ENERGY AUDITING AND SAVING FOR A FOUR FLOOR BUILDING

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FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT

Department of Building, Energy and Environmental Engineering

ENERGY AUDITING AND SAVING FOR A FOUR FLOOR BUILDING

Diös building, ventilation and heating system

Sofia BOUCHANE

2015

Student thesis, Master degree (one year), 15 HE Energy Systems

Master Programme in Energy Systems Course 2014-2015

Supervisor: Roland FORSBERG – Mathias CEHLIN Examiner: Hans WIGÖ

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ABSTRACT

The residential and services sector is responsible of more than 40% of the whole world energy consumption. Therefore saving energy is an important goal in this project. It is about a four floor offices building located in Gävle, where the ventilation and heating system needed to be reviewed. The building is equipped with a constant air flow (CAV) ventilation system, which means that the ventilation is operating the whole day with a high air flow either there were somebody or not in the offices. And the heaters are not equipped with any regulation valve, which means that the energy is used for heating without any regulation and when the temperature is higher than the set point one, the cooling option in the ventilation start using more energy. The study suggest to install the regulation valves and to change the ventilation system from a CAV to a variable air flow (VAV) ventilation system and adding a heat recovery. It shows that 38% of the energy used usually for the ventilation and the cooling in this building can be saved.

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Table of figures

Figure 1: Operation of a VAV ventilation system- CO2 control ... 4

Figure 2: Heat exchanger operation ... 5

Figure 3: Diös building ... 7

Figure 4: IDA-ICE General page ... 8

Figure 5: Defaults information ... 9

Figure 6: Thermal bridges ... 10

Figure 7: Pressure coefficients ... 10

Figure 8: Infiltration ... 11

Figure 9: Air handling unit ... 12

Figure 10: The floor plan ... 13

Figure 11: Zone information tab... 14

Figure 12: Operating hours schedule ... 14

Figure 13: 3D model of the building ... 15

Figure 14: Simulation data ... 16

Figure 15: Heating power ... 17

Figure 16: Cooling power ... 18

Figure 17: Supply and return air temperature ... 19

Figure 18: Supply and return air flows, CAV ... 20

Figure 19: Supply and return air flows, VAV ... 20

Figure 20: Return air flow, storage zone ... 21

Figure 21: CO2 level for a CAV and a VAV ventilation system ... 22

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Table of tables

Table 1: Emitted heat per some units ... 13 Table 2: Heating power ... 17 Table 3: Different energy uses ... 22

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1. INTRODUCTION

Saving energy is nowadays an effective challenge. With a continuous world population increase and a demanding lifestyle, energy consumption knew a huge growth those last years [1]. Building and services sector is using more than 40% of the whole world energy [2]. On the other hand energy prices following the demand, increase as well. Therefor energy saving measures in this sector has to be taken seriously. However those measures should not be purchased to neglect the indoor air quality that affects the building occupant [3].

Indoor comfort comes with a continuous rate of fresh air and an adequate temperature.

Installing ventilation and heating/cooling systems is then necessary. About ventilation, it is there to dilute internal contaminants to levels that are not harmful for the occupant [4], the CO2 level is then maintained under a certain level. About heating, the indoor temperature has to be comfortable. Heat recovery through ventilation seems to a good measure in order to save some energy.

1.1 AIM:

The energy saving is the main aim of the study. Through some changing of the actual energy use and with some more efficient energy technologies the object should be reached.

After exploring the theory part of the ventilation and heating systems in relation with saving energy measures, several simulations will be exposed; their conditions and most important the results.

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2. THEORY

Through ventilation system, saving energy correspond to reduce the energy used by the fans.

This comes in relation with ventilation air flow and operating hours [5]. Over ventilating is behind a considerable energy waste; more than 30 % of the heating and cooling yearly energy is used for the new fresh air supply in the building [6, 7]. Variable airflow ventilation system using some methods, can estimate the real fresh air needed and provide it according to the number of occupant actually present. CO2 level control, humidity control or temperature control are some of the options available to adjust the fresh air supply to the demand. The VAV ventilation system unlike the constant air flow (CAV° ventilation system is perfectly adequate to the building with varying occupancy like a building offices [8].

CO2 is an excellent substitute for the occupancy-contaminants concentration. Recently it was extensively used to measure the occupancy and avoid over-ventilation [9, 10]. The advantage of this method is the fast response time detecting the change of occupancy [11]. Using the CO2 concentration to control the ventilation demand goes with a CO2 concentration set point;

1000 ppm CO2 level is a recommended value to be used for good indoor air quality [12].

As an example of the VAV ventilation system operation, the figure 1 chows that the rate of fresh air supplied follows the occupancy. The CO2 sensors inform about the occupancy and the fresh supply air is adjust.

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Figure 1: Operation of a VAV ventilation system- CO2 control

Lately saving energy is no longer an aim only for new buildings. Old building are actively renovated; envelope insolation and window replacement. It is even possible to save 50% of the energy [13]. Moreover some more saving can be realized through the heat recovery. Indeed integrating a heat exchanger in the ventilation system is a measure that enable saving 7% of the energy per degree of ΔT difference of temperature between Tin (outside temperature) and Tout (the temperature of airflow out of the exchanger to the inside) based on the calculation below (figure2):

= × × × ( − ) (1) Where Q air flow (m³/s)

C specific heat of air 1 kJ/(kg.K) ρ density of air (kg/m³)

T air temperature coming from inside the building (°C) T air temperature coming from outside the building (°C)

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Figure 2: Heat exchanger operation

Plus the ventilation heat recovery had a great success in the Scandinavian countries [14]. A study shows that integrating heat exchanger in the ventilation system lead to a reduction of 40% of the energy used for the heating [15].

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3. METHODS

The auditing of the building is here necessaire to evaluate the energy uses. Ventilation, heating and cooling are our point of interest. For that, using IDA-ICE software seems appropriate.

3.1 IDA-ICE software:

IDA Indoor Climate and Energy (ICE) is a simulation tool that offers the possibility to make a whole year and dynamic simulation with a multizone model. It allows knowing the

consumption of a whole building and its results are well compared with the experimental one.

In this project IDA will be used to build the basic model and to include some changes in order to realize some energy savings.

3.2 Simulation conditions:

Diös building is a four floor building located in Gävle next to the train station as we can see in the picture below. It’s an offices building equipped with constant air volume ventilation (CAV) with a cooling possibility.

Figure 3: Diös building

All the information about the offices employees and electrical devices were collected in order to complete the data for the simulation:

Number of employees in each office;

Equipment ;

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8 Lighting;

Working schedule;

Ventilation schedule.

Designing the building was the first step. The company provides the drawings of each floor and some information necessary to start were collected during some visits to the building:

External walls composition Glazing Windows

Windows shadings

Ventilation (supply/extract and CAV/VAV) Heating

Cooling

Every zone it’s utility (storage, office…)

As the building is located in Gävle, IDA-ICE needs a specific Gävle climate file. The file used is one that collects the information about Gävle climate between 2008 and 2013. As you can see in the figure below the “General” page of IDA-ICE needs to be filed with some more

information.

Figure 4: IDA-ICE General page

In the defaults information, the external wall were changed to brick/ concrete wall specific to Diös building with a U-value of 0.95 W/(m².K). Internal wall are with insulation and the windows are a two pane glazing windows as shown in the figure 5.

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Figure 5: Defaults information

For the site shading and orientation, everything around the building was considered in order not to neglect the radiation influence. Measures and studies about thermal bridges and

pressure coefficients would take so long; typical was the choice for the first and the auto fill for the second as shown in the figures below.

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Figure 6: Thermal bridges

Figure 7: Pressure coefficients

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To fulfill the infiltration window, the air tightness was needed. According to Gävleborg energy efficiency report on 2012 [16] it is 0.63 L/ (s.m²ext.surf), like in the Figure 8.

Figure 8: Infiltration

Back to the general page of IDA-ICE, one last step there is to complete the HVAC system. It is a CAV ventilation system with cooling possibility and no heat recovery. In the figure below the cooling possibility is translated by the number 1 under the cooling coil (1) and the non- existence of the heat recovery is translated by the number 0 under the b=heat exchanger (2).the set point for the supply air temperature is 18 °C. In the software the set point temperature is applied before the supply fans, what make the supply air gain one degree Celsius after the supply fans. In order then to have the good temperature, the set point temperature considered in the software is 17°C (3).

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Figure 9: Air handling unit

As mentioned before it is a four plan building the study is about. The company furnished some ventilation and building drawings that were used to help for the design of the building

(appendix 1). In IDA-ICE it is possible to draw a building plan by plan, each plan by adding every zone needed. Offices, conference rooms or storage room, adding a zone can be made clicking on the new zone button and by filling the size of the zone. In this case the drawings will help designing a zone without the offices size; they will be used as a building body. Another detail was to discuss; the windows were considered always closed and the doors always open. The figure below is an example of the second floor of the building.

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Figure 10: The floor plan

Some offices were reunited in one zone and later the number of equipment and occupant will be acquired for the whole offices in the zone. The supply and return air flow will be sum up as well for all the offices in the zone. All the supply and return air flow can be found in appendix 2.

When a zone is designed still all the information about the room units, the internal gains and ventilation to fill. The figure 11 is an example of zone tab information.

Room units: only ideal heater.

Internal gains:

• Light -> a power of 10 W/m²

• Equipment -> according if we have computers, printers or other devices.

Table 1: Emitted heat per some units

Computer Printer

160 W working 100% of the scheduled time

1000W working 25% of the scheduled time

Or

250W working 100% of the scheduled time

• Occupant -> counting the workers was done when collecting information.

Ventilation: supply and return air flow were filled according to the data in a CAV ventilation system.

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Figure 11: Zone information tab

Moreover a schedule was necessary for every equipment, light or occupant and the fans of the ventilation. The working hours in the offices were from 7 a.m to 6 p.m but in order to smooth the schedule and make it more coherent (because not all the devices are going to start suddenly at the same time) the schedule was considered like the figure below.

Figure 12: Operating hours schedule

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Finally outside the building, shading on the second third and fourth floor were added on the south and west side of the building (always according to the information collected about the building). The figure below is a 3D model of the building in IDA-ICE.

Figure 13: 3D model of the building

Ones the basic model is built, 5 simulations will be run:

• Simulation 1: the actual model building situation;

• Simulation 2: adding a heat recovery in the ventilation system of the basic model, Efficiency 70%;

• Simulation 3: adding a heat recovery in the ventilation system of the basic model, Efficiency 90%;

• Simulation 4: changing the ventilation system, to a variable air flow (VAV) system, in the basic model;

• Simulation 5: combination a VAV ventilation system with heat recovery in the basic model.

A one year simulation will be run for all the models. The dynamic type of data has been selected (figure 14).

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Figure 14: Simulation data

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4. RESULTS

As presented before, 5 simulations will be run. Different models have been built by adding a heat recovery system to the main one, the original CAV ventilation system, or by changing this one from a CAV to a VAV ventilation system. In the theory chapter, different VAV ventilation systems were mentioned. The one used in the simulations is a VAV with a CO2 level control.

After running all the simulation, comes the analyzing of the results.

4.1 Heating and cooling power:

In appendix 3 the power used in every month is exposed for each simulation. Comparing the heating power between all the models showed (the figure 15) that with a VAV ventilation system instead of a CAV system decrease the energy consumption. Same it is when adding a heat recovery to the ventilation system and the best option is a VAV ventilation system equipped with heat recovery. The table below shows the power consumption of each model.

Figure 15: Heating power

Table 2: Heating power

CAV VAV CAV-Heat

recovery 70%

CAV-Heat recovery 90%

VAV-Heat recovery 90%

Max heating power 40771 34202 29998 28701 26394

total heating power

177473 142134 122997 118579 105118

0 5000 10000 15000 20000 25000 30000 35000 40000 45000

1 3 5 7 9 11 13

CAV VAV

CAV-Heat recovery 70%

CAV-Heat recovery 90%

VAV-Heat recovery 90%

Months

power(W)

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When comparing the cooling power, no change happened when a heat recovery system is added. Since cooling is needed during summer, so adding a heat recovery system doesn’t save any energy when it comes to cooling. However, the VAV ventilation system makes the saving energy possible as shown in the figure below.

Figure 16: Cooling power

4.2 Supply and return air temperature:

Changing the ventilation system has an impact on the supply and return air temperature as well. Tables of IDA-ICE simulation results in appendix 4 show how the supply air temperature changed for every model. The figure below exposed the variation of the ventilation supply and return air during the year. The heat recovery system increases the supply air temperature, so then less heating is needed. Moreover when the efficiency of the system is better the supply air temperature is higher and the energy needed for heating is lower.

0 500 1000 1500 2000 2500 3000

1 3 5 7 9 11 13

CAV VAV

Months

power(W)

CAV VAV

Months

power(W)

Max power : 2230 W

Max power :

1436 W

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Figure 17: Supply and return air temperature

4.3 Ventilation air flows:

To observe closer the difference between all the models especially between the CAV and the VAV ventilation system, analyzing the air flow values seems to be appropriate. The study will be made for two kind of zones; an office one and a storage one. Tables are available in the appendix 5.

In the office zone, the supply air flow is around 39 L/s and the return air flow around 35 L/s when the ventilation system is a CAV (figure 18). When it is a VAV system, supply and return air flow are equal and around 20 L/s (figure 19). The VAV system controlled by the CO2 level decreased the ventilation air flow according to the real air flow needed in the office.

-10 -5 0 5 10 15 20 25 30 35

1 3 5 7 9 11 13

Months

Temperature( C°)

Return air

Supply air

CAV-Heat recovery 90%

CAV-Heat recovery 70%

CAV

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Figure 18: Supply and return air flows, CAV

Figure 19: Supply and return air flows, VAV 10

15 20 25 30 35 40 45 50

1 3 5 7 9 11 13

Exauhst air Supply air

months

flow(L/s)

10 15 20 25 30 35 40 45 50

1 3 5 7 9 11 13

Exhaust air Supply air

months

flow(L/s)

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In the storage zone there is no supply air. With the VAV ventilation system, the return air decreased as well comparing to when the CAV ventilation system was running (figure below).

Figure 20: Return air flow, storage zone

Decreasing the supply air has as a normal consequence to decrease the return air flow as well.

The main interest in on the supply air, less new air volume is coming les heating is needed. So this is how come the energy saving.

4.4 Ventilation air quality:

A comfort zone is up to 1000 ppm CO2 level. As a set point for the simulations with a VAV system, the CO2 level must be below 1000 ppm. Comparing then the CO2 level between the models with a CAV and VAV ventilation system, the CO2 level is higher when the building is equipped with a VAV system. However, the CO2 level is still under the limit the offices and the building is still in the comfort zone.

0 1 2 3 4 5 6 7 8 9 10

1 3 5 7 9 11 13

CAV VAV

months

flow(L/s)

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Figure 21: CO2 level for a CAV and a VAV ventilation system

4.5 Energy:

In the table below, different energy used are exposed. In the appendix 7 are exposed tables more detailed than this one.

Cooling is usually needed in summer and more for the models with a CAV ventilation system.

Heat recovery system in the simulation 2, 3 and 5 has a huge impact, more consequent for the CAV ventilation system when the supply air flow is still high comparing to the VAV system. The energy used for the fans is higher when the ventilation system is a CAV, due to the high

ventilation air flow.

Table 3: Different energy uses

Heating

(kWh)

Cooling (kWh)

AHU heat recovery (kWh)

AHU cold recovery (kWh)

Humidi- fication (kWh)

Fans (kWh)

simulation 1 0 3224.3 0 0 0 6911.3

simulation 2 0 3219.6 46039.7 0 0 6825.7

simulation 3 0 3219.8 49393.4 0 0 6820.5

simulation 4 0 2072.5 0 0 0 4196

simulation 5 0 2073.6 31246 0 0 4147.1

The VAV ventilation system compared to the CAV, saves 35% of the energy used for the cooling and 40% of the energy used for the fans. So around 38 % for both.

500 550 600 650 700 750 800 850

1 3 5 7 9 11 13

VAV

CAV

Months

ppm

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5. DISCUSSION

All the study has been made for an old building, with an old heating system and a CAV ventilation system. The old heating system without any regulation valve keep heating even when the set point temperature is reached, therefore the cooling option in the ventilation system is used to decrease or maintain the set point temperature. So heating and cooling are on at the same time.

In this project some hypothesis has been made, the set point temperature doesn’t exceed 21°C and all the heaters are equipped with the regulation valves. So the results obtained are valid only when the valves are installed.

Also the study didn’t include the lunch break that is around one hours and a half where, with a VAV ventilation system, the supply air flows will be at it least value.

All the simulations that have been run are with the typical thermal bridges and an autofill for the pressure coefficient. The influence and the uncertainties due to those options should be taken in consideration.

Furthermore changing the ventilation system is a complex operation. The possibility of installing the VAV ventilation must be determined.

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7. CONCLUSION

The project was about the energy auditing and saving of a building through its ventilation system. The actual one is a CAV ventilation system and the suggestion was to change it to a VAV ventilation system with heat recovery. Heat recovery increased the supply air

temperature and so decrease the energy used for the heating. The VAV ventilation system decreased the supply air flow according to the CO2 level needed and again by decreasing the volume of new air, decrease the energy needed for the heating as well as for cooling.

Moreover the study shows that the VAV ventilation system makes saving at least 38% of the energy.

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6. FUTURE WORK

The project didn’t include the economic study. The extent of the work can be noticed once the whole building inspected; checking the actual possibilities and the future roadwork that should be done. So a quotation of the global cost must be executed as a future work.

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REFERENCES

[1] Global Energy Statistical Yearbook 2015. ENERNADA intelligence+ consulting available on the web site: https://yearbook.enerdata.net/

[2] SEA (Swedish Energy Agency), (2011). Energy in Sweden 2011. Swedish Energy Agency Publication Department, Eskilstuna.

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HVAC&R Res. , 18 (1)(2012), pp. 1-17.

[4] A.Persily. Challenges in developing ventilation and indoor air quality standards: The story of ASHRAE Standard 62. Building and Environment 91 (2015) pp.61-69.

[5] Amalie Gunnera, Göran Hultmarka, Anders Vorreb, Alireza Afsharia, Niels Christian

Bergsøea. Energy-saving potential of a novel ventilation system with decentralised fans in an office building. Energy and Buildings, Volume 84, December 2014, Pages 360–366.

[6] Rock BA, Wu CT. Performance of 4xed, air-side economizer,and neural network demand- controlled ventilation in CAV systems. ASHRAE Transactions 1998;104(2):234–45.

[7] Warren BF. Energy saving in buildings by control of ventilation as a function of indoor carbon dioxide concentration. Building Services Engineering Research & Technology 1982;3(1):4–12.

[8] C.Y.H. Chao∗, J.S. Hu. Development of a dual-mode demand control ventilation strategy for indoor air quality control and energy saving. Building and Environment 39 (2004) 385 – 397.

[9] Ke YP, Mumma SA. Using carbon dioxide measurements to determine occupancy for ventilation control. ASHRAE Transactions 1997;103(1):365–74

[10] Giacomo SMD. Differential CO2 based demand control ventilation (maximum energy savings & optimized IAQ). Energy Engineering 1999;96(5):58–76.

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[12] Hong Kong Environmental Protection Department. Guidance Notes for the Management of the Indoor Air Quality in Offces and Public Places (Draft). Hong Kong, 1999.

[13] A. Blumberga, A. Kamenders, G. Žogla. Energy Performance of Renovated Soviet Time Apartment Building. RTU zinātniskie raksti. Vides un klimata tehnoloģijas, 13 (1) (2008), pp.

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[15] J. Laverge, A. Janssens. Heat recovery ventilation operation traded off against natural and simple exhaust ventilation in Europe by primary energy factor, carbon dioxide emission, household consumer price and exergy. Energy and Buildings, 50 (7) 2012, pp 315–323

[16] SanneGodow Bratt and Gustav Persson. Energiffektivisering av flerbostadsfastigheter- elvalokala exempel ar 2012. Available at Högskolan I Gävle.

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APPENDIX

Appendix 1: Ventilation system Floor 1:

Floor 2:

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32 Floor 3:

Floor 4:

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33 Appendix 2: Supply and return air flows

Floor 1:

Floor 3

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34 Floor 4:

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35 Appendix 3: Total heating and cooling

Simulation 1, Total heating and cooling:

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36 Simulation 2, Total heating and cooling:

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37 Simulation 4, Total heating and cooling:

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38 Appendix 4: AHU temperature

Simulation 1, AHU temperature:

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39 Simulation 3, AHU temperature:

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40 Simulation 5, AHU temperature:

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41 Appendix 5: ventilation air flows

Simulation 1, ventilation air flows for an office zone:

Simulation 1, ventilation air flows for a storage zone:

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42 Simulation 2, ventilation air flows for an office zone:

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46 Appendix 6: Indoor air quality

Simulation 1, indoor air quality for an office zone:

Simulation 1, indoor air quality for a storage zone:

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47 Simulation 2, indoor air quality for an office zone:

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51 Appendix 7: AHU energy

AHU energy, simulation 1:

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52 AHU energy, simulation 4:

ENERGY AUDITING AND SAVING FOR A FOUR FLOOR BUILDING

FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT