FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT
Department of Building, Energy and Environmental Engineering
ENERGY IMBALANCE IN A MULTY FAMILY HOUSE
María Campoy López
2014
Master Thesis,15 ECTS Master program in Energy Systems
Supervisor: Peter Hansson Examiner: Ulf Larsson
ACKNOWLEDGMENTS
This project has been carried out thanks to the supervision from Peter Hansson. I want to thanks him for all his support and dedication.
I would like to thank the professor Mathias Cehlin who has been supporting me with IDA ICE software during the work, for his dedication, his worry about the work and to help to overcome all the difficulties encountered during the simulation.
I would also like to express my appreciation to all my college, for the good and not that good moment lived, but with the feeling that we have just done something special for ourselves.
ABSTRACT
Nowadays, construction and development of more energy efficient buildings is a fact.
The EU, each day it is more worried about the importance of decrease the usage of energy and avoid its squandering.
In Sweden and in the rest of the world we face the problem how to create a sustainable development. At the same time the Swedish million program, a housing program made in the 1960s and 1970s, is facing a renewal due to lack of maintenance during many years.
This project is focused in the study of how the imbalance ventilation in a building built in the time of multi family houses programme, which has been renovated, works. The aim will be focused on two principal aspects. The first one will be related to the change of heat exchanger efficiency.
The second one will study how the air infiltration and mechanical supply air losses will change due to this imbalance. The imbalance is produced when the kitchen hood works.
For this reason, when the construction of the reference in IDA Software is done, two air handling units will be supposed; one basic air-handling unit, which provide supply and exhaust air, and the second one, which only represent extract air of kitchen hoods.
Concerning the results, it should be stated that the imbalance (kitchen hood works) produce a decrease approximately of 3 % in the mechanical air supply losses. It related with the change of exhaust air temperature, which will change the efficiency of the heat exchanger and the amount of heat needed to pre-heat the supply flow will decrease as well.
Regarding the infiltration losses, they increase 12 %. When the kitchen hood works, it causes a variation in the gradient pressure, which will make easier the leakages through the enclosure.
To conclude with the results, the amount of energy needed per meter squared when the basic air handling unit works is 117,9 kWh whereas the amount of energy when the kitchen hood works is 118,0 kWh. To summarize, the imbalance in the air infiltration is able to save 0,1 kWh/m2 in the reference building.
To sum up, the aim studied in this project shows how some small changes, which have to be taken into account, can save energy thanks to the variation of other auxiliary devices such as heat exchanger.
INDEX
1. INTRODUCTION ... 1
1.1 BACKGROUND ... 1
1.2 PURPOSE AND OBJECTIVE ... 1
1.3 LIMITATIONS ... 1
1.4 METHODOLOGY ... 2
1.5 IDA INDOOR CLIMATE AND ENERGY ... 2
1.5.1 Definition ... 2
1.5.2 Interfaces ... 3
1.5.3 Location and climate design ... 3
1.5.4 Boundary Conditions ... 4
1.6 BUILDING DESCRIPTION ... 5
1.6.1. Miljonprogrammet. ... 8
1.6.2. Location, orientation and climate. ... 7
1.7 PERFORMING THE BUILDING ... 8
1.7.1. Geometry ... 8
1.7.1.1 Roof ... 9
1.7.1.2 Ground ... 9
1.7.2. Thermal transmittance ... 10
1.7.2.1. WALL CONSTRUCTIONS ... 10
1.7.2.2. DOORS AND WINDOWS ... 10
1.7.2.3. ROOF ... 10
2. THEORY ... 12
2.1. THEORY OF AIR INFILTRATIONS ... 12
2.1.1. Basic concepts ... 12
2.1.2. Mechanical air supply ... 12
2.1.1.1. Mechanical systems with heat exchangers. ... 14
2.1.3. Residential air leakages ... 15
2.1.3.1. Multifamily Building Leakage ... 16
2.2. INDOOR ENVIRONMENT QUALITY IN MULTI FAMILY HOUSES ... 16
2.2.1. Thermal comfort ... 16
2.2.2. Air quality ... 18
2.2.2.1. Classes of air contaminants ... 18
3. METHOD ... 20
3.2. HEAT LOAD ... 25
3.2.1. Light and equipment ... 25
3.2.2. Air ventilation ... 27
3.2.3. Heater ... 30
3.2.4. Infiltrations ... 30
3.2.5. Thermal bridges ... 31
3.2.6. Occupants ... 32
4. RESULTS ... 34
4.1. SENSIBLE ANALYSIS OF AIR HANDLING UNIT ... 34
4.2. SENSIBLE ANALYSIS OF AIR HANDLING UNIT + KITCHEN HOOD ... 37
4.3. IMBALANCE BETWEEN THE DIFFERENT AIR HANDLING UNITS ... 41
5. DISCUSSION ... 49
6. CONCLUSSION ... 52
7. REFERENCES ... 52
8. APPENDIX ... 56
APPENDIX A ... 56
APPENDIX B ... 57
APPENDIX C ... 58
APPENDIX D ... 61
APPENDIX E ... 68
APPENDIX F ... 62
External walls ... 62
Above and below windows ... 64
Between windows ... 64
Internal walls ... 65
INDEX TABLES
Table 1: Composition of the ground layers outside the basement walls ... 10
Table 2: Composition and thickness for the roof 1 ... 11
Table 3: Composition and thickness for the roof 2 ... 11
Table 4: Values of shielding coefficients according to different factors ………..13
Table 5: values of Met depending on the activity. [14]……….17
Table 6: values of clo coefficient [15] ... 18
Table 7: Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 35
Table 8: Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 38
Table 9: Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 41
Table 10: Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 42
Table 11: energy saving depending on the ventilation where are included all the values needed. ... 45
Table 12: energy balance in the reference building with the basic air-handling unit and the kitchen hood AHU. ... 46
Table 13: energy balance in the reference building with the basic air-handling unit ... 46
Table 14: Comparison between the energy recovery according to theoretical values and IDA Software results. ... 47
Table 15: Energy use of lighting, electric cooling and HVAC aux measured in kWh and kWh/m2 ... 48
Table 16: composition, thickness, heat conductivity, density, heat capacity and U-value of each one of the walls in the reference building. ... 57
Table 17: suppositions of occupants, equipment and light for each room in the building 58 Table 18: Schedule of occupant in the defined rooms. ... 58
Table 19: Areas above and below the ground for each one of the façade. ... 58
Table 20: total area above and below the ground and percentage of each one ... 59
Table 21: walls, which have been supposed to be in contact with the air. ... 59
Table 22: Supply and exhaust airflows for the different rooms of each apartment ... 61
Table 23: Composition of external walls floor 1 ... 62
Table 24: Composition of external walls floor 1 ... 63
Table 25: Compisition of external walls floor 6 ... 63
Table 27: composition between windows ... 64
Table 28: airflow rates when the existence of an imbalance ventilation. ... 65
Table 29: values of uncontrolled airflow and airflow rate for imbalanced ventilation ... 66
Table 30: airflow rates when the existence of balance ventilation. ... 66
Table 31: values of uncontrolled airflow and airflow rate for balanced ventilation ... 66
Table 32: airflow rates when the existence of extra exhaust air flow because of kitchen hood AHU ... 66
Table 33: Values of uncontrolled airflow and airflow rate for extra exhaust airflow ... 67
INDEX GRAPH
Graph 1: graph of Energy losses obtained by IDA ICE for the whole building when the basic ... 35 Graph 2: graph of Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 36 Graph 3: graph of Energy losses obtained by IDA ICE for the whole building when the basic Air Handling Unit works ... 37 Graph 4: graph of Energy losses obtained by IDA ICE for the whole building when the air-handling unit per kitchen hoods is included. ... 38 Graph 5: graph of mechanical supply air losses obtained by IDA ICE for the whole building when the kitchen hood AHU is included. ... 39 Graph 6: graph of infiltration and openings losses obtained by IDA ICE for the whole building when the kitchen hood AHU is included ... 40 Graph 7: graph of infiltration and openings losses obtained by IDA ICE for the whole building when the kitchen hood AHU is included. ... 43
INDEX FIGURES
Figure 1: Façade east of Sicksackvägen 17 ... 5
Figure 2: Façade north of Sicksackvägen 17 where is defined the name done for each level. ... 5
Figure 3: Plant of floor 1 with the division between flats ... 6
Figure 4: Plant floor between level 2 and 5. ... 6
Figure 5: Plant of floor 6, which corresponds with the attic. ... 7
Figure 6: Image Google maps of Sicksackvägen 17, Gävle……….. 7
Figure 7: Façades of the reference building located in Sicksävägen 17 ………...9
Figure 8: Image importing from IDA ICE showing the two different roofs ……….11
Figure 9: Airflow depending on the pressure [9] ……….15
Figure 10: Construction of the different rooms by IDA ICE Software ... 20
Figure 11: Control set point defined in IDA ICE Software ... 19
Figure 12: Definition of Setting for a new zone in IDA ICE Software ... 21
Figure 13: Window in IDA ICE software to include different wall part, windows and doors. ... 22
Figure 14: External wall of living room of Flat 2 ... 22
Figure 15: Information about the selected window for the reference building ... 23
Figure 16: common window in IDA ICE Software to define the new composition of a wall part. ... 23
Figure 17: Common window in IDA ICE for input data of a room. ... 24
Figure 18: common window in IDA ICE to define a new composition of a wall. ... 24
Figure 19: façade east of the reference building seen from northeast. ... 25
Figure 20: Common window in IDA ICE for input data of equipment. ... 26
Figure 21: Common window in IDA ICE for input data of light. ... 26
Figure 22: Schema of the standard air-handling unit, which provide supply and exhaust air ventilation. ... 27
Figure 23: Schema of the air-handling unit for the kitchen hood, which provides only exhaust air ventilation. ... 28
Figure 24: Common window in IDA ICE to defined a schedule. ... 28
Figure 15: Image of a tipica heat exchanger ... 29
Figure 26: Variation of efficiency regarding the airflow rate for the heat exchanger model VEX 370 H ... 30
Figure 27: Common window in IDA ICE Software to defined the infiltration condition in the reference building. ... 31
Figure 28: Window of thermal bridges in IDA ICE software. ... 32
Figure 29: Window in IDA ICE software where it is observed the occupant. ... 32
Figure 30: Façade west of the reference building. ... 60
Figure 31: Façade north of the reference building seen from northeast. ... 60
Figure 32: Section of floor 0. ... 61
Figure 33: Section of floor 2-5. ... 62
Figure 34: Section of floor 6. ... 62
Figure 35: Section of the wall, which includes windows. ... 63
Figure 36: Section of the wall with different composition between the windows ... 63
1. INTRODUCTION
1.1 Background
Nowadays, construction and development of more energy efficient buildings is a fact. It is much dependent on the decisions in the EU, which each day it is more worried about the importance of decrease the usage of energy and avoid its squandering. The European leaders set the goal of decrease up to 2020, the annual energy use of the European Union by 20% compared to 1995 [1]. Efficient energy changes are consider not only a method to reach a sustainable way to reduce the emissions of greenhouse gases but also a way to promote the competitiveness between companies and the save of money.
Regarding the country of Sweden, its national goal is also related to the total energy use, based on the building´s total heated area, and should be reduce by 50 percentage by 2050 compared to 1995 energy use. In addition, Sweden has also the goal of 50 percentage of the energy produced from renewable sources by 2020. In Glävleborg, it was approved in 2011; new energy and climate change stating that the country will be climate neutral by 2050 [2].
1.2 Purpose and objective
The aim of this master thesis is to obtain the calculation models of air infiltration in a building built in the seventies during the time of million programs in Sweden. The model will compare how much energy is wasted by having an imbalance in airflow rated over a typical year in Gävle.
1.3 Limitations
Several aspects restrict the scope of this thesis. In order to understand limitations of the thesis, these aspects should be pointed out:
• It is possible to exist differences in constructions, between the real building and the one built in IDA ICE Software.
• Difference of input data in IDA ICE and real materials, such as windows and internal walls compositions.
1.4 Methodology
The project begins with a simulation of an existing building. Firstly, knowledge of the building energy software at an advanced level had to be acquired. Afterwards, It has been carried out an energy balance analysis. When all the simulations were done, both the most important results and guidelines for modelling entrances have been represented.
1.5 IDA Indoor Climate and Energy
1.5.1 Definition
IDA Indoor Climate and Energy 4.6 is a whole-building simulator allowing simultaneous performance assessments of all issues fundamental to a successful building design: form, fabric, glazing, HVAC systems, controls, light, indoor air quality, comfort, energy consumption etc. It has more than 900 registered users (mostly in the Scandinavian countries), mostly HVAC designers but also educators and researchers. The original development of IDA ICE was requested, specified and partly financed by a group of thirty leading Scandinavian AEC companies. The mathematical models were originally developed at the Royal Institute of Technology in Stockholm (KTH) and at Helsinki University of Technology, now both part of the ICE academic network. [3]
The building model used in IDA Indoor Climate and Energy is very detailed and has been validated against measurements and other calculation software in several projects. Unlike many similar programs a radiation balance is established based on view factors for the entire room. This makes it possible to calculate the operative temperature’s variation in different positions.
The correct dynamic temperature response of the building is calculated. In many other programs this completely fundamental element of the heat balance is treated by rough approximations.
Air movements in the room cannot be calculated with this type of model. Calculating this
room includes a few hundred variables. As for any computation, the calculation time required is strongly linked to the size of the model.
The user interface has been designed to make it easy to build up and simulate simple cases, but also to offer the advanced user the full flexibility of IDA, to facilitate the simulation of complex or unusual cases.
1.5.2 Interfaces
The IDA user interface is divided into three different levels with different user supporting and scope [4]:
• Wizard Level: the user is allowed to introduce input into one or more forms that are shown in sequence. The user can perform a simulation directly, or he she can transfer the data that has been introduced to the next level.
• Standard Level: the user has got more options of designing the building. In this level the user can define geometry, material, loads, control settings and so on, therefore, that should be understood easily by majority of engineers without any specific simulation knowledge.
• Advanced Level: with the Expert Edition, the user can edit the automatically created schematic display of a simulation model (including systems). Using a large library of available components, you can build your own air handling units, plants and control systems.
1.5.3 Location and climate design
IDA ICE uses for the outdoor climate two types of weather data:
A synthetic design day: it is based on the daily extreme wet and dry bulb temperatures, wind direction and speed, and the reduction factor for the direct and diffuse sunlight.
• A climate file with measured data: contains the information all as a function of time about the air temperature, relative humidity, the wind direction and speed, the direct normal and diffuse radiation on horizontal surface. [5]
In order to describe the location of the reference building, it has to be included some aspects such as:
• Latitude
• Longitude
• Height over the sea level
• Time zone
• Wind profile.
1.5.4 Boundary Conditions
The next list collects the aspects, which IDA ICE software asks for, so as to elaborate the boundary conditions that build the model and make it unique.
• Weather data.
• Location of the building.
• Wall objects.
• Furniture.
• Light and equipment.
• Occupants of the building.
• Heating and cooling devises.
• Ventilation.
• Possible shading by other buildings and windows
• Building orientation.
• Geometry of the building.
• Wind pressure coefficients along the facades of the building.
• Walls composition.
• Air leakage area.
1.6 Building description
The building, which has been studied, is located in Sätra (Gävle). This building was built in the 70s. The reference object consists of a residential building of 30 flats. It has got a total of seven levels. In the following Figure 1, it is possible to observe real images of the building.
Figure 1: Façade east of Sicksackvägen 17
To guarantee the best comprehension possible, the different levels have been named as it is stated in the following drawing Figure 2:
Right after, it had been explained the different levels. Firstly, floor 0 corresponds with the basement. The drawing of this floor is included in APPENDIX VII.
FLOOR 1 FLOOR 0 FLOOR 4
FLOOR 2 FLOOR 3 FLOOR 5 FLOOR 6
Figure 2: Façade north of Sicksackvägen 17 where is defined the name done for each level.
Secondly, floor one corresponds with the entry hall. This floor offers five flats. The distribution of this flat can be observed in the next Figure 3:
Figure 3: Plant of floor 1 with the division between flats
Regarding floors between level 2 and 5, all have got the same flat distribution. It is possible to observe them in the upcoming draw Figure 4.
Figure 4: Plant floor between level 2 and 5.
Conclusively, the floor 6 corresponds with the attic. The area of this floor is rather small that the one of the other floors. It is possible to visualize it in the Figure 5:
Figure 5: Plant of floor 6, which corresponds with the attic.
To obtain information about the measures and area of rooms, flats and so on, in APPENDIX VII are including all the drawing of each floor.
1.6.1. Location, orientation and climate.
As it was mentioned before, the building is located in Sicksäckvagen Street in the neighbourhood of Sätra (Gävle).
Gävle is located in Baltic Sea near the mouth of Gavleån River (Figure 6). The weather is similar to the rest of central Sweden. The average temperature is -5 ºC in January and +17 ºC. [6]
The city of Gävle is positioned in the coordinates 60,4N and 17,1E.
This building was built in the 70s.
The orientation of the building corresponds with 0º south.
The level above the sea is 3 metres approximately.
Figure 6: Image Google maps of Sicksackvägen 17, Gävle
1.6.2. Miljonprogrammet.
Miljonprogrammet is the common name in Swedish of the ambitious housing program made in the 1960: s and 1970:s, is facing a renewal due to lack of maintenance during many years. [7]. The program was implemented by the governing Swedish social democratic party to make sure that everyone could have a home at a reasonable price.
The aim of the programme was to build a million new dwellings in 10-year period. In the end, about 1.006.000 new dwellings were built. The net result was an increase in Sweden’s housing stock of 650.000 new apartments and houses, with a general rise in quality though arguably at the expense of aesthetics.
The new Million Programme residential areas were greatly inspired by early suburban neighbourhoods such as Vällingby and Årsta. One of the main aims behind the planning of these residential areas was to create “good democratic citizens“. The means of achieving this were to build at high quality with a good range of services including schools, nurseries, churches, public spaces, libraries, and meeting places for different groups of households. A principal aim, although ultimately unsuccessful, was to mix and integrate different groups of households through the spatial mixing of tenures. Most of the apartments were of the “standard three room apartment”. This is 75 m² of area, planned for a model family of two adults and two children. [8] [23]
1.7 Performing the building
The following section will describe several aspects important to understand the modelling of the reference building by means of IDA ICE software. First of all, it has to be taken into account that some simplifications have been done due to the shape of the building studied. These simplifications had been explained in the following paragraph.
1.7.1. Geometry
The modelling of the building has been built in IDA ICE by means of importing AutoCAD files. It has to be taken heed of two important points regarding the geometry of building.
1.7.1.1 Roof
This building was built using a pitched roof. In this case, it has been supposed a horizontal roof due to the fact that it is not relevant to obtain the results in IDA ICE Software.
1.7.1.2 Ground
The building, which has been studied, has got a controversial dimension of floor 0, which corresponds with the basements plant. The following figures (Figure 7) show the floor 0 along the four façades where it is possible to observe which walls are in direct contact with the ground. (The orange rectangles mark the controversial zone in contact with the ground).
As it can be observed in the previous figures, not all the floor 0 is in contact with the air, almost all the walls of floor 0 are buried and in contact with the ground. For this reason, and due to the difficult geometry of the wall, which is in contact with the air, it has been obtained an equivalent area of the wall and the windows situated in south façade.
Figure X: Façade south of Sicksäckvagen 17
Figure 7: Façades of the reference building located in Sicksackvägen 17
In the APPENDIX III there is the table, which shows the total area below the ground and above the ground, just like the total area of windows.
The ground has been defined in IDA ICE regarding the ISO-13370. On the other hand, the ground layers outside the basement walls had been defined as follow in Table 1:
Table 1: Composition of the ground layers outside the basement walls
MATERIAL THICKNESS (mm) CONCRETE DRY 500
EXP. PLASTICS. 21 49
1.7.2. Thermal transmittance
1.7.2.1. Wall constructions
The most controversial matter of the reference building is the composition of the walls, due to the fact that depending on the floor studied, the compositions of the walls are rather different. The company “Sweco” has provided all the information of the materials.
Afterwards, the materials have been defined in IDA ICE, taken into account the heat conductivity, density and heat capacity. (For further information, looks APPENDIX I).
Regarding the different types of composition, they had been divided into four different groups to know and understand easily the different constructions of it. It exists different composition for the external and internal wall, the wall above and below the windows and the composition between windows. All this information is detailed in APPENDIX V.
1.7.2.2. Doors and windows
There are different U-values depending on the function of the doors. The balcony door have U-values = 1,1 W/m2K. Regarding the entre hall, the entry door and glass parts is U=1,5 W/m2K for both. The windows have U-value equal to 1,1 W/m2K.
1.7.2.3. Roof
The design of the roof of the reference building involves different constructions. These different constructions are shown in the following Table 2 and Table 3:
Table 2: Composition and thickness for roof 1 Table 3: Composition and thickness for roof 1
ROOF 1 ROOF 2
MATERIALS THICKNESS (mm) MATERIALS THICKNESS (mm)
AIRCRETE 300 30 MINERAL WOOL 31 129
MINERAL WOOL 31 290 AIRCRETE 300 200
AIRCRETE 300 200
In the following Figure 8, it is possible to observe the two different roofs of the building by an image of IDA software.
ROOF 2
ROOF 1
Figure 8: Image importing from IDA ICE showing the two different roofs.
2. THEORY
2.1. Theory of air infiltrations
In this chapter, the theoretical basis about “Air infiltrations in multifamily buildings” had been explained.
2.1.1. Basic concepts
The air leakage through the cracks and interstices around the windows and doors and through floors and walls is called as infiltration and the intentional displacement of air through specified openings such as windows, doors, and ventilators is called as natural ventilation in buildings. The accurate estimation of infiltration and ventilation has an importance on HVAC design either from energy consumption or from indoor air quality point of view. Uncontrolled infiltration and ventilation could cause additional energy losses or unhealthy internal air conditions at terminal levels. [10]
2.1.2. Mechanical air supply
Some of the aspects, which have to be taken into account, is the theory about mechanical air supply. The total airflow rate is determined as the sum of the ventilation rate determined from the average airflow rates through the system fans when in operation, Vf, and an additional airflow rate, Vx, induced by wind effects through ventilation openings and infiltration cracks according to equation:
V = Vx + Vf (1)
Where:
• Vf is the average airflow rate through the system fans when in operation. (m3/s)
• Vx is the additional airflow rate with fans on, due to wind effects. (m3/s)
For supply-only systems, Vf is equal to the supply airflow rate, V1, and for exhaust only systems it is equal to the exhaust flow rate V2
STUDY OF IMBALANCE IN A MULTY FAMILY HOUSE
For balanced ventilation systems, Vf is equal to the greater of the supply airflow rate, V1, and the exhaust airflow rate, V2.
The additional airflow rate, Vx, an be calculated according to the following equation:
𝑉𝑥 = !·!!"·!
!!!!·[!!!!!!·!!"]! (2)
The different symbols of the previous equation, corresponds with the different concepts explained below:
• V is the ventilated volume.
• n 50 is the air change rate resulting from a pressure difference of 50 Pa between inside and outside, including the effects of air inlets.
• 𝑒 and 𝑓 are shielding coefficients, which can be found in the following tables
“X” and “X:
On the other hand, if there is mechanical ventilation switched on for a part of the time, the airflow rate is calculated according to the next equation:
𝑉 = 𝑉𝑜 + 𝑉𝑥 · 1 − 𝛽 + 𝑉𝑓 + 𝑉𝑥 · 𝛽 (3) Where
• Vo is the airflow rate with natural ventilation, including airflow through ducts of the mechanical system.
16
C.5 Mechanical ventilation systems
The total airflow rate is determined as the sum of the ventilation rate determined from the average airflow rates through the system fans when in operation, V , and an additional airflow rate, f V , induced by wind x effects through ventilation openings and infiltration cracks according to Equation (C.2):
f x
V V V (C.2)
where
V is the average airflow rate through the system fans when in operation; f
V is the additional airflow rate with fans on, due to wind effects. x
For supply-only systems, V is equal to the supply airflow rate,f V , and for exhaust only systems it is equal to 1 the exhaust flow rate, V .2
For balanced ventilation systems, V is equal to the greater of the supply airflow rate,f V , and the exhaust 1 airflow rate, V .2
The additional airflow rate,V , can be calculated according to Equation (C.3): x
x 50 2
1 2
1 50
V n e
V f V V
e V n
ª º
« »
¬ ¼
(C.3)
where
V is the ventilated volume;
n50 is the air change rate resulting from a pressure difference of 50 Pa between inside and outside, including the effects of air inlets;
V is the supply airflow rate; 1
V is the exhaust airflow rate; 2
e, f are shielding coefficients, which can be found in Table C.4.
NOTE Equation (C.3) is empirical, derived from numerical simulations over complete years. It is based on additional flow when there are large wind-induced pressure differences, assuming no additional flow for lower wind speeds.
Table C.4 — Shielding coefficients, e and f, for calculation of the additional air flow rate using Equation (C.3)
Shielding class Description Coefficient More than one
exposed facade One exposed facade No shielding Buildings in open country, high
rise buildings in city centres 0,10 0,03
Moderate shielding Buildings in the country with trees or other buildings around them, suburbs
0,07 0,02
Heavy shielding Buildings of average height in city centres, buildings in forests
e
0,04 0,01
All shielding classes All types of buildings f 15 20
Table 4:Values of shielding coefficients according to different factors
• 𝛽 is the fraction of the time period with fans on.
In non-residential buildings, mechanical ventilation systems can be off for a large part of the time. This is taken into account through the definition of different periods or through the evaluation of. A poor evaluation of or a poor definition of periods can lead to large errors in the results.
For mechanical systems with variable design airflow rate, Vf is the average airflow rate through the fans during their running time.
2.1.1.1. Mechanical systems with heat exchangers.
For buildings with heat exchange between exhaust air and supply air, the heat transfer by the mechanical ventilation is reduced by the factor where v is the global efficiency of the heat recovery system. This efficiency is always smaller than the effectiveness of the heat exchanger itself. It should take account of differences between supply and extract airflow rates, heat losses from ductwork outside the conditioned space, leakage and infiltration through the building envelope, recirculation of air, and de-frosting of the heat exchanger.
The effective airflow rate for the heat transfer calculation when fans are on is determined according to the next equation:
𝑉 = 𝑉𝑓 · 1 − 𝜂𝑣 + 𝑉𝑥 (4)
Where
• Vf is the design airflow rate due to mechanical ventilation. (m3/s)
• Vx is the additional airflow rate with fans on, due to wind effects. (m3/s)
• V is the global heat recovery efficiency; taking into account the differences between supply and extract airflow rates. Heat in air leaving the building through leakage cannot be recovered.
For systems with heat recovery from the exhaust air to the hot water or space heating system via a heat pump, the ventilation rate is calculated without any reduction. Instead, the reduction in energy use due to heat recovery is allowed for in the calculation of the
STUDY OF IMBALANCE IN A MULTY FAMILY HOUSE
2.1.3. Residential air leakages
Envelope leakage of a building can be measured with pressurization testing, commonly called a blower-door test. Fan pressurization is relatively quick and inexpensive, and it characterizes building envelope airtightness independent of weather conditions. In this procedure, a large fan or blower is mounted in a door or window and induces a large and roughly uniform pressure difference across the building shell. The airflow required to maintain this pressure difference is then measured. The leaiker the building is, the more airflow rate is generally measured at a series of pressure differences ranging form about 10 Pa to 75 Pa. [11]
This is the most important item to reach a proper comprehension of the project. The air tightness of the building cover is determined by the air leakages. This topic is expressed as an air exchange rate or an air leakage area.
The air leakage is closely related to the building construction, design and deterioration along the time. If the leakage increases, the infiltrations will increases as well. [12]
Moreover, wind pressure coefficients are influenced by a wide range of parameters, including building geometry, facade detailing, position on the facade, the degree of exposure/sheltering, wind speed and wind direction. [13]
The Figure 9, which is presented above, shows the relation between the airflow and the pressure in the enclosure building. The predicted airflow rate can be converted to an equivalent or effective air leakage using the next equation derived from Bernoulli equation:
𝐴𝐿 = 1000 ∗ 𝑄𝑟 ∗
!
!∗!"#
!" (5)
12. Openings with areas much larger than calculated are some- times desirable when anticipating increased occupancy or very hot weather.
13. Horizontal windows are generally better than square or vertical windows. They produce more airflow over a wider range of wind directions and are most beneficial in locations where pre- vailing wind patterns shift.
14. Window openings should be accessible to and operable by occupants.
15. Inlet openings should not be obstructed by indoor partitions.
Partitions can be placed to split and redirect airflow but should not restrict flow between the building’s inlets and outlets.
16. Vertical airshafts or open staircases can be used to increase and take advantage of stack effects. However, enclosed staircases intended for evacuation during a fire should not be used for ventilation.
RESIDENTIAL AIR LEAKAGE
Most infiltration in residential buildings in the U.S. is dominated by envelope leakage. However, trends in new construction are towards tighter envelopes such that envelope leakage is reduced in newer housing.
Envelope Leakage Measurement
Envelope leakage of a building can be measured with pressur- ization testing (commonly called a blower-door test). Fan pressur- ization is relatively quick and inexpensive, and it characterizes building envelope airtightness independent of weather conditions.
In this procedure, a large fan or blower is mounted in a door or win- dow and induces a large and roughly uniform pressure difference across the building shell (ASTM Standards E779 and E1827; CGSB Standard 149.10; ISO Standard 9972). The airflow required to maintain this pressure difference is then measured. The leakier the building is, the more airflow is necessary to induce a specific indoor-outdoor pressure difference. The airflow rate is generally measured at a series of pressure differences ranging from about 10 Pa to 75 Pa.
The results of a pressurization test, therefore, consist of several combinations of pressure difference and airflow rate data. An exam- ple of typical data is shown in Figure 8. These data points charac- terize the air leakage of a building and are generally converted to a single value that serves as a measure of the building’s airtightness.
There are several different measures of airtightness, most of which involve fitting the data to a curve describing the relationship between the airflow Q through an opening in the building envelope and the pressure difference ∆p across it. This relationship is called the leakage function of the opening. The form of the leakage function depends on the geometry of the opening. Background theoretical material relevant to leakage functions may be found in Chastain et al. (1987), Etheridge (1977), Hopkins and Hansford (1974), Kronvall (1980), and Walker et al. (1997).
The openings in a building envelope are not uniform in geometry and, generally, the flow never becomes fully developed. Each open- ing in the building envelope can be described by Equation (32), commonly called the power law equation:
(32) where
Q = airflow through opening, m3/s c = flow coefficient, m3/(s·Pan) n = pressure exponent, dimensionless
Sherman (1992b) showed how the power law can be developed analytically by looking at developing laminar flow in short pipes.
Equation (32) only approximates the relationship between Q and
∆p. Measurements of single cracks (Honma 1975; Krieth and Eisenstadt 1957) have shown that n can vary if ∆p changes over a wide range. Additional investigation of pressure/flow data for sim- ple cracks by Chastain et al. (1987) further indicated the importance of adequately characterizing the three-dimensional geometry of openings and the entrance and exit effects. Walker et al. (1997) showed that for the arrays of cracks in a building envelope over the range of pressures acting during infiltration, n is constant. A typical value for n is about 0.65. Values for c and n can be determined for a building by using fan pressurization testing.
Airtightness Ratings
In some cases, the predicted airflow rate is converted to an equiv- alent or effective air leakage area as follows:
(33)
where
AL= equivalent or effective air leakage area, cm2
Qr= predicted airflow rate at ∆pr (from curve fit to pressurization test data), m3/s
ρ= air density, kg/m3
∆pr= reference pressure difference, Pa CD= discharge coefficient
All the openings in the building shell are combined into an over- all opening area and discharge coefficient for the building when the equivalent or effective air leakage area is calculated. Some users of the leakage area approach set CD = 1. Others set CD ≈ 0.6 (i.e., the discharge coefficient for a sharp-edged orifice). The air leakage area of a building is, therefore, the area of an orifice (with an assumed value of CD) that would produce the same amount of leakage as the building envelope at the reference pressure.
An airtightness rating, whether based on an air leakage area or a predicted airflow rate, is generally normalized by some factor to account for building size. Normalization factors include floor area, exterior envelope area, and building volume.
Fig. 8 Airflow Rate Versus Pressure Difference Data from Whole-House Pressurization Test
Fig. 8 Airflow Rate Versus Pressure Difference Data from Whole-House Pressurization Test
Q = c(∆p)n
AL 10 000Qr ρ 2 p⁄ ∆ r CD -------------------------
=
Figure X: airflow depending on the pressure Figure 9: airflow depending on the pressure [11]
Where:
AL= equivalent air leakage area (cm2) Qr = predicted air flow rate at ΔPr (m3/s) ρ = air density (kg/m3)
ΔPr = reference pressure difference (Pa) CD = discharge coefficient
In this equation resides the basic theory to understand the changes in the infiltration losses that it had been obtained by means of the software.
2.1.3.1. Multifamily Building Leakage
Leakage distribution is especially important in multifamily apartment buildings. These buildings often cannot be treated as single zones due to the internal resistance between apartments. Moreover, the leakage between apartments varies widely, tending to be small in modern construction and ranging as high as 60 % of the total apartment leakage in turn-of-the century brick walk-up apartment buildings. [12]
2.2. Indoor environment quality in multi family houses
Indoor environment quality is important in order to fulfil the thermal comfort requirements. In this part, it has been carried out an outline about the more important facts to reach a comfort and healthy atmosphere. [22]
2.2.1. Thermal comfort
A principal purpose of HVAC is to provide conditions for human thermal comfort, “ that condition of mind that expresses satisfaction in the thermal environment”. This definition leaves open what is meant by “ condition mind” or “ satisfaction”, but it correctly emphasizes that judgment of comfort is a cognitive process involving many inputs influenced by physical, physiological, psychological and other processes. [16] [21]
In addition to environmental parameters, the following parameters describing a person´s thermal susceptibility are similar important for the het balance.
- Metabolic rate of the human.
- Thermal resistance
Metabolic rat depends on the activity level of a person and is traditionally measured in the unit met. One met is the activity level of a relax stated person, and it is equivalent to 58 W/m2, where the area refers to the surface of the human body. The following Table 5 gives metabolic rates for some typical activities. [24]
Table 5: values of Met depending on the activity. [13]
One important unit that should be explained is “clo”. Thermal resistance of clothing is measured in the unit clo. One clo is equivalent to 0,154 m2 K/W. The next Table 6 gives typical thermal insulation for some clothing ensembles.
9.6 2009 ASHRAE Handbook—Fundamentals
extent that im is constant, and any combination of to and pa that gives the same tcom results in the same total heat loss.
Two important environmental indices, the humid operative tem- peraturetoh and the effective temperature ET*, can be represented in terms of Equation (31). The humid operative temperature is that temperature which at 100% rh yields the same total heat loss as for the actual environment:
toh = to + wimLR(pa – poh,s) (32) wherepoh,s is saturated vapor pressure, in psi, at toh.
The effective temperature is the temperature at 50% rh that yields the same total heat loss from the skin as for the actual environment:
ET* = to + wimLR(pa – 0.5pET*,s) (33) wherepET*,s is saturated vapor pressure, in psi, at ET*.
The psychrometric chart in Figure 2 shows a constant total heat loss line and the relationship between these indices. This line repre- sents only one specific skin wettedness and permeation efficiency index. The relationship between indices depends on these two parameters (see the section on Environmental Indices).
ENGINEERING DATA AND MEASUREMENTS Applying basic equations to practical problems of the thermal environment requires quantitative estimates of the body’s surface area, metabolic requirements for a given activity and the mechanical efficiency for the work accomplished, evaluation of heat transfer coefficients hr and hc, and the general nature of clothing insulation used. This section provides the necessary data and describes how to measure the parameters of the heat balance equation.
Metabolic Rate and Mechanical Efficiency
Maximum Capacity. In choosing optimal conditions for com- fort and health, the rate of work done during routine physical ac- tivities must be known, because metabolic power increases in proportion to exercise intensity. Metabolic rate varies over a wide range, depending on the activity, person, and conditions under
which the activity is performed. Table 4 lists typical metabolic rates for an average adult (AD = 19.6 ft2) for activities performed contin- uously. The highest power a person can maintain for any continuous period is approximately 50% of the maximal capacity to use oxygen (maximum energy capacity).
A unit used to express the metabolic rate per unit DuBois area is the met, defined as the metabolic rate of a sedentary person (seated, quiet): 1 met = 18.4 Btu/h·ft2 = 50 kcal/h·m2. A normal, healthy man at age 20 has a maximum capacity of approximately Mact = 12 met, which drops to 7 met at age 70. Maximum rates for women are about 30% lower. Long-distance runners and trained athletes have maximum rates as high as 20 met. An average 35-year-old who does not exercise has a maximum rate of about 10 met, and activities with Mact > 5 met are likely to prove exhausting.
Intermittent Activity. Often, people’s activity consists of a mixture of activities or a combination of work/rest periods. A weighted average metabolic rate is generally satisfactory, provided that activities alternate frequently (several times per hour). For example, a person whose activities consist of typing 50% of the
Fig. 2 Constant Skin Heat Loss Line and Its Relationship to toh and ET*
Fig. 2 Constant Skin Heat Loss Line and Its Relationship to toh and ET*
Table 4 Typical Metabolic Heat Generation for Various Activities
Btu/h·ft2 met*
Resting
Sleeping 13 0.7
Reclining 15 0.8
Seated, quiet 18 1.0
Standing, relaxed 22 1.2
Walking (on level surface)
2.9 fps (2 mph) 37 2.0
4.4 fps (3 mph) 48 2.6
5.9 fps (4 mph) 70 3.8
Office Activities
Reading, seated 18 1.0
Writing 18 1.0
Typing 20 1.1
Filing, seated 22 1.2
Filing, standing 26 1.4
Walking about 31 1.7
Lifting/packing 39 2.1
Driving/Flying
Car 18 to 37 1.0 to 2.0
Aircraft, routine 22 1.2
Aircraft, instrument landing 33 1.8
Aircraft, combat 44 2.4
Heavy vehicle 59 3.2
Miscellaneous Occupational Activities
Cooking 29 to 37 1.6 to 2.0
Housecleaning 37 to 63 2.0 to 3.4
Seated, heavy limb movement 41 2.2
Machine work
sawing (table saw) 33 1.8
light (electrical industry) 37 to 44 2.0 to 2.4
heavy 74 4.0
Handling 110 lb bags 74 4.0
Pick and shovel work 74 to 88 4.0 to 4.8
Miscellaneous Leisure Activities
Dancing, social 44 to 81 2.4 to 4.4
Calisthenics/exercise 55 to 74 3.0 to 4.0
Tennis, singles 66 to 74 3.6 to 4.0
Basketball 90 to 140 5.0 to 7.6
Wrestling, competitive 130 to 160 7.0 to 8.7 Sources: Compiled from various sources. For additional information, see Buskirk (1960), Passmore and Durnin (1967), and Webb (1964).
*1 met = 18.4 Btu/h·ft2
