saving of 21 000 SEK/year with the district heating price of 0.735 SEK/kWh.
The total investment cost for this measure is estimated to be 250 000 SEK based on data from Kostnadsguiden (Kostnadsguiden, 2020) which results in a payback time of about 12 years.
Table 11. The annual energy loss due to transmission when the display windows in B2 and B3 has been changed into windows with triple glazing instead of the existing windows with double glazing.
Building extension Qt, windows [W/K] Et [MWh/year]
B1 132
B2 422 241
B3 192 103
B4 82
Total 558
5.8 Additional insulation
The annual energy loss due to transmission for B2 before adding the loose wool is 253 MWh/year and after adding the loose wool this loss has decreased to 220 MWh/year. The additional insulation of 0.2 m loose wool to receive a U-value of 0.13 W/m2·K in the roof of B2 results in a total annual energy loss due to
transmission of 553 MWh as shown in table 12. This corresponds to a reduced annual energy loss of 33 000 kWh and a reduced energy cost of 24 000 SEK/year.
The investment cost for this measure is estimated to 50 000 SEK based on information from Bro & Tak (Bro & Tak, 2020) this gives a payback time of approximately 2 years.
Table 12. Annual energy loss due to transmission when additional insulation in the roof of B2 has been implemented.
Building extension Qt, outer roof [W/K] Et [MWh/year]
B1 132
B2 75 220
B3 118
B4 82
Total 553
5.9 Lower the indoor air temperature with one degree
The property’s calculated total annual energy use is 438 MWh/year. To lower the indoor temperature with one degree reduces the energy use for heating with 5 %.
This results in an annual energy saving for heating of 22 000 kWh and a decreased energy cost of about 16 000 SEK/year.
5.10 Investigate further the electricity use during non-working hours
Further investigation regarding the property’s high electricity use during non- working hours has a high energy savings potential. By reducing the electricity use by 10 % results in an annual energy saving of 7 000 kWh/year. Which is a cost saving of about 10 000 SEK/year, using an electricity price of 1.3 SEK/kWh.
5.11 Summary of the measures
Table 13 shows a summary of the measures and in the order that they are recommended to be implemented at the property.
Table 13. Summary of the measures and in what order they are recommended to be implemented.
Measure Energy saving [MWh/year]
Electricity Heat
Cost saving [SEK/year]
Investment cost [SEK]
Payback [years]
Turn off lighting - - - - -
Investigate electricity use - - - - -
Lower indoor air temp - 22 16 000 - -
Optimize operational hours
- - - - -
Clean heat exchangers 26 19 000 16 000 0.8
Convert to LED with presence control
10 13 000 48 000 4
38 49 000 48 000 1
Additional insulation 33 24 000 50 000 2
Convert office windows 13 10 000 222 000 22
Convert display windows 28 21 000 250 000 12
Presence control T8 11 15 000 10 000 0.7
52 67 000 10 000 0.2
6 Discussion
The focus of this study has been to find energy saving measures that will reduce energy use and the cost for the property. The majority of the calculations in the study are based on estimations and assumptions since there is not enough
information about the property. This enables errors in these calculations that will affect the results and the reliability of the results. Therefore should the payback period be used as an approximate value.
6.1 Energy use
The property’s use for district heating, district cooling and electricity has decreased in 2019 in comparison to 2018. This decrease is because B4 was used as a printing house in 2018 with a lot of heavy machines that demanded a lot of energy and a lot of cooling. Hence the higher use of district heating, district cooling and electricity in 2018.
6.2 Transmission energy losses
The purchased energy for heating of the property from Övik energy is higher than the calculated total energy loss. Which indicates that there are some errors in the calculations. Most of the U-values that has been used in the calculations are
collected from BBR from the time when they were built. Thus these values are the minimum U-values that was required at that time. This means that the U-values that has been used in the calculations are probably not the same as the actual U-values of the building envelope. There is probably some errors in the calculations of the areas as well. Measurements from the field studies and floor plan drawings were used when calculating the areas and the floor plans might not correspond to the real distances of the property.
It should also be considered that the degree hours that has been used in the
calculations do not represent the actual degree hours for the year when the energy audit was performed. Since it depends on how hot or how cold the year has been, this also affects the reliability of the results.
6.3 Ventilation energy losses
The air flows used in the calculations are the minimum demand for the ventilation.
The actual air flows in the ventilation are most definitely higher than the ones that has been used in the calculations. This implies that the actual energy losses due to ventilation are probably higher than those that are calculated. The efficiencies for the heat exchangers are based on assumptions which also affects the results. Some of the actual efficiencies might be higher and some of them might be lower. Which was confirmed when the actual efficiencies of the heat exchanger in LA01 and LA08 was calculated. The night walk shows that the ventilation AHUs are operating as they should when it comes to operational hours, except LA04 that is still operating at 20:35. However, this AHU is now turned off. The air leakages for the property has not been measured, thus an estimated value of the ACH has been used when
calculating the air leakages for the property. The estimated value of the ACH for the property represents an old building that is fairly air tight, which might not be the case. Therefore, measurements are required to obtain a more reliable ACH for the property.
6.4 Internal heat generation
The total annual internal heat generation for the property is 287 MWh/year. The effect of heat gains from insolation has not been considered in the calculations.
Which means that the internal heat gain should be higher. The values that has been used in the calculations are taken from Sveby (Sveby, 2013), which is considered a reliable source. However, this also means that the calculations of the internal heat generation might not be the same as the actual value of the internal heat generation.
6.5 Electricity use
One of the most important findings from carrying out the energy audit was that the electricity usage are high during non-working hours. The electricity usage should be significantly lower when the building is empty. Considering that there is no need for lighting, ventilation and equipment such as computers that are the most electricity demanding parts of an office building. Although there is always need for some electricity in the property, even when there is no occupants in the building.
Approximately 57 % of the total annual electricity demand is being used when the building is empty. This indicates that there is an extensive energy savings potential during these hours. According to Masoso and Groebler (2010) the largest energy users during non-working hours are ventilation, equipment and lighting, which seems to be the case for this property as well. However, this needs to be
investigated further to figure out exactly were the electricity is being used. Masoso and Groebler (2010) also highlights the importance of occupant behavior to reduce this energy use. Since a lot of occupants leave equipment and lighting switched on when leaving a room. Furthermore there is also an issue that occupants leave devices such as computers switched on when they go home from work. As mentioned earlier, to change occupant behavior is not always an easy task.
6.6 Heat exchanger
The calculation of the actual efficiency of the heat exchangers in LA01 and LA08 showed that the efficiency in LA01 was 82.7 % and the efficiency in LA08 was 67.3
%. The efficiency of LA08 indicates that the heat exchanger is probably
contaminated since the efficiency should be approximately 80 %. Which means that there is probably an energy savings potential in cleaning the heat exchangers even in the other AHUs. However this need to be investigated further.
6.7 Windows
To change the windows into windows of triple glazing type windows has a long payback period for both measures. The investment cost varies a lot depending on the type of windows that is being used. A better U-value also means that the cost will be higher as well as the investment cost, which will also affect the payback period.
6.8 Lighting
To turn off the lights when not needed is considered a simple measure. Although this requires that the occupants changes their behavior, as mentioned earlier this is not always easy. According to Gentile & Dubois (2017) for old lighting the standby effect amounts to approximately 30 % of the lightings total energy use. Which means that the lighting uses energy even when they are switched off.
The system effect and the standby effect for the old luminaires is not known, although it is assumed to be about 30 %. Since it should be considered that the energy use is higher than just the installed power of the lighting. Presence control for the old lighting will of course decrease the energy use, although there will still be a standby effect that uses energy which can be considered a waste of energy. The standby effect can only be lowered by converting old luminaires into new luminaires and in this case LED-luminaires. Mata, Kalagasidis & Johnsson (2013) mean that a reduction of electricity for lighting will increase the need for heating. Which is true, although lighting should not be considered a source of heating. Since there are other more efficient alternatives for heating.
Both lighting measures with calculations have two results based on the operational hours for the old lighting that has been used in the calculations. Which means that there are two scenarios for the old lighting in both measures. The first scenario is when the old lighting is operating all hours during work hours and the second scenario is when the old lighting is assumed to operate at all hours of the year. The actual potential energy saving is difficult to calculate, since no measurements of the luminaires electricity usage has been performed. Such measurements would present information about the standby effect and the actual operational hours for the old lighting. Although the actual energy savings potential is probably somewhere in between these calculated results. Measurements of the lightings actual electricity use during a week or so is required to get a more accurate result.
