M A S T E R’S T H E S I S
2006:256 CIV
Karl Ivan Alexander Ekberg
Energy Strategy for Salford University, the AMSS Building
MASTER OF SCIENCE PROGRAMME Engineering Physics
Luleå University of Technology
Department of Applied Physics and Mechanical Engineering
Division of Energy Engineering
Energy Strategy For
Salford University the AMSS Building
Prepared by:
Karl Ivan Alexander Ekberg
MASTER OF SCIENCE PROGRAMME Department of Physics Engineering
Division of Energy Engineering
PREFACE
I started my industrial trainee position in September 2005 at Arup Manchester as a part of my final year at University. This thesis corresponds to more than twenty weeks of full time work and will be vital for the designing and planning process of this project, working in parallel with architects and other engineering disciplines.
I would like to say thank you to the following persons that made my work achievable: James Chimeura, Laura Pottinger, Roger Hermansson, Stephen Platt and Tim Withley.
Manchester UK, August 2006
Karl Ivan Alexander Ekberg
SUMMARY
My aim with this report is to investigate the building’s energy strategy and explain the theoretical basis behind the mechanical design process. The report considers the following design problems:
• Flow rates
• Riser sizes
• Energy modelling
• Building issues
• Gains
• Novel methods of heating and cooling
• Renewable energy alternatives
• Part L 2006 building regulations and yearly carbon dioxide emissions estimated with Heva Comp, SBEM.
• Environmental impacts
The flow rates are estimated with a simple calculation model, and then modelled in Cymap, Heva Comp and ETA to confirm the calculated airflows. The airflows are used in the mechanical design process for the drawings that are issued to the client. The air flows are also used in the part L 2006 carbon dioxide emission calculation. There are two systems; one with a yearly CO 2 emission per square meter of 54.00 kg, which is 5.6 kg over the target 48.40 kg CO2/ m2 per year, and one system with reduced airflows with an annual carbon emission of 51.50 kg CO 2 per square meter. This is 1 kg under the target 52.50 kg CO2/ m2, year.
The last part of the report concerns environmental impacts and the moral of buildings
using glazing facades.
NOMENCLATURE
A = Approximated Duct size [m 2 ] a = Gap for duct work insulation [m]
Ao = Area of the opening [m 2 ] c = Litres per occupant [12 l/s]
C d = Discharge coefficient
C p = Constant pressure specific heat 1, 02 kJ / Kg, K c p = Wind pressure coefficient
C pi = Limit of concentration of pollutant in indoor air [ppm]
C po = Concentration of pollutant in outdoor air [ppm]
C v = Ventilation conductance [W/K]
E v = Ventilation effectiveness F air = Fresh air [ACH]
g = Acceleration due to gravity [m/s 2 ] H = Heat loss [W]
I = the light intensity coming out of the element I 0 = light intensity of the light source
k = Flow coefficient [m 3 /s Pan]
L = Length of a thermal bridge [m]
=
•
m Supply air flow rate [m
3/s]
n = Flow exponent.
N = Infiltration Rate [ACH]
O = Number of occupants P = Pollutant emission rate [l/s]
P w = Pressure acting on a buildings surface
A
=
Q Assumed Cooling [ACH]
Q = Design Flow rate [m
D3 /s]
Q
E•
= Equipment Gain [W]
Q
EX•
= External gains [W]
=
•
Q
FMinimum Fresh air gain [W]
Q
F= Approximated flow rate [m
3/s]
Q
I•
= Infiltration Gain [W]
Q
L•
= Lighting Heat Gain [W]
Q
M=Maximum Cooling [ACH]
Q
o= Amount of airflow through an opening [m
3/s]
Q
O•
= Occupant Sensible Gain [W]
Q
P= Required ventilation rate [l/s]
Q
S•
= Steady state heat gain [W/m 2 ]
Q
T•
= Sensible gain removal [W].
R i = Riser Area [m 2 ]
T 0 = Out side temperature [ºC]
T i = Internal Room temperature [ºC]
T s = Supply air temperature [ºC]
T T = Thermal transmittance U= Thermal transmittance [W/m 2 ]
v = Assumed Velocity in duct in riser [m/s]
V = Room Volume [m 3 ]
v z = Mean wind speed at height z [m/s]
∆P = Pressure gradient [Pa]
∆T = Temperature difference.
ρ= Density of air [Kg/m 3 ]
ρ 0 = Density of air at 0ºC [kg/m 3 ]
Ψ = Linear Thermal transmittance of a thermal bridge [W/m K]
CONTENT
PREFACE ... 1
SUMMARY... 2
NOMENCLATURE ... 3
CONTENT ... 5
1. INTRODUCTION ... 8
1.1 A RUP H ISTORY ... 9
1.2 A RUP TODAY ... 10
1.3 O WNERSHIP AND FINANCE ... 10
1.4 A RUP N ORTH W EST ... 11
2. THE PROJECT ... 12
2.1 I NTRODUCTION ... 12
2.1.1 Stages in the project ... 13
2.1.2 Salford ... 14
2.1.3 University of Salford... 14
2.1.4 The Brief ... 15
2.1.5 The Site ... 16
2.1.6 The Existing Buildings at site ... 17
2.1.7 The AMSS building ... 18
2.2 P ART L B UILDING REGULATIONS ... 19
2.2.1 AMSS Building and Part L ... 20
2.3 C LIENT E NERGY T ARGET ... 21
3. THEORETICAL BASES ... 22
3.1 I NFILTRATION ... 22
3.1.1 Wind pressure ... 22
3.1.2 Stack effect... 23
3.1.3 Natural Ventilation ... 24
3.2 D OWN DRAFTS ... 25
3.3 H EAT G AINS ... 25
3.3.1 Infiltration gain... 26
3.3.2 Lighting gain... 26
3.3.3 Equipment Gain... 26
3.3.4 Occupant Gain... 27
3.3.5 Minimum Fresh air gain... 27
3.3.6 External Heat Gains ... 28
3.4 H EAT LOSSES ... 31
3.4.1 Infiltration losses ... 32
3.5 P ROPERTIES OF GLASS COMBINATIONS AND SCREENS ... 33
4. ENGINEERING THEORY ... 34
4.1 M ETHODS OF H EATING AND C OOLING ... 34
4.1.1 Air handling units ... 34
4.1.2 Duct work distribution... 38
4.1.3 Duct mounted heating batteries... 39
4.1.4 Radiators ... 40
4.1.5 Under Floor Heating and Cooling ... 40
4.2 O THER C OOLING METHODS ... 41
4.2.1 Heat pumps ... 41
4.2.2 Beam systems... 43
4.2.3 Displacement Ventilation... 44
5. CALCULATION TOOLS... 45
5.1 CIBSE ... 45
5.2 C YMAP ... 45
5.3 SBEM AND ISBEM ... 45
5.4 H EVA C OMP ... 46
5.5 E+TA ... 46
5.6 M ICROSOFT E XCEL ... 46
6. MECHANICAL DESIGN PROCESS... 47
6.1 I NTRODUCTION ... 47
6.2 A PPROXIMATION OF F LOW R ATES ... 49
6.2.1 Numerical ... 52
6.3 A PPROXIMATION OF R ISER S IZES ... 54
6.3.1 Calculation of Approximated Riser Size ... 55
6.4 A NALYSIS OF B ASEMENT R EQUIREMENT ... 58
6.5 D ESIGN F LOW R ATE ... 58
6.6 H EAT L OSSES ... 60
6.7 H EVA C OMP , SBEM AND ROOM DEFINITIONS ... 60
6.8 F ACADE DESIGN ... 61
6.8.1 Model Construction of the facade... 61
7. RESULTS ... 64
7.1 F LOW R ATES ... 64
7.1.1 Approximated Flow Rates... 64
7.1.2 Design Flow Rates based on sensible gain... 65
7.1.3 Approximated Flow Rates and Design Flow Rate ... 66
7.2 R ISER SIZES ... 67
7.2.1 Riser Sizes based on approximated Flow Rates ... 67
7.2.2 Riser Sizes based on the Sensible Gain... 69
7.2.3 Issued to the client ... 70
7.3 B UILDING H EIGHT ... 70
7.4 B ASEMENT ... 70
7.5 D ISTRIBUTION SYSTEM ... 71
7.6 N OVEL M ETHODS F OR H EATING A ND C OOLING ... 71
7.6.1 Down drafts ... 71
7.6.2 Displacement Ventilation... 71
7.6.3 Natural Ventilation ... 72
7.6.4 Renewable Energy Alternatives ... 72
7.7 H EVA C OMP , SBEM AND R OOM D EFINITIONS ... 73
7.8 E NERGY M ODELS ... 74
7.8.1 Cymap... 74
7.8.2 HevaComp ... 77
7.8.3 SBEM and part L 2006 ... 78
7.8.4 E+TA and naturally ventilated offices... 82
8. DISCUSSION AND CONCLUSION ... 92
8.1 F LOW R ATES ... 92
8.1.1 Approximated Flow Rates and Sensible Flow Rates ... 92
8.1.2 Heva Comp ... 92
8.2 B UILDING ISSUES ... 93
8.2.1 Occupancy level... 93
8.2.2 Natural ventilated offices... 93
8.3 E NERGY MORAL ... 94
8.3.1 Façade ... 94
8.3.2 Increased Expectations and Standards... 94
8.4 A N E NVIRONMENTAL PERSPECTIVE ... 95
8.4.1 Climate Change ... 95
REFERENCES ... 96
ANNEXES... 97 A PPENDIX 1 - A IR VELOCITY AND ROOM NOISE CRITERIA ...
A PPENDIX 2 - A IR H ANDLING U NIT D ATA ...
A PPENDIX 3 - R ISERS ...
A PPENDIX 4 - B UILDING H EIGHT ...
A PPENDIX 5 - D ISTRIBUTION S YSTEM B ASEMENT ...
A PPENDIX 6 - D ISTRIBUTION S YSTEM ...
A PPENDIX 7 - C HILLED BEAM OPTION ...
A PPENDIX 8 - H EVA C OMP R OOM D EFINITIONS ...
A PPENDIX 9 – A LL A IR H ANDLING U NITS MOUNTED ON ROOF LEVEL ...
A PPENDIX 10 – U NDER F LOOR H EATING AND C OOLING ...
1. INTRODUCTION
Arup are leading a design team for a project at Salford University in
Northwest England. They are tasked with designing an exemplary building to house the Arts Media and Social Science faculty. This building is to be iconic in nature but also energy efficient with an energy target of 75 kWh/m 2 yr for electricity and 185 kWh/m 2 yr for fossil fuels. This will require a holistic design integrating architecture and engineering.
The new building will house the major performance arts, media (TV, radio and journalism) and art and design facilities of the university. It will contain lecture theatres and seminar rooms, group and individual learning spaces, facilities for digital design work, fine art, music recording, TV media production, dance and drama rooms.
Ensuring that energy efficiency is integrated into the planning stage, Arup will demonstrate that they have considered different solutions such as renewable sources and recycling potential, when specifying materials and systems.
The yearly energy consumption will be calculated and compared with a
comparable theoretical building to demonstrate compliance with the new Part
L Building Regulations. This is called The National Calculation Methodology
(NCM). To accomplish this, a computer program has been developed called
SBEM (Simplified Building Energy Model). This program analyses the
buildings energy consumption and the carbon dioxide emissions of the
building with given inputs.
1.1 Arup History
• 1946 - Ove Arup opens the two first offices in London and Dublin after leaving the construction company he and his cousin founded eight years earlier.
• 1956 - There are 30 people working within the company, which is growing in volume and significance, due to the big spending in the public sector that occurred in the UK in the 1950s to 1960s. They worked closely with the most advanced group of architects and broke new ground for economical solution for buildings. This is when the process of multidisciplinary work started by taking on specialist engineers with knowledge in computer analysis, shell structure, cost management, highways, bridges and civil engineering.
• 1966 - Arup has made itself a respected name in many disciplines of engineering from roads to bridges. New departments are established such as structural pathology and materials technology along with geotechnics transport planning and industrial engineering groups.
• 1976 - The project planning and offshore engineering, maritime industrial and energy businesses are getting bigger. Projects like the Sydney opera house and the Pompidou in Paris are completed. There are offices in Northern Europe, Southern Africa, South East Asia and Australasia.
• 1986 - The specialist services continue to develop, including acoustics economics, planning, facades, communication and IT, project
management.
• 1996 – There are offices across Europe, North America, Africa Australasia and South East Asia. Important projects such as Stansted Airport (UK) designed by Faster and Partners, and the Wandloo offshore drilling platform reflect an increasingly specialist portfolio.
Arup’s services now includes airport master planning, logistics, project creation, product design, manufacturing and value management,
• 2003 – Arups Portfolio continues to increase, bringing in stadium
operations, vehicle design and styling, business continuity planning,
visualisation and sustainability. Important projects include Öresund
link, joining Sweden and Denmark and the first step of the Channel
Tunnel Rail Link, between England and France.
1.2 Arup today
There are more than 7000 members of staff working for Arup worldwide today, operating 73 offices in 32 countries. Arup have a yearly turnover exceeding £400M.
It is not the biggest engineering organisation in the world but Arup is extremely well respected for its technical and strategic knowledge.
1.3 Ownership and finance
Arup is an independent company entirely owned buy its staff without external shareholders. This benefits the company in that it can develop its own course without external pressure or influence. Arup consists of independent
connected practices that function in partnership with the Ove Arup group as shown in figure 1. The corporation is united under a common culture and set of values that can be directly traced back to the founder, the Danish engineer and philosopher, Ove Arup.
Figure 1 - Corporate ownership structure
1.4 Arup North West
Arup North West operates as Ove Arup & partners Ltd and the design studios provide an international multidisciplinary consultancy service with a local practical and value for money delivered solution. They have been based in the North West for 45 years and today there are about 180 staff members within two offices Manchester and Liverpool. Arup North West have contributed to numerous projects in the North West of England and its city regions, and have designed and delivered a number of nationally and internationally important projects within a multi disciplinary field.
2. THE PROJECT
2.1 Introduction
There are many issues to consider to accomplish sustainable performance of a project, to achieve a robust, flexible design to maximise the usage and service life of an efficient building. The project is performed by way of strong
cooperation between various design teams within different disciplines. The different design teams involved in the design of the AMSS Building are:
• Salford University, Client
• 3xN, Architect
• Leach Rhodes Walker, 3xN’s Local Architect
• Arup, Buildings Services: Mechanical, Acoustic, Structural
• EC Harris: Quantity Surveyor
• Buro 4, Project Management
• Faber Maunsell, Planning Supervisor
Buro 4 have reviewed a programme that targets September 2008 as opening
date. To achieve this, the completion of the main contract must be in August
2008, which will assume no delays to the construction programme. There are
many risks in a big project, therefore August 2008 could be achieved but not
guaranteed. With a floating period and an increased contract period the
anticipated opening date is estimated at January 2009.
2.1.1 Stages in the project
Plan of Work is a document, which has been developed to provide a model procedure to the design team within different stages. Each stage is the basis of the development of the next. There are stages A to M, this report just concerns Stages B to E.
Stage A: The aim of this stage is to prepare the general outline of the
requirements of the project. This is done by setting up a client organisation for briefing, such as select architect. This stage is often called “briefing”.
Stage B: The aim in this stage is to provide the client with an appraisal and recommendation as to what order and form the project will proceed. This will ensure that the project is reasonable functionally and financially. This is checked by research of user requirements, site conditions, planning, design and cost. In this stage client representatives, architect, engineers and quantity surveyors are involved.
Stage C: The aim of this stage is to determine the general approach to layouts, design and construction. The design team develop the concept for the new building and focus on areas and adjacencies, allowing the building footprint and volume to be developed by means of studies of user requirements, technical problems, planning, design and cost. This is the key stage in the development and the client sign off against the information.
Stage D: The aim with this stage is to complete the brief and decide which proposals, including planning arrangement, constructional method, outline specifications and costs are to be used in the construction. This stage will form the first tender that is issued to the prospective contractor. The information will allow the University to review the design team’s work as a result a recommendation can be provided for budget and brief. The client brief is frozen at the end of this stage.
Stage E: The aim of this stage is to obtain final decisions on every subject
related to the design specifications, construction and cost. This is completed
by full detail design of every part and component of the building.
2.1.2 Salford
Salford is on the Western side of Greater Manchester and started as a village next to the river Irwell. The city grew with the industries making cloth and silk and the processes of dyeing and bleaching. With the opening of the Manchester Ship Canal in 1894 and construction of the Salford Docks it became one of the biggest cotton towns. Salford became one of the first boroughs in the United Kingdom, a town with certain rights that sends a representative to Parliament. Its City status was not conferred until 1926.
Today Salford is home to about 220, 000 people.
2.1.3 University of Salford
The University of Salford was founded in 1967 and has roots in two Victorian institutions, the Salford Working Men’s College and Pendleton Mechanics Institute. The two institutions combined in 1896 and formed the Salford Technical Institute. These institutions were set up and founded by local industrialists. In 1996 the University merged with the University College Salford to form the existing campus.
Today the University encompasses 18000 students, including 2500
postgraduates and 2000 international students from 80 countries. There are
about 3000 staff members.
2.1.4 The Brief
The brief of the project has been prepared by The School of Art and Design, The School of Media, Music and Performance, Information Service Division (ISD), Campus Residential Services (CARS) and the Arts Unit. These
departments have demanding specifications in terms of space standards that an average building do not, such as:
• Art and Design – Studio space with great day light requirement and open plan with internal reconfiguration within the structural layout.
Workshop suites for craft, sculpture, fibre, print and photography use needing specialist ventilation.
• Media Production - TV studios requiring large volumes and specialist servicing. Radio studios and video suites requiring specialist fit out.
• Performance Arts - Dance and rehearsal studios requiring large volumes specialist flooring and finishes. Supporting accommodation such as showers, laundry room, and wardrobe workrooms.
• Music – Practice rooms requiring specified proportions and finishes for acoustic performance. Recording studios requiring specialist fit out.
• Support Spaces-Teaching Theatre, Flexible Performance Space and Exhibition Space, Library, Catering Facilities, Student Union Facilities that necessitate specialist fit out and services.
• Circulation spaces- Creative activities require collaboration between
departments and schools. Thus the circulation spaces are utilized for
exhibition and display, spill out activities from creative spaces as well
as passing through.
2.1.5 The Site
The site decided for the development is 12000 m 2 and is defined by Adelphi Street towards the West, Peru Street towards North, Cleminson Street towards South and the residential area Devine Close towards the East.
Figure 2 – The site
This location of Salford has been used for heavy industry since the mid 19 th century and this was the location of the Sir James Farmer Norton factory that produced machinery for the cotton industry. The factory was demolished about ten years ago.
Today the site is owned by the Salford City Council and leased from the
Council by the university and serves as a car park.
2.1.6 The Existing Buildings at site
The Adelphi Building was built in 1915 as a factory for Boots the Chemist, today it house the University’s Performing Arts and Media Studies
Department. The building is expected to be vacated when the new building is complete.
Figure 3 – Adelphi house 2006-03-31
The Centenary building was planned and constructed in 1996 and won the Stirling Prize for being one of the best buildings of the recent university boom. The Stirling Prize is a British annual prize for architecture, named after the architect James Stirling. The prize is awarded to the architect of a building that has made the best contribution to British architecture during the year.
The Centenary building will be retained and will be well integrated with the new AMSS building.
Figure 4 – The Centenary Building 2006-03-31
2.1.7 The AMSS building
The new building of Arts, Media and Social Sciences (here after the AMSS building) will stand as a symbol for the University of Salford, and house student and staff of the Schools of Media Art & Performance and Art &
Design. The building is intended to support a greater integration with the public through the exhibition spaces and the TV studios.
The building has an area of 12.112 m 2 and can house about 4000 students. The
project cost is estimated to about £38,430,000, inclusive of inflation and
special equipment of about £5,800,000. After a more detailed assessment in
stage D, the project cost stands at £43,960,000. This is £5,530,000 over
budget.
2.2 Part L Building regulations
The United Kingdom government attempts to combat climate change through a better energy performance of buildings. The contribution of Part L will perhaps reduce the carbon emission by 60 percent before 2050. The goal is to achieve a reduction of about 20 percent of the annual 15.2 million tonnes of CO 2 emissions by 2010. The New Part L 2006 documents present a method called TER to Target CO 2 Emission Rates. This will apply to new buildings and extensions to existing buildings if the extension is 25% of the existing floor area and is bigger then 100 m 2 . The changes will take effect in April 2006.
The new regulations will require that:
• All Carbon Dioxide emissions are within defined limits
• There are set standards that must be complied with, such as U-values for certain elements.
• Measurements are made to avoid high internal temperatures due to solar heat gains.
• A quality check of the construction is made by pressure testing of new buildings. For development buildings the testing requirements may be reduced.
• Operating and maintenance instructions of an operating building are in place, so that no more fuel or power is used than is reasonable.
There are two calculation methods approved by the Government to analyse TER:
• Government’s Standard Assessment Procedure (SAP2005). This is used for residential with a floor area under 450 m 2 .
• Simplified Building Energy Model (SBEM). This method is used for
residential with a floor area greater than 450 m 2 and for building types
other than dwellings.
2.2.1 AMSS Building and Part L
The building will be designed to fit the new criteria in Part L related to carbon dioxide emissions, building fabric, lighting and hot water system performance, overall building performance and provisions for energy efficient building operation.
The new regulations are achieved by:
• The building carbon emission is compared with that of a theoretical building of same area.
• There will be an operational rating associated with the building based on the operational energy consumption of the building.
• A carbon dioxide emissions target, which will provide a minimum 28% reduction when compared with a building that complied with the 2002 regulations.
• There are minimum acceptable set standards that needs to be complied:
Maximum U-values [10]:
o Walls 0.27 W/m 2 ,ºC o Glazing 1.8-2.0 W/m 2 ,ºC o Floor 0.22 W/m 2 ,ºC o Roof 0.18 W/m 2 ,ºC
Target efficiencies for building services [10]:
o Boiler Efficiency 89%
o HVAC Heat recovery 50%
o Lighting Load 12 W/m 2
• Pressure testing. The buildings air tightness target is 7m 3 /h/m 2 at 50
pa.
2.3 Client Energy Target
[8] In England the energy cost in the public sector is more than £200 million per year and is the result of at least 3 million tons carbon dioxide emission a year. Therefore it is important to reduce the energy consumption and cost in this sector as much as possible. At the start of a project the initial brief has to be prepared to maximise the potential energy saving and ensure that all possibilities are considered to accomplish an efficient building.
To understand the energy usage the building type and categories of space are determined. The occupancy level and period of occupation of a space has a large impact on the energy consumption. The longer a space is used the more energy usage and risk of waste.
In large rooms such as lecture theatres and libraries, the occupant has no control over the energy consumption. In small rooms such as single offices and tutorial rooms the occupant can control the energy consumption
individually. Therefore the control strategy plays a significant function in the energy saving and cost.
[8] The annual energy target of The AMSS building is 75 kWh/m 2 for electricity and 185 kWh/m 2 for fossil fuel.
3. THEORETICAL BASES
3.1 Infiltration
Infiltration can be described as air leakage through cracks and gaps in the buildings fabric and is a measurement of air tightness of a building.
Infiltration is affected by the building construction quality and architectural design decisions.
3.1.1 Wind pressure
When wind blows on the building façade pressure difference between the inside and outside occurs. The pressure caused by the wind differs around the building perimeter.
The pressure at the windward face increases while the pressure on the leeward face decreases, thus air leaks into the building (infiltration) on the windward face. If the pressure on the leeward face is lower than the internal building pressure exfiltration will occur. The amount of air being circulated is dependent on wind velocity, wind path, and building construction.
Figure 5 – Infiltration caused by wind
The pressure acting on a point on the building’s surface can be expressed as follows [9]:
5
2.
0
P ZW
c v
P = ⋅ ρ ⋅ ⋅ [Pa] Equation (1)
ρ = Density of air [Kg/m 3 ]
P
=
c Wind pressure coefficient
z
=
v Mean wind speed at height z [m/s]
3.1.2 Stack effect
Air density varies with temperature, cold air is heavier than warm air, thus warm air rises and cold air sinks. A vertical pressure gradient will occur if there is a temperature difference between external and internal air of a building. If the internal air temperature is greater than the external air temperature, air infiltrates at low level and ex-filtrates at higher level. If external air is warmer than internal air, the process is reversed. The pressure gradient between two heights can be described as [9]:
− +
− +
⋅
⋅
−
=
∆ 273
1 273
) 1 (
273
0 1 2 0
T
ih T h g
P ρ Equation (2)
0
=
ρ The density of air at 0ºC [kg/m 3 ]
=
g The acceleration due to gravity [m/s 2 ]
0
=
T The out side temperature [ºC]
i
=
T The inside temperature [ºC]
Air warmed by a heating system, people, equipment or solar gain becomes less dense and rises in a building. Thus the air pressure increases in the upper part of the building and becomes greater than the outside air pressure, as a result the air leaks out from the construction and cooler air from low level starts to move upwards in the building.
Figure 6 – Infiltration caused by the stack effect
3.1.3 Natural Ventilation
Natural ventilation is controlled infiltration through specified routes such as openable windows, ventilators, ducts etc. Thus natural ventilation is based on integration within different disciplines; architectural, acoustical,
environmental and mechanical.
The amount of airflow through an opening is function of the pressure difference across the opening and its size. This can be expressed with the following equation [9]:
n
o
k p
Q = ⋅ (∆ ) [m 3 /s] Equation (3)
k= The flow coefficient [ m
3/ s ⋅ Pa
n] n= The flow exponent
=
∆p The pressure difference across the opening [Pa]
The flow coefficient k is related to the opening size. The flow exponent n is dependent on the flow characteristic and can be between 0.5 for fully turbulent flow and 1.0 for laminar flow.
For openable windows it is useful to describe equation (2) in direct terms of opened area A, equation (3) can be written as [9]:
5 .
)
0/ 2
( p ρ
A C
Q
o=
d⋅
o⋅ ∆ [m 3 /s] Equation (4)
C d = The discharge coefficient A o = the area of the opening [m 2 ]
=
∆p The pressure difference across the opening [Pa]
ρ = Density of air [kg/m 3 ]
[9] The discharge coefficient C d for sharp edged opening is 0.61
3.2 Down drafts
Down draft can be described as a small strip of air that drops to ground level.
Air that is cooler than its surrounding will drop to ground level influenced by the buoyancy force.
Down drafts can be generated by a vertical surface which is cooler than the space it encloses but are unlikely in modern buildings with superior insulation and double glazing, except for spaces with full height glazing and double storey exposed walls. A problem can occur when the down draft is strong enough to sink to the floor level and flow across the room.
3.3 Heat Gains
Heat gains are either sensible or latent. Sensible gains increase the air temperature and latent gains cause an increase in moisture content. The following sources are considered in the design of air condition systems:
• Humans or animals o Occupant gain
o Minimum fresh air gain
• Lighting
• Equipment
• Electric motors
• Cooking appliances
• External gains
o Infiltration gain o Solar heat gain
Sensible heat gain removal can be described as follows [2]:
) (
i sP
T
m C T T
Q = ⋅ −
•
•
[W] Equation (5)
=
•
m Supply air flow rate [m 3 /s]
02 .
= 1
C
PkJ / Kg , K
i
=
T The room temperature [ºC]
s
=
T The supply air temperature [ºC]
3.3.1 Infiltration gain
The infiltration gain can be expressed as follows [9]:
) (
o iv
v
C T T
Q = −
•
[W] Equation (6)
v
=
C The Ventilation conductance [W/K]
o
=
T The outside temperature in summer [ºC]
i
=
T The inside control temperature [ºC]
3.3.2 Lighting gain
In a light bulb the electricity input is transformed to heat. Energy is
transmitted into the space in the form of radiation, conduction and convection.
To determine the internal heat gains from artificial lighting the total electricity input power, the quantity of heat which enters the space, radiant components, convective components and conductive components need to be recognized.
The quantity of heat entering the space depends on the type of light fitting and where it is installed. When the light source is suspended from the ceiling, wall or floor the heat input will come out as internal heat for the space. If the light source is surface mounted some of the heat input will radiate underneath the surface and into the internal space.
The occupant’s forehead and the back of their hands are usually more sensitive to heat than other parts of the body, therefore radiant heat can be detected easier and cause discomfort.
3.3.3 Equipment Gain
Equipment will emit heat gains into the space equal to its power input.
General equipment for a university can be:
• Desktops
• Laptops
• Projectors
• Specialist Equipment
Computers today generally emit less heat than they did in pervious years. A lot of the reduction is due to flat screen monitors that often are standard today.
3.3.4 Occupant Gain
All humans lose heat to their surroundings, which is an effect of assimilation and utilisation of food. The occupant gain can be in the range from 40W/m2 to 500 W/m2 and varies with the activity. Harder working occupants radiate more into the space than passive occupants.
The latent heat gain emitted from a human results in an addition to the moisture content of the air while the sensible gain increases the air
temperature. How much of the sensible gain that is radiant depends on the clothing, radiant temperature and air velocity.
3.3.5 Minimum Fresh air gain
The fresh air gain is estimated from the minimum fresh air requirements.
When the main pollutants are humans the minimum fresh air requirement is dependent on their activities, and is proportional to the number of occupants within the space. If there is a known source of pollution emitting at constant rate the required ventilation rate is given by the following expression [9]:
) (
) 10
(
6po Pi v
Pi
P
E C C
C Q P
−
= − [l/s] Equation (7)
=
P The pollutant emission rate [l/s]
po
=
C The concentration of pollutant in outdoor air [ppm]
pi
=
C The limit of concentration of pollutant in indoor air [ppm]
v
=
E The ventilation effectiveness
The fresh air gain can be expressed as follows [9]:
Minimum Fresh Air Gain
1000 T Cp Q
F⋅ Q
P⋅ ⋅ ∆
=
•
ρ
[W] Equation (8)
2 . 1
ρ = Kg / m
3Q = Fresh Air requirement [l/s]
P02 .
= 1
C
PkJ / Kg , K
i
=
T Summer Design Space Temperature [24 ºC]
o
=
T Summer Design outside Temperature [26 ºC]
o
i
T
T T = −
∆
3.3.6 External Heat Gains
In comfort air conditioning design, solar radiation through window walls and roof are taken as sensible gains.
The energy source in the sun is from a fusion process in the core where nitrogen is transformed to helium which heats up the suns photosphere that radiates heat. Thus the sun radiates as a black body with a surface temperature of [2] 6000 ºC with a wavelength interval of [2] 300 to 470nm. About nine percent of the energy is in the ultra violet region and the rest in the visible part of the spectrum. The average solar radiation that reaches the earths
atmosphere is about [2] 1.4 10 3 W/m 2 , giving the sun an power of [2] 4 10 26
W. The solar radiation intensity, when the earth is at an average distance from
the sun in its orbit, is defined as the solar constant [2] I s =1367 W/m 2 .
3.3.6.1 Solar heat gain through windows
The solar irradiation impact on the thermal load within the space depends on the radiation transmittance and absorption in the glazing system. The quantity of radiation transmitted and absorbed is a function of the intensity of the incident radiation and the angle of incidence between the solar beam and the glass. To get an accurate result of the load, measurements must be made at various times during the day. This is often done with computer programs.
The amount of thermal transmittance that passes through the glass can be described as follows:
I
0T
T= I Equation (9)
Where I 0 is the light intensity of the light reaching the window and I is the light intensity coming out of the glass.
3.3.6.2 Heat gain through walls
The heat gain through walls is due to a steady state flow, which occurs because of the temperature difference on both sides of the wall, and unsteady state gain due to the solar radiation on the outer surface of the wall.
The steady state heat gain can be described as follows [2]:
) (
i oS
U T T
Q = −
•
[W/m 2 ] Equation (10)
U = The thermal transmittance [W/m 2 ] T = The internal temperature [Cº]
iT
o=The outside temperature [Cº]
Figure 7 – Steady state temperature drop through a wall
Under the steady state condition the temperature drop through the wall is constant, because of the constant steady outside temperature. The wall’s height and width is large so the calculations can be one-dimensional.
In the unsteady state gain the temperature drop through the wall is not
constant and varies with time. Thus the temperature drop through the wall can be illustrated as in figure x.
Figure 8 – Unsteady state temperature through a wall
At time t=t0 the temperature at point A is Tt0, this temperature is caused by sun radiation. At the time t=t1 the sun radiation does not radiate at point A, but the remaining temperature from time t0 has increased the temperature in point B. At time t2 the sun radiation at point A is greater than it was at time t0, the temperature at point C is less than in point B. Thus as shown the
temperature drop through the wall is not linear, but can be described if the temperature drop is combined for the time period.
3.4 Heat losses
Heat lost in a building occurs by transmission through building fabric and by infiltration. The thermal transmittance U [W/m 2 K] of the construction corresponds to the thermal property of the building.
The heat loss through a building component can be described as follows [9]:
Heat loss H = ( ∑ A ⋅ U + ∑ L Ψ ) ⋅ ∆ T [W] Equation (11)
=
A Element area [m 2 ]
U = Thermal transmittance [W/m 2 K]
=
L Length of a thermal bridge [m]
=
Ψ Linear Thermal transmittance of a thermal bridge [W/m k]
=
∆T Temperature difference, between two sides of the component.
∑ L Ψ is the sum over all thermal bridges, this is often taken into account in
the calculation of the U value of the component.
3.4.1 Infiltration losses
Infiltration has an important impact on a building’s heating cost; a leaky building may reduce any benefits from heat recovery systems and optimised start and stop control systems for space heating.
The infiltration gain can be described as:
) (
o iv
C
vT T
Q = −
•
[W] Equation (12)
v
=
C The Ventilation conductance [W/K]
o
=
T The outside temperature in winter [ºC]
i
=
T The control temperature [ºC]
The air leakage through the building can be measured by using a
pressurisation method. Air is supplied into the building with different airflow
rates and the pressure difference across the building is measured.
3.5 Properties of glass combinations and screens
The properties of glazing systems can be calculated from the properties of the individual components. The transmission, absorption and reflection (here after TAR) for double-glazing can be described with the following equations [9]:
) 1
/(
) (
' T
0T
iR
0R
iT = ⋅ − ⋅ Equation (13)
)]
1 /(
) [(
'
0 0 0 00
A T A R
iR R
iA = + ⋅ ⋅ − ⋅
) 1
/(
) (
'
0 i 0 ii
T A R R
A = ⋅ − ⋅
' ' ' 1
' T A
0A
iR = − − −
Figure 9 – Double-glazing system
The AMSS building will have an additional screen at level 2 to 4, which will
reduce the solar energy transmittance. This is archived by filtering daylight
through thousands of little holes. The amount of solar energy transmitted is
related to the percentage of holes in the solid steel screen.
4. ENGINEERING THEORY
There are several solutions of mechanical systems in a building. Different systems are fitted into a building depending on space requirements and structural limitations. The internal design is often driven by the architect and sometimes the most efficient system can be neglected in favour of a system that better suits the space.
4.1 Methods of Heating and Cooling
This section describes different systems and techniques that are considered in the mechanical design of the AMSS building.
4.1.1 Air handling units
To obtain a comfortable condition, the areas that cannot utilize natural ventilation will use efficient mechanical ventilation systems to provide the right amount of fresh air. The buildings HVAC system will contain both constant and variable air volume air-handling units.
Most of the units in the building will have:
• Inlet louver, for the external units
• Mixing box with motorized dampers
• Pre filter
• Heat recovery plate heat exchanger with bypass damper
• Secondary filter
• CHW cooling coil
• LPHW heater
• Supply air fan
• Return air fan.
Figure 10 – Air Handling Unit
The unit will take outdoor air and mix it with the returning air from the space.
The air mixture is filtered, conditioned, cooled or heated and discharged back into the building space.
4.1.1.1 Inlet louver
Air handling units installed outside have inlet louvers, to protect from water penetration.
4.1.1.2 Attenuator
An attenuator is a component that reduces noise. The unit has four attenuators;
two in the inlet and two in the outlet. Spaces with strict acoustic criteria have supplementary duct mounted attenuators.
4.1.1.3 Heating Battery
A heating battery contains one or more rows of tubes, mounted in a steel sheet casing. The tubes can be connected in series or in parallel to a hot water system.
Figure 11– Heating battery
Equation (7) shows that to remove the sensible gain, the supply airflow rate is inversely related to the temperature difference between the room and supply air temperature. A low supply air temperature gives a small supply airflow rate. A smallair flow rate requires a small air distribution system and smaller air handling unit, this will save fan power and running costs.
Thus in the summer the supply air temperature should be as low as possible and is often 8° to 11° less than the control room temperature.
In some cases in the summer when the outside air temperature is high this results in a very low supply air temperature. For that reason the air needs to be dehumidified, especially for the spaces that are conditioned with chilled beams.
The air is therefore cooled in the cooling coil and then reheated in the heating battery. This will decrease the moisture content and therefore condensation does not occur.
In the winter the batteries are used for heating the outside air to desired supply temperature.
4.1.1.4 Cooling coil
A cooling coil contains tubes mounted in a steel sheet casing. The
effectiveness of a coiling coil depends on the contact factor which depends on the number of tubes. In the tubes chilled water or liquid refrigerant is
circulated and as a result the necessary dehumidification and cooling of the air stream is accomplished. All cooling coils should have a drainage system to remove the condensed moisture from the air. The AMSS building will use chilled water cooling coils.
Figure 12– Cooling Coil
4.1.1.5 Mixing Box
In the mixing box the returned air is mixed with fresh outside air. The quantity of fresh air and returned air that is mixed is controlled with dampers.
4.1.1.6 Filter
The unit drags in air from different parts of the room and outside. This air can be polluted. Thus the purpose of the filter is to remove containments, often solid particles such as dust, pollen, mould, and bacteria.
4.1.1.7 Frost coil
The frost coil works exactly like a cooling coil but its purpose is to preheat the outside air.
4.1.1.8 CO
2Control
If fresh air systems supply at a constant rate based on the maximum occupancy level, excessive energy consumption can take place when the occupancy level is low. To avoid energy waist CO 2 sensors can be utilized to adjust the fresh air supply to just efficient, therefore no unnecessary extraction and loss of conditioned air takes place.
4.1.1.9 VAV System
VAV stands for Variable Air Volume and is varying the amount of conditioned air to a space. The system maintains the airflow at constant temperature but supplies the quantity to meet the given cooling load. This is an efficient technique to save energy.
4.1.1.10 Free cooling
A free cooling system takes the advantage of outside air. If the outside air
temperature is less than the internal design temperature and the outside air can
meet the given cooling load, the chillers in the air-handling unit shut down or
just help sufficiently. If the external air temperature is much higher than the
internal temperature the air handling goes into a full circulation method. With
this technique the amount of energy and CO 2 emissions can be reduced.
4.1.1.11 Heat recovery
Most techniques that can provide free cooling can provide heat recovery in the winter. The system will minimise the amount of external air entering the building and maximise the warm re-circulated air, with the dampers A, B and C in. Recirculation systems are the most energy efficient systems for heat recovery.
Figure 13 – Air Handling Unit
4.1.2 Duct work distribution
It is important that the ductwork distribution system is well planned to reduce
the fan power and additional noise. The ducts need to be balanced; if balance
cannot be achieved regulating devices are installed to accomplish pressure
drop balance. Each main branch shall be designed to serve zones with
different cooling and heating loads to give the most economical solution.
4.1.2.1 Access
Additional space is required around the ductwork and other components of the system for:
• Installation
• Testing
• Commissioning
• Maintenance
• Inspection and cleaning
• Insulation
• Support brackets
It is significant that the required additional space is planned before the architectural details are completed.
4.1.3 Duct mounted heating batteries
There are several spaces with very strict noise criteria, in theses spaces a VAV system is not suitable. The damper that controls the air volume in a VAV system can be too noisy. Therefore constant airflow systems and heating batteries are used in noise sensitive spaces to meet the cooling load.
For example if room C is fully occupied and room B is 50 percent occupied, the occupants in Room B will feel uncomfortable. Thus heating batteries reheat the cooled air to get the required supply air temperature for the actual cooling load.
Figure 14- Heating batteries for reheat for spaces without VAV
4.1.4 Radiators
A radiator system transfers energy into a room in the form of convection and infrared radiation. Convection has two stages; the air in the radiator is heated by means of conduction and radiation. The warmer air rises to high level and cooler air takes its place, thus internal circulation occurs in the heated space.
There are several methods to create heat, the most common are to lead warm water through a radiator or to conduct electricity through wires with resistance that produce heat.
Figure 15– Radiator that transfers energy into the room by convection
4.1.5 Under Floor Heating and Cooling
In an under floor heating system the energy is transferred by means of radiation from pipes installed in loops under the floor void. This system is suitable for spaces with high floor to ceiling height, where the convection effect can cause major heat losses through the ceiling.
Figure 16– Radiator that transfers energy into the room by convection
An under floor heating system uses lower temperature than a convection system to achieve the same comfort.
4.2 Other Cooling methods
4.2.1 Heat pumps
A heat pump collects heat from a location and transfers it to another. A heat pump can be used for both heating and cooling. About 70 metres from the west edge of the site is River Irwell. Research has been performed to decide if the river could be used as a heat rejection source in the summer and a heat source in the winter. Two different systems are considered.
4.2.1.1 Closed System
In the closed system water circulates in a closed loop and a heat exchanger is placed in the river. The substance circulates through a heat exchanger on land and provides heating or cooling to the building.
Figure 17–Heat pump closed system
4.2.1.2 Open system
The open system would use water extracted from the river that will pass through a heat exchanger on land and provide heating or cooling to the building and then is discharged back into the river, further downstream.
Figure 18– Heat Pump open system
4.2.2 Beam systems
A cooled beam system can be used for ventilation, cooling and heating. For an active beam an air-handling unit supplies air to the space through the beam’s air plenum, through a heat exchanger in the beam. The heat exchanger can circulate either cold or hot water depending on the space demand.
Figure 19– Active Beam
In a static beam heat transfer occurs by means of natural convection and radiation.
Figure 20– Passive Beam
Because of the forced convection in an active beam it suits spaces with higher load than static beams.
Due to the cool surface of the beam’s heat exchanger, the air entering or being supplied to the beams must be dehumidified so that condensation does not occur. The positioning of the beam has to take into account convection from other heat sources that can effect the operation and cooling capacity of the beam.
4.2.3 Displacement Ventilation
Displacement ventilation uses the buoyancy force of warm air to provide ventilation and comfort.
The supply air temperature in a displacement system is usually 1 to 3 Cº lower
than the room temperature; thus the air drops to floor level and spreads across
the floor. Displacement is suitable for spaces with a large concentration of
occupants within in a relative small proportion of volume. It is also a suitable
solution where the systems acoustic performance is significant.
5. CALCULATION TOOLS
This section describes the calculation tools used in the design.
5.1 CIBSE
The Charted Intuition of Building service Engineers, called CIBSE, is an international organisation with a membership of 17 000. They characterize and provide services to the building services profession. The institution embraces a broad field of design in installation, maintenance and manufacturing in building service engineering. CIBSE aims to develop superior buildings through education, research, and communications and play a significant role in determining governmental regulations and legislation.
5.2 Cymap
Cymap consists of a collection of programs designed for building service calculations. The programs use a database from CIBSE. Cymap is a tool for basic heating and cooling load calculations, pipe and duct sizing and pressure drop calculations. Cymap is not a complex analytical program and has some drawbacks; it does not include fluid dynamics calculation capabilities and it is not very accurate for advanced structures with a complex geometry. Cymap can be seen as a useful tool and as a guideline for mechanical calculations.
5.3 SBEM and ISBEM
The Energy Performance of Buildings Directive (EPBD) of the European Parliament and Council (dated 16 December 2002) requires that the energy performance of new buildings have to be calculated with a method that complies with the set regulations. The United Kingdom Office of the Deputy Prime Minister (ODPM) has completed the National Calculation Methodology (NCM) for energy performance of buildings.
SBEM stands for Simplified Building Energy Model and is based on a Dutch
methodology NEN 2916:1998. SBEM analyses the buildings monthly energy
consumption and carbon dioxide emissions. The aim with this is to show how
much energy is consumed for the amount of use it provides. A simple way to
measure this figure is to compute the energy use by floor area in Wh/m 2 . This
does not tell what kind of energy is used or what the environmental impacts
are. Therefore a better method is to measure the energy ratings in energy cost or carbon emissions.
ISBEM is the interface where the building’s geometry, construction, usage, HVAC and lighting equipment is defined.
ISBEM and associated databases are available for all users and are an implementation of non-domestic buildings of NCM.
5.4 Heva Comp
Heva Comp is similar to Cymap; a collection of programs for building service calculations. In the Heva Comp package there is a tool where the model can be exported to an SBEM model. This tool is time saving because of the time consuming interface in ISBEM.
5.5 E+TA
E+TA stands for Environmental and Thermal Analysis, which is formed from data inputs, utility and analysis programs to complete criteria, for internal building services.
The new building regulations Part L 2006 will involve an assessment of naturally ventilated spaces to ensure that they do not suffer from overheating.
ETA can give great 3D visual diagrams of mean radiant temperature and percentage of people dissatisfied within a space. This makes the program very useful for natural ventilation analysis.
5.6 Microsoft Excel
A powerful tool for repetitive calculations is an Excel sheet. All rooms of the
building are put into a list where the different rooms’ criteria are defined such
as area, height, occupancy level and ventilation type. The room definitions are
used for further calculations and are used as a guideline in the design process.
6. MECHANICAL DESIGN PROCESS
6.1 Introduction
• Room definitions
The first step in the design process is to determine the different rooms’ criteria and definitions. The room definitions are vital for further design. Definitions such as room size, occupancy and room usage are the frame for further calculations.
• Flow rate Approximation
After the rooms’ criteria are defined approximation of necessitated cooling loads can be made for each space, Assumed Cooling.
• Approximated riser sizes
From the Assumed Cooling flow rate, the duct sizes can be estimated and from the duct sizes the risers can be calculated. The final riser is planned and integrated with the architectural design and includes ductwork, pipe work and access.
• Air-handling Units
The Assumed Cooling flow rate is used to size the air-handling units.
• Basement requirement
With the given sizes, the required space for the air-handling units can be estimated. The architect prefers the units at roof level, thus an assessment to fit the units at roof level is made. If this is not possible an optimised basement is necessary because of the excavation cost.
• Distribution system
An efficiently planned and workable distribution system, well integrated with
the structural design is necessary to create an efficient building.
• Building Height
If the building exceeds 18 meters in height from the fire service access level to the highest occupied floor level the building will need at least one fire shaft. A fire shaft is a space enclosed by walls forming an enclosing structure that is fire resistant for a longer period of time. If the buildings highest floor plate is lower than 18 meters, the buildings perimeter has to be accessible for fire services. The aim for the AMSS building is to try to design the highest floor plate to just 18 meters.
An assessment is made to see if this is possible with the ceiling voids for the needed duct sizes.
• Novel Methods of Cooling and Heating
Efficient selection of cooling and heating systems based on loads and losses from the energy model programs and calculations. The selection will be influenced by the room usage, such as acoustic considerations, occupation and structural limitations.
• Issue Schematics and layouts of systems
When the design process is finished, drawings of distribution system and schematics of selected system are issued to the client.
• Energy models
The building is modelled with energy modelling programs to verify the space loads. The building is modelled in a Simplified Building Energy Model to prove that the building compiles with the new Part L 2006 regulations.
6.2 Approximation of Flow Rates
There are three different airflow rate assumptions that are based on the estimated sensible gain. For example, a room with high occupancy and specialist equipment will require a greater supply of air to keep the designated room temperature, while a single office or a average room with low
occupancy and normal lighting requires a lower supply of air or could perhaps be naturally ventilated.
To get an idea of the required cooling flow rate two test rooms with the floor area 400 m 2 and a height of 5m are studied. The rooms are located at the South West façade to give the peak solar heat gains and at the North East Façade to give a lower solar heat gain. Because the building withholds major glazing facades the external gain will have the largest contribution to the Sensible Gain.
Figure 22– Test room 1 and test room2
The gains considered in the calculation for the total sensible gain are as follows [9]:
• Infiltration Gain Q
I•
[W]
• Lighting Heat Gain Q
L•
[W]
• Equipment Gain Q
E•
[W]
• Occupant Sensible Gain Q
O•
[W]
• Minimum fresh air Gain Q
F•
[W]
• External gains Q
EX•
